Productivity is closely related to yield, the fraction of dies on the wafer that are functional at the end of the manufacturing process. Yield loss results from:
- Parameters that are out of specifications or improperly specified.
- Process or equipment failures.
- Chemical contamination.
- Particulate defects.
The issues of parameters such as overlay and linewidths were discussed in the prior two chapters. Process or equipment failures, which might occur, for example, when a resist pump malfunctions and wafers are not completely covered with resist, are more properly the subjects of a book on equipment maintenance, and will not be covered in this text. Chemical contamination typically results from contaminated photochemicals, and will not be considered in detail. Particulate contamination is the primary source of yield loss that lithography engineers need to address and will be the subject of this chapter.
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