Masatoshi Hirono

Study of EUV mask inspection technique using DUV light source for hp22nm and beyond

EUV lithography is expected to be not only for hp 2Xnm node device production method but also for hp 1X nm node. We have already developed the mask inspection system using 199nm wavelength with simultaneous transmitted and reflected illumination optics, which utilize p-polarized and s-polarized illumination for high defect detection sensitivity, and we developed a new image contrast enhancement method which changes the digitizing rate of imaging sensor depending on the signal level. Also, we evaluate the mask structure which improve the image contrast and defect detection sensitivity. EUVL-mask has different configuration from transmitted type optical-mask. A captured image simulator has been developed to study the polarized illumination performance theoretically of our inspection system. Preferable mask structure for defect detection and possibility of miss defect detection are considered.

A novel defect detection optical system using 199-nm light source for EUVL mask

Lithography potential expands for 45nm node to 32nm device production by the development of immersion technology and the introduction of phase shift mask. We have already developed the mask inspection system using 199nm wavelength with simultaneous transmitted illumination and reflected illumination optics, and is an effectual candidate for hp 32nm node mask inspection. Also, it has high defect sensitivity because of its high optical resolution, so as to be utilized for leading edge mask to next generation lithography. EUV lithography with 13.5nm exposure wavelength is dominant candidate for the next generation lithography because of its excellent resolution for 2x half pitch (hp) node device. But, applying 199nm optics to complicated lithography exposure tool option for hp2x nm node and beyond, further development such as image contrast enhancement will be needed. EUVL-mask has different configuration from transmitted type optical-mask. It is utilized for reflected illumination type exposure tool. Its membrane structure has reverse contrast compared with optical-mask. This nature leads image profile difference from optical-mask. A feasibility study was conducted for EUV mask pattern defect inspection using DUV illumination optics with two TDI (Time Delay Integration) sensors. To optimize the inspection system configuration, newly developed Nonlinear Image Contrast Enhancement method (NICE) is presented. This function capability greatly enhances inspectability of EUVL mask.

Novel EUV mask inspection tool with 199-nm laser source and high-resolution optics

A novel EUV mask inspection tool with 199nm laser source and super-resolution technique has been developed. This tool is based on NPI-5000PLUS, which is a photo-mask inspection tool for hp2X nm node and beyond. In order to implement EUV mask inspection with only a short time for mask set-up, reflected illumination type alignment optics to guide alignment mark and adjust mask coordinate with visible illumination light are equipped. Moreover, to inspect EUV masks for hp2X nm and beyond, the image detection optics with the novel polarized illumination technique is incorporated in this tool. Image contrast enhancement was confirmed by experiments and simulations.

The study of EUVL mask defect inspection technology for 32-nm half-pitch node device and beyond

In this paper, we will report on our experimental and simulation results on the impact of EUVL mask absorber structure and of inspection system optics on mask defect detection sensitivity. We employed a commercial simulator EM-Suite (Panoramic Technology, Inc.) which calculated rigorously using FDTD (Finite-difference time-domain) method. By using various optical constants of absorber stacks, we calculated image contrasts and defect image signals as obtained from the mask defect inspection system. We evaluated the image contrast and the capability of detecting defects on the EUVL masks by using a new inspection tool made by NuFlare Technology, Inc. (NFT) and Advanced Mask Inspection Technology, Inc. (AMiT). This tool is based on NPI-5000 which is the leading-edge photomask defect inspection system using 199nm wavelength inspection optics. The programmed defect masks with LR-TaBN and LRTaSi absorbers were used which had various sized opaque and clear extension defects on hp-160nm, hp-225nm, and hp- 325nm line and space patterns. According to the analysis, reflectivity of EUVL mask absorber structures and the inspection optics have large influence on image contrast and defect sensitivity. It is very important to optimize absorber structure and inspection optics for the development of EUVL mask inspection technology, and for the improvement of performance of EUV lithographic systems.

Study of advanced mask inspection optics with super-resolution method for next generation mask fabrication

The lithography potential of an ArF (193nm) laser exposure tool with high numerical aperture (NA) will expand its lithography potential to 45nm node production and even beyond. Consequently, a mask inspection system with a wavelength nearly equal to 193nm is required so as to detect defects of the masks using resolution enhancement technology (RET). A novel high-resolution mask inspection platform using DUV wavelength has been developed, which works at 199nm. The wavelength is close to the wavelength of ArF exposure tool. In order to adapt 199nm optics for hp2x nm node and beyond defect detection on next generation mask with appropriate condition, further development such as the illumination condition modification technique has been studied. The illumination optics has the advantageous feature that super-resolution method is applied by adding the optics. To evaluate the super-resolution effect of illumination condition control optics, the interaction of light with mask features is calculated rigorously using RCWA (Rigorous Coupled-Wave Analysis) method. In this paper, image contrast enhancement effect using newly designed super-resolution optics which is applied to transmitted and reflected light image acquisition system are presented with simulation and experiment.

Development of a captured image simulator for the differential interference contrast microscopes aiming to design 199 nm mask inspection tools

Recently, technologies of ArF laser exposure tools and alternating phase shifting masks (Alt-PSM) are expected to be used in actual production. To utilize such newly developed technologies, it is inevitable to develop a mask inspection technology to check them properly. But it is currently difficult to check them precisely because sufficient image contrast is hard to obtain with any conventional mask inspection tools. Among many observation methods, the differential interference contrast (DIC) is one of a few methods that can be used to observe a differentiated phase shift of transmitted light of an object with high resolution. To study precisely the performance of this optical configuration, we built a new captured image simulator in which Wollaston prisms were modeled as a kind of phase modulation plates. We built this simulator as an extension of the captured image simulator we reported formerly), which is based on Rigorous Coupled- Wave Analysis (RCWA) to calculate diffractions; this enables us to properly treat effects of polarization, high NA, and 3-dimensional mask structures. We applied this simulator to see sensitivities of DIC against bumps and divots with various sizes. We found that the image contrast for small phase defects 20 to 50 nm in sizes is much higher in DIC microscopes than in conventional optical setup with coherence factor less than 1. We also found the dependence of captured images on polarizations and optical axis directions. We expect our simulator to be a useful tool for studying, designing, and developing mask inspection tools.

Computational analysis of electric field distribution in dual-layered phase-change disc

We developed a Finite-Difference Time Domain (FDTD) Method based simulator that can analyze Dual-Layered phase-change disc structure. Because of a substrate thickness error, it is necessary to consider spherical aberration. The electric field distributions have been calcuated on Single-Layered and Dual-Layered phase-change discs. We found differences between the electic distributions focused on a groove and on a land. These calculation results can explain the corresponding experimental results clearly.

Computational Analysis of Cross-Erase Phenomenon for High-Density Phase-Change Recording

In order to increase the recording density and decrease the track pitch of the digital versatile discs (DVD) media using the land-and-groove recording format, it is essential to suppress the magnitude of the cross-erasure of the recorded marks. A computational analysis to estimate the mark and erasure shapes was carried out, and comparisons with the experimental results have shown good agreement. The cross-erasure was reduced under the conditions given in this paper by increasing the duty ratio of land width to groove width (L/G) while keeping the groove pitch constant.

Computational analysis of cross-erase phenomena for high-density phase-change recording

In accordance with the increase of the recording density of DVD media, the track pitch is required to be smaller and the cross-erase phenomena becomes more prominent. In order to realize large capacity by using the land-and-groove recording format, it is essential to suppress the magnitude of the cross-erasure. In this paper, the computational analysis to estimate the mark and erasure shapes is described and the cross-erase phenomenon obtained from the analysis is discussed in terms of the duty ratio of land width to groove (L/G). The computational analysis mainly consists of two parts, the electromagnetic analysis and thermal analysis. The former computes the electromagnetic field induced from the incident beam by using the finite difference time domain (3D-FDTD) method. The latter simulates the temperature distributions by the finite volume method (3D-FVM). The cross-erase phenomenon is observed by mapping the mark and erasure areas that are obtained from the transient results of temperature distributions.