Boo-Yeon Choi

Focusing and leveling system using position-sensitive detectors for the wafer steppers

An optical focus and leveling system for ETRI KrF excimer laser stepper is developed using position sensitive detectors (PSD) and optical magnification method. This type of detection method showed focusing and leveling accuracies of about +/- 0.1 micrometers and +/- 1.0 arcsec (+/- 0.5 X 10-5 rad) respectively. Also, we confirmed experimentally the autofocus system has +/- 0.15 micrometers signal stability within the controlled temperature range of +/- 0.1 degree(s)C. In this paper, we report the design concepts of the focusing and leveling system and the characteristics of the system parameter applied to ETRI KrF excimer laser stepper.

Dry etching of Cr layer and its loading effect

The Cr etch rate is affected by Cr density to be etched at the photomask and the Cr loading effect has become main obstacles to overcome for the next generation photomask process. Different mask-to-mask and within-mask pattern densities have made difficult to control the final CD (critical dimension). We have tested loading effect using binary Cr mask with ZEP7000 (3000 angstroms) photoresist. The loading effect was evaluated for the masks fabricated at the same process condition with the different mask-to-mask Cr loading and different within-mask Cr loading. The CD variations of dark field and clear field were observed and the phenomenological approach was proposed for the loading effect by some simplified equations.

Applications of MICP source for next-generation photomask process

As critical dimensions of photomask extends into submicron range, critical dimension uniformity, edge roughness, macro loading effect, and pattern slope become tighter than before. Fabrication of photomask relies on the ability to pattern features with anisotropic profile. To improve critical dimension uniformity, dry etcher is one of the solution and inductively coupled plasma (ICP) sources have become one of promising high density plasma sources for dry etcher. In this paper, we have utilized dry etcher system with multi-pole ICP source for Cr etch and MoSi etch and have investigated critical dimension uniformity, slope, and defects. We will present dry etch process data by process optimization of newly designed dry etcher system. The designed pattern area is 132 by 132 mm2 with 23 by 23 matrix test patterns. 3 (sigma) of critical dimension uniformity is below 12 nm at 0.8 - 3.0 micrometers . In most cases, we can obtain zero defect masks which is operated by face- down loading.

Loading effect parameters of dry etcher system and their analysis in mask-to-mask loading and within-mask loading

The Cr etch rate is affected by Cr density to be etched at the photomask. Different mask-to-mask and within-mask pattern densities have made difficult to control the final CD. We have tested loading effect using binary Cr mask with ZEP7000 photoresist. The loading effect was evaluated for the masks fabricated at the various dry etch conditions with different within-mask Cr loading. The Cr etch rate and selectivity was observed at various process conditions and relations between parameters of dry etch process and Cr loading were evaluated. The horizontal and the vertical Cr etch rates were investigated and the process parameter dependence on the Cr loading was analyzed. The horizontal and the vertical photoresist etch rates were evaluated for the photoresist loading effect. The cause of mask-to-mask loading and within-mask loading are mainly from Cr loading and photoresists loading, respectively. The Cr loading is mainly affected by source power, pressure, and Cl2/O2 ratio. In our system, within-mask Cr loading is strongly dependent on the process parameters when the selectivity of Cr to PR is below 1. If uniformity and selectivity are acceptable, high DC bias, high ga flow, low pressure, and high Cl2/O2 ratio are recommended to reduce loading effect.

Dry Etching Technology of Cr and MoSi Layers Using High-Density Plasma Source

We have manufactured dry etcher system for photomask process utilized the new plasma source and process optimizations have been done for CD (critical dimension) uniformity and loading effects. The 3 ? of CD uniformity(final CD - develop CD, point by point subtraction) of Cr pattern, with 132 x 132 mm2 area and 11 x 11 pattern arrays, was obtained below 10 nm, where the target CD is 0.8 um clear pattern. Cr and MoSi slopes are 88° ~ 90° , which shows highly anisotropic etch. The selectivity of PR to Cr was over 1.6 at the clear area ratios of < 50 % and the selectivity was mainly affected by oxygen partial pressure and clear area ratio. Phase uniformity for PSM was 180 ± 1° and transmittance uniformity is within 6.3 ± 0.02 %. Validity and probability of dry etcher system to produce next generation photomask were discussed.

Design and development of a prototype excimer-laser-based stepper

This paper describes the design and development of a KrF excimer laser stepper and discusses the detailed system parameters and characterization data obtained from the performance test. We have developed a deep UV step-and-repeat system, operating at 248 nm, by retrofitting commercial modules such as a KrF excimer laser, precision wafer stage and fused silica illumination and 5X projection optics of numerical aperture 0.42. What we have developed, to the basic structure, are wafer alignment optics, reticle alignment system, autofocusing/leveling mechanisms and an environment chamber. Finally, all these subsystems were integrated under the control of microprocessor-based controllers and a computer.

Highly anisotropic etching of phase-shift masks using ICP of CF4-SF6-CHF3 gas mixtures

There is considerable interest in phase shift masks as a route to extending the resolution, contrast, and depth of focus of lithographic tools beyond what is achievable with the normal chrome mask technology. A problem that has so far hindered the introduction of phase shift masks has been the difficulty of phase and transmittance control when a phase shift mask is applied to practical use. Also, to apply phase shift layer (MoSiON), it remains that effects several critical mask parameters including sidewall slope, surface roughness, and critical dimension. For these reasons, this process requires a high degree of control of the etch process of shift layer. So in this paper, we described a technique for the fabrication of phase shift masks by etch rate of a MoSiON layer. Etching experiments of MoSiON were performed using different fluorinated gas mixtures. Four of them, CF4/O2/He, SF6/O2/He, CHF3/O2/He and Cl2/CF4/O2/He were chosen for high etch rate, sidewall slope, and surface morphology. Each added gases had a unique property on the etch rate, anisotropy, surface roughness and sidewall morphology. Result indicates that vertical slope and smooth surface are obtained using the Cl2/ CF4/O2/He and SF6/O2/He mixture. With increasing O2 flow rate to the SF6/O2/He Plasma and added Cl2 gas to the CF4/O2/He Plasma, the MoSiON etching profile becomes anisotropic without undercutting and trench profile. It is probably due to both increasing etch rate and sidewall passivation of Cl2 ion flux. When Cl2 gas was added to the CF4/O2/He Plasma, the small addition of chlorine was enough to protect the exposed sidewall of the undercutting, therefore, higher flow rate of chlorine had to be added to protect the sidewall of the undercutting by forming a sidewall passivation layer. These results show that both increasing O2 flow rate to the SF6/O2/He Plasma and the addition of Cl2 to the CF4/O2/He plasma are necessary in order to achieve a vertical profile and a smooth surface morphology.

Application of multiple-wavelength absorption endpoint system in photomask dry etcher

Recently dry etcher system is a key process technology in preparation of photomask for next generation microelectronic device and endpoint detection system is an important part of the dry etch process, because mask CD control of Cr mask is more critical issues than before. In this paper, we describe real time endpoint system which is operated by optical emission multiple wavelength absorption for dry etch process of binary photomask. The end point detection system absorbs optical emission signal in real time, using optical cable from plasm chamber in dry etcher, and the signal is absorbed 200-800nm wavelength for a lot of grating manufactured by etch angel. The signal detects endpoint of process by association of one or several wavelength. We have tested newly developed EPD system and installed at PKLs dry etcher system, using various open area Cr mask with ZEP70000 resist. This study showed that multiple wavelength absorption technique is enough to detect endpoint down to 2 percent Cr loading masks and the EPD signal reproducibility was within 2 percent of EPD time at the same patterned masks.

Plasma etch of Cr masks utilizing TCP source for a next-generation plasma source

In the photomask manufacturing, dry etch process is one of important process and the etch process mainly affects CD uniformity, skew, and Cr slope. We will present newly developed dry etcher system using TCP (transformer coupled plasma) source and its Cr etch performance. We will investigate the performance of TCP source for the uniformity, linearity, and loading effects. CD uniformity of 0.8 um Cr space pattern at 11 x 11 arrays with 135 x 135 mm2 area is below 8 nm and 15 nm in 3 sigma in case of ZEP7000 and IP3500 as resists, respectively. The skew (ASI - ADI) linearity of clear and dark CDs from 0.4 um to 2 um is below 35 nm in case of IP3500. The Cr loading characteristics of TCP source is investigated and the etch process parameter dependence on the loading is verified.