Ryuji Koitabashi

Study and improvement approach to 193-nm radiation damage of attenuated phase-shift mask

The exposure tools have been advanced for finer patterns and higher throughput. However, it causes the increase of accumulation of exposure dose on mask, which induces the mask CD growth. This issue has been reported as the radiation damage and brought the low yield of device chips [1, 2, 3]. As the solution, the radiation damage can be reduced by the ultra extreme dry air in exposure tool [4]. It is difficult to adopt dry air to all exposure tool due to cost. In this work, we tried to solve the radiation damage from photomask making approach. The attenuated phase-shift mask (att. PSM) was chosen for this evaluation because its damage is severest. The test plates of att. PSM were exposed by ArF laser, and the amount of CD degradation and the composition change in damage area were investigated. By the analyses of TEM and EDX, it was confirmed that the root cause of radiation damage is oxidation of MoSi film. Therefore, the approaches from mask process and material were tried to prevent MoSi film from oxidation. As a result, the approach from mask material, especially modification of MoSi film is effective. And the characteristics of new MoSi film, such as CD performances, cross section, and cleaning durability, were compared with conventional att. PSM. These results show the characteristics of two masks are equivalent. Att. PSM with new MoSi film is promising solution to improve radiation damage.

Attenuated phase-shift mask with high tolerance for 193nm radiation damage

In the semiconductor technology using the 193nm ArF excimer laser, the problem of radiation damage on photomask becomes more serious. This phenomenon is regarded as serious issue for semiconductor device fabrication. Some approaches have been tried to prevent the radiation damage. One of reports indicates that the radiation damage can be reduced by using an exposure tool with ultra clean extreme dry air [1]. However, it is difficult to adopt dry air into all exposure tools due to high cost. In our previous work, two facts were ascertained; radiation damage is caused by MoSi film oxidation, and depends on MoSi film composition [2]. In this paper, radiation damage was tried to decrease by MoSi film modification of att. PSM. MoSi film composition for PSM is optimized in consideration of cleaning durability, mask defect repair and processability. The new PSM is named AID (Anti Irradiation Damage). Radiation damage of AID PSM can be improved by 40[%] from conventional PSM. Cleaning durability can be also improved by AID PSM. The other evaluation items such as CD performance, cross section, defect level and repair, are equal between the AID PSM and conventional one. Additionally, the lithography performances by simulation of AID PSM are equivalent with that of conventional PSM. Therefore, it can be expected that there is no difficulty in converting conventional PSM into AID PSM. From these evaluation results, development of AID PSM was completed, and preparation for production is now going.