Mototaka Kamoshida

Characterization of 31P+‐implanted Si layers by ellipsometry

Ellipsometry has been used to investigate damage in 1013‐1016/cm2 31P+‐implanted Si and crystallinity recovery by subsequent annealing. Implantation‐induced changes in optical constants, calculated from measured ellipsometric data, become prominent for implantation over the critical dose for amorphization. The refractive index increases with increasing implant dose, except when the implant dose exceeds 1015/cm2. The extinction coefficient increases monotonically with increasing implant dose and decreasing implant temperature. The dose dependence of the change in reflectivity shows a good agreement with the results by channeling effect analysis. For a sample implanted over the critical dose, optical constants and sheet resistances rapidly recover after annealing at around 500 °C, corresponding to epitaxial regrowths of implantation‐induced amorphous layers.

Low‐temperature diffusion of Al into polycrystalline Si

Diffusion of Al into a polycrystalline Si layer chemically deposited at 640 °C was studied by capacitance‐voltage characteristics, sheet resistance, and electron microprobe measurements in the 180–550 °C temperature range. It has been found that diffusion of Al into polycrystalline Si takes place at temperatures as low as 300 °C, and that the polycrystalline Si becomes electrically conductive. The sheet resistance of polycrystalline Si decreases with increasing annealing temperature. Annealing at a higher temperature, however, induces migration and recrystallization of Si in Al, and the original polycrystalline‐Si layer loses its integrity.

Annealing characteristics of highly P+‐ion‐implanted silicon crystal—two‐step anneal

Single‐step and double‐step annealing behavior of highly P+‐ion‐implanted layers was investigated by means of four‐point probe measurements, x‐ray double‐crystal spectrometry, and electron diffraction patterns. The x‐ray double‐crystal spectrometry data indicated that, in the case of single‐step annealing, the layer implanted with doses lower than 3×1015/cm2 ions was recovered with the increase of annealing temperature, while the sample implanted with doses of 1×1016/cm2 ions showed the opposite behavior. That is, the latter sample showed a very bad recrystallized layer with polycrystalline regions when it was annealed at temperatures higher than 1000 °C. However, in the case of double‐step annealing, the higher‐temperature annealing process, conducted after long 560 °C annealing, made it possible to obtain a good recrystallized layer, compared with the single‐step annealing case. These results were confirmed by electron diffraction patterns.

Electrical characteristics of boron-implanted n-channel MOS transistors

Abstract Back-gate-bias V BG dependence of threshold voltage V T and gate-bias V G dependence of “gain” term β (and effective mobility μ eff ) of 50-keV-boron-implanted n -channel MOS transistors are described as functions of implant dose. In low field region, e.g. forward-biased V BG , the slopes of √[−( φ sub + V BG )] vs V T characteristics depend on the implant dose, while under high reverse bias, the slopes are constant and determined by the unimplanted substrate impurity concentration. Corresponding to this, the V G vs β ( μ eff ) characteristics indicate strong dose dependence and reduction of β ( μ eff ) in low field, while in high field the reduction of β ( μ eff ) is observed but not so significant. The effect is clear in the case of a deeply implanted layer or in case of a large ratio of effective channel length to width, as predicted by transistor equations.

Noise Characteristics of Ion-Implanted Mos Transistors

Low‐frequency excess noise characteristics of ion‐implanted MOS transistors annealed above 1000 °C were investigated. Noise characteristics strongly depended on implant species, implant condition, and measurement conditions. In the case of implantation into opposite‐type conductivity substrates, such as 11B+‐implanted p‐channel or 31P+‐implanted n‐channel transistors, the equivalent input noise voltages measured at lower drain currents exhibited generation‐recombination (G‐R) noise caused by residual damage in the substrate. This noise component increased with increasing acceleration energy or implant dose. The G‐R noise decreased with increasing drain current. At higher drain currents the G‐R noise disappeared and the noise voltages of the implanted samples were somewhat smaller than that of the unimplanted samples. On the contrary, in the case of implantation into the same‐type conductivity substrate, such as 31P+‐implanted p‐channel or 11B+‐implanted n‐channel transistors, no G‐R noise component was ob...

Precise Measurements of the Infrared Spectra near 9µm Obtained from RF-Sputtered Silicon Oxide (SiOX) Films

Optical properties of RF-sputtered silicon oxide films is studied as a function of sputtering voltage, film thickness and heat treatment conditions. The wavelength of 9-µm absorption band becomes shorter with increasing sputtering voltage and film thickness for as-sputtered films, but this is not the case for films heat-treated above 700°C in Ar. This phenomenon can be explained by oxygen deficiency in the sputtered films, the degree of which is estimated at 6% after the heat-treatment.

Annealing characteristics of ion‐implanted p‐channel MOS transistors

The annealing characteristics of 50‐keV (2–3) × 1011/cm2 11B+‐implanted p‐channel MOS transistors were investigated from 300 to 900°C. Below 500°C, the number of activated atoms NII decreased rapidly with decreasing anneal temperature and the C‐V characteristics showed gradual distortions. This was presumably due to surface states induced by the ion implantation. Above 500°C, NII increased only slightly with increasing anneal temperature and the slope of the C‐V characteristics in the transition region was larger than that of the unimplanted sample. Corresponding to the above features, the gain term increased near 500°C to a value about 30% larger than that of the unimplanted sample, while the breakdown voltage decreased below 500°C. Equivalent noise voltage decreased abruptly from 500 to 600°C. However, at lower drain current levels, the generation‐recombination noise spectrum did not disappear, even after a 900°C anneal. In addition, reverse‐annealing‐like phenomena were observed in the equivalent noise...

Characterization of laser-annealed Si layers by ellipsometry

Abstract Ellipsometry has been used to investigate the effect of laser annealing on the 75As+-implanted layers of single crystal and polycrystalline Si by Q-switched Nd: YAG laser. Recovery of implantation-induced changes in optical constants by laser irradiation has been measured, and compared with observation by electron diffraction analysis and electrical measurement. Epitaxial regrowth of the layer implanted to 1016/cm2 occurs above 2–3 J/cm2 incident energy density. Good correlation has been obtained between the results by different analytical techniques. The threshold energy density for recrystallization decreases with increasing the implant dose due to increase in the absorption coefficient of the implanted surface layer. It has also been shown that implanted CVD polycrystalline Si layer can grow epitaxially on Si substrate by laser annealing.

Implant dose profile dependence of electrical characteristics of ion‐implanted MOS transistors

Ion‐implanted MOS transistors were fabricated and their electrical characteristics, such as threshold voltage, effective mobility, etc., were measured. In the 11B+‐implanted p‐channel case, threshold voltage VT can be shifted linearly with implant dose. These shifts ΔVT were entirely determined by the net dose entering silicon. On the other hand, in the 11B+‐implanted n‐channel case, threshold voltage shift ΔVT varied sublinearly with dose and showed strong dose profile dependence. The profiles were varied with changing implantation energies and annealing times. These results can be interpreted in accordance with the rapid decrease of the maximum surface depletion layer Xd max with the implant dose increase. Numerical calculations of threshold voltage shifts accounting for nonuniformly implanted profiles were compared with observed results. Good agreement was obtained. Effective mobilities μeff of 11B+‐implanted p ‐ and n ‐channel MOS transistors also showed different dose dependences. In the low‐dose reg...

Threshold voltage and ``gain'' term β of ion‐implanted enhancement‐mode n‐channel MOS transistors

Strong dose dependence was observed in the relation between threshold voltage and forward back‐gate bias, although in the case of thick depletion layers (reverse back‐gate bias) the characteristics showed no dependence of the subsurface concentration. Due to the higher concentration at the subsurface, the gain term β, which decreases with increasing implantation dose, also shows stronger reduction at low field, so that the concave β‐vs‐field characteristics change to convex curves in the case of higher dose.