Mitsuhiro Ohkuni

Simulation approach for achieving layout independent polysilicon gate etching

Profile and dimension control mechanism in polysilicon gate etching is studied systematically by the use of two-dimensional (2-D) etching topography simulator. Reaction rates are calculated by taking into account interactions between incoming ion/radical fluxes and an ever-changing macroscopic adsorbed particle layer on the film surface. A qualitative guideline is presented for achieving both anisotropic etched-profile formation and the dimension difference minimization between the inner line pattern width w/sub i/ and the outermost line pattern width w/sub e/ in repeated line and space configuration. When w/sub c/>w/sub i/>w/sub m/ (resist mask width), following two possible measures are necessary. One is to make gas pumping speed large for shortening the residence time of depositive radicals. The other is to make cathode temperature high for lowering sticking coefficient of depositive radicals. These are effective in reducing the amount of deposited film especially at the sidewall of external part of the outermost line pattern (SEP). Higher gas pressure is also effective in sputtering the deposited film especially at SEP.

High Performance Etching Process for Organic Films using SO2/O2 Plasma

The anisotropic etching of organic films such as anti reflective coating (ARC) and resist for dry development using inductively coupled plasma (ICP) was studied. In ARC etching, the controllability of critical dimension (CD) and the selectivity to underlayers were investigated for O2 based gas chemistries by adding N2, He, CHF3, Cl2, HBr and SO2. The SO2/O2 chemistry has the advantage of both the CD controllability and the selectivity to underlayers. Field emission Auger electron spectroscopy (FE-AES) analysis revealed that the SO2 gas is useful for sidewall protection due to the sulfur deposition. In dry development etching, the controllability of the etched profile was investigated. It was dicovered that the Vpp (peak to peak voltage of RF bias) increases with increasing SO2 flow ratio to O2 so that a recession occurs in the silylated layer due to high ion energy. A vertical profile was obtained for a 0.13 µm pattern of resist and poly-Si optimizing SO2/O2 gas chemistry.

Consideration of Silylation Contrast in an ArF Liquid-Phase Silylation Process

We have studied what determines the silylation contrast for the liquid-phase silylation process in ArF excimer laser lithography. In the liquid-phase silylation, the diffusion kinetics is dependent on the concentration of the diffusion promoter, which acts as the relaxation of the polymer film. The silylating condition of a proper concentration induces the equilibrium state of relaxation and diffusion: Case II diffusion. It was found that the Case II diffusion condition resulted in a higher silylation contrast. Next, attention was paid to the photo-crosslinking density for improving the silylation contrast. The soft-baking temperature had an influence on the crosslinking density. The densification of the polymer film by soft-baking increases the photo-crosslinking density, but an extreme densification decreases it, when the soft-baking temperature is near glass transition temperature (T g). It is considered that the arrangement of the polymer chains is closely linked with the efficiency of photo-crosslinking.