Wafer coating system

Semiconductor wafers having patterns of steps and grooves defining microcircuit elements thereon are coated with metallic film by supporting the wafers individually adjacent a respective ring-shaped sputtering source in stationary relationship thereto. To effectuate such individual wafer processing on a continuous basis and preserve the evacuated argon environment, a vacuum chamber sputter coating apparatus is provided which has a number of work stations therein, at least one of which includes said ring-shaped sputtering source. Also included is a load lock, and an intermittently rotting vertical plate-like wafer carrier means therewithin positioned closely adjacent the chamber entrance, and carrying wafers in turn from the load lock to the work stations. The carrier includes apertures each accepting a wafer therewithin in an upright position, with the wafers edgewise resiliently supported by clip means, without the use of any externally-originating supports such as platens. Both surfaces of wafer can be accessed by processing equipment, for example, heating or cooling means at some of the work stations. Only a few wafers inside the chamber are at risk at any one time, and introduction of contaminants, debris, as well as disturbances to the chamber environment minimized.

 

We claim:

1. Apparatus for individually processing semiconductor wafers held stationary during processing, said apparatus comprising:

processing chamber means having an entrance opening for wafers in a wall thereof;

a wafer carrier assembly movably supported inside said chamber means, said carrier assembly comprising wafer holding means for releasably holding a wafer adjacent the periphery of the wafer and supporting the wafer for resilient movement;

said wafer carrier assembly further comprising sealing means in the form of a first continuous annular planar sealing surface;

pressure sealing means having a second continuous annular planar sealing surface matching said first annular sealing surface;

said wafer holding means being positioned on said carrier assembly inwardly of said first annular sealing surface, whereby a wafer in said holding means is supported for resilient movement relative to said first annular sealing surface;

wafer processing means spaced from said entrance opening for processing a wafer held on said carrier assembly by said wafer holding means;

means for moving said carrier assembly to move said wafer holding means along a first path for positioning said wafer holding means selectively in alignment with one or the other of said entrance opening and said processing means, said moving means including means for stopping said movement along said first path when said wafer holding means is in alignment with either said entrance opening or said processing means; and

means for causing relative movement between said first and second annular planar sealing surfaces in a direction transverse to said first path when said carrier assembly movement along said first path is stopped, whereby a seal is formed between said first and second annular planar sealing surfaces.

2. Apparatus as claimed in claim 1 wherein said pressure sealing means is aligned with said entrance opening.

3. Apparatus as claimed in claim 1 wherein said wafer holding means is adapted for movement between an open position for accepting a wafer and a closed position for holding a wafer;

said apparatus further comprising moveable chuck means supported outside said chamber means and adapted to releasably support a wafer; and

means for moving said chuck means to insert a wafer through said entrance opening and automatically release a wafer directly to said wafer holding means on said carrier assembly when said aperture is in alignment with said entrance opening.

4. Apparatus as claimed in claim 3 further comprising actuating means for contacting and moving said movable wafer holding means, said actuating means being connected to said chuck means for movement with said chuck means.

5. Apparatus as claimed in claim 4 further comprising means for moving said actuating means relative to said chuck means.

6. Apparatus for individually processing semiconductor wafers comprising:

processing chamber means having an entrance opening for wafers in a wall thereof;

a wafer carrier assembly movably supported inside said chamber means, said carrier assembly comprising wafer holding means for releasably holding a wafer adjacent the periphery of the wafer and supporting the wafer for resilient movement;

said carrier assembly further comprising sealing means in the form of a first continuous annular planar sealing surface;

pressure sealing means having a second continuous annular sealing surface matching said first annular planar sealing surface and adapted for sealing therewith;

said wafer holding means being positioned on said carrier assembly inwardly of said first annular planar sealing surface, whereby a wafer in said holding means is supported for resilient movement relative to said first annular sealing surface;

wafer processing means spaced from said entrance opening for processing a wafer held on said carrier assembly by said wafer holding means; and

means for moving said carrier assembly to move said wafer holding means along a first path for positioning said wafer holding means selectively in alignment with one or the other of said entrance opening and said processing means, said moving means including means for stopping said movement along said first path when said wafer holding means is in alignment with either said entrance opening or said processing means.

7. Apparatus as claimed in claim 6 further comprising:

a moveable chuck means supported outside said chamber means and adapted to releasably support a wafer; and

means for moving said chuck means to insert a wafer through said entrance opening and automatically release a wafer directly to said wafer holding means on said carrier assembly when said apertures is in alignment with said entrance opening.

BACKGROUND OF THE INVENTION

The present invention relates to the coating of thin substrates by deposition under vacuum. More particularly, the field of the invention is metallization of semiconductor wafers, and apparatus for effecting such metallization of wafers individually, and on a serial, continuous basis. Semiconductor wafer fabrication techniques have evolved rapidly over the past decade. Individual microcircuit devices have become progressively smaller, thereby increasing the number of such devices that can be put onto a wafer of a given size, Additionally, wafers of larger diameter are coming into use. A few years ago wafers of 2-inch diameter were commonplace, and 3-inch diameter wafers were considered large. Today such of the device fabrication is done with 4-inch diameter wafers and widespread use of 5-inch wafers within a very few years is foreseen. The reductions in device size, coupled with the increased size of wafers, have served to greatly increase the economic value of individual wafers, and thus the need to process and metallize such wafers in an improved manner.

Most semiconductor and microcircuit fabrication techniques require deposition of metallic coatings of high quality upon the semiconductor wafer upon which the microcircuits are defined. Whether a coating is of "high" quality will of course ultimately be determined by the degree of satisfaction with the ultimate yield of microcircuit devices from the wafer, and their utility, for example, as meeting the higher military or industrial standards, or the lesser consumer and hobbyist standards. Although therefore difficult to quantify, it is generally agree that metallization quality, and thus ultimate quality and quantity of yield, will in turn be a function of the following factors: uniformity of coverage upon the uppermost and main planar surface of the wafer ("planar coverage"); contamination levels incorporated into the final coating; defect level caused by debris; symmetry and homogeneity, or in other words freedom from "layering" and the manner of distribution of contaminant levels in the film; the degree of reproducibility and control, especially of temperatures during coating deposition; and step coverage, that is, the continuity and evenness of the coating across not only the main plane of the surface, but also the side and bottoms of such features within the surface as steps, grooves, depressions, and raised portions which define the microcircuits.

Some of these characteristics are harder to achieve or more critical than others, or have been thought to require definite specialized processing steps to achieve. For example, because of the constraints of geometry, step coverage has been a particularly difficult requirement to fulfill. The sidewalls of the steps and grooves are generally perpendicular to the uppermost surface of the main plane of the wafer, and may face both inwardly and outwardly of the wafer center. Covering of such perpendicular surfaces, particularly the outer-facing ones, while at the same time covering the planar surfaces, is obviously an especially difficult problem, yet such "step coverage" is of particular importance in determining the quality of the metallization overall. It has generally been thought that in order to achieve the required uniformity of planar surface coverage as well as adequate step coverage, relative motion between the wafers and the deposition source during coating deposition is necessary. However, such motion carries with it certain disadvantages, especially the heightened possibility of generation of debris, as by dislodgement of deposits of coating material on various internal structures of the apparatus due to the motion, a heightened possibility of mechanical shock and vibration damage to the wafer, and the build-up of deposition on the wafers in a nonsymmetrical and inhomogeneous fashion, as will be further explained below. Naturally, contamination level will depend on the maintenance of the quality of the vacuum environment during deposition and the concentration of contaminants relative to the speed of deposition. Thus the adequacy of "outgassing", or the evacuation of gas and vapors from the wafer and accompanying wafer supports which are introduced into the coating chamber will also be important.

The manner in which the prior art has attempted to achieve one or more of the above characteristics, and the attendant difficulties and trade-offs involved in achieving the above criteria of coating quality, may be best appreciated by considering the two main types of vacuum deposition systems which are in current use for metallizing wafers: batch and load lock. A typical batch system comprises a pumping station, an evacuable bell jar, an isolation valve between the pumping station and the bell jar, heat lamps, one or more deposition sources, and planetary fixtures which hold the semiconductor wafers and rotates them above the deposition source or sources. At the start of a deposition cycle the isolation valve is closed and the bell jar is open. Wafers are loaded manually from cassettes into the planetary fixtures (a load of 75 wavers of 3-inch diameter is typical). The planetary fixtures are then mounted in the bell jar, the bell jar closed, and the system evacuated. After a prescribed base pressure is reached, the wafers are further outgassed through the application of radiant energy from the heat lamps. In some cases the wafers are sputter-etch cleaned prior to the start of deposition. A typical coating is aluminum or an aluminum alloy sputtering onto the wafer to provide interconnect metallization. In order to achieve the required coating uniformity and step coverage, relative motion is provided by rotation of the planetary fixtures. After deposition, the wafer and system are allowed to cool, the isolation valve is closed, the bell jar vented to atmosphere, the bell jar opened, and the planetary fixtures are removed and unloaded manually into cassettes. This completes a typical cycle, which takes approximately 1 hour.

Although such batch systems are in widespread use in production today for metallizing semiconductor wafers, certain of their characteristics pose limitations and disadvantages. For one, the entire relatively large batch of wafers is inherently "at risk" of a partial or total loss during the deposition cycle. The manual loading of wafers from cassettes into planetary fixtures provides ample opportunity for contamination and breakage. Air exposure of the entire system inside the bell jar for loading and unloading leads to possible contamination and adds a very large outgassing load for the vacuum pumps to contend with (the outgassing area ascribable to the wafers alone is typically less than ten percent (10%) of the total air-exposed area which must be outgassed). Long deposition throw distances (typically 6 to 14 inches) from the source are needed to obtain the large area coverage for the many wafers to be coated within the batch system. This leads to low deposition rates (typically 600 angstroms per minute for sputter deposition source), which make the films more susceptible to poisoning by reaction with background gases , and thus more sensitive to the quality of the evacuated environment. Outgassing of the wafers and the air-exposed areas of the system is accelerated by application of radiant energy from heat lamps, but since the wafers are in uncertain thermal contact with the planetary fixtures, their temperatures are also uncertain. Moreover, the heating source normally cannot be operated during sputter deposition, so that the wafers cool in an uncontrolled fashion from the temperature attained during preheat. Lack of control of wafer temperature during deposition limits certain aspects of film characteristics which can be reliably and reproducibly attained. Of course the mechanical motion of the planetary fixtures for achieving uniformity and step coverage can dislodge particles of coating material deposited elsewhere within the system other than on the wafers, which in turn can cause debris to become attached to the wafers, in turn reducing yield of good devices.

A typical load lock system comprises a pumping station, an evacuable processing chamber, an isolation valve between the pumping station and the processing chamber, a heating station, a deposition source, a load lock, and a platen transport system. At the start of a deposition cycle, wafers are loaded manually from a cassette into a metal platen (a 12-inch by 12-inch platen size is typical), which then acts as a carrier for the wafers during their journey through the load lock and processing chamber. After introduction through the load lock into the processing chamber, the platens and wafers are transported to the heating station, where they are further outgassed by the application of radiant energy. Additional cleaning of the wafers by means of sputter etch may also be performed at the heating station. Metal film deposition is accomplished by translating the platen and wafer relatively slowly past the deposition source, which may be a planar magnetron type of sputtering source with a rectangular erosion pattern, with the long dimension of the erosion pattern being greater than the platen width. Relatively high deposition rates (10,000 angstroms per minute) are achieved by moving the platen past the sputter source over a path which passes the wafers within several inches of the sputter source. After deposition, the platen and wafer are returned to the load lock where they pass from the processing chamber back to atmosphere. The wafers are then unloaded manually back into a cassette. This completes a typical cycle, which take typically 10 to 15 minutes. In another type of load lock system, the wafers are mounted on an annular plate which rotates past the deposition source. Each wafer makes multiple passes below the deposition source until a film of sufficient thickness is built up.

The above load lock systems overcome some of the disadvantages of batch systems, but not all. Of primary importance is the fact that the use of a load lock allows wafers on a platen to be introduced into and removed from the processing chamber without allowing the processing chamber pressure to rise to atmospheric. This greatly reduces the amount of air-exposed surface that must be outgassed prior to deposition. While the processing chamber does need to be opened to atmosphere periodically (for cleaning and for replacing deposition targets), the frequency of such air exposure is much less than with batch systems.

Another important factor is that the size of the wafer load which is "at risk", that is, subject to being rejected due to a defect or failure of the process, is significantly smaller in the load lock system (16 3-inch wafers in the first load lock system, compared with 75 3-inch wafers in the batch system in the above example). Because the number of wafers per load is much smaller with the load lock system, it is not necessary to employ the long deposition throw distances required with batch systems. Higher deposition rates are therefore attainable by closer coupling between wafer and source.

Despite the advantages afforded by load lock systems, many disadvantages and shortcomings still remain. In both bath and load lock systems, wafers are typically transferred manually between platen and cassette, with attendant risks of contamination and breakage. Although the use of the load lock avoids exposure of the processing chamber to the atmosphere, the platen which carries the wafers is air-exposed on each load and unload cycle. Thus its surfaces must also be outgassed, which raises the total outgassing load well beyond that of only the wafers themselves. In addition, sputtered deposits that build up on the platen become stressed due to repeated mechanical shock and air exposure, leading to flaking and debris generation. As with bach systems, wafers are still in uncertain thermal contact with their carrier. Controls over wafer temperature during outgassing and during deposition remain inadequate. The metal films are put down on the wafers in a non-symmetrical fashion, since the film deposited on the wafer builds up in different ways depending upon its location on the platen, i.e., whether the wafer is outboard, inboard, approaching the source, or moving away from the source. Translation of the platen during deposition to provide uniformity and step coverage heightens the risk of generation of debris and flakes, and thus contamination of the wafers. In certain load lock systems, symmetry and homogeneity are further compromised by causing the wafer to make multiple passes below the deposition source. Thus the metal film is deposited in a "layered" fashion because the deposition rate tapers off to almost nothing when the wafers are rotating in a region remote from the deposition source. The low rates of deposition in such regions heighten the rick of contamination due to incorporation of background gases into growing film, and non-uniformities in the distribution of any contaminants which may be present result from the non-uniformities in deposition rate.

Even though a much smaller number of wafers is being processed at any one time in load lock systems as compared with batch systems, a significant number of wafers still remains "at rick". From this point of view, it would be best to process wafers individually on a serial continuous basis, but the time needed for adequate pumpdown of the load lock during loading and unloading, and for wafer outgassing and the outgassing of wafer supports, coupled with the time needed to coat a wafer individually in an adequate manner, has rendered the concept of such individual processing impractical until now as compared to batch systems or load lock systems handling a plurality of wafers with each load. It would also be much better from the viewpoint of prevention of debris generation and consequent reduction in yield of good microcircuit devices, as well as lessening the risk of abrasion and mechanical shock and vibration, to hold wafers stationary during coating deposition. However, as we have seen, this has been considered inconsistent with the need to obtain adequate deposition uniformity and step coverage, since this normally requires establishing relative motion between the source and wafer. Further, there has been no basis for expecting greater control over reproducibility and temperature of the coating process in a individual wafer processing system as opposed to a batch or load lock system coating a plurality of wafers with each load.

Accordingly, an object of the invention is to provide apparatus for rapidly coating wafers individually with a higher quality coating than possible previously.

A related object of the invention is to provide apparatus for depositing metallization layers of superior quality with respect to the aggregate considerations of step coverage, uniformity, symmetry and homogeneity, contamination level, debris damage, and reproducibility.

Also an object of the invention is to provide apparatus for rapidly coating wafers individually with improved step coverage and good uniformity.

Another related object of the invention is to provide an improved load lock system for metallizing wafers individually yet at a high rate.

Yet another object of the invention is to provide an improved load lock system for metallizing semiconductor wafers individually on a production-line basis with enhanced quality, including uniformity and step coverage.

A related object is to provide a system for coating wafers which reduces the number of wafers at risk at any one time due to processing.

Another related object is to provide a system for metallization or other vacuum processing of wafers individually on a serial continuous basis, with a plurality of work stations operating simultaneously on individual wafers.

Also a related object is to reduce the outgassing load and minimize disturbance to the evacuated coating environment due to introduction of wafers into a load lock system for coating.

Yet another object of the invention is to improve the yield of microcircuit devices subsequently derived from the wafer by reducing generation of debris and the probability of damage from abrasion and incorporation of contaminants.

Yet another object is to provide a load lock type system which accomplishes transport between various work stations and into and from the vacuum regions without the use of platen-like supports for the wafers.

Also a related object of the invention is to provide a load lock type system as above which does not use platen-like wafer supports, in which loading and unloading are effected of certain wafers while yet others are being processed.

A further related object is to provide a system as above which is compatible with automatic wafer handling from cassettes.

Also a related object is to provide improved control over wafers, especially their temperature, throughout the processing thereof.

Yet a further object of the invention is to provide a system for production-line use in which reliability, maintainability, and ease of use are improved.

SUMMARY OF THE INVENTION

The broadest objects of the invention are met by providing apparatus for coating a wafer individually, which includes a ring-shaped sputtering source emitting coating material and having a diameter larger than that of one of the wafers, means for locating an individual one of the wafers in facing stationary relationship to the source, and at a distance less than the diameter of the source, as well as means for maintaining the source and wafer in an argon environment of up to 20 microns pressure (1 micron=10.sup.-3 millimeters of mercury=1 millitorr=0.133 Pa) during coating of the wafer. In this manner a coating of improved quality with good uniformity is rapidly deposited on the wafer without need for relative motion between wafer and source and the added complexity and debris generation risk attendant thereto.

The objects of the invention are also met by providing apparatus for repetitively sputter coating individual wafers in minimal time, useful with vacuum chamber means continuously maintaining a controlled subatmospheric environment. The apparatus includes internal wafer support means positioned within the chamber immediately inside of the entrance thereof, including means for releasably and resiliently gripping edgewise an individual wafer, to immediately accept a wafer upon insertion and permit instant release and removal upon completion of coating. Also included is a sputtering source mounted in the chamber and having a cathode of circular outline emitting coating material upon the wafer in a pattern approximating that from a distributed ring source. The source has a diameter which is larger than that of the wafer and is spaced from the wafer by a distance less than that of the source diameter. The wafer support means holds the wafer stationary during coating. Finally, the apparatus includes load lock means including a movable member within the chamber to seal the wafer support means off from the remainder of the chamber interior and when the door of the entrance is opened, isolating the wafer and support means from the chamber environment during insertion and removal of a wafer. In this manner, individual coating of wafers can be repetitively performed, with disturbances to the chamber environment by outside wafer support expedients, consequent contaminants, and large load lock volumes minimized, while overall wafer coating time is improved.

Objects of the invention are also met by apparatus for individually processing wafers continuously in a controlled subatmospheric environment, which includes a vacuum chamber having a first opening in a first wall thereof and a door for closure of the opening, at least one wafer processing means mounted in a wall of the chamber and defining at least one processing location of the chamber spaced from the first opening, and movable carrier means within the chamber movable between the first opening and the processing location. The carrier means is provided with at least two apertures and spaced a first distance to enable the apertures to be aligned respectively with the first opening and the processing location. Each of the carrier apertures mounts clip means for releasably and resiliently gripping a wafer. The apparatus also includes closure means within the chamber for closing off one of the carrier apertures when said aperture aligns with the first chamber opening, the closure means and chamber defining therebetween a small load lock volume with the closure means sealing off the aperture from the chamber when the chamber door is opened to load or unload a wafer into the clip means. In this manner wafers can be continually serially introduced into the vacuum chamber with minimal disturbance of the controlled atmosphere therein, and the wafers individually processed at the processing location while loading and unloading of another wafer takes place at the load lock without use of external wafer support means, the presence of which would greatly increase the gas load to be eliminated by the load lock and chamber, as well as increasing the possibility of contaminants. Furthermore, the load lock volume is minimized to only that absolutelynecessary to accommodate a single wafer, thus also reducing the amount of pumpdown load for the load lock and chamber.

In one preferred embodiment, the movable carrier means may be provided in the form of a disc-like transfer plate mounted for rotation about its axis with various wafer processing stations symmetrically disposed around the same axis. Besides sputtering stations, the stations may also be heating or cooling stations, and the heating, for example, may be applied to the side of the wafer opposite that of the sputtering deposition, since the clip means support the wafers edgewise, thereby allowing processing of both sides thereof. The wafer transfer plate preferably rotates in a vertical plane to better combat accumulation of debris on the wafers. When fully loaded, the apparatus limits the number of wafers at risk at any one time to only those loaded in the wafer transfer plate, and enables several processing operations to be carried on at the same time, for example, coating of one wafer simultaneously with the heating of another and with the unloading and loading of still others. The use of the internal wafer clip support means, thin load lock, and individual processing of wafers enables easy loading and unloading, including simplified automatic loading. In one particular aspect, a vertically-acting blade-like elevator means raises a wafer edgewise to a point immediately adjacent the chamber entrance. Vacuum means associated with the door of the chamber then grip the rear surface of the wafer and propel same into the clip means as the door is closed, thereby loading the load lock and sealing means simultaneously. Further details of a fully automatic system for loading the vacuum processing chamber from a conveyor-driven cassette containing a plurality of wafers to be coated may be found in the co-pending application of G. L. Coad, R. H. Shaw, and M. A. Hutchinson for "Wafer Transfer System", filed contemporaneously herewith, U.S. Pat. No. 4,311,427. Similarly, the details of the means for resiliently supporting the wafers within the vacuum chamber and associated means for aiding the loading and unloading of same into said supports within a chamber may be found in the co-pending application of R. H. Shaw for "Wafer Support Assembly", filed contemporaneously herewith, U.S. Pat. No. 4,306,731.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of the complete wafer coating system of the invention, showing the main cylindrical processing chamber, the door arrangement at the entrance of the load lock the chamber, and the four remaining work stations of the processing chamber, together with portions of the wafer cassette load/unload assembly;

FIG. 2 is a broken-away perspective view of the processing chamber of FIG. 1, showing the load lock and sputter coating stations in more detail;

FIG. 3 is a perspective view of the cassette load/unload assembly of FIG. 1, showing its manner of cooperation with cassettes of vertically-oriented wafers and the door assembly of the processing chamber, and the manner in which wafers are transferred therebetween and into the chamber load lock;

FIG. 4 is a cross-sectional elevational view of the door and load lock of FIGS. 1 through 3, showing the manner in which the door assembly loads a wafer into the load lock, and the manner in which the load lock is sealed from the remainder of the processing chamber interior;

FIG. 5 is a view similar to FIG. 4, showing the relative positions of the elements of the load lock upon completion of loading of the wafer therewithin;

FIG. 6 is a view similar to FIGS. 4 and 5, showing the position of the wafer and the load lock elements just subsequent to the extraction of a wafer from the internal wafer support assembly, and prior to the opening of the door, or just before the loading of a wafer into the internal wafer support assembly immediately after closure of the door for loading;

FIG. 7 is a cross-sectional elevational view taken across line 7--7 of FIG. 1, showing a wafer heating station within the chamber of FIG. 1;

FIG. 8 is an elevational cross-sectional view taken along line 8--8 of FIG. 1, showing a wafer cooling station within the wafer processing chamber of FIG. 1;

FIG. 9 is a cross-sectional elevational vie taken alone line 9--9 of FIG. 1, showing the wafer sputtering station of the chamber of FIGS. 1 and 2;

FIG. 10 is a schematic cross-sectional view focusing on the wafer and sputtering source target of FIG. 9, which shows the spatial relationships, relative positioning, and dimensions of these elements in greater detail;

FIG. 11 is a graph illustrating the uniformity of thickness of deposition on the main planar surface of the wafer by the source of FIGS. 9 and 10 as a function of the radial position on the wafer, for each of several wafer-to-source distances;

FIG. 12 is a plot similar to FIG. 11, but for only a single wafer-to-source distance, one curve being for a deposition environment of 2 microns argon pressure and the other being for a deposition environment of 10 microns argon pressure;

FIG. 13 plots thickness of coating coverage on the sidewall of grooves within the wafer surface as a function of the radial position on the wafer, both for outwardly-facing (relative to the center of the wafer) sidewalls, as well as inwardly facing sidewalls, for a source-to-wafer distance of 4 inches, one curve being taken at 10 microns argon pressure, and the other at 3 microns argon pressure;

FIG. 14 is a plot similar to FIG. 13, except that the source-to-wafer distance is 3 inches;

FIG. 15 is a plot of uniformity of planar coverage as a function of argon pressure of the coating environment, one curve being for the radial position 1.5 inches, and the other being for the radial position 2.0 inches.

DETAILED DESCRIPTION

The wafer coating system of FIG. 1 principally includes a generally cylindrical vacuum processing chamber 10 having five work stations, one of which comprises load lock arrangement 12; and one of which comprises coating station 14. Remaining further elements of the coating system found within chamber 10 may be seen in more detail in FIG. 2, which also shows a wafer 15 within load lock 12; and also a wafer at coating station 14. Further elements include pressure plate 16, wafer carrier plate assembly 18, and clip assemblies 20 (better shown in FIG. 3), by which a wafer is retained within wafer carrier plate assembly 18. Door assembly 22, which seals the entrance opening 23 of chamber 10, and which cooperates with the just mentioned elements to form the chamber load lock arrangement 12, completes the principal elements of processing chamber 10. These elements, together with cassette load/unload assembly 24 and the various ancillary vacuum pumps 25 for chamber and load lock evacuation, and control means, are all housed compactly in cabinet 26.

The system desirably includes several other work stations other than load lock arrangement 12 and coating station 14, in particular wafer heating station 28, auxiliary station 29, and wafer cooing station 130. All five work stations are equally spaced laterally from each other and from the central axis 36 of the vacuum chamber. Although five stations are provided, the design could be equally well adapted to both a greater or fewer number of stations. Also included are at least two pneumatic rams 30 and 31 which function to drive pressure plate 16 and wafer carrier plate assembly 18 against the front wall 32 of chamber 10, and carrier plate drive 35, which centrally mounts carrier plate assembly 18, which is circular and of nearly the diameter of front wall 32, for rotation about the central axis 36 of the vacuum processing chamber.

In general, wafers are individually presented and loaded by door assembly 22 into load lock arrangement 12 and thereby within wafer carrier plate 42. The wafer is then passed in turn to each of the work stations, where it is heated for completion of outgassing and/or sputter-etch cleaned, coated, optionally coated with a second layer, cooled, and then returned again to load lock 12 for removal from wafer carrier plate assembly 18, again by door assembly 22. Although the foregoing generally-described system is a rotary one and a multi-station one, the load lock and coating steps are equally applicable to a single station or dual station configuration, or a non-rotary or in-line arrangement as well.

Now considering the system in more detail from the view point of an incoming wafer, the load lock arrangement 12 through which a wafer 156 must be passed in order to enter the evacuated environment of the chamber is of key importance. FIGS. 4-6 are especially important in appreciating the operation of the movable elements of load lock 12. As pointed out above, the load lock is defined by a sandwich arrangement of elements between the chamber door assembly in its closed position against the front wall of the processing chamber and the pressure plate in its driven position. The load lock is built around a circular aperture 37 within wafer carrier plate assembly 18, which is positioned internally of the chamber just inside the chamber entrance 23 associated with load lock 12, with plate assembly 18 generally parallel to wall 32 and the pressure plate 16, positioned within the chamber rearwardly of plate assembly 18. Wafer 15 is loaded and held within the load lock and within the plate assembly by means which will be described below. The controlled subatmospheric environment which may be provided within chamber 10 for certain wafer processing operations may be, for example, up to 20 microns of argon or other inert gas for sputter coating operations. Because of this evacuated environment, the load lock region must be sealed off from the remainder of the chamber interior whenever door 22 is open in order to preserve the evacuated environment. Pressure plate 16 serves the function of isolating the load lock area from the chamber interior (and checks also several other functions simultaneously at other work stations, as will be shown below). Pneumatic rams 30 and 31, mounted to the rear plate of the processing chamber, drive the pressure plate and plate assembly against front chamber wall 32, with pneumatic ram 30 bein gapplied particularly to the pressure plate concentrically with load lock arrangement 12 to effect the sealing of the load lock. Both pressure plate 16 and chamber front wall 32 are equipped with O-rings 38 arranged in a circular pattern concentric with chamber entrance 23 which provide vacuum seals in the sandwich arrangement of elements defining the load lock. Chamber door assembly 22, which in its closed position seals against the outside surface of chamber front wall 32 and also includes a concentric O-ring 39 to provide the vacuum seal, completes the load lock by sealing off the chamber entrance 23 from the outside atmosphere. FIGS. 4 and 6 show the completed load lock, with pressure plate 16 in its forward, advanced position, compressing plate assembly 18 against chamber wall 32, and sealing off aperture 37; and door 22 closed to seal off chamber entrance 23 to form the load lock about aperture 37, which is only of a size no larger than necessary to accommodate a single wafer. It may be seen that an unusually thin low-volume load lock is thereby defined with a minimum of elements, and of a minimum size necessary to accommodate wafer 15 therewithin. For further details of the load lock arrangement, see the commonly owned U.S. Pat. No. 4,311,427 "Wafer Transfer System". FIG. 5 shows pressure late 16 in its withdrawn, rest position, and with the wafer already secured within plate assembly 18 within the chamber.

Cooperating with this thin load lock arrangement is wafer carrier plate assembly 18, which includes a plurality of circular apertures such as at 37 (as best seen in FIG. 2) matching the number and spacing of work stations within chamber 10. The apertures 37 are of a diameter larger than the wafers, are equally spaced from each other, and centered at the same radial distance from the central axis of the processing chamber. The aforementioned work stations are likewise spaced, so that when any aperture of the wafer carrier plate assembly 18 is aligned with any work station of the processing chamber, the remaining apertures are each similarly aligned with a respective one of the remaining work stations. Thus, if a wafer is secured within each of the apertures of carrier assembly 18, each of such wafers can be individually processed at a work station simultaneously with the processing of other wafers respectively at the remaining work stations. In this manner, a wafer is individually processed at a given station, yet during the same time, several other wafers may also undergo other operations at the remaining work stations. In particular, while a wafer is being unloaded and/or loaded at load lock 12, another wafer may be coated at coating station 14, while still another wafer may be heated at heating station 28. Carrier plate drive 35 intermittently operates to move plate assembly 18 by the distance of one station so as to serially present each of the wafers in turn to each of the processing stations in a counterclockwise direction, until a given wafer finally returns to the load lock for unloading therefrom.

As the wafer is transported from work station to work station as above described, it is important that the wafer be supported within carrier plate assembly 18 so as to avoid any risk of mechanical damage and abrasion due to being moved about, and generally so as to be protected from mechanical shock, vibration, and abrasion. To this end, wafer carrier aperture 37 is of a diameter such that both a wafer and a set of clip assemblies 20 can be accommodated within the periphery of the aperture, and recessed and parallel with the carrier plate, thereby protecting the wafer. The set of thin edgewise-acting clip assemblies also is important to the formation of the thin load lock arrangement 12, and edgewise resiliently supports the wafer in an upright position within plate assembly 18. An especially advantageous form of such an edgewise acting clip assembly is shown in cross section in FIGS. 4 through 8, and is disclosed in detail in the aforementioned commonly assigned U.S. Pat. No. 4,305,731 "Wafer Support Assembly." A set of four clip assemblies 20 is mounted within retaining rings 47 which are removably attached to the disc-like circular wafer carrier plate 42 concentrically with each of the plate apertures 37, thus forming the complete wafer carrier plate assembly 18. This arrangement mounts a set of clip assemblies 20 in spaced relationship within the periphery of each circular aperture 37. Retaining rings 41 are of U-shaped cross section, with each having flanges 46 and 47 defining the inner and outer peripheries thereof, and clip assemblies 20 are recessed within these flanges. Although it is preferred that four clip assembles be used within an aperture 37 it is possible to use three, or a number greater than four. However, a set of four has been found to provide greater reliability than three.

As may be seen in any of the FIGS. 3 through 8, clip assemblies 20 each include a block 50 of generally rectangular cross section, which may be of insulating material for applications such as sputter etch for which electrical isolation of the wafer is desired, and an elongated spring clip 53 firmly engaged in wraparound fashion about block 50. Each clip 53 includes at the end thereof opposite the block an arcuate finger portion or tip 55, which is of a curvature in radius appropriate to gripping an edge of a wafer. Extending from block 50 is proximal flat portion 56, which lies within a plane closely adjacent and parallel with the plane defined by plate aperture 37. On the other hand, distal portion 57 is angled away from portion 56 down toward the plane of plate aperture 39 and defines an obtuse angle with portion 56. This clip arrangement results in a plurality of arcuate tips 55 lying on a circular pattern of diameter somewhat less than that of a typical wafer 15 (such circular pattern also lies within the plane of wafer carrier plate 42).

Wafer insertion into load lock 12 may be effected manually by simply pushing a wafer by its edge or rear face into clip assemblies 20. This will, however, involve some edge rubbing of the wafer against distal portion 56, to spread apart the clips somewhat to accept the wafer within tips 55. In order to insert a wafer without such rubbing contact therewith, the clips must first be slightly spread, and then allowed to rebound against the edge of the wafer upon insertion thereof into the load lock. Although both wafer insertion and clip spreading may be done manually, it is far preferable to avoid all such manual operations, and the consequent added risk of damage, error, and contamination associated therewith. Chamber door assembly 22 carried thereon a vacuum chuck 60 centrally axially therethrough, and a plurality of clip actuator means 62 near the periphery thereof. These elements, along with wafer cassette load/unload assembly 24, provide an automated wafer loading and unloading arrangement for load lock 12 which avoids all such manual handling of the wafers, and automates the loading process.

As thus seen in FIGS. 1 and 3, chamber door assembly 22 is attached to front wall 32 of chamber 10 by a heavy-duty hinge 63 having a vertical axis, to allow the door to open and close in a conventional manner to a fully open position as shown, wherein the door and its inside face 64 are vertical and perpendicular to the plane of chamber entrance 23, as well as to plate assembly 18. As shown in FIG. 1, door assembly 22 is moved between its open and closed positions by means of a conventional push-pull actuator 196, and pivot linkage 197 which is attached to hinge 63 for causing rotation of the hinge and door. Vacuum chuck 60, which extends axially and centrally through the door so that the active end thereof forms part of the inside face 64 of the door, engages a wafer presented vertically to the inside face of the door and holds the wafer by vacuum suction as the door is closed, whereupon the vacuum chuck axially extends from the inner door face as shown in FIG. 4 to carry the wafer into engagement with clip assemblies 20. The vacuum chuck will then withdraw, and wafer 15 is held in the chamber by the clip assemblies and undergoes processing, and movement to the various work stations in turn by rotation of plate assembly 18. The above-described axial movement of chuck 60 relative to the door face 64 is accomplished by means of a conventional pneumatic cylinder 61. In this preferred embodiment, the vertical presentation of the wafer to the inside face 64 of the door is effected by load/unload assembly 24, as will be further detailed below.

It should be noted that the load lock arrangement, wafer carrier plate assembly 18, and door assembly 22 need not be limited to a vertical orientation, although this is preferred to help obviate any possibility of debris settling upon a surface of the wafer. The clip assembly, carrier plate and load lock arrangement of the invention, as well as all of the work stations, function equally well is oriented horizontally. Indeed, although the load/unload assembly 24 for the vertically-oriented wafer cassette is meant for vertical operation, the door assembly 22 could easily be made to load wafers into the load lock in a horizontal plane, yet accept wafers in a vertical orientation, by suitable modification of its manner of mounting to the chamber wall in a conventional manner.

As noted above, it is preferable to avoid simply loading a wafer into the clip assemblies 20 within the load lock by pushing a wafer against the angled distal portion 57 of the clips. In order to insert a wafer without such rubbing contact, the clips must first be slightly spread, and then allowed to rebound against the edge of the wafer upon insertion thereof into the load lock. This is accomplished automatically as the wafer is being inserted by vacuum chuck 60 by four clip actuating means 62 mounted within the door as aforementioned. Each clip actuating means 62 is mounted so as to be in registration with a corresponding one of clip assemblies 20 when the door is in its closed position. Each clip actuating means 62, shown in detail toward the lower end of FIG. 4 includes a pneumatic cylinder 65, and a contact pin 66 which moves axially inwardly and outwardly and is propelled by cylinder 65, and Pins 66 are each in registration with one of flat proximal clip portions 56 when the door is in its closed position. With door 22 closed, pins 66 are extended just prior to insertion of a wafer; or as a wafer is to be withdrawn. The pressure of a pin 66 against the facing flap clip proximal portion 56 presses the clip and causes the tip 55 to swing back and outwardly, thereby releasing the clips, to facilitate insertion or removal of a wafer without rubbing contact therewith.

During wafer unloading after completion of the wafer processing, these operations are reversed, with the chuck again extending and applying vacuum to the backside of the wafer to engage same, with the clip actuating means again cooperating to release the clips, whereupon the door opens and the chuck retains the wafer on the inside face of the door by vacuum suction until the wafer is off-loaded by load/unload assembly 24.

As we have seen, when in its fully opened position, door assembly 22 is poised to accept a wafer for insertion into the load lock arrangement 12, or it has just opened and carried a finished wafer from load lock 12, which must then be unloaded from the vacuum chuck. The function of presenting a wafer to the door assembly 22 for loading, or for removing a processed wafer therefrom for unloading, is performed by cassette load/unload assembly 24, which includes wafer elevator assembly 68 and wafer cassette conveyor assembly 69. Extending below and on either side of chamber entrance 23 and attached to wall 32 of the chamber is the conveyor assembly, which moves cassettes 70 of wafers generally along from the right of the entrance as shown in FIG. 1 to left. The cooperating wafer elevator assembly 68 lifts wafers individually from the cassettes conveyed by conveyor assembly 69 to the operative end of vacuum chuck 60 within the inside face 64 of door assembly 22, or lowers such wafers from the door upon completion of processing.

Conveyor assembly 69 includes a spaced pair of parallel rails 72 and 73 extending horizontally and longitudinally across the front of wafer processing chamber 10. The rails support and convey cassettes 70, and the spacing of rails 72 and 73 is such that the sidewalls of the cassettes straddle the rail and enable the cassettes to be slidably moved along the rails across the conveyor assembly. Motive power for the movement of the cassettes is provided by chain drive means 75 which includes various guides and gear arrangements causing a roller chain to be moved alongside rail 72. The chain is provided at regular intervals with guide pins 76, which engage a matching cutout on the bottom of cassette wall 77 adjacent rail 72. Thus, the cassette is caused to move at the same rate as the chain toward and away from elevator assembly 68, as required. A stepper motor means 80 is provided as the driving power for the chain means 75, to provide precise control over the movement of the cassettes, so that any chosen individual wafer within a cassette may be positioned for interaction with the wafer elevator assembly 68. A conventional memory means is coupled to stepper motor 80 and wafer elevator assembly 68, which stores the location of an individual wafer within a cassette. Thus, although several further wafers may have been loaded into processing chamber 10 and the cassette accordingly advanced several positions since a first wafer was loaded, yet upon emergence of the completed first wafer, the stepper motor maybe reversed the required number of steps to return the completed wafer to its original position, then again resume its advanced position to continue its loading function.

The cassettes 70 hold a plurality of the wafers 15 in spaced, facing, aligned and parallel relationship, and are open at the top as well as over a substantial portion of their bottom, to permit access from below and above the wafers. They must be loaded so that the front faces of the wafers, which contain the grooves, steps, and other features defining the microcircuit components, face away from the inside face 64 of the open door 22, and so that the rear faces of the wafers face toward the door assembly. This ensures that when the vacuum chuck 60 engages the wafer, no contact is made with the front face containing the delicate microcircuits, and that the wafer is properly positioned upon insertion into the load lock 12 so that it will be oriented properly with respect to processing equipment within the processing chamber 10.

The wafer elevator assembly 68 is positioned below and just to the left side of chamber entrance 23 and includes an upper guide plate 82, a blade-like elevator member 83, and an actuating cylinder 84 connecting to the lower end of member 83. Elevator blade member 83 is guided for movement up and down in a vertical path intersecting at right angles conveyor 69 between rails 72 and 73 to inside face 64 of door 22. Guide slot 85 in guide plate 82 just below the inside face of the door in the open position provides the uppermost guide for blade 83, while a vertical guide member 86 extending below the conveyor toward the actuating cylinder also aids in retaining blade 83 on its vertical path. The width of the blade 83 is less than that of the spacing between rails 72 and 73, and also less than the spacing between the main walls of the cassettes 70 which straddle rails 72 and 73. Blade 83 is also thinner than the spacing between adjacent wafers retained in cassettes 70.

Blade member 83 is further provided with an arcuate upper end 87 shaped to match the curvature of the wafers, and a groove within this end adapted to match the thickness of a wafer and retain a wafer edgewise therewithin. Thus, elevator blade member 83 passes between guide rails 72 and 73 and intersects conveyor and cassette at right angles thereto, upon stepper motor means 80 and chain drive 75 brining a cassette and wafer into registration over the path of the blade. As may be seen, the cassettes are constructed to allow access from below to the wafers, and to allow elevator blade 83 to pass completely therethrough. Accordingly, upon stepper motor means 80 and chain means 75 placing a cassette and a wafer in registration over the path of the blade, blade 83 moves upwardly between the conveyor rails to engage from below a wafer within the groove of its upper end 87, and elevate the wafer upwardly to a position in registration concentrically with and immediately adjacent inside face 64 of chamber door 22 in its open position. Note that since the wafers are vertically oriented, gravity aids in holding the wafers firmly yet gently and securely in the grooved end 87 of the blade. Contact with the delicate front face of the wafer, upon which the delicate microcircuits are defined, is therefore virtually completely avoided, unlike the case of typical automated handling when the wafer is in a horizontal orientation. Thus the risk of damage or abrasion to the wafer is greatly lessened.

Upon arrival of the wafer at the door 22, vacuum chuck 60 engages wafer 15 at tis rear face by suction, and elevator blade 83 then is lowered through guide slot 85 and the cassette to a point below conveyor 69. Door 22 then closes with the wafer retained by the chuck 60, and the wafer is thereby loaded into the load lock arrangement 12 and chamber entrance 23 sealed simultaneously as described above for processing within chamber 10. Prior to completion of processing for wafer 15, still further wafers may be loaded within the remaining ones of apertures 37 of plate assembly 18; therefore the stepper motor and chain drive step the cassette one wafer position to move the next wafer serially in position over blade 83. Blade 83 then rises to repeat its operation of moving this next wafer upwardly to the open door, whose vacuum chuck then again engages that wafer for insertion into the load lock. Meanwhile, upon completion of processing for original wafer 15 by rotation in turn to each station, it is again at load lock 12, and vacuum chuck 60 again extends to the backside of the wafer while the door is still in its closed position, and clip actuating means 62 simultaneously depress the clips to disengage same from the wafer to enable the removal thereof by chuck 60, whereupon the door is opened and the wafer again positioned over the path of blade 83. Meanwhile, stepper motor means 80 and chain means 75 move the cassette back to that the original position of wafer 15 is presented over the blade path. Blade 83 then rises through conveyor rails 72 and 73 and slot 85 upwardly to engage the lower edge of wafer 15, whereupon chuck 60 releases the wafer, and enables blade 83 to lower the wafer back into its original position within the cassette. The cassette is then propelled forward to the position of the next wafer to be processed serially.

Prior to the elevation of the individual wafers by the elevator assembly 69 and loading into the load lock, it is desirable to insure a standard orientation for the wafers, so that the usual guide flat 91 across a cord of each wafer is aligned to be lowermost in the cassettes. In this manner, each of the wafers is assured to assuming the same position with respect to the processing equipment within the chamber. Further, making certain that the guide flat is in a given predetermined position assures that clip assemblies 20 within plate assembly 18 will function properly, and not accidently engage a flat of the wafer instead of a portion of the main circular edge. To ensure such standard orientation, a pair of opposed rollers 90 is provided which are longitudinally extended along and between rails 72 and 73 so that the roller axes are parallel with the rails. The rails are positioned in the path of the cassettes just prior to the position of the elevator assembly 68, so that orientation of the wafers is completed prior to their reaching the elevator assembly. Upon passage of the cassette over the rollers, the rollers are elevated and then are driven serially and in opposed senses, one clockwise and the other counterclockwise, and lightly contact the circular edge of the wafers. Contact with moving rollers 90 then has the effect of rotating the wafers within the cassettes until the guide flat 91 of each wafer is positioned at a tangent to the moving rollers, whereupon contact with the roller is lost and the wafers are all positioned with guide flats facing downwardly and in alignment, whereupon the rollers 90 are retracted downwardly.

As aforementioned, pressure plate 16 is driven against carrier plate 42 and wall 32 whenever door 22 is in its opened position, to protect the evacuated interior environment of the chamber from the atmosphere. We have seen that FIGS. 4 and 5 show in more detail the relative positioning of the pressure plate and wafer carrier plate, with FIG. 4 showing the aforementioned sandwich arrangement of the elements defining the load lock arrangement 12, and FIG. 5 showing the relative positioning of the elements when the pressure plate is in its withdrawn position. Note also that FIG. 4 shows vacuum chuck 60 in its extended position as the wafer is inserted into clip assemblies 20 with pins 66 of clip actuating means 62 partially extended after having spread the clips; while in FIG. 5, the vacuum chuck has withdrawn, as have the pins of the clip actuating means, and the wafer is now securely mounted in wafer carrier plate assembly 18. With pressure plate 16 withdrawn, the wafer is not ready to be rotated to subsequent processing stations. In FIG. 6, the vacuum chuck is also in the withdrawn position; however, the vacuum suction is operative, and the wafer is shown in its position against the inner face 64 of chamber door 22. This is, of course, the position of the elements of the load lock and the wafer just after the wafer has been withdrawn from clip assemblies 20, prior to its being removed from the load lock; or, it also represents the position of the elements just after the door has been closed and the vacuum chuck has not yet advanced the wafer to its position within aperture 37 of the wafer carrier assembly. Pins 66 of the clip actuating means 62 are shown bearing upon the clips just prior to depressing same to spread the clips in order to accept the wafer therewithin.

Upon completion of loading of the load lock with a wafer 15, the load lock is rough-pumped during a cycle lasting much less than a minute down to a level which, though still a good degree less evacuated than the chamber, does not appreciably disturb the chamber environment when the pressure plate is withdrawn as shown in FIG. 5, and the wafer 15 rotated to the next work station. This may be effectively done in such a short time frame not only because the load lock is of such small volume compared to the chamber (being only essentially that required to contain the wafer itself), but also because the outgassing load which was introduced therein is essentially only that of the wafer surfaces themselves, since no ancillary support equipment is utilized from sources outside of the load lock region, and since in any event the are of the clip assemblies supporting the wafer within the chamber is small relative to the wafer. This should be contrasted with the situation of prior art systems in which platens and other outside supports are introduced into the load lock, when supports have considerable area which contributes very greatly to the gas pumpdown load. Of course, the lack of such supports introduced from the outside also contributes significantly to a lessened risk of contamination. It should also be noted that the situation gets even better as the wafer advances to the subsequent work stations, since that portion of the pressure plate at the load lock region which is exposed to atmosphere (or the loading environment, which preferably is enclosed in a dry nitrogen environment) does not rotate with the wafer, but rather remains in the same loading station location, away from the remaining work stations and moreover is sealed off from the chamber environment during deposition.

While a wafer is being loaded into and/or unloaded from load lock station 12, pressure plate 16 is in its active advanced position of FIG. 4, whereby the planar annular portions of the plate assembly 18 is forced against front wall 32 of the chamber, the pressure plate is similarly urg