Low pressure chemical vapor deposition chamber scheme.

Fabrication involves many steps where thin films of various materials are deposited on the surface of the wafer.  These include evaporation, chemical vapor deposition (CVD) and sputtering. Evaporation and sputtering need vacuum systems operating at low pressure but CVD and epitaxy can be performed at reduced pressure and sometime at atmosphere pressure.

CVD systems deposit films from chemical reactions that take place in a gas steam passing over the wafer.  Polysilicon, silicon dioxide, silicon nitride and metals like tungsten (W) can be deposited using these techniques.  CVD can be performed at pressures for which the mean free path of gas molecules is quite small and the use of high temperatures can result in excellent uniformity over many designs.

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The CVD reactor system shown above is a “hot-wall LPDCVD system using a three-zone furnace”. (Whew say that ten time fast)  This would be commonly used to deposit polysilicon, silicon dioxide and silicon nitride.  This is referred to as a low pressure CVD (LPCVD) system.  The reactant gases are introduced at one end and forced through a three-zone furnace out the other end. (The spike thermo-couples are the 3 zones) 

Excellent uniformity can be achieved on hundreds of wafers which can be processed in a single run.  A disadvantage of hot-wall systems is that the deposited film coats the inside of the tube and requires cleaning or replacement to minimize particle contamination.  hot-wall LPCVD systems are used extensively in the making of semiconductors and IC’s.

CVD can also be achieved in a plasma reactor.  Plasma allows CVD  to take place at lower temperatures.

Summary

Chemical Vapor Deposition is a gaseous process that deposits insulating films or metal onto a wafer at elevated temperature. Often, reduced pressure is used to promote the chemical reaction.

Contact tmcconec@gulf.uvic.ca with any questions or comments.