Kazuhisa Koyama

Selective heteroepitaxial growth of Si1−xGex using gas source molecular beam epitaxy

Si1−xGex heteroepitaxial layers have been grown on Si(100) surfaces by gas source molecular beam epitaxy. Si2H6 and GeH4 were used as the Si and Ge source gases, respectively. The Ge mole fraction x in the grown film was found to be controlled by the GeH4 flow rate. The growth rate decreased gradually with increasing GeH4 flow rate. Selective epitaxial growth of Si1−xGex using a SiO2 mark on a Si(100) substrate was successfully achieved.

Gas source Si-MBE

Abstract We have devised a gas source Si-MBE apparatus. Using this apparatus, we have investigated characteristic advantages of gas source Si-MBE. In gas source Si-MBE, spitting-defect-free films were obtained. B, Sb and P doping were possible using a HBO2 cell, an ionization cell and a PH3 gas doping method, respectively. Selective epitaxial growth was achieved. P- and B-doped selective epitaxial growth using gas source Si-MBE was applied to bipolar transistor fabrication. The fabricated transistor showed normal common-emitter I–V characteristics (hFE ∼ 30). Si1-xGex selective epitaxial growth was also achieved using disilane and germane source gases. This Si1-xGex selective epitaxial growth was applied to Si1-xGex/Si hetero-diode and Si1-xGex base heterojunction bipolar transistor fabrication.

Intensity oscillations in reflection high-energy electron diffraction during disilane gas source molecular beam epitaxy

Reflection high‐energy electron diffraction (RHEED) intensity oscillations during growth in disilane gas source Si molecular beam epitaxy (MBE) on Si(100) and (111) surfaces were observed under low substrate temperature and high disilane flow rate conditions. As has been observed in solid source Si MBE, these oscillations included periods corresponding to periods for monolayer and bilayer growth. On Si(100) surfaces, growth rate, which was estimated from the periods of the oscillations, was limited by a reaction process whose activation energy was 47 kcal/mol. This rate limitation is thought to stem from hydrogen desorption from monohydride phase on the Si(100). On Si(111) surfaces, oscillations in specular beam intensity were clearly observed. Although clear oscillations in the 7×7 diffraction spots could not be observed because of intensity weakness of the fractional order spots under disilane exposure. At high disilane flow rates, 7×7 diffraction spots almost disappeared and only fundamental spots were...

Heterojunction bipolar transistor fabrication using Si1−xGex selective epitaxial growth by gas source silicon molecular beam epitaxy

B doping in Si1−xGex was successfully achieved using HBO2 cell in gas source Si molecular beam epitaxy (Si‐MBE). Combining this B doping method and selective epitaxial growth of Si1−xGex by gas source Si‐MBE, B‐doped Si1−xGex selective epitaxial growth was found to be possible. This B‐doped Si1−xGex selective epitaxial growth was applied to Si1−xGex/Si heterojunction diode and Si1−xGex base heterojunction bipolar transistor (HBT) fabrications. The Si1−xGex base HBT (x=0.16, 0.22, 0.31) showed higher hFE in as‐grown condition than that for a homojunction transistor. The band‐gap difference between the Si1−xGex base and the Si emitter was estimated by the temperature dependence of the collector current ratio between the HBT and the homojunction transistor.

Etching characteristics of Si1−xGex alloy in ammoniac wet cleaning

Etching characteristics of Si1−xGex alloys in ammoniac wet cleaning (RCA cleaning) were examined. The etching rate of Si1−xGex became larger with increasing Ge ratio (X). Temperature dependence of the etching rate was studied and the etching rate was large at high temperatures. However, no obvious difference was observed in the temperature dependence of Si1−xGex etching rate at different Ge ratio (X). A surface morhology degradation after RCA cleaning was observed at high Ge ratio (X). A stoichiometry change of Si1−xGex surface after RCA cleaning was observed by x‐ray photoelectron spectroscopy (XPS). The etching rate increase and the surface morphology degradation are thought to be due to the rapid etching of Ge atoms at the top surface layer.

B doping using B2H6 in gas source Si molecular beam epitaxy

A new gas mixing system was devised for the control of a gaseous dopant during gas source Si molecular beam epitaxy. The performance of this gas mixing system was demonstrated using B2H6 gas dopant for B doping. B doping level control over five decades was successfully achieved. The B‐doping concentration was found to be proportional to the B2H6/Si2H6 flow rate ratio. This relationship holds in both the supply‐controlled and the reaction‐controlled growth regions. This result indicates that B2H6 is incorporated into epitaxial layers by a similar dissociative adsorption mechanism on Si2H6.

B doping effect on reflection high‐energy electron diffraction intensity oscillation during gas source silicon molecular beam epitaxial growth

B doping effect on reflection high‐energy electron diffraction (RHEED) intensity oscillation was studied during gas source Si molecular beam epitaxial growth. During high doping of B above 1020 cm−3, no RHEED oscillation was observed on Si (100) surfaces. This is caused by surface B atoms which disturb surface migration of disilane (Si2H6) molecules. On the other hand, RHEED oscillation was observed on Si (111) √3×√3 B surfaces. At √3×√3 B surfaces, B exists in a subsurface substitutional site, directly underneath a Si adatom. This is the reason why surface migration was not disturbed by surface B atoms on Si (111) √3×√3 B surfaces.

Bipolar transistor fabrication using selective epitaxial growth of P- and B-doped layers in gas-source Si molecular beam epitaxy

Si n-p-n bipolar transistor fabrication using selective epitaxial growth in disilane gas-source Si molecular beam epitaxy (Si-MBE) is discussed. Selective growth of B-doped and P-doped Si was used for the base- and emitter-layer formation, respectively. The growth temperature was 600 degrees C. No ion-implantation process was used. The base ohmic contact was formed using Al selective chemical vapor deposition. The fabricated transistor showed normal emitter-base and base-collector I-V characteristics. The common-emitter characteristics revealed a maximum current gain of 30.<<ETX>>

Gas Source Silicon Molecular Beam Epitaxy

Gas source silicon molecular beam epitaxial (Si-MBE) growth is microscopically governed by a disociative adsorption of silicon hydrides, such as Si 2 H 6 source gas molecules on Si surface. The dissociative adsorption generates SiH species on the surface. From this hydride phase, hydrogen desorbs thermaly. The temperature dependence of the growth rate indicated that the hydrogen desorption from the SiH is the rate limiting step. In HBO 2 Knudsen cell doping, B adsorbates block the surface migration. Such a blocking effect can be avoided by B2H6 gas dopant, because of the similar incorpration mechanism of B 2 H 6 to that of Si 2 H 6 . However, in PH 3 gas doping, a crystal quality degradation was observed at a high doping range due to the preferentially high sticking coefficient of PH 3 and the resulting surface dangling bond termination. The selective epitaxial growth of a B doped layer using Si 2 H 6 and B 2 H 6 was applied to a novel structured base fabrication for super self-aligned selectively grown base transistor (SSSBT). A successful achievement of the SSSBT fabrication indicates the high potentiality of gas source Si-MBE to the sub-micron size ultra-high speed bipolar large scale integrated (LSI) circuits.

TiW/Cu/TiW interconnection lines patterned by IR-assisted RIE

This paper presents a new Cu-metallization technology which consists of TiW/Cu/TiW film structure formation and the followed IR-assisted RIE. It is demonstrated that line structure Cu lines, which have low electrical resistivity and high EM resistance, are obtained without peeling. Further, MOS diodes and MOSFETs using these lines have fine characteristics and they are stable up to 700/spl deg/C annealing.