Browsing by Author "Chou, SY"

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Anti-reflection strategies for sub-0.18-mu m dual damascene structure patterning in KrF 248nm lithography
(1999)
Chou, SY
;
Wang, CM
;
Hsia, CC
;
Chen, LJ
;
Hwang, GW
Finding high performance and low cost anti-reflection strategies is a common goal for all photolithographers. This task is getting tough for dual damascene process than the metal-etch process because the oxide thickness variation enhances the thin film interference effect. In this paper, different ARC strategies using organic and inorganic material were examined to compare their CD control performance in sub-0.18 mu m dual damascene structure for KrF 248nm lithography. The organic bottom ARC (BARC) achieves reflectivity control through modulating its thickness. The first and second minimal points in BARC swing curve were chosen as the film thickness to be evaluated. The inorganic ARC, which referred to dielectric ARC (DARC) using PECVD silicon oxynitride (SiOxNy) in this article, was investigated with single layer and double layer structures. The double-layer DARC structure consists of two layers with different extinction coefficient K values. The optimal refractive index (N, K) and thickness of each ARC structure were calculated from some available photolithography simulators. A PECVD process for DARC growth chat provides easily tunable range of refractive index and thickness was established to meet the DW process requirement fr om simulation. The performances of each ARC structure were evaluated on patterning 0.18 mu m trench and 0.20 mu m via in back-end-of-line (BEOL) dual damascene process. It showed that the double-layer DARC provided the most effective CD control ability among these ARC structures. The double-layer DARC should be one of the most potential candidates for sub-0.18 mu m dual damascene process.
Evaluating the impact of spherical aberration on sub-0.2-micron contact/via hole patterning
(2001)
Chou, SY
;
Lou, JC
;
Lai, CM
;
Liang, FJ
;
Chen, LJ
Several super resolution techniques, such as phase-shifting mask (PSM) and off-axis illumination (OAI), have been reported to extend the resolution limit and increase the depth-of-focus ( DOF) of optical lithography. However, these techniques provide less immunity to spherical aberration than the conventional approaches like chrome binary mask and low coherent illumination. Best focus position shift is the most well known anomalous phenomenon resulted from spherical aberration. In this paper, the origin of best focus shift is explained in pictorial and analytical forms. The phenomenon is evaluated by observing the exposure-defocus windows of sub-0.2mum hole patterns from an 18 % transmission rim-type attenuated PSM combined with several types of illumination. Under high coherent illumination, severe focus shift was observed in sparse patterns as strong phase-shifting effect is applied. For dense hole patterns,, OAI results in abrupt focus position variation at specific pattern pitch. The experimental results show that spherical aberration would induce best focus shift, distortion of process windows, loss of DOF, and shrink-age of iso/dense process window overlap. Two approaches were proposed to suppress the impact of spherical aberration. One is introducing proper amount of phase bias in attenuated PSM to adjust the wave aberration in the lens. The other more feasible method is using a customized illumination. A synthesized illumination aperture was proposed to compensate the focus shift. Excellent lithographic performance was obtained in the experiment from this method.
Focus latitude enhancement of symmetrical phase mask design for deep submicron contact hole patterning
(2001-11-01)
Chou, SY
;
Lou, JC
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Chen, LJ
;
Shiu, LH
;
Liu, RG
The mechanism of focus latitude enhancement for contact/via hole printing is explained by approximating the axis intensity distribution of an image as a series of cosine functions to characterize the interference between each pair of diffraction beams. It is found that a phase-shifting mask (PSM) with symmetrical assist features improves the depth of focus (DOF) by introducing destructive interference to counterbalance the intensity fluctuation from constructive interference as defocus. A simple formula was derived to represent the capability of focus latitude enlargement. It shows that the extent of enhancement depends on the exposure wavelength and numerical aperture of a projection lens only. Increasing the degree of partial coherence degrades the focal range enlargement because a larger illumination angle elongates the destructive interference pattern in the optical-axis direction to weaken its ability for intensity compensation. On the other hand, the lack of constructive interference in dense hole imaging fails the mask pattern transfer, which limits the application of the phase-shifting method to pattern pitch greater than root2lambda/NA. A tiny amount of spherical aberration results in prominent asymmetrical defocus behavior because the wave deformation in the projection lens shifts the distribution of constructive and destructive interference patterns to opposite defocus directions. The printing characteristics of 0.17 mum contact using an 18% transmission, rim-type attenuated phase-shifting mask are investigated to corroborate our analysis of defocus behavior. The dependence of depth of focus on pattern duty is stressed to elucidate the difference in mechanisms of focus latitude improvements for a sparse hole and periodic dense hole. (C) 2001 American Vacuum Society.
Parallel DSMC simulation of a single under-expanded free orifice jet from transition to near-continuum regime
(2005-11-01)
Wu, JS
;
Chou, SY
;
Lee, UM
;
Shao, YL
;
Lian, YY
This paper describes the numerical analysis of the flow structure of a single underexpanded argon free jet issuing into a lower-pressure or vacuum environment using the parallel three-dimensional direct simulation Monte Carlo (DSMC) method employing dynamic domain decomposition. Unstructured and tetrahedral solution-based refined mesh depending on the local mean free path is used to improve the resolution of solution. Simulated Knudsen numbers of the stagnation conditions based on orifice diameter, Reynolds numbers based on the conditions at the orifice exit, and stagnation-to-background pressure ratios are in the range of 0.0005-0.1, 7-1472, and 5-infinity, respectively, where "infinity" represents vacuum condition in the background environment. Results shou, that centerline density decays in a rate proportional to the inverse of the square of the axial distance (z(-2)) from the orifice for all ranges of flow in the current stud's The more rarefied the background condition is, the longer the z(-2)-regime is. In addition, a distinct flow structure, including barrel shock, Mach disk and jet boundary, is clearly identified as the Knudsen number reaches as low as 0.001. Predicted location and size of Mach disk in the near-continuun limit (Kn = 0.001, 0.0005) are found to be in reasonable agreement with experimental results in the continuum regime.