R. Leuschner

Chemical amplification of resist lines (CARL)

Abstract A novel lithographic technique- CARL - is introduced that allows the optical resolution limit to be overcome by a controllable size reduction of resist spaces, i.e. chemical widening (‘amplification’) of adjacent resist lines. The process is based on the treatment of specially developed anhydride-containing resist for NUV or DUV exposure with aqueous solutions of aminic reagents and can be carried out on standard puddle development tracks . Thus, using the CARL principle in a positive tone bilayer/O 2 -RIE scheme ( Si-CARL ) and a 0.4 NA i-line optic, spaces down to 150 nm can be printed and transfered to a 1.8 μm thick planarizing layer without linewidth variation. The new CARL resist chemistry, preliminary process characteristics and some prospects, e.g. enlarged alignment budget in critical mask steps, are described and first results are discussed.

Patterning of organic layers using negative and positive working Top-CARL process

Abstract The Top-CARL process is a technique for patterning of some ten microns thick organic materials by top resist silylation and pattern transfer via oxygen reactive ion etching. The influence of exposure dose, temperature and the top resist layer thickness on the silylation process is studied. A dyed version of the resist is examined. Its polarity can be changed from negative to positive working by addition of a small amount of a photobase.

Aqueous phase silylation a new route to plasma developable high resolution resists

Abstract A novel O 2 /RIE developable photoresist system with aqueous phase silylation of the exposed areas is presented. The silylation includes a spontaneous crosslinking reaction between the anhydride groups of the base resin and the aminosiloxane silylating reagent. The silylation leads to a considerable growth of the film thickness which is promoted by higher exposure dose, acidity of the exposed resist, normality of the aminosiloxane solution, silylation time and temperature. The system demonstrates several benefits such as fast silylation with existing equipment (puddle development track) at room temperature, high etch resistance of the silylated layer against O 2 /RIE (same as polyphenylmethylsilane), possibility of water inspection after silylation and applicability of the same resist formulation for 366 nm and 248 nm . First i-line stepper experiments gave 0.5μm lines and spaces with an aspect ratio of 4.5.

Bilayer resist process for exposure with low-voltage electrons (STM-lithography)

Abstract With STM lithography employing a bilayer resist system, an electron sensitive top resist and a conductive bottom resist, it is possible to generate patterns with dimensions of 100 nm and less. Patterns with aspect ratios up to 8 at a width of 50 nm in flat silicon oxide surface have been achieved. We also demonstrate, that it is possible to operate on prepatterned substrates using a third planarizing resist layer. The exposure mechanism in our CARL top resist has been determined to work differently from the mechanism in the high electron energy regime. The low energy electrons directly cleave the t-butyl ester group. Chemical amplification was not observed. The maximum writing speed for complete exposure in the resist was 1–5 μm/s at 20 pA writing current.

Bilayer resist based on wet silylation (CARL process) for e-beam lithography

The TBMA-resist made from t- butylmethacrylate and maleic acid anhydride is a highly sensitive bilayer resist for aqueous/ alcoholic silylation of the developed top resist patterns. When diphenyl-iodonium tosylate instead of the corresponding triflate salt is used as photo acid generator the resist shows a better delay time stability before the post-exposure bake (~ 1 hour) but less sensitivity. The catalytic chain length of the ester cleavage is then only 60 at a post-exposure bake temperature of 130 ^oC. But due to the high reactivity of the iodonium salt towards e-beam radiation the resist has sufficient sensitivity to print 0.25 @mm L&S with low radiation damage (dose < 10 @mC/cm^2) using a variable-shaped e-beam writer. Down to 0.4 @mm L&S the resist is linear and shows a vacuum stability of better than 4 hours.

Positive Near-UV Resist For Bilayer Lithography

A novel alkaline-soluble silicon-containing copolymer for use in bilayer lithography has been developed. This copolymer (CVPVS)consists of p-vinylphenol and vinyltrimethylsilane and was prepared in a two-step process: anionic polymerization of a p-alkoxystyrene with vinyltrimethylsilane followed by ether cleavage of the alkoxy group. The copo-lymer used for lithographic application has a number average molecular weight of 2700 and shows very good solubility in a variety of organic solvents. CVPVS has nearly no absorption above 300 nm and at 248 nm its absorption is six times lower than that of a commercially available poly(p-vinylphenol). The silicon-containing photoresist (SPR) prepared from this copolymer and a diazoquinone photosensitizer is completely compatible with current resist processing.