Hiromu Inoue

CW 198.5-nm light generation in CLBO

A continuous-wave 198.5-nm light is produced by sum-frequency generation in CLBO for advanced photolithography mask inspections. Two fundamental lights are frequency-stabilized and mixed in an external cavity. The output power of 50mW was demonstrated with a single-resonance cavity.

Mask defect inspection method by database comparison with 0.25-0.35 μm sensitivity

Photomasks used in the fabrication of ultra-LSI (ULSI) circuits must be inspected for defects. For 256 Mbit dynamic random access read write memory (DRAM), it is necessary to inspect defects as small as 0.15 µ m. Moreover, inspection of defects of phase-shift masks is becoming an important task of an inspection system. This paper describes an automated mask inspection system (MC-100) based on die-to-database comparison, and a defect inspection method with 0.15 µ m sensitivity for edge and pindot defects. System configuration and the defect inspection method are discussed in detail, including the difficulties of defect detection in an attenuated phase-shift mask.

257-nm wavelength mask inspection for 65-nm node reticles

We have developed a new photomask inspection method which has capability for inspecting 65nm technology node reticles using 257nm wavelength light source. This new method meets the requirement for the current mask inspection system using KrF inspection light source to be employed even in the fabrication of photomasks for 65nm technology node by the appearance of immersion technology using ArF wavelength. This paper discusses the detection capability of the 257nm wavelength inspection system for the defects on the 6% ArF attenuated phase shifting masks for 65nm node, using DSM based test pattern mask.

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

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.

Newly developed mask inspection system with DUV laser illumination

A new mask inspection system for 150nm and 130nm semiconductor devices which utilizes a DUV laser of 257nm wavelength for an inspection illumination has been developed. A newly developed optical phase shift disk cancels the speckle nose caused by the high coherency of a laser. The phase shift disk has micro pits with different depth disposed randomly over the entire plate surface. The speckle pattern changes randomly by rotating the plate, and averaging pattern image by TDI sensor cancels the speckle noise of the laser illumination. Using this method, inspection of masks was realized at DUV wavelength.

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

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.

DUV inspection tool application for beyond optical resolution limit pattern

Mask inspection tool with DUV laser source has been used for Photo-mask production in many years due to its high sensitivity, high throughput, and good CoO. Due to the advance of NGL technology such as EUVL and Nano-imprint lithography (NIL), there is a demand for extending inspection capability for DUV mask inspection tool for the minute pattern such as hp4xnm or less. But current DUV inspection tool has sensitivity constrain for the minute pattern since inspection optics has the resolution limit determined by the inspection wavelength and optics NA. Based on the unresolved pattern inspection capability study using DUV mask inspection tool NPI-7000 for 14nm/10nm technology nodes, we developed a new optical imaging method and tested its inspection capability for the minute pattern smaller than the optical resolution. We confirmed the excellent defect detection capability and the expendability of DUV optics inspection using the new inspection method. Here, the inspection result of unresolved hp26/20nm pattern obtained by NPI-7000 with the new inspection method is descried.

Detection of half-tone PSM pinhole with DUV reflected light source

The defect detection capability for a minute pinhole by a newly developed mask inspection system MC-3500 with DUV reflected light source is reported. The detection sensitivity of a minute pinhole less than 180 nm on a KrF phase shift mask (PSM) with transmitted light source is limited because the pinhole signal intensity is influenced by the diffraction light. The signal intensity of the pinhole both by the reflected light source and transmitted light source was calculated by an optical simulator, and the actual pinhole signal of the KrF PSM and that of the ArF PSM were measured using the MC-3500 with reflected light source. It was found that the 100 nm minute pinhole, which was not detected by the inspection with the transmitted light source, was detected by the inspection with the reflected light source. This shows the effectiveness of the reflective inspection, thus proved that the newly developed MC-3500 inspection system with reflective inspection capability has very high defect detection sensitivity for the advanced masks of 100-130 nm rule and below devices.

Mask Inspection Technology for 65nm (hp) Technology Node and Beyond

The application of the high numerical aperture, 193nm‐ArF laser exposure system is expected to be extended to 65nm node device production and beyond. The extension of 193nm lithography means that the pattern transfer using this exposure system is done under lower k1 condition than previously. This leads to the increase of mask error enhancement factor (MEEF) in the exposure process. Since mask critical dimension (CD) uniformity and defects on a mask are more difficult to control, defect detection consistency with lithography wavelength for the mask inspection system is strongly required. A novel high‐resolution mask inspection platform is developed to enable the high‐quality mask defect inspection for 65–45nm node. The system is operated at wavelength of 198.5nm, which wavelength is nearly equal to that of the 193nm‐ArF laser exposure system. The defect detection performance of 20–60nm defect detection sensitivity is certified at the early stage test. The system capabilities for 65nm node inspection and b...

Advanced die-to-database inspection technique for embedded attenuated phase shift mask

We have developed a deep ultraviolet die-to-database inspection system MC-3500 for the 130 nm node and beyond. The system involves comparison of a mask image scanned at a wavelength of 257 nm and a reference data calculated from complex amplitude of objects with 200 Mpixel/s throughput. An approximation of Hopkins formulation in the region of a large partial coherence factor gives a nonlinear filtering scheme for embedded attenuated phase shift mask (EPSM). The nonlinear filtering was evaluated for intensity fidelity of the reference image using comparison with Hopkins formulation. Evaluation results show that phase optimization is effective in eliminating excessive image ringing and the minimum feature size to maintain fidelity is found to be over 3 pixels. The technique is promising in applications to high-transmission EPSM.