Photoresist removal

Abstract

Disclosed herein is a composition and method for semiconductor processing. In one embodiment, a wet-cleaning composition for removal of photoresist is provided. The composition comprises a strong base; an oxidant; and a polar solvent. In another embodiment, a method for removing photoresist is provided. The method comprises the steps of applying a wet-cleaning composition comprising about 0.1 to about 30 weight percent strong base; about one to about 30 weight percent oxidant; about 20 to about 95 weight percent polar solvent; and removing the photoresist.

Description

FIELD OF THE INVENTION

[0002] The present invention relates to semiconductor processing and, more particularly, to photoresist removal.

BACKGROUND OF THE INVENTION

[0003] Integrated circuits are manufactured by a general sequence of steps wherein photoresist is coated onto a substrate, the photoresist layer is patterned by exposure and development, the pattern is transferred to the substrate, and the photoresist removed. This sequence of steps is repeated to build up multiple layers of patterned circuitry. For the photoresist removal step, plasma ashing is commonly used since etched photoresist residues may be difficult or impossible to remove using only wet cleaning, especially without damaging other materials that are present.

[0004] Positive photoresist is soluble in alkaline aqueous solutions as well as in compositions consisting of select organic and inorganic compounds. However, photoresist that has been exposed to a gas-phase plasma etch, such as a gas-phase plasma etch used for etching dielectric materials, will typically develop a hardened crust or residue, on the surface. The residue typically consists of cross-linked organic polymers, and may contain small amounts of silicon, metal, and halogen or other atoms.

[0005] Damascene or dual damascene processes commonly utilize a plasma etch such as that described above. The plasma etch may be a fluorine-based plasma etch to etch silicate-based interlayer dielectric (ILD) materials. These materials may include silicates, organosilicates and fluorosilicates. Fluorine-based plasma etching may cause fluorination of the cross-linked organic polymers that form the residue described above. This fluorination typically increases chemical resistance. Thus, the residue becomes difficult, if not impossible, to remove by conventional wet stripping techniques. Ashing using an oxidative or reductive plasma can remove the residue. However, plasma ashing is prone to damage to the ILD materials, especially low-k ILD materials.

[0006] Therefore, a need exists for photoresist removal that can remove photoresist residue but does not damage the ILD materials.

SUMMARY OF THE INVENTION

[0007] Disclosed herein is a composition and method for semiconductor processing. In one embodiment, a wet-cleaning composition for removal of photoresist is provided. The composition comprises a strong base; an oxidant; and a polar solvent. In another embodiment, a method for removing photoresist is provided. The method comprises the steps of (i) applying a wet-cleaning composition comprising about 0.1 to about 30 weight percent strong base, about one to about 30 weight percent oxidant, and about 20 to about 95 weight percent polar solvent; and (ii) removing the photoresist.

[0008] A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0009] Disclosed herein is a composition and method for semiconductor processing. According to one aspect of the invention, a wet-cleaning composition for removal of photoresist is provided. The composition includes a strong base. For example, the strong base may yield a solution having a pH greater than about 11.5, even where the strong base makes up no more than about 3.5% of the solution. That is, the strong base may be no more than about 3.5 weight percent of the solution. However, as described further herein, higher strong base concentrations may be desirable. The strong base assists in the removal of the photoresist, e.g., unexposed positive photoresist. The composition also includes an oxidant and a polar solvent. Strong bases of the formula I, shown below, may be used in accordance with the teachings of the present invention. 1

[0010] wherein R1, R2, R3 and R4 are each one of hydrogen, alkyl or substituted alkyl groups. Suitable strong bases include, but are not limited to, ammonium hydroxide, tetramethylammonium hydroxide (TMAH), choline hydroxide, as well as combinations comprising at least one of the foregoing strong bases. In an exemplary embodiment, the strong base comprises tetramethylammonium hydroxide.

[0011] The cleaning compostion or solution described is particularly useful for cleaning photoresist residue from a semiconductor substrate. For example, in one embodiment, a semiconductor substrate is patterned to form trenches therein. This is done in a manner employing a photoresist. The photoresist and any residue may be removed from the trench and substrate with the described cleaning solution. A semiconductor feature such as a metal line may be formed in the trench followed by chemical mechanical planarazation to isolate the metal line. Further semiconductor processing may follow to form a completed semiconductor device.

[0012] In an exemplary embodiment, the composition of the present invention comprises greater than or equal to about 0.1 weight percent strong base, with greater than or equal to about one weight percent strong base preferred and greater than or equal to about five weight percent strong base more preferred. In the exemplary embodiment, the composition of the present invention further comprises less than or equal to about 30 weight percent strong base, with less than or equal to about 20 weight percent strong base preferred and less than or equal to about ten weight percent strong base more preferred.

[0013] The composition further comprises an oxidant. Suitable oxidants include, but are not limited to, inorganic oxidizers, organic oxidizers, e.g., amine-N-oxides, perborate salts, persulfate salts, percarbonate salts, as well as combinations comprising at least one of the foregoing oxidants. In an exemplary embodiment, the oxidant comprises organic oxidizers. Organic oxidizers of the general formula II, shown below, may be used in accordance with the teachings of the present invention. 2

[0014] wherein R1, R2 and R3 may be hydrogen, methyl or further substituted or unsubstituted alkyl groups. R1 and R2 may form two ends of an alkyl chain.

[0015] While peroxides, e.g., hydrogen peroxide and substituted alkyl or aryl peroxides, may be used in accordance with the teachings of the present invention, amine-N-oxides have the advantage of being a more mild oxidant as compared to the peroxides in general. Further, amine-N-oxides decompose less rapidly as compared to peroxides in general. In particular, it is well-known that hydrogen peroxide in alkaline environments decomposes rapidly, yielding oxygen and water, a condition that leads to a short bath life especially at temperatures greater than ambient. Also, hydrogen peroxide may be unstable in the presence of oxidizable organic species, for example, amines and alcohols. Thus, in accordance with the teachings of the present invention, a non-peroxide oxidant is preferred.

[0016] In an exemplary embodiment, the composition of the present invention comprises greater than or equal to about one weight percent oxidant, with greater than or equal to about five weight percent oxidant preferred and greater than or equal to about ten weight percent oxidant more preferred. In the exemplary embodiment, the composition of the present invention further comprises less than or equal to about 30 weight percent oxidant, with less than or equal to about 20 weight percent oxidant preferred and less than or equal to about 15 weight percent oxidant more preferred.

[0017] The composition further comprises a polar solvent. The polar solvent solubilizes ionic components both in the photoresist and in the photoresist residues. Suitable polar solvent include, but are not limited to, water, ethylene, propylene, other glycol solvents, glycol ethers, alcohols, amides, carbonates, as well as combinations comprising at least one of the foregoing polar solvents. In an exemplary embodiment, the polar solvent comprises water due to its low cost and non-toxicity.

[0018] In an exemplary embodiment, the composition of the present invention comprises greater than or equal to about 20 weight percent polar solvent, with greater than or equal to about 30 weight percent polar solvent preferred and greater than or equal to about 40 weight percent polar solvent more preferred. In the exemplary embodiment, the composition of the present invention further comprises less than or equal to about 95 weight percent polar solvent, with less than or equal to about 85 weight percent polar solvent preferred and less than or equal to about 75 weight percent polar solvent more preferred.

[0019] The composition may further comprise a chelator. Suitable chelators include, but are not limited to, unsubstituted triazoles, substituted triazoles, thiazoles, tetrazoles, imidazoles, phosphates, thiols and azines, glycerols, amino acids, carboxylic acids, alcohols, amides, quinolines, as well as combinations comprising at least one of the foregoing chelators.

[0020] Unsubstituted triazoles include, but are not limited to, 1,2,3-triazole and 1,2,4-triazole. Further, triazoles may be substituted with alkyl groups, amino groups, benzo groups, thiol groups, mercapto groups, imino groups, carboxy groups, nitro groups, as well as combinations comprising at least one of the foregoing substituted groups. Substituted triazoles include, but are not limited to benzotriazole, polyltriazole, 5-phenyl-benzotriazole, 5-nitro-benzotriazole, 1-amino-1,2,3-triazole, 1-amino-1,2,4-triazole, 1-amino-5-methyl-1,2,3-triazole, hydroxybenzotriazole,2-(5-amino-pentyl)-benzotriazole, 3-amino-1,2,4-triazole,3-isopropyl-1 ,2,4-triazole, 3-mercapto-1,2,4-triazole, 5-phenylthiol-benzotriazole, halo-benzotriazoles, napthotriazole. Thiazoles, tetrazoles, imidazoles, phosphates, thiols and azines include, but are not limited to, 2-mercaptobenzoimidizole, 2-mercaptobenzothiazole, 5-aminotetrazole, 5-amino-1,3,4-triadiazole-2-thiol, thiazole, triazine, methyltetrazole, 1,3-dimethyl-2-imidazolidinone, 1,5-pentamethylenetetrazole, 1-phenyl-5-mercaptotetrazole, diaminomethyltriazine, mercaptobenzothiazole, imidazoline thione, mercaptobenzoimidazole, 4-methyl-4H-1,2,4-triazole-3-thiol, benzothiazole, tritolyl phosphate, indiazole, as well as combinations comprising at least one of the foregoing. Glycerols, amino acids, carboxylic acids, alcohols, amides, quinolines include, but are not limited to, guanine, adenine, glycerol, thioglycerol, nitrilotriacetic acid, salicylamide, iminodiacetic acid, benzoguanamine, melamine, thiocyranuric acid, anthranilic acid, 8-hydroxyquinoline, 5-carboxylic acid-benzotriazole, 3-mercaptopropanol, boric acid and iminodiacetic acid.

[0021] The chelator may be added to the composition to prevent the etching or corrosion of metal surfaces, e.g., copper, tungsten, aluminum and alloys thereof, exposed to the composition. As such, the chelator may be used to increase the compatibility of the composition with the metals and dielectric materials used in the semiconductor device.

[0022] In an exemplary embodiment, the composition of the present invention comprises less than or equal to about ten weight percent chelator, with less than or equal to about seven weight percent chelator preferred and less than or equal to about four weight percent chelator more preferred.

[0023] The composition may further comprise a co-solvent. The co-solvent may be added to improve compositional properties, namely the ability of the composition to swell, dissolve, and lift off photoresist residues. Suitable co-solvents include, but are not limited to, substituted alkylamines or alkanolamines such as N,N-dimethyldiglycolamine, 1,8-diazabicyclo[5.4.0]undecene, aminopropylmorpholine, triethanolamine, methylethanolamine, glycol solvents such as ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, glycol ethers such as di(ethylene glycol)monoethyl ether, di(propylene glycol)propyl ether, ethylene glycol phenyl ether, di(propylene glycol)butyl ether, butyl carbitol, polyglycol ethers, as well as combinations comprising at least one of the foregoing co-solvents.

[0024] Further, the co-solvent should be polar. A polar compound will remain miscible with the polar solvent and will keep ionic species such as tetramethylammonium hydroxide dissolved. In an exemplary embodiment, the composition of the present invention comprises less than or equal to about 50 weight percent co-solvent, with less than or equal to about 30 weight percent co-solvent preferred and less than or equal to about 20 weight percent co-solvent more preferred.

[0025] The composition may further comprise a surfactant. The surfactant may be added in order to assist in both the lifting-off of insoluble photoresist residues and reduce silicon etching, which may occur under exposure to strong bases. Suitable surfactants include, but are not limited to, anionic, cationic, nonionic surfactants, such as fluoroalkyl surfactants, polyethylene glycols, polypropylene glycols, polyethylene or polypropylene glycol ethers, carboxylic acid salts, dodecylbenzenesulfonic acid or salts thereof, polyacrylate polymers, silicone or modified silicone polymers, acetylenic diols or modified acetylenic diols, alkylammonium or modified alkylammonium salts, as well as combinations comprising at least one of the foregoing surfactants.

[0026] In an exemplary embodiment, the composition of the present invention comprises less than or equal to about 20 weight percent surfactant, with less than or equal to about 15 weight percent surfactant preferred and less than or equal to about ten weight percent surfactant more preferred.

[0027] Another aspect of the invention provides a method for removing photoresist. The method comprises the steps of applying a wet-cleaning composition comprising about 0.1 to about 30 weight percent strong base; about one to about 30 weight percent oxidant; and about 20 to about 95 weight percent polar solvent; and removing the photoresist.

[0028] The term photoresist as used herein is generally applicable to any layer comprising photoresist. Thus, for example, in accordance with the teachings of the present invention, the composition and method herein may be used to remove photoresist as well as photoresist residue. Additionally, the teachings of the present invention apply to the removal of any photoresist residue, i.e., resulting from an etching process including, but not limited to, fluorine-based plasma etching.

[0029] Although illustrative embodiments of the present invention have been described herein, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention. The following examples are provided to illustrate the scope and spirit of the present invention. Because these examples are given for illustrative purposes only, the invention embodied therein should not be limited thereto.

EXAMPLES

[0030] The following formulations produced substantial cleaning of photoresist from a semiconductor substrate. Substantial cleaning, according to the teachings of the present invention, is defined as being greater than 80 percent removal of the photoresist from the semiconductor device, and may be determined by optical and electron microscopy. The substrate employed herein consisted of chemically amplified photoresist coated onto an orgariosilicate dielectric coated silicon wafer. Additionally, the photoresist was exposed to patterned radiation and developed, and the pattern was then transferred to the dielectric by a plasma etch.

Example 1

[0031] Composition A was prepared as follows:

Composition A
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 7.3
Water                            79.2

[0032] The N-methylmorpholine-N-oxide was supplied and used as a 50 weight percent solution, and tetramethylammonium hydroxide (TMAH) was supplied and used as a 25 weight percent solution in the present example, as well as in further examples employing N-methylmorpholine-N-oxide and tetramethylammonium hydroxide (TMAH).

[0033] A photoresist substrate was cleaned by immersion in composition A for 20 minutes at 70° C. All of the photoresist and etch residues were removed from the substrates as observed by optical and electron microscopy. Significant etching of the dielectric material was not observed.

Example 2

[0034] Compositions B, C and D were prepared, each containing 13.5 weight percent N-Methylmorpholine-N-oxide, 7.3 weight percent TMAH, 78.9 weight percent water and 0.3 weight percent of the inhibitor 2-mercaptobenzimidazole (2-MBI) as shown below. 2-MBI was included in the formulation in order to retard etching of copper or other metals by the solution, as may be seen in Example 3.

Composition Additive
B           2,4-Diamino-6-methyl-1,3,5-triazine
C           5-Amino-1,3,4-thiadiazole-2-thiol
D           2-Mercaptobenzimidizole

[0035] Photoresist substrates were cleaned by immersion in the stripper for 20 minutes at 70° C.

Example 3

[0036] Etch rates of a blanket coating of copper (Cu) on a silicon wafer were measured using compositions A through D, as prepared above. The copper layer was deposited by physical vapor deposition and was about 1000 angstroms (A) in thickness. Samples were immersed in the composition for a fixed time, and the thickness was measured both before and after using four-point probe electrical measurements. Etch rates were calculated by dividing the difference in thickness, i.e., the thickness before etching, less the thickness after etching, by the time in minutes. The etch rates for compositions A through D are given below.

            Cu Etch Rate at
Composition 70° C. (Å/min)
A           15.8
B           1.5
C           3.2
D           1.1

Example 4

[0037] Composition E was prepared as follows:

Composition E
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 7.5
2-Mercaptobenzimidizole          0.08
Water                            64.1
N,N-Dimethyldiglycolamine        15.0
polyethyleneglycol 4-nonylphenyl ether 0.05

[0038] Polyethyleneglycol 4-nonylphenyl ether is a surfactant containing about 5 ethyleneglycol repeat units. After immersion in Composition E for 15 minutes at 70° C., there was 100 percent photoresist residue removal from all areas of the semiconductor.

Example 5

[0039] Composition F was prepared as follows:

Composition F
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 6.5
2-Mercaptobenzimidizole          0.01
Water                            76.09
Non-ionic fluorosurfactant       0.1

[0040] The potential etching effects of compositions A and F on polysilicon were determined by immersing 1000 Å wafer sections of polysilicon on silicon, in each composition, for 15 minutes at 70° C. Composition F showed no observable etching or roughening of the polysilicon surface. Composition A did show slight observable roughening of the polysilicon surface.

Example 6

[0041] Composition G was prepared as follows:

Composition G
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 6.5
2-Mercaptobenzimidizole          0.01
Water                            79.9
modified acetylenic diol surfactant 0.1

[0042] A photoresist substrate was cleaned by immersion in composition G for 20 minutes at 70° C. All of the photoresist and etch residues were removed from the substrates, as observed by optical and electron microscopy. However, etching or roughening of polysilicon was observed under the same conditions.

Example 7

[0043] Composition H was prepared as follows:

Composition H
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50   13.5
weight percent solution)
TMAH (25 weight percent          3.5
solution)
2-Mercaptobenzimidizole          0.01
Water                            82.89
2,4,7,9-tetramethyl-5-decyne-4,7-diol 0.1

[0044] A polysilicon coated wafer, as described in Example 5, did not show observable etching or roughening when immersed in composition H for 15 minutes at 70° C. However, Composition H failed to remove the bulk of the photoresist crust from the substrate.

Example 8

[0045] Composition I was prepared as follows:

Composition I
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 7.3
2-Mercaptobenzimidizole          0.2
Water                            43.9
Non-ionic fluorosurfactant       0.1
Butyl carbitol                   5
N,N-Dimethyldiglycolamine amine  15
1,8-diazabicyclo [5.4.0] undecene 15

[0046] Use of composition I showed removal of the photoresist with moderate protection of the polysilicon. Some etching or roughening was exhibited when the polysilicon was immersed in the sample for 15 minutes at 70° C. The copper etch rate remained low at 0.15 Å/minute and the tungsten etch rate was 0.67 Å/minute. The copper and tungsten samples were immersed for 40 minutes at 70° C.

Example 9

[0047] Composition J was prepared as follows:

Composition J
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 7.3
2-Mercaptobenzimidizole          0.2
Water                            49
Pentamethyldiethylenetriamine    30

[0048] Composition J resulted in complete removal of photoresist and residues from the trench features and about 40 percent photoresist residue removal from the bond pad area. The trench features consisted of 1:1 line/space pairs of about 0.2 micron dimension, and the bond pad areas consisted of a square array of square dummy features of about 2 microns dimension.

Example 10

[0049] Composition K was prepared as follows:

Composition K
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 7.3
2-Mercaptobenzimidizole          0.2
Water                            58.0
Pentamethyldiethylenetriamine    20.0
Boric Acid                       1.0

[0050] Composition K resulted in some residual photoresist on the trench features with five percent of the bond pad area cleaned with immersion in composition K for 20 minutes at 70° C.

Example 11

[0051] Composition L was prepared as follows:

Composition L
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 7.3
2-Mercaptobenzimidizole          0.2
Water                            49.0
N-(3-Aminopropyl)-morpholine     30.0

[0052] Composition L resulted in complete photoresist removal from the trench features and greater than 99.9 percent removal from the bond pad area when immersed for 16 minutes at 70° C.

Example 12

[0053] Composition M was prepared as follows:

Composition M
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 7.3
2-Mercaptobenzimidizole          0.2
Water                            49.0
N-Hydroxyethylmorpholine         30.0

[0054] Composition M resulted in ten percent photoresist removal in the trench features and zero percent in the bond pad area when immersed for 16 minutes at 70° C.

Example 13

[0055] Composition N was prepared as follows:

Composition N
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 13.5
percent solution)
TMAH (25 weight percent solution) 7.3
2-Mercaptobenzimidizole          0.08
Water                            64.1
N,N-Dimethyldiglycolamine amine  15.0

[0056] Composition N resulted in complete photoresist crust removal from the trench features and 95 percent photoresist removal from the bond pad areas when immersed for 20 minutes at 70° C.

Example 13

[0057] Composition O was prepared as follows:

Composition O
Component                        Weight Percent
N-Methylmorpholine-N-oxide (50 weight 12.6
percent solution)
TMAH (25 weight percent solution) 11.7
2-Mercaptobenzimidizole          0.08
Water                            75.3
Polyethyleneglycol dinonylphenyl ether 0.3

[0058] Polyethyleneglycol dinonylphenyl ether is a surfactant containing about 150 ethyleneglycol repeat units. Composition O resulted in complete photoresist crust removal from the trench features and complete percent photoresist removal from the bond pad areas when immersed for 20 minutes at 70° C.

Comparative Example 1

[0059] Comparative composition I consisted of ten weight percent hydroxylamine, ten weight percent water and 80 weight percent diglycolamine. Etched photoresist substrates were immersed in the composition for 30, 50 and 60 minutes at 70° C., followed by a rinsing with water. Inspection by optical and electron microscopy revealed that comparative composition I dissolved photoresist from under the top layer of photoresist residue, but left the layer of residue collapsed and attached to the samples in all regions.

Claims

1. A cleaning solution comprising: a polar solvent; and a base rendering a pH of greater than about 11.5 to said solution when composing no more than about 3.5% of said solution by weight.

2. The cleaning solution of claim 1 wherein said polar solvent is one of water, an alcohol, ethylene, an amide, propylene, a carbonate, and a glycol.

3. The cleaning solution of claim 1 wherein said base is a nitrogen containing compound with one of hydrogen, an alkyl, and a substituted alkyl as a side chain.

4. The cleaning solution of claim 1 wherein said polar solvent composes between about 20% and about 95% of said solution by weight.

5. The cleaning solution of claim 1 wherein said base is one of ammonium hydroxide and tetramethyl ammonium hydroxide.

6. The cleaning solution of claim 1 wherein said base composes between about 0.1% and about 30% of said solution by weight.

7. The cleaning solution of claim 1 further comprising one of an oxidant, a co-solvent, and a chelator.

8. A cleaning solution having a pH of greater than about 11.5 and comprising: a polar solvent; a base; and one of an oxidant, a co-solvent, a surfactant and a chelator.

9. The cleaning solution of claim 8 wherein said oxidant composes between about 1% and about 30% of said solution.

10. The cleaning solution of claim 8 wherein said oxidant is one of an amine-N-oxide, a perborate salt, a percarbonate salt, and a peroxide.

11. The cleaning solution of claim 8 wherein said oxidant is a nitrogen containing compound including one of a hydrogen, a methyl, and a alkyl side group.

12. The cleaning solution of claim 8 wherein said co-solvent composes up to about 50% of said solution by weight.

13. The cleaning solution of claim 8 wherein said co-solvent is one of an alkylamine, and aldanolamine, and a glycol.

14. The cleaning solution of claim 8 wherein said surfactant composes up to about 20% of said solution by weight.

15. The cleaning solution of claim 8 wherein said surfactant is one of a fluroroalkyl, a glycol, a carboxylic acid salt, dodecylbenzene sulfonic acid, a dodecylbenzene sulfonic acid salt, a silicone polymer, a polyacrylate polymer, and acetylenic diol, alkylammonium and alkylammonium salt.

16. The cleaning solution of claim 8 wherein said chelator composes up to about 10% of said solution by weight.

17. The cleaning solution of claim 8 wherein said chelator is one of a triazole, a thiazole, a tetrazole, an imidizole, a phosphate, a thiol, an azine, a glycerol, an amino acid, a carboxylic acid, an alcohol, an amide, and a quinoline.

18. An apparatus comprising: a semiconductor substrate having a trench patterned thereinto; and a metal line accommodated by the trench, the trench cleaned with a solution to accommodate the metal line, the solution having a pH of greater than about 11.5

19. The apparatus of claim 18 wherein the solution includes one of a polar solvent, and oxidant, a co-solvent, a surfactant, and a chelator.

21. A method comprising: patterning a photoresist on a semiconductor substrate; and cleaning the semiconductor substrate with a cleaning solution having a pH of greater than about 11.5

22. The method of claim 20 wherein the cleaning solution includes one of a polar solvent, an oxidant, a co-solvent, a surfactant, and a chelator.

23. The method of claim 20 wherein said cleaning includes removing the photoresist from the semiconductor substrate.

24. The method of claim 20 further comprising: forming a trench in the semiconductor substrate after said patterning; depositing a metal line in the trench after said cleaning; and subjecting the seminconductor substrate to chemical mechanical planarization.