Methods of Making Thermal Oxide Silicon Wafers

One simplest way to produce thermal oxide silicon wafers is to oxidize silicon with oxygen.

Silicon Dioxide is a main insulating material, which is widely used in micro technology. Thermal oxidation is the most common technique, used to produce insulating oxide layer in a furnace.

There are two common methods to produce oxide layers on Si wafers:

• Dry thermal oxidation, when the wafer is exposed to oxygen at ~ 1000 degree C. The high quality oxide for MOS gate insulation is formed using this technique.
• Wet thermal oxidation, mixture of high purity oxygen and hydrogen at ~ 1000 degree C is burned, creating water vapour environment. The main benefit of this process is high growth rate. Although “wet” oxide features not very good quality and may be used only as a masking layer for instance.

The aim of this exercise is to grow the layer of the oxide and measure its thickness employing an ellipso meter. The wet oxidation method will be used for growth, but due to safety regulation, hydrogen must not be used in the lab. The growth of a silicon oxide layer on the surface of silicon can be formed using high dry and wet oxidation process. In both cases, Silicon reacts with oxygen leading to a moving interface towards the substrate.

When you plan to buy thermal oxide silicon wafers, you should have idea what thickness you require. Generally, the thickness is 2 to 6” in which dry SiO2 films are from 20 to 500 nm and wet thermal oxide is from 50 nm up to 2 µm. Dry oxidation typically happen at temperature ranging between 850 and 1200 degree C and shows low growth rates. This process allows good thickness uniformity and purity. Therefore, this is highly preferred method to produce high-quality thermal oxide silicon wafers.

Thicker wafers are produced by wet oxidation where the growth rate is drastically increased. Single side silicon oxide wafer used to have thermal oxidation on one side only. In order to get only one side oxidized, a protection is being used on one side. The opposite side is then dissolved in BHF. As the thermal oxidation process is typically run of 25 to 50 wafers and the dissolution is made wafer by wafer, you can  buy thermal oxide silicon wafers in the same batch.