Masaharu Nishiguchi

Evaluation of dry etching and defect repair of EUVL mask absorber layer

EUVL mask process of absorber layer, buffer layer dry etching and defect repair were evaluated. TaGeN and Cr were selected for absorber layer and buffer layer, respectively. These absorber layer and buffer layer were coated on 6025 Qz substrate. Two dry etching processes were evaluated for absorber layer etching. One is CF4 plasma process and the other is Cl2 plasma process. Etch bias uniformity, selectivity, cross section profile and resist damage were evaluated for each process. Disadvantage of CF4 plasma process is low resist selectivity and Cl2 plasma process is low Cr selectivity. CF4 plasma process caused small absorber layer damage on isolate line and Cl2 plasma process caused Cr buffer layer damage. To minimize these damages overetch time was evaluated. Buffer layer process was also evaluated. Buffer layer process causes capping layer damage. Therefore, etching time was optimized. FIB-GAE and AFM machining were applied for absorber layer repair test. XeF2 gas was used for FIB-GAE. Good selectivity between absorber layer and buffer layer was obtained using XeF2 gas. However, XeF2 gas causes side etching of TaGeN layer. AFM machining repair technique was demonstrated for TaGeN layer repair.

Defect repair performance using the nanomachining repair technique

Nanomachining is a new technique for repairing photomask defects. The advantages of this technique are no substrate damage, precise edge placement position and Z height accuracy when compared with current Laser zapper or FIB GAE repair techniques. This technique can be applied to any type of opaque defects at any type of film materials and quartz bump defects on Alternating Aperture Phase Sifting Masks (AAPSM). Furthermore, these characteristics enable complex pattern repairs of most advanced photomasks for 193nm lithography and enables iterative repair to achieve improved printing performance when analyzed with an AIMS 193nm tool. Dai Nippon Printing Co., Ltd. (DNP) has been producing AAPSMs in mass production for quite some time. The standard type of AAPSMs manufactured has been etched quartz, single trench with an undercut structure. On this structure, there is a potential for quartz defects underneath the chrome overhang based on the combination of dry and wet etching to create the undercut. For this study, we fabricated this kind of designed quartz defects and repaired them using the nanomachining system. These types of defects are particularly difficult to repair perfectly because they exist underneath the chrome overhang. We will show some options to achieve better printing results through the repair of these kinds of defects. In this report, we confirmed basic performance of this technique such as edge placement accuracy, Z height accuracy and AIMS printability. Additionally, we also tried to repair some complex defects such as quartz defects of AAPSM, quartz defects of CPL mask and oversized Serifs for application options. We will show these nanomachining repairs with evaluation results of printing performance simulated by the AIMS 193nm tool.

Study of mask process development for EUVL

EUVL mask process of absorber layer dry etching and defect repair were evaluated. TaGeN and Cr were selected for absorber layer and buffer layer, respectively. These absorber layer and buffer layer were coated on 6025 Qz substrate. Two dry etching processes were evaluated for absorber layer etching. One is CF4 gas process and the other is Cl2 gas process. CD uniformity, selectivity, cross section profile and resist damage were evaluated for each process. FIB-GAE and AFM machining were applied for absorber layer repair test. XeF2 gas was used for FIB-GAE. Good selectivity between absorber layer and buffer layer was obtained using XeF2 gas. However, XeF2 gas causes side etching of TaGeN layer. AFM machining repair technique was demonstrated for TaGeN layer repair.

Study of Defect Printability Analysis on Alternating Phase Shifting Masks for 193 nm Lithography

For alternating aperture phase shift masks (AAPSM), phase-defect detection and disposition is more difficult for 193 nm (ArF) lithography than for 248 nm (KrF) lithography, as pattern geometry is tighter and quartz etching is shallower. For ArF lithography, we designed and fabricated a new test mask to confirm detectability and printability of phase defects, extending our previous work for KrF lithography. This test mask has precise defect sizes and phase-error angles of 25, 50, and 75 degrees. Detectability was demonstrated on KLA-Tencor’s SLF27 and investigated by acquiring defect images on SLF27 and LaserTec’s MD3000 inspection systems. Printability was compared between actual wafer prints, and simulations from Carl Zeiss’ Aerial Image Measurement System (AIMS). Wafer prints were also simulated using Numerical Technologies’ software-based Virtual Stepper System, which takes inspection images as input and models the optical aspects of lithography. Virtual Stepper critical-dimension measurements show good general agreement with those from AIMS images and wafer-print SEM images. Compared to AIMS, which is a hardware-based simulator that uses the actual mask as input, the software-based Virtual Stepper System is easier to adapt to different processes and to integrate into the production flow.

Feasibility study of manufacturing process and quality control for the new alternating PSM structure

Alternating phase-shifting mask (Alt.PSM) technology is the most effective approach to expand resolution limitation and expand the process window of lithography. Currently, etched quartz Alt.PSMs have been introduced not only for device development but also for production use. We have been supplying Alt.PSMs with Single trench + Undercut structures for the mass-production of KrF lithography and reported this structure is applicable for ArF lithography. On the other hand, we have introduced preliminary manufacturing results of the new Alt.PSM structure. This structure has the advantages, which are exempted from biasing issues and narrow chrome width limitations. In order to make sure the adaptability of this new Alt.PSM structure in mass-manufacturing, we started to investigate productivity for this structure. In this paper, we will discuss about the feasibility study of manufacturing process and quality control which include CD performance results, alignment error tolerance evaluations and defect assurance evaluations.

Optimization of nanomachining repair condition for ArF lithography

Nanomachining is a new technique for repairing photomask defects. The advantages of this technique are no substrate damage, precise edge placement position and Z height accuracy when compared with current Laser zapper or FIB GAE repair techniques. We have reported that this technique can be applied to any type of opaque film material defects, quartz bump defects on Alternating Aperture Phase Sifting Masks (AAPSM) and complex pattern defect repairs. In this report, we have evaluated about the optimization of Nanomachining condition for repairing most advanced photomasks for 193nm lithography on the materials of binary chrome and MoSi HT-PSM. Evaluation items are adequate edge position and Z height for targeting to achieve better printing performance when analyzed with an AIMS 193nm tool.

Defect printability analysis on alternating phase-shifting masks

In this paper, we demonstrate new simulation capabilities for defect dispositioning of alternating aperture phase shift masks (AAPSM). A defect mask for use in a 248 nm exposure tool was fabricated with programmed phase defects. Inspection images of the defects were taken on Lasertecs MD3000 and KLA-Tencors SLF27 inspection systems. The simulation tool takes defect images as input and simulates photolithography performance via aerial image modeling. We present preliminary modeling results that show good agreement between simulated CDs and the CDs from Aerial Image Measurement System (AIMSTM) measurements. This work shows the potential for extending Virtual Stepper?System to AAPSMs on a variety of inspection platforms.

Improvements of AIMS D2DB matching for product patterns

AIMSTM is mainly used in photomask industry for verifying the print impact of mask defects on wafer CD in DUV lithography process. AIMS verification is typically used in D2D configuration, wherein two AIMS images, reference and defect, are captured and compared. Criticality of defects is then analyzed off these images using a number of criteria. As photomasks with aggressive OPC, sub-resolution assist features (SRAFs), and single-die are being routinely manufactured in production environment, it is required to improve cycle time through the AIMS step by saving time in searching for and capturing an adequate reference AIMS image. One solution is to use AIMS D2DB methodology which compares AIMS defect image with a reference image simulated from the corresponding mask design data. In general, such simulation needs calibration with the native images captured on the AIMS tool. In our previous paper we evaluated a calibration procedure directly using the defect AIMS image and compared the analysis results with a D2D capture using AIA (Aerial Image Analyzer) software product from Luminescent Technologies (now part of KLA-Tencor Corporation). The results showed that calibration using defect AIMS image does not influence AIMS judgment as long as the defect size is less than 100nm in case of typical basic patterns. When applying this methodology to product patterns, it was found that there were differences between reference AIMS image and simulation image. These differences influenced AIMS verification. Then new method to compensate would be needed. Our approach to compensate the difference between AIMS image and simulated image is examination with some factors likely to cause the difference.

Evaluation of AIMS D2DB simulation without calibration images

AIMS™ is mainly used in photomask industry for verifying the impact of mask defects on wafer CD in DUV lithography process. AIMS verification is used for D2D configuration, where two AIMS images, reference and defect, are captured and compared. Criticality of defects is identified using a number of criteria. As photomasks with aggressive OPC and sub-resolution assist features (SRAFs) are manufactured in production environment, it is required to save time for identifying reference pattern and capturing the AIMS image from the mask. If it is a single die mask, such technology is truly not applicable. A solution is to use AIMS die-to-database (D2DB) methodology which compares AIMS defect image with simulated reference image from mask design data. In general, simulation needs calibration with AIMS images. Because there is the difference between an AIMS image except a defect and a reference image, the difference must be compensated. When it is successfully compensated, AIMS D2DB doesn’t need any reference images, but requires some AIMS images for calibration. Our approach to AIMS D2DB without calibration image is systematic comparison of several AIMS images and to fix optical condition parameters for reducing calibration time. And we tried to calibrate using defect AIMS image to this approach. In this paper, we discuss performance of AIMS D2DB simulation without calibration images.

Photomask repair performance of the SiON/Ta-Hf attenuating PSM

Recently, a new attenuating phase shift film utilizing a bilayer of SiON film and TaHf alloy film was developed for F2 and high transmission ArF lithography. Basic data, showing their optical properties, chemical durability, and dry-etch performance was introduced during the Photomask Japan 2003. Currently a lot of lithographers are paying their attention on this new material, because of its capability for high transmission ArF, as one of the solution for 65nm node with 193nm extension. As it is becoming more and more recognized by both mask manufacturers and mask users, repair capability of the film material has a great impact on the mask yield, which determines the potential cost and cycle time of the photomask. In this paper, we investigated the capability of this material on critical mask repair, focusing on high transmission and attenuating ternary PSM. We evaluated the repair capability with currently used FIB tools. This new material shows excellent repair capability because of the bilayer structure, where the Ta-Hf film, which was initially designed as a transmission control layer and as an etch stop for the SiON etch, works as a stopper during the FIB repair process assisted by β gas. We also report preliminary test results with the nanomachining repair system RAVE.