Calibration Method for Lithographic Inspection Apparatus
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithographic apparatuses face challenges in accurately calibrating metrology tools due to wafer surface non-uniformity, leading to residual focusing errors and poor pattern definition, as existing methods fail to account for local focus deviations caused by unflatness within the exposure field.
Innovation Solution
A method and apparatus for calibrating inspection tools by obtaining surface level measurements across a substrate, determining focus settings for exposure fields, and using these measurements to calibrate the inspection apparatus, accounting for both focus offsets and local surface unflatness to produce accurate focus-dependent property measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a leveling profile is created to correct wafer unflatness, then wafer-level focus correction is improved, but residual focusing errors remain when unflatness occurs on a scale smaller than the exposure field
Solution Approach 1:
The patent divides the exposure field into multiple measurement locations and performs separate focus measurements at each location. By segmenting the field and accounting for local focus deviations at each measurement point, the method resolves residual focusing errors that persist when using a single wafer-level leveling profile, thereby improving pattern definition while maintaining focus measurement accuracy.
2Reliability
If focus set points are corrected using a wafer-level leveling profile, then overall focus accuracy is improved, but local set point errors remain due to unflatness smaller than the exposure field scale
Solution Approach 1:
The patent applies local quality by performing focus measurements at multiple discrete locations across the exposure field and determining focus offsets specific to each location. This local approach to focus control accounts for small-scale unflatness variations that a uniform wafer-level profile cannot capture, thereby improving local focus set point accuracy while maintaining overall focus control stability through the comprehensive measurement approach.
3Measurement precision
If multiple focus measurements are performed across the exposure field, then local focus deviations are detected, but measurement time and process complexity increase
Solution Approach 1:
The patent performs focus measurements at multiple locations across the exposure field during the calibration step before actual production exposure. By conducting these comprehensive measurements in advance and storing the focus offset data for later use, the method achieves high local focus measurement accuracy without incurring time penalties during production, as the measurements are performed once during calibration rather than repeatedly during manufacturing.
Data Source
AI summary
A method of calibrating an inspection apparatus. Obtaining a surface level measurements (LS) at respective level sensing locations LS(x,y). Determining focus settings (LPA, LPB) for exposure field regions (EFA, EFB) in accordance with surface level measurements (LSA, LSB) having level sensing locations corresponding to the respective exposure field region. Exposing exposure field regions (EFA, EFB) with focus offsets (FO1, FO2) defined with reference to the respective focus settings (LPA, LPB) to produce target patterns at respective target locations. Obtaining focus-dependent property measurements, such as Critical Dimension (CD) and/or side wall angle (SWA) of the target patterns measured using the inspection apparatus; and calibrating the inspection apparatus using the focus-dependent property measurements (CD/SWA) and the respective focus offsets (FO1, FO2). The calibration uses surface level measurements (e.g., LSB(3)) having a level sensing location (e.g., LSLB(3)) corresponding to the respective target location (TLB). Each offset value is thus corrected in the calibration for the local wafer stack unflatness present during exposure.