Specific Process Knowledge/Cross Contamination

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Cross Contamination

As explained for the Process Flow, there are a large variety of cleanroom fabrication and characterization methods that can be combined to create new materials or structures. Some processes are very sensitive to contaminations and equipment cannot always be cleaned easily running pre-process cleaning step.

For example, contaminations during a thermal oxidation process to grow silicon dioxide (SiO₂) layers on silicon wafers can significantly degrade the quality and functionality of the resulting oxide layer. Especially metal ions pose a serious issue as they increase leakage currents, reduced the breakdown voltage, reduce the dielectric strength, and cause threshold voltage shifts in MOS devices. But contaminants can also alter the stoichiometry or uniformity of the oxide layer due to non-uniform growth rates and the formation of defective or porous oxides

Special attention has to be paid to Cross Contamination and compatibility of layers on your substrate with subsequent fabrication steps. For example, oxidation and LPCVD furnaces are often extremely clean and any contamination can destroy the functionality of the thin film. Therefore, wafers processed in other machines, such as dry etching equipment, require special cleaning to avoid cross-contamination.