Yoh-ichi Yamaguchi

Suppression of etch pit and hillock formation on carbonization of Si substrate and low temperature growth of SiC

A carbonized layer on a Si substrate was formed with hot-wall type LPCVD. The Si substrate was heated up to 1020 ° C at various C2H2 partial pressures from 1.0 to 18 mTorr. A lot of etch pits and hillocks were observed on the carbonized substrate at lower C2H2 partial pressures, which are supposed to be formed by Si migration via the SiC layer. Formation of etch pits and hillocks was suppressed with increasing C2H2 partial pressure because of sealing-off the Si diffusion via the SiC layer. After carbonization of Si the substrate at 8.1 mTorr C2H2 partial pressure at 1020 ° C, SiH2Cl2 and C2H2 were alternately introduce at 1000 ° C to grow SiC films. The growth rate of SiC was 8 A/cycle; this seems to imply that the growth might occur by atomic level controlled surface reactions.

Heteroepitaxial growth and ESR evaluation of 3C-SiC

Abstract The heteroepitaxial growth of 3C-SiC on Si substrates has been studied in a hot-wall type LPCVD reactor with an alternating supply of SiH2Cl2 and C2H2 in the temperature range of 750 to 1050°C. Silicon carbide films have been grown only at temperatures above 800°C. The growth rate of the SiC films increases with temperature above 900°C, while a constant growth rate (4.4 A/cycle) is obtained in the temperature range between 800 and 900°C. The characteristics of the growth rate of the SiC films can be understood by taking into account the decompositions of adsorbed SiCl2 on the surface of the substrates. The defect structures of grown SiC layer has been studied by the ESR (electron spin resonance) method. Three paramagnetic defects, that is, Si-dangling bonds (g = 2.0055, ΔHpp = 5.5 Oe) in the Si amorphous region, Si-dangling bonds with C atom neighbors (g = 2.0033, ΔHpp = 3.0 Oe), and C-dangling bonds with C atom neighbors (g = 2.0030, ΔHpp = 15.0 Oe) were observed by ESR analysis.

X-Ray Mask Distortion Induced in Back-Etching Preceding Subtractive Fabrication: Resist and Absorber Stress Effect

The influence of resist and absorber stress distributions on X-ray mask distortion induced during back-etching preceding subtractive fabrication is analyzed experimentally and simulated. The stress distribution (gradient) in a resist and/or that in an absorber film causes larger pattern displacement rather than the film average stress. Some resists have considerably high stress after coating on a wafer, and this stress also changes during exposure, causing local pattern displacements. However, use of chemically amplified resist systems, in which the reaction after exposure is limited to a small amount acid generation, might solve this problem. Low-stress positive-tone resists should thus be developed.

Mechanisms of SiC growth by alternate supply of SiH2Cl2 and C2H2

Abstract Heteroepitaxial growth of 3C-SiC on Si(001) substrate has been realized by the use of a hot-wall type LPCVD with an alternating supply of acetylene (C 2 H 2 ) and dichlorosilane (SiH 2 Cl 2 ) in the temperature range 1000–1050°C. By synchronizing hydrogen (H 2 ) supply with C 2 H 2 supply, the reduction of SiCl 2 molecules on the surface of the substrate during SiH 2 Cl 2 supply was suppressed, resulting in the realization of the self-limiting process of SiCl 2 adsorption in the SiC growth process. The growth rate of 3C-SiC was independent of the temperature, the flow rate of the SiH 2 Cl 2 and the duration of the SiH 2 Cl 2 supply. To suppress the reduction of the SiCl 2 molecules during the SiH 2 Cl 2 supply seems to be a necessary condition to realize layer-by-layer growth of SiC. Since residual C 2 H 2 molecules hinder the SiCl 2 molecules from being adsorbed on the substrate, the C 2 H 2 molecules on the surface of the substrate may give rise to a suppression of SiC growth.

Properties Of SiC Film As X-Ray Mask Membrane

Many properties of LPCVD SiC film as X-ray mask membrane have been investigated in detail. The film has an atomic ratio of 1.0 and negligible impurities, and was found to be damage-free to SR X-rays up to 500 KJ/cm 2 . An integrated transparency of 1.05 μm thick SiC membrane for SR X-rays was measured to be 76%. The interference peak at 633 nm of optical spectrum has given the membrane of around 1.0 μm in thickness the transmittance peak of 70% and increased to more than 80% after an AR coating or planarizations by polishing and etching-back. The attainable transmittance was found to be limited to about 84%, theoretically and experimentally, due to the absorption of the membrane. The peak transmittance of 87% is obtainable by the AR coating on the polished SiC membrane. The internal stress was found to be independent of thicknesses above 0.6 μm and the measured Youngs modulus is 4.5×10 11 Pa irrespective of the thickness and stress. Some extremely polished (0.1 nm Ra) and all the etched-back membranes studied withstood breakage at the pressure as high as the as-deposited ones. The stress uniformity in 30 mm square of the membrane was found to be ± 10 % by measuring five local stresses with a bulge method.

Effect of Anodic Bonding Temperature on Mechanical Distortion of SiC X-Ray Mask Substrate

Distortion of SiC X-ray mask substrate during anodic bonding has been found to occur due to the difference in the thermal expansions of SD glass frame and Si wafer deposited with SiC, and the distortion characteristics can be explained by the bi-metal effect. The reduction in the difference in the expansion is required to obtain lower substrate distortion, and has been realized by using the SD-2 glass, which has the most accurate matching of the expansion to Si, and by lowering the bonding temperature. Any other parameters than the bonding temperature, such as the applied voltage and the bonding time, have been found not to cause the distortion. Homogeneously concave mask substrate bonded at 230°C, using 4-mm-thick SD-2 glass frame and 1-mm-thick wafer, has the flatness values of 2.18 µm and 0.26 µm for the wafer and the membrane area, respectively.

Smoothing Roughness of SiC Membrane Surface for X-Ray Masks

We have obtained a smoother surface of SiC membranes than that of as-deposited SiC using etch-back and polishing methods, and investigated the influence of surface roughness of SiC films on internal stress and film structure of X-ray absorber films and optical transmittance of SiC membrane. Surface roughness for the as-deposited SiC surface is 15 nm (Ra), whereas that for etch-backed SiC is 6.9 nm (Ra) and that for polished SiC is 4.3 nm (Ra). Optical transmittance of as-deposited SiC membrane is 48% (λ=633 nm) and increases by a few percent with decrease in the Ra value. Internal stress of sputtered Ta tends to show gentler change with increasing surface roughness of SiC film. Film structure of Ta film is largely influenced by the surface roughness of SiC films at low Ar pressure. Sub-half micron absorber patterns with vertical walls, however, have been obtained even on rough surface SiC.

Stress‐free and amorphous Ta4B or Ta8SiB absorbers for x‐ray masks

We have succeeded in obtaining practical x‐ray absorber films, Ta4B and Ta8SiB, using an rf magnetron sputtering method. The internal stress of these films can be controlled precisely within ±1.0×107 N/m2. The stress has thermal stability at 350 °C. The stress is also quite insensitive to the film thickness and substrates used. These excellent stress properties are attributed to the amorphous structure of the film. The amorphous structure also ensures quarter‐micron pattern fabrication. Densities of 15.3 g/cm3 for Ta4B and 15.6 g/cm3 for Ta8SiB are high enough to yield sufficient contrast for x‐ray exposures.

Radiation stability of SiO2‐antireflective film coated SiN and SiC x‐ray mask membranes

Radiation stability of SiO2 antireflective film coated SiN and SiC x‐ray mask membranes was studied. Although the transmission at 633 nm of the SiO2‐coated SiN was reduced by about 8% after synchrotron radiation (SR) exposure with an absorber dose of 100 MJ/cm3, the oscillation of the transmission due to interference was considerably suppressed even after the SR absorption. Furthermore, the optical transmission spectrum of the SiO2‐coated SiC was nearly equal to that of uncoated SiC after the SR absorption of 100 MJ/cm3. The pattern displacement induced by the SR absorption of 10 MJ/cm3 for the SiO2‐coated SiN and for the SiO2‐coated SiC was σx=6 nm, σy=7 nm and σx=8 nm, σy=6 nm on the 25‐mm‐square area, respectively, the values of which were within the reproducibility of the displacement measurement. Electron spin resonance analysis indicated that no significant difference of spin density between the SiO2‐coated and uncoated SiN membranes was recognized before and after the SR absorption.

Synchrotron Radiation Damage Mechanism of X-Ray Mask Membranes Irradiated in Helium Environment

The mechanism of X-ray mask membrane displacement induced by synchrotron radiation (SR) has been discussed. Silicon nitride (SiN) and silicon carbide (SiC) membranes were irradiated by SR in a 1 atm helium ambient. SR-induced displacement for both membranes was 25-97 nm (σ). Oxygen concentration in both SiN and SiC was below 0.01 in O/Si atomic ratio. Although an increase in dangling bond density of SiN was observed, no remarkable increase in spin density was detected in SiC. Moreover, the most important finding was that thin oxides were grown on the membrane surface after SR irradiation. From these results, it is considered that the oxide growth on SiC membrane surfaces, and both the oxide growth and the increase of dangling bond density in SiN play an important role in the SR-induced displacement for the X-ray mask membranes.