Phase-shift mask

About: Phase-shift mask is a research topic. Over the lifetime, 2088 publications have been published within this topic receiving 18058 citations.

Comparison of clear-field and dark-field images with optimized masks

Abstract: Clear-field photo-masks offer significant advantages over dark-field photo-masks for some important classes of target patterns, including small isolated features and dense arrays of contacts. This work compares lithographic performance of clear-field and dark-field images when mask patterns are optimized for respective mask tones. Since the purpose is to study optical behavior, computed images without resist models were compared. In order to explore performance limits, optimized masks were not constrained to limit their complexity. Calculated images were compared for clear-field and dark-field masks, with either opaque or 6% transmission, 180-degree phase-shifted absorbers. In each case, mask patterns were independently optimized to print the targets, which were a set of square and rectangular arrays of contact holes with various dimensions and pitches. The range of the target patterns extended to the limits of ArF resolution with water immersion. Because the intent was to compare inherent optical performance of positive and negative-tone imaging, the study did not use resist models that would combine materials properties or behaviors into the results, but simply applied a constant threshold to calculated intensities to obtain images. Contrast, MEEF, and deviation of images with defocus were the basis of optimizing the mask patterns, and were compared for the four combinations of mask tones and absorbers. Best contrast and MEEF were obtained with bright-field masks that had attenuated, phase-shifting absorbers. The amount of improvement depended on the size of the mask patterns relative to that of their corresponding targets, set here by varying the intensity threshold for the images during mask optimization. Differences in how the images of the four types of masks changed with defocus were statistically insignificant.

Pushing KrF photolithography limit for 3D integrated circuit

Abstract: In this paper, a study of shrinking a 3-D memory circuit beyond 0.26mm pitch by currently available KrF photolithography tool is described. Line/space patterns and post structures are included in this study due to the architecture of 3-D memory. Resolution capability of various OAI techniques such as annular, QUASAR, and dipole illumination are analyzed by simulation and wafer printing images. Both attenuated and alternating type phase shifting masks are used to test the resolution limit of various memory structures. A new method of making “alternating-type” phase shifting mask for post pattern is presented in this study. This new phase shifting mask provides a great improvement for resolving small post structures, which have limited process window due to 2-D optical interference effect. This study presents an application of KrF RET to 3-D memory circuit by smart circuit design.

Single exposure general vortex phase-shift mask for contact hole

Abstract: Vortex phase-shift mask had been shown to have excellent image quality by Marc Levenson et al. [1, 2]. However, its application has been restricted to uniform contact-hole arrays and non-uniform contact holes on uniform grid requiring double exposure technique. In this paper, we show that random contact holes in a real layout can be imaged using vortex phase shift mask, with a single exposure. We use a DRAM contact-hole layout as an example. At minimum half-pitch size of 80nm (k1=0.28) and pitch of 160nm, using 193nm stepper with 0.68 numerical aperture and 0.3 degrees of partial coherence, we are able to achieve 0.4um DOF with 10% exposure latitude. The possibility of using a single exposure and low NA stepper should far outweigh the increased cost of vortex mask for high volume products. In comparison, the corresponding alternating phase-shift mask, however, can only achieve 0.2um DOF at 10% exposure latitude, even with the aid of higher numerical aperture of 0.90 and high degrees of partial coherence of 0.15. For non-uniform contact holes, image asymmetry is an issue. We show OPC-corrected images that are substantially symmetrical. Phase error is always a concern for any phase-shift mask. We show that substantial process windows remain even in the presence of phase errors. Furthermore, we demonstrate that random contact-hole layout can be successfully phase-shifted using vortex phase-shift method. Finally, we shall that the same phase-shift mask design technology for vortex mask can be applied to double line-space phase-shift mask method [3].

Phase shift mask and its production

Abstract: PURPOSE:To simplify the stage for forming a phase shifter and to improve a phase shift effect. CONSTITUTION:The phase shifter is constituted of a gelatin layer 1 which is provided in the unexposed part region on a transparent substrate 3 and does not contain a silver component and a silver salt-contg. gelatin layer provided by having a level difference from the gelatin layer 1 in the exposed part region adjacent to the unexposed part region. The intricate stage for forming the phase shift mask is simplified and the surface contamination of the phase shifter is prevented. The dealing with light of short wavelengths of (i) line or below is possible for the excellent transmissivity of the gelatin and the free adjustment of phase differences is possible. There is an effect of expanding the width of the phase shift effect. Further, the silver salt-contg. gelatin layer existing in the exposed part regions of the pattern parts is reduced. There is thus advantage that even the concn. of the blacked silver salt 2 is freely controllable.

Models for characterizing phase-shift defects in optical projection printing

Abstract: An algebraic model is developed for characterizing the printability, inspection, and repair of phase-shift defects in optical projection printing. Phase-shift defects are particularly difficult to characterize because of the many parameters associated with the exposure tool and with the attenuating phase shift mask (PSM) pattern. Furthermore, the parameters change during inspection of the attenuating PSM because the mask is examined under illumination conditions which differ from the exposure illumination. An algebraic model which encompasses this large set of variables is derived by considering the electric fields under the mask to be a combination of the electric fields from the feature and defect. These fields are then combined according to the mutual coherence function for the mask illumination. A notable difficulty is the relative phase shift due to defocus between large and small features. The model is shown to be valid for defects up to 0.35 /spl lambda//NA by comparison to SPLAT. Experimental verification is made for defects impacting a 6% transmitting PSM for 0.35-/spl mu/m features at i-line. The reliability of the model is illustrated by giving rules of thumb for defect printing in attenuating PSM's. >