Koichi Moriizumi

True CW 193.4-nm light generation based on frequency conversion of fiber amplifiers

We present a source of line-narrowed continuous-wave (CW) radiation at 193.4 nm with over 10 mW of output power for the first time, to our knowledge. The system configures four successive frequency conversions of outputs from three single-frequency fiber amplifiers at 1064, 1107, and 1963 nm. The 266-nm beam produced by frequency quadrupling of 1064-nm light is sum-frequency mixed with the 1963-nm light to generate 234.3-nm radiation, which is consequently mixed with the 1107-nm light to generate 193.4-nm radiation. Both mixings are achieved in temperature-tuned non-critically phase-matched (NCPM) crystals.

Maskless Submicrometer Pattern Formation of Cr Films by Focused Sb Ion Implantation

Maskless submicrometer patterning of Cr films was done by implanting focused Sb+ ion and by plasma etching using CCl4 gas. Dose and depth dependence of the etching rate and Sb profiles were measured to investigate the concentration dependence of Sb. The present patterning characteristics are compared with conventional patterning characteristics using Au masks. It was found that a sharp threshold dose exists to form an etch resistant layer and this enables formation of few hundred nanometer thick, submicrometer patterns with vertical side walls. It was also found that the resistivity of patterned Cr films increase only 10%.

Electron beam pattern inspection system using digital image processing

An electron beam pattern inspection system (EBIS) using digital image processing is presented. A pattern‐to‐data comparison method is used in this system to detect systematic, random and repeating defects of VLSI circuit patterns. The inspection data are generated from the design data, and transferred from a computer aided design (CAD) system via a computer network. In order to obtain the information of mask or wafer patterns, a low‐energy scanning electron microscope, which has the advantage of avoiding damage to the active devices and not charging the surface, is used. Frame memories are installed to store the inspection data and the actual pattern image. An extra image processor preprocesses the pattern image to obtain high signal‐to‐noise ratio and manipulates these images to extract defects. Two algorithms extracting the defects are studied. Spatial differentiation followed by a thresholding operation is a suitable procedure for the signal with drift.

Fast and accurate optical proximity correction based on aerial image simulation

Because optical lithography requires precise CD control, we developed a fast, accurate proximity correction method based on aerial image simulation. Simple formulas using a linear combination of simulated aerial image intensities both at and around mask edge were found effective for fast, precise CD prediction. Using the developed CD prediction and the fine biasing correction methods, we verified that various two-dimensional patterns printed by an i- line stepper using modified illumination and binary intensity mask are satisfactorily corrected; i.e., CD deviations from designed values, line shortening and feature deformations are effectively reduced.

Application of Proximity Effect Correction Using Pattern-Area Density to Patterning on a Heavy-Metal Substrate and the Cell-Projection Exposure

Proximity effect correction for electron beam (EB) direct writing is studied in this paper. An iterative calculation of exposure-dose modulation by equalizing the deposited energy of all figures requires an extremely long calculation time, especially in the case of high EB acceleration voltage. Therefore it is not practical for the correction of LSI. The correction method using pattern-area density, however, could realize the high-speed proximity effect correction. In this paper, this method is first investigated from the standpoint of the correction accuracy. Next, the applicability of this method to two critical cases is examined. One is the patterning on a heavy-metal substrate, on which backscattering yield of electrons is high. The other is the application to the cell-projection exposure, in which it is impossible to modulate exposure dose inside the cell. Lastly, the calculation time of the proximity effect correction is evaluated for 64 Mbit dynamic random access memories (MbDRAMs).

Fabrication technologies for advanced 5X reticles for 16M‐bit dynamic random access memory

Fabrication technologies for advanced photomasks with a molybdenum silicide (MoSi) film have been developed by using a variable‐shaped electron‐beam (e‐beam) system. These technologies were applied to the fabrication of 5X reticles for 16M‐bit DRAMs. The variable‐shaped e‐beam system is very effective in increasing the throughput for writing reticles which have a great number of figures, such as 16M‐bit DRAMs. The average writing time was 100 min, which was ∼ (1)/(3) of the time when using a conventional raster‐scan e‐beam system. Photomasks with the MoSi film have advantages in comparison with those with conventional chromium (Cr) film. Pattern defects did not appear during the photomask cleaning because of strong adhesion of the MoSi film to the quartz substrate. Moreover, an accurate feature size on the photomasks was obtained, because the MoSi film was easily dry etched. The feature size accuracy obtained was 0.03 μm in 3σ all over the 5 in. blanks.

Precision Improvement in Optical Proximity Correction by Optimizing Second Illumination Source Shape

We have achieved precision improvement by optimizing the second illumination source shape in our optical proximity correction system. Based on the consideration that the optical proximity effect is significantly dependent on interference conditions, we have applied a new type of modified illumination to projection optics in order to improve the correction accuracy. A new second illumination source is formed by an illumination aperture with a spindle-shaped opaque region, whose curvature is the same as that of the projection lens pupil. Through use of this aperture, pattern edges can be definitely classified according to the interference condition, and resultant improvement of the pattern size accuracy, within ±0.01 µm, which is nearly the same level as the detection limit, can be achieved.

Electron‐beam inspection technology for x‐ray masks

An electron‐beam inspection system with a capability of detecting quarter‐micron defects has been developed and is applied to the inspection of the x‐ray mask itself. The accuracy of this system is measured and discussed. The distortion of the electron‐beam deflection is 0.08 μm (root‐mean‐square error) within 70×90 μm area in the scan field of 100 μm2. A sample x‐ray mask has Au absorption patterns with the thickness of 0.8 μm on a 2.0‐μm‐thick SiN membrane. An accelerating voltage of 3 kV was found to give a stable signal with a minimum of charging effects. The inspection is performed by means of die‐to‐die comparison scheme. Detection of 0.3 μm defects was demonstrated, indicating the potential of electron‐beam technology for x‐ray mask inspection.

Continuous-wave 193.4 nm laser with 120 mW output power

This Letter describes an all-solid-state continuous-wave, deep-ultraviolet coherent source that generates more than 100 mW of output power at 193.4 nm. The source is based on nonlinear frequency conversion of three single-frequency infrared fiber laser master-oscillator power-amplifier (MOPA) light sources.

Advanced 5x reticle inspection technologies for ULSI devices

This paper describes new database inspection technologies for pattern inspection of ULSI 5x reticles. An improved inspection system architecture which addresses three important factors: sensitivity, data volume, and inspection throughput is studied. To improve defect detection sensitivity, the high resolution optical images which are captured by the inspection system are enhanced using programmable finite impulse response filters. New defect detection algorithms are utilized. Increased resolution is also incorporated in the database images. Higher resolution database images are especially effective in improving sensitivity and reducing false detections in small pattern geometry. The database format has also been optimized to minimize the disk storage requirements and network file transfer time. The new database generator is capable of expanding compacted data and creating grey level bit mapped images in real time. Experimental results are reported using actual 5x reticle inspection results and simulated reticle data for ULSI chips, such as 64Mbit DRAM and l6Mbit SRAM. The results indicate that 5x reticles can be inspected for O.3im defects with an acceptable level of false detections and throughput that is comparable to eleciron beam write times.