Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/004—Photosensitive materials
  • G03F7/09—Photosensitive materials characterised by structural details, e.g. supports, auxiliary layers
  • G03F7/094—Multilayer resist systems, e.g. planarising layers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S438/00—Semiconductor device manufacturing: process
  • Y10S438/942—Masking
  • Y10S438/948—Radiation resist
  • Y10S438/95—Multilayer mask including nonradiation sensitive layer

Definitions

• Trilevel resists have been utilized in the formation of electronic devices and are especially suitable for the lithographic definition of small features, i.e., features smaller than 2 ⁇ m.
• These resists include an underlying layer generally deposited directly on the substrate being processed.
• the substrate in this context is the semiconductor body including, if present, various levels of, for example, metallization, doped semiconductor material, and/or insulators.
• this layer is usually deposited with a thickness that is sufficient, despite the underlying irregularity, to present an essentially planar upper surface. An intermediary layer is then formed on this planarizing layer.
• the composition of the intermediary layer is chosen so that it is etched at least 5 times slower than the planarizing layer by a plasma that is capable of removing the underlying resist layer.
• a third layer (an overlying layer) that is delineable by exposure to radiation and by subsequent treatment with a suitable developing medium, is formed on the intermediary layer.
• the trilevel resist is patterned by first delineating the overlying layer in the desired pattern.
• This pattern is then transferred to the intermediary layer through conventional techniques such as dry processing, e.g., reactive ion etching, causing an uncovering, in the desired pattern, of the underlying layer.
• dry processing e.g., reactive ion etching
• the uncovered regions generally of organic materials, are then removed with an oxygen plasma.
• Intermediary layers of materials such as silicon dioxide, that are essentially unaffected by an oxygen plasma, are employed to avoid its destruction during plasma processing and thus degradation of the transferred pattern.
• the trilevel resist has proven to be an excellent expedient for producing fine features during semiconductor device fabrication, it does involve several discrete processing steps. Since there is always a desire to reduce processing steps and the associated costs, there has been a significant effort to develop a bilevel system yielding the advantages, i.e., planarization and high resolution, of a trilevel system. Attempts typically have been made to combine the attributes of the intermediary layer and the overlying layer into a single layer. To effect this combination, the resultant layer must be both delineable and also be at least 5 times more resistant than the underlying layer to the medium utilized to develop the underlying layer. Several materials have been reported as candidates for use as this combined overlying material. For example, materials represented by the formulae
• This invention relates to fabrication of electronic devices utilizing a novel bilevel resist that yields a planar surface, has excellent stability, undergoes a positive exposure to radiation, e.g., ultraviolet radiation, and which allows excellent resolution, e.g., resolution of 1 ⁇ m or finer.
• This bilevel resist includes a conventional underlying layer, e.g., a novolac based resist such as hard baked HPR-204 (a proprietary product of the Philip A.
• Hunt Chemical Company which is basically a novolac resin with a naphthoquinone diazide sensitizer), and an overlying layer containing material formed by the condensation of monomers including formaldehyde and/or acetaldehyde and a silicon-substituted phenol, e.g., mtrimethylsilylphenol or p-trimethylsilylmethylphenol.
• R is hydrogen or methyl and X contains silicon, e.g., Si(CH 3 ) 3 or CH 2 Si(CH 3 ) 3 .
• X contains silicon, e.g., Si(CH 3 ) 3 or CH 2 Si(CH 3 ) 3 .
• solubility inhibitor such as a substituted naphthoquinone diazide, where they are sensitive to electromagnetic radiation in the wavelength range 250 nm to 450 nm.
• the inventive bilevel resist includes an underlying planarizing layer, 5, and an overlying layer, 3, that is delineable and that is resistant to the medium utilized to develop the underlying layer. These layers are formed on a substrate, 7.
• the material utilized for the underlying layer is not critical and typically includes organic materials such as novolac and polyimide resins, e.g., 1) HPR-204 or AZ-1350 or AZ ⁇
• the underlying layer material unlike a typical resist, need not undergo a chemical change upon exposure to radiation. It is only necessary that the material of the underlying resist layer be removable with an oxygen plasma and not appreciably dissolve in the solvent utilized to form the overlying layer. (See VLSI Technology, Chapter 8, edited by S. M. Sze, McGraw-Hill, New York (1983) for a complete description of the removal of materials through plasma techniques.) Appreciable dissolution in this context means the intermixing of the overlying layer with the underlying layer to a depth of more than 50 nm of the underlying layer.
• the thickness of the underlying layer depends on the size of the surface irregularities in the substrate. For typical structures utilized in the formation of semiconductor devices, layer thicknesses greater than 1 ⁇ m yield an essentially planar surface. However, thicknesses greater than 4 ⁇ m, although not precluded, are generally uneconomic and require excess processing time.
• the thickness of the overlying layer depends on the desired resolution. Generally, the thicker the layer, the poorer the resolution. For resolutions less than 2 ⁇ m, layer thicknesses in the range 0.3 ⁇ m to 1.0 ⁇ m are generally utilized. Suitable layer thicknesses for either the underlying or overlying layers are easily obtained by conventional techniques such as by dissolving the material that is to form the layer in a solvent, e.g., cyclopentanone or 2-methoxyethyl acetate, and spin-coating the final layer onto the substrate. (A full description of spin-coating is found in Photoresist Materials and Processes, W. S. DeForrest, page 223, McGraw-Hill, New York, 1975.) The spinning speed utilized in the coating procedure determines the layer thickness and is controlled to yield the desired result.
• a solvent e.g., cyclopentanone or 2-methoxyethyl acetate
• the material of the overlying layer should include a polymer that can be postulated as the condensation product of 1 ) formaldehyde and/or acetaldehyde with 2) at least one compound represented by the formulae where R is preferably hydrogen or methyl and where X is a silicon containing entity such as (C y H 2y )SiR'R''R'' and where 0 ⁇ y ⁇ 3 and R', R' ' ,and R''' are individually either methyl, ethyl, or phenyl and optionally, if desired, with 3) phenol or a substituted phenol.
• the T g of the polymer is excessively low, i.e., lower than 30°C, if extremely long carbon chains, i.e., chains having more than 3 carbons, are utilized, or if the substituents bound to the silicon have a chain length greater than that associated with ethyl, methyl, or phenyl groups.
• the amount of phenol incorporated, the amount of substituted phenol incorporated, and the substituents on any substituted phenol should also be chosen so that the polymer T g remains above 30°C.
• the polymers are also typically relatively slowly exposed by ultraviolet radiation, i.e., require an exposure dose greater than
• the inhibitor is used at a concentration of 5 to 40 weight percent of the polymer.
• the overlying layer is exposed with suitable radiation, such as ultraviolet radiation.
• suitable radiation such as ultraviolet radiation.
• radiation in the wavelength range 250 nm to 450 nm is generally utilized.
• incident exposure doses in the range
• the specific exposure dose employed should be sufficient to cause a chemical reaction from the surface of the region that is subjected to radiation, through the volume underlying the exposed surface region, to the underlying resist material. Thus, the exposure should be sufficient so that upon development, the underlying resist material in the exposed regions is uncovered.
• solvents such as an aqueous base, e.g., sodium hydroxide or tetramethyl ammonium hydroxide.
• the solvent should remove the exposed region of the overlying layer without removing more than 25 volume percent of the unexposed regions of the overlying layer.
• This pattern transfer is accomplished by subjecting the substrate to an oxygen plasma. This oxygen plasma technique has been extensively described in Introduction to Microlithography, Chapter 6, edited by L. F. Thompson, C. G. Willson, and M. J. Bowden, American Chemical Society, Symposium Series 219,
• power densities in the range 0.0015 watts/cm 3 to 0.15 watts/cm 3 are utilized to maintain the plasma so that removal rates for the underlying layer in the range 0.1 ⁇ m/minute to
• the overlying layer is etched at 0.01 ⁇ m/minute to
• the plasma is struck in a gas containing oxygen.
• Total gas pressures in the range
• the delineated bilevel resist is utilized for processing steps such as metallization, dopant diffusion, or etching for the substrate, 7 in the Figure.
• the resist is then removed, and the processing of the substrate is completed to form the desired electronic devices.
• the following example is illustrative of the invention.
• m-TSPTS mtrimethylsilylphenoxytrimethylsilane
• m-TSPTS Approximately 30 grams of m-TSPTS was dissolved in 9 ml of 95 percent ethanol. To this solution was added 1 drop of hydrochloric acid and 4 ml of distilled water. The resulting mixture was agitated for 5 minutes, allowed to stand for 15 minutes, and washed twice with 30 ml aliquots of distilled water. The aqueous fraction was discarded, and the remaining fraction was dried and collected to yield about 22 grams of mtrimethylsilylphenol.
• a 500 ml flask fitted with a mechanical stirrer and condenser was charged with 20 grams (0.21 mole) of phenol, 20 grams (0.12 mole) of m-trimethylsilylphenol, 26 ml of 37 percent aqueous formaldehyde, and 1.26 grams (0.1 mole) of oxalic acid.
• the mixture was stirred and heated at reflux temperature for 1 hour and allowed to cool to room temperature.
• the resulting mixture was washed with 50 ml of distilled water.
• the aqueous fraction was discarded, and the remaining fraction was heated at 120°C at a pressure of 1999.8 Pa (15 mm Hg) for 30 minutes.
• HPR-204 (a proprietary product of the Philip A. Hunt Chemical Company which is basically a novalac based resist with a quinone diazide inhibitor) was spun on a silicon substrate (7.62 cm in diameter) to yield a resist layer thickness of approximately 1 ⁇ m. The resist material was baked in an air oven for 1 hour at 200°C. Approximately 5 grams of the polymer prepared in Paragraph A was dissolved together with 1.25 grams of oquinone diazide in 20 ml of cyclopentanone. The resulting solution was filtered through a 1.0 ⁇ m Teflon (a registered trademark of E. I. dupont deNemours and Company, Inc.) filter.
• Teflon a registered trademark of E. I. dupont deNemours and Company, Inc.
• a mercury arc lamp was utilized to expose the resulting resist for 9 seconds through a chrome-on-glass contact resolution mask having feature sizes ranging from 0.5 ⁇ m to 10 ⁇ m. (This exposure was performed on a Kulicke and Soffa aligner.) The exposed resist was immersed for 60 seconds in AZ developer (a proprietary product of Shipley Co., Inc., which is basically an aqueous potassium hydroxide solution) diluted in a ratio of 1:8 with distilled water. The resulting structure was then rinsed for 15 seconds with distilled water.
• AZ developer a proprietary product of Shipley Co., Inc., which is basically an aqueous potassium hydroxide solution
• the pattern of the upper layer was transferred to the lower layer utilizing a Model C71 r.f./d.c. sputtering module purchased from Cook Vacuum Product, Inc.
• An oxygen flow rate of 15 ml/minute was established to yield an etching chamber pressure of approximately 2.67 Pa (20 ⁇ m Hg).
• An r.f. discharge was struck in the resulting ambient utilizing an r.f. power of approximately 15 watts with a bias of 225 volts.
• the etching was continued for approximately 10 minutes.
• the resulting structure was then inspected using scanning electron microscopy on a Cambridge stereoscan 100 SCM which indicated a resolution as good as 1 ⁇ m.

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• Engineering & Computer Science (AREA)
• Architecture (AREA)
• Structural Engineering (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)
• Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)

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• 1984
  • 1984-05-24 US US06/613,884 patent/US4521274A/en not_active Expired - Lifetime
• 1985
  • 1985-04-29 EP EP85902382A patent/EP0185030B1/en not_active Expired
  • 1985-04-29 DE DE8585902382T patent/DE3566051D1/de not_active Expired
  • 1985-04-29 JP JP60502023A patent/JPS61502219A/ja active Granted
  • 1985-04-29 WO PCT/US1985/000787 patent/WO1985005470A1/en not_active Ceased
  • 1985-05-14 CA CA000481475A patent/CA1248403A/en not_active Expired

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