Z. Ma

REACTIVE ION ETCHING OF GAN USING BCL3

Reactive ion etching with SiCl4 and BCl3 of high quality GaN films grown by plasma enhanced molecular beam epitaxy is reported. Factors such as gas chemistry, flow rate, and microwave power affecting the etching rate are discussed. The etch rate has been found to be larger with BCl3 than with SiCl4 plasma. An etch rate of 8.5 A/s was obtained with the BCl3 plasma for a plasma power of 200 W, pressure of 10 mTorr, and flow rate of 40 sccm. Auger electron spectroscopy (AES) was used to investigate the surface of GaN films after etching. Oxygen contamination has been detected from the AES profiles of etched GaN samples.

Defect ordering in epitaxial α‐GaN(0001)

The microstructure of nominally undoped epitaxial wurtzite‐structure α‐GaN films, grown by gas‐source molecular‐beam epitaxy, plasma‐assisted molecular‐beam epitaxy, and metalorganic chemical‐vapor deposition, has been investigated by transmission electron microscopy (TEM) and high‐resolution TEM. The results show that undoped α‐GaN films have an ordered point‐defect structure. A model of this defect‐ordered microstructure, based upon a comparison between experimental results and computer simulations, is proposed.

In-Situ Studies of the Formation Sequence of Silicides During Vacuum (10 -7 TORR)Thermal Annealing of TI/Polysilicon Bilayers

The formation of suicides during the thermal reaction of Ti/polysilicon bilayers has been investigated using both in-stu four point sheet resistance measurements and ex-situ measurements including X-ray diffraction, cross-sectional transmission electron microscopy and Auger electron spectroscopy. For a series of samples annealed at a ramp rate of 10°C/min the following sequence of changes in the bilayers occurred. At temperatures exceeding 350°C and prior to the silicidation oxygen from the vacuum system diffuses into the Ti film forming a solid solution of Ti(O) with O levels up to 20 %. An amorphous TixSiy layer is the first major suicide reaction observed at temperatures near 440°C. The first major crystalline phase is observed at 500°C and identified as C49 TiSi 2 . This phase was found to coexist at these temperatures with the partially consumed Ti(O) and the amorphous TixSiy layers. Further annealing above 700 °C results in the final structural transformation from C49 TiSi 2 to C54 TiSi 2 .

MANIPULATION OF THE TI/SI REACTION PATHS BY INTRODUCING AN AMORPHOUS GE INTERLAYER

Evolution of the Ti/a‐Ge/Si trilayer reactions has been investigated using transmission electron microscopy and Auger electron spectroscopy. Instead of amorphous phase formation, as usually observed in the Ti/Si bilayer reaction, the crystalline Ti6Ge5 is the first phase observed during the reaction. Preceding the equilibrium C54‐Ti(Si,Ge)2, a substitutional solid solution type C49‐Ti(Si,Ge)2 forms upon annealing at 550–600u2009°C, regardless of the replacement of amorphous phase by the crystalline phase. The C49‐to‐C54 polymorphic transformation occurs at ∼650u2009°C. The reaction path is also correlated with the change in film resistance obtained from a four‐point sheet resistance measurement.

Evolution of Microstructure During Low-Temperature Solid Phase Epitaxial Growth of Si ξ Ge 1-ξ on Si(001)

The evolution of microstructure during Au-mediated solid phase epitaxial growth of a SiGe alloy film on Si(001) (c-Si) was investigated by in situ resistance measurements, X-ray diffraction, conventional and high-resolution transmission electron microscopy, and chemical microanalyis. Annealing a-Ge/Au bilayers on c-Si to temperatures below 120°C caused changes primarily in the microstructure of the Au film. Increases in temperature to ≃150°C resulted in the diffusion of Ge through the grain boundaries of Au. The Au, displaced by crystalline Ge at the grain boundaries, diffused along columnar voids of amorphous Ge (a-Ge) leading to the formation of Au-rich crystallites in the top layer. Results indicate that the Ge that had reached the Au/c-Si interface grew epitaxially on c-Si at temperatures below 150°C. As the temperature was further increased, some Si from the substrate dissolved into Au and got incorporated in the growing epilayer. At 310°C, the initial Au film was displaced completely by a laterally continuous Si ξ Gei. ξ (ξ ∼ 0.2) epilayer whose thickness was limited by that of the initial Au film. Twins, and residual amounts of Au near the SiGe/c-Si interface, were the predominant defects observed in the SiGe epilayer.

Wafer Bonding for Hybrid Circuit Technology Using Solid-State Reactions

In this study, we report a new wafer bonding technique for the integration of GaAs- and InP-based optical devices with prefabricated Si electronic devices in hybrid circuit technology. This technique uses a Au-Ge eutectic alloy as the bonding materials between GaAs and Si wafers, and between InP and Si wafers. This process takes advantage of the low temperature solid-state reactions at GaAs/Au-Ge, InP/Au-Ge, and Si/Au-Ge interfaces. The bonding was carried out by annealing the samples at 280–300°C in an alloying furnace. The reliability of the joined wafers was evaluated by both cleavage test and standard thermal cycling test. The joining interfaces were characterized by scanning electron microscopy and transmission electron microscopy. The results reveal that the bonding is achieved by low temperature reactions at the GaAs/Au-Ge and InP/Au-Ge interfaces as well as solid-phase epitaxial regrowth at the Si interfaces. The joined structure has very good integrity.