Solvent composition for cleaning silicon wafers

Abstract: There is provided an improved solvent especially adapted for cleaning silicon wafers and consisting essentially of a haloalkylhydrocarbon and a partially fluorinated alcohol. This solvent provides excellent cleaning and drying of the wafer.

Description: This invention relates to an improved solvent composition, especially useful in cleaning and drying silicon semiconductor wafers. In the production of integrated circuits, "chips" formed of silicon metal and on which are etched intricate circuits, are an essential component. The silicon semiconductor wafers are carefully cut from a single crystal of silicon. These semiconductor wafers have generally a diameter of 50,8 mm (2 inches). In the processing of these semiconductor wafers, they become contaminated with dirt, dust, grease and like pollutants . Before processing inot the final "chips" the semiconductor wafers must be carefully cleaned. In the semicondutor industry, semiconductor wafers are rinsed in water after many process steps, then carefully dried prior to the continuation of the fabrication process. At the present time, the silicon semiconductor wafers are placed in a "boat" and dipped or sprayed with deionized water. The boats are subsequently loaded into a high speed centrifuge where the semiconductor wafers are spin-dried. Recent technology has made use of vapour driers utilizing isopropyl alcohol as a drying agent. The method creates a significant amount of waste over the period of a month, for example, and also a significant fire hazard. It was desired, therefore, to develop a solvent system that was easily recovered and recycled, had excellent cleaning properties, had a convenient boiling point in the range of from 40°C to 120°C, and a very high, or no flash point. JP-A-61/255977 thermally stabilizes a working medium including a hydrocarbon (e.g., methane, heptane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane or n-heptane), alcohol, e.g., methanol, ethanol, 2,2,2-trifluoroethanol or 2,2,3,3,3,-pentafluoropropanol, a mixture of fluorinated alcohol and water or ammonia, a C₄-C₈ perfluoroalkane, or Freon (Registered Trade Mark), an azeotropic mixture of CCl₂F₂ and CHF₂-CH₃, or an azeotropic mixture of CHClF₂CF₃. To the working medium there are added phosphine sulphide and glycidyl ether, and, optionally, a lubricating oil. This composition is used to treat steel, aluminium alloys, or brass. JP-A-58/1229980 teaches a processing fluid for use in a heat transfer device for a closed fluid cycling system with evaporation and condensing sections. The processing fluid is composed of trifluoroethanol and contains up to a maximum 15% water. The fluid used contains water, ethanol, Freon (Registered Trade Mark), mercury, cesium, pentane and heptane. EP-A-0 120 319 discloses a cleaning composition for wax removal, comprising a halogenated (or not) hydrocarbon, a fluorinated alcohol and a facultative polar organic solvent other than the components enumerated above. GB-A-2 188 059 discloses solvent mixtures comprising 1,1,1-trifluoroethanol and fluorinated hydrocarbons, with facultative additives and alcohols. EP-A- 0 199 288 discloses a method for removing small particles from a surface essentially consisting in washing the particle-contaminated surface in a solution of a high-molecular-weight fluorinated surfactant in a non-polar fluorinated carrier liquid, to remove the particles from the surface and to disperse them in the solution. The invention provides a solvent composition comprising: (a) from 30 parts to 90 parts by weight of a perhalogenated haloalkylhydrocarbon containing from 5 to 12 carbon atoms, and (b) from 10 to 70 parts by weight of a partially fluorinated alcohol containing from 2 to 4 carbon atoms, the total of the components (a) and (b) being 100 parts by weight as a maximum. The system is unique especially for cleaning silicon semiconductor wafers in that the acidic nature of the alcohol provides excellent cleaning, and the perhalogenated haloalkylhydrocarbon aids in drying the semiconductor wafer without leaving any residue. The vapour may be recovered, condensed and reused. The compositions hereof are used in the usual manner of rinsing in a boat or in a hot vapour system and then heating to a temperature sufficient to volatilize the solvent. Centrifuging may be used, but is unnecessary. As indicated above, the solvent compositions of the present invention contain two essential ingredients. One of these |hereinafter referred to as component (a)| is a perhalogenated haloalkylhydrocarbon containing from 5 to 12 carbon atoms. In perhalogenated haloalkylhydrocarbons, all the hydrogen atoms are replaced with a halogen, selected from fluorine and chlorine . The second essential component |hereinafter referred to as component (b)| is a partially fluorinated alcohol containing from 2 to 4 carbon atoms. These alcohols contain carbon, hydrogen, fluorine and oxygen as the only elements therein. Component (a) is present in the solvent compositions hereof in an amount of from 30 parts by weight to 90 parts by weight per 100 parts of composition . For most purposes, component (a) is the major component although as will be seen from the examples below, it may be the minor component. Component (b) is the component primarily responsible for the cleaning action of the solvent compositions hereof. It is present in an amount of from 10 to 70 parts by weight based on 100 parts of solvent composition . For most purposes, component (b) is the minor component although as will be seen from the examples below, it may be the major component. It is contemplatyed hereby that two or more materials qualifying as component (a) ingredients, and two or more materials qualifying as component (b) ingredients may used in place of the single compound. The compositions of (a) and (b) may on standing absorb minor amonts of moisture not to exceed 5 parts by weight. Such insignificant amounts of moisture are not deleterious to the compositions hereof, and may, although it is not recommended, be added in amounts up to 1 part or 2 parts per 100 parts of solvent prior to use. The compositions, initially, are preferably nonaqueous. Other ingredients in very minor amounts, less than 5 parts/100 parts by weight such as low-boiling alcohols, ethers, ketones and esters may also be included. Both components (a) and (b) desirably contain fluorine. Specific examples of component (a) are: 1,1,1,2-tetrachloro-perfluorobutane Perfluoroheptanes Perfluorohexanes Perfluorooctanes Perfluorodecanes Perfluorododecanes. Specific examples of partially fluorinated alcohols contain carbon, hydrogen, fluorine and oxygen, the latter atoms as part of an -OH group, and include: Trifluoroethanol 3,3,3-trifluoropropanol 4,4,4-trifluorobutanol 2-monofluoroethanol 2,3,3,3-tetrafluoropropanol 2,2,3,3-tetrafluoropropanol 4-fluorobutanol 2,2-difluoroethanol 3,3-difluoropropanol 3-monofluoropropanol 2,2,3,3,3-pentafluoropropanol. As above indicated, components (a) and (b) are simply mixed together to formulate the solvent compositions of the present invention. Typical examples of such solvent compositions are: EXAMPLE 1 Perfluoroheptane 70 parts Trifluoroethanol 30 parts EXAMPLE 2 Perfluorohexanes 70 parts 3,3,3-trifluoropropanol 30 parts EXAMPLE 3 Perfluorohexanes 45 parts Tetrafluoropropanol 55 parts EXAMPLE 4 Perfluorodecanes 60 parts Trifluoroethanol 40 parts EXAMPLE 5 Perfluoroheptanes 70 parts Trifluoroethanol 20 parts 3,3,3-trifluoropropanol 10 parts EXAMPLE 6 Perfluoroheptanes 35 parts Perfluorohexanes 35 parts Trifluoroethanol 30 parts EXAMPLE 7 Trifluoroethyl-trifluoroacetate 0 to 5 parts Perfluoroheptane 70 parts Trifluoroethanol 30 parts EXAMPLE 8 Perfluoroheptanes 70 parts 2,2,3,3-tetrafluoropropanol 30 parts EXAMPLE 9 Perfluoroheptanes 80 parts 2,2,3,3,3-pentafluoropropanol 20 parts The foregoing examples are illustrative of the manner of composing the compositions of the present invention. The ingredients are generally mutual solvents for each other, and hence no special techniques are involved in mixing the proper proportions of the components. The compositions are generally stable and,if necessary, they may be heated slightly to aid in dissolution of the ingredients, and to preserve stability in use.

Claims: A solvent composition comprising: (a) from 30 parts to 90 parts by weight of a perhalogenated haloalkylhydrocarbon containing from 5 to 12 carbon atoms, and (b) from 10 to 70 parts by weight of a partially fluorinated alcohol containing from 2 to 4 carbon atoms, the total of the components (a) and (b) being 100 parts by weight as a maximum. Composition according to Claim 1, which is water free at the time of use. Composition according to Claim 1, wherein the boiling point of said composition is from 40°C to 120°C. Composition according to Claim 1, wherein the (a) component is a perfluoroalkylhydrocarbon. Composition according to Claim 1, wherein the (a) component is a perhalogenated fluorochlorohydrocarbon. Composition according to Claim 4, wherein the perfluoroalkylhydrocarbon is perfluoroheptane. Composition according to Claim 4, wherein the perfluoroalkylhydrocarbon is perfluorohexane. Composition according to Claim 1, wherein the partially fluorinated alcohol is trifluoroethanol. Composition according to Claim 1, wherein the partially fluorinated alcohol is trifluoropropanol. Composition according to Claim 1, wherein the partially fluorinated alcohol is 2,2,3,3,3-pentafluoropropanol. Composition according to Claim 1, wherein the partially fluorinated alcohol is a partially fluorinated n-butanol. Composition according to Claim 1, wherein the (a) component is perfluorohexane and the (b) component is 3,3,3-trifluoropropanol. Composition according to Claim 1, comprising 70 parts by weight of perfluoropheptanes as the (a) component, and 30 parts by weight of trifluoroethanol as the (b) component. Composition according to Claim 1, wherein the partially fluorinated alcohol as the (b) component is 2,2,3,3-tetrafluoropropanol. Composition according to Claim 1, wherein the (a) component is a perfluorodecane. A solvent composition according to Claim 1, for cleaning silicon semiconductor wafers, wherein the (a) component is from 30 parts by weight to 90 parts by weight of perfluoroheptane, and the (b) component is from 10 parts by weight to 70 parts by weight of trifluoroethanol, the total of the (a) and the (b) components being 100 parts by weight as a maximum. Use of the solvent composition as defined in Claim 1, for cleaning semiconductor wafers.

Inventors: KREMER PAUL WILLIAM, KREMER, PAUL WILLIAM
Applicants: PCR GROUP INC, PCR GROUP, INC.
Application year: 1989
Main classification: C11D7
IPC codes: C11D7