**2.1 Introduction**

According to ITRS Roadmap 2007 Update Version [12], EUVL is currently the most promising candidate for 22 nm half-pitch lithography. The component technologies required for EUVL mass production must be established before the start of mass production of DRAM half-pitch, currently scheduled for 2016. RLS specifications for realizing 22 nm halfpitch resolution were presented at the 7th EUVL Symposium [13] in Lake Tahoe, California, in October 2008.

Fig. 9. RLS specifications targeting 22 nm half-pitch

A resolution of 22 nm half-pitch requires sensitivity of 5 to 10 mJ/cm2 and LER of less than 1.2 nm. At an international conference, it has been pointed out that although resolutions have reached the target value, sensitivity lags, at 15 mJ/cm2, while LER (Line Edge Roughness) is no less than 4 nm. These are the best values achieved to date. Lithography simulations should prove highly effective in advancing the state of current research, given the time required to perform experiments.

The VLES consists of the EUVES-7000 EUV open-frame exposure system, RDA-800EUV development rate analyzer, and Prolith lithography simulator. We used the VLES to compare the sensitivity and development contrast of negative- and positive-type resists with EUV exposure. We also simulated EUV exposures using development rate data for the EUVR-2, which showed the highest development contrast of all resists tested. The results of the experiment suggest that it should be possible to obtain resolutions of 32 nm with L&S patterns and 22 nm with isolated patterns. We also calculated defocus characteristics with a 32 nm L&S pattern. Based on these calculations, we estimate a focus margin of approximately 0.2 μm in defocus width. We believe using the system as described in this paper will permit the development of photoresist materials for EUV and expedite process

development without requiring the purchase of costly EUV exposure equipment.

**2. Simulating EUV Resists (Comparison of KrF and EUV Exposures)** 

According to ITRS Roadmap 2007 Update Version [12], EUVL is currently the most promising candidate for 22 nm half-pitch lithography. The component technologies required for EUVL mass production must be established before the start of mass production of DRAM half-pitch, currently scheduled for 2016. RLS specifications for realizing 22 nm halfpitch resolution were presented at the 7th EUVL Symposium [13] in Lake Tahoe, California,

A resolution of 22 nm half-pitch requires sensitivity of 5 to 10 mJ/cm2 and LER of less than 1.2 nm. At an international conference, it has been pointed out that although resolutions have reached the target value, sensitivity lags, at 15 mJ/cm2, while LER (Line Edge Roughness) is no less than 4 nm. These are the best values achieved to date. Lithography simulations should prove highly effective in advancing the state of current research, given

**1.5 Conclusion** 

**2.1 Introduction** 

in October 2008.

Fig. 9. RLS specifications targeting 22 nm half-pitch

the time required to perform experiments.

The conventional EUVL simulation method involves obtaining parameters by exposing the resist to EUV. However, EUV exposure equipment is costly, and the types of exposure equipment available are limited. For these reasons, we explored the possibility of performing EUVL simulations using parameters obtained with KrF exposures. The idea was that if we detected no significant differences between parameters obtained with KrF and EUV exposures, we could use the simpler KrF exposure method to obtain valid simulation parameters for EUVL. Using EUV resists, we obtained parameters by performing both KrF and EUV exposures, then compared the parameters and simulation results. This chapter discusses this comparison.
