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.
As the ArF lithography technology is going to progress to 90nm node from 130nm node, it has been more difficult to inspect all types of mask defects, which influence wafer. Photomask for 90nm node, the aggressive OPC mask and Phase Shift Mask (PSM) might be inevitable in production devices due to the slow progresses in lithography equipment itself compared to shrinkage speed in device manufacturing.
Recently, due to the similiar effect such like MEEF (Mask Error Enhancement Factor) phenomenon many mask defects become to detect difficult even printable defects even the lots of improvements mask inspection equipments. In this paper, we will present the inspection capability of advanced DUV inspection tool LM7000 (NEC) with various programmed defect masks (e.g. aggressive OPC masks, half-tone PSM, tri-tone PSM) with, and discuss the relationship between inspection sensitivity and mask defect printability.
We have improved DUV laser reticle inspection system LM7000 for 90 nm technology node devices. To increase inspection sensitivity, we developed a reflected light inspection as a supplementary method to transmittance light inspection. We have also strengthened inspection algorithm to distinguish between real defects and very small features from optical proximity effect correction (OPC). Finally, we have improved reference image for die to database inspection. With the merit of short wavelength of LM7000 (266 nm), the inspection sensitivity of the high-transmittance half-tone phase shift mask (HTPSM) does not deteriorated so severely compared to that of binary mask. With the help of these series of improvements, LM7000 could shows inspection capability for OPC masks and HTPSM for ArF lithography. The inspection capability of LM7000 was proved with the programmed defect masks and printability experiment using ArF scanner.
Today, many IC manufacturers use OPC (Optical Proximity effect Correction) technique to obtain finer circuit geometries by adding serifs and jogs to conventional binary mask. Moreover, for endless device shrink in the absent of alternative lithography solution, successful below-half-wavelength lithography requires “much stronger OPC” which consisted of complicate patterns generated from the finer grid size of OPC software or many assist patterns to the main patterns. The mask industry, therefore, is now facing significant problems induced by both increasing write time and defect-like-small complicated OPC patterns. It is questionable that current inspection system could detect all the defect-sources as the aggressiveness of OPC is accelerated. It is not everything to detect small defect only. The direction of development of new reticle inspection tool should be directed by a smart strategy under such an aggressive environment. This paper details the lithographic effects under the 193nm wavelength and inspection sensitivity using newly developed DUV inspection system for various defects on OPC reticle. The relationship between lithographic effects and reticle inspection sensitivity was investigated according to the defect type, defect size, defect position and the aggressiveness of OPC. From this study the requirements of next generation inspection system would be clarified to necessitate good OPC mask manufacturing.
Semiconductor industry still inspect reticle with the i-line wavelength and ITRS indicates only minimum defect size corresponds to 20 percent of the pattern size on mask in the same light. Currently defect definition, however, varies from the fixed minimum defect size to non-printable-maximum defect size due to increased reticle cost. This paper provides an investigation of requirements of current inspection system 193nm lithography. The lines and contact holes patterns were also investigated by both simulation and experiment. The printability of defects was observed under the various circumstances such as pitch variation and transmission of halftone film. From the defect printability study we found that defect printability behave non-linearly as the exposure condition varies and the size defect should be treated importantly as the ArF lithography extends till 70nm era. It is also understood that there is a possibility to miss the important meaning of the size defects from the simple definition of reticle defect. From the analysis of various types of defects and exposure conditions we suggested detail level of inspection sensitivity that new reticle inspection system should be ready.
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.