Specific Process Knowledge/Wafer cleaning/RCA: Difference between revisions
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Since RCA1 can oxidize silicon to silicon dioxide, an HF dip is sometimes used between RCA1 and RCA2. This will also remove contaminants that can be trapped in the formed oxide. However, this step is often omitted, since RCA1 removes the native oxide and then re-oxidizes the surface. This in itself has a cleaning action. It is generally not advised to do an HF dip after RCA-2 if the samples will be processed by wet chemical processes afterwards. This is because the hydrogenated surface will be extremely reactive and therefore attract contaminants from both the air and processing liquids. In this case it is better to continue processing with the passivated oxide surface. RCA clean is often done prior to furnace processes, an in these cases an HF dip after RCA-2 makes sense. Ideally the wafers should be transferred to the furnace immediately after RCA cleaning, because the samples will be very sensitive to recontamination as mentioned above.<br> | Since RCA1 can oxidize silicon to silicon dioxide, an HF dip is sometimes used between RCA1 and RCA2. This will also remove contaminants that can be trapped in the formed oxide. However, this step is often omitted, since RCA1 removes the native oxide and then re-oxidizes the surface. This in itself has a cleaning action. It is generally not advised to do an HF dip after RCA-2 if the samples will be processed by wet chemical processes afterwards. This is because the hydrogenated surface will be extremely reactive and therefore attract contaminants from both the air and processing liquids. In this case it is better to continue processing with the passivated oxide surface. RCA clean is often done prior to furnace processes, an in these cases an HF dip after RCA-2 makes sense. Ideally the wafers should be transferred to the furnace immediately after RCA cleaning, because the samples will be very sensitive to recontamination as mentioned above.<br> | ||
A crucial part of the RCA cleaning procedure is the oxidation by H<sub>2</sub>O<sub>2</sub> at elevated temperatures. Therefore, the lifetime of RCA1 and RCA2 solutions is limited to about 1 hour after preparation and heating to 70<sup>o</sup>C because H<sub>2</sub>O<sub>2</sub> decomposes at this temperature. A temperature of 70°C is optimal. RCA solutions should never be heated above 80°C since this will lead to excessive decomposition and loss of NH<sub>3</sub>. | A crucial part of the RCA cleaning procedure is the oxidation by H<sub>2</sub>O<sub>2</sub> at elevated temperatures. Therefore, the lifetime of RCA1 and RCA2 solutions is limited to about 1 hour after preparation and heating to 70<sup>o</sup>C because H<sub>2</sub>O<sub>2</sub> decomposes at this temperature. A temperature of 70°C is optimal. RCA solutions should never be heated above 80°C since this will lead to excessive decomposition and loss of NH<sub>3</sub>.<br> | ||
*RCA1 contains: H<sub>2</sub>O, NH<sub>4</sub>OH and H<sub>2</sub>O<sub>2</sub> (5:1:1). It is used for removal of light organics, particles and metals.<br> | *RCA1 contains: H<sub>2</sub>O, NH<sub>4</sub>OH and H<sub>2</sub>O<sub>2</sub> (5:1:1). It is used for removal of light organics, particles and metals.<br> | ||