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.

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

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.

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

A novel high-resolution mask inspection platform using DUV wavelength has been developed. This platform is designed to enable the defect inspection of high quality masks for 65nm node used in 193nm lithography. In this paper, newly developed optical system and its performance are reported. The system is operated at wavelength of 198.5nm, which wavelength is nearly equal to 193nm-ArF laser exposure tool. Some defect image data and defect inspection sensitivity due to simulation-base die-to-die (D/D) inspection are shown on standard programmed defect test mask. As an initial state D/D inspection performance, 20-60 nm defects are certified. System capabilities for 65nm node inspection and beyond are also discussed.

Advanced mask inspection optical system (AMOS) using 198.5-nm wavelength for 65-nm (hp) node and beyond: system development and initial state D/D inspection performance

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.

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

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.

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

In order to perform mask inspection with the high reliability for 150 nm-rule and below devices, the inspection system with high resolution is indispensable. The phase shift masks like DUV HT masks must also be inspected with high sensitivity. A next generation mask inspection system MC-3000 which used DUV optics has been developed, in order to achieve these requirement. The wavelength of this optics is 257 nm that is shorter than that of current UV inspection systems, and is nearly equal to that of current DUV lithography systems. Short wavelength light and high NA optics obtain high resolution, so the defect detection of 130 nm or less is attained. The special issues for the DUV optics were solved by several new techniques. This paper reports the system configuration, basic characteristics for defect detection and inspection performances.

Noboru Kobayashi

Papers

Advanced mask inspection optical system (AMOS) using 198.5-nm wavelength for 65-nm (hp) node and beyond: system development and initial state D/D inspection performance

High-resolution DUV inspection system for 150-nm generation masks