The RCA clean is a standard set of wafer cleaning steps which needs to be performed before high temp processing steps (oxidation, diffusion, CVD) of silicon wafers in semiconductor manufacturing. RCA cleaning includes RCA-1 and RCA-2 cleaning procedures. RCA-1 involves removal of organic contaminants, while RCA-2 involves removal of oxides and RCA-3 metallic contaminants.
Werner Kern developed the basic procedure in 1965 while working for RCA, the Radio Corporation of America [1] It involves the following :
The wafers are prepared by soaking them in DI water. The first step (called SC-1, where SC stands for Standard Clean) is performed with a 1:1:5 solution of NH4OH (ammonium hydroxide) + H2O2 (hydrogen peroxide) + H2O (water) at 75 or 80 °C[1] typically for 10 minutes. This treatment results in the formation of a thin silicon dioxide layer (about 10 Angstrom) on the silicon surface, along with a certain degree of metallic contamination (notably Iron) that shall be removed in subsequent steps. This is followed by transferring the wafers into a DI water bath.
The second step is a short immersion in a 1:50 solution of HF + H2O at 25 °C, in order to remove the thin oxide layer and some fraction of ionic contaminants[1].
The third and last step (called SC-2) is performed with a 1:1:6 solution of HCl + H2O2 + H2O at 75 or 80 °C. This treatment effectively removes the remaining traces of metallic (ionic) contaminants[1].
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In his book, "Handbook of Semiconductor Wafer Cleaning Technology" [2], Werner Kern writes that the first step in the ex situ cleaning process is ultrasonically degrease in trichloroethylene, acetone and methanol.
RCA cleaning (also known as SC1/SC2 etching) submits silicon wafers to oxidation by NH3:H2O2:H2O mixtures, oxide removal in diluted HF, further oxidation by HCl:H2O2:H2O mixtures, and final etching in diluted HF.