Jeung-woo Lee

Detailed analysis of capability and limitations of CD scatterometry measurements for 65- and 45-nm nodes

Control of critical dimension (CD) of 65nm and beyond nodes is the hot issue now. As feature size reduces it becomes difficult to measure CD precisely. A lot of factors can influence on accuracy of measurement. Scatterometry method is applicable for both production and development purpose, and can be used for in-situ or ex-situ control. In this work we study influence of CD non-uniformity and sidewall angle as well as influence of parameters of measurement system on precision of result. TE, TM and unpolarized light with different angle of incidence on grating structure is considered to find the best conditions for CD measurements of 65 and 45nm nodes. Rigorous coupled-wave analysis (RCWA) is used for theoretical spectra calculation and least square method for results extraction. Reflected spectrum from structures containing non-uniform or uniform CDs with variation of sidewall angle is compared with the set of theoretical spectra, and CD value with layer thickness is extracted in the same way as in the real experiment. It is shown that CD non-uniformity and sidewall angle can be estimated through comparison of results obtained with different polarization state of light. Best choice of polarization, angle of light incidence, range of wavelength for spectrum measurement and parameters of library for spectrum analysis are obtained in order to provide precise and fast scatterometry measurement for 65 and 45nm nodes mask structures.

The choice of mask in consideration of polarization effects at high NA system

Strong resolution enhancement techniques (RETs) are highly demanded to overcome the resolution limit of sub-60nm lithography. ArF immersion lithography may be the best candidate for sub-60nm device patterning. However, the polarization effect becomes more prominent to degrade the image quality in high NA immersion lithography as the feature size shrinks. Therefore, it is important to understand the polarization effect in the mask. The induced polarization effect shows the different aspects between the binary and the attenuated phase shift mask (PSM). In this paper, we considered the effects of polarization state as a function of mask properties. We evaluated the performances of the binary mask and the attenuated PSM by using simulation, AIMSTM (Aerial Image Measurement System) tool, and real wafer printing. We find out that there are no differences between the binary mask and the attenuated PSM in view of image contrast and mask error enhancement factor (MEEF).

Optical performance enhancement technique for 45-nm-node with binary mask

As the pattern half pitch on the mask gets shorter than the wavelength by smaller device design rule, 3-D effect of the mask pattern topology becomes greater. The resolution approaches to that of the attenuated Phase Shift Mask (attPSM), when pattern size is smaller than 45 nm node. The binary mask was therefore selected due to the simple fabrication process and the advantage with no-haze, and its performance was evaluated both numerically and experimentally by newly designing the mask structure that may have mask immersion effects. This new mask can be made by depositing transparent oxide materials on a conventional patterned binary mask. When the change of NILS (Normalized Image Log Slope) was checked quantitatively according to duty ratio and oxide thickness, the NILS increased more than 10% on the average from the simulation and about 10-30% from the experiment, when compared with the binary mask. In other words, the mask structure with the transparent oxide layer improves the NILS and has the advantage in the DOF margin. Since only the deposition process is required after the binary mask is made, the manufacturing is relatively simple.

Which Mask is Preferred for Sub-60 nm Node Imaging?

ArF immersion lithography may be the best candidate for sub-60 nm device patterning. However, the polarization effect is the most prominent root cause for the degradation of the image quality in high numerical aperture (NA) immersion lithography as the feature size shrinks. Therefore, it is important to understand the polarization effect in the mask. It is common knowledge that a small mask pattern is considered as the wave guide of transmission light. The induced polarization effect shows the different aspects between the conventional mask and the attenuated phase-shift mask (PSM). In this paper, we considered the effects of polarization state as a function of mask properties. The aerial image depends on the polarization states induced by the mask. We evaluated the performances of the conventional mask and the attenuated PSM by using the Solid-ETM simulation and AIMSTM (Aerial Image Measurement System) tool along with real wafer printing.