Takuya Yara

Low Temperature Fabrication of Diamond Films with Nanocrystal Seeding

Well-faceted diamond films have heen fabricated at 200° C on the silicon substrate by the magnetoactive microwave plasma chemical vapor deposition (CVD) method. The substrate was seeded with nanocrystal diamond about 5 nm in diameter synthesized by the explosion process. The nanocrystal seeding brought about the improvement in quality of the fabricated films and the decrease in the time required for diamond nucleation. It took about 5 h to seed the scratched Si substrate at temperatures below 300° C.

Fabrication of Diamond Films at Low Pressure and Low-Temperature by Magneto-Active Microwave Plasma Chemical Vapor Deposition.

We succeeded in fabrication of diamond films at substrate temperature of 80° C by using the magneto-active microwave plasma chemical vapor deposition (CVD) method at low pressure (0.1 Torr) with forced substrate cooling. The magneto-active microwave discharge enables us to use high-density microwave plasma under low pressure. High-density plasma-enhanced CVD under low-pressure is advantageous for low-temperature synthesis of diamond films because of decrease in thermal flux to the substrates from neutral gases heated in the plasma. Deposited films were investigated by scanning electron microscopy (SEM), Raman scattering spectroscopy, thin-film X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The fabricated films are randomly oriented polycrystalline diamond of fine crystallite size (below 100 A). The deposition rate of the diamond films decreased with decreasing substrate temperature in the range below 400° C.

Fabrication of diamond films by a magneto-active plasma CVD using alcohol-hydrogen system

Good-quality diamond films have been synthesized by a magneto-active plasma chemical vapor deposition (CVD) system using the alcohol-hydrogen system. CnH2n+1OH/H2 (n =1 to 3). The regions to fabricate polycrystalline diamond films are similar for all alcohols for the C/H ratios of the original gas mixtures and are independent of the reaction gases. The films have been studied using scanning electron microscopy (SEM) and X-ray photoelectron microscopy (XPS). A quantitative relationship between morphologies of SEM images of diamond films and the full width at half maximum (FWHM) of diamond carbon ls (C ls) core photoemission spectra has been set up for the first time. The FWHM of the C ls XPS peak of the best diamond film is 0.951 eV and is of good value. The FWHM of diamond C ls peak is very sensitive to the morphology of diamond film. Optical emission spectroscopy (OES) of the plasma shows that the growth rate and the FWHM of diamond C ls peak depend on the ratio of carbon and hydrogen in the plasma. OH radicals are shown to play a role on etching of non-diamond phases.

Irradiation-Damages in Atmospheric Plasma Used in a Resist Ashing Process for Thin Film Transistors

We used an on-wafer UV photon monitor to measure the amount of UV photon irradiation on the substrate surface of a thin film transistor (TFT) device in N2/O2 atmospheric plasma. We found that the amount of UV photon irradiation on the surface strongly depended on the ratio of N2 to O2 in the plasma. On the other hand, no irradiation of charged particles was observed by using this method. Additionally, we used TFTs with a single drain (SD) and lightly doped drain (LDD) structures as well as UV filters of slide glass (transparent above 280 nm) and synthetic quarts (transparent above 170 nm) to investigate the degradation of the TFTs. We found that UV photon irradiation significantly degraded TFT electrical characteristics in atmospheric plasma. An on-current decrease was observed only for LDD TFT when UV wavelength below 280 nm was irradiated. On the other hand, we observed an off-current increase for both types of TFT when UV light with a wavelength of less than 170 nm was irradiated. We will discuss a possible mechanism of the degradation.

Initial features of diamond growth on silicon

The initial stage of chemical-vapor- deposited (CVD) diamond growth on Si substrates has been investigated using transmission electron microscopy (TEM). The samples for TEM study have been observed from their lateral sides (side-view observation). The diamond particles are formed on Si protuberances fabricated by etching of substrate surface. These diamond particles nucleate randomly without respect to the orientation of the substrate surface. The top of the Si protuberance extends to the center of the diamond particle. High resolution TEM image shows that there is an amorphous layer underneath this particle and that this particle is surrounded by uneven {111} surfaces, where the multi-nucleation growth process can be observed.