Chemistry Reference
In-Depth Information
in the range between 0.005 and 0.04M, the effect of temperature is found to be minimal,
in agreement with the small activation energies in these solutions.
239
Most practical etching processes use buffered HF solutions (BHF) prepared by
addition of to avoid depletion of fluoride ions. There are many kinds of BHF with
various combinations of HF and concentrations. Figure 4.4 shows that the etch
rate of thermal oxide in BHF solutions increases when the concentration is low
but is relatively independent of concentration when the latter is higher than about
5%. Above 5% the etch rate is determined predominantly by HF concentration.
452
Figure
4.5 shows the effect of dilution of a BHF solution with water.
97
Addition of many chemical reagents other than is also used to control
certain aspects of the etching process. Figure 4.6 shows that addition of
to a HF
