Hiroaki Kakinuma

Structural properties of polycrystalline silicon films prepared at low temperature by plasma chemical vapor deposition

Evolution with thickness of the structure of the polycrystalline silicon (poly‐Si) films prepared at 300 °C has been studied by plasma decomposition of SiF4/SiH4/H2 source gases. The poly‐Si films with varied thickness are characterized mainly by Raman spectroscopy, x‐ray diffraction (XRD), and supplementarily by reflection high‐energy electron diffraction, transmission electron microscopy, Fourier‐transform infrared (FT‐IR) spectroscopy, electron‐spin resonance (ESR), and secondary‐ion‐mass spectroscopy (SIMS) measurements. The crystalline fraction of the film was calculated to be 87% by deconvoluting the Raman spectra. The grains indicated a strong 〈110〉 preferred orientation by XRD. The thickness (d) dependence of the diffracted (220) intensity is divided into three regions: an incubation region (d<200 nm, region 1), a linear region (200 nm ≤d<300–500 nm, region 2) where the deposition parameter (SiF4 flow rate, substrate temperature, and rf power) dependence is weak, and a linear region with steeper (...

Plasma Etching of ITO Thin Films Using a CH4/H2 Gas Mixture

Plasma etching of ITO (In2O3:Sn indium tin oxide) thin films has been performed using a CH4/H2 plasma. Etching occurs above a substrate temperature (Ts) of 60°C and the etch rate increases with increasing Ts, while amorphous like or polymer-like carbon deposits onto the ITO films below 60°C. The apparent activation energy of the etching is 4.12 kcal/mol (0.18 eV). This small activation energy suggests that the desorption of produced volatiles is the rate-limiting process. Fine ITO patterns (1.5 µmL/S) were obtained using this gas mixture.

Influence of RF Power on Properties of a-Si1-xGex:H Prepared by RF Glow Discharge Decomposition

The electrical and structural properties of hydrogenated amorphous silicon germanium alloys prepared by the rf glow discharge method have been measured as a function of the rf power and the gas flow rate. The photoconductivity of a-Si1-xGex:H films increases by a factor of 103 at x=0.45 with increasing rf power density, and the microstructure of the films changes from heterogeneous to homogeneous. This paper discusses the deposition mechanism inducing these results.

Mechanism of low‐temperature polycrystalline silicon growth from a SiF4/SiH4/H2 plasma

A model for the low‐temperature growth of poly‐Si by plasma‐enhanced chemical‐vapor deposition using SiF4/SiH4/H2 gases is presented. The model is based on the existing so‐called etching model in which growth and etching take place simultaneously. In this model a set of chemical reactions are postulated. The crucial factors to obtain high‐quality poly‐Si films are (1) the flux of precursors, (2) the concentration of F radicals in the vicinity of the growing surface which determines the etching rate, and (3) the H‐covered surface which ensures long diffusion length of precursors. The flow rate of SiH4 [factor (1)] determines whether the film becomes crystalline or amorphous, and variation in the other gas flow rates and plasma parameters affect factors (2) and (3). According to the model the electrode spacing and rf power predominantly determine the concentration of F radicals diffused to the growing surface, while the gas pressure changes the residence time of radicals which predominantly affects the etching reaction. Natural consequences of the model are that an excess supply of F radicals will in turn deteriorate the crystallinity by stripping the hydrogen covering the surface and increasing nucleation sites. The crystallinity of poly‐Si films prepared by changing the above plasma parameters are characterized by x‐ray diffraction, and their dependence on the above parameters are found to be consistent with the model. A high degree of hydrogen exchange between the growing surface and the plasma is observed by secondary‐ion‐mass spectroscopy for the film prepared with SiF4/SiH4/D2 gases.

Characterization of Oxygen and Carbon in Undoped AlGaAs Grown by Organometallic Vapor-Phase Epitaxy

We have systematically characterized oxygen (O) and carbon (C) impurities in undoped gallium aluminum arsenide ( Alx Ga1-x As) epitaxial layers grown by organometallic vapor-phase epitaxy (OMVPE). The concentrations of O and C impurities are evaluated by secondary-ion mass spectroscopy. For x≤0.63 the increase rate of O concentration, [O], with x is nearly proportional to the flow rate of trimethylaluminum (TMA), indicating that the oxygen is contained in the TMA molecules. In contrast, [O] and [C] increase superlinearly with x for x≥0.83, and particularly, [O] exceeds 1018 cm-3. The vibration mode of Al–O bonds is observed at 900–1050 cm-1 for the x=0.83 sample using Fourier-transformation infrared measurements. The superlinear increase of [O] with x is attributed to the increased adsorption of residual O2 or H2O molecules. The mechanism of the superlinear increase is discussed in terms of statistic consideration of the –Al– arrangement on the Alx Ga1-x As surface. Hall measurements show that the hole concentration markedly decreases for x>0.63 and the Alx Ga1-x As layer becomes semi-insulating, which was attributed to hole compensation by the O-related deep hole traps. The hole mobility also decreases in the same x range.

Very-Low-Temperature Preparation of Poly-Si Films by Plasma Chemical Vapor Deposition Using SiF4/SiH4/H2 Gases

Polycrystalline-Si (poly-Si) films have been prepared on glass substrates (Corning 7059) at a very low temperature (300°C) by conventional plasma chemical vapor deposition (plasma CVD) using SiF4/SiH4/H2 gases. The crystallinity was characterized by X-ray diffraction, reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM) and Raman spectroscopy measurements. The effect of the SiH4 flow rate on crystallization proved to be large. The films indicated a strong -preferred orientation. The crystalline fraction was estimated to be more than 80%. The average and maximum grain sizes were estimated to be 60 nm and 130 nm, respectively.

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.

Influence of Deposition Conditions on Properties of Hydrogenated Amorphous Silicon Prepared by RF Glow Discharge

The electrical and structural properties of amorphous silicon films prepared by pure silane rf glow dicharge have been measured as a function of the rf power, the substrate temperature, the gas flow rate and the gap between the two electrodes. The properties of the deposited films show a very different dependence on the rf power from those reported previously. The films prepared at high rf power density (1?2 W/cm2) reveal a photoconductivity comparable with that of device-grade films prepared at low rf power density (0.02 W/cm2). Increasing the gas flow rate increases the deposition rate up to 70 A/s at 2 W/cm2. The photoconductivity of films prepared at this high deposition rate is 1.2?10-5 (??cm)1 at 600 nm, 1 mW/cm2. This paper discusses the deposition mechanism inducing these results.

Phosphine Doping Effects in the Plasma Deposition of Polycrystalline Silicon Films

The effects of phosphine doping on the electronic and structural properties of polycrystalline silicon (poly-Si) films prepared by plasma chemical vapour deposition using SiF4/SiH4/H2 gases have been investigated. With increasing doping ratio, the conductivity rapidly increases and takes a maximum value of 80 Scm-1 at [PH3]/[SiH4](=γ)~1.7×10-2, while it decreases at larger doping ratios. This change is found to be caused mainly by the change in the carrier density, by Hall measurements. X-ray diffraction and transmission electron microscopy indicate that this electronic change is associated with the change in the preferred orientation of grains from to with a slight decrease in grain size, and the structural change from crystalline to amorphouslike with increasing γ.