S. Nishikawa

Reduction of transient boron diffusion in preamorphized Si by carbon implantation

Boron diffusion in preamorphized Si is studied as a function of dose of carbon ion implantation. The boron was implanted at 20 keV with a dose of 1×1015 cm−2, and carbon was implanted at 60–90 keV. The preamorphized depth was 230 nm. It is shown that transient enhanced diffusion occurs even in the preamorphized region without C+ implantation. The diffusion constant is larger than the standard one by about one order of magnitude in the case of 1000 °C annealing for 15 s. This enhancement is eliminated by C+ implantation at a dose of about 1015 cm−2. This implantation also reduces the defects at the amorphous/crystal interface. These findings indicate that the implanted carbon acts as a sink of excess interstitials.

Pattern dependence in selective epitaxial Si1−xGex growth using reduced‐pressure chemical vapor deposition

Pattern dependence of the growth rate and Ge content in selective epitaxial Si1−xGex growth using reduced‐pressure chemical vapor deposition has been examined for the SiH2Cl2‐GeH4‐H2 system. Contrary to selective epitaxial Si growth where pattern dependence diminishes at low growth temperatures, the growth rate of selectively grown Si1−xGex layers depends on the ratio of the exposed Si area to the oxide‐covered area on a wafer, at temperatures as low as 600 °C. The Ge content in the layers also depends on the ratio, and the dependence is greater at higher temperatures. Adding HCl to the gas phase decreases the pattern dependence of both growth rate and Ge content. Although, in terms of the growth rate, an optimum HCl flow rate for pattern‐insensitive growth exists, the Ge content in the layers is always higher for the wafer with a smaller exposed area.

Elimination of secondary defects in preamorphized Si by C+ implantation

In preamorphization of Si, secondary defects formed at the original amorphous/crystal (a/c) interface were studied as a function of the dose of carbon ion implantation. The preamorphized depth was 230 nm. The carbon was implanted at 78 or 90 keV at 2×1012–2×1015/cm2. The size and density of dislocation loops near the a/c interface decreased with increasing C+ dose. The C+ implantation at a dose of 1×1015/cm2 reduced the density of atoms bound by dislocation loops from 5.9×1014/cm2 to 2.6×1013/cm2. At C+ doses higher than about 1×1015/cm2, additional defects with a diameter of less than about 5 nm were observed. These defects are SiC agglomerates that act as a sink for excess self‐interstitials, which results in a reduction in the density of secondary defects.

Intrinsic stress and hydrogen bonding in glow‐discharge amorphous silicon films

We have found a strong correlation between intrinsic stress and hydrogen bonding in glow‐discharge amorphous silicon (a‐Si:H) films. The stress of high‐deposition‐rate (HDR) films continuously changes from tensile to compressive with increasing rf power. In contrast, low‐deposition‐rate (LDR) films indicated compressive stress in all the rf power range which was varied. However, adding a small amount of Ar to SiH4 in the LDR film deposition changes its stress from compressive to tensile as in the HDR films. IR absorption spectroscopies showed that films with compressive stress always indicated a smaller ratio of absorptions at 2070 and 2000 cm−1 α(2070)/α(2000) than the value Rc(=0.9–1.2), whereas those with tensile stress showed a larger ratio. Consequently, zero or very weak stress is reached at the ratio approximately equal to Rc, regardless of varying deposition parameters. It is also shown that annealing alters the stress of all the HDR films to strong tensile, and that α(2070)/α(2000) decreases, dif...

Optical properties of a-Si:H/a-Si1−xCx:H and a-Si:H/a-SiNx:H superlattice

Abstract The optical energy gap and photoluminescence of amorphous semiconductor superlattice a-Si:H/a-SiC:H and a-Si:H/a-SiN:H are measured as a function of the thickness of a-Si:H and a-SiN:H sublayer and the optical energy gap of a-SiC:H. The results for optical energy gap are compared with the calculated result using a one dimensional quantum well model. The results of photoluminescence are discussed in terms of the carrier confinement effect.

Properties of multilayered photoreceptor with amorphous silicon and its alloys, and application to optical printer

Abstract Amorphous silicon photoreceptor drum (a-Si drum) for positive corona has been fabricated in multilayered structure (a-SiC/a-Si/p-type a-Si/Al) at high deposition rate (12μm/H) by RF glow discharge. The a-Si drum exhibits an excellent photosensitivity and gives a high resolutive image with an optical printer. The a-SiC layer sufficiently reduces the fatigue of the charge retentivity by repeated cycles. Furthermore, the photoreceptor with a-SiGe has been developed to increase the sensitivity in the GaAlAs diode laser emission region.

Kinetics of epitaxial Si1−xGex growth using SiH2Cl2–GeH4–H2 mixture in reduced‐pressure chemical vapor deposition

The dependences of the Ge/Si ratio in epitaxial Si1−xGex layers grown using a SiH2Cl2–GeH4–H2 mixture by reduced‐pressure chemical vapor deposition on the flow rate ratio of GeH4/SiH2Cl2 and on the total flow rate have been examined in the temperature range from 480 to 600 °C. As previously reported, the Ge/Si ratio does not increase linearly with the flow rate ratio; instead, the rate of increase decreases at high flow rate ratios. Additionally, it increases with increasing total flow rate when the ratio of GeH4/SiH2Cl2 is fixed. It is found that these flow rate dependences are well accounted for by assuming that the reaction order for SiH2Cl2 adsorption is twice as large as that for GeH4 adsorption.

Thickness dependence of staebler-wronski effect in a-Si:H

Abstract We have studied the thickness dependence (TD) of the Staebler-Wronski effect in undoped a-Si:H. In annealed state, the dark conductivity σ d and the activation energy E a showed a large TD; an upward band bending exists at the surface and interface. After the illumination of intense light, the σ d decreased and the E a increased more largely for films thicker than 1μm, in consequence, the TDs of the σ d and E a reduced, which means the bulk change. Photoconductance G p measurements with two lights of different wavelength indicate that the upward band bending reduced after the illumination. These results are discussed relating to the change of the band bending.

Arf Laser-Induced Chemical-Vapor Deposition of Tungsten for Gate Electrodes

The deposition of W films by ArF laser-induced chemical-vapor deposition (LCVD) was investigated as a function of incident laser power, WF 6 and H 2 partial pressures, and substrate temperature. The deposition of W films by LCVD is discussed dividing that into two parts, thermal CVD (TCVD) and photon assisted CVD (P h CVD). The rate of P h CVD has been defined as the difference between the rates with and without laser irradiation. The reaction orders for P h CVD are 1, 0 with respect to WF 6 and H 2 partial pressures, respectively, and the rate linearly increases with increase in laser repetition rate. The activation energy in P h CVD is 0.17 eV. These facts indicate that, in LCVD, P h CVD takes place independently of TCVD and that the deposition rate in P h CVD is determined by the formation of F radicals in the dissociation of WF 6 molecules by laser irradiation. MOS capacitors with LCVD-W gates were fabricated and their characteristics were compared with those with sputtered-W gates. It was shown that the level of contamination due to mobile ions in the capacitor with the LCVD-W gate was extremely low.

Amorphous carbon coating on amorphous silicon photoreceptors

Hard hydrogenated amorphous carbon (a‐C:H) films were coated on amorphous silicon photoreceptors by the plasma decomposition of acetylene (C2H2). This overlayer proved to be a much better protective layer for the adsorption of external species compared to an a‐SiNx or a‐Si1−xCx overcoating layer, and the image degradation induced by such adsorption was considerably reduced. The highly protective properties were attributed to the hydrophobic nature of C–Hn (n=1–3) and C–C bonds contained in the a‐C:H film. The optical properties of the a‐C:H films are also described.