Microprocessor Production: The Use of a Plasma Barrel Etcher to Make Microchips Mentor: Erik Muehlenkamp Advisor: Dr. Chih-Hung Chang Done by Sarah Bronner and Vinu Lakkur

Acknowledgement- Partial support for this work was provided by the Intel Faculty Fellowship and National Science Foundation’s course, Curriculum and Laboratory Improvement Program under grant DUE

Procedure Clean wafer with solvents Dry with Nitrogen Soft bake Spin to coat with photo resist Soft bake Expose mask with UV light Develop pattern Hard bake Weigh and record weight Put in etcher and change variables such as spacing, etch time, power, and oxygen flow Record final weight

Problems What effect does wafer spacing have on mass loss of a wafer in the etcher? How does this weight loss progress as the time the wafer is left in the etcher is increased? How does the power level and oxygen flow affect the weight loss?

The Etcher... The etcher produces a plasma that cleans off excess photo resist from the wafer. A plasma is a highly energized ionized gas, which is a source of monatomic oxygen. The inside of the etcher has an extremely low pressure and a relatively low temperature, which allows it to use radio energy to create the monatomic oxygen. When the oxygen comes into contact with the photo resist on the wafer surface, it combusts away and the wafer loses mass.

The Mask... A mask contains layout information for where the circuitry lines are going to be on the wafer. This pattern is made by exposing the wafer which is covered with photo resist to UV light. Photo resist is a polymer that chemically changes by being exposed to light. The mask covers the wafer and determines which parts are exposed, so that the pattern can be defined on the wafer.

The Importance of Silicon Wafers Silicon is used to make wafers because it is a metalloid; silicon has qualities of both metals and nonmetals. This means that when silicon is doped with other elements, it can either have a positive or negative charge. Silicon wafers are very important in the manufacturing of electronic devices, particularly integrated circuits.

Conclusions Our data is too inconclusive to determine what effects the wafer spacing, oxygen flow, power and time in the etcher have on weight loss. Our data could have been improved if we had washed the developer off of the wafers. Because the effect of noise on the scale may be approximately the same degree as the change in weight that the wafer experiences in the etcher, experimental error is great. If we had consistently used wafer tongs, the wafer would not have gained additional weight due to finger prints.