Ryo Tajima

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.

Capability of model EBEYE M for EUV mask production

According to the ITRS Roadmap [1], within a few years the EUV mask requirement for defect will be detection of defect size of less than 25 nm. Electron Beam (EB) inspection is one of the candidates to meet such a severe defect requirement. EB inspection system, Model EBEYE M※1, has been developed for EUV mask inspection. Model EBEYE M employs Projection Electron Microscope (PEM) technique and image acquisition technique to acquire image with Time Delay Integration (TDI) sensor while the stage moves continuously [2]. Therefore, Model EBEYE M has high performance in terms of sensitivity, throughput and cost. In a previous study, we showed the performance of Model EBEYE M for 2X nm in a development phase whose sensitivity in pattern inspection was around 20 nm and in particle inspection was 20 nm with throughput of 2 hours in 100 mm square [3], [4]. With regard to pattern inspection, Model EBEYE M for High Volume Manufacturing (HVM) is currently under development in the production phase. With regard to particle inspection, Model EBEYE M for 2X nm is currently progressing from the development phase to the production phase. In this paper, the particle inspection performance of Model EBEYE M for 2X nm in the production phase was evaluated. Capture rate and repeatability were used for evaluating productivity. The target set was 100% capture rate of 20 nm. 100% repeatability of 20 nm with 3 inspection runs was also set as a target. Moreover, throughput of 1 hour in 100 mm square, which was higher than for Model EBEYE M for 2X nm in the development phase, was set as a target. To meet these targets, electron optical conditions were optimized by evaluating the Signal-to-Noise Ratio (SNR). As a result, SNR of 30 nm PSL was improved 2.5 times. And the capture rate of 20 nm was improved from 21% with throughput of 2 hours to 100% with throughput of 1 hour. Moreover, the repeatability of 20 nm with 3 inspection runs was 100% with throughput of 1 hour. From these results, we confirmed that Model EBEYE M particle inspection mode could be available for EUV mask production.

Capability of particle inspection on patterned EUV mask using model EBEYE M

According to the road map shown in ITRS [1], the EUV mask requirement for defect inspection is to detect the defect size of sub- 20 nm in the near future. EB (Electron Beam) inspection with high resolution is one of the promising candidates to meet such severe defect inspection requirements. However, conventional EB inspection using the SEM method has the problem of low throughput. Therefore, we have developed an EB inspection tool, named Model EBEYE M※. The tool has the PEM (Projection Electron Microscope) technique and the image acquisition technique with TDI (Time Delay Integration) sensor while moving the stage continuously to achieve high throughput [2]. In our previous study, we showed the performance of the tool applied for the half pitch (hp) 2X nm node in a production phase for particle inspection on an EUV blank. In the study, the sensitivity of 20 nm with capture rate of 100 % and the throughput of 1 hour per 100 mm square were achieved, which was higher than the conventional optical inspection tool for EUV mask inspection [3]-[5]. Such particle inspection is called for not only on the EUV blank but also on the patterned EUV mask. It is required after defect repair and final cleaning for EUV mask fabrication. Moreover, it is useful as a particle monitoring tool between a certain numbers of exposures for wafer fabrication because EUV pellicle has not been ready yet. However, since the patterned EUV mask consists of 3D structure, it is more difficult than that on the EUV blank. In this paper, we evaluated that the particle inspection on the EUV blank using the tool which was applied for the patterned EUV mask. Moreover, the capability of the particle inspection on the patterned EUV mask for the hp 2X nm node, whose target is 25 nm of the sensitivity, was confirmed. As a result, the inspection and SEM review results of the patterned EUV masks revealed that the sensitivity of the hp 100 nm Line/Space (LS) was 25 nm and that of the hp 140- 160 nm Contact Hole (CH) was 21 nm. Therefore, we confirmed that particle inspection on the patterned EUV mask using Model EBEYE M could be available for the EUV mask of the hp 2X nm node. In the future, we will try to inspect the production mask of the hp 2X nm node, and try to confirm the performance for the EUV mask of the hp 1X nm node.