Random defect limited yield using a deterministic model

To be successful in the competitive semiconductor industry, the need to reduce cost per die is necessary and always challenging. It is important to produce better die per wafer by minimizing the cycle time to detect and fix yield problems associated with the technology. Yield, or wafer sort yield (number of good chips/wafer) can be separated into three components: random defect limited yield, systematic yield, and repeating yield loss. Random defect limited yield is caused by defects. Process equipment and byproducts primarily cause defects. Defects, usually randomly distributed, can also be localized to one, or multiple die on a wafer. In-line QC inspection tools can detect most defects. Systematic yield losses are process-related problems that can affect all die on a wafer, some die on a wafer, or die by region on a wafer. Systematic yield losses are not detectable by in-line QC defect inspection tools. Repeating yield loss is due to reticle defects. Reticle defects occur on the same die within a reticle field, e.g. a repeating defect can be caused by contamination on the stepper lens, by contamination on the pellicle that protects the reticle, or by contamination on the reticle itself. Reticle defects are sometimes detectable by in-line QC inspection tools. The focus of this paper is on the calculations and results of random defect limited yield (DLY) using the deterministic yield model. This model is used to prioritize defect problems, and to drive yield improvements. Examples are used to illustrate the benefits and strengths of the deterministic model. We also discuss the methodology, assumptions, and limitations of this model.