미량의 알칼라인 화학액이 첨가된 반도체 세정액 내 메가소닉 조사에 따른 세정 특성 평가

Abstract

In the semiconductor wafer cleaning, ammonium hydroxide based APM (ammonium peroxide mixture) has been widely used to remove particles and organic contaminants. However as the film thickness and line width dimensions of the semiconductor structure scales down rapidly, the material losses by etching reaction of alkaline chemicals can cause serious problem in yield loss due to electric failure. The presence of H2O2 could enhance the material loss on silicon wafer. Very dilute alkaline chemicals might be of interest since it could minimize any possible ionic contamination or chemical residues from chemicals as long as we control the surface roughness and particle removal efficiency. Also the characterization of these very dilute alkaline chemicals will be very useful for particle removal in gas dissolved DI water. This cleaning method which uses dilute alkaline chemicals has many advantages. That process is environmental-friendly and minimize the ionic contamination and there is no chemical residues. For dilute alkaline solutions, we are focusing on the three types of alkaline chemicals. One is ammonium hydroxide (NH4OH) which is used conventionally. The others are choline hydroxide (CH3)3N(CH2CH2OH)OH and tetramethyl ammonium hydroxide (TMAH, (CH3)4NOH). In the case of choline and TMAH, even though these chemicals were reported in the literature and used for cleaning before, there is no extensive and comparative study on cleaning. In this paper, first Fundamental characteristics of these alkaline solutions were evaluated by measuring pH, conductivity and zeta potential. Then the silicon etch rate and roughness changes were measured using ICP-AES and AFM. Finally these dilute alkaline solutions were used to clean silicon substrate to understand the particles removal behavior with megasonic irradiation. The effect of dissolved gas with megasonic was also evaluated. The cleaning process using the gas dissolved dilute alkaline solutions with megasonic was also optimized to prevent the damages to the pattern. Consequently, it was found that the dilute alkaline solutions have low silicon etch rate and roughness compared to conventional SC-1 cleaning and Ar gas dissolved water with ammonium hydroxide showed high particle removal efficiency with low pattern damage ratio when compared SC-1 cleaning. Alkaline solutions with dissolved gas can be proposed as an alternative cleaning solution for material loss free and damage free cleaning.