Did you know that the cleaning process is a crucial step in the silicon wafer manufacturing process? Now that semiconductor devices and geometries are getting smaller in size, eliminating particulates as tiny as a speck of dust from the surface of each wafer is even more vital. However, the strong electrostatic forces between these impurities and the wafer substrate make it even more challenging to remove the unwanted particles without altering the surface of the wafer.
For this reason, semiconductor companies employ wafer cleaning techniques to ensure the elimination of chemical and particle impurities and substrate surface conditioning. Besides reducing defect density, efficient wafer cleaning processes can also increase yields.
This cleaning process uses acidic hydrogen peroxide and ammonium hydroxide solutions to remove organic residue from silicon wafers effectively. It also leaves a thin layer of oxidized silicon on the surface of the wafer. An RCA cleaning solution comprises five parts water, one part 30% hydrogen peroxide, and one part 27% ammonium hydroxide.
Although this cleaning method is widely used in the industry, it requires strict control measures to be effective. Piranha solution, also known as Piranha etch, removes photoresist and eliminates large amounts of organic contaminants from wafer substrates. In most cases, the mixture ratio is one part of 30% hydrogen peroxide and three parts of sulfuric acid.
However, other protocols also use sulfuric acid ratios as high as seven to one. Since its mixture is a potent oxidizing agent, it hydroxylates most surfaces and makes them hydrophilic. Special care is required when preparing and handling this highly corrosive mixture.
Besides requiring a significant equipment capacity, pre-diffusion cleaning methods are performed several times during the course of the manufacturing sequence. It effectively minimizes particle and metallic contamination while optimizing etch uniformity and maintaining high throughput.
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