A PROCESS FOR PRODUCING A NEGATIVE TONE RESIST IMAGE

Abstract: A negative tone resist image is produced by the suc­ cessive steps of exposing a film to a pattern of radiation, the film having such a composition that after exposure to the radiation it contains a polymer which reacts with an or­ ganometallic reagent; treating the exposed film with the organometallic reagent; and developing a relief image by further treating the exposed film with an oxygen plasma.

Description: This invention relates to a process for producing a negative tone resist image. GB-A-2097143 discloses a process for obtaining negative tone plasma resist images. That publication is concerned with a process involving entrapment of a silicon containing monomer into a host film at the time of exposure to radiation and requires a processing step to expel the unincorporated silicon monomer from the film before plasma development of the relief image. US-A-4,307,178; 4,389,482 and 4,396,704 disclose the use of oxygen plasmas in developing negative resist images. US Patent 4,307,177 discloses the use of onium salts as sensitizers. JA 59-61928(A) discloses the use of an organic compound steam including Si to form a resistive polymer film on the irradiated areas of a polymer thin film, prior to development with an oxygen plasma. Extended Abstracts Vol. B 82, Oct. 1982, p 321-322 describes a method for making a resist pattern on a film of poly(methyl methacrylate) by first irradiating the film with an electron beam and then treating the film with chlorosilanes, prior to development with an oxygen plasma. The invention seeks to provide an improved process for producing such a negative tone resist image. A process for producing a negative tone resist image comprises, according to the invention, the successive steps of: exposing a film of a polymer bearing a masked reactive functionality to a pattern of radiation, the film having such a composition that after exposure to the radiation the masked reactive functionality is unmasked and the exposed areas of the film react with an organometallic reagent; treating the exposed film with the organometallic reagent; and developing a relief image by further treating the exposed film with an oxygen plasma. We have found that a high resolution negative tone resist image can be produced by carrying out the following procedure: 1. A substrate is coated with a film of polymer bearing a masked reactive funtionality. 2. The film is imagewise exposed and then processed so that the masking group is removed in the exposed areas to liberate the reactive functionality. 3. The film is then contacted with an appropriate organometallic reagent. This reagent is chosen so that it will react with the unmasked polymer functionality, and contains an element such as silicon or tin which forms a non-volatile oxide. 4. The film is then put into an oxygen plasma environment. The unexposed areas of the film are etched by this oxygen plasma treatment but the exposed areas are not etched. This results in a high resolution, negative tone relief image. Compositions suitable for use in the present invention can take several forms. In one embodiment, the masking group is directly removed upon exposure to radiation. The unmasked functionality which is generated in such a fashion is reactive towards several organo metallic reagents, while the masked polymer is not. Such materials, for example, include but are not restricted to poly(p-formyloxystyrene) and copolymers prepared from p-formyloxystyrene. In a second embodiment, the formulation consists of a polymer containing a reactive functionality that is masked by an acid labile protecting group and a species that is capable of generating acid upon exposure to radiation. In such systems, exposure or exposure followed by heat, serves to unmask the reactive functionality. Examples of such polymers include, but are not restricted to to poly(t-butyl methacrylate) and poly(t-butyloxycarbonyloxystyrene) and copolymers derived from t-butyl methacrylate or t-butyloxycarbonyloxystyrene. Examples of materials that produce acid upon exposure are well known in the art and include various onium salts and haloalkanes. Organometallic reagents that are capable of selective reaction with the unmasked side chain functionality are well known in the art. A wide range of readily available organometallic reagents are useful in this process. These include, for example, but are not limited to trimethylstannyl chloride, hexamethyldisilazane and trimethylsilyl chloride. These reagents, which can be used in either an appropriate solvent or in the vapor phase, will react with unmasked functional groups such as -COOH, -OH, -NH₂ etc. The development of the relief image uses oxygen plasma or reactive ion etching techniques that are performed in a conventional fashion. The preferred polymers for use in the present invention are those having acid labile groups pendant from a polymer backbone. Particularly preferred are those in which such groups are esters of a carboxylic acid or a carbonic acid. Polymers of this sort are described in US-A-4,491,628. That document also refers to the onium sensitizers which are most preferred for use in the present invention. These include diaryliodonium salts, triarylsulfonium salts and substituted aryldiazonium salts. The most preferred gegenanions of the salts are complex metal halides such as tetrafluoroborate, hexafluoroantimonate, hexafluoroarsenate and hexafluorophosphate. In general, the sensitizer onium salt should be present in the polymers in an amount from about 1 to 100% on a weight to weight basis. The preferred organometallic species, for use in the present invention are those that are capable of reacting with the unmasked pendant functionality. Particularly preferred are silylating reagents which are well known in the art and any suitable one may be used. As an example of a preferred reagent hexamethyldisilizane (HMDS) may be mentioned. In one embodiment of the present invention, a thin film of polymer sensitized by the addition of an onium salt is used as an overcoat for a thick film of an organic polymer which need not be sensitized (the thick film is on a substrate such as silicon). In general, the thin sensitized, overcoating film is about 1 micron thick, and the overcoated film about 4 to 6 microns thick. In this way, high aspect ratio relief images are generated in a general organic film. In another embodiment of the present invention, a dye is added to the thin film formulation. Dyes useful for this purpose include, for example, polycyclic aromatic compounds and their derivatives. Perlyene is a particularly useful dye. The development step using oxygen reaction ion etching is carried out in conventional fashion. EXAMPLE One micron thick films of p - t -butoxycarbonyloxystyrene (PBOCS) containing triphenylsulfonium hexafluoroarsenate (18.5% to the total solid) in methyl cellosolve acetate, were spin-coated onto silicon wafers and prebaked at 100°C for 30 minutes. The films were exposed through a mask to 254nm wavelength radiation (dose: 14.4 mj/cm² or 5.0 mj/cm²), baked at 100°C for 30 seconds, and dried at 85°C at a pressure of 26.6 Pascals (0.2 mm Hg) for 1 hour in a vacuum oven. The oven was opened under nitrogen and a 50 ml beaker containing 10 ml of Hexamethyldisilazane (HMDS) was placed into the chamber. The oven was evacuated and filled with nitrogen and subsequently partially evacuated, to vaporize the HMDS. The wafers were allowed to stand at 85°C in the HMDS vapor for one hour and were then transferred into a Tegal parallel-plate etch tool. The relief image was dry developed with 80 minutes of O₂-RIE (100 watts RF, 6.7 Pascals (50 m torr), and 10 sccm O₂). After RIE development the processed wafers were dipped into dilute buffered HF and then rinsed with water. The relief images produced by this process had vertical wall profiles and showed high resolution. The present invention has several distinct and unpredictable advantages over known negative tone resist processes. First, the process does not require a solvent development step and therefore has the advantage of being both simple and more environmentally acceptable in use. It has been demonstrated to operate at extremely low doses of exposing radiation and over a wide range of exposing wavelengths. These wavelengths include, but are not limited to, X-ray, electron beams and ultraviolet light from 220 to 450 nm. The images obtained from this process exhibit vertical wall profiles, and show minimal thickness loss in the exposed regions when processed in the prescribed manner.

Claims: A process for producing a negative tome image resist comprising the successive steps of: a) exposing a film of a polymer to a pattern of radiation; b) treating the exposed areas of the polymer film with an organometallic reagent; and c) developing a relief image by further treating the exposed film with an oxygen plasma, characterised in that said polymer contains a reactive functional group chemically bonded to a masking group that is removed by exposure to the radiation. A process as claimed in claim 1, in which the masking group is removed directly on exposure to the radiation. A process as claimed in claim 2, in which the polymer is poly(pformyloxystryrene). A process as claimed in claim 1, in which the film comprises (A) a polymer containing an acid labile group pendant from the polymer backbone, and (b) a monomeric substance that liberates acid upon exposure. A process as claimed in Claim 4, in which the polymer is poly(t-butylmethacrylate). A process as claimed in Claim 4, in which the polymer is poly(t-butyloxycarbonyloxy styrene). A process as claimed in any of claim 4 to 6, in which the monomeric substance is an onium salt. A process as claimed in any of claim 4 to 6, in which the monomeric substance is triphenylsulfonum hexafluoroarsenate. A process as claimed in any of claims 4 to 6, in which the monomeric substance is triphenylfulfonum hexafluoroantimonate. A process as claimed in any preceding claim, in which the organometallic reagent is an organosilane. A process as claimed in any of Claims 1 to 9, in which the organometallic reagent is an organostannane. A process as claimed in any of Claims 1 to 9, in which the organometallic reagent is hexamethyldisilazane. A process as claimed in any of Claims 1 to 9, in which the organometallic reagent is trimethyl silyl chloride. A process as claimed in any preceding claim, in which a thick film of unsensitized polymer is positioned between the first-mentioned film and a substrate.

Inventors: ITO, HIROSHI, MACDONALD, SCOTT ARTHUR, MILLER, ROBERT DENNIS, WILLSON, CARLTON GRANT
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1985
Main classification: G03F7
IPC codes: G03F7, H01L21