Takehiro Kondoh

Defectivity reduction studies for ArF immersion lithography

Immersion lithography is widely expected to meet the manufacturing requirements of future device nodes. A critical development in immersion lithography has been the construction of a defect-free process. Two years ago, the authors evaluated the impact of water droplets made experimentally on exposed resist films and /or topcoat. (1) The results showed that the marks of drying water droplet called watermarks became pattern defects with T-top profile. In the case that water droplets were removed by drying them, formation of the defects was prevented. Post-exposure rinse process to remove water droplets also prevented formation of the defects. In the present work, the authors evaluated the effect of pre- and post-exposure rinse processes on hp 55nm line and space pattern with Spin Rinse Process Station (SRS) and Post Immersion Rinse Process Station (PIR) modules on an inline lithography cluster with the Tokyo Electron Ltd. CLEAN TRACKTM LITHIUS TM i+ and ASML TWINSCAN XT:1700Fi , 193nm immersion scanner. It was found that total defectivity is decreased by pre- and post-exposure rinse. In particular, bridge defects and large bridge defects were decreased by pre- and post-exposure rinse. Pre- and post-exposure rinse processes are very effective to reduce the bridge and large bridge defects of immersion lithography.

Comparison of Flow Models for Photoresist Behavior at Contact Holes in Thermal Flow Processes

The behavior of the photoresist between contact holes during the thermal flow process was investigated. When the photoresist width was smaller than 200 nm, the amount of shrinkage of the contact hole increased almost linearly with the photoresist width between contact holes. However, the amount of shrinkage was saturated and rarely changed with the photoresist width when the resist width was larger than 400 nm. We examined three models to investigate this phenomenon. The first one is the simple one-dimensional model, and the second one is the viscoelastic model with constant fluid viscosity. The third one is the viscoelastic model for the Bingham fluid. We calculated the amount of shrinkage of the contact hole vs the photoresist width, and the values calculated using the viscoelastic model for the Bingham fluid was consistent with the measured values. We also synthesized a contact-hole image by expanding this one-dimensional model to two dimensions. The average total hole radius error between the measured and the synthesized image was less than 7 nm, and the calculated image was almost the same as the measured one. We concluded that the viscoelastic model for the Bingham fluid is adequate for describing the photoresist behavior in the thermal flow process.

Characteristics of negative-tone chemically amplified resist (MES-EN1G) for 50-keV EB mask writing system

This report shows characteristics of a new negative-tone CAR (MES-EN1G), that we have developed. The CAR is adopted new cross linker that is concentrated more at the bottom of the resist film. The new cross linker raises cross-linking reaction rate at the bottom of resist film. Therefore, undercut profile on chromium film is not observed and vertical resist profile is obtained. The CAR can resolve 150 nm L and S pattern, and so the CAR has the ability to form assist bar feature. Vertical chromium profile is obtained and residual resist thickness is 260 nm after reactive ion etching. The CAR has enough etching durability. Regarding post exposure delay stability in vacuum (PED(Vac.), CD change is 0.3 nm even if exposed mask is left in vacuum for 10 hours. Dependence on PEB temperature is 3.0nm / degrees C. Regarding post coating delay (PCD) effect, the maximum CD error is within +/- 5.0 nm even though masks coated with the CAR are left in a conventional blanks case for 39 days. Dependence on fogging effect is 4.1 nm /percent. Opaque line CD uniformity (3s) of 600 nm L and S pattern in local area with MES-EN1G and with positive-tone CAR is 4.6 nm and 11.9 nm, respectively.

Advantages of using the CAR for photomask manufacturing

This report shows characteristics of the chemical amplified positive-tone resist (CAR) we have developed for 50keV electron beam (E-beam) mask writing system. The CAR includes newly developed polymer. Including the polymer, CD change is negligible small even if exposed mask is left in vacuum for dozens of hour. 0.4, 0.3, 0.2 micrometers L&S resist pattern profiles at a dose of 7.5micrometers C/cm2 and Cr pattern profiles after reactive ion etching are printed. Dependence on PEB temperature is 3.4 nm / degree(s)C. As post coating delay effect (PCD), CD change can not be observed for 53 days. And characteristics of the CAR were compared with that of ZEP7000 (Nippon Zeon Co., Ltd.). Dose latitude of the CAR is about two times of that of the other. Writing time of photomask with the CAR is about half of that the other. Above mentioned, the CAR has ability for photomasks manufacturing. So, we have succeed in making 0.18micrometers design rule photomasks with the CAR and 50keV EB writing system.