Takehiko Nomura

Six-axis controlled nanometer- order positioning stage for microfabrication

A compact, low-height prototype of a six-axis precise positioning stage for microfabrication has been developed. X and Y stage positioning requires nanometer positioning resolution and robustness against atmospheric turbulence. The stiffness and dead play of the traveling mechanism were improved by using rolling contact guides, and the positioning resolution was improved by using a friction drive mechanism. Analog signals from an optical linear scale are influenced little by atmospheric turbulence. Using these advantages of the optical linear scale and with a newly developed positioning algorithm, one-nanometer resolution was obtained.

Die-to-database mask inspection with variable sensitivity

The cost of mask is increasing dramatically along with the continuous semiconductor scaling. ASET started a 4-year project to reduce mask manufacturing cost and TAT by optimizing Mask Data Preparation (MDP), mask writing, and mask inspection in 2006, with the support from the New Energy and Industrial Technology Development Organization (NEDO). We report on the development of a new low cost mask inspection technology with short Turn Around Time (TAT), as a result of adopting a method of selecting defect detection sensitivity level for every local area, defined by such factors as defect judgment algorithm and defect judgment threshold, as one of the pseudo-defect-reduction technique necessary to shorten mask inspection TAT. Those factors are extracted from the database of Mask Data Rank (MDR) and converted on the basis of pattern prioritization determined at device design stage, using parallel computation.

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.

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.

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.

Review of carriage feed mechanism with nanometer resolution

A carriage feed is a mechanism composed of a guide and a feed. The four parameters of carriage feed accuracy are: feed reference accuracy, feed resolution, guide reference accuracy and guide component constraint accuracy. Each parameter can be improved through the use of servo techniques. This paper discusses, on the basis of kinematic principles, a carriage feed mechanism with no lost motion and a fine feed resolution with high reliability and accuracy in the nanometer range. For nanometer positioning of carriage feed mechanisms, both ball and roller bearing and hydrostatic support mechanisms controlled by force-operated position control can be used. Capacitive transducers and feedback sensors of optical linear scale are also applicable in consideration of S/N ratio.

Image sensing method and defect detection algorithm for a 256-Mb and 1-Gb DRAM mask inspection system

This paper describes an image sensing method and defect detection algorithm applied for a newly developed mask inspection system, the MC-2000, for 256 Mbit and 1 Gbit DRAM masks. The MC-2000, which utilizes i-line wavelength optics, is designed for less than 0.2 micrometer defect detection capability. An image sensing system employing a TDI (time delay integration) CCD image sensor is used for i-line image acquisition with an 80 Mpixel/sec data rate. Defect detection is done by comparing sensor image data with CAD data. Here we utilized our original differential comparison method which has very high sensitivity for defect detection.

New die-to-database mask inspection system with i-line optics for 256-Mb and 1-Gb DRAMs

For mask defect inspection in 256 Mbit and 1 Gbit DRAMs, it is necessary to have high sensitivity of 0.2 - 0.1 micrometer. A new die-to-database mask inspection system MC-2000 for 256 Mbit and 1 Gbit DRAMs has been developed. This system has high resolution optics with i-line light and high NA lens, and high speed and high accuracy data processing circuit by new multilevel bit map pattern generator, so the system has both high detectability and high throughput. This paper describes system configuration which include optical system and mechanical system, the defect inspection method, and inspection performance including defect sensitivity.

Phase measurement using Hg-Xe lamp and KrF excimer laser

We have developed a new system to measure the phase shift caused by the phase shift mask (PSM) for a deep-UV stepper. The system uses two types of 248 nm wavelength deep-UV light sources. One is an Hg-Xe lamp, and the other is a KrF excimer laser. These are interchangeable to match the illumination light source of the stepper. The phase is measured with a polarizing shearing interferometer. It has two wollaston prisms, a condenser lens, and an objective. The objective has a long working distance of more than 7 mm. This is necessary in order to measure the PSM with a pellicle. A light beam is separated into two orthogonal polarized light beams and sheared on the PSM, and then recombined on a sensor. The transmission beams through a shifter and a substrate interfere each other. Then the phase difference from the shifter is obtained from the difference between the two beams. We evaluated phase measurement repeatability and the measurable minimum pattern width. In the measurement of a halftone PSM, the repeatability was +/- 1 degree over several months, and the minimum pattern width was 2 micrometers or less.