Multichip reticle approach for OPC model verification

The complexity of current semiconductor technology due to shrinking feature sizes causes more and more engineering efforts and expenses to deliver the final product to customers. One of the largest expense in the entire budget is the reticle manufacturing. With the need to perform mask correction in order to account for optical proximity effects on the wafer level, the reticle expenses have become even more critical. For 0.13um technology one can not avoid optical proximity correction (OPC) procedure for modifying original designs to comply with design rules as required by Front End (FE) and Back End (BE) processes. Once an OPC model is generated one needs to confirm and verify the said model with additional test reticles for every critical layer of the technology. Such a verification procedure would include the most critical layers (two FE layers and four BE layers for the 0.13 technology node). This allows us to evaluate model performance under real production conditions encountered on customer designs. At LSI we have developed and verified the low volume reticle (LVR) approach for verification of different OPC models. The proposed approach allows performing die-to-die reticle defect inspection in addition to checking the printed image on the wafer. It helps finalizing litho and etch process parameters. Processing wafers with overlaying masks for two consecutive BE layer (via and metal2 masks) allowed us to evaluate robustness of OPC models for a wafer stack against both reticle and wafer induced misalignments.