Peroxide solutions, silicon-wafer cleaning

RCA [Radio Corporation of America] Also called RC A-2 and HPM. A process for cleaning silicon wafers used in electronics. The wafers are washed successively by three solutions. The first is an alkaline solution of hydrogen peroxide, which oxidizes organic matter. The second is an acid fluoride solution, which removes silica. The third is an acidic solution of hydrogen peroxide, which removes transition metals. The process was developed by RCA Corporation in 1970 and widely used thereafter by the electronics industry. 

The SC-1 cleaning solution is used as part of the RCA cleaning process for silicon wafers and is a mixture of ammonium hydroxide, hydrogen peroxide, and water. This process is used to remove undesired particles and contaminants from silicon wafers. It is important to maintain the composition of the solution because an improper ratio of ammonium hydroxide to hydrogen peroxide can lead to etching of the silicon surface, ineffective cleaning of the wafer, or damage to both the thermal oxide or doped silicon dioxide layers. 

Ultra-thin Hquid films of PDMS or poly(methyl-hydrodimethyl)siloxane on siHcon substrates were also prepared [50], The silicon wafers were cleaned by immersion in a freshly prepared piranha solution (a mixture of 70% sulfuric acid and 30% hydrogen peroxide), rinsing with deionized water, followed by etching in HF solution. Then the wafers were rinsed with deionized water and blown dry under a stream of nitrogen. The uniform thin films were spread by dipping the clean substrates in dilute solutions of silicone polymers in hexane and withdrawing the wafers at a constant speed. It was shown that solution concentration and withdrawal speed affected the final film thickness. Typical thickness was in the range of 3-8 nm. 

The PDMS (M = 6000 g/mol) and the carboxylated PDMS (CPDMS) were synthesized by Owens-Corning Corporation. The ionic groups (4.6 mol %) were randomly distributed along the PDMS chain. Lithium salts of the PDMS carboxylated ionomer (Li-CPDMS) were prepared by neutralizing the acid derivative with Lithium acetate dihydrate. The li ionomer was a rubbery solid at room temperature and exhibited viscous flow above 100°C. The substrates used were atomically smooth silicon wafers with a 100 orientation and one side polished. These were washed in an ultrasonic bath for 10 min. and then a 30/70 (v/v) concentrated hydrogen peroxide/concentrated sulfuric acid solution for 1 h. to clean the surface. The wafers were then rinsed thoroughly with deionized water and dried under a stream of dry nitrogen. Since silicon oxidizes very rapidly, the surface of the wafers that were used in these experiments was actually silicon dioxide (silica). 

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