Tokushige Hisatsugu

130 nm and 150 nm line-and-space critical-dimension control evaluation using XS-1 x-ray stepper

Critical-dimension (CD) control for 130 and 150 nm line-and-space (L/S) patterns printed with the XS-1 x-ray stepper was evaluated using two kinds of resists: SAL606 and TDUR-N908. The largest factor in the CD variation was the nonuniformity of the x-ray dose, which was ±4.4% in a 20 mm×20 mm field. In replicated resist patterns, the CD variation due to mask-CD variation dropped to less than half the mask-CD variation because of Fresnel diffraction. For 130 nm L/S patterns, the CD variation for an 8-in.-diam wafer was 7.9 nm (3σ) for SAL606, and 12.0 nm (3σ) for TDUR-N908. For 150 nm L/S patterns, the values were 10.5 nm (3σ) and 14.6 nm (3σ), respectively. Although the major factors causing CD variation are dose nonuniformity and mask-CD variation, different resist materials reflect the effects of these factors to different degrees. The CD variation of 150 nm L/S patterns among seven wafers exposed on the same day was ±2.8 nm for SAL606 and ±3.7 nm for TDUR-N908, which is most likely due to fluctuations ...

Measurement of spectral and spatial intensity distributions of synchrotron radiation in soft x‐ray region by means of helium gas scattering

We measured the spectral and spatial intensity distributions of synchrotron radiation (SR) in the soft x‐ray region using an energy‐dispersive method with a Si(Li) detector at the Photon Factory. By measuring the intensity of x rays scattered by helium gas, we could reduce the high SR intensity to the sensitivity range of a Si(Li) detector and, by selecting the scattering angle, we used this method as a polarimeter. In the soft x‐ray region above 2 keV, the measured spectral and spatial profiles of the direct beam transmitted through a Be window were almost the same as the calculated values, but absolute intensity was about 30% less than calculated. This is largely due to the geometric errors of the measuring system. We also measured the intensity distribution of the beam reflected from fused quartz mirrors. The spectrum profiles agreed with the calculated values, but absolute intensity was somewhat less than expected, and the spatial distribution had a complicated profile because of imperfections in the ...

Low-dose exposure technique for 100-nm-diam hole replication in x-ray lithography

In this article, we describe a new exposure technique for printing hole patterns with diameters of 100 nm or below in x-ray lithography. By using mask patterns approximately twice the size of the required resist patterns, 100-nm-diam holes can be replicated with doses less than those required to clear a large exposed area (D0) with a 20–30 μm gap. A 540-nm-thick UVII-HS resist was used for the exposure experiment. With a proximity gap of 20 μm, a 100-nm-diam hole was replicated with a 200-nm-diam mask pattern by exposing it with 0.56 D0 dose. Both the experimental and the simulation results indicated that this technique provides a higher resolution and a larger exposure latitude compared to normal-dose exposure. In terms of mask biasing, this technique corresponds to the mask bias optimization at doses below D0.

Synchrotron radiation beamline for x‐ray lithography

We designed a synchrotron radiation (SR) beamline for x‐ray lithography and optimized the beamline based on ray‐tracing calculations. For a beamline with a single toroidal mirror, the intensity uniformity in the horizontal direction can be improved by making the meridian radius different from that of the general focal condition. We used this method to determine beamline parameters. Converging the SR beam gave an intensity gain of about 4, and we reduced the nonuniformity of intensity distribution to less than 3%. We also estimated the overlay error due to incorrect mirror parameters to be a maximum of 14 nm with a gap of 20 μm. We calculated an exposure‐gap diagram using simulation codes; the calculation accounted for absorbed energy distribution due to Fresnel diffraction, penumbral blur, electron ranges of the secondary electrons in the resist, and development properties. We found that there is a dose margin of at least ±5% to achieve ±10% linewidth control for 0.15 μm feature size for gaps below 20 μm. We made preliminary measurements of spectra and intensity distributions for the constructed beamline, and showed that the performance is as predicted by our calculations.

A Design Of Beamline Optics For Large Field Exposure

New mirror designs for an X-ray lithography (XRL) beamline have been devised for the large-field, high-power irradiation of wafers. In contrast to analytically described mirrors, such as toroids, ellipsoids, etc., the new shapes were numerically determined. The design method employed was developed by Xiao, et al. A beamline employing such an optimized mirror design should provide a high X-ray power density of 58 mW/cm2 over a 50-mm-square exposure area, and 88 mW/cm2 over a 40-mm-square exposure area, with a uniformity of better than ±2%. The slope error margin was also estimated using numerical simulations, and it was found that the exposure characteristics do not degrade when the slope error is less than 25 arcsecs over the whole surface of the mirror.

X-ray lithography beam line BL-17C at the photon factory

Abstract We constructed a beam line, BL-17C, for X-ray lithography at the Photon Factory. In this beam line, two parallel mirrors are used to cutoff high-energy photons and to keep the light path of the reflected beam unchanged when the glancing angle of the mirrors changes. We studied the reflective characteristics of mirrors using He gas scattering to measure reflected and incident light spectra. The obtained reflectivity for a fused quartz mirror with a roughness of 0.3 nm nearly equaled the theoretical value.

Photon Stimulated Desorption from Finely Polished Metals Irradiated with Synchrotron Radiation

Photon-stimulated desorption (PSD) from electrolytic-abrasively polished stainless steel, copper, and titanium was evaluated using synchrotron radiation (SR) in the spectral range of 1-7 A. Typical desorption yield of the finely polished samples, measured with the throughput method, ranges from 2×10-4 to 5×10-4 molecules/photon with desorption species of H2, CO and CO2. The difference in yields among the materials was quite small after considerable irradiation. We also found that the yields of electrolytically and electrolytic-abrasively polished stainless steel are almost the same, except for in the initial period of irradiation. This similarity was consistent with the result of surface inspection with XPS.

Reactive Sputter Etching System with Floating Grid

A reactive sputter etching (RSE) system with a floating grid (FG) is studied in an effort to eliminate damage to Si wafers during the etching process. In this system, an FG is used as a third electrode between the anode and cathode in an otherwise conventional diode-type RSE system. This causes the discharge current to increase because the FG, together with the cathode, acts as an electrode to generate the hollow cathode effect in glow discharge. As a result, the etch rates for various materials increase, and the self bias voltage at the cathode drops sharply as compared with that of a conventional system. Since the damage depends on the self-bias voltage, it is possible to etch specimens without damage. This paper presents the etching characteristics of the RSE system with the FG.