Surface treating composition for micro processing

Abstract

Hydrofluoric acid has incorporated therein a hydrocarbon nonionic surfactant having an HLB value of 7 to 17. The composition exhibits improved wetting and other properties for use in surface treatment for micro processing.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to surface treating compositions for micro processing, and more particularly to such a surface treating composition for use removing or etching an oxide film on silicon by the wet method, and cleaning the surface of silicon.

2. Description of the Prior Art

Hydrofluoric acid is used as a surface treating agent (hereinafter referred to briefly as a "treating solution") in fabricating semiconductor devices. While such treating solutions need to have a high purity and high cleanness in view of the purpose of the treatment, a perfect and comprehensive surface-treating function has further been required of the solution to produce semiconductor devices of higher integration density or complexity and higher performance in high yields.

Stated more specifically, the surface treating process, for example, for removing an oxide film from silicon surfaces is an important process which governs the quality of the fine circuit to be subsequently formed, and should completely uniformly perform a chemical action over the entire surface area of the silicon substrate. Furthermore, the process must produce a reliable cleaning effect to finish the resulting highly active surface to a flawless extremely smooth clean surface. Accordingly, it is essential that the surface to be treated be effectively wettable with hydrofluoric acid.

In the etching process for forming LSI circuits, the patterns used have become smaller and more complex with an increase in the density of integration, such that the micro processing can not be fabricated uniformly and perfectly over the entire grooved area unless hydrofluoric acid effectively penetrates into micro clearances or grooves and completely cleans the grooves through a chemical action. Thus, the wetting and penetrating properties are of extreme importance to the treating solution.

The grooves formed by patterning are conventionally cleaned with sulfuric acid-hydrogen peroxide aqueous solution, hydrochloric acid-hydrogen peroxide aqueous solution or ammonia water-hydrogen peroxide aqueous solution, whereas it is the necessary to remove the resulting oxide film. Hydrofluoric acid is a liquid of low viscosity and low surface tension (8.6 dynes/cm) when 100% in concentration, but the surface tension approaches that of water as is is diluted to a greater extent. Hydrofluoric acid has a contact angle of 58 to 76 degree on the surface of silicon, which is therefore difficult to wet with this acid. The surface tension is 50 to 73 dynes/cm. When thus having high surface tension and a great contact angle, dilute hydrofluoric acid is unable to uniformly penetrate onto micro grooves and encounters difficulty in treating finely processed surfaces as by etching or cleaning. Table 1 shows data as to the surface tension and contact angle. Also shown for reference is data as to ultrapure water. Table 1 shows the surface tension and contact angle of ultrapure water and hydrofluoric acid.

To evaluate the wettability of the surface of silicon, treating solutions as applied dropwise to the silicon surface were checked for contact angle by the liquid droplet method. The surface tension was measured by the vertical plate method.

TABLE 1______________________________________ Surface tension Contact angle on (dyn/cm) Silicon surface (degree)______________________________________Ultrapure water 72.5 760.5% hydrofluoric acid 71.7 765.0% hydrofluoric acid 68.1 7330% hydrofluoric acid 58.6 6550% hydrofluoric acid 51.0 58______________________________________

The surface tension is an action at a gasliquid interface, and the contact angle is an action at a solid-liquid interface, so that the wettability of silicon surface should of course be evaluated in terms of contact angle. As previously stated, the wetting property is an important function of the treating solution. Although addition of a surfactant is necessary to give a wetting property, some kinds of surfactants are likely to become adsorbed by the surface treated (silicon oxide film), failing to remove the oxide film. Measures for effectively improving the wetting property of the treating solution without adversely affecting the substantial function thereof have not been proposed and still remain to be developed.

Surfactants differ in chemical structure and in the mechanism of their activity. It is necessary to conduct a comprehensive investigation as to what surfactant is to be added to the treating solution to give a treating composition for micro processing (hereinafter referred to briefly as a "treating composition") which is suitable for use in semiconductor fabrication processes, and also as to what influence the presence of a particular surfactant produces on the properties of the treating composition.

We have conducted detailed research on the phenomena resulting from the addition of surfactants to the treating solution and found the following problems.

1. When added, the surfactant readily reduces the surface tension of the treating solution but does not always diminish the contact angle on the surface of silicon. In other words, the treating composition does not always effectively wet the silicon surface or smoothly penetrate into micro clearances. 2. In the case where the treating solution, which contains the surfactant as dispersed therein without dissolving, is subjected to circulating filtration which is generally practiced in semiconductor fabrication processes to remove particles from the solution, the surfactant is adsorbed and trapped by the filter to result in lowered activity (increase in surface tension or contact angle) not infrequently. It is further likely that the surfactant, if dissolving in the treating solution immediately after addition, will separate from the solution in a long period of time to entail impaired activity. 3. The addition or the surfactant is likely to increase the number of particles in the treating composition or to increase the amount of impurities, such as alkali metals, alkaline earth metals or heavy metals, which are said to exert an adverse effect on semiconductor devices. This phenomenon leads to an increased likelihood of particles becoming deposited on the silicon surface or in micro processed clearances, and also contributes to the impairment of performance of semiconductor devices due to impurities. 4. Addition of an excess of surfactant often produces an excessive amount of micelles in the treating composition, causing various troubles to the micro processing as will be described below. (a) Micelles of the surfactant adhere to the surface to be etched, causing irregular or imperfect etching. (b) Micelles adhere to the surface of silicon when wafers are withdrawn from the treating composition to create stains or cause hazing of the water surface, which then scatters a laser beam when the surface is observed by a wafer inspection system. (c) Addition of an excess of the surfactant causes troubles such as frothing to the waste treatment process for the treating composition.

Thus, the addition of surfactants, although necessary to improve the wetting property of the treating solution, at the same time entails the likelihood of adversely affecting the important functions of the treating composition.

The cleaning step included in semiconductor fabrication processes and executed with use of hydrofluoric acid is very important, and attention has been directed especially to the smoothness of cleaned surfaces as a critical factor in submicron devices.

However, when the surfaces of silicon wafers as cleaned with hydrofluoric acid were observed under an Atomic Force Microscope (AFM) at an atom discernible magnification, the surface smoothness was found to be impaired. Silicon wafers become rough-surfaced also when etched with use of buffered hydrofluoric acid (acid mixture of hydrofluoric acid and ammonium fluoride in a suitable ratio). Techniques for ensuring smoothness by incorporating a suitable surfactant into treating solutions have been developed as disclosed, for example, in Unexamined Japanese Patent Publications 1988-283028 and 1991-179737. Nevertheless, even it the surfactant added to the buffered hydrofluoric acid is added to hydrofluoric acid, the contemplated effect is not available. Conversely, observation under AFM has revealed that some silicon wafers, for example, P-type (100) wafers, become rough-surfaced when immersed in the resulting composition for at least 30 minutes.

Such a surface defect becomes a serious objection in integrated circuits of high complexity, for example, in forming shallow junctions. Accordingly, it is extremely important to develop means for giving a wetting property to the treating solution to obtain surface smoothness also in cleaning silicon surfaces with hydrofluoric acid.

There are a wide variety of surfactants, which are divined generally into hydrocarbon surfactants and fluorine-containing surfactants. Each of these types include cationic, anionic, amphoteric and nonionic surfactants. Although Unexamined Japanese Patent Publication 1989-183824 discloses that any surfactants are useful insofar as they are of the hydrocarbon type, this is not true of the application contemplated by the present invention.

The surfactants used in Unexamined Japanese Patent Publications 1983-55323 and 1983-42019 include those increasing the number of particles that will adhere to the surface of silicon and those roughing silicon surfaces, such as primary amine salts, secondary amine salts, tertiary amine salts and quaternary ammonium salts. These surfactants are not suited to use in etching or cleaning agents for silicon and silicon oxide films.

Dodecylbenzenesulfonic acid used in Unexamined Japanese Patent Publication 1986-203800 has exceedingly high ability to froth and therefore the drawback of being liable to pose problems such as etching faults in semiconductor fabrication processes.

Examined Japanese Patent Publication 1992-16011 discloses a method of etching a silicon oxide film formed on the bottom surfaces of micro groove of 1 to 5 .mu.m square with a composition comprising hydrofluoric acid and a nonionic surfactant added thereto. Although polyethylene glycol lauryl ether, polyethylene glycol alkylphenyl ethers and polyethylene glycol fatty acid esters are given in the publication as examples or nonionic surfactants, the sole example of composition mentioned is one comprising, hydrofluoric acid diluted to a ratio of 1:20 and 1 vol. % of polyethylene glycol lauryl ether added thereto. Presently, with advances made in integrated circuits of high complexity, the size of micro groove or line width to be etched are not larger 1 .mu.m. The treating composition of Examined Patent Publication 1992-16011 is not serviceable as such in the current stage of progress in circuits of high complexity, and there is a need to use compositions fulfilling more stringent requirements as to surface tension, contact angle and characteristics to be described herein. Thus, surfactants suited to the fabrication of advanced semiconductor devices of higher integration density or complexity can not be selected from among those which are disclosed in the publication 1992-16011 and which are not suitable for use in etching agents and cleaning agents.

There are cases wherein IPA (isopropyl alcohol) or the like is added in an amount of about 10% in treating solution to give reduced surface tension, whereas problems then arise in treating the resulting waste water. Accordingly, unless the surfactant to be used is effective in a small amount, the contemplated object is not attainable.

Hydrofluoric acid is used generally at a concentration, for example, of 0.5 wt. % or 5 wt. %. However, since it is not economical to commercially prepare such hydrofluoric acid, it is desired to prepare hydrofluoric acid having a concentration of 50 wt. % which remains unchanged in activity when diluted for use.

SUMMARY OF THE PRESENT INVENTION

To overcome the problems relating to the treating composition, we have conducted careful technical investigations and carried out experiments with meticulous consideration given thereto from the viewpoint of cleaning technology. Surfactants are used for a very wide variety of applications under diversified conditions, and are divided generally into hydrocarbon surfactants and fluorine-containing surfactants. These two types are further divided into cationic, anionic, amphoteric and nonionic types.

Each of these types includes many compounds each having characteristic surface activity. We have conducted investigations to select surfactants suited to the object of the invention, and selected those which are satisfactory in all the items (1) to (6) given below from among these surfactants. The treating composition incorporating such a surfactant is used mainly for the purpose of etching a silicon oxide film, or removing an oxide film as formed over the entire surface of a silicone wafer or in etched grooves therein when the wafer is cleaned with sulfuric acid-hydrogen peroxide aqueous solution, hydrochloric acid-hydrogen peroxide aqueous solution or ammonia-hydrogen peroxide aqueous solution or when the wafer is further washed with ultrapure water. Accordingly, the treating composition was checked for repellency on the wafer to ascertain whether the presence of the surfactant is not detrimental to the contemplated effect (7).

(1) Reduction in the number of particles present in treating composition (2) Silicon surface wetting property of treating composition and property thereof to penetrate into contact grooves and via grooves (3) Smoothness of silicon surface (4) Diminished adhesion of particles to silicon surface (5) Stability of treating composition (6) High purity of treating composition (7) Silicon surface cleaning effect or oxide film etching effect

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the relationship between the concentration of surfactants and the number of particles in a solution.

FIG. 2 is a diagram showing the relationship between the concentration of surfactants and the number of adhering particles.

The following check means or methods were used to quantitatively evaluate the suitability of the surfactant to be incorporated into treating compositions fulfilling the above seven requirements. The treating solutions used for testing were 0.5 wt. %, 5 wt. % and 50 wt. % in the concentration of hydrofluoric acid.

(1) Reduction in the number of particles present in treating composition

Being low in particle content is one of the important properties required of the treating composition for use in surface treating processes for micro processing because improper etching due to the presence of particles is a great factor to result in a lower yield in semiconductor fabrication. As shown in FIG. 1, there are surfactants which reduce the number of particles present in the treating solution when added to the solution, followed by circulating filtration. However, the mechanism of reduction in the number of particles or particle content still remains to be clarified. FIG. 1 is a diagram showing the relationship between the concentration of surfactants and the number of particles present in the solution which is 0.5 wt. % in HF concentration.

There are very large number of surfactants which fail to reduce the number of particles in the treating composition which is prepared by addition of the surfactant and circulating filtration. These surfactants are not suited to the object of the invention. To find out surfactants which attain the object, we investigated various surfactants (hydrocarbon type and fluorine-containing type including nonionic, anionic, cationic and amphoteric surfactants). The results is shown in Tables 2 to 14, in which the compounds of the same kind but different in molecular weight are designated by A, B, C, . . . . These symbols A to H in Tables 2 to 14 stand for the following surfactants.

A: hydrocarbon nonionic surfactant B: hydrocarbon anionic surfactant C: hydrocarbon cationic surfactant D: hydrocarbon amphoteric surfactant E: fluorine-containing nonionic surfactant F: fluorine-containing anionic surfactant G: fluorine-containing cationic surfactant H: fluorine-containing amphoteric surfactant TABLE 2______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Polyoxy- Polyoxyethylene 4 Acceptable Aethylene lauryl ether Aalkyl ether Polyoxyethylene 8 Acceptable A alkyl ether B Polyoxyethylene 5 Acceptable A nonylphenyl ether A Polyoxyethylene 8 Acceptable A nonylphenyl ether B Polyoxyethylene 3 Acceptable A nonylphenyl ether C Polyoxyethylene 8 Acceptable A alkylphenyl ether A Polyoxyethylene 4 Acceptable A alkylphenyl ether B Polyoxyethylene 5 Acceptable A octylphenyl ether Polyoxyethylene 3 Acceptable A oleyl ether Polyoxyethylene 7 Acceptable A alkylallyl ether A Polyoxyethylene 7 Acceptable A alkylallyl ether B Polyoxyalkylene 8 Acceptable A alkyl ether Polyoxyethylene 9 Acceptable A higher alcohol ether A Polyoxyethylene 4 Acceptable A higher alcohol ether B______________________________________ TABLE 3______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Nonionic Polyoxyethylene 9 Acceptable Asurfactant derivative Polyoxyethylene 7 Acceptable A derivative A Polyoxyethylene 7 Acceptable A derivative B Polyoxyethylene 8 Acceptable A derivative C Specified non- 8 Acceptable A ionic surfactant Specified non- 8 Acceptable A ionic surfactant Specified ether 28 Unacceptable A nonionic sur- factant A Specified ether 34 Unacceptable A nonionic sur- factant B Specified ether 54 Unacceptable A nonionic sur- factant C Specified ether 19 Unacceptable A nonionic sur- factant D Mixture of 19 Unacceptable A specified sur- factantsSorbitan Sorbitan mono- 8 Acceptable Afatty acid oleate Aester Sorbitan mono- 2 Acceptable A oleate B Sorbitan sesqui- 5 Acceptable A oleate Sorbitan mono- 2 Acceptable A laureate Sorbitan sesqui- 1 Acceptable A oleatePolyoxy- Polyoxyethylene 1 Acceptable Aethylene sorbitan fattysorbitan acid esterfatty acid (laureate)ester______________________________________ TABLE 4______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Fatty acid Monoglycerol ester 8 Acceptable Amono-glyceridePoly- Polyoxyalkylene 8 Acceptable Aalkylene glycol derivativeglycol A Polyoxyalkylene 7 Acceptable A glycol derivative B Polyoxyalkylene 9 Acceptable A glycol derivative C Polyoxyalkylene 5 Acceptable A glycol derivative D Polyoxyalkylene 4 Acceptable A glycol A Polyoxyalkylene 6 Acceptable A glycol B Polyethylene glycol 2 Acceptable A ester Polyethylene glycol 1 Acceptable A A Polyethylene glycol 1 Acceptable A B Polyglycol type 3 Acceptable A product A Polyglycol type 3 Acceptable A product B Polyglycol type 5 Acceptable A product C Polyglycol type 5 Acceptable A product D______________________________________ TABLE 5______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Polyoxy- Polyethylene 8 Acceptable Aethylene glycol fatty acidfatty acid esterester Polyoxyethylene 8 Acceptable A oleic acid ester A Polyoxyethylene 7 Acceptable A oleic acid ester B Polyoxyethylene 8 Acceptable A oleic acid ester C Polyoxyethylene 7 Acceptable A oleic acid ester D Polyoxyethylene 8 Acceptable A oleic acid ester E Polyoxyethylene 8 Acceptable A fatty acid esterAlcohol Octanol 8 Acceptable A Nonanol 8 Acceptable A Lauryl alcohol 7 Acceptable A Lanolin alcohol 7 Acceptable ABlock Polyoxyethylene 5 Acceptable Apolymer polyoxypropylene block polymer A Polyoxyethylene 5 Acceptable A polyoxypropylene block polymer B Polyoxyethylene 8 Acceptable A polyoxypropylene block polymer C Polyoxyethylene 8 Acceptable A polyoxypropylene block polymer D______________________________________ TABLE 6______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Fatty acid Valeric acid 8 Acceptable Band salt Caproic acid 7 Acceptable Bthereof Enanthic acid 6 Acceptable B Caprylic acid 10 Acceptable B Pelargonic acid 11 Unacceptable B Capric acid 12 Unacceptable B Lauric acid 20 Unacceptable B Fatty acid type 15 Unacceptable BAlkyl Alkyl sulfonate 25 Unacceptable Bsulfate Higher alcohol 11 Unacceptable Bester sodium sulfatesalt Lauryl sulfate 15 Unacceptable B triethanol amineAlkyl- Dodecylbenzene 5 Acceptable Bbenzen sulfonic acidsulfonate sodium A Dodecylbenzene 5 Acceptable B sulfonic acid sodium B Dodecylbenzene 3 Acceptable B sulfonic acidDialkyl Dialkyl sulfo- 12 Unacceptable Bsulfo- succinic acidsuccinic sodium Aacid Dialkyl sulfo- 20 Unacceptable B succinic acid sodium B Dialkyl sulfo- 55 Unacceptable B succinic acid ester sodium salt______________________________________ TABLE 7______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Polyoxy- Polyoxyethylene 18 Unacceptable Bethylene alkylphenylalkyl and ether ammoniumalkylallyl sulfate Aether sul- Polyoxyethylene 36 Unacceptable Bfuric acid alkylphenylester salt ether ammonium sulfate ACarbox- Polycarboxylic 25 Unacceptable Bylic acid acid ammoniumtype high- saltpolymerOther Alkyl diphenyl 88 Unacceptable B ether disulfonate Oleayl sarcosine 55 Unacceptable B A mixture of 36 Unacceptable B acylmethyl taurinic acid sodium and anionic surfactant Addition product 22 Unacceptable B of anionic surfactant______________________________________ TABLE 8__________________________________________________________________________ Number of particles Substance >0.5 .mu.m (per ml) Acceptability Kind__________________________________________________________________________Alkylamine salt Heptylamine 5 Acceptable C Dimethyloctylamine 8 Acceptable C Benzylamine 8 Acceptable C Coconut-amine acetate 25 Unacceptable C Laurylamine 55 Unacceptable C Octylamine 26 Unacceptable C Trioctylamine 12 Unacceptable C Amylamine 15 Unacceptable C Hexylamine 11 Unacceptable C Cyclohexylamine 23 Unacceptable CQuaternary Alkylbenzyldimethyl- 18 Unacceptable Cammonium salt ammonium chloride Dodecyltrimethyl- 18 Unacceptable C ammonium chloride Lauryltrimethyl- 19 Unacceptable C ammonium chloride (RN.sup.+ (CH.sub.3).sub.2 CH.sub.2 .sup.- C.sub.6 H.sub.6)Cl.sup.- 1 33 Unacceptable COther 25 Unacceptable C__________________________________________________________________________ TABLE 9______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Alkyl- Dimethylalkyl- 69 Unacceptable Dbetaine betaineImidazol- 2-alkyl-N-carbox- 55 Unacceptable Dinium ylalkyl-N-betain hydroxyethyl imidazolinium betainOther 59 Unacceptable D______________________________________ TABLE 10______________________________________ Number of particles >0.5 .mu.m Substance (per ml) Acceptability Kind______________________________________Ethyleneoxide Perfluoro ethylene- 8 Acceptable Eaddition oxide addition productproduct A Perfluoro ethylene- 5 Acceptable E oxide addition product B Perfluoro ethylene- 6 Acceptable E oxide addition product C Perfluoro ethylene- 7 Acceptable E oxide addition product DEster Perfluoro alkyl ester A 8 Acceptable E Perfluoro alkyl ester B 7 Acceptable EAmine oxide Perfluoro alkyl amine 6 Acceptable E oxideAlcohol Fluoro alcohol 3 Acceptable EOther R.sub.1 C.sub.2 H.sub.4 O(C.sub.2 H.sub.4 O).sub.x H 10 Acceptable E______________________________________ TABLE 11______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Carboxy- Perfluoro alkyl 2 Acceptable Flic acid carboxylic acid Aand car- Perfluoro alkyl 2 Acceptable Fbonate carboxylic acid B Perfluoro alkyl 5 Acceptable F carbonate A Perfluoro alkyl 4 Acceptable F carbonate B Perfluoro alkyl 36 Unacceptable F carbonate C Perfluoro alkyl 12 Unacceptable F carboxylic acid potassium Perfluoro alkyl 15 Unacceptable F carboxylic acid ammoniumSulfonic Perfluoro alkyl 36 Unacceptable Facid sulfonic acid pottasium Perfluoro alkyl 22 Unacceptable F sulfonic acid sodium Perfluoro alkyl 23 Unacceptable F sulfonic acid lithium Perfluoro alkyl 23 Unacceptable F sulfonic acid ammonium A Perfluoro alkyl 89 Unacceptable F sulfonic acid ammonium B Perfluoro alkyl 77 Unacceptable F sulfonic acid ammonium C Perfluoro alkyl 12 Unacceptable F sulfonic acid ammonium D Perfluoro alkyl 55 Unacceptable F sulfonate A Perfluoro alkyl 56 Unacceptable F sulfonate B______________________________________ TABLE 12__________________________________________________________________________ Number of particles Substance >0.5 .mu.m (per ml) Acceptability Kind__________________________________________________________________________Phosphate ester Perfluoro alkyl phosphate ester 89 Unacceptable F A Perfluoro alkyl phosphate ester 12 Unacceptable F BOther C.sub.8 F.sub.17 SO.sub.2 N(C.sub.3 H.sub.7)C.sub.2 H.sub.4 23(OH) Unacceptable F R.sub.1 C.sub.2 H.sub.4 SC.sub.2 H.sub.4 CO.sub.2 Li 55 Unacceptable F R.sub.1 C.sub.2 H.sub.4 OPO(ONH.sub.4).sub.2 55 Unacceptable F R.sub.1 C.sub.2 H.sub.4 OPO(ONH.sub.4).sub.2 + Non 77 Unacceptable F Fluorinated Surfactant R.sub.1 SO.sub.2 NRCH.sub.2 COOK 15 Unacceptable F Mixture of amide type sub- 89 Unacceptable F stances Mixture of alcohol and sulfonate 99 Unacceptable F (R.sub.1 SO.sub.2 NRC.sub.2 H.sub.4 O).sub.2 PO(ONH.sub.4) 46 Unacceptable F__________________________________________________________________________ TABLE 13__________________________________________________________________________ Number of particles Substance >0.5 .mu.m (per ml) Acceptability Kind__________________________________________________________________________Alkylamine salt Perfluoro alkyl trimethyl 11 Unacceptable G ammonium saltQuaternary Perfluoro alkyl ammonium 8 Acceptable Gammonium salt iodide A Perfluoro alkyl ammonium 2 Acceptable G iodide B Perfluoro alkyl ammonium 8 Acceptable G saltOther R.sub.1 C.sub.2 H.sub.4 SC.sub.2 H.sub.4 N(CH.sub.3).sub.3 CH.sub.3 SO.sub.4 56 Unacceptable G R.sub.1 SO.sub.2 NRC.sub.2 H.sub.4 N.sup.+ (CH.sub.3).sub.3 I.sup.- 66 Unacceptable G__________________________________________________________________________ TABLE 14______________________________________ Number of particlesSubstance >0.5 .mu.m (per ml) Acceptability Kind______________________________________Alkyl- Perfluoro alkyl 15 Unacceptable Hbetaine betaine A Perfluoro alkyl 55 Unacceptable H betaine B Perfluoro alkyl 66 Unacceptable H betaine C Perfluoro alkyl 12 Unacceptable H betaine D______________________________________

The surfactant was evaluated as being satisfactory for the object of the invention when giving a treating composition wherein the number of particles 0.5 .mu.m and larger was up to 10 pieces/ml. FIG. 1 shows the relationship between the concentration of surfactants and the number of particles in the solution.

The number of particles in the treating composition was measured by a laser liquid-borne particle counter after the composition was subjected to 24 cycles of circulating filtration at a flow rate of 750 kg/m.sup.2 .multidot.hr using a fluorocarbon resin filter with a pore size of 0.1 .mu.m.

(2) Silicon surface wetting property of treating composition and property thereof to penetrate into contact grooves and via grooves.

The treating composition was checked for silicon surface wetting property and property to penetrate into small patterns formed on silicon surfaces. Consequently, we found that when silicon wafers were dipped in the treating composition, the composition failed to smoothly wet the silicon surface unless the composition had a contact angle of not larger than 50 degree on the silicon surface and surface tension of not greater than 45 dynes/cm.

The composition was unable to smoothly penetrate into small patterns of up to 10 .mu.m and to properly etch a silicon oxide film, confirmed by sectional photographs obtained with use of an electron microscope and observation under AFM.

The hydrocarbon surfactants and fluorine-containing surfactants include a considerably large number of those which give the treating solution a contact angle of up to 50 degree and surface tension of up to 45 dynes/cm when added to the solution. These surfactants are evaluated as being suitable for the object of the invention if the treating compositor still retains these properties after circulating filtration at a concentration of up to 1000 ppm at which no trouble occurs due to excessive use of the surfactant.

Accordingly, the surfactants which were found acceptable in respect of the item (1) were checked for the present item (2). The result is given in Tables 15 to 23, wherein the symbols A to H each have the same meaning as above.

Surface tension is measured at 20.degree. C.

TABLE 15______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Polyoxy- Polyoxyethylene 40 45 Acceptable Aethylene lauryl etheralkyl ether Polyoxyethylene 36 40 Acceptable A alkyl ether Polyoxyethylene 33 40 Acceptable A nonylphenyl ether A Polyoxyethylene 36 41 Acceptable A nonylphenyl ether B Polyoxyethylene 38 42 Acceptable A nonylphenyl ether C Polyoxyethylene 39 48 Acceptable A alkylphenyl ether A Polyoxyethylene 44 48 Acceptable A alkylphenyl ether B Polyoxyethylene 41 49 Acceptable A octylphenyl ether Polyoxyethylene 44 49 Acceptable A alkylallyl ether A Polyoxyethylene 37 42 Acceptable A alkylallyl ether B Polyoxyethylene 35 45 Acceptable A oleyl ether Polyoxyealkylene 38 45 Acceptable A alkyl ether Polyoxyethylene 41 41 Acceptable A higher alcohol ether B Polyoxyethylene 39 42 Acceptable A higher alcohol ether B______________________________________ TABLE 16______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Nonionic Polyoxyethyl- 44 48 Acceptable Asurfactant ene derivative Polyoxyethyl- 44 49 Acceptable A ene derivative A Polyoxyethyl- 44 49 Acceptable A ene derivative B Polyoxyethyl- 44 48 Acceptable A ene derivative C Specified non- 49 52 Unacceptable A ionic surfactant Specified non- 58 65 Unacceptable A ionic surfactantSorbitan Sorbitan mono- 40 48 Acceptable Afatty oleate Aacid ester Sorbitan mono- 41 49 Acceptable A oleate B Sorbitan ses- 42 49 Acceptable A quioleate Sorbitan mono- 38 49 Acceptable A laureate Sorbitan ses- 35 47 Acceptable A quioleatePolyoxy- Polyoxyethyl- 41 47 Acceptable Aethylene ene sorbitansorbitan fatty acid esterfatty (laureate)acid esterFatty acid Monoglycerol 44 49 Acceptable Amono- esterglyceride______________________________________ TABLE 17______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Polyalkyl- Polyoxyalkyl- 41 44 Acceptable Aene glycol ene glycol derivative A Polyoxyalkyl- 40 45 Acceptable A ene glycol derivative B Polyoxyalkyl- 43 48 Acceptable A ene glycol derivative C Polyoxyalkyl- 39 49 Acceptable A ene glycol derivative D Polyoxyalkyl- 38 42 Acceptable A ene glycol A Polyoxyalkyl- 41 48 Acceptable A ene glycol B Polyethylene 41 49 Acceptable A glycol ester Polyethylene 44 65 Unacceptable A glycol A Polyethylene 44 65 Unacceptable A glycol B Polyglycol 41 55 Unacceptable A type product A Polyglycol 42 55 Unacceptable A type product B Polyglycol 41 51 Unacceptable A type product C Polyglycol 39 52 Unacceptable A type product D______________________________________ TABLE 18______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Polyoxy- Polyethylene 41 48 Acceptable Aethylene glycol fattyfatty acid acid esterester Polyoxyethyl- 42 45 Acceptable A ene oleic acid ester A Polyoxyethyl- 42 48 Acceptable A ene oleic acid ester B Polyoxyethyl- 44 47 Acceptable A ene oleic acid ester C Polyoxyethyl- 43 49 Acceptable A ene oleic acid ester D Polyoxyethyl- 44 45 Acceptable A ene oleic acid ester E Polyoxyethyl- 44 47 Acceptable A ene fatty acid esterAlcohol Octanol 41 64 Unacceptable A Nonanol 44 51 Unacceptable A Lauryl alcohol 50 70 Unacceptable A Lanolin alcohol 55 71 Unacceptable ABlock Polyoxyethyl- 41 55 Unacceptable Apolymer ene polyoxy- propylene block polymer A Polyoxyethyl- 44 58 Unacceptable A ene polyoxy- propylene block polymer B Polyoxyethyl- 41 59 Unacceptable A ene polyoxy- propylene block polymer C Polyoxyethyl- 41 52 Unacceptable A ene polyoxy- propylene block polymer D______________________________________ TABLE 19______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Fatty acid Valeric acid 70 75 Unacceptable Band salt Caproic acid 64 74 Unacceptable Bthereof Enanthic acid 55 77 Unacceptable B Caprylic acid 50 68 Unacceptable BAlkyl- Dodecyl- 36 20 Acceptable Bbenzen benzene sul-sulfonate fonic acid sodium A Dodecyl- 31 25 Acceptable B benzene sul- fonic acid sodium B Dodecyl- 29 18 Acceptable B benzene sul- fonic acid______________________________________ TABLE 20______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Alkyl- Heptylamine 31 55 Unacceptable Camine salt Dimethyloctyl- 32 58 Unacceptable C amine Benzylamine 33 55 Unacceptable C______________________________________ TABLE 21______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Ethylene- Perfluoro ethyl- 25 44 Acceptable Eoxide eneoxide addi-addition tion product Aproduct Perfluoro ethyl- 23 32 Acceptable E eneoxide addi- tion product B Perfluoro ethyl- 22 33 Acceptable E eneoxide addi- tion product C Perfluoro ethyl- 28 44 Acceptable E eneoxide addi- tion product DEster Perfluoro alkyl 33 56 Unacceptable E ester A Perfluoro alkyl 31 58 Unacceptable E ester BAmine Perfluoro alkyl- 35 51 Unacceptable Eoxide amine oxideAlcohol Fluoroalcohol 24 66 Unacceptable E______________________________________ TABLE 22______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Car- Perfluoro alkyl 30 42 Acceptable Fboxylic carboxylic acid Aacid and Perfluoro alkyl 26 44 Acceptable Fcarbonate carboxylic acid B Perfluoro alkyl 35 58 Unaccept- F carbonate A able Perfluoro alkyl 33 66 Unaccept- F carbonate B able______________________________________ TABLE 23______________________________________ Surface tension ContactSubstance (dyne/cm) angle Acceptability Kind______________________________________Quatern- Perfluoro alkyl 25 42 Acceptable Gary ammoniumammon- iodide Aium salt Perfluoro alkyl 33 33 Acceptable G ammonium iodide B Perfluoro alkyl 20 37 Acceptable G ammonium salt______________________________________ (3) Smoothness of silicon surface

It is said that with semiconductor devices, the smaller the subnanometer irregularities on the silicon wafer surface, i.e., the microroughness of the surface, the higher is the reliability of the device and the higher are the characteristics thereof. Accordingly, the roughness of silicon surfaces was measured by immersing a silicon wafer in the treating composition for 100 minutes and then determining the average surface microroughness (Ra) of the wafer surface under AFM. When the roughness was not greater than 0.3 nm (3 angstroms), the treating composition was evaluated as being satisfactory for the object of the invention.

The surfactants which were found satisfactory with respect to items (1) and (2) were checked for the present item (3). Tables 24 to 30 show the result.

TABLE 24______________________________________ Surface roughness Substance (Ra: nm) Acceptability Kind______________________________________Poly- Polyoxyethylene lauryl 0.21 Acceptable Aoxyethylene ether Aalkyl ether Polyoxyethylene alkyl 0.22 Acceptable A ether B Polyoxyethylene non- 0.19 Acceptable A ylphenyl ether A Polyoxyethylene non- 0.15 Acceptable A ylphenyl ether B Polyoxyethylene non- 0.16 Acceptable A ylphenyl ether C Polyoxyethylene alkyl- 0.28 Acceptable A phenyl ether A Polyoxyethylene alkyl- 0.29 Acceptable A phenyl ether B Polyoxyethylene octyl- 0.22 Acceptable A phenyl ether Polyoxyethylene alkyl- 0.15 Acceptable A allyl ether A Polyoxyethylene alkyl- 0.16 Acceptable A allyl ether B Polyoxyethylene oleyl 0.22 Acceptable A ether Polyoxyethylene alkyl 0.18 Acceptable A ether Polyoxyethylene 0.25 Acceptable A higher alcohol ether A Polyoxyethylene 0.21 Acceptable A higher alcohol ether B______________________________________ TABLE 25______________________________________ Surface roughness Substance (Ra: nm) Acceptability Kind______________________________________Nonionic Polyoxyethylene 0.33 Unaccept- Asurfactant derivative A able Polyoxyethylene 0.56 Unaccept- A derivative B able Polyoxyethylene 0.77 Unaccept- A derivative C able Polyoxyethylene 0.33 Unaccept- A derivative D ableSorbitan fatty Sorbitan monooleate A 0.56 Unaccept- Aacid ester able Sorbitan monooleate B 0.55 Unaccept- A able Sorbitan sesquioleate 0.33 Unaccept- A able Sorbitan monolaureate 0.38 Unaccept- A able Sorbitan sesquioleate 0.46 Unaccept- A ablePolyoxy- Polyoxyethylene sor- 0.55 Unaccept- Aethylene bitan fatty acid ester ablesorbitan fatty (laureate)acid esterFatty acid Monoglycerol ester 0.33 Unaccept- Amonoglyceride able______________________________________ TABLE 26______________________________________ Surface roughness Substance (Ra: nm) Acceptability Kind______________________________________Poly- Polyoxyethylene gly- 0.29 Acceptable Aalkylene col derivative Aglycol Polyoxyalkylene gly- 0.25 Acceptable A col derivative B Polyoxyalkylene gly- 0.22 Acceptable A col derivative C Polyoxyalkylene gly- 0.22 Acceptable A col derivative D Polyoxyalkylene gly- 0.21 Acceptable A col A Polyoxyalkylene gly- 0.25 Acceptable A col B Polyethylene glycol 0.23 Acceptable A esterPolyoxy- Polyethylene glycol 0.23 Acceptable Aethylene fatty acid esterfatty acid Polyoxyethylene oleic 0.28 Acceptable Aester acid ester A Polyoxyethylene oleic 0.23 Acceptable A acid ester B Polyoxyethylene oleic 0.33 Unaccept- A acid ester C able Polyoxyethylene oleic 0.35 Unaccept- A acid ester D able Polyoxyethylene oleic 0.36 Unaccept- A acid ester E able Polyoxyethylene fatty 0.36 Unaccept- A acid ester able______________________________________ TABLE 27______________________________________ Surface roughness Substance (Ra: nm) Acceptability Kind______________________________________Alkylbenzen Dodecylbenzene sul- 0.32 Unaccept- Bsulfonate fonic acid sodium A able Dodecylbenzene sul- 0.31 Unaccept- B fonic acid sodium B able Dodecylbenzene sul- 0.35 Unaccept- B fonic acid able______________________________________ TABLE 28______________________________________ Surface roughness Substance (Ra: nm) Acceptability Kind______________________________________Ethyleneoxide Perfluoro ethylene- 0.32 Unaccept- Eaddition oxide addition ableproduct product A Perfluoro ethylene- 0.39 Unaccept- E oxide addition able product B Perfluoro ethylene- 0.39 Unaccept- E oxide addition able product C Perfluoro ethylene- 0.33 Unaccept- E oxide addition able product D______________________________________ TABLE 29______________________________________ Surface roughness Substance (Ra: nm) Acceptability Kind______________________________________Carboxylic acid Perfluoro alkyl 0.28 Acceptable Fand carbonate carboxylic acid A Perfluoro alkyl 0.25 Acceptable F carboxylic acid B______________________________________ TABLE 30______________________________________ Surface roughness Substance (Ra: nm) Acceptability Kind______________________________________Quaternary Perfluoro alkyl 0.39 Unaccept- Gammonium salt ammonium able iodide A Perfluoro alkyl 0.36 Unaccept- G ammonium able iodide B Perfluoro alkyl 0.55 Unaccept- G ammonium salt able______________________________________

The symbols A to H in the above tables each have the same meaning as previously stated.

(4) Diminished adhesion of particles to silicon surface

A previously described in connection with the item (2), the particles present on the wafer exert a fatal effect on the semiconductor device to be fabricated. A wafer inspection system was used to count the number of particles adhering to the surface of silicon.

Wafers were treated with hydrofluoric acid without surfactant or hydrofluoric acid with a surfactant, and then checked for the number of particles adhering to the wafer surface for comparison. Since the treatment with hydrofluoric acid is the final step of etching and cleaning processes, the wafer treated with the treating composition is thereafter treated only by washing with ultrapure water. Accordingly, the reduction of the number of particles adhering to the wafer surface is a very important item. The number of adhering particles which is satisfactory for the object of the invention is not greater than 100 particles of 0.3 to 0.5 .mu.m on 5-inch bare silicon wafer.

FIG. 2 shows the relationship between the concentration of surfactant and the number of adhering particles. FIG. 1, showing the relationship between the concentration of a surfactants and the number of particles, indicates that the surfactant concentration is effective even if low, whereas it is seen that an increase in the concentration (beyond 1000 ppm) markedly increases the number of particles in the treating composition and also in the number of particles adhering to the silicon surface. Thus, it is desired to add the surfactant in an amount of up to 1000 ppm.

Accordingly, the surfactants found satisfactory with respect to the items (1) to (3) were checked for the present item (4). Tables 31 to 33 show the result.

TABLE 31______________________________________ Number of adhering particles Substance (per 5 in.) Acceptability Kind______________________________________Poly- Polyoxyethylene lauryl 36 Acceptable Aoxyethylene ether Aalkyl ether Polyoxyethylene alkyl 55 Acceptable A ether B Polyoxyethylene non- 22 Acceptable A ylphenyl ether A Polyoxyethylene non- 88 Acceptable A ylphenyl ether B Polyoxyethylene non- 56 Acceptable A ylphenyl ether C Polyoxyethylene alkyl 77 Acceptable A phenyl ether A Polyoxyethylene alkyl 66 Acceptable A phenyl ether B Polyoxyethylene octyl 35 Acceptable A phenyl ether Polyoxyethylene alkyl- 46 Acceptable A allyl ether A Polyoxyethylene alkyl- 55 Acceptable A allyl ether B Polyoxyethylene oleyl 48 Acceptable A ether Polyoxyethylene alkyl 44 Acceptable A ether Polyoxyethylene 78 Acceptable A higher alcohol ether A Polyoxyethylene 177 Unaccept- A higher alcohol ether B able______________________________________ TABLE 32______________________________________ Number of adhering particles Substance (per 5 in.) Acceptability Kind______________________________________Poly- Polyoxyalkylene gly- 55 Acceptable Aalkylene col derivative Aglycol Polyoxyalkylene gly- 33 Acceptable A col derivative B Polyoxyalkylene gly- 44 Acceptable A col derivative C Polyoxyalkylene gly- 45 Acceptable A col derivative D Polyoxyalkylene gly- 44 Acceptable A col A Polyoxyalkylene gly- 44 Acceptable A col B Polyethylene glycol 56 Acceptable A esterPoly- Polyethylene glycol 55 Acceptable Aoxyethylene fatty acid esterfatty acid Polyoxyethylene oleic 55 Acceptable Aester acid ester A Polyoxyethylene oleic 155 Unaccept- A acid ester B able______________________________________ TABLE 33______________________________________ Number of adhering particles Substance (per 5 in.) Acceptability Kind______________________________________Carboxylic acid Perfluoro alkyl 44 Acceptable Fand carbonate carboxylic acid A Perfluoro alkyl 232 Unaccept- F carboxylic acid B able______________________________________

The symbols A to H in these tables each have the same meaning as previously stated.

(5) Stability of treating composition

Treating compositions fulfilling the foregoing four requirements were prepared, then allowed to stand for 6 months, thereafter tested for the four requirements and thereby checked for changes.

Treating compositions containing one of surfactants which were satisfactory in respect of the term (4) were tested for the number of particles therein, surface tension, contact angle, the number of particles adhering to a wafer and surface roughness of the wafer after standing to exhibit the same result as immediately after preparation.

(6) High purity of treating composition

Treating compositions having a surfactant incorporated therein were analyzed to determine the components and checked for increases in the amounts of alkali metals, alkaline earth metals or heavy metals that would produce an adverse effect on semiconductor fabrication processes to evaluate the purity of the composition.

The surfactants satisfactory with respect to the term (5) were checked by analyzing the composition incorporating the surfactant upon lapse of 6 months after preparation to determine impurities. Consequently none of the surfactants increased the amounts of alkali metals, alkaline earth metals or heavy metals that would adversely affect semiconductor fabrication processes.

The surfactants satisfying all the foregoing requirements (1) to (6) were checked for the last requirement (7) of rendering hydrofluoric acid usable for the main purpose contemplated, i.e., for etching a silicon oxide film, or removing an oxide film as formed over the entire surface of a silicon wafer or in etched grooves therein when the wafer is cleaned with sulfuric acid-hydrogen peroxide aqueous solution, hydrochloric acid-hydrogen peroxide aqueous solution or ammonia-hydrogen peroxide aqueous solution or when the wafer is further washed with ultrapure water.

(7) Silicon surface cleaning effect or oxide film etching effect.

The first purpose of the present treating composition is to remove a natural oxide film from silicon surfaces. Growth of the natural oxide film occurs not only in the atmosphere but also when silicon wafers are rinsed with ultrapure water or when sulfuric acid-hydrogen peroxide aqueous solution, hydrochloric acid-hydrogen peroxide aqueous solution or ammonia water-hydrogen peroxide aqueous solution is used for cleaning in semiconductor fabrication processes.

The oxide film thus occurring needs to be removed with the present treating composition, whereas some surfactants are firmly adsorbed by the surface off silicon oxide film and hamper removal of the film. Whether the natural oxide film on a silicon surface has been removed can be checked by immersing a silicon oxide film grown by the wet method in the treating composition for 1 minute, rinsing the substrate with ultrapure water for 1 minute and measuring the contact angle of ultrapure water as applied dropwise to the substrate, that is, by checking whether the contact angle of ultrapure water on the immersed and rinsed substrate is 72 degree which is the contact angle of water on the silicon substrate. Tables 34 to 36 show the result.

TABLE 34__________________________________________________________________________ Contact angle (degree) Before After Substance immersion immersion Acceptability Kind__________________________________________________________________________None 12 72Polyoxyethylene Polyoxyethylene lauryl ether 12 72 Acceptable Aalkyl ether Polyoxyethylene alkyl ether 12 72 Acceptable A Polyoxyethylene 12 72 Acceptable A nonylphenyl ether A Polyoxyethylene 12 72 Acceptable A nonylphenyl ether B Polyoxyethylene 12 72 Acceptable A nonylphenyl ether C Polyoxyethylene 12 72 Acceptable A alkylphenyl ether A Polyoxyethylene 12 72 Acceptable A alkylphenyl ether B Polyoxyethylene octylphenyl ether 12 72 Acceptable A Polyoxyethylene alkylallyl ether A 12 72 Acceptable A Polyoxyethylene alkylallyl ether B 12 72 Acceptable A Polyoxyethylene oleic ether 12 72 Acceptable A Polyoxyalkylene alkyl ether 12 72 Acceptable A Polyoxyethylene 12 72 Acceptable A higher alcohol ether__________________________________________________________________________ TABLE 35__________________________________________________________________________ Contact angle (degree) Before After Substance immersion immersion Acceptability Kind__________________________________________________________________________Polyalkylene Polyoxyethylene glycol ether 12 72 Acceptable Aglycol Polyoxyalkylene 12 72 Acceptable A glycol derivative A Polyoxyalkylene 12 72 Acceptable A glycol derivative B Polyoxyalkylene 12 72 Acceptable A glycol derivative C Polyoxyalkylene 12 72 Acceptable A glycol derivative D Polyoxyalkylene glycol A 12 72 Acceptable A Polyoxyalkylene glycol B 12 72 Acceptable APolyoxyethylene Polyoxyethylene oleic acid ester 12 72 Acceptable Afatty acid Polyethylene glycol 12 56 Unaccept- Aester fatty acid ester able__________________________________________________________________________ TABLE 36______________________________________ Contact angle (degree) Before AfterSubstance immersion immersion Acceptability Kind______________________________________None 12 72Carboxylic Perfluoro 12 85 Unacceptable Facid alkyl carboxylic acid______________________________________

The symbols A to H each have the same meaning as previously mentioned.

The ultrapure water applied dropwise to the silicon oxide film formed by the wet method has a contact angle of 12 degree, and spreads thin over the oxide film. However, ultrapure water on the surface of silicon from which the oxide film has been removed with the treating composition forms a round drop and is 72 degree in contact angle. This indicates that the silicon oxide film has been removed with the treating composition.

However, some surfactants cover the silicon oxide film and hamper removal of the oxide film with hydrofluoric acid. Accordingly, even if the silicon substrate is immersed in the treating composition for one minute, it is likely that ultrapure water will not exhibit a contact angle of about 72 degree. The surfactant becomes adsorbed by the surface of the oxide film, not only hampering etching of the oxide film but also forming a hydrophobic surface characteristic of fluorine-containing surfactants, such that ultrapure water exhibits a contact angle of at least 85 degree on the surface. Hydrocarbon surfactants are highly hydrophilic, become adsorbed by the natural oxide film on the wafer surface and permit the oxide film to remain partly unremoved with an HF solution, so that water exhibits a diminished contact angle of about 50 degree on the surface. Water on a natural oxide film grown by the dry method shows a large contact angle (36 degree), so that is is difficult to check whether the oxide film has been removed. For this reason, the film grown by the wet method was used.

The investigations conducted to find out surfactants fulfilling all the foregoing seven requirements revealed that some kinds of nonionic surfactants and mixtures thereof only were found suitable for the contemplated object. The present invention has been accomplished based on such various novel findings. When checked for characteristics, these surfactants suitable for the object were found to be in the range of 7 to 17 in HLB.

The HLB value of a surfactants is the hydrophile-lipophile balance of the chemical structure thereof. As is well known, it is a numerical value indicating the balance between the hydrophilic properties of the surfactant and the lipophilic properties thereof. However, the fact that the contact angle on the silicon surface is dependent on the HLB value is not known up to date but has been found for the first time by the present invention.

The micro processing surface treating composition of the present invention comprises hydrofluoric acid and at least one specific nonionic surfactant fulfilling the foregoing requirements and admixed with the acid, the surfactant having an HLB value in the range of 7 to 17.

The term "hydrofluoric acid" refers to an aqueous solution of hydrofluoric acid containing 0.01 to 55 wt. % of hydrogen fluoride.

Nonionic surfactants have a basic structure of polyoxyalkyl, comprise a group of chemical structures of the ether type, ester type, glycol type or the like, greatly vary in detailed structure, are greatly different in the structure of the molecule, i.e., in molecular weight, number of carbon atoms, substituents, etc., and are nevertheless identified by common chemical names usually. Accordingly, the characteristics and behavior exhibited by a particular surfactant in the treating composition can not be characterized by a chemical structural formula. However, since characterization of its effect is very important, attempts to characterize the acceptable surfactant were made from every angle.

Consequently, we have discovered very apparent chemical structural regularity, i.e., a relationship between the contact angle on the silicon surface of the treating composition incorporating a surfactant and the HLB value of the surfactant.

Surfactants having a series of HLB values were checked for the contact angle on the surface of silicon. Table 37 shows the result.

The result has revealed that there is a region of minimized contact angles over a range of HLB values. More specifically, the contact angle was not greater than 50 degree when the group of compounds mentioned are in the range of 7 to 17 in HLB value. When the HLB value is less than 7 or more than 18, the contact angle exceeds 50 degree, and the silicon surface becomes unwettable.

TABLE 37______________________________________ Contact angle on Si surfaceHLB 0.01% HF 0.5% HF 5% HF 50% HF______________________________________3.7 84 74 69 686.0 67 65 60 536.7 61 53 51 517.0* 50 49 46 428.0* 43 39 37 349.0 35 32 28 25 10.0* 24 22 18 1610.8 19 15 14 1213.1 23 21 20 1913.7 26 24 24 2114.0 29 25 24 21 14.0* 30 25 24 2215.1 38 33 33 3016.0 41 40 36 3217.0 49 49 48 4618.0 65 62 60 60______________________________________

Table 37 shows the relationship between the HLB value and the contact angle. The mark* in the table indicates a mixture.

The HLB value has the additive property, that is, when W.sub.A g of a surfactant with HLB.sub.A is mixed with W.sub.B g of a surfactant with HLB.sub.B, the HLB.sub.AB of the mixture is expressed by the equation 1

HLB.sub.AB -(HLB.sub.A .times.W.sub.A +HLB.sub.B .times.W.sub.B)/(W.sub.A .div.W.sub.B) as is known. The dependence of the contact angle on HLB was substantiated also in the case of mixtures; we have found that there is a region of minimized contact angles.

Table 38 shows the result of an experiment for determining the relationship between the HLB value and the number of particles. The result indicates that the HLB value, when at least 7, results in a reduced number of particles, and that the number of particles in the treating composition can not be decrease despite circulating filtration if the composition has incorporated therein a surfactant which is less than 7 in HLB value.

TABLE 38______________________________________ Number of particles >0.5 .mu.mHLB 0.01% HF 0.5% HF 5% HF 50% HF______________________________________3.7 >10 >10 >10 >106.0 >10 >10 >10 >106.7 >10 >10 >10 >107.0* 9 6 6 48.0* 8 7 6 69.0 9 9 8 7 10.0* 3 7 5 510.8 4 7 6 613.1 2 6 5 613.7 5 3 5 214.0 4 3 3 3 14.0* 4 4 7 315.1 4 4 6 316.0 3 3 4 217.0 4 1 2 118.0 2 2 3 2______________________________________

Table 38 shows the number of particles as determined after circulating filtration. The mark* indicates a mixture.

While the mechanism through which the presence of surfactant permits very fine particles to be filtered off appears to be associated with formation of micelles of surfactant particles, we have found for the first time that the mechanism is dependent also on the HLB value of the surfactant.

In view of the all the foregoing novel findings, the range of HLB values of surfactants suitable or use in the treating composition is to be determined. More specifically, at least one nonionic surfactant to be mixed with hydrofluoric acid should be in the range of 7 to 17 preferably 10 to 15 in HLB value.

Examples of nonionic surfactants for use in the present invention are glycol esters, condensates of higher alcohols, condensates of higher fatty acids and condensates of alkyl phenols. More specific examples of preferred surfactants are as follows.

Polyoxyethylene higher alcohol ethers (10.5, 12.1, and 13.3 in HLB value)

C.sub.12 H.sub.25 .about.C.sub.14 H.sub.29 O(CH.sub.2 CH.sub.2 O).sub.n H

Polyoxyethylene oleic acid esters (9, 12, 14 and 16 in HLB value)

C.sub.17 H.sub.33 COO(CH.sub.2 CH.sub.2 O).sub.n H

Polyoxyethylene lauryl ethers (8, 9.4, 9.7, 10, 10.5, 12.1, 13.8, 13.9, 14, 15.3, 16, 16.3, 17, 17.3, 19 and 20 in HLB value)

C.sub.12 H.sub.25 O(CH.sub.2 CH.sub.2 O).sub.n H

Polyoxyethylene nonyl phenyl ethers (7.8, 9.2, 10.8, 12.2, 12.4, 13.7, 14.5, 15.1, 15.5, 17, 17.5, 18.2, and 18.9 in HLB value) ##STR1##

Polyoxyethylene octyl phenyl ethers (9, 11, 12, 13.1, 14, 15, 18, 19 and 20 in HLB value) ##STR2## Polyoxyethylene alkyl allyl ethers (8, 8.8, 10.0, 12, 13, 13.6, 14, 15, 16, 16.2 and 17 in HLB value)

R-CH.sub.2 CHCHO(CH.sub.2 CH.sub.2 O).sub.n H wherein R is alkyl.

These surfactants are used singly, or at least two of them are used in admixture. The surfactant is used as it is, i.e., in the form of a solid, or in the form of a liquid. The amount of surfactant to be used is 10 to 1000 ppm based on the whole composition.

The hydrofluoric acid to be present in the treating composition of the invention is generally dilute hydrofluoric acid having a concentration, for example, of 5 wt. % or 0.5 wt. %, so that the surfactant may be added in an amount of 10 to 1000 ppm to hydrofluoric acid of the desired concentration. In the case where the surfactant is to be added at a concentration, or example, of 250 ppm, the surfactant may be added to 50 wt. % hydrofluoric acid to a concentration of 2500 ppm or 25000 ppm, which is then diluted to 5 wt. % or 0.5 wt. % hydrofluoric acid. Even in this case, the resulting composition exhibits the same activity as the composition prepared by adding 250 ppm of the present surfactant. In fact, the natural oxide film on the surface of silicon and the natural oxide film in grooves formed by patterning were found removable with such a composition. When the present treating composition was checked for metal impurities which were detrimental to surface treatment for micro processing, no increase was found in the amount of these impurities, with the result that the composition retained the high purity of the treating solution.

When the treating composition of the invention was used for etching silicon surfaces, the number of particles adhering to the etched surface was small.

Further when silicon wafers were immersed in the treating composition of the invention for 100 minutes, the composition achieved a remarkable improvement in the roughness of the etched surface as compared with hydrofluoric acid free from any surfactant of the invention.

The treating composition of the invention was stored for 3 months and then checked for surface tension, contact angle and the number of particles to find that the composition prepared remained unchanged. Further the composition was subjected to circulating filtration but was found still satisfactory with respect to the foregoing seven requirements. These results indicate that the treating composition has long-term stability.

The micro processing surface treating composition of the invention exhibits an improved wetting property on the surface of silicon, permits smaller etching and more uniform etching for the fabrication of devices of higher integration density and further cleans the surface of silicon. Even when stored for a long period of time, the composition remains free of any changes in properties and retains its properties even when filtered. These features enable the composition to exhibit a high degree of uniformity in micro processing. Especially because the treating composition is reduced in the number of particles therein and further because the surface to be etched is effectively wettable with the composition, the surface can be etched with a reduced likelihood of particles adhering thereto and further given a smooth finish.

EXAMPLES

The present invention will be described in greater detail with reference to the following examples.

Example 1

A surfactant was added in an amount of 200 ppm to 0.5, 5.0 or 50 wt. % hydrofluoric acid, and the resulting composition was checked for surface tension, contact angle on silicon and number of particles (at least 0.5 .mu.m in size). Further a 5-inch silicon wafer was immersed in a solution prepared by adding 200 ppm of a surfactant to 0.5, 5.0 or 50 wt. % hydrofluoric acid, and thereafter checked for the number of particles (0.3 .mu.m to 1.0 .mu.m) adhering to the wafer surface by a wafer inspection system. The roughness of the wafer surface was measured under AFM after the wafer was held immersed in the composition for 100 minutes. Tables 39 to 44 show the result.

TABLE 39__________________________________________________________________________ Surface Contact Number of Number of SurfaceSurface active agent tension angle particles adhering particles roughness(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml) (0.3 .mu.m.about.1.0 .mu.m) Ra (nm)__________________________________________________________________________POE alkylallyl ether 16.0 37 40 3 47 0.28POE lauryl ether 12.1 38 10 2 38 0.22POE lauryl ether 15.3 39 46 1 66 0.23POE lauryl ether 16.3 39 38 2 59 0.17POE lauryl ether 17.0 45 50 1 67 0.19POE oleyl ether 13.6 33 15 5 41 0.15POE oleyl ether 16.2 40 41 3 48 0.17POE nonylphenyl ether 10.8 38 15 7 58 0.22POE nonylphenyl ether + 12.0 32 11 5 45 0.11POE nonylphenyl etherPOE nonylphenyl ether 13.7 30 24 3 31 0.14POE nonylphenyl ether 15.1 36 33 4 39 0.27POE nonylphenyl ether 15.5 36 35 3 41 0.23POE nonylphenyl ether 14.5 39 26 2 57 0.29__________________________________________________________________________ TABLE 40__________________________________________________________________________ Surface Contact Number of Number of SurfaceSurface active agent tension angle particles adhering particles roughness(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml) (0.3 .mu.m.about.1.0 .mu.m) Ra (nm)__________________________________________________________________________POE oleic acid ester 9.0 31 32 9 81 0.24POE oleic acid ester 14.0 38 25 3 45 0.24POE nonylphenyl ether 14.5 41 29 2 41 0.19POE higher alcohol ether 10.5 29 20 9 67 0.23POE higher alcohol ether 13.3 32 14 3 48 0.16POE octylphenyl ether 19.1 28 21 6 58 0.24POE oleyl ether + POE nonyl- 10.0 27 22 7 75 0.27phenyl etherPOE oleyl ether + POE nonyl- 7.0 44 49 6 44 0.20phenyl etherPOE oleyl ether + POE nonyl- 14.0 38 25 4 44 0.23phenyl etherPOE oleic acid ester + POE 8.0 33 39 7 39 0.28nonylphenyl etherPOE oleic acid ester + POE 12.0 33 13 4 53 0.23nonylphenyl etherPOE oleic acid ester + POE 14.0 35 29 4 35 0.20nonylphenyl etherPolyethylene glycol derivative 11.6 35 12 8 56 0.26__________________________________________________________________________ TABLE 41__________________________________________________________________________ Surface Contact Number of Number of SurfaceSurface active agent tension angle particles adhering particles roughness(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml) (0.3 .mu.m.about.1.0 .mu.m) Ra (nm)__________________________________________________________________________POE alkylallyl ether 16.0 35 36 4 57 0.25POE rauryl ether 12.1 36 11 2 68 0.26POE rauryl ether 15.3 37 45 5 45 0.21POE rauryl ether 16.3 37 35 2 47 0.14POE rauryl ether 17.0 40 48 2 56 0.17POE oleyl ether 13.6 32 16 3 47 0.16POE oleyl ether 16.2 39 44 3 55 0.19POE nonylphenyl ether 10.8 36 14 6 39 0.25POE nonylphenyl ether + 12.0 31 12 5 29 0.10POE nonylphenyl ether 13.7 30 24 5 22 0.14POE nonylphenyl ether 15.1 34 33 6 30 0.26POE nonylphenyl ether 15.5 34 35 2 26 0.26POE nonylphenyl ether 14.5 37 29 2 44 0.26__________________________________________________________________________ TABLE 42__________________________________________________________________________ Surface Contact Number of Number of SurfaceSurface active agent tension angle particles adhering particles roughness(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml) (0.3 .mu.m.about.1.0 .mu.m) Ra (nm)__________________________________________________________________________POE oleic acid ester 9.0 30 29 8 61 0.23POE oleic acid ester 14.0 37 24 3 75 0.25POE nonylphenyl ether 14.5 40 28 2 61 0.19POE higher alcohol ether 10.5 27 24 5 66 0.29POE higher alcohol ether 13.3 30 17 6 32 0.14POE octylphenyl ether 13.1 27 20 5 68 0.25POE oleyl ether + POE nonyl- 10.0 25 18 5 39 0.21phenyl etherPOE oleyl ether + POE nonyl- 7.0 41 46 6 55 0.22phenyl etherPOE oleyl ether + POE nonyl- 14.0 38 24 7 43 0.22phenyl etherPOE oleic acid ester + POE 8.0 33 37 6 50 0.22nonylphenyl etherPOE oleic acid ester + POE 12.0 31 18 4 45 0.26nonylphenyl etherPOE oleic acid ester + POE 14.0 34 29 5 45 0.21nonylphenyl etherPolyethylene glycol derivative 11.6 34 12 7 45 0.25__________________________________________________________________________ TABLE 43__________________________________________________________________________ Surface Contact Number of Number of SurfaceSurface active agent tension angle particles adhering particles roughness(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml) (0.3 .mu.m.about.1.0 .mu.m) Ra (nm)__________________________________________________________________________POE alkylallyl ether 16.0 37 32 4 49 0.22POE rauryl ether 12.1 39 13 1 58 0.21POE rauryl ether 15.3 37 44 1 25 0.25POE rauryl ether 16.3 38 33 2 56 0.19POE rauryl ether 17.0 42 46 1 55 0.12POE oleyl ether 13.5 33 15 4 51 0.12POE oleyl ether 16.2 42 40 2 40 0.18POE nonylphenyl ether 10.8 39 12 6 68 0.26POE nonylphenyl ether + 12.0 34 13 4 30 0.17POE nonylphenyl etherPOE nonylphenyl ether 13.7 36 21 2 34 0.18POE nonylphenyl ether 15.1 37 30 3 34 0.26POE nonylphenyl ether 15.5 37 31 3 40 0.24POE nonylphenyl ether 14.5 39 27 2 57 0.29__________________________________________________________________________ TABLE 44__________________________________________________________________________ Surface Contact Number of Number of SurfaceSurface active agent tension angle particles adhering particles roughness(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml) (0.3 .mu.m.about.1.0 .mu.m) Ra (nm)__________________________________________________________________________POE oleic acid ester 9.0 33 25 7 89 0.25POE oleic acid ester 14.0 39 21 3 48 0.24POE nonylphenyl ether 14.5 43 26 2 48 0.21POE higher alcohol ether 10.5 32 22 7 47 0.22POE higher alcohol ether 13.3 35 16 3 68 0.17POE octylphenyl ether 13.1 32 19 6 58 0.29POE oleyl ether + POE nonyl- 10.0 37 16 5 35 0.28phenyl etherPOE oleyl ether + POE nonyl- 7.0 37 42 4 49 0.28phenyl etherPOE oleyl ether + POE nonyl- 14.0 39 22 3 23 0.26phenyl etherPOE oleic acid ester + POE 8.0 37 34 6 55 0.21nonylphenyl etherPOE oleic acid ester + POE 12.0 36 16 4 43 0.21nonylphenyl etherPOE oleic acid ester + POE 14.0 38 20 3 39 0.25nonylphenyl etherPolyethylene glycol derivative 11.6 32 12 7 38 0.22__________________________________________________________________________

Tables 39 and 40 show the characteristics measurements obtained with the treating composition comprising 0.5 wt. % HF, Tables 41 and 42 show those obtained at an HF concentration of 5.0 wt. %, and Tables 43 and 44 show those obtained at an HF concentration of 50.0 wt. %. POE in the tables stands for polyoxyethylene.

Example 2

A surfactant was added in an amount of 2000 ppm to 50 wt. % hydrofluoric acid to obtain a treating composition, which was then diluted to 5.0 wt. %. Further a treating composition prepared with use of 20000 ppm of a surfactant was diluted to 0.5 wt. %. Tables 45 to 48 show the characteristics of the resulting compositions.

TABLE 45______________________________________ Surface Contact Number ofSurface active agent tension angle particles(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml)______________________________________POE alkylallyl ether 16.0 33 33 4POE rauryl ether 12.1 35 12 2POE rauryl ether 15.3 35 43 5POE rauryl ether 16.3 34 42 2POE rauryl ether 17.0 37 48 2POE oleyl ether 13.6 31 16 3POE oleyl ether 16.2 38 42 3POE nonylphenyl ether 10.8 36 20 5POE nonylphenyl ether + 12.0 30 14 2POE nonylphenyl etherPOE nonylphenyl ether 13.7 30 25 5POE nonylphenyl ether 15.1 33 32 4POE nonylphenyl ether 15.5 33 37 3POE nonylphenyl ether 14.5 37 30 5______________________________________ TABLE 46______________________________________ Surface Contact Number ofSurface active agent tension angle particles(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml)______________________________________POE oleic acid ester 9.0 31 24 9POE oleic acid ester 14.0 35 20 7POE nonylphenyl ether 14.5 40 30 2POE higher alcohol ether 10.5 27 27 5POE higher alcohol ether 13.3 29 16 3POE octylphenyl ether 13.1 28 25 2POE oleyl ether + POE nonyl- 10.0 26 24 6phenyl etherPOE oleyl ether + POE nonyl- 7.0 42 44 4phenyl etherPOE oleyl ether + POE nonyl- 14.0 37 22 6phenyl etherPOE oleic acid ester + POE 8.0 33 37 4nonylphenyl etherPOE oleic acid ester + POE 12.0 31 22 4nonylphenyl etherPOE oleic acid ester + POE 14.0 34 27 3nonylphenyl etherPolyethylene glycol derivative 11.6 33 14 9______________________________________ TABLE 47______________________________________ Surface Contact Number ofSurface active agent tension angle particles(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml)______________________________________POE alkylallyl ether 16.0 38 42 5POE rauryl ether 12.1 38 11 2POE rauryl ether 15.3 36 44 2POE rauryl ether 16.3 35 36 2POE rauryl ether 17.0 42 49 2POE oleyl ether 13.5 32 17 3POE oleyl ether 16.2 37 39 3POE nonylphenyl ether 10.8 35 21 6POE nonylphenyl ether + 12.0 31 13 4POE nonylphenyl etherPOE nonylphenyl ether 13.7 32 26 5POE nonylphenyl ether 15.1 34 31 3POE nonylphenyl ether 15.5 32 36 3POE nonylphenyl ether 14.5 36 28 3______________________________________ TABLE 48______________________________________ Surface Contact Number ofSurface active agent tension angle particles(Addition of 200 ppm) HLB (dyn/cm) (degree) (per ml)______________________________________POE oleic acid ester 9.0 30 30 7POE oleic acid ester 14.0 36 26 4POE nonylphenyl ether 14.5 39 24 6POE higher alcohol ether 10.5 28 22 8POE higher alcohol ether 13.3 28 17 2POE octylphenyl ether 13.1 29 21 5POE oleyl ether + POE nonyl- 10.0 27 22 8phenyl etherPOE oleyl ether + POE nonyl- 7.0 41 46 4phenyl etherPOE oleyl ether + POE nonyl- 14.0 39 31 6phenyl etherPOE oleic acid ester + POE 8.0 34 37 6nonylphenyl etherPOE oleic acid ester + POE 12.0 30 10 4nonylphenyl etherPOE oleic acid ester + POE 14.0 35 28 1nonylphenyl etherPolyethylene glycol derivative 11.6 36 15 8______________________________________

Tables 45 and 46 show the result achieved with the 10-fold dilution of the treating composition (50.0 wt. % HF), and Tables 47 and 48 show result obtained with the 100-fold dilution of like composition. POE in these tables stands for polyoxyethylene.

Claims

1. A micro processing surface treating composition having an excellent wetting property and consisting essentially of hydrofluoric acid and a hydrocarbon nonionic surfactant having an HLB value of 7 to 17.

2. A micro processing surface treating composition according to claim 1 in which the hydrocarbon nonionic surfactant is at least one species selected from the group consisting of polyoxyethylene higher alcohol ether, polyoxyethylene oleic acid ester, polyoxyethylene lauryl ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether and polyoxyethylene alkyl allyl ether.

3. A micro processing surface treating composition according to claim 1 in which the hydrocarbon nonionic surfactant is incorporated in an amount of 10.about.1000 ppm.

4. A micro processing surface treating composition according to claim 1 in which the HLB value of a hydrocarbon nonionic surfactant is 10 to 15.