Nobutaka Kikuiri

Development of a new mask pattern inspection tool NPI-7000 and applied results to EUV mask inspection

Photo lithography potential expands for 32nm node to 2xnm device production by the development of immersion technology and the introduction of phase shift mask, and NPI-6000 using 199nm laser source was developed to correspond to 2xnm node photo mask pattern inspection. On the other hand, EUV lithography with 13.5nm exposure wavelength is dominant candidate for the next generation lithography because of its excellent resolution for 1x 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. Therefore, a new mask inspection tool, NPI-7000, has been developed. This tool can implement not only photo mask pattern (hp1x) inspection, but also EUV mask pattern inspection (hp2x) and blanks inspection with high throughput. In this paper, features of NPI-7000 and new developed technologies were described and applied results to EUV mask inspections were introduced.

Evaluation of EUVL-mask pattern defect inspection using 199-nm inspection optics

In this paper, we will report two evaluation results. One is the relationship between EUVL mask structure and image contrast values captured by 199nm inspection optics. The other is the influence of mask structure on defect inspection sensitivity. We utilized a commercially available DUV inspection system that has the shortest inspection wavelength at 199nm. Using the 199nm inspection optics, enough image contrast values on hp32nm 1:1 lines and spaces using ArF-half tone (HT) mask were obtained. On the other hand, image contrast values were not sufficient for conventional EUVL mask that have a 70nm absorber layer thickness. To improve the contrast values of mask pattern image, we evaluated the effect of absorber layer thickness on inspection image contrasts. As a result, reducing the thickness of the absorber layer to 44nm, enough image contrast values of hp32nm 1:1 lines and spaces patterns were obtained. In this paper, the influence of the thickness of absorber layer on inspection sensitivities for opaque and clear extension defects are also discussed.

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.

Highly Reliable 198 nm Light Source for Semiconductor Inspection Based on Dual Fiber Lasers

Highly reliable DUV light sources are required for semiconductor applications such as a photomask inspection. The mask inspection for the advanced devices requires the UV lightning wavelength beyond 200 nm. By use of dual fiber lasers as fundamental light sources and the multi-wavelength conversion we have constructed a light source of 198nm with more than 100 mW. The first laser is Yb doped fiber laser with the wavelength of 1064 nm; the second is Er doped fiber laser with 1560 nm. To obtain the robustness and to simplify the configuration, the fundamental lights are run in the pulsed operation and all wavelength conversions are made in single-pass scheme. The PRFs of more than 2 MHz are chosen as an alternative of a CW light source; such a high PRF light is equivalent to CW light for inspection cameras. The light source is operated described as follows. Automatic weekly maintenance within an hour is done if it is required; automatic monthly maintenance within 4 hours is done on fixed date per month; manufacturers maintenance is done every 6 month. Now this 198 nm light sources are equipped in the leading edge photomask inspection machines.

Development of advanced mask inspection optics with transmitted and reflected light image acquisition

The lithography potential of an ArF (193nm) laser exposure tool with high numerical aperture (NA) will expand its lithography potential to 65nm node production and even beyond. Consequently, a mask inspection system with a light source, whose wavelength is nearly equal to 193nm, is required so as to detect defects of the masks using resolution enhancement technology (RET). Wavelength consistency between exposure tool and mask inspection tool is strongly required in the field of mask fabrication to obtain high defect inspection sensitivity. Therefore, a novel high-resolution mask inspection platform using DUV wavelength has been developed, which works at 198.5nm. This system has transmission and reflection inspection mode, and throughput using 70nm pixel size were designed within 2 hours per mask. In this paper, transmitted and reflected light image acquisition system and high accuracy focus detection optics are presented.

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.

Study of EUVL mask defect inspection using 199-nm inspection tool with super-resolution method

In this paper, we will report on our experimental results on the impact of inspection system optics on mask defect detection sensitivity. We evaluated the capability of detecting defects on the EUVL masks by using a new inspection tool (NPI6000EUVα) 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 mask with LR-TaBN absorber was used which had various sized opaque and clear extension defects on hp-180nm, hp-128nm, and hp-108nm line and space patterns. According to the analysis, to obtain optimum sensitivity for various types of defects, using both C- and P-polarized illumination conditions were found to be effective. At present, sufficient defect-detection sensitivity is achieved for opaque and clear extension defects in hp128nm (hp32nm at wafer). For hp108nm (hp27nm at wafer), using both C- and P- polarized illumination is effective. However, further developments in defect-detection sensitivity are necessary.

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.

Evaluation of EUVL mask pattern defect inspection using 199nm inspection tool with super-resolution method

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.