Etch depth materials

The majority of micromechanical devices require 3D machining of the bulk silicon material with etching depths of up to wafer thickness. Generally, three basic etching process types can be distinguished ... 

Masking is required for many micromechanical applications. While Si3N4 is only suitable for a small etching depth because of its significant etch rate in HF, noble metals like gold are sufficient mask materials. In contrast to alkaline etchants, organic materials like certain resists or even some adhesive tapes are well suited to protect the silicon surface in isotropic etchants. 

The AO exposure of 0, 3.5, 7.0, 8.75 wt % Si8On MC-POSS-PI (POSS R group is cyclopentyl) films was carried out in a simulated LEO environment where films of these materials were etched by exposure to a hyperthermal O-atom beam [2]. The difference in etch depth between the eroded and stainless steel screen-protected areas of the samples, made it possible to calculate an AO reaction efficiency (Re) or erosion rate of the material for a given AO flux. 

Various heuristic models have been developed for describing the features of the etching curves. The most usual one is the so-called blow-off model [1], based on the assumption that for an incident fluence, all material within a depth such as Fpenetrated>Fthr is removed. In this case, assuming Beer s law for the absorption process, the dependence of the etching depth on the incident laser fluence is given by ... 

By adding small amount of O2 gas, the etch rate can be accelerated. In general, in this approach, the etch rate is relatively small and in the range of few nanometers to tens nanometers per minute. The RIE process is not applicable for bulk material micromachining, and therefore, it is suitable only to etch thin films with thickness of few micrometers. However, RIE is a suitable process to etch shallow microchannels in silicon substrate with good etch-depth control. 

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