Chromeless phase lithography reticle defect inspection challenges and solutions

CPL(TM) Technology is a promising resolution enhancement technique (RET) to increase the lithography process window at small feature line widths(1-4). Successful introduction of a reticle based RET needs to address several reticle manufacturing areas. One key area is reticle inspection. A CPL reticle inspection study has been completed and a best known methodology (BKM) devised. Use of currently available inspection tools and options provides a robust solution for die-to-die inspection. Die-to-database inspection challenges and solutions for optically completed CPL reticles are discussed. Core to the devised BKM is the concept of in-process inspections where the highest sensitivity inspection may not necessarily be performed after the last manufacturing step. The rationale for this BKM is explained in terms of actual manufacturing process flow and most likely defect sources. This rationale also has implications for programmed defect test mask designs in that the choice of defect types need to be linked to a plausible source in the manufacturing process. Often, the choice of a programmed defect type ignores the fact that a naturally occurring defect's origin is early in the manufacturing process and would be detected and either repaired or the reticle rejected before subsequent manufacturing steps. Therefore, certain programmed defect types may not be representative of what should be expected on a production mask. Examples such defects are discussed.