Photoresist compositions comprising acetals and ketals as solvents

#This invention relates to photoresist compositions and to a process for forming an image on a substrate utilizing said photoresist compositions.

#Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The photoresist coated on the substrate is next subjected to an image-wise exposure to radiation.

#The radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation exposed or the unexposed areas of the photoresist.

#The following specific examples will provide detailed illustrations of the methods of producing and utilizing compositions of the present invention. These examples are not intended, however, to limit or restrict the scope of the invention in any way and should not be construed as providing conditions, parameters or values which must be utilized exclusively in order to practice the present invention. Unless otherwise specified, all parts and percents are by weight, all temperatures are in degrees Centigrade, and all molecular weights are weight average molecular weight.

#Two samples of a thick resist were prepared as depicted below in Table 1. In Sample A, the resist was made using a typical resist solvent while in Sample B, a portion of the solvent was replaced with 1,3-dioxolane (a cyclic acetal which can be made by condensation of formaldehyde with 1,2-ethylene diol). 1 TABLE 1 Ingredients Sample A Sample B Novolak Resin* 42.11 g 42.17 g Photoactive Compound** 5.42 g 05.42 g PGMEA 52.41 g 36.17 g 1,3-dioxolane — 14.24 g Total 100 g 100 g *condensation product of formaldehyde with 47.8% p-cresol, 42% m-cresol, 5.6% 2,4-xylenol and 4.6% 2,5-xylenol under acid conditions (available from AZ Electronic Materials, Clariant Corporation as “Alnovol SPN 400”) **95% tris sulfonate ester of 2,3,4-trihydroxy benzophenone with 2,1,5 quinone diazide sulfonyl chloride (available from Clariant Corporation as “PW 2484”) PGMEA = propylene glycol methyl ether acetate

#Silicon wafers were coated to the same nominal coating thickness of 65 μm and were exposed at 365 nm through a positive photomask. The wafers were then developed with a tetramethyl ammonium hydroxide developer and the images were analyzed. Sample A required 4000 mJ/cm2 for optimum resolution while Sample B could be exposed in only 1500 mJ/cm2 showing almost a 2.5 fold increase in photospeed. Both resists could resolve 50 μm contact holes under the same conditions.