Akira Shintani

Leakage‐Current Increase in Amorphous Ta2 O 5 Films Due to Pinhole Growth during Annealing Below 600°C

Effects of high temperature annealing over the range 400/sup 0/-1000/sup 0/C on the leakage current of tantalum pentoxide (Ta/sub 2/O/sub 5/) films deposited by reactive sputtering are investigated. Leakage current of polycrystalline Ta/sub 2/O/sub 5/ film (annealed above 700/sup 0/C) is about 10/sup 7/-10/sup 8/ times larger than that of as-deposited amorphous film. However, i is found that leakage current in Ta/sub 2/O/sub 5/ film annealed at 600/sup 0/C increases drastically as well, even though the films have no yet recrystallized. TEM observation reveals that pinholes ranging from 5 nm to 15 nm in diameter are formed near the bottom of the depressions in Ta/sub 2/O/sub 5/ film annealed even at 600/sup 0/C. Electrical properties of the Ta/sub 2/O/sub 5/ films are discussed in terms of crystallographic properties such as pinhole growth and grain boundaries.

Effect of Si and SiO2 thermal nitridation on impurity diffusion and oxidation induced stacking fault size in Si

The effect of thermal nitridation on impurity diffusion and Oxidation induced Stacking Fault size in Si are clarified by selective nitridation. Enhanced B and P diffusion, retarded Sb diffusion, and growth of OSF’s are found in Si masked with SiO2 films. Retarded B and P diffusion, enhanced Sb diffusion and rapid OSF shrinkage are found in nonmasked Si that has undergone NH3 heat treatment. On the other hand, in N2 or N2+H2 (1:3) ambients, no significant ambient effect on impurity diffusion is found in Si masked with SiO2 films. However, retarded B and P diffusion and enhanced Sb diffusion are found in nonmasked Si with N2 ambient. The results are shown to be consistent with the model that shows that interstitials and vacancies effect thermal equilibrium.

Etching of GaN Using Phosphoric Acid

Hot phosphoric acid is found to be useful for etching and characterizing epitaxial crystals grown on (0001) sapphire substrates. The obtained etch rates are 0.2–1.0 μm/min and the activation energy is about 4.4 kcal/mole in the temperature region of 50°–200°C. Hydration of Ga ion is considered the rate‐determining step of the etching action. The x‐ray diffraction and the infrared spectrometric studies indicate that the ortho and meta phosphoric ions play an important role as attacking ions in etching. This phosphoric acid etching reveals crystal defects in undoped (n), Zn‐doped (i), and i‐n structure epitaxial crystals. Conical hexagonal pyramid pits and truncated hexagonal pits develop in the undoped layers, and they tend to be arranged along the slip direction and are attributed to certain dislocations. These hexagonal pits are densely generated near the interface of the epitaxial layer and the substrate. The density of the pits decreases exponentially with crystal growth. The pits are apt to increase in density and size when the carrier concentration is high (1019–1020 cm3). The rounded etch figures develop in Zn‐doped crystals and sometimes in the undoped crystals with a high carrier concentration (1019 cm−3). Etching also indicates that there is a significant difference in growth patterns between the Zn‐doped and the undoped crystals even if the Zn‐doped layer is continuously deposited on the undoped layer. This implies a difference in the crystal growth mechanism between these crystals.

Temperature dependence of stresses in chemical vapor deposited vitreous films

Thermal stresses in chemical vapor deposited (CVD) vitreous silicate and phosphosilicate glass (PSG) films on Si substrates are measured in situ from room temperature (RT) to 900 °C. As‐deposited films grown at one atmospheric (APCVD) and lower pressures (LPCVD) are found to be inherently under a tensile and compressive stress at RT, respectively. On heating to 500 °C, the tensile component of the stress develops in both CVD films. Tensile stress increases with time at a given temperature. In the range 500–900 °C, the tensile component is reduced with temperature and time. During the cooling process from a temperature between 700 and 900 °C, the stress component of APCVD and LPCVD films changes from tension to compression. With APCVD film, the temperature dependence of the stress in the range RT–500 °C can be represented as a function of phosphorous concentration in mol % P2O5. Temperature and time dependence, and thermal hysteresis are attributable to water content, sintering, and viscoelastic properties...

Excimer laser initiated chemical vapor deposition of tungsten films on silicon dioxide

Photochemical vapor deposition technique using an ArF excimer laser has been employed to deposit W films on SiO2 and Si from a WF6 and H2 system. Adhesion characteristics of the film to SiO2 are found to depend both on substrate temperature and on H2/WF6 gas flow ratio: good adhesion is obtained with an increase in the temperature or the ratio. Film formation has reaction orders of 1, 1/2 , and 1 with respect to deposition time, and WF6 and H2 partial pressures, respectively. An activation energy of 0.36 eV is estimated for this film formation on both SiO2 and Si; this energy is plausibly due to H atom diffusion on the W surface. These findings are different from conventional thermal chemical vapor deposition. Film resistivities as low as about 2× the value of bulk W have been observed in the substrate temperature range 250–500 °C. The crystalline structure of the film deposited in this temperature range is uniquely of the α phase. The crystal orientation of the film depends both on substrate temperature ...

Electric properties of GaN light‐emitting diodes

The mechanisms of electrical conduction processes in MIS GaN : Zn, yellow and green light‐emitting diodes (LED’s), are analyzed by considering the I‐V characteristics at room temperature and nitrogen temperatures and the temperature dependences of currents through the diodes with a constant forward bias. The diode current transport mechanisms are different between the two temperature regions, lower or higher than 150 K. The forward conduction current I is the sum of two contributions: I=I1+I2, where I1∝V1/2 exp(λV) and I2∝V exp(λ′V). At temperatures lower than 150 K, I1 dominates the current conduction controlled by tunnel‐induced impact ionization. The electrons tunnel through a triangular potential barrier at the i‐n junction. At temperatures higher than 150 K, I2 dominates as a result of electron thermal excitation, tunneling, and impact ionization. The electron thermal excitation occurs from the conduction band of the n layer to shallow donors of the i layer at the i‐n junction. The thermal activation...

Analysis of Interface States between Plasma‐CVD Silicon Nitride and Silicon‐Substrate Using Deep‐Level Transient Spectroscopy

Deep‐level transient spectroscopy (DLTS) has been employed to measure interface state density, at the interface of plasma chemical vapor‐deposited silicon nitride and a silicon‐substrate interface, using metal‐insulator‐semiconductor (MIS) diodes. The DLTS signal‐height increases with increasing emission pulse voltage in the negative direction. This finding is remarkable, especially for the silicon‐rich film, This is equivalent to a capacitance‐voltage hysteresis effect in the MIS diodes. The three major DLTS signals originating from the interface states are observed for each case of silicon‐rich, stoichiometric, and silicon‐poor films, It is shown that the electrons trapped at the interface states are emitted with several emission time constants. The minimum , , at the midgap, is obtained for a N/Si atomic ratio of near‐stoichiometric composition, A decrease in excess silicon and nitrogen atoms is effective for the reduction of .

Temperature dependence of the stress in PSG/AlSi structures

Abstract The temperature dependence of the stress in each layer of a film system comprising chemically vapour-deposited phosphosilicate glass (PSG) on an AlSi alloy film on a silicon substrate was investigated in the range 20–500°C. During a heating process in which the temperature exceeded 150°C, the deformation of the AlSi film was found to be caused by diffusional creep, and the stresses in both the AlSi film and the PSG film increased with increasing silicon concentration in the AlSi film. Deformation of AlSi film during a cooling process in which temperatures were higher than 150°C was found to be caused by the generation of dislocation loops or by grain boundary sliding. These phenomena are interpreted as representing relaxation of the total elastic energy of the system which results from the deformation of the AlSi film.