Papers by Author: Chin Che Tin

Abstract: An electroless nickel film contains 5-14% by weight of phosphorus. Because of the presence of such a high concentration of phosphorus, electroless nickel can be a useful and convenient source of phosphorus dopant in the fabrication of n-type ohmic contacts for SiC. This paper describes the successful deposition of a Ni:P layer on 4H-SiC through electroless nickel plating followed by a discussion of the results of surface science and electrical measurements. Specific contact resistivity on lightly-doped samples with carrier concentration of 2.5 ´ 10¹⁶ cm^-3 has been found to be about 4.8 ´ 10^-6 Ωcm² without any need for ion implantation. This metallization technique is especially useful in broad area ohmic contact formation on the back of n-type SiC substrate.

Abstract: FTIR, Visible and UV Raman scattering, as well as synchrotron radiation X-ray absorption, in combination, have been employed to investigate a series of CVD grown 3C-SiC/Si (100). Significant results on the optical and atomic bonding properties are obtained from these comparative studies.

Abstract: Synchrotron radiation X-ray absorption and UV 325 nm excitation Raman scattering- photoluminescence (PL) have been employed to investigate a series of 4H-SiC wafers, including bulk, epitaxial single or multiple layer structures by chemical vapor deposition. Significant results on the atomic bonding and PL-Raman properties are obtained from these comparative studies.

Abstract: The characteristics of boron diffusion in 3C-SiC at low temperature have been measured using spreading resistance technique and electroluminescence spectroscopy. The coefficient of boron diffusion in the temperature range of 1150 –1250°С has been found to be about 5.5 x 10-11–5.0 x 10-10 cm2/sec and the activation energy of boron diffusion was determined to be about 0.9 –1.15 eV. Electroluminescence spectra of 3C-SiC p-n junction structures showed peaks at 750 and 630 nm due to growth defects and carbon-silicon divacancies respectively.

Abstract: Silicon has been the semiconductor of choice for microelectronics largely because of the unique properties of its native oxide (SiO2) and the Si/SiO2 interface. For high-temperature and/or high-power applications, however, one needs a semiconductor with a wider energy gap and higher thermal conductivity. Silicon carbide has the right properties and the same native oxide as Si. However, in the late 1990’s it was found that the SiC/SiO2 interface had high interface trap densities, resulting in poor electron mobilities. Annealing in hydrogen, which is key to the quality of Si/SiO2 interfaces, proved ineffective. This paper presents a synthesis of theoretical and experimental work by the authors in the last six years and parallel work in the literature. High-quality SiC/SiO2 interfaces were achieved by annealing in NO gas and monatomic H. The key elements that lead to highquality Si/SiO2 interfaces and low-quality SiC/SiO2 interfaces are identified and the role of N and H treatments is described. More specifically, optimal Si and SiC surfaces for oxidation are identified and the atomic-scale processes of oxidation and resulting interface defects are described. In the case of SiC, we conclude that excess carbon at the SiC/SiO2 interface leads to a bonded Si-C-O interlayer with a mix of fourfold- and threefold-coordinated C and Si atoms. The threefold coordinated atoms are responsible for the high interface trap density and can be eliminated either by H-passivation or replacement by N. Residual Si-Si bonds, which are partially passivated by H and N remain the main limitation. Perspectives for the future for both Si- and SiC-based MOSFETs are discussed.

Abstract: We have performed a combined investigation of experiment and theory on the infrared reflectance from cubic SiC grown on Si by chemical vapor deposition. A damping behavior of the interference fringes away from the reststrahlen band and a dip or notch within the “flat top” are observed from some samples while they does not occur in high quality 3C-SiC/Si samples. The former is interpreted due to an interfacial transition layer existed between SiC-Si and a rough surface, while the latter can be demonstrated by a three-component effective medium model.

Abstract: Silicon carbide (SiC) field plate terminated Schottky diodes using silicon dioxide (Si02) dielectric experience high electric field in the insulator and premature dielectric breakdown, attributed to the lower dielectric constant of the oxide. This problem can be addressed by using high-k dielectrics such as silicon nitride (Si3N4) that will reduce the field, increase the breakdown voltage and consequently improve the lifetime of the devices. While the advantages of single step field-plate terminated diodes are well-known, the breakdown voltage can be improved even further using a dual-step field-plate termination. Our 2D-numerical simulations using MEDICI have shown an improvement in breakdown voltages in excess of 25% compared to the traditional single-step field-plate terminated diodes.

Abstract: Reactive ion etching of SiC induced surface damage, e.g., micromasking effect induced coarse and textured surface, is one of the main concerns in the fabrication of SiC based power devices [1]. Based on CHF3 + O2 plasma, 4H-SiC was etched under a wide range of RF power. Extreme coarse and textured etched surfaces were observed under certain etching conditions. A super-linear relationship was found between the surface roughness and RF power when the latter was varied from 40 to 160 W. A further increase in the RF power to 200 W caused the surface roughness to drop abruptly from its maximum value of 182.4 nm to its minimum value of 1.3 nm. Auger electron spectroscopy (AES) results revealed that besides the Al micromasking effect, the carbon residue that formed a carbon-rich layer, could also play a significant role in affecting the surface roughness. Based on the AES results, an alternative explanation on the origin of the coarse surface is proposed.

Abstract: In this work, we present results on the study of bonding and concentration of carbon in 4H-SiC MOS structure by x-ray photoelectron spectroscopy (XPS). The XPS spectra were fitted by several Gaussian lineshape functions. It is found that the so-called carbon clusters (C-C bonds) appear at the interface of SiO2/SiC, but are not seen in the oxide bulk. However, there are still some SiOxCy and Si-C bonds inside the oxide and the integrated area ratio of SiOxCy/Si-C bonds increases when further away from the SiO2/SiC interface. These observations can be interpreted in terms of the dynamic oxidation process that transforms Si-C bonds into SiOxCy bonds, which are then further oxidized to form SiO2 bonds.

Abstract: The drain-induced barrier lowering (DIBL) effect in 4H-SiC MESFETs has been studied using the physical drift and diffusion model. Our simulation results showed that the high drain voltage typically applied in short-channel 4H-SiC MESFETs could substantially reduce the channel barrier and result in large threshold voltage shift. It is also found that the DIBL effect is more dependent on the ratio of the gate length to channel thickness (Lg/a), rather than the channel thickness itself. In order to minimize the DIBL effect, the ratio of Lg/a should be kept greater than 3 for practical 4H-SiC MESFETs.