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 9×10<sup>8</sup> mJ/cm<sup>2</sup> 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 1.2×10<sup>9</sup> mJ/cm<sup>2</sup> 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 N<sub>2</sub> / XCDA performance based on wafer exposure shows that
no significant difference can be observed.
Various studies have been published on the formation and prevention of reticle haze; however, yield loss due to reticle
haze is still an issue for most of the IC makers. For a mass production IC manufacturing fab, an easy and practical
solution is needed to prevent haze generation. In this study, we focus on the solution, which can be easily implemented
inside production fab and does not require a total implementation of specific type of gas or equipment. A reticle carrier
with purging function combining with the use of a purge station for purging and storage is used. After implementing this
solution in a 12" DRAM fabrication facility, the number of wafers printed without haze development on reticles protected
by this solution can be up to 150,000 wafers, and this is great achievement in help ramping up the production and also
maintain high yield. This solution has been proven to be effective in reducing the generation of haze.
Haze is a kind of contamination on the surface of mask which observed in the wafer production clean room only on reticles exposed with 193nm or 248nm wavelength process. Analyses have been provided an approach with enhance reticle purging efficiency method for investigating the required purging flow of clean, dry gas to prevent the ingestion of external contaminants into the reticle.
In this study, we investigate the purging parameters theoretically by using natural convection with the purpose of avoiding rupturing the pellicle and expediting the overall purging process as shown in fig.1. Accordingly, a parametric analysis of important geometric variables including the size and number of purging holes is performed. Our study then process to identify the optimized parameters (number of holes, position of holes, purging flow rate) by using computational fluid dynamic (CFD) simulation. As indicated by our results, a parametric analysis investigating the effect of the pellicle variables shows that the purging time were sensitive to the number of purging or vent holes. As shown in fig.2 and fig.3, the total purging time can be reduced by increasing the number of purging or vent holes from 2 to 4. An increase in the number of purging holes from 2 to 4 help shorten the purging time by 20 to 40seconds. So the production throughput can be expected to rise while the consumption of gas can be reduced.