Development of a dual-phase virtual metrology scheme

This work proposes a Dual-phase virtual metrology scheme. To consider both promptness and accuracy, this scheme generates dual-phase virtual metrology (VM) values. Phase I emphasizes promptness; that is to immediately calculate and output the Phase-I VM value (denoted VM_I) of a workpiece (wafer or glass) once the entire process data of the workpiece are completely collected. Phase II intensifies accuracy; that is not to re-calculate and output the Phase-II VM values (denoted VM_II) of all the workpieces in the cassette (also called FOUP in the semiconductor industry) until an actual metrology value (required for tuning or re-training purposes) of a workpiece in the same cassette is collected. Besides, in this scheme, the accompanying reliance index (RI) and global similarity index (GSI) of each VM_I and VM_II are also generated. The RI and GSI are applied to gauge the degree of reliance. If the reliance level of a VM value is lower than the threshold, this VM value may not be adopted. An illustrative example involving fifth-generation TFT-LCD CVD equipment is presented. Experimental results demonstrate that the proposed scheme is applicable to the wafer-to-wafer or glass-to-glass advanced process control for semiconductor or TFT-LCD factories.