The ZEISS WLCD measures the critical dimension (CD) on photomasks under scanner relevant illumination conditions with high throughput. Proven aerial imaging technology is used to qualify the printing performance of the mask.
The WLCD system by ZEISS provides high precision in-die CD measurement, predicting wafer level photomasks performance. Actinic CD metrology is based on aerial imaging technology by high resolution 193 nm optics.
Scanner equivalent illumination settings include FreeForm Illumination to support SMO technologies. ZEISS WLCD captures OPC and optical MEEF effects and simplifies CD measurements for complex mask designs. Pellicle capability allows fast mask qualification and performance monitoring.
- Utilization of 193 nm lithography for up-to-date node forces the mask shop to produce complex mask designs and tighter lithography specifications. These requirements make in turn process control more important than ever. High yield with regards to chip production requires accurate process control. Critical Dimension Uniformity (CDU) is one of the key parameters neccessary to assure good performance and reliable functionality of any integrated circuit. ZEISS WLCD measures the CD based on proven aerial imaging technology and defines the mask CD non-uniformity. This data can be used as input to the ZEISS CDC32 process.
- ZEISS CDC32 utilizes an ultrafast femto-second laser to write intra-volume shading elements inside the bulk material of the mask. By adjusting the density of the shading elements the light transmission through the mask is locally changed in a manner that improves wafer CDU when the corrected mask is printed.
- The ZEISS CDC32 improvement can finally be verified by ZEISS WLCD predicting the intra-field CD Uniformity at wafer-level. This is why ZEISS WLCD builds up an unique closed loop solution: WLCD measures the CDU on photomask as input for the CDC32 and verifies the improvement of CDU after CDC process.