Q. Z. Hong

Solid phase epitaxy of stressed and stress‐relaxed Ge‐Si alloys

Solid phase epitaxy of 3500‐A‐thick GexSi1−x (0.04≤x≤0.12) films on (100) Si substrates has been investigated. The thickness of regrown layers increased linearly with annealing time in the temperature range of 475–575 °C. The regrowth rates of stressed alloys were less than those of pure Si, while stress‐relaxed alloys have larger rates than Si. The difference in regrowth rates was explained by the activation‐strain tensor model (Aziz, Sabin, and Lu, to be published in Phys. Rev. B). The first element of the activation‐strain tensor obtained in this experiment was in excellent agreement with that deduced by Aziz et al. For low Ge concentrations (x<0.08), the recrystallized region was of good crystalline quality. However, threading dislocations were observed in a stressed Ge0.1Si0.9 alloy after complete recrystallization. During the regrowth at 550 °C, the Ge‐Si alloy first regrew coherently up to 300 A, above which threading dislocations started to nucleate. On the other hand, no dislocations were detecte...

Thermal reaction between Pt thin films and SixGe1−x alloys

Thermal reaction of Pt with amorphous SixGe1−x alloys (x=0.25–0.75) was investigated in the temperature range of 200–650 °C. At low temperatures (200–400 °C), a uniform reacted layer containing a mixture of Pt2Si and Pt2Ge was produced. The reaction continued with the formation of monosilicide and monogermanide. The formation of the first phases was diffusion controlled with a measured activation energy of 1.2 eV for all the SixGe1−x alloys. At high temperatures (400–650 °C), phase separation occurred in depth with a surface layer enriched with Si and a bottom layer enriched with Ge. At the same time, the formation of PtGe2 and the crystallization of unreacted amorphous SixGe1−x were observed.

Thermal and ion-induced metastable-cubic Al3M phases in Al-Ti and Al-Hf thin films

Thermal and ion‐induced reactions in codeposited, multilayer and bilayer Al‐Ti and Al‐Hf structures were studied by transmission electron microscopy and Rutherford backscattering. A metastable Al3 M (M being Ti or Hf) phase was found by both ion beam mixing and thermal annealing. The metastable phases have a cubic structure with lattice parameters a=3.98±0.01 A and 4.08±0.01 A for Al‐Ti and Al‐Hf, respectively, at a composition of Al3M. The metastable phase transforms to the tetragonal equilibrium compound at annealing temperatures approximately 400 °C. The effectiveness of ion beam mixing is demonstrated by its lower formation temperatures and faster reaction rates. The thermally induced metastable phase formation is ascribed to a lower nucleation barrier than that of the equilibrium phase.

Interfacial reaction between a Ni/Ge bilayer and silicon (100)

The sequential formation and dissociation of compounds in the Ni/Ge/Si(100) system have been studied by using Rutherford backscattering spectroscopy, Auger depth profiling, x‐ray diffraction, and cross‐sectional transmission electron microscopy. Ni2Ge phase is formed first on the Si substrate at 250 °C. A layered structure of NiGe/NiSi/Si(100) is formed after thermal annealing at 350 °C. Upon annealing from 350 to 425 °C, the NiGe phase dissociates, inducing further growth of NiSi phase at the nickel germanide/Si(100) interface. The NiSi phase grows with a (time)1/2 dependence and with an activation energy of 2.1 eV. Marker experiment shows that Ni is a dominant moving species. The dissociation of NiGe lead to an extensive redistribution of Ge and Ni with a configuration of Ge66Si17Ni17/NiSi/Si(100) and this layered structure remains stable until 680 °C. Cross‐sectional transmission electron microscopy results show that there are polycrystalline Ge plus a ternary NiSiGe phase on the top layer. High‐temper...

Regrowth rates and dopant activation of Sb+‐implanted Si‐Ge alloys

Epitaxial regrowth and dopant activation of Sb‐implanted Si and Si0.93Ge0.07 were investigated with ion channeling techniques and transmission electron microscopy. The presence of Sb greatly enhanced the regrowth rate of both Si and Si0.93Ge0.07. The initial crystallinity of Si0.93Ge0.07 was fully recovered after furnace annealing at 500–550 °C. Approximately 95% of Sb atoms were found on substitutional sites and most of them were electrically active.

Thermal and ion induced silicide formation

Abstract It is well established that strong correlations exist in thermal annealing and ion mixing. Recent investigations show pronounced differences between the two processes, even if the mixing is performed in the thermally activated regime. The growth kinetics of near-noble silicides is governed by the metal motion with an apparent activation energy of about 1.5 eV, whereas the mixing in the same systems exhibits a weak temperature dependence and the Si motion plays an important role in atomic transport. The substantial Si motion upon ion irradiation significantly affects the outcome of the metal alloy-Si reaction. Phase separation is observed with thermal annealing, but uniform mixing is achieved with ion mixing. The formation of the crystalline metastable phase Pt4Si9 by hot substrate ion mixing of PtSi on Si indicates the possibility of altering interfacial reaction in a thermally stable system.

Pt4Si9 formation by hot substrate ion beam mixing

Direct, ion induced formation of metastable compounds in the Pt‐Si system has been investigated by implantation with Xe ions through the PtSi‐Si interface in the temperature range of 35–325 °C. The mixing increased parabolically with dose and exhibited an exponential dependence on reciprocal temperature with an apparent activation energy of about 0.11 eV. The mixed layer became progressively uniform in composition with increasing temperatures and a well‐defined surface layer with a composition of Pt4Si9 was obtained at relatively high temperatures. The Pt4Si9 phase was indexed as a hexagonal crystal structure and transformed back into PtSi and Si at temperatures above 550 °C by thermal steady‐state annealing.

Thermally and ion-induced reaction between Si and binary metallic alloys

Thermally and ion‐induced reactions, between Si and binary metallic alloys of PtV (solid solution), NiTa (amorphous phase), and PtTi (intermetallic compound) were investigated. Thermal annealing was carried out at temperatures of 500–700 °C. Separated binary silicides were formed in Pt‐V and Ni‐Ta systems, while the ternary compound of PtTiSi was observed in the Pt‐Ti system. Ion irradiation was performed at temperatures of 200–440 °C. Uniform mixed amorphous layers were produced in all the three systems upon irradiation at relatively low temperatures. The difference in reactions between thermal annealing and ion mixing was attributed to the enhanced Si mobility. The mixtures of PtVSi2 and NiTaSi2 were transformed to separated binary silicides by post‐annealing, but the PtTiSi2 underwent an amorphous‐metastable phase transformation. It was also found that ion mixing and thermal annealing behaved similarly when ion irradiation was carried out at relatively high temperatures.

Ion mixing in amorphous and crystalline Si/Ge layered structures

Abstract Thermal interdiffusion in Si/Ge layered structures shows large variations in diffusivity between Si/Ge amorphous multilayer films and symmetrically strained superlattice structures. Amorphous layered structures exhibit much higher diffusivities and much lower activation energy for interdiffusion. We have used Rutherford backscattering (RBS) and transmission electron microscopy (TEM) to (1) investigate the mixing behavior in Ge/Si structures under ion mixing condition, (2) study the dependence of mixing on the microstructure of the multilayered films (amorphous layers vs. crystalline layers) and (3) study the effects of electrically active ions (e.g. A.s+ ions) on ion mixing behavior. We found that the ion mixing efficiency of the Si/Ge system shows two regimes upon ion irradiation: a thermally activated regime where the efficiency of mixing increases exponentially with the irradiation temperature and a nonthermal regime where the amount of mixing is independent of the irradiation temperature. The critical temperature for the onset of the thermally activated regime is found to be around 200°C. Comparison between thermal interdiffusion and ion-induced intermixing in the Si/Ge system is also made.

Ion mixing of near‐noble monosilicides with Si substrates

Xe ion irradiation of NiSi, PdSi, and PtSi on Si was performed at various substrate temperatures. The phase formation and mixing behavior of the three monosilicides with their Si substrates are quite different. For NiSi, NiSi2 was formed on amorphous Si substrates at 350 °C, while NiSi remained stable on crystalline Si substrates even at 400 °C. PtSi reacted with Si to form a metastable Pt4Si9 phase, which decomposed back to PtSi and Si by successive irradiation at higher temperatures. The decomposition of the metastable Pt4Si9 was easier on crystalline Si substrates than on amorphous substrates. No mixing was observed for PdSi on Si in the temperature range of 35–400 °C. The ion mixing results were compared with those from thermal annealing. The importance of demixing of a thermally stable system was explored.