Ex-situ Rapid Thermal Annealing Research Articles

Secondary epitaxy of high Sn fraction GeSn layer on strain-relaxed GeSn virtue substrate by molecular beam epitaxy

Strain relaxation is critical for GeSn alloys transforming from indirect to direct bandgap nature with Sn fraction above 6.5%, but difficult for them grown by molecular beam epitaxy (MBE), in which low temperature has to be set up to avoid Sn segregation. In this work, compressively strained Ge0.935Sn0.065 thin films grown on Si with a Ge buffer layer by MBE are firstly treated by ex-situ rapid thermal annealing, rendering partially strain relaxation in the Ge0.935Sn0.065 by generation of misfit dislocation networks without Sn segregation. Then, secondary epitaxy of Ge0.905Sn0.095 layer is carried out on the thermally annealed Ge0.935Sn0.065 virtual substrate. The secondary epitaxial GeSn layers exhibit partial strain relaxation and strong photoluminescence with red-shift of peak position, compared to that of fully compressive strained GeSn thin films with the same structure grown primary epitaxially. Those results manifest that secondary epitaxy, combining with ex-situ rapid thermal annealing for strain relaxed GeSn virtual substrate, is a practical way to achieve strain relaxed GeSn thin films with direct bandgap nature by MBE.

In-situ and ex-situ face-to-face annealing of epitaxial AlN

AlN films have been deposited on c-plane sapphire substrates by metalorganic-vapor-phase-epitaxy (MOVPE). The changes in the film structure have been investigated by applying different annealing processes which are ex-situ rapid thermal annealing (RTA) and in-situ process after the nucleation-layer (NL). The AlN nucleation-layer grown on sapphire has been annealed face-to-face with ex-situ (RTA) process for 3 min and with in-situ process for 3 h, then pulsed-atomic-layer-epitaxy AlN film has been grown at a high temperature. The samples have been characterized by high-resolution X-ray diffraction, atomic force microscopy, Ultraviolet–visible spectrometry, and Raman scattering to examine the structural properties, surface morphology, and optical properties. The sample annealed with the ex-situ (RTA) process, where rapid diffusion took place, has reached larger grain sizes and the dislocation density has decreased as the grain boundary decreased. Although better crystal quality has been obtained with the ex-situ (RTA) process, it has been observed that the surface roughness of the sample annealed with the ex-situ (RTA) process is higher than that of the sample annealed with the in-situ process. Considering the results, a schematic prediction of the growth process after face-to-face annealing has been proposed. Experimental findings have shown that different annealing processes after growing the AlN-NL have a great effect on the properties of the AlN.

Investigations of rapid thermal annealing induced structural evolution of ZnO: Ge nanocomposite thin films via GISAXS

In this work, we present in depth structural investigations of nanocomposite ZnO: Ge thin films by utilizing a state of the art grazing incidence small angle x-ray spectroscopy (GISAXS) technique. The samples have been deposited by sequential r.f. and d.c. sputtering of ZnO and Ge thin film layers, respectively, on single crystal Si(100) substrates. Transformation of Ge layers into Ge nanoparticles (Ge-np) has been initiated by ex-situ rapid thermal annealing of asprepared thin film samples at 600 °C for 30, 60, and 90 s under forming gas atmosphere. A special attention has been paid on the effects of reactive and nonreactive growth of ZnO layers on the structural evolution of Ge-np. GISAXS analyses have been performed via cylindrical and spherical form factor calculations for different nanostructure types. Variations of the size, shape, and distributions of both ZnO and Ge nanostructures have been determined. It has been realized that GISAXS results are not only remarkably consistent with the electron microscopy observations but also provide additional information on the large scale size and shape distribution of the nanostructured components.

Tailoring film agglomeration for preparation of silver nanoparticles with controlled morphology

Thin metal films can disintegrate into nanoparticles upon thermal annealing. In this work, to obtain silver nanoparticles with controlled morphology, we performed a comparison study on the surface topography evolutions and agglomeration mechanisms of Ag films deposited by magnetron sputtering within-situ annealing (the heating rate is 0.33°C/s) and ex-situ rapid thermal annealing (the heating rate is 100°C/s) treatments, respectively. The results confirm that the in-situ annealed Ag films agglomerate via voids nucleation followed by the fractal growth of voids. Moreover, we found that the critical void radius upon which the void growth is favored decreases with increasing the annealing temperature. For the case of rapid annealing, the agglomeration of Ag films follows the grain boundary grooving mechanism due to the rather higher heating rate. Compared with the in-situ heating process, the rapid annealing treatment allows a more uniform size distribution of the nanoparticles. Our findings highlight the key role of heating rate on the size, shape and functionalities of Ag nanoparticles for a wide range of practical applications, and enrich the understandings of the agglomeration mechanism of thin metal films.

The strain dependence of Ge1 − xsnx (x = 0.083) Raman shift

We report an investigation of strain-dependent Raman frequency shift in Ge0.917Sn0.083 epilayer where the Sn composition is near the indirect-to-direct band gap transition point. The strain is modulated by ex-situ rapid thermal annealing and the amount of strain relaxation is determined by X-ray diffraction measurement. The results show that the Raman shift of Ge–Ge longitudinal optical phonon is linearly dependent on the in-plane strain of the GeSn layers with a coefficient b=−299.3cm−1. Such a relationship enables characterization of GeSn epilayers using the readily accessible Raman spectroscopy.

Effects of rapid thermal annealing on the structural and local atomic properties of ZnO: Ge nanocomposite thin films

We have investigated the structural and local atomic properties of Ge nanocrystals (Ge-ncs) embedded ZnO (ZnO: Ge) thin films. The films were deposited by sequential sputtering of ZnO and Ge thin film layers on z-cut quartz substrates followed by an ex-situ rapid thermal annealing (RTA) at 600 °C for 30, 60, and 90 s under forming gas atmosphere. Effects of RTA time on the evolution of Ge-ncs were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), hard x-ray photoelectron spectroscopy (HAXPES), and extended x-ray absorption fine structure (EXAFS). XRD patterns have clearly shown that fcc diamond phase Ge-ncs of sizes ranging between 18 and 27 nm are formed upon RTA and no Ge-oxide peak has been detected. However, cross-section SEM images have clearly revealed that after RTA process, Ge layers form varying size nanoclusters composed of Ge-ncs regions. EXAFS performed at the Ge K-edge to probe the local atomic structure of the Ge-ncs has revealed that as prepared ZnO:Ge possesses Ge-oxide but subsequent RTA leads to crystalline Ge structure without the oxide layer. In order to study the occupied electronic structure, HAXPES has been utilized. The peak separation between the Zn 2p and Ge 3d shows no significant change due to RTA. This implies little change in the valence band offset due to RTA.

Rapid thermal annealing induced formation of Ge nanoparticles in ZnO thin films: A detailed SAXS study

In this study, germanium nanoparticles (Ge-np) embedded ZnO multilayered thin films were produced on z-cut quartz and Si substrates by sequential r.f. sputtering of ZnO and d.c. sputtering of Ge targets followed by an ex-situ rapid thermal annealing (RTA) process performed at 600°C for 30, 60, and 90s. Evolution of Ge-np via an RTA process has been investigated in detail especially by using a small angle x-ray scattering (SAXS) technique. X-ray diffraction (XRD) patterns showed that fcc diamond phase Ge-np were successfully formed in c-axis oriented ZnO host. Crystallite sizes of diamond phase Ge-np calculated by the Scherrer formula were in the range of 18–27nm. Analysis of SAXS patterns revealed that optimum RTA time at 600°C to form monodispersed Ge-np is 60s. Moreover, 30s RTA was inadequate for the complete crystallization and segregation of crystalline Ge-np; 90s RTA turned out to be improving the crystallite size as well as deteriorating the isolation of Ge-np possibly by inter diffusion of Ge atoms back to ZnO host. These results suggest that RTA applied under certain conditions is a robust and scalable route to form monodispersed well crystallized Ge-np in ZnO multilayered thin films for various applications.

Surface Treatment of Ge Grown Epitaxially on Si by Ex-Situ Annealing for Optical Computing by Ge Technology

Ge is becoming an increasingly popular semiconductor material with high Si compatibility for on-chip optical interconnect technology. For a better manifestation of the meritorious material properties of Ge, its surface treatment should be performed satisfactorily before the electronic and photonic components are fabricated. Ex-situ rapid thermal annealing (RTA) processes with different gases were carried out to examine the effects of the annealing gases on the thin-film quality of Ge grown epitaxially on Si substrates. The Ge-on-Si samples were prepared in different structures using the same equipment, reduced-pressure chemical vapor deposition (RPCVD), and the samples annealed in N2, forming gas (FG), and O₂ were compared with the unannealed (deposited and only cleaned) samples to confirm the improvements in Ge quality. To evaluate the thin-film quality, room-temperature photoluminescence (PL) measurements were performed. Among the compared samples, the O₂-annealed samples showed the strongest PL signals, regardless of the sample structures, which shows that ex-situ RTA in the O₂ environment would be an effective technique for the surface treatment of Ge in fabricating Ge devices for optical computing systems.

Influence of Nd and Cu content on the microstructural and magnetic properties of NdFeB thick films

In this study, Nd(Cu)-Fe-B single layer thick films (up to 5 μm) have been prepared by triode sputtering and the effect of excess Nd and Cu content on the magnetic properties and microstructures have been investigated. The films were deposited at 450 °C and depending on the Nd and Cu content, they are either amorphous or crystalline in the as-deposited state. All films were submitted to an ex-situ rapid thermal annealing (500 °C/10 min). While films with a lower Nd and Cu content are characterized by a homogeneous microstructure, those with a higher Nd-Cu content have a wide distribution in grain size (in some cases, peculiar flower-like structures are formed close to the substrate). The inhomogeneous microstructure, together with direct crystallization in the as-deposited state in high Nd-Cu containing films, is attributed to an exothermic reaction. The highest coercivity (2.75 T) is achieved for the lower Nd (17.5 at. %)-Cu (1.5 at. %) content, higher Nd (up to 35 at. %)-Cu (up to 3 at. %) content leading to a reduction in both coercivity and degree of texture.

Self Organized Compound Semiconductor Nanocrystallite Distributions in SiO2 on Silicon Synthesized by Ion Implantation

ABSTRACTThe temporal and spatial evolution of sequentially and single ion implanted Cd and Se concentration distributions into thermally grown SiO2 on (001)-Si were investigated. Ex-situ rapid thermal annealing was performed to initiate the reaction-diffusion driven material transport, nanocrystal nucleation and growth. Finally this leads to the formation of buried distinct layers of CdSe nanocrystals. The spatiotemporal evolution of the concentration distributions were quantitatively analyzed by dynamic Secondary Ion Mass Spectrometry (SIMS). It will be shown, that there is a correlated diffusion of Cd and Se when both elements were implanted in overlapping concentration profiles, whereas the single implanted Cd and Se exhibit a completely different diffusion behaviour. In the region of the supersaturated solid solution reaction to thermodynamically stable CdSe clusters takes place. The steep concentration gradient provokes indiffusion of the stoichiometric compound. In the case of a surplus of Cd over Se and long annealing times self-organized, nearly periodic and correlated concentration variations of Cd and Se can be observed. Comparison of the profiles indicate that this pattern formation is controlled by the diffusion and precipitation of the over stoichiometric Cd.

Growth and Characterization of Self-Aligned Erbium Silicide on N-Type, (100) Oriented Silicon

ABSTRACTIn view of its low barrier height to n-type Si, ErSi2 has potential applications as an infrared detector, as low-resistance ohmic contacts and as source/drain regions in Schottky barrier MOSFETs. Although there is a substantial body of work on ErSi2 grown on Si(111), there are relatively few published papers on the growth and properties of ErSi2 on Si(100). In order to develop a CMOS-compatible process, we have studied the growth of ErSi2 using a multi-source, UHV magnetron system to sputter-deposit 20 nm Ti/(10–50) nm Er bilayers on chemically cleaned n-Si(100) substrates followed by ex-situ rapid thermal annealing in N2. Highly oriented ErSi2 in the hexagonal phase was formed at an annealing temperature of 400°C with ErSi2 (100) Si(100). The Ti overlayer and the unreacted Er were selectively etched in HF and HNO3, respectively, leaving behind an ErSi2 layer with a smooth surface morphology, a uniform bulk composition and a planar ErSi2/Si interface. Results of electrical sheet resistance and Schottky barrier height measurements on these layers will be reported.

Degree of order and magnetic properties of τ-MnAl films

The relationship between the crystalline order and the magnetic properties of MBE-grown τ-MnAl films on GaAs/AlAs is studied using ex-situ rapid thermal annealing (RTA). An increase in magnetization and a reduction of the coercive field are clearly correlated to an increase in crystalline order.

Hydrogen Release and Si-N Bond-Healing Infrared Study of Rapid Thermal Annealed Amorphous Silicon Nitride Thin Films

ABSTRACTWe address aspects of hydrogen bonding and its thermal evolution in amorphous Silicon nitride films grown by Remote Plasma Enhanced Chemical Vapor Deposition (RPECVD) from SiH4 and NH3 (or ND3) source gases. Rapid Thermal Annealing (RTA) decreases the Si-H(D) and SiN-H(D) bond populations. The hydrogen bonds break, and H2 (HD, D2) forms and evolves from the film with the heat treatment. This molecular hydrogen release is accompanied by Si- and N- bond healing as detected by a SiN infra red stretch mode signal gain. The ex-situ RTA experiment temperatures ranged from 400 °C to 1200 °C, in 100 °C steps and the film structural changes were monitored by Fourier Transform Infrared spectroscopy (FTIR) after each incremental anneal. Gas flow ratios R=NH3/SiH4 > 2 produced films in which SiN-H(D) bonds dissociated, and a gas desorption rate equation estimated an activation energy barrier of Ea = 0.3 eV. The release of hydrogen from the films in the form of H2 (D2) and ammonia radicals was detected by mass spectrometry and is shown here. The re-bonding of nitrogen to silicon upon thermal dissociation of hydrogen's is consistent with the improvement of the electrical properties of a-SiN:H films following RTA treatment.