As the feature size decreases to 90nm and 65nm, the role of phase shift mask as a RET method becomes more and more important. Although alternating PSM has been one of the possible methods to improve the resolution, however, the difficulty of mask manufacturing prevent us from adopting the technology. One of the main issues is microloading effect including RIE lag, pattern density effect that cause especially the imbalance of phase shifting due to the etch depth difference in the patterns with different CD size and different pitch as the feature size downs to subhalf micron. This leads to the space CD difference with the DOF variation in the wafer image.
In this paper, characteristics of RIE lag and other phenomenon were evaluated with the DOE method that included such parameters: source power, bias power and pressure. Etch depth difference was confirmed with AFM measurement and calculated to phase shift angle. Results were analyzed with statistical method and major effects and interaction effects were found.
The etch characteristics of MoSiON were investigated when chlorine was utilized as the main etch gas in an ICP dry etch system. MoSiON and glass are easily etched with fluorine-based plasmas such as: CF4, SF6, and CHF3. These plasma chemistries generate carbon-containing and fluorine-containing polymers as byproducts, which can be responsible for generating particles or hard defects on the mask during the MoSiON etch step. They also cause damage to the glass surface, manifesting themselves as a phase or transmission errors.
In this paper, new plasma chemistry was applied to etch MoSiON, and its characteristics were examined focusing on the effects of each parameter. These parameters included: ICP power, bias power, pressure, and gas concentration. It is difficult to etch MoSiON with good selectivity to Cr because MoSiON and Cr can be etched simultaneously after the photoresist layer has been removed. It will be shown how to increase the selectivity to Cr using an optimized process leveraging a new hardware modification. The etch characteristics of the chlorine plasma will also be compared to that of fluorine plasmas. It was found that using a chlorine plasma to etch MoSiON instead of a fluorine plasma yields good etch properties and good morphology.
Embedded-attenuated phase shift masks (EAPSMs) have been an indispensable enabling technology for <130 nm node device fabrication. The precise etching of MoSiON is a key process in high quality phase shift mask manufacturing. Fluorine-based plasma chemistry has been used widely to date, but it is difficult to control CD (Critical Dimension) and phase uniformity. This stems mainly from the large Cr undercut and surface roughness due to the reaction of fluorine radicals with the phase shifting layer. In this paper, etch characteristics of the MoSiON layer using CF4, O2, and He in an inductively coupled plasma (ICP) were examined for the manufacturing of phase shift masks for 90-nm node design rules. The dependency of etch parameters such as ICP power, bias power (DC bias voltage), pressure, CF4 concentration, and O2 concentration on the etch properties of MoSiON were tested. We have investigated vertical slope, surface morphology, and minimum CD bias. This optimized process condition showed that intra-mask phase uniformity was below 1% (3-sigma) over a 135 mm × 135 mm mask area and transmittance uniformity was 8.68% ± 0.09%. CD uniformity was 5.5nm (3-sigma), CD linearity was 5.0nm over 300nm to 1300nm, and Cr-to-MoSiON CD bias was 2.0nm. The MoSiON profile was nearly vertical and the surface morphology was very clean.
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.
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.
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.
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.
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.
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.
This paper describes a design study of the KAO (Korea Astronomy Observatory) 1m telescope. The telescope uses an F/2.7 zerodur primary mirror which has a double arch back contour shape. For the zenith pointing, the primary mirror is to be held by a 6-point axial support system at the back surface. For Horizon, a 3-lateral support system is to be designed and located at the center of gravity of the mirror. In this paper, a parametric design study of a double arch back contour shape is to be performed to meet an optical surface deflection requirement, a surface RMS wavefront error of (lambda) divided by 10, using the finite element program, ANSYS, for the mechanical surface deformation, and the PCFRINGE program for the evaluation of the optical performance. Additionally, the static and modal frequency analysis of the truss structure and yoke were performed.