Kenji Terao

Patterned mask inspection technology with projection electron microscope technique on extreme ultraviolet masks

Abstract. High-sensitivity extreme ultraviolet (EUV) mask pattern defect detection is one of the major issues remaining to be addressed in device fabrication using extreme ultraviolet lithography. In order to achieve inspection sensitivity and suitability for the 1× nm node, a projection electron microscope (PEM) system is employed that enables high-speed/high-resolution inspection, which is not possible using conventional deep ultraviolet or electron beam inspection systems. By employing higher electron energy in the electron optics (EO) exposure system and by improving the PEM design, we have minimized the aberration that occurs when working with EO systems and we have improved the transmittance of the system. Experimental results showing the improved transmittance were obtained by making electron throughput measurements. To guarantee the tool’s aptness for 16-nm node EUV mask inspection, corresponding sized programmed defects on masks were designed, and the defect detection sensitivity of the EO system was evaluated. Improvements in image resolution and electron throughput have enabled us to detect 16-nm sized defects. The PEM system was integrated into a pattern inspection system for defect detection sensitivity evaluation.

Performance of EBeyeM for EUV Mask Inspection

According to the ITRS Roadmap, the EUV mask requirement for 2X nm technology node is detection of defect size of 20 nm. The history of optical mask inspection tools involves continuous efforts to realize higher resolution and higher throughput. In terms of productivity, considering resolution, throughput and cost, we studied the capability of EUV light inspection and Electron Beam (EB) inspection, using Scanning Electron Microscope (SEM), including prolongation of the conventional optical inspection. As a result of our study, the solution we propose is EB inspection using Projection Electron Microscope (PEM) technique and an image acquisition technique to acquire inspection images with Time Delay Integration (TDI) sensor while the stage is continually moving. We have developed an EUV mask inspection tool, EBeyeM, whole design concept includes these techniques. EBeyeM for 2X nm technology node has the following targets, for inspection sensitivity, defects whose size is 20 nm must be detected and, for throughput, inspection time for particle and pattern inspection mode must be less than 2 hours and 13 hours in 100 mm square, respectively. Performance of the proto-type EBeyeM was reported. EBeyeM for 2X nm technology node was remodeled in light of the correlation between Signal to Noise Ratio (SNR) and defect sensitivity for the proto-type EBeyeM. The principal remodeling points were increase of the number of incident electrons to TDI sensor by increasing beam current for illuminating optics and realization of smaller pixel size for imaging optics. This report presents the performance of the remodeled EBeyeM (=EBeyeM for 2X nm) and compares it with that of the proto-type EBeyeM. Performances of image quality, inspection sensitivity and throughput reveal that the EBeyeM for 2X nm is improved. The current performance of the EBeyeM for 2X nm is inspection sensitivity of 20 nm order for both pattern and particle inspection mode, and throughput is 2 hours in 100 mm square for particle inspection mode.

EUV patterned mask inspection system using a projection electron microscope technique

The concept and the current status of a newly developed PEM pattern inspection system are presented. An image-processing technique with learning functions to enhance the system’s detection capability is investigated. Highly accelerated electrons employed here in electron-optics function as an enabler to improve the image resolution and transmittance in the system, and to acquire an image contrast of 0.5 in a half pitch (hp) 64 nm lines and space pattern. This process also results in the formation of an electron image with more than 3000 electrons per pixel on a sensor. The image-processing system was also developed for die-to-die inspection. The alignment error is minimized to a negligibly small size by a continuous 2D pattern matching. An ensemble of signal characteristics enables the identification of any defect signal in a noisy electron image. The developed detection system met the requirements for hp16 nm generation.

Development of inspection system for EUV mask with novel projection electron microscopy (PEM)

In order to realize EUV mask pattern defect inspection in 16nm node, we have developed new optics on a novel projection electron microscopy (PEM) and a new inspection system with the new optics and a new mask handling and imaging units, e.g., a high precision stage, an imaging detector, an imaging processing system, and so. on. This inspection system enables us to make the inspection in high resolution and high speed as compared with conventional DUV and EB inspection systems. The new optics on the novel PEM comprises an exposure and an imaging electron beam optics (EOs). The optics is based on the new design concept to meet the required progress for 1Xnm EUV mask inspection as compared to the current inspection system for 2Xnm node; The concept employs new techniques to achieve the features: high energetic electron imaging optics to have low aberration, high transmittance efficiency, e.g., on the ratio of exposure current/emitted current, in the exposure and the imaging optics, respectively. The new handling and imaging system are also based on the design concept of imaging in high resolution by combination operation among the new optics on the novel PEM, the stage, and the detector. In this paper, we describe the basic performance evaluation as concerning these features and the operation: 1) MTF inclination in hp44~100nm L/S pattern of the developed imaging optics. 2) Secondary electron imaging by the integrated optics, i.e., both of the exposure and the imaging EOs, on the novel PEM, 3) Secondary electron image acquisition operation in still mode on the new inspection system assembled with the new optics on the novel PEM, the high precision stage, the detector, and so. on.. The results show the new optics on the novel PEM is capable to meet the required progress for 1Xnm EUV mask inspection and the new inspection system with the novel PEM operates in much feasibility in the electron image acquisition.

Development of EB inspection system EBeyeM for EUV mask

We are developing new electron beam inspection system, named EBeyeM, which features high speed and high resolution inspection for EUV mask. Because EBeyeM has the projection electron microscope technique, the scan time of EBeyeM is much faster than that of conventional SEM inspection system. We developed prototype of EBeyeM. The aim of prototype system is to prove the concept of EBeyeM and to estimate the specification of system for 2Xnm and 1Xnm EUV mask. In this paper, we describe outline of EBeyeM and performance results of the prototype system. This system has two inspection mode. One is particle inspection and the other is pattern defect inspection. As to the sensitivity of EBeyeM prototype system, the development target is 30nm for the particle inspection mode and 50nm for pattern defect inspection mode. The performance of this system was evaluated. We confirmed the particle inspection mode of the prototype system could detect 30nm PSL(Polystyrene Latex) and the sensitivity was much higher than conventional optical blank inspection system. And we confirmed that the pattern defect sensitivity of the prototype system was around 45nm. It was recognized that both particle inspection mode and pattern defect inspection mode met the development target. It was estimated by the performance results of the prototype system that the specification of EBeyeM would be able to achieve for 2Xnm EUV mask. As to 1Xnm EUV mask, we are considering tool concept to meet the specification.

Extreme ultraviolet lithography patterned mask defect detection performance evaluation toward 16- to 11-nm half-pitch generation

Abstract. High-sensitivity and low-noise extreme ultraviolet (EUV) mask pattern defect detection is one of the major issues remaining to be addressed in device fabrication using extreme ultraviolet lithography (EUVL). We have designed a projection electron microscopy (PEM) system, which has proven to be quite promising for half-pitch (hp) 16-nm node to hp 11-nm node mask inspection. The PEM system was integrated into a pattern inspection system for defect detection sensitivity evaluation. To improve the performance of hp 16-nm patterned mask defect detection toward hp 11-nm EUVL patterned mask, defect detection signal characteristics, which depend on hp 64-nm pattern image intensity deviation on EUVL mask, were studied. Image adjustment effect of the captured images for die-to-die defect detection was evaluated before the start of the defect detection image-processing sequence. Image correction of intrafield intensity unevenness and L/S pattern image contrast deviation suppresses the generation of false defects. Captured images of extrusion and intrusion defects in hp 64-nm L/S patterns were used for detection. Applying the image correction for defect detection, 12-nm sized intrusion defect, which was smaller than our target size for hp 16-nm defect detection requirements, was identified without false defects.

EUV patterned mask inspection performance of an advanced projection electron microscope (PEM) system for hp 16 nm and beyond

The framework and the current status of a newly developed PEM pattern inspection system are presented. A die-to-die defect detection sensitivity of the developing system is investigated. A programmed defect mask was used for demonstrating the performance of the system. Defect images were obtained as difference images by comparing the PEM images “with-defects” to the PEM images “without-defects”. The image-processing system was also developed for dieto- die inspection. A targeted inspection-throughput of 19-hour inspection per mask with 16 nm pixel size for image capture was attained. Captured images of extrusion and intrusion defects in hp 64 nm L/S pattern were used for detection. Then 16 nm sized intrusion defect, which was our target size for hp 16 nm defect detection requirement, was identified without false defects. To improve the performance of hp 16 nm patterned mask inspection, defect detection requirements for hp 11 nm EUVL patterned mask inspection was studied.

Evaluation of novel projection electron microscopy (PEM) optics for EUV mask inspection

In order to achieve inspection sensitivity and a attainability for 1× node, a projection electron microscopy (PEM) system is employed that enables us to do high-speed/ high-resolution inspection that is not possible with the conventional DUV and EB inspection systems. By selecting a higher electron energy in imaging using Electron Optics (EO) exposure, and by applying a newly designed model to the basic PEM optics model, we have minimized the aberration in imaging that occurs when working with EO; and we have improved the related transmittance of such a system. The experimental result by showing designs for the improved transmittance, is obtained by making electron throughput measurement.

EUV patterned mask inspection with an advanced projection electron microscope (PEM) system

The framework and the current status of a newly developed PEM pattern inspection system are presented. A die-to-die defect detection sensitivity of the developing system is investigated. A programmed defect mask was used for demonstrating the performance of the system. Defect images were obtained as difference images by comparing PEM images with-defects to the PEM images without-defects. The image-processing system was also developed for die-to-die inspection. A targeted inspection throughput of 19-hour inspection per mask with 16nm pixel size for image capture was attained. Captured image of 28 nm intrusion defect in hp 64 nm L/S pattern was used for detection. The defect is clearly identified by the image processing. But several false defects are also detected. To improve the defect detection sensitivity to reach the targeted level of achieving a higher than 10 S/N value at 16 nm defect size, by applying a higher current density and a developed inspection algorithm adjustment is, currently an on-going program.

Recent results from EUVL patterned mask inspection using projection electron microscope system

The recent status of a newly developed PEM pattern inspection system for hp 16 nm node defect detection is presented. A die-to-die defect detection sensitivity of the developing system is also investigated. A programmed defect mask was used for demonstrating the performance of the system. Defect images were obtained as difference images by comparing the PEM images “withdefects” to the PEM images “without-defects”. This image-processing system was also developed for die-to-die inspection. Captured images of extrusion and intrusion defects in hp 64 nm L/S pattern were used for detection. 12 nm sized intrusion defect, that was smaller than our target size for hp 16 nm defect detection requirement, was identified without false defects. To improve the performance of hp 16 nm patterned mask inspection for hp 11 nm EUVL patterned mask inspection, defect detection signal characteristics, which depend on hp 64 nm pattern image intensity deviation on EUVL mask, was studied.