Thermal,Oxidation,Process,Micr technology Thermal Oxidation Process to Microfabricate Silicon Wafers
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Thermal oxidation is an important step in the microfabrication of silicon Wafers. In this process, a thin layer of oxide is deposited on the surface of Si wafers. Usually, this layer of oxide is known as silicon dioxide.In this technique, an oxidizing agent is diffused into the wafer. The procedure is usually followed at very high temperature so that oxide layer can diffuse evenly and react. By utilizing the Deal-Grove model, the rate of oxide growth is predicted.Thermal oxidation of Si wafer is usually performed at a temperature around 800 and 1200°C. Therefore, resulting oxide is known as a High Temperature Oxide layer. The oxidant used may generally be either water vapor or molecular oxygen.Thermal oxidation process can be of two types:Wet Thermal OxidationDry Thermal oxidationThe oxidizing agent may be hydrochloric acid (HCl) or other similar chemicals. The chlorine removes metal ions from the oxide. Thermal oxide incorporates silicon consumed from the substrate.Method of Formation of Thermal oxide Layer: The thermal oxidation process occurs at temperatures between 800 and 1200 °C. The process is followed in an electrical furnace. A single furnace has the capabilty to accept several wafers at the same time.The wafers lie vertically inside the tube of the furnace. The heat convection and temperature gradient causes the wafer to have a thicker oxide than the bottom layer. This allows the use of load locks to purge the wafers. The nitrogen is used for purging before oxidation. This is helpful in limiting the growth of native oxide on the Si surface.Oxide Quality:Wet oxidation is preferred over dry oxidation for growing thick oxides. The wet oxidation process is helpful in achieving the higher growth rate in the Thermal oxidation of silicon wafers. However, fast oxidation leaves more dangling bonds at the silicon interface. Thick oxides are usually grown with a long wet oxidation.Dry oxidation also takes place at temperatures range between 850 and 1200°C. It demonstrates low growth rates. It does allow very good thickness uniformity and purity. Consequently, this is the preferred method for the production of high quality thin silicon oxide layers. Thicker oxide layers are produced by the wet oxidation method.Benefits of Thermal Oxidation of Silicon Wafers: This layer plays an important role in IC technology.The Role of Oxide layer in IC fabrication:It acts as a diffusion mask.It permits only selected material into a silicon wafer.It is used for surface passivation.?Helps in protecting the junction from moisture.It serves as an insulator on the water surface.Acts as the active gate electrode in MOS device structure.Used to isolate one device from another.It provides electrical isolation in VLSI.Bottom Line:silicon can form a protective Thermal oxide layer on its surface. Or else, we have to depend insulators for surface layer protection. Insulators are not dependable, due to low temperature stability. Since Silicon wafers make a stable layer, this has held back germanium from IC technology.