Thermal oxidation is a way to produce a thin layer of oxide on the surface of a wafer. The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it. Let’s take a deeper look at thermal oxidation and how it pertains to ultra flat wafers.
Thermal oxidation of silicon is usually performed at a temperature between 800 and 1200 °C. This results in something called the High-Temperature Oxide layer. It may use either water vapor or molecular oxygen as the oxidant and is referred to as either wet or dry oxidation. Thermal oxide incorporates silicon consumed from the substrate and oxygen supplied from the ambient.
Most thermal oxidation is performed in furnaces. A single furnace accepts many wafers at the same time, in a specially designed quartz rack called a boat. Historically, the boat entered the oxidation chamber from the side and held the wafers vertically, beside each other. However, many modern designs hold the wafers horizontally, above and below each other, and load them into the oxidation chamber from below.
Wet oxidation is preferred to dry oxidation for growing thick oxides because of the higher growth rate. Wet oxidation also yields a lower-density oxide, with lower dielectric strength.
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