An aqueous and acidic stripping and cleaning composition is provided which contains a polyhydric alcohol, ammonium fluoride, dimethylsulfoxide and water. The pH of the composition is greater than about 4 but less than 7. Also provided is a method of stripping and cleaning utilizing the compositions of the invention. Optionally, the composition may contain a phosphate buffer.
However, the standard buffered HF solution will attack P+ or N doped silicon formed during semiconductor processing. This is particularly true when the etching solution is in contact simultaneously with exposed highly doped silicon and platinum silicide. The cause is possibly an electrochemical reaction between the silicon and the platinum silicide, with the reaction connection being completed when the semiconductor is dipped into the standard buffered HF solution. This tends to dissolve the silicon, especially P+ silicon.
Kinsbron et al, U.S. Pat. No. 4,343,677 discusses film patterning and disclose an etching solution which uses buffered ammonium fluoride/hydrofluoric acid in a molar ratio of about ten to one, mixed with a suitable solvent such as ethylene glycol. Gajda, U.S. Pat. No. 4,230,523, discloses an etchant comprised of a solution of hydrogen fluoride dissolved in organic solvents such as glycerine or another polyhydric alcohol. The etchant is used for etching silicon dioxide while not attacking silicon. Gajda requires that the solution be free of unbound water and ammonium fluoride. Maeda et al, U.S. Pat. No. 3,979,241, teach an etching liquid with ammonium fluoride or an alkali fluoride dissolved in a polyhydric alcohol, such as ethylene glycol, polyethylene glycol, and glycerine. The etching solution is used for selectively etching silicon dioxide or silicon nitride on a semiconductor wafer.
U.S. Pat. No. 5,320,709 to Bowden et al discloses a composition for selectively removing oxidized organometallic residues, oxidized organosilicon residues and oxides with a composition which is essentially pH neutral and comprises a polyhydric alcohol and an anhydrous ammonium fluoride salt. The present invention provides a specific improvement over the compositions of this patent by utilizing aqueous ammonium fluoride and an organic polar solvent in a buffered acidic pH.
SUMMARY OF THE INVENTION
The present invention provides an aqueous acidic stripping and cleaning composition for the removal of organic materials, organometallic residues, organosilicon residues, sidewall polymer (SWP) and inorganic residues which has a controlled oxide etch rate. The buffered acidic composition which has a pH of more than 4 and less than 7 comprises the admixture of:
a) about 55 to 85% by weight of a polyhydric alcohol having the formula selected from the group consisting of HO›CH.sub.2 --CH.sub.2 O!.sub.n H and ##STR1## more;
b) about 5 to 35% by weight of an organic water soluble polar solvent;
c) about 0.5 to 20% by weight of ammonium fluoride; and
d) the remainder being water typically in the range of about 1-20%.
Generally, the ammonium fluoride is used as a 40% aqueous solution.
The preferred polar solvents used in the invention are dimethylsulfoxide, dimethyl acetamide (DMAC), N-methylpyrrolidone, gamma butyllactone, and the like.
The compositions of the inventions are suitable for both VIA and contact hole applications as well as connector lead/multi-layer metal stack applications due to their high resistance to metal and metal alloy corrosion.
Advantageously, the compositions of the invention are free of ethylene glycol and hydrofluoric acid.
The compositions of the invention may contain a corrosion inhibitor.
It is a general object of the invention to provide a cleaning and stripping composition having a controlled etch and sidewall polymer removal capability.
It is another object of the invention to provide a stripping composition which is free of ethylene glycol and hydrofluoric acid.
It is yet another object of the invention to provide a stripping composition which is water soluble having high resistance to metal corrosion.
It is still another objection of the invention to provide a cleaning composition which removes inorganic and ash residues.
It is still another objection of the invention to provide a method for stripping which provides for a silicon or controlled oxide etch.
The advantages and further objects of the invention will become more apparent from the following description of the preferred embodiments and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the undoped polysilicon etch rate of the compositions of the invention.
FIG. 2 illustrates the thermal oxide etch rate of the compositions of the invention.
FIG. 3 illustrates the time to remove 160.ANG. thick ARC vs. temperature with the compositions of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to a slightly acidic stripping and cleaning composition comprising a polyhydric alcohol having the formula selected from the group consisting of HO›CH.sub.2 --CH.sub.2 O!.sub.n H and ##STR2## more, dimethylsulfoxide or the like, ammonium fluoride and a medium having a pH of more than about 4 but less than 7. Advantageously, the composition contains a corrosion inhibitor which forms a 5- or 6- membered ring coordination complex with a metal substrate as described in copending application Ser. No. 07/983,257 or an alkylated phenol.
The compositions of the present invention are particularly suitable for removing organic or inorganic material from a substrate such as sidewall polymers (SWP) and/or for controlled etching of contaminated or uncontaminated oxide surfaces. The composition are also effective in removing many forms of resist ash and etch residues without the presence of hydrogen fluoride.
The stripping and cleaning compositions of the invention contain about 65 to 85% by weight of composition of a polyhydric alcohol which excludes ethylene glycol, for example propylene glycol, glycerol, polyethylene glycol, etc.
Ammonium fluoride in an amount of about 0.5 to 20% by weight of composition is an essential component of the composition. Ammonium fluoride is commercially available as a 40% aqueous solution.
The use of about 5 to 35% by weight of dimethylsulfoxide, together with a polyhydric alcohol other than ethylene glycol, surprisingly stabilizes the performance of the formulations and enhances their process latitude at elevated temperatures. The use of water with DMSO and the like as the solvent allows use of ammonium fluoride in the formulation when propylene glycol is the polyhydric alcohol.
Other additives normally used in buffered oxide etchant solutions may be included in the novel etching solutions of the present invention. For example, polar solvent diluents such as acetic acid and ammonium acetate may be included. Ammonium acid phosphate buffers represent another choice.
These additives may be used in an amount of up to about 20% by weight, for example.
Corrosion inhibitors in an amount of up to about 15% by weight can be added to the stripping compositions. Preferably, the inhibitor concentration is from about 0.5 to 8% by weight, and most preferably, about 5% by weight. Suitable inhibitors are disclosed in U.S. Pat. No. 5,417,877 to Ward et al, which is herein incorporated by reference. The inhibitor is a compound selected from the group consisting of: ##STR3## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different and each represent lower alkyl, H, OH, NHR.sub.5, CO.sub.2 R.sub.6, COR.sub.7 and SH, wherein R.sub.5 and R.sub.6 are the same or different and each represent H or lower alkyl, and R.sub.7 represents lower alkyl, with the proviso that when R.sub.4 is H, not more than one of R.sub.1, R2 and R.sub.3 is the same as R.sub.4, and when R.sub.3 is not H, not more than one of R.sub.1, R.sub.2 and R.sub.4 is hydrogen, the remainder being the same or different than R.sub.3. Preferred inhibitors include catechol, pyrogallol, anthranilic acid, gallic acid, gallic esters, and the like.
The compositions of this invention are especially useful and advantageous for numerous reasons among which may be mentioned the following. The compositions are water soluble, non-corrosive to substrate, non-flammable and of low toxicity to the environment. The compositions evidence high stripping and cleaning efficiency at low temperatures for a wide variety of coating residues and substrates. The compositions are particularly suitable for removal of residues from plasma processing used in integrated circuit fabrication since they also prevent the redeposition of metal ions, especially sodium and potassium ions and have a faster more complete removal of trace metals. The compositions provide controlled oxide etch and controlled silicon and/or polysilicon and/or silicon nitride etch.
The process of the invention is carried out by contacting a substrate containing an organic or metal-organic polymer, inorganic salt, oxide, hydroxide or complex or combination thereof as a film or residue, (e.g. sidewall polymer (SWP)), with the described stripping composition. The actual conditions, e.g., temperature, time, etc., depend on the nature and thickness of the complex (photoresist and/or SWP) material to be removed, as well as other factors familiar to those skilled in the art. In general, for stripping, the substrate is contacted or dipped into a vessel containing the stripping composition at an elevated temperature, preferably between 25.degree.-80.degree. C. and usually about 25.degree.-40.degree. C. for a period of about 1-15 minutes and then rinsed with water.
Representative organic polymeric materials include positive photoresists, electron beam resists, X-ray resists, ion beam resists, and the like. Specific examples of organic polymeric materials include positive resists containing phenolformaldehyde resins or poly (p-vinylphenol), polymethylmethacrylate-containing resists, and the like. Examples of plasma processing residues side wall polymers (SWP) include among others, metal-organic complexes and/or inorganic salts, oxides, hydroxides or complexes which form films or residues either alone or in combination with the organic polymer resins of a photoresist. The organic materials and/or SWP can be removed from conventional substrates known to those skilled in the art, such as silicon, silicon dioxide, aluminum, aluminum alloys, copper, copper alloys, etc.
Examples illustrating the removal of a coating from a substrate under varying conditions are described further below. The following examples are provided to further illustrate the invention and are not intended to limit the scope of the present invention.
Examples of compositions according to the invention are set forth below in Table I. The amounts indicated are in percent by weight of composition.
TABLE I
______________________________________
Propylene 40% aq.
Stripping Glycol DMSO Ammonium
Compositions
(wt %) (wt %) Fluorine
______________________________________
A 77.5 20.0 2.5
B 76.3 18.7 5.0
C 73.2 16.8 10.0
D 68.7 11.3 20.0
______________________________________
The undoped polysilicon etch rate for composition B at 20.degree. C. and 60.degree. C. is shown in FIG. 1. The average etch rate at 20.degree. C. was 3.ANG./min and at 60.degree. C. 50.ANG./min.
EXAMPLE I
A stripping and cleaning composition was prepared by admixing the following ingredients:
______________________________________
Ingredient % Wt.
______________________________________
Propylene glycol 77.5
DMSO 16.3
40% ammonium fluoride
5.0
Acetic acid 0.5
Ammonium acetate 0.7
______________________________________
The pH of the composition is 5.2.
EXAMPLE II
A stripping and cleaning composition was prepared by admixing the following ingredients:
______________________________________
Ingredient % Wt.
______________________________________
Propylene glycol 73.0
DMSO 12.3
Ammonium fluoride
5.0
Acetic acid 4.0
Ammonium acetate 5.2
Catechol 0.5
______________________________________
The pH of the composition is 4.8.
The thermal oxide etch rate for the composition of Example II at 60.degree. C. is shown in FIG. 2. The average etch rate at 60.degree. C. was 203.ANG./min.
EXAMPLE III
A stripping and cleaning composition was prepared by admixing the following ingredients:
______________________________________
Ingredient % Wt.
______________________________________
Propylene glycol 73.0
DMSO 12.0
Ammonium fluoride 5.0
Catechol 0.5
Buffer* 9.5
100%
______________________________________
The buffer solution was prepared from a range of 7% (NH.sub.4)H.sub.2 PO.sub.4 and 3% (NH.sub.4).sub.2 HPO.sub.4 to 9% (NH.sub.4)H.sub.2 PO.sub.4 and 3% (NH.sub.4).sub.2 HPO.sub.4 to 9% (NH.sub.4)H.sub.2 PO.sub.4 and 1% (NH.sub.4).sub.2 HPO.sub.4, the remainder being deionized water.
EXAMPLE IV
Example III illustrates the removal of a photoresist from a substrate using a stripping composition of the invention.
More specifically, an immersion tank containing composition A of Table I is held at room temperature and the stripping composition is recirculated at an exchange rate of about 1.0 (i.e. pump flow rate/bath volume.about.1.0).
A rinse tank with standard overflow cascade containing deionized water with a CO.sub.2 sparge is also prepared.
The photoresist wafer specimen is immersed into the stripping composition for 1-20 minutes in accordance with the oxide etch rate and the amount of removal desired.
The specimen is removed from the stripping bath and immersed into the rinse tank for 2-4 minutes using continuous CO.sub.2 sparging.
The specimen is then removed and spun dry in a heated nitrogen atmosphere.
EXAMPLE V
Table II shows the admixture of components together with buffering additives.
The time to remove 160.ANG. thick ARC vs. temperature of compositions E, F and G is shown in FIG. 3.
TABLE II
______________________________________
COMPONENT E F G
______________________________________
Propylene glycol
68.4 75.9 64.2
DMSO 12.4 12.4 12.4
NH.sub.4 F (40%)
10.0 2.5 5.0
HOAc (glacial)
4.0 4.0 8.0
NH.sub.4 OAc (salt)
5.2 5.2 10.4
pH (5% aqueous
4.8 4.8 4.8
sol'n)
ER.sub.TOX @ RT
12.4 3 4.6
(.ANG./min)
ER.sub.TOX @ 60.degree. C.
348 78 141
(.ANG./min)
ER.sub.PS @ RT
4 5 2.2
(.ANG./min)
ER.sub.PS 60.degree. C.
71 44 37
(.ANG./min)
______________________________________
