Abstract
Wet-cleaning processes using chemicals will continue to play an important role in VLSI manufacturing. It is, thesefore, vital to reduce metal concentrations and particles in chemicals, because the dimension of VLSI continues to shrink. The metal concentrations are believed to have an adverse effect on pn junctions leakage current. In particular, the number of residual heavy atoms on wafer surface is to be kept within 1010 atoms/cm2. Metal concentration level in the chemicals is not less than 1 ppb at present. The true impact of particle control, however, has not yet been realized. The constituent elements of particles in the chemicals were analyzed by an electron microanalyzer (SEM-EDX) which can detect light-element as well. Samples used in this study were prepared by filtering various chemicals with 0.2 μm Nuclepore filter. After undergoing filtering, the filter was repeatedly put on sheets of wet filter paper until the contamination of the back side of the filter was removed. Then, the filter was dried on a filter paper under clean atmosphere. Carbon or Pt-Pd film was then sputter-deposited on the surface of the filter. From the results of analysis, it was found that the particles were mainly composed of Si and unknown materials with a little amount of Al, Mg, Fe, Cr, Ti etc. In case of H2SO4, only Si concentration increased a little by an elution test for 2 months.
