Etch Rates in Alkaline Solutions of Mono-Crystalline Silicon Wafers Produced by Diamond Wire Sawing

Abstract

The objective of this work has been to identify the root cause of the reduced etch rate of fixed abrasive sawing (FAS) cut wafers during damage etching. The etch rate in alkaline solutions was measured as a function of time, temperature and different pre-cleaning processes, both for FAS and standard slurry wafers. The results showed a maximum etch rate for KOH concentrations around 20-30 wt%. The etch rate of FAS wafers was lower compared to slurry wafers during the initial 5-10 minutes of etching, dependent upon KOH concentration and temperature. In order to characterize the wafer surface, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), as well as reflectance measurements were used. By comparing the cross sections of the surface structure of as cut slurry and as cut FAS wafers, both an amorphous silicon layer and a defect layer were observed, but is concluded to not limiting initial higher etch rate. Furthermore during the initial stage of damage etching inverted square pillars were always formed. The walls of the pillars were constructed by the fast etching {110} planes. The depth of the pillars is found to be shallower for FAS cut wafers due to initially lower surface roughness. Therefore, the surface area exposed for the damage etch solution is larger for the slurry cut wafers, which explains the larger etching rate for the slurry cut wafers during the initial stage of the etching.