Low Sample Temperature

Low Sample Temperature

Material Name: Silicon
Record No.: 95
Primary Chemical Element in Material: Si
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: No data
Reference: Burkhard E. Volland, Profile simulations of gas chopping etching processes, PhD Thesis, Institute of Physics, University of Kassel, 2004, p. 39.

Figure 1: Anisotropy caused by low sample temperature. Due to the low sample temperature, the spontaneous etching of fluorine with silicon reduces dramatically. This effect is enhanced by the addition of oxygen to the process gas mixture (a). Etching proceeds only due to ion bombardment (ion-enhanced etching). Because of the direct flow of ions, etching proceeds only at the bottom, not at the sidewalls (a). Samples have been etched in an ICP reactor (Oxford Instruments Plasma Technology System 100) with a 90 sccm SF6/9 sccm O2 process gas mixture, 20 mTorr operating pressure, 60 W ICP power, 40 V dc bias, and a helium backing of 15 Torr, at -60 C (b) or -125 C (c). The vertical etching rate reduces from 3 µm/min (b) to 0.5 µm/min (c) as the sample temperature decreases from -60 C to - 125 C, but the anisotropy of the profile increases with decreasing sample temperature. The sample etched at - 60 C (b) still suffers considerable lateral etching due to the spontaneous etching reaction of fluorine with silicon, which vanishes at a sample temperature of -125 C (c).