Shuichi Asahina

Epitaxial growth of 3C-SiC on Si(111) using hexamethyldisilane and tetraethylsilane

Hexamethyldisilane (HMDS, Si2(CH3)6) and tetraethylsilane (TES, Si(C2H5)4) were used as safe organosilane sources for the chemical vapor deposition of SiC films on Si(111) substrates. The surface morphology and crystalline quality of SiC films were investigated. On increasing temperature in H2 ambient after carbonization, voids appeared at the interface of SiC/Si causing the formation of hillocks on the grown SiC films. The formation of voids was prevented by supplying C3H8 and HMDS or TES during the heating process to the growth temperature, leading to the growth of SiC films with a good surface morphology. In the case of TES, the excess carbon incorporated in the film due to the high C/Si ratio was removed by reducing TES flow rate. It was found that the control of the flow rate of organosilane sources during heating plays a vital role in the formation of a high-quality SiC film with a smooth surface.

Growth of SiC Films using Tetraethylsilane

Tetraethylsilane (TES, Si(C2H5)4) was used as a safety source for the growth of SiC thin films on Si(111) substrates by chemical vapor deposition method. Carbonization of Si substrate was carried out to form a buffer layer using C3H8 gas. SiC thin films were grown at various substrate temperatures and TES flow rates for the purpose of forming carbon-free SiC films. The excess carbon incorporated in the film due to high C/Si ratio was removed by means of decreasing the TES flow rate. Moreover, high quality SiC films were grown at high growth temperature of 1350°C.

Stable Molecules in N2–H2 Plasmas Measured Using a Quartz Sensor

Stable molecules of N2, H2, and NH3 in N2–H2 plasmas were investigated using a quartz sensor (Q-sensor). Changes in the pressure- and temperature-normalized Q-sensor output (NQO) induced by plasma with radio-frequency (rf) input power were measured near plasma electrodes and shown to correlate to the relative ion signal intensity from NH3. The results confirm that gas composition changes in N2–H2 plasmas can be successfully measured from the NQO changes using the Q-sensor. The spatial distribution of NQO indicates that NH3 molecules are produced near plasma electrodes rather than by secondary gas reactions in the plasma, which also means that Q-sensor measurements can provide information regarding stable gas molecules in plasma.

Quartz Sensor Measurement for N2–H2 Plasmas

N2–H2 plasmas, which are used for plasma nitriding, were investigated using a quartz sensor (Q-sensor), by gas analysis, and by optical emission spectroscopy (OES). The results of Q-sensor measurement showed the production of NH3 in N2–H2 plasmas, which were related to the results of gas analysis using a quadrupole mass spectrometer. On the other hand, OES showed emission signals from H, N2, and Fe, where Fe emission was from the material of the plasma electrode. It is concluded that Q-sensor measurement can detect the gas composition in plasmas better than the emission generated by surface sputtering, and Q-sensor measurement is applicable to the diagnosis of the plasma nitriding process.

Dependence of composition of stable molecules in N2–H2 plasmas on nitrogen gas flow rate ratio measured using a quartz sensor

Compositions of stable molecules in N2–H2 plasmas measured using a quartz sensor (Q-sensor) were compared with those measured using a quadrupole mass spectrometer (QMS) under various nitrogen gas flow rate ratio to determine the applicability of Q-sensor measurement to N2–H2 plasmas. The nitrogen flow rate ratio dependence of the Q-sensor results obtained 20 mm from the edge of the plasma electrodes (Z = 20 mm) tended to agree more qualitatively with the NH3 density measured by QMS compared with those measured at 70 mm. For pure nitrogen or hydrogen plasma, the results measured at Z = 20 mm differed from those of gas analyses using QMS. The analysis indicated that Q-sensor results obtained near discharges with various nitrogen flow rate ratios reflect information on stable molecules such as N2, H2, and NH3 but yield information on other stable molecules or other chemical species in pure N2 and H2 plasmas.

Spectroscopic Ellipsometry of 3C-SiC Thin Films Grown on Si Substrates Using Organosilane Sources

Dielectric function spectra of 3C-SiC films on Si substrates in the energy region of 0.73–6.43 eV were measured by spectroscopic ellipsometry. Hexamethyldisilane (Si2(CH3)6) and tetraethylsilane (Si(C2H5)4) were used as safe organosilane sources for the growth of SiC films. The measured spectra were compared with those of 3C-SiC on a Si(001) substrate grown with disilane (Si2H6). First, the pseudodielectric function spectra gave a shoulder structure corresponding to the direct X5–X1 interband transition in the Brillouin zone. Secondly, the dielectric function of 3C-SiC was determined by applying a four-layer model in which we took into account the surface roughness and mixed crystals of a carbonized interface layer. Finally, the third-derivative lineshape of the imaginary part e2 of the complex-dielectric function provided the values of the interband transition energy Eg and the broadening parameter Γ for the X5–X1 interband transition. The measured values of Γ indicated that the crystalline quality of SiC films grown using organosilane sources is comparable to that of SiC films grown using Si2H6.