Takeshi Nishizaka

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.

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.

Evaluation of overlay accuracy for the x‐ray stepper TOXS‐1

This article presents the overlay accuracy for the newly developed prototype x‐ray stepper TOXS‐1. Checkerboard gratings on a mask and wafer were used for an optical‐heterodyne interferometry alignment system so that the alignment signals from the mask and wafer gratings can be detected independently without mutual interference. The alignment signal varied slightly with the mask‐to‐wafer gap due to multiple reflection of the alignment beams between the mask and wafer, which deteriorates the alignment accuracy. To reduce the multiple reflection, the mask grating and the mask alignment window were coated with opaque film and antireflecting film, respectively. A 0.025 μm (mean+3σ) overlay accuracy has been achieved for SiO2 processed wafers. The overlay accuracy was further measured for four different kinds of processed wafers, and a 0.035 μm (mean+3σ) accuracy has been obtained except for an aluminum processed wafer.

X‐ray stepper aiming at 0.2 μm synchrotron orbital radiation lithography

A vertical x‐ray stepper has been developed for 0.2 μm synchrotron orbital radiation lithography. The key features of this prototype stepper are a new gap setting algorithm, an optical heterodyne alignment system, and a newly developed fine motion mask stage. Gap setting is executed so as to make the mask and wafer parallel to the travel plane of the wafer x–y stage so that only one gap setting per wafer is required. The gap setting accuracy between 20 and 50 μm gaps is better than ±1.5 μm (3σ) for each exposure position. The optical heterodyne alignment signal obtained by detecting the diffraction beams from two checkerboard gratings has a detectable resolution of better than 0.01 μm and has only a small dependence of ±0.02 μm on gap variation. The alignment signals are fed back to the mask stage which can align the mask and wafer with a resolution of 5 nm. In exposure experiments, 0.15 μm lines and spaces were printed on a negative resist (SAL 601) and a 0.05 μm overlay accuracy has been obtained.

0.05 µm (3σ) Overlay Accuracy Through-the-lens Alignment in an Excimer Laser Lithography System

This paper presents a through-the-lens (TTL) alignment, called separated mark TTL alignment (SMART), applied to a KrF excimer laser lithography system. This SMART optical system does not require any complicated compensation mechanisms for longitudinal chromatic aberration. Several advanced methods for SMART optics to obtain higher overlay accuracy, such as optical heterodyne interferometry, real-time alignment system, and alignment signal processor, have been developed and adopted. The performance of such an improved SMART in an excimer laser lithography system was experimentally evaluated using dynamic random access memory (DRAM)-processed wafers. An overlay accuracy of 0.05 µm (3σ) has been achieved.

A Chromatic Aberration-Free Heterodyne Alignment for Optical Lithography

This paper describes the principle of a new alignment method (SMART) and alignment optics using an optical-heterodyne technique. This SMART dose not need to correct chromatic aberration. Therefore, it dose not require any mechanism, such as mirrors, a prism or a lens system to correct chromatic aberration for the projection lens. A pair of one-dimensional gratings for the mask mark and a checker grating for the wafer mark were used in SMART optics. The relation displacement between the mask and the wafer can be directly detected by measuring the phase difference of the heterodyne beat signals. The experimental result for the phase difference was similar to the calculation result. An alignment signal variation of less than 10 nm was obtained.

High-performance DUV inspection system for 100-nm generation masks

Mask inspection has become a much more important factor in LSI manufacturing. In order to perform mask inspection with high reliability for devices of 100-130 nm rule and below, a high-resolution and high-speed die-to-database inspection system is indispensable. In order to satisfy these requirements, the Toshiba MC-3500, a next-generation mask inspection system using 257nm DUV short wavelength optics, has been developed. The MC-3500 employs a die-to-database comparison method and a high-performance data processing system that is newly developed. This paper reports the system configuration, basic characteristics for defect detection and inspection performance.

The Estimation and Improvement of TTL Alignment Error Budgets for an Excimer Laser Aligner.

This paper describes studies on the alignment error budgets caused by a TTL (through the lens) alignment optical system (SMART : separated mark TTL alignment) for an excimer laser aligner. Alignment error factors, such as the optical phase fluctuation of the alignment beam, the inclination variation of the alignment incident beam, the tilt of the wafer and the reticle, and the defocus of the reticle, have been analyzed and estimated. It was demonstrated that the total error of the alignment optical system was required to be better than 0.02 μm in order to satisfy the positioning strategy of the excimer laser aligner with a 0.05 μm (3σ) overlay accuracy. Several compensation methods have been developed and adopted to SMART. As a result, it was obtained experimentally that the total error of the alignment optical system became better than 0.02 μm. It has met the development goal. The new SMART optical system which was adopted to the KrF excimer laser aligner showed an excellent performance with a better than 0.05 μm (3σ) overlay accuracy.