Wet chemical processes

Wafer cleaning and isotropic thin layer etching

The wet chemical processes are necessary for all semiconductor research tasks of the Institute  and include the following standard techniques:

Standard silicon wafer cleaning

RCA-1-(SC-1)-cleaning (NH4OH/H2O2/H2O)
RCA-2-(SC-2)-cleaning (HCl/H2O2/H2O)
Piranha-(SPM)-cleaning (H2SO4/H2O2)
Specialized cleaning techniques

Hydrophilling of Si surfaces (e.g. for silicon wafer bonding)
Standard silicon oxide etching

Diluted HF (1%HF in H2O)
Buffered oxide etch (BOE), (HF/NH4F/H2O)

Isotropic silicon etch

HF/HNO3 solutions with well defined etch rates between 6 and 1000 nm/min
Standard silicon nitride etching Hot H3PO4
Metal contact layer etching

H3PO4/HNO3/CH3COOH/H2O and TMAH
for Al-contact layer etching and Al/Si-contact layer etching

Specialized etching techniques for:

Metals, glasses, poly-Si, etc.

Anisotropic and selective etching for silicon bulk micromachining

Anisotropic etching allows for the precise three-dimensional structuring of silicon structures.The anisotropy arises due to the dependence of the etch rate on crystal orientation, dopant concentration or, in the case of eletrochemical etching, on the applied electrical potential. Both KOH and TMAH can be used to etch silicon with etch masks of Si3N4 or SiO2 respectively.

Anisotropic etching can lead to very precise lateral and vertical machining of micromechanical devices. The dependence on the dopant concentration and on electrical potential allows for the incorporation of well defined etch stop layers by either using a high boron concentration with NB > 5×1019 cm-3, or else exploiting the potential drop across a pn-junction. SiO2 and/or Si3N4 layers can be used as masking layers without problems for creating 3D-structures were very deep patterns are required.

Doping of etch stop layers is carried out by conventional ion implantation or writing focused ion beam (FIB) implantation and subsequent annealing or drive in diffusion.