Effective purging solution to reticle haze formation

The control of haze contamination on reticles has been gaining an ever-increasing focus because of its contribution to the huge yield loss in semiconductor manufacturing. Yield improvement through the reduction of haze on reticles has been a significant challenge as the use of 193nm light source and the shrinkage of line width on reticles. For a mass production IC manufacturing fab, an easy and practical solution is needed to prevent haze generation. In our previous study (Tseng et al., 2008), we demonstrated a practical and effective solution to reticle haze formation at a mass production DRAM factory. After implementing this solution, the number of wafers printed without haze development on reticles can be up to 150,000 wafers, and the maximum exposure dosage can be up to 9×10⁸ mJ/cm² without the detection of any printable haze. Using the average data from more than 20 reticles, the average wafer printed before cleaning of reticle was more than 100,000 wafers. This solution has been proven to be effective in reducing the generation of haze on reticles. In current study, our focus is on further improvement of this haze solution and the ultimate goal is to reduce the haze generation effectively, but also economically. First, we use ultra low outgas material, antistatic PEEK, as the material of reticle carrier to perform the study and investigate its effect on haze generation. The total outgas data, leaching, electrical field shielding, and surface resistance data of different polymer materials are also compared. Secondly, we optimize the purging flow rate to reduce the running cost, but also maintain the performance. Our approach is to design purge nozzles, which can create a smooth flow field inside reticle SMIF pod (RSP) and make the maintenance of an ultra clean RSP environment with the smallest flow rate be possible. The results show the PEEK RSP with newly designed purge nozzles can provide great haze prevention result with a lower flow rate. Detailed data is provided and compared with previous design. By using this new solution, the number of wafers printed without haze development on reticles can be up to 300,000 wafers, and the maximum exposure dosage can be up to 1.2×10⁹ mJ/cm² without the detection of any printable haze. The average wafer printed before cleaning of reticle was more than 170,000 wafers. This is a significant improvement to delay the generation of haze on reticles. The comparison of N₂ / XCDA performance based on wafer exposure shows that no significant difference can be observed.