Susumu Tsuzuku

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 ...

Reduction of gap state density in a-SiGe : H alloys

The reduction of the gap states in a-SiGe:H alloys down to the level in a-Si:H was realized by the low-pressure microwave plasma chemical vapour deposition (CVD) which utilizes hydrogen plasma stream. It was found that the densities of defect states and tail states in the alloy vary with the flow rate of hydrogen introduced into the deposition chamber, and a-SiGe:H alloy with low defect density was attained with an optimized flow rate of hydrogen when the flow rate of source gas (SiH4 and GeH4) was reduced. The Urbach energy also decreased when the flow rate of hydrogen was optimized, and a-SiGe:H alloy with an Urbach energy of 48 meV was obtained. It was also found that the photoconductive property of a-SiGe:H alloys is not sensitive to the density of gap states.