A simple graphic analysis technique named the illumination chart method is introduced to aid the customization of the illumination aperture filter for synergistic combination with a high transmission rim-type attenuated phase-shifting mask (PSM) for deep submicron contact hole printing. This graphic method gives direct visualization of the relationship between the interference condition in the pupil and the incident angle of illumination. The working ranges of oblique illuminations with different numbers of diffraction beams taking part in imaging can be easily clarified by this graphic method, which explains the dependence of depth of focus (DOF) on pattern duty. A customized illumination aperture filter (CIF) is synthesized by collecting the effective source elements for every pattern pitch to remedy the inability of the attenuated PSM for dense patterns. To preserve the merits of off-axis illumination to dense patterns and on-axis illuminations to sparse patterns in a single exposure, the illumination chart suggests a zeroth-order-reduction mask design for dense hole pattern. We applied this integrated resolution enhancement technique to 0.17 μm contact hole printing in 248 nm wavelength, 0.55 numerical aperture optics. The experimental results show our CIF illumination not only balances the DOF enhancement throughout the pattern pitches but also suppresses the best focus shift due to spherical aberration.
In an attempt to develop the dual damascene process in 0.13 micrometer design rule, the trench optics, resist usage, reflectivity control and BARC strategy for 0.18 micrometer S/L on 0.20 micrometer via dual damascene process are discussed. The difficulty of 0.18 micrometer trench process will be concentrated by two reasons: First, the trench optics is totally different from the traditional L/S patterns either observing the pupil plane wave vector or the aerial image versus defocus, it contains the intrinsic limitation to drive and enough process DOF. Secondly, the PR residues remain in via due to the weak light incidence into via as soon as trench exposure. The side issues are the MEEF problem in dark field exposure and lens aberration problem enhanced in the use of PSM or some kinds of special customized illumination filter CIFs. As a result, the negative resist together with NA equals 0.55, (sigma) equals 0.8, annular 1/2 illumination were applied, it reveals that all mentioned issues are properly compromised by this optimized condition. It is also found that the PR window and profile is quite sensitive to substrate acidity and reflectivity. When BARC protecting coating and reflectivity control problems are taken into account simultaneously, the thin conformal BARC and fully filled polymer on dual SiOXNY underlayer are introduced to get a good profile and CD control. Experimental results exhibit the feasibility in manufacturing.
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-0.2micrometers 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 shrinkage 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.
High NA illumination system and off-axis illumination (OAI) have been shown as two of the most practical resolution enhancement techniques (RET) available for micro-lithography. However, these two illumination approaches may reduce the DOF of iso-patterns. To overcome this problem, scattering bar (SB) assignment has been wildly used. In this paper, the discussions are focused on SB variables of iso-features. The most important variable of SB usage is where is the suitable assignment position. A simply efficient rule has been found to easily catch the optimal position of SB assignment. For OAI illumination, the optimal SB position is exactly the same with the defocus side-lobe position of iso-line. The effect of the secondary pair of SB is also discussed in this paper, and it is found that if the secondary SB pair was not at the optimal position, the process window would be reduced. Another major topic in this paper is the specification of SB width. Here we design a test pattern to target the specification of SB width. The experimental results might give us a clear specification of SB width.
A great deal of progress has been made in the design of dual damascene process, including via first, trench first, and self-aligned. For overlay, via-first process provides the largest process tolerance to misalignment. However, the positive tone resist face to some difficulties in dual damascene via first approach of photo process, because the 0.18micrometers positive tone trench resist can not be exposed and removed in the 0.20micrometers via hole, observed residues from the SEM cross section profiles after development. In contrast, the negative tone resist show s great advantage in the via first process and producing desired patterns without resist residues in the via hole. In this paper, the design of dual damascene photo process using commercial N702Y (JSR) negative tone resist on DUV43 (Brewer Sc.) Bottom anti reflective coating is evaluated. To improve the depth of focus (DOF) of negative tone resist process, the different resolution enhancement techniques (RET) are investigated fro dense and isolated trench patterns: off-axis illumination (annular ½), attenuated phase shift mask (halftone 6%) with 248nm (NA 0.55) exposure technology, and experimental results regarding to its process performance are presented.
Manufacturing of reticles, which combine both OPC and PSM, is becoming more and more challenge. Materials cost is high, several accurate writing processes are needed and repair is almost impossible. This makes inspection a critical and very complicated process. This study describes an inspection of a test vehicle consisting of 55 cells targeted for sub- wavelength design rule technology. This study describes an inspection of the 55 cells test plate targeted for 0.17 micrometer design rule technology. The plate is written on a MoSi layer with 18% transmission for 248 nm lithography. The MoSi has higher transmittance in I-line and G-line that reduces the contrast between the MoSi and the glass (relative to the usual contrast in binary plates). The technique for inspection by Applied Materials RT8000ES 436nm die-to-database is described. The technique is based on expansion of the reduced dynamic range of gray level that results from the lower contracts, re-gaining the inspection capability. This paper reviews the results of G-line versus I-line inspection of high transmission PSM and describes the method of the sensitivity verification including CD defects analysis.
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-0.81micrometers dual damascene structure for KrF 248nm lithography. The organic bottom ARC (BARC) achieves reflectivity control through modulation 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 in this article, was investigated with single layer and double layers structures. The double- layer DARC structure consists of two layers with different extinction coefficient K values. The optimal refractive index and thickness of each ARC structure were calculated from some available photolithography simulators. A PECVD process for DARC growth that provides easily tunable range of refractive index and thickness was established to meet the DUV process requirement from simulation. The performances of each ARC structure were evaluated on patterning 0.18 micrometers trench and 0.20 micrometers via in back-end- of-line 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 micrometers dual damascene process.
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