Hisashi Nishinaga

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.

An aberration control of projection optics for multi-patterning lithography

In order to realize further improvement of productivity of semiconductor manufacturing, higher throughput and better imaging performance are required for the exposure tool. Therefore, aberration control of the projection lens is becoming more and more important not only for cool status performance but also heating status. In this paper, we show the improvements of cool status lens aberration, including scalar wavefront performance and polarization aberration performance. We also discuss various techniques for controlling thermal aberrations including reduction of heat in the lens, simulation, compensating knob, and adjusting method with actual imaging performance data during heating and cooling.

Self-calibration of wafer scanners using an aerial image sensor

To improve both the versatility and stability of leading edge wafer scanners, the functionality of an integrated aerial image sensor has been expanded. The system performance of current wafer scanners is a strong function of the quality of image formation of the projection lens. Current wafer scanners use aerial image sensors for best image plane calibration, illumination telecentricity calibration, coma aberration calibration, and distortion calibration. The aerial image sensor is used not only for a scanners self-calibration but also during the projection lens manufacturing purposes. The slit-scan type aerial image sensor is used for measurement of the intensity distribution of the aerial images. This type of the image sensor can detect the intensity distribution of the aerial image from 110nm L/ S to 6micrometers L/ S. Therefore this aerial image sensor covers most aerial image measurement requirements. In this paper we will focus on the aerial image measurement for self-calibration purposes and their actual performances. We evaluate the actual performance of illumination telecentricity and coma aberration measurement. Evaluation is based upon not only measurement repeatability but also its agreement with resist image measurement results.

Polarized light for resolution enhancement at 70 nm and beyond

We have investigated the impact of light polarization on the imaging performance of a high NA 193nm wafer scanner. This system allows the usage of well linear polarized light for imaging at several illumination modes. The printing performance of critical DRAM features have been investigated for various mask types like attenuated, chrome-less and alternating PSM using polarized and depolarized light. Moreover various illumination schemes such as circular, cross-pole and dipole illumination have been tested for different light polarization settings. An improvement of the resolution and the process window, and a reduction of the mask error enhancement factor compared to depolarized light have been obtained using appropriately chosen linear polarization. The influence of light polarization on the proximity behavior has been studied. Under investigation was specifically the proximity behavior change for mask features with attached sub-resolution assist features. Experimental data of the influence of the polarization on the intra-field CD uniformity of densely packed features of critical DRAM layers are presented. Based on the obtained measurement data the CD control improvement potential has been analyzed. Our experimental and simulation results verify that light polarization has resolution enhancing potential already for features of the 70nm node and - of course - beyond.

An intelligent imaging system for ArF scanner

The k1 factor continues to be driven downwards, even beyond its theoretical limit 0.25, in order to enable the 32 nm feature generation and beyond. Due to the extremely small process-window that will be available for such extremely demanding imaging challenges, it is necessary that not only each unit contributing to the imaging system be driven to its ultimate performance capability, but also that the final integrated imaging system apply each of the different components in an optimum way with respect to one another, and maintain that optimum performance level and cooperation at all times. Components included in such an integrated imaging system include the projection lens, illumination optics, light source, in-situ metrology tooling, aberration control, and dose control. In this paper we are going to discuss the required functions of each component of the imaging system and how to optimally control each unit in cooperation with the others in order to achieve the goal of 32 nm patterning and beyond.

Imaging control functions of optical scanners

For future printing based on multiple patterning and directed self-assembly, critical dimension and overlay requirements become tighter for immersion lithography. Thermal impact of exposure to both the projection lens and reticle expansion becomes the dominant factor for high volume production. A new procedure to tune the thermal control function is needed to maintain the tool conditions to obtain high productivity and accuracy. Additionally, new functions of both hardware and software are used to improve the imaging performance even during exposure with high-dose conditions. In this paper, we describe the procedure to tune the thermal control parameters which indicate the response of projection lens aberration and reticle expansion separately. As new functionalities to control the thermal lens aberration, wavefront-based lens control software and reticle bending hardware are introduced. By applying these functions, thermal focus control can be improved drastically. Further, the capability of prediction of reticle expansion is discussed, including experimental data from overlay exposure and aerial image sensor results.

Effect of azimuthally polarized illumination imaging on device patterns beyond 45nm node

For an ultra-high numerical aperture (NA), such as that exceeding 0.9, the p-polarized component of light that has passed through a region at the limit of the NA of a high-NA lithography tool, degrades contrast because of the so-called vector imaging effect, and is therefore detrimental to the formation of optical images. Polarized illumination removes the effect of the p-polarized light component and provides illumination light composed of s-polarized light. The higher the NA, the greater are the benefits of polarized illumination. Therefore, in lithography at the 45-nm node and below, polarized illumination is viewed as an indispensable technology. We explore the applicability of polarized illumination to device manufacturing processes at the 45-nm node and beyond, with a focus on the utilization of azimuthally polarized illumination, which enables one mask exposure. The data used in this research were obtained through imaging simulations and experiments using a dry lithography tool equipped with a 0.92-NA projection lens. In imaging simulations using a lithography simulator, the application of azimuthally polarized illumination improved image contrast in resists by approximately 20% for half pitch (HP) 65-nm dense patterns. As a result, device patterns showed enhanced robustness with respect to exposure dose error; extended process windows; and reduced mask error enhancement factor (MEEF), line edge roughness (LER), and line end shortening (LES). This paper examines the results of experiments conducted using imaging simulations and lithography tools on other product device like patterns (besides special patterns in which benefits can clearly be expected, including dense (L/S) patterns), and reports the results.

Source mask optimization study based on latest Nikon immersion scanner

The 2x nm logic foundry node has many challenges since critical levels are pushed close to the limits of low k1 ArF water immersion lithography. For these levels, improvements in lithographic performance can translate to decreased rework and increased yield. Source Mask Optimization (SMO) is one such route to realize these image fidelity improvements. During SMO, critical layout constructs are intensively optimized in both the mask and source domain, resulting in a solution for maximum lithographic entitlement. From the hardware side, advances in source technology have enabled free-form illumination. The approach allows highly customized illumination, enabling the practical application of SMO sources. The customized illumination sources can be adjusted for maximum versatility. In this paper, we present a study on a critical layer of an advanced foundry logic node using the latest ILT based SMO software, paired with state-of-the-art scanner hardware and intelligent illuminator. Performance of the layers existing POR source is compared with the ideal SMO result and the installed source as realized on the intelligent illuminator of an NSR-S630D scanner. Both simulation and on-silicon measurements are used to confirm that the performance of the studied layer meets established specifications.

Performance of Polarized Illuminators in Hyper NA Lithography Tools

Polarized light illumination is essential for hyper-NA imaging such as immersion lithography. This is confirmed by comparison of optical images between unpolarized light illumination condition and polarized light illumination condition. In this paper, we introduce our polarized light illumination apparatus and some experimental results, which confirm the effect of improvement of the imaging performance by utilization of polarized light illumination. In addition, required quality of the polarized light illumination for hyper NA lithography is discussed