Wet etching

Structure generation through wet chemistry

Wet Chemical Etching

Wet chemical etching is commonly used for uniform stripping or patterning through a mask of dielectric and metallization layers. In contrast to RIE all processes are more or less isotropic and mask underetching is present. Selectivities toward mask and substrate materials are usually much better than with RIE processes. Another special wet etching process used in bulk micromaching technology is the anisotropic, crystal-oriented, KOH or TMAH etch.

Standard RCA process (SC1, SC2, HF-dip) is used for wafer cleaning. Special Solvent bathes are available for resist stripping. All standard etch bathes are SPC controlled (etch rate monitoring).

Standard Processes

The following standard processes are available:

  • BOE (buffered oxide etch, NH4F/HF/H2O) Used for etching of thermal oxide, LPCVD oxide (LTO), PECVD oxide, and PECVD. Patterning can be done using a positive AZ resist of 1.2, 1.8 or 6.5 µm thickness.
  • TMAH and KOH silicon etch Used for crystal oriented anisotropic etching of mono silicon. Thermal oxide or LPCVD nitride masks are commonly used for patterning
  • HF-dip Used for etching of thin silicon oxide (gate oxides, native oxide layers)
  • Phosphoric acid (H3PO4) Used for uniform stripping of silicon nitride layers (LPCVD nitride/LOCOS process, PECVD nitrides).
  • Aluminum etch A special mixture of acids is in use for etching of aluminum layers (e.g., interconnection lines)
  • Polysilicon etch A mixture of HF and HNO3 is in use for isotropic etching of polysilicon layers.
  • Special etch application There are many further chemicals in use for etching of metal layers (Au, Cr, Ni, Cu, Ti).