Wet chemical isotropic etching procedures of silicon - A possibility for the production of deep structured microcomponents

We have observed the etch rate and the underetch rate of <100>-, <110>- and <11 l>-oriented silicon substrates in isotropic etching solutions. We have studied the influence of the composition of the solution and the temperature on the etch rates. Further we also have examined the stability of different masking materials. The stability of thermally grown SiO₂ is very poor. Silicon nitride films show a comfortable stability at low etching temperatures. The stability of these films decreases with significant differences depending on the deposition temperature. The best stability were found with metal masks and photoresist masks. The values of the etch rates were in a range between 1 μm/min and about 900mu;m/min. A controlled procedure could be achievable up to etch rates of about 100μm/min. The etch rates and the undercut rates as well as the etch rates of the differently oriented materials are different under the same process conditions. In some cases we found profiles that are known from anisotropic dry etching procedures. All achieved results indicate an anisotropic etching behaviour of silicon in etchants based on compositions of HNO₃-HF-H₂O.