According to the invention, an aqueous polishing composition comprises, abrasive particles and water of basic pH to remove a barrier layer by CMP using a polishing pad, the aqueous polishing composition further comprising, solely polar molecules each having multiple, polar bonding sites forming respective hydrogen bonds with silanol bonding groups on a hydrated silica dielectric layer of a semiconductor substrate, which form an hydrophilic protective film of the polar molecules that minimizes erosion.
U.S. Pat. No. 5,614,444 discloses a slurry having molecules with at least one apolar component. The molecules bond with respective surface silanol bonding groups to form attached, apolar molecules, which apolar molecules are inherently hydrophobic to form a surface film that reduces erosion while CMP is performed.
SUMMARY OF THE INVENTION
According to the invention, an aqueous polishing composition has abrasive particles and water of basic pH to remove a barrier layer from a dielectric layer by CMP, and the aqueous polishing composition further comprises; solely polar molecules each having multiple, polar bonding sites forming bonds with bonding groups on a hydrated dielectric layer of a semiconductor substrate, to form an hydrophilic protective film of the polar molecules on the dielectric layer.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings.
FIG. 1 is a cross section of a semiconductor substrate having a metal layer.
FIG. 2 is a view similar to FIG. 1, with the metal layer removed from an exposed barrier layer of the semiconductor substrate.
FIG. 3 is a view similar to FIG. 2, with the barrier layer removed from an underlying oxide layer or dielectric layer.
DETAILED DESCRIPTION
FIG. 1 discloses a semiconductor substrate having, a layer 10 of conductive material, metal, a barrier layer 11 and an underlying dielectric layer 12 on a substrate 13. The dielectric layer 12 has trenches 14, one shown, that are filled with the conductive material. The conductive material comprises, copper, tungsten or aluminum. FIG. 3 discloses that the barrier layer 11 lines the trenches to prevent migration of metal ions into the dielectric layer. The barrier layer 11 comprises, tantalum, tantalum nitride, titanium and/or titanium nitride or an alloy thereof. The dielectric layer comprises, a silicon oxide, for example, a silicon oxide derived from tetraethyl orthosilicate (TEOS).
FIG. 2 discloses a semiconductor substrate of FIG. 1 with the conductive metal layer 10 of FIG. 1 removed, resulting in an exposed barrier layer 21 and a trench 22 filled with metal. The metal layer 10 is removed by a known CMP operation.
FIG. 3 discloses the semiconductor substrate after the barrier layer 21 has been selectively removed by CMP, to obtain a planar surface 31 on a dielectric layer, with minimized erosion, and with a trench 32 filled with metal.
With reference to FIG. 2, CMP is performed to selectively remove the barrier layer 21 from the underlying dielectric layer 12, while minimizing erosion of the dielectric layer 12 by CMP. An aqueous polishing composition that is sufficient for removal of Ta or TaN barrier layer 21 from the underlying dielectric layer 12 by polishing with a polishing pad and with the aqueous polishing composition, has, abrasive particles and water of basic pH.
According to an embodiment, the aqueous polishing composition contains abrasive particles at about 0.0001, 0.05, 0.1, 0.25, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, to 30% by weight. An embodiment of an aqueous polishing composition comprises substantially all abrasive particles having a mean size less than 5.mu.. Substantially all abrasive particles includes, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, 99.9% of the particles. An embodiment of the abrasive particles comprises colloidal silica particles.
Alternatively, the aqueous polishing composition comprises, one or more of; a pH buffer, a surfactant, a deflocculant, a viscosity modifier, a wetting agent, a cleaning agent, and a biocide. An embodiment of the biocide comprises Neolone M50 available from Rohm and Haas Co., Philadelphia, Pa., with an active ingredient of 5-chloro-2-methyl-4-isothiazolin-3-one. According to the invention, the aqueous polishing composition further comprises, solely polar molecules each having multiple, polar bonding sites forming respective hydrogen bonds with silanol bonding groups on a hydrated silica dielectric layer of a semiconductor substrate, which form an hydrophilic protective film of the polar molecules. The solely polar molecules are hydrophilic. Solely polar is a terminology that refers to a molecule having multiple polar bonding sites without having an apolar bonding site.
According to an embodiment, the invention pertains to CMP of a substrate wherein the dielectric layer having the surface 31 is silicon dioxide. The silicon dioxide surface 31 is hydrated to have silanol and siloxane groups wherein the siloxane linkage (Si--O--Si) is formed by self condensation of silanol (Si--OH) groups. The silanol bonding groups are of high acidity, and tend to form hydrogen bonds with the solely polar molecules that have solely polar, hydrogen bonding sites, also known as, electron donor sites. The solely polar molecules have nitrogen atoms at nuclei of functional groups that are capable of forming intermolecular hydrogen bonds with silanol bonding groups on the surface 31 of the hydrated dielectric layer. Removal of the dielectric layer by CMP is suppressed by such polar molecules attached by formation of hydrogen bonds with respective silanol bonding groups on the hydrated surface 31 of the dielectric layer, which form an hydrophilic protective film on the surface 31 of the dielectric layer.
According to an embodiment, an aqueous polishing composition comprises, solely polar molecules forming bonds with bonding groups on the hydrated dielectric layer. According to an embodiment, the molecules are derived from a nitrogen-containing polymer compound, including but not limited to; polyacrylamide, polyvinylpyrrolidone, polyethyleneimine, and polyethyleneimine.
For example, polyethyleneimine molecules have nitrogen atoms at nuclei of bonding sites, the bonding sites forming intermolecular hydrogen bonds with respective silanol bonding groups on the surface of the dielectric layer, and forming a hydrophilic film that suppresses removal of the dielectric layer during the performance of CMP to remove the barrier layer. Polyethyleneimines have a general chemical structure:
(--NH--CH.sub.2 --CH.sub.2 --)m(--N(CH.sub.2 --CH.sub.2 --NH.sub.2)--CH.sub.2 --CH.sub.2 --)n
wherein m and n are integers that can be varied independently of each other, and with each having a value greater than or equal to 1.
Branched polyethyleneimines have a general chemical structure:
H.sub.2 N--(--CH.sub.2 --CH.sub.2 --NR--)m--(--CH.sub.2 --CH.sub.2 --NH--)n--
where R is (--CH2--CH2--N--) and m and n are greater than or equal to 1, respectively.
The multiple nitrogen atoms in respective solely polar molecules, such as molecules of polyethyleneimine, are at nuclei of respective sites for forming intermolecular hydrogen bonds with silanol bonding groups on the hydrated dielectric layer to result in a protective film of attached polar molecules, which enable controlled amounts of erosion, or which minimize erosion, of the dielectric layer during the performance of CMP to remove the barrier layer.
EXAMPLE 1
A neutral pH to basic pH, polishing composition according to the invention was used to polish semiconductor substrates having, copper in trenches; TEOS, a silicon dioxide dielectric layer; and a Tantalum barrier layer. An IPEC472 polisher was used with an aqueous polishing composition flow rate of 200 ml/min. Each formulation contained a biocide (Neolone M50 obtained from Rohm and Haas Company, Philadelphia, Pa.) at a concentration of about 0.01% by weight; Benzotriazole (BTA) at about 0.1% by weight as an inhibitor preventing dishing of metal in trenches; a surfactant onto copper at about 2% by weight; and colloidal silica particles known as Klebesol 1501-50 (obtained from Clariant Corp) at about 8.5% by weight of the polishing composition. The removal rates in Angstroms/minute were observed with polyethyleneimines, PEIs, at different weight concentrations of various average molecular weights, which are entered in the following table.
TEOS Ta:TEOS
Sample PEI PEI PEI RR Ta RR Selectivity
No. (800K) (50K) (750K) pH A/min A/min Ratio
1 -- -- -- 7 729 400 0.5:1
2 -- -- -- 11 715 400 0.55:1
3 0.25 -- -- 11 11 298 27.1:1
4 -- 0.68 -- 11 122 462 3.8:1
5 -- 0.2 -- 11 33 387 11.7:1 See
Note (1),
below
6 -- -- 0.2 11 50 200 4:1
Note (1): This data set was obtained using an AMAT Mirra Polishing Machine
in place of an IPEC 472 polisher, with an IC1010 polishing pad (available
from Rodel, Inc., Newark,Delaware) with a downforce of 3 psi, a carrier
speed of 103 rpm, an aqueous polishing composition flow rate of 200 ml/min
and a polishing time of 60 seconds.
A selectivity ratio comprises a ratio of barrier layer 21 removal rate to dielectric layer removal rate during CMP. The selectivity ratio is further referred to in the table, disclosed herein, by, Ta:TEOS selectivity ratio. The table indicates an unanticipated result that, when the average molecular weight of the solely polar molecules of polyethyleneimine increases to 800K from 750 K, the Ta:TEOS selectivity ratio increased from 4 to 27.1 (6.78 times) while the weight percent concentration of such molecules was substantially the same, as indicated in the table by a nominal amount of change from 0.2 to 0.25 weight percent concentration. Accordingly, minimized erosion corresponds with the high selectivity ratio, as provided by increasing the average molecular weight to at least 800K from lower levels of molecular weights.
A lower selectivity ratio is provided by lowering the average molecular weight from 800K to 750K. A lower selectivity ratio is provided by lowering the average molecular weight from 750K to 50K. Yet, to produce a selectivity ratio of 3.8, by molecules of 50K average molecular weight, requires a 0.68 weight percent concentration. A conclusion can be drawn that increases in selectivity ratio, corresponding with decreases in a rate of removal of the dielectric layer, are produced by increasing the average molecular weight of the molecules. Further, selecting the average molecular weight (for example, selecting a lower average molecular weight) adjusts the selectivity ratio (for example, adjusts the selectivity ratio lower), to remove a controlled amount of the dielectric layer, upon removal of the barrier layer 21 by CMP. Still further, selecting the concentration (for example, selecting a lower concentration) of the molecules adjusts the selectivity ratio (for example, adjusts the selectivity ratio lower), to remove a controlled amount of the dielectric layer, upon removal of the barrier layer 21 by CMP. The importance of adjusting the selectivity ratio will now be explained.
Sometimes the process of CMP, as described with reference to FIG. 2, removes copper in the trenches 22, producing a manufacturing effect known as dishing. Because of dishing, some of the copper in the trenches 22 has a lower elevation than the elevation of the dielectric layer 12. Such a manufacturing effect is reversed according to a feature of the invention. An aqueous polishing composition according to the invention adjusts the selectivity ratio toward lower numerical values, to purposely remove a controlled amount of the dielectric layer 12, when CMP is performed to remove the barrier layer 21. A controlled amount of the dielectric layer is removed, which lowers the elevation of the dielectric layer, until the dielectric layer becomes substantially coplanar with the copper in the trenches. A substantially coplanar dielectric layer and copper in trenches comprise a desirable manufacturing effect known as planarization. Planarization is sufficiently familiar, that chemical mechanical polishing, as described herein, is further known by an alternative terminology, chemical mechanical planarization.
According to an embodiment, the solely polar molecules are provided by a polymer compound comprising, polyethyleneimine (PEI) with an average molecular weight, in one of the following ranges, from about 100, 200, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10,000, 20,000, 30,000, 40,000, 50,000, 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, or 700,000, to about 1,000,000. Each of such ranges includes an advantageous range of molecular weights of at least 800K to optimize the selectivity ratio, Ta:TEOS, for minimizing erosion. Each of such ranges includes an advantageous range of molecular weights below 800K to adjust the selectivity ratio, Ta:TEOS, for removing a controlled amount of the dielectric layer.
According to an embodiment, the average molecular weight is obtained by a single average weight distribution of the solely polar molecules of polyethyleneimine. According to another embodiment, the average molecular weight is obtained by a mixture of polyethyleneimines of different molecular weights, which are mixed according to proportions that attain a desired average molecular weight. For example, the desired average molecular weight is obtained by a mixture of polyethyleneimines, of which, some comprise a first molecular weight distribution (e.g., a distribution in a range from about 100 to about 5,000), and some comprise at least one additional molecular weight distribution (e.g., a distribution in a range from about 5,000 to about 1,000,000).
An aqueous polishing composition has abrasive particles and water of basic pH to remove a barrier layer from a dielectric layer by CMP, and the aqueous polishing composition further comprises; solely polar molecules each having multiple, polar bonding sites forming bonds with bonding groups on a hydrated dielectric layer of a semiconductor substrate, to form an hydrophilic protective film of the polar molecules on the dielectric layer.
An aqueous polishing composition comprises, solely polar molecules forming bonds with bonding groups on the hydrated dielectric layer. According to an embodiment, the molecules are derived from a nitrogen-containing polymer compound, including but not limited to; polyacrylamide, polyvinylpyrrolidone, polyethyleneimine, and polyethyleneimine.
Embodiments of the invention have been disclosed, and other embodiments and modifications of the invention are intended to be covered by the spirit and scope of the appended claims.
