Mitsuru Ura

Alignment of nematic liquid crystals on ruled grating surfaces

Ruled gratings of 0.33–3.33‐μm wavelength fabricated with SiO, SiO2, and In2O3‐SnO2 are used to study the topographical effects of the surface on the twisted nematic (TN) alignments of liquid crystals (LC’s). The types of LC’s are Schiff base, azoxy, biphenyl, biphenyl ester, and phenyl cyclohexane. All of the LC’s, except the azoxy, used in this study take good homogeneous and TN alignments on all grating films of wavelength less than 0.8 μm. The azoxy takes homeotropic alignment on the SiO and SiO2 grating surfaces. The agreement between experimental results and Frank elasticity theory is fairly good. Topographical effects can take precedence over chemical effects between the LC and surface when chemical anchoring is weak. Making use of the calculated elastic deformation energy of LC’s on grating and rubbed surfaces, we estimate the anchoring energies of homogeneous and homeotropic alignments. The application of grating cells to optical display is limited by the occurence of tilt domains.

In-process monitoring and control of doping gas concentration during vapor phase silicon epitaxial growth by using a flame photometric detector

Abstract An in-process monitoring and control method of the doping gas concentration during epitaxial growth of Si was developed. A flame photometric detector (FPD) can be used as a monitor for the PH 3 and B 2 H 6 dopant concentrations in the injected doping gases. A combination of this dopant monitor with an automatic control system of the silicon source (SiHCl 3 ) gas concentration using an infrared spectrophotometer as a monitor, makes possible an automatic in-process control of the concentrations of dopant and of silicon source gas supplied to the reactor. The present system provides an accurate and reproducible control of impurity concentrations in Si epitaxial layers. Good correlation between the monitored signal (or the doping gas concentration) and the impurity concentration incorporated into the growth layers was confirmed for PH 3 (n-type) and B 2 H 6 (p-type) doping. For the B 2 H 6 doping, a divergence from the linear relationship between the doping gas concentration and the impurity concentration in the layers was observed in the level of acceptor concentration below about 10 15 atoms/cm 3 . The transient response of the present system was measured by growing epitaxial layers with increasing and decreasing step-changes in the dopant gas flow during continuous deposition of the layers. Some interesting, but complicated, transient responses of impurity concentration in the growth layer were observed. The responses are different between the PH 3 doping and the B 2 H 6 doping, and also different between increasing and decreasing steps especially for the B 2 H 6 doping.

Elimination of Stacking Fault in Si Epitaxial Layer by Heat Treatment

Elimination of stacking faults in Si epitaxial layer by heat treatment is investigated by observing repeated etch patterns. Two types of stacking faults are observed. One of them (about 70~90%) is eliminated easily by heat treatment and the other (about 10~30%) is stable and cannot be eliminated. Heat treatment at a temperature higher than 450°C is required to eliminate the faults in either atmosphere of O2, Ar and H2. In the temperature range higher than 600°C, the elimination is completed within a few minutes. Contrary to Mendelsons model, the observations on the initial stage of elimination process show that the elimination proceeds locally from the surface of growth layer to the substrate-growth interface.