Takehito Kudo

Development of polarized-light illuminator and its impact

Nikon has developed an illuminator with special options for RET (Resolution Enhancement Technique). For one of the solutions of RET, Nikon has pursued the development of a loss-less polarized illumination system. When the polarization direction is the same as the direction of the printed pattern, this technique improves image contrast and extends the process margin. We have simulated the impact of the RET with polarized illumination, in the case of dipole illumination and phase-shift masks, and we have estimated the dominant parameters for high performance polarized illumination. In addition, we have constructed a polarized-light illuminator and installed it in an ArF full-field scanner. We have measured and optimized the degree and distribution of polarization at the wafer plane with a special tool, and we have investigated image performance with polarized dipole illumination. Results show that the new polarized-light illuminator has extended the process margin, especially with respect to dose latitude. The results of the image simulations and experiments will be reported.

Challenging to meet 1nm iso-dense bias (IDB) by controlling laser spectrum

According to the ITRS Roadmap, for 45nm Node (as 65nm Half Pitch), the requirement of Gate CD Control is defined as 2.6nm. One of the most challenging CD errors is Iso-Dense Bias (IDB). Assuming 40% of CD errors are dominated by IDB, IDB should be less than 1nm. In general, the majority of IDB is due to: primarily, exposure tool- related factors such as aberrations, flare, and sigma fluctuation, and secondly, the change in photoresist characteristics. However, due to the rapidly increasing usage of ArF exposure tools, Band Width (BW) characteristics of the laser source is an additional factor whose contribution is becoming more critical. Ideally, BW is monochromatic, thereby not affected by chromatic aberration change. However, in reality, the BW exhibits a shape of spectral distribution with a finite width. This study describes experimental and simulation results for E95%, and how performance of both CDs and Laser is dependent on E95% in order to meet 1nm of IDB towards 45nm Node. -IDB vs. E95% -CD at through pitch vs. E95% -Process Latitude vs. E95% -DOF -EL -Pattern shortening vs. E95%

Lens aberration control for fine patterning with PSM

The impact of lens aberration on linewidth control and pattern shift is investigated with aerial image simulation using Zernike sensitivity method through focus to secure sufficient depth-of-focus (DOF). We found 0 and even theta component has large amount of impact on linewidth control in defocused condition due to best focus shift. This phenomenon makes degradation of DOF performance. For actual phase shift mask (PSM) application, DOF performance is very important, so as to reduce the focus shift by lens aberration, and the lens is controlled with pre-correction of best focus deviation in the field. This method is effective to obtain large DOF with PSM.