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
  • G03F7/091—Photosensitive materials characterised by structural details, e.g. supports, auxiliary layers characterised by antireflection means or light filtering or absorbing means, e.g. anti-halation, contrast enhancement

Definitions

• This invention relates to the production of elec ⁇ trical devices using photolithography. More parti- 5 cularly, this invention relates to improvements in photolithography utilizing positive photoresist to provide sharper resolution by reducing reflected radiation.
• the photosensitive layer is partially transparent and that the underlying substrate (e.g., polysilicon, aluminum, or sili-
• inter ⁇ mediate resist layer which is chemically dissimilar so that neither layer is soluble in the other's developer.
• Near-UV radiation is used to expose the top layer while deep-UV is used to expose the
• Specht et al U.S. Patent 4,289,844 is directed to a photopolymerizable composition and a method of using the composition.
• the composition is de ⁇ scribed as having utility in microelectronics pho- tofabrication wherein an underlying foil is etched into desired configurations.
• a compatible binder acts as a negative resist which is exposed and developed to form, for example, annular-shaped spacers for beam-leads which are etched out of the metal foil using a positive- working resist for the beam-lead portions of the metal.
• the absorbing agent is used in an amount sufficient to absorb enough radiation to prevent any substantial reflection back through the photo ⁇ sensitive coating layer of radiation initially passing through the layer from an external radia- tion source to the material beneath said photosen ⁇ sitive coating layer.
• Figure 1 is a fragmentary cross-sectional * view of the first step of the process of the invention.
• Figure 2 is a fragmentary cross-sectional view of a subsequent stage of the process.
• Figure 3 is a fragmentary cross-sectional view of a further step of the process.
• Figure 4 is a photomicrographic top view in section illustrating the prior art practice.
• Figure 5 is a photomicrographic top view in section showing the same pattern made using the process of the invention.
• the invention comprises an improved photolitho ⁇ graphy process which results in the reduction of reflection damage in microlithographic imaging by increasing the optical density or absorbance of a positive photosensitive layer or photoresist through the addition to the positive photosensitive layer of a suitably chosen unbleachable light ab ⁇ sorbing agent.
• the principal requirements of the unbleachable absorbing agent are: 1) to absorb a predetermined amount of light in a selective band of wavelengths corresponding to the exposure wave- length range of the light source used in patterning the photosensitive layer and to be transparent in the wavelength range used for alignment of the wafer or substrate beneath the photosensitive lay ⁇ er; 2 ) to be fully soluble in the solvents used in the particular photosensitive material (typically Cellosolve Acetate, n-butyl acetate and xylene) " , i.e., to not recrystallize or volatilize out of solution even after extended periods, and to be fully chemically compatible with the resist includ- ing leaving its shelf life unaffected; and 3) to not affect any the resist salient lithographic parameters, such as adhesion to various surfaces, glass transition temperature, chemical activity and developer, etc. , except those associated with light absorption. It is also desirable that the absorb ⁇ ing agent not be highly toxic.
• the beneficial effects of the invention include the reduction of thickness or line width loss in nomi ⁇ nally unexposed regions due to laterally scattered light (known as resist notching) and reduction in the variations of bulk light energy absorption in the resist as thickness changes over variable wafer surface topography (at least for topographical deviations less than 0.5 microns).
• the concentration of the unbleachable absorbing agent, when added as a dye to the photoresist, may vary from 0.1 to 1.0% by weight of the total photo- sensitive material.
• the dye is used in a concentration of from 0.25 to 0.5 weight per cent.
• the amount of dye used is very important because a minimum amount must be used to realize the beneficial effects of the invention, i.e., to provide sufficient absorption of reflected light.
• the amount of dye used will permit the passage of enough light through the layer to properly expose the photoresist but will be present in an amount sufficient to absorb light reflected from the substrate beneath the photore- sist back into the photoresist layer.
• the amount of -dye used should, therefore, add about 0.225 to 0.45 micron " to the absorption coefficient to provide sufficient additional absorbance to inhibit reflec ⁇ tion of light back through the positive photore- sist.
• the dye is preselected to have a high absorption at the wavelength used to pattern the photosensitive coating, e.g., 436 nm, while exhibiting high transmission of light at another preselected wavelength used to align the mask used in patterning with previous patterns in layers underlying the photosensitive coating, e.g., 633 nm. , or, in some cases, a broad band of from 500 -700 nm.
• the absorbing dye used will be one which also will fluoresce upon exposure to radiation thereby pro ⁇ viding, as an additional benefit, the potential ability to measure and inspect micron-level- resist features through the use of fluorescence microscopy as opposed to conventional bright-field microscopy.
• a particularly preferred dye which has been found to be useful in the practice of the invention is a dye distributed under the trademark COUMARIN 504 by Exciton Corporation of Dayton, Ohio, or COUMARIN
• COUMARIN 504 or COUMARIN 314 by Eastman Kodak Company.
• the chemical name of COUMARIN 504 or COUMARIN 314 is 1 ,2 ,4,5 ,3H,6H,10H- tetrahydro-9-carbethoxy(l)benzopyrano(9,9a, 1-gh) quinolizin-10-one.
• Other dyes which may also be useful in the invention include photosensitive compounds such as described in Specht et al U.S. Patent 4,289,844.
• the unbleachable absorbing agent need not necessarily be in the form of an added dye, but may rather, for example, comprise a modification of the photosensitive material itself to increase its absorbance sufficiently to inhibit reflection at the normal range of photoresist coat ⁇ ing thicknesses used.
• FIG. 1 a micro- electronic structure is shown having a previously applied metal interconnect or substrate layer 10 and a previously patterned oxide layer 20 thereon.
• a metal interconnect layer 30 is placed over oxide layer 20 and a photoresist layer 40, having incor- porated therein a light absorbing dye in accordance with the invention, is placed over metal intercon ⁇ nect layer 30.
• the dye-containing photo ⁇ resist layer 40 is exposed to a pattern of light at a preselected wavelength 436 nm in this instance.
• underlying metal interconnect layer 30 has been selectively etched through the openings provided by patterned photoresist layer 40 to se ⁇ lectively etch out portions of layer 30 leaving only connections 32.
• Figure 4 illus- trates a prior art structure wherein the line width has been severely eroded as shown by the arrow at 70 indicative of poor resolution of the patterning due to reflectance and scattering of the light used to expose the photoresist used in forming the lines.
• Figure 5 shows the identical pattern produced, however, using the process of the invention wherein the photoresist material had incorporated therein a dye which is selectively absorbent of the wavelength of light used to expose the photoresist. It will be seen that at the same point 70' as in Figure 4, the line width resolution is markedly improved.
• a 1 micron film of aluminum containing 1% silicon and 0.5% copper was sputter deposited on a sub ⁇ strate.
• a positive photoresist coating containing 0.3% by weight COUMARIN 504 was deposited on the aluminum film. to a thickness of 1.6 micron.
• the dye-containing photoresist was soft baked at 100°C for 300 seconds in an infrared convection track oven.
• the baked resist was then exposed to a pattern of 436 nm light for about 0.50 seconds at an intensity of roughly 300 milliwatts per square centimeter.
• the exposed resist was then developed with an AZ351 developer in a ratio of 1 part devel ⁇ oper to 5 parts water at 21°C for 180 seconds.
• the resist was then rinsed with deionized water and allowed to dry.
• the developed photoresist was then exposed to a deep-UV cure of 100 millijoules per square centimeter exposure at 254 nm wavelength and then baked at 200°C for 60 minutes.
• the pattern of exposed aluminum was then plasma etched in a reac- tive ion etch with carbon tetrachloride gas mixed with chloroform. Finally, the resist was removed by stripping in an oxygen plasma.
• the resultant product was examined and found to exhibit high resolution with very little variation in line width indicating that very little damage was done to the resolution by scattering and standing waves from reflected light.
• the invention provides an improved process wherein a' photoresist material is provided with a selected amount of a light absorbing dye capable of absorbing a sufficient amount of light at the wave length of exposure whereby the radiation used to expose the photoresist will be absorbed sufficient ⁇ ly by the dye therein to prevent or inhibit the reflectance back into the photoresist layer of light from the underlying* substrate thereby reduc- ing or eliminating standing waves as well as scat ⁇ tered light which would otherwise result from such reflection.

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

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• 1985
  • 1985-09-12 EP EP19850904900 patent/EP0193603A4/en not_active Withdrawn
  • 1985-09-12 WO PCT/US1985/001745 patent/WO1986001914A1/en not_active Application Discontinuation
  • 1985-09-12 JP JP50426985A patent/JPS62500202A/ja active Pending

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Non-Patent Citations (6)

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