|
For obvious cost reasons, semiconductor manufacturers are constantly striving to produce ever smaller wafer geometries with the current installed base of wafer steppers. Many techniques (phase shifting, optical proximity correction, etc.) have been used successfully to 'squeeze' more resolution from these steppers than was once thought possible. Wafers processed using non-aggressive k1 factors provided a linear correlation between mask and wafer feature sizes. However, it has been shown that pushing k1 factors to very low levels causes a nonlinear response between changes in photomask and wafer critical dimension. This non-linearity demands extremely tight photomask CD control specifications. Total CD errors 50 nm and smaller can cause unacceptable wafer CD variation. Current high end reticle manufacturers are capable of meeting a total CD uniformity specification of approximately 40 nm as measured by sampling strategies using optical metrology tools. These tools are very useful for detecting macro changes in CD; however, they will only detect a localized error if it happens to occur precisely at the point of measurement. In contrast, a pattern inspection system employing a linewidth measurement algorithm can ensure detection of all localized errors within the detection and review capability of the system. The problem with reticle CD error detection capability is that there is a large discrepancy between currently available detection of greater than or equal to 150 nm and required detection of less than or equal to 50 nm necessary for proper wafer functionality at low k1 lithography. In this paper, defect sensitivity and false detection performance of a new advanced line measurement algorithm was tested. The test vehicles included both an industry standard and a custom designed programmed defect test mask. In addition, production masks with naturally occurring localized CD errors that caused wafer pattern bridging were analyzed. This new experimental algorithm has shown localized CD error detection of less than or equal to 100 nm reticle defects.
|
