This study explores the feasibility of Automated Defect Classification (ADC) with a Surface Scanning Inspection System (SSIS). The defect classification was based upon scattering sensitivity sizing curves created via modeling of the Bidirectional Reflectance Distribution Function (BRDF). The BRDF allowed for the creation of SSIS sensitivity/sizing curves based upon the optical properties of both the filmed wafer samples and the optical architecture of the SSIS.
The elimination of Polystyrene Latex Sphere (PSL) and Silica deposition on both filmed and bare Silicon wafers prior to SSIS recipe creation and ADC creates a challenge for light scattering surface intensity based defect binning. This study explored the theoretical maximal SSIS sensitivity based on native defect recipe creation in conjunction with the maximal sensitivity derived from BRDF modeling recipe creation.
Single film and film stack wafers were inspected with recipes based upon BRDF modeling. Following SSIS recipe creation, initially targeting maximal sensitivity, selected recipes were optimized to classify defects commonly found on non-patterned wafers. The results were utilized to determine the ADC binning accuracy of the native defects and evaluate the SSIS recipe creation methodology.
A statistically valid sample of defects from the final inspection results of each SSIS recipe and filmed substrate were reviewed post SSIS ADC processing on a Defect Review Scanning Electron Microscope (SEM). Native defect images were collected from each statistically valid defect bin category/size for SEM Review.
The data collected from the Defect Review SEM was utilized to determine the statistical purity and accuracy of each SSIS defect classification bin.
This paper explores both, commercial and technical, considerations of the elimination of PSL and Silica deposition as a precursor to SSIS recipe creation targeted towards ADC. Successful integration of SSIS ADC in conjunction with recipes created via BRDF modeling has the potential to dramatically reduce the workload requirements of a Defect Review SEM and save a significant amount of capital expenditure for 450mm SSIS recipe creation.
KEYWORDS: Process control, Lithium, Data analysis, Data modeling, Statistical analysis, Error analysis, Software development, Time metrology, Computer simulations, Information operations
The quality of an Automated Process Control (APC) depends highly on the amount of relevant measurement data points. The quality of APC for low volume products is lower than high volume products, since there is not enough data to respond to tool parameters drift or incoming variations. In order to improve low volume runners control it is proposed to use high volume runners data to generate feedback for low volume runners. Product to product differences can be minimized by applying bias. This bias does not remain stable due to tool parameters drift or incoming variations. The current paper addresses these issues and reviews different methods for bias control/change if needed. Intel Litho APC is using EWMA time based weighting for parameters like Overlay parameters, Focus and Dose control. The data for each set of feedback list is segmented by several partition variables (tool, operation, etc.) within a defined expiration period. For low volume runners it is possible to widen the partition by adding main runners data with applied bias. Historical data shows possible bias variability following process or tool drifts over time. Different cases of partition biases are reviewed based on Litho parameters examples. Various algorithms for bias control and bias calculation are reviewed. Simulation studies are performed to predict the impact of deploying this strategy in production.
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