Hiroaki Hanafusa

Strain-Relaxed Si1-xGex and Strained Si Grown by Sputter Epitaxy

Strained Si on our previously proposed strain-relief relaxed thin quadruple-Si1-xGex-layer buffer was formed by sputter epitaxy, the buffer relaxation mechanism and controllability of which were basically the same as those of gas-source molecular beam epitaxy (GS-MBE); the strained-Si crystallinity obtained by sputter epitaxy was largely comparable to that obtained by GS-MBE. By using sputter epitaxy, a flatter strained Si surface that exhibits almost no cross-hatch undulation morphology is obtained. The strain rate of the topmost 60-nm-thick strained Si layer grown on the quadruple-Si1-xGex-layer buffer with a total thickness of 240 nm and a top Ge content of 0.35 was 0.84% in the lateral direction. The results suggest that our environmentally light-load sputter epitaxy method can be applied to the fabrication of high-density Si/Si1-xGex strained devices.

Direct observation of grain growth from molten silicon formed by micro-thermal-plasma-jet irradiation

Phase transformation of amorphous-silicon during millisecond annealing using micro-thermal-plasma-jet irradiation was directly observed using a high-speed camera with microsecond time resolution. An oval-shaped molten-silicon region adjacent to the solid phase crystallization region was clearly observed, followed by lateral large grain growth perpendicular to a liquid-solid interface. Furthermore, leading wave crystallization (LWC), which showed intermittent explosive crystallization, was discovered in front of the moving molten region. The growth mechanism of LWC has been investigated on the basis of numerical simulation implementing explosive movement of a thin liquid layer driven by released latent heat diffusion in a lateral direction.

Ge Flat Layer Growth on Heavily Phosphorus-Doped Si(001) by Sputter Epitaxy

We have investigated layer-by-layer Ge growth methods on phosphorus (P)-doped Si(001) with our sputter epitaxy method at a growth temperature (TG) of 350 °C. With the sputter epitaxy method, relaxed Ge islands are formed on P-doped 3.5 Ω cm Si with Ge–Si intermixing at the Ge/Si interface; however, a partially strained flat Ge layer is grown directly on P-doped 0.015 Ω cm Si. For comparison with a gas-source molecular beam epitaxy (GS-MBE) method using GeH4, Ge islands are formed on 0.015 Ω cm Si at TG = 350 °C. It has been suggested that the P dopants together with the sputter epitaxy method effectively suppress Ge islanding and induce Ge layer-by-layer growth.

Properties of Al Ohmic Contacts to n-type 4H-SiC Employing a Phosphorus-Doped and Crystallized Amorphous-Silicon Interlayer

Contact property of aluminum and 4H-SiC wafer with crystallized amorphous-silicon (a-Si) interlayer was investigated. A phosphorus-doped a-Si layer on SiC wafer was crystallized by annealing at 1377 °C. Good ohmic contact behavior and contact resistivity of 2.1 × 10-6 Ωcm2 were obtained without silicidation annealing process. Furthermore, non-doped crystallized a-Si layer insertion layer also showed ohmic contact property. However, high contact resistivity of 8.2×10-4 Ωcm2 was obtained in the non-doped a-Si sample. X-ray photo-electron spectroscopy analysis suggests that conduction band offset is significantly reduced between crystallized a-Si and SiC wafer. Therefore, a-Si insertion layer is effective for Schottky barrier height decreasing and high doping into Si layer forms low contact resistivity between Al and SiC, indirectly.

High Efficiency Activation of Phosphorus Atoms in 4H-SiC by Atmospheric Pressure Thermal Plasma Jet Annealing

In this study, the application of atmospheric pressure thermal plasma jet (TPJ) annealing for impurity activation in 4H–SiC is reported. The activation of phosphorus atoms implanted at 300°C in 4H–SiC by TPJ irradiation and analysis of its crystallinity are investigated. At the maximum annealing temperature of 1630°C, the minimum resistivity value is 3.1 mΩ·cm and the maximum carrier concentration value is 2.0 × 1020 cm−3. Orientation analysis suggests that the sample implanted at 300°C was recrystallized to a 4H–SiC(0001) structure after 1630°C annealing. Furthermore, a significant increase in the carrier concentration was observed with the increasing cooling rate during the activation annealing process. Rapid cooling may suppress the impurity deactivation. These results suggest that short-time high-temperature TPJ irradiation annealing is effective for P dopant activation in 4H–SiC.

High-efficiency impurity activation by precise control of cooling rate during atmospheric pressure thermal plasma jet annealing of 4H-SiC wafer

We have investigated high-temperature and rapid annealing of a silicon carbide (SiC) wafer by atmospheric pressure thermal plasma jet (TPJ) irradiation for impurity activation. To reduce the temperature gradient in the SiC wafer, a DC current preheating system and the lateral back-and-forth motion of the wafer were introduced. A maximum surface temperature of 1835 °C within 2.4 s without sample breakage was achieved, and aluminum (Al), phosphorus (P), and arsenic (As) activations in SiC were demonstrated. We have investigated precise control of heating rate (Rh) and cooling rate (Rc) during rapid annealing of P+-implanted 4H-SiC and its impact on impurity activation. No dependence of resistivity on Rh was observed, while increasing Rc significantly decreased resistivity. A minimum resistivity of 0.0025 Ωcm and a maximum carrier concentration of 2.9 × 1020 cm−3 were obtained at Rc = 568 °C/s.

High-temperature and high-speed oxidation of 4H-SiC by atmospheric pressure thermal plasma jet

The application of atmospheric pressure thermal plasma jet (TPJ) annealing to the high-temperature and high-speed thermal oxidation of Si-face of 4H-SiC wafer is reported. A high SiO2 film growth rate of 288 nm min−1 was obtained at an oxidation temperature of 1640 °C without intentional dry O2 gas feeding. Ambient analysis suggested that ozone generated from oxygen in the ambient air by the plasma irradiation was supplied to the SiC surface. It is implied that a mono-oxygen decomposed from ozone was diffused into the oxide growth interface. As a result, high-speed oxidation occurred by combination of high-temperature TPJ annealing and ozone feeding.

Activation of impurity atoms in 4H-SiC wafer by atmospheric pressure thermal plasma jet irradiation

High temperature annealing of 4H-silicon carbide (SiC) wafers was performed by atmospheric-pressure thermal-plasma-jet (TPJ) irradiation. A maximum surface temperature of 1835°C within 2.4 second without sample breakage was achieved, and aluminum (Al), phosphorus (P), and arsenic (As) activations in 4H-SiC wafers were demonstrated. We have investigated the effects of heating rate (R_h) and cooling rate (R_c) during rapid annealing of P-implanted 4H-SiC on the activation efficiency. No dependence of resistivity on R_h was observed, while increasing Rc significantly decreased resistivity. The minimum resistivity of 0.0025 Ω·cm, the maximum electron concentration of 2.9 × 10²⁰ cm^-3, respectively, were obtained under R_c = 568 °C /s.

Estimation of Phosphorus-Implanted 4H-SiC Layer Recrystallization by Electron-Back-Scattering Diffraction Pattern Analysis

Image quality (IQ) values of an electron-back-scattering diffraction (EBSD) pattern were used to investigate layer recrystallization for the phosphorus-implanted 4H SiC. We prepared a slope-structured amorphous Si on a Si substrate sample to simulate the recrystallization model of the ion-implanted layer after activation annealing. Phosphorus-implanted and recrystallize-annealed Si and SiC samples were also investigated and the Kikuchi-pattern obscuration was observed for a thicker a-Si layer on the slope-structured sample. The IQ values also decreased. Our results show that ion-implantation damage recovery can be estimated by the EBSD pattern analysis. IQ value variation is in good agreement with the sheet resistance changing with the annealing temperature. The IQ values obtained from the EBSD measurements can be used for crystalline recovery estimation on impurity-implanted SiC layer in a nanoscale resolution.

As and Al Activation in SiC Wafer by Atmospheric Thermal Plasma Jet Annealing

We studied atmospheric-pressure thermal plasma jet irradiation for SiC annealing to activate impurity dopants. 1830 o C within 2sec of rapid thermal annealing with no surface roughening and quite small dopant diffusion were demonstrated. Sheet resistance of 289Ω/□ for a As implanted layer and that of 8kΩ/□ for a Al implanted layer were obtained, respectively.