Techniques - wet bench processing

Wet chemical processes
Wafer cleaning is commonly the first step and may be used repeatedly throughout a process fabrication sequence. This may involve the use of solvents such as acetone and isopropanol alcohol (IPA) or acid and basic solutions, followed by a water rinse.

Cleans are designed to remove organic or metallic surface contamination as well as 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. Micro Electro-Mechanical Systems (MEMS) processes can utilize a long buffered oxide etches (BOE) 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. Oxygen plasma cleans can be done to help remove any organic residues.

Wet Bench Processing Standard Operating Procedures

Pre-diffusion cleans
Most furnace steps require pre-diffusion cleans that often consist of several steps such as the following:  

  1. Piranha clean, (H3SO4 + H2O2), 85-100C, 10 minutes. Use caution, this is a very exothermic reaction.  
  2. SC1 clean (1 NH4OH + 1 H2O2+ 5 H2O), 60-80C, 10-20 minutes   
  3. SC2 clean (1 HCl + 1 H2O2 + 5 H2O), 70-90C

Wet chemical etching is available for the following materials:     

  1. SiO2; Buffered oxide etch (BOE = NH4F + HF) and HF solutions (such as 10 parts H2O + 1 part 49%HF)   
  2. Si3N4; H3PO4 at 160C    
  3. Si; HF + HNO3 + HAc   
  4. Al; 80% H3PO4 + 5% HNO3 + 5%HAc + 10% H2O (commercial mix)  
  5. Cr; (NH4)2Ce(HNO3)6 plus H2O (commercial mix)  
  6. Plasma cleans & PR strip    
  7. Descum etches in O2 are available on most of the etch tools    
  8. PR can be removed using O2 plasma etch tools

Equipment and hoods    

  1. Two acid hoods    
  2. Two base hoods    
  3. Two solvent hoods    
  4. Other chemistries can be used. Please check with NanoFab staff.