Why Pre-Diffusion Cleans Are Important for Silicon Wafer Cleaning

Pre-diffusion cleans are done many times during the semiconductor manufacturing process, and each time the chemical residues and particles left on the wafers must be removed as completely as possible. If silicon wafers still have surface contamination when they are placed in the diffusion oven, the diffusion will become uneven and the resulting semiconductor products will come out defective or inferior.

Pre-diffusion cleans are a critical requirement in the silicon wafer cleaning process.  Particle contamination on silicon wafer surfaces prior to diffusion can significantly reduce the yield of electronic components in semiconductor manufacturing plants and research facilities.

Particle contaminants may be diffused into the silicon and create electric defects, or they may block diffusion behind the particle. After diffusion, these contaminants may affect etching and interfere with the microscopic conductors. The resulting semiconductor components may have to be discarded. As silicon microscopic structures become smaller, particles have become more disruptive on both the electrical and the physical scale.

Pre-diffusion cleaning is carried out by immersing silicon wafers in chemical or megasonic baths. Surface impurities are dislodged, dissolved or chemically neutralized. The complete wafer cleaning process may take more than one process and the following methods are commonly used:

RCA cleaning – Consists of two components, SC1 and SC2 (SC stands for “standard clean”). For SC1, the wafers are immersed in a solution of ammonium hydroxide and hydrogen peroxide, which remove all the organic compounds from the wafer surfaces. In SC2, the wafers are placed in a solution of hydrochloric acid and hydrogen peroxide that removes any remaining metal ions.

Piranha cleaning – Consists of a sulfuric and hydrogen peroxide mixture that quickly removes material such as photo resist. It also produces hydroxylation of the silicon wafer surface, making it hydrophilic or attractive to water, a characteristic useful for some subsequent process steps.

Megasonic cleaning – Uses high-frequency sound waves in a cleaning solution to dislodge contaminants from the surface of the silicon wafer. This cleaning method does not use harsh chemicals, and the generator used to produce a signal in the MHz range at a specified power level can be fine tuned to optimize cleaning.

For more details read the complete article titled, “Why Pre-Diffusion Cleans Are Important for Silicon Wafer Cleaning”. For a free quote or consultation contact Modutek at 866-803-1533 or email Modutek@modutek.com.