Kenichi Matsumura

Development of advanced reticle inspection apparatus for hp 65 nm node device and beyond

The usage of ArF immersion lithography for hp 65nm node and beyond leads to the increase of mask error enhancement factor in the exposure process. Wavelength of inspection tool is required to consistent with wavelength of lithography tool. Wavelength consistency becomes more important by the introduction of phase shift mask such as Tri-tone mask and alternating phase shift mask. Therefore, mask inspection system, whose inspection light wavelength is 199nm, has been developed. This system has transmission and reflection inspection mode, and throughput, using 70 nm pixel size, were designed within 2hours per mask. The experimental results show expected advantages for Die-to-Die and Die-to-Database inspection compared with the system using 257nm inspection optics. Shorter wavelength effect makes transmission inspection sensitivity increase, and realizes 40nm size particle inspection. As for the phase shift mask, the difference of gray value between the area with phase defect and without phase defect was clear relatively. In this paper, specifications and design, experimental results are described.

Performance of novel 198.5-nm wavelength mask inspection system for 65-nm node and beyond optical lithography era

In 65nm node and some more technology node probably may go with current optical lithography and industry has predicted many challenges. In patterning point of view, quality and cost of mask became more and more important than ever. Particularly, mask defect engineering technology is key area not only inspect the defects but also mask process monitoring and improvements. In mask inspection technology there were a lot of new progresses to enhance the defect inspection sensitivity and stability. The key solution to achieve better sensitivity may be short inspection wavelength and adequate detection algorithm. In this paper, we will propose defect size specifications of 65nm and beyond optical mask with various OPC and RET environments. In addition, we will present initial data of newly developed 198.5nm inspection wavelength system. Through this study, we found future optical mask faces new challenges in defect inspection and to solve these problems, we need advanced mask inspection system and collaborations among patterning related fields.

Improvement of image quality and inspection speed in LM7500 reticle inspection system

By refining the entire optical system in our LM7500 reticle inspection system, we have successfully improved the image quality and inspection speed. The LM7500 system uses a beam scanning method in which the inspection pixel size is switched by changing the magnification ratio of the telescope in the section subsequent to the scanners optical system. The telescope magnification ratio is designed to meet the requirements of the light spot diameter and beam scanning width on a reticle, and specifies the scanning speed. We have realized a smaller light spot diameter by improving the design of the section prior to the optical system, including the AOD (acousto-optic deflector), which is the starting point of the scanners optics. This has led to faster scanning. We have also succeeded in minimizing the adjustment error by optimizing the magnification ratio of the telescope, thus increasing the adjustment margin of the incident light beam entering the section subsequent to the scanners optical system. This means that the difference in the X and Y directions of an image can be suppressed to a remarkable extent for a beam scanning system. Moreover, because the LM7500 scans both transmitted and reflected light simultaneously, pattern inspections, particle inspections and even scribe-tri-tone inspections can be carried out at the same time. We have also succeeded in increasing the inspection speed by 30% through optical system optimization.

Photomask quality assessment solution for 90-nm technology node

As 90 nm LSI devices are about to enter pre-production, the cost and turn-around time of photomasks for such devices will be key factors for success in device production. Such devices will be manufactured with state-of-the-art 193nm photolithography systems. Photomasks for these devices are being produced with the most advanced equipment, material and processing technologies and yet, quality assurance still remains an issue for volume production. These issues include defect classification and disposition due to the insufficient resolution of the defect inspection system at conventional review and classification processes and to aggressive RETs, uncertainty of the impact the defects have on the printed feature as well as inconsistencies of classical defect specifications as applied in the sub-wavelength era are becoming a serious problem. Simulation-based photomask qualification using the Virtual Stepper System is widely accepted today as a reliable mask quality assessment tool of mask defects for both the 180 nm and 130 nm technology nodes. This study examines the extendibility of the Virtual Stepper System to 90nm technology node. The proposed method of simulation-based mask qualification uses aerial image defect simulation in combination with a next generation DUV inspection system with shorter wavelength (266nm) and small pixel size combined with DUV high-resolution microscope for some defect cases. This paper will present experimental results that prove the applicability for enabling 90nm technology nodes. Both contact and line/space patterns with varies programmed defects on ArF Attenuated PSM will be used. This paper will also address how to make the strategy production-worthy.

High-performance reticle inspection tool for the 65-nm node and beyond

A new DUV high-resolution reticle defect inspection platform has been developed. This platform is designed to meet the reticle qualification requirements of the 65-nm node and beyond. In this system, the transmitted and reflected inspection lights are collected simultaneously to produce reticle images at high speed. Transmitted and reflected inspections in the die-to-die (DD) and the die-to-database (DB) modes can be executed concurrently. Both images can be gathered at full synchronization with low noise. Basically, both inspection modes are needed to detect as many types of hard and soft defects as possible. Concurrent inspection saves time from using transmitted and reflected lights sequentially. In this presentation, results of DD and DB inspection using standard programmed defect test reticles as well as advanced 65-nm production reticles, are given, showing high-sensitivity and low-false-count detections being achieved with low operating cost.

Development of next-generation mask inspection method by using the feature of mask image captured with 199-nm inspection optics

We have developed a mask inspection system using 199nm inspection light wavelength. This system performs transmission and reflection inspection processes concurrently within two hours per plate. By the evaluation result of mask images and inspection sensitivity, it is confirmed that the 199nm inspection system has the advantage over the system using 257nm and has the possibility corresponding to next generation mask inspection. Furthermore, advanced die-to-database (D-DB) inspection, which can generate high-fidelity of a reference image based on the CAD data for alternating phase shift mask (PSM) or tri-tone, is required for next generation inspection system, too. Therefore, a reference image generation method using two-layer CAD data has been developed. In this paper, the effectiveness of this method is described.

Optical mask inspection strategy for 65-nm node and beyond

As semiconductor integration goes down to nano-meter scale, finer patterning technology is inevitable. Therefore it is more and more important not only new lithographic development but also mask quality enhancement. Particularly, due to the delay of NGL technology, optical lithography is growing candidate for 65nm and beyond node device. In that case, mask CD uniformity and defect control issues are more important than ever. In mask inspection technology, there were a lot of new progresses to enhance the defect inspection sensitivity and stability via short-wavelength and advanced defect inspection algorithms. In this paper, we will present a concept and on going status of newly developed short-wavelength DUV inspection tool that is co-worked by Selete, Toshiba, and NEC. Moreover, we will discuss defect specifications that is required 65nm node and beyond technology node by simulations. This will include relations between defect inspectability and printability in the case of ArF, ArF immersion, and F2 lithography in various layouts and patterns. Through this study, we can conclude stable short-wavelength inspection tool and proper inspection algorithms are essential for future generation mask to cope with low k1 lithography.

LM5000: As a strong mask analyzing tool

The prompt progress of photomask pattern shrinking leads to the overlooking for significant defects. To improve the defect detection performance, patterns must be observed thoroughly at first. These observations are also important for a total diagnostic of the lithography process. Our developing reticle inspection machine LM5000 is very suitable for such analyses. With LM5000, users are able to point any positions on the reticle very easily, view the images, measure the lengths or widths of the patterns, and the intensity at each pixel. Users are also able to apply various image processing algorithms. To follow the growth of the semiconductor processes, inspection algorithms should be developed within very short terms. LM5000 adopts a special image processing core consisted of IMAP. It has strong processing power of a super computer class, and it is programmable even by a C-like language. Libraries for development include most of the standard image processing functions. Its flexibility helps us for reducing the development periods of the new algorithms. In this presentation, the functions of the user interface of LM5000 are displayed as a mask analyzing tool, and the effects of the IMAP processing is explained.