Wet Chemical Processes
Wafer cleaning is commonly the first step in a process and may be used repeatedly throughout a process fabrication sequence. This may involve the use of solvents such as acetone and/or isopropal alcohol (IPA) or else acid and/or basic solutions followed by a water rinse. Cleans are designed to remove organic and/or metallic surface contamination along with particulates. Furnace pre-cleans consist of a Piranha clean followed by “silicon clean 1 (SC1) and then “silicon clean 2 (SC2). Short etch steps are often done prior to metallization to ensure good contacts to semiconductors. MEMS processes can utilize a long BOE etches for the release step. Descum (O2 plasma) etch processes are commonly done prior to dry etch steps to ensure the removal of any residual PR (link to Plasma etch). Oxygen plasma cleans can be done to help remove any organic residues.
- Pre-diffusion cleans: Most furnace steps require pre-diffusion cleans that often consist of several steps such as the following:
- Piranha clean, ( H3SO4 + H2O2), 85C to 100C, 10 min; note: this is a very exothermic reaction!
- SC1 clean (1 NH4OH + 1 H2O2+ 5 H2O), 60C to 80C, 10-20 min
- SC2 clean (1 HCl + 1 H2O2 + 5 H2O), 70C-90C
- Wet chemical etching is available for the following materials:
- SiO2; Buffered oxide etch (BOE= NH4F + HF) and HF solutions (such as 10parts H2O + 1 part 49%HF)
- Si3N4; H3PO4 at 160C
- Si; HF + HNO3 + HAc
- Al; 80% H3PO4 + 5% HNO3 + 5%HAc + 10% H2O (commercial mix)
- Cr; (NH4)2Ce(HNO3)6 plus H2O (commercial mix)
- PR strip? (see PR section or add notes here?)
- Solvent cleans?
- Plasma cleans & PR strip
- Descum etchs in O2 are available on most of the etch tools (link to Plasma etch page)
- PR can be removed using O2 plasma etch tools (link to Tegals)
- Equipment & Hoods
- Acid hoods (2) (link to reservation page)
- Base hoods (2)
- Solvent hoods (1)
- Other etches can be used; please check with nanofab staff.