Fundamentals of Semiconductor Cleaning Equipment

1. Objects to be cleaned

Wafer, also known as wafer or wafer. Its main component is the crystallization of sand, which is pulled into single crystals at high temperatures to form a cylindrical shape. Then, slice according to industry standards. However, there are various scratches on the surface of the cut silicon wafer at this time, and the surface is very rough, with many cutting objects or oil stains.

2. Specific process

The first step is to polish and polish the cut silicon wafers. At this point, there will definitely be many particles of different sizes and various types on the surface of the silicon wafer, including metal foam, oil stains, etc. These particles are what we need to clean.

The second step is the cleaning process, which is explained as follows: RCA Company in the United States is a pioneer in the semiconductor cleaning industry. Due to its leading position in the semiconductor cleaning industry, current cleaning processes are based on RCA Company's process as a reference and have become industry standards. The cleaning process is shown in Figure 1:

Figure 1 Schematic diagram of RCA cleaning process

The solution in SC-1 is NH4OH+H2O2

The solution in SC-2 is HCl+H2O2

3. Method of increasing cleaning intensity

There are four methods to increase cleaning intensity:

1、 Heating. Assuming a room temperature of 20 ℃, use a heater to heat the cleaning solution to 80 ℃, which can accelerate the reaction of acid and alkali at high temperatures and achieve better cleaning results. There are two methods of heating, one is to directly heat the cleaning solution with a resistance wire. The disadvantage of this method is that during the heating process of the solution, the heat transfer is not very uniform, which is easy to form a temperature gradient. At the same time, direct heating can also easily generate excess pollutants. Another method is to use indirect heating, which uses a pump to send the heated solution back to the cleaning tank. This cleaning method can solve the problem of uneven temperature inside the cleaning tank, and at the same time, there is no problem of pollutants generated during the direct heating process. It is also a method we often use.

2、 Ultrasound. Using ultrasound to generate bubbles can also achieve the goal of absorbing impurities on the surface of silicon wafers. This situation is used when the temperature requirement cannot be too high. If high temperature and ultrasound work together, the cleaning effect is best.

3、 Throw. In order to prevent impurities from sticking to the surface of the silicon wafer, a shaking method is used to allow the basket containing the silicon wafer to fully contact the solution in the cleaning solution, increase friction, and effectively remove dirt.

4、 Ozone. Use the strong oxidation of ozone to produce foam. In order to achieve the goal of absorbing dirt on the surface of silicon wafers.

In general, these four methods are to increase the foam generated by the reaction, so as to absorb the impurities on the surface of the silicon wafer. These four methods can be combined to achieve better cleaning results.