Flash Annealing Research Articles

Unusual energy separation of subbands in Si(111) p-channels induced by In adsorption

We investigated the dispersion structure of the hole subbands in vicinal Si(111)4 × 1-In surfaces directly by angle-resolved photoelectron spectroscopy. In this study, three inversion layers with different impurity concentrations and numbers of times of flash annealing (FA) were investigated. We observed wider energy separations of subbands levels for the sample with a less number of FA and a higher impurity concentration. However, the observed energy levels and separations had smaller binding energy than those calculated by triangle potential approximation. We found that the discrepancies were due to the out-diffusion of Arsenic atoms from the sub-surface region of silicon via high temperature FA. The possible potential profile of the space charge layer after considering the out-diffusion of Arsenic dopant atoms at the sub-surface region was proposed.

High-quality, single-layered epitaxial graphene fabricated on 6H-SiC (0001) by flash annealing in Pb atmosphere and mechanism

High-quality epitaxial graphene is produced on silicon carbide by flash annealing of 6H-SiC in a lead (Pb) atmosphere at ∼1400 °C for 30 s. Nearly three top bilayers of SiC are decomposed due to fast heating and cooling, and sublimation of Si atoms from SiC is retarded by the Pb atmosphere. The synergetic effects promote the growth of continuous single-layered graphene sheets on the SiC terraces, and a model is established to elucidate the effects and growth mechanism.

Effect of the Flash Annealing on the Impurity Distribution and the Electronic Structure in the Inversion Layer

Effect of the Flash Annealing on the Impurity Distribution and the Electronic Structure in the Inversion Layer

(Invited) Oxygen Precipitation and Defect Generation in Cz Silicon during Second and Millisecond Annealing

The precipitation of oxygen was investigated after rapid thermal annealing pre-treatments for 30 s in the range 1100-1250 °C and after flash lamp annealing for 3 ms and 20 ms with different irradiances up to melting of the wafer surface. It was found that the difference between thermal processing on the second and on the millisecond scales is based on the temperature profiles generated by the different types of processing. These profiles influence the shrinking of grown-in oxide precipitate nuclei and the generation, diffusion, and annihilation of intrinsic point defects. It was further found that pre-existing dislocations propagate into the wafer during flash anneals. The dislocation propagation can be well described by a three-dimensional mechanical model.

Invited; Oxygen Precipitation and Defect Generation in Cz Silicon during Second and Millisecond Annealing

Oxygen precipitation in Czochralski silicon is still an issue in various device technologies. On the one hand it is exploited for internal gettering of metallic impurities by oxygen precipitates and on the other hand it is undesired because oxygen precipitates are known to degrade the lifetime of minority carriers. At the end, it depends on the application of the silicon material how precipitation of interstitial oxygen is controlled.The reduced thermal budgets due to continuous scaling of features sizes in high end device technologies lead to the development of faster and faster anneal processes. The earlier device technologies were dominated by conventional annealing processes. Today rapid thermal processes working on the second scale are common steps in microelectronic processing. Recent developments utilize already thermal processes on the millisecond scale as e. g. flash and laser anneals. All these different time scales influence the generation of intrinsic point defects and thus also the kinetics of oxygen precipitation in a different way.Rapid thermal annealing (RTA) is a widely used thermal pretreatment to create an internally gettering bulk defect zone and a defect denuded zone below the surface. This is possible because the precipitation of interstitial oxygen strongly depends on the supersaturation of intrinsic point defects. During RTA vacancies supersaturate facilitating the formation of VmOn complexes which are the initial stages of oxygen precipitation. However, the strength of the effect depends on the temperature and cooling rate of the RTA pre-treatment.Flash lamp annealing is used first of all for the creation of shallow dopant profiles in high end electronic device technologies. The surface of a silicon wafer can be heated with this technique to temperatures up to the melting point within a few milliseconds. With the help of a thermal model we can simulate the temperature profiles. We combined this model with a second model describing the generation and annihilation of intrinsic point defects. The results of modeling help to understand the experimental results of oxygen precipitation. After 3 ms of annealing a defect denuded zone below the front surface is generated while after 20 ms annealing oxygen precipitation is suppressed in the wafer.Flash lamp annealing leads to steep temperature profiles in the wafers causing stress. Silicon wafers with etched, ground, and sawed surfaces were subjected to flash lamp annealing for 20 ms. Such wafers contain different densities of pre-existing dislocations which propagate into the wafer during flash lamp annealing up to a certain depth which is different on the front and back sides. Plastic deformation was not observed if no pre-existing dislocations were present in the wafer before flash lamp annealing. The elastic and plastic deformation was simulated by a mechanical model.In summary, the difference between thermal processing on the second and on the millisecond scales is based on the temperature profiles generated by the different types of processing. These profiles influence the shrinking of grown-in oxide precipitate nuclei and the generation, diffusion, and annihilation of intrinsic point defects and thus the oxygen precipitation during further processing.

Influence of laser annealing on the structural properties of sputtered AlN:Ag plasmonic nanocomposites

We propose a process of deposition of plasmonic nanocomposites comprising magnetron sputtering of AlN:Ag multilayers combined with intermediate steps of flash annealing. When the AlN matrix structure was amorphous, thermal annealing induced the break-up of silver layers and the formation of homogeneously distributed spherical nanoparticles. On the other hand, in the case of a nanocrystalline AlN matrix, the larger nanoparticles were observed to form only at an interfacial and a surface zone. Further treatment by laser annealing was employed in order to photo-modulate the localized surface plasmon resonances (LSPRs) by promoting ripening of the nanoparticles. Using high resolution transmission electron microscopy, it was observed that laser annealing caused nanoparticle enlargement with a concurrent improvement of their separation, while retaining their average spherical shape. Optical reflectance measurements showed that better LSPR was obtained when the AlN matrix was amorphous due to the restrained nanoparticle ripening inside nanocrystalline AlN. Roughening at the film/substrate interface and film degradation after laser annealing at the employed radiation wavelength where reduced compared to similar samples grown by pulsed laser deposition. Based on finite difference time domain simulations and X-ray reflectivity measurements, this was attributed to the improved quality of the AlN matrix.

Structure–property characterization of an age hardenable Al–Mg–Si alloy after straining and flash annealing

The objective of this research is to characterize the structure–property relationship of a heat-treatable Al–Mg–Si aluminum alloy that is subjected to various straining and heat treatments. The effects of paint bake cycle (PBC), pre-straining and annealing on mechanical tensile properties were investigated. Pre-straining combined with rapid, high temperature annealing can noticeably improve ductility and increase formability. While pre-straining by itself does not change the hardening behavior of the as-received material, combining pre-straining with rapid, high temperature annealing does alter the hardening behavior and decreases the final post-PBC yield strength. It is well documented that PBC increases the yield stress in Al–Mg–Si alloys by precipitation of the β″ phase. The reduction in precipitation hardening after pre-straining and annealing is caused by the high temperature annealing treatment that promotes over-aging and conversion of the β″ phase to β′ and β precipitates, even with a short annealing time. The yield stress after PBC can be increased if the pre-strained and annealed material is strained a second time after annealing, although this increase may not reach the strength levels of the alloy without the annealing step. Hence, the intermediate annealing and forming technology is most useful for age hardenable alloys if applied locally to complex areas of a panel where increased formability is more important than high strength.

Flash annealing influence on structural and electrical properties of TiO2/TiO/Ti periodic multilayers

Multilayered structures with a 40nm period composed of titanium and two different titanium oxides, TiO and TiO2, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. These multilayers were sputtered onto Al2O3 sapphire to avoid substrate compound diffusion during flash annealing (ranging from 350°C to 550°C). Structure and composition of these periodic TiO2/TiO/Ti stacks were investigated by X-ray diffraction, X-ray photoemission spectroscopy and transmission electronic microscopy techniques. Two crystalline phases α-Ti and fcc-TiO were identified in the metallic-rich sub-layers whereas the oxygen-rich ones were composed of a mixture of amorphous and rutile TiO2 phase. DC electrical resistivity ρ measured for temperatures ranging from 25 to 200°C was influenced by the thermal treatments. The temperature coefficients of resistance of these periodic TiO2/TiO/Ti multilayers were modified from 11.7×10−04 to −8.81×10−04K−1. Local changes of crystallinity were reported and the resistivity responses of these annealed films could be linked to the typical electrical behavior of a metal–oxide mixture.

Fabrication of SiGe rings and holes on Si(0 0 1) by flash annealing

We show that SiGe islands are transformed into nanoholes and rings solely by annealing treatments and without Si capping. Rings are produced by a rapid flash heating at temperatures higher than the melting point of Ge, whereas nanoholes are produced by several minutes of annealing. The rings are markedly rich in Si with respect to the pristine islands, suggesting that the evolution path from islands to rings is driven by the selective dissolution of Ge occurring at high temperatures.

Comparison of the Impact of Thermal Treatments on the Second and on the Millisecond Scales on the Precipitation of Interstitial Oxygen

The precipitation of oxygen was investigated after rapid thermal annealing pre-treatments for 30 s in the range 1100-1250 {degree sign}C and after flash lamp annealing for 3 ms and 20ms with different irradiances up to melting of the wafer surface. The difference between thermal processing on the second and on the millisecond scales is based on the temperature profiles generated by the different types of processing. These profiles influence the shrinking of grown-in oxide precipitate nuclei and the generation, diffusion, and annihilation of intrinsic point defects and thus the oxygen precipitation during further processing. Oxygen precipitation can be suppressed by flash anneals or bulk defect zones and defect denuded zones for internal gettering can be created both depending on the flash duration and energy density.

Large-scale uniform bilayer graphene prepared by vacuum graphitization of 6H-SiC(0001) substrates

We report on the preparation of large-scale uniform bilayer graphenes on nominally flat Si-polar 6H-SiC(0001) substrates by flash annealing in ultrahigh vacuum. The resulting graphenes have a single thickness of one bilayer and consist of regular terraces separated by the triple SiC bilayer steps on the 6H-SiC(0001) substrates. In situ scanning tunneling microscopy reveals that suppression of pit formation on terraces and uniformity of SiC decomposition at step edges are the key factors to the uniform thickness. By studying the surface morphologies prepared under different annealing rates, it is found that the annealing rate is directly related to SiC decomposition, diffusion of the released Si/C atoms and strain relaxation, which together determine the final step structure and density of defects.

Effects of ECAP and Aging on Mechanical and Superelastic Behaviors of Ti-Mo-Based and Ti-25at.%Nb SMAs

Ni-free Ti-based shape memory alloys (SMAs) are increasingly recognized as promising functional materials for medical applications. The mechanical properties of these metastable Ti-based SMAs are sensitive to aging and thermomechanical treatment. Effects of severe plastic deformation (SPD)-equal channel angular pressing (ECAP) and aging on superelastic behavior of Ni-free Ti-based SMAs, Ti-9.8Mo-3.9Nb-2V-3.1Al wt.% (TMNVA) and Ti-25at.%Nb, have been investigated. The results show that the yielding strength of TMNVA alloy increases sharply with the number of ECAP processes—to greater than 1,400 MPa after two passes ECAP—but elongation of TMNVA alloy decreases severely and the plasticity is lost completely after two passes ECAP. Both ECAP process and flash annealing treatment have weak contribution to the superelastic recoverable strains of Ti-Mo-based alloy. For Ti-25at.%Nb alloy, after one pass ECAP process at 400 °C, the yielding stress increases obviously, and the recovery strain increases a little. With the further increase in the number of ECAP processes, the yielding stress and the recovery strain change little. Aging treatment at low temperature after ECAP process is in favor of superelasticity of Ti-25at.%Nb alloy. An almost completely recoverable strain of 1.5% is obtained in Ti-25at.%Nb alloy after two passes ECAP and aging at 300 °C for 1 h. The mechanisms of the effects of SPD and aging are also discussed.

Magnetic properties of Dy-diffused Nd-Fe-B powder prepared by crystallization from amorphous state

The method of enhancing coercivity of isotropic Nd-Fe-B flakes using simultaneous diffusion of Dy and crystallization from the amorphous state was also applied to Nd-Fe-B powders, in this study. Metal Dy coating was synthesized on amorphous Nd2.36Fe14B1.05 powders by the vapor deposition method, and the powders were crystallized by a flash annealing. Simultaneous diffusion of Dy from their surfaces using the crystallization enhanced the coercivity of isotropic Nd-Fe-B powders. The coercivity Hc increased and the remanence Mr decreased nearly linearly with the amount of Dy, and the coating of 4.5 wt.% Dy resulted in 25.3% increase in Hc and 6.5% decrease in Mr. The decrease in Mr of the Nd-Fe-B powders is nearly the same in magnitude to that previously reported for Nd2.36Fe14B1.05 flakes, which suggests that the method of Dy diffusion using crystallization from amorphous state is applicable to Nd-Fe-B amorphous powders as well as flakes. The energy-dispersive X-ray spectroscopy revealed that Dy coating is inhomogeneous, and a further enhancement in Hc is expected by improving the coating method.

B segregation to grain boundaries and diffusion in polycrystalline Si with flash annealing

Three-dimensional atom probe tomography was used to characterize the segregation of B dopant atoms to grain boundaries in polycrystalline Si after flash-assisted rapid thermal annealing. Tomographic reconstructions allowed direct measurement of segregation coefficients, which were found to be greater at lower flash temperatures with thermal budgets that limit grain growth. Hall measurements confirmed the deactivation of B at the grain boundaries, while secondary ion mass spectrometry was used to measure B diffusion in the film. Experimental parameters were then simulated in a diffusion model which accurately predicts the diffusion of B in polycrystalline Si at flash temperatures of 1150 °C, 1250 °C, and 1350 °C, as well as with conventional rapid thermal annealing.

Comparison of the Impact of Thermal Treatments on the Second and on the Millisecond Scales on the Precipitation of Interstitial Oxygen

The precipitation of oxygen was investigated after rapid thermal annealing pre-treatments for 30 s in the range 1100–1250°C and after flash lamp annealing for 3 ms and 20 ms with different irradiances up to melting of the wafer surface. The difference between thermal processing on the second and on the millisecond scales is based on the temperature profiles generated by the different types of processing. These profiles influence the shrinking of grown-in oxide precipitate nuclei and the generation, diffusion, and annihilation of intrinsic point defects and thus the oxygen precipitation during further processing. Oxygen precipitation can be suppressed by flash anneals or bulk defect zones and defect denuded zones for internal gettering can be created both depending on the flash duration and irradiance.

Rapid flash annealing of thermally reactive copolymers in a roll-to-roll process for polymer solar cells

Light induced thermocleaving of a thermally reactive copolymer based on dithienylthiazolo[5,4-d]thiazole (DTZ) and silolodithiophene (SDT) in contact with the heat sensitive substrate the heat sensitive substrate polyethyleneterphthalate (PET) was effectively demonstrated with the use of high intensity pulsed light, delivered by a commercial photonic sintering system. Thermally labile ester groups are positioned on the DTZ unit of the copolymer that can be eliminated thermally for enhanced photochemical stability and advantages in terms of processing (solubility/insolubility switching). The photonic sintering system was successfully implemented in a full roll-to-roll process on flexible PET substrates and large-area polymer solar cell modules were prepared by solution processing of five layers under ambient conditions using the photonic sintering system for thermocleaving of the active layer. The PET foil did not show any deformation after exposure to the high intensity light only leaving the insoluble thermocleaved active layer. The active layer remained planar after light exposure thereby allowing the coating of supplementary material on top.

Impact of Millisecond Flash-Assisted Rapid Thermal Annealing on SiGe Heterostructure Channel pMOSFETs With a High-k/Metal Gate

Preserving the integrity (e.g., Ge concentration, strain, and lattice perfection) of pseudomorphically grown silicon germanium (SiGe) heterostructure channels on Si substrates is one of the most critical factors in obtaining optimal pMOSFET performance from high hole mobility of strained SiGe. A millisecond Flash-assisted rapid thermal annealing (RTA) technique was applied to source/drain (S/D) dopant activation of high-Ge-concentration SiGe channel MOSFETs with a high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> /metal gate stack. Flash annealing of SiGe channel pMOSFETs is shown to be an effective way to preserve channel integrity while achieving a low S/D resistance. Excellent mobility and short-channel device performance are realized. In addition, as the concentration of Ge in the SiGe layer is increased, high B activation can be achieved with a lower peak temperature Flash anneal. As a result, the sheet resistance of the implanted p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> junction can be comparable with that of higher temperature Flash-annealed (or optimal spike-annealed) Si. Furthermore, minimizing Ge diffusion reduces performance variation (such as statistical threshold voltage variation), which may be caused by the introduction and/or growth of defects in the strained SiGe heterostructure channel. It is shown that high-performance SiGe channel pMOSFETs with high Ge concentrations and a scaled high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> /metal gate can be achieved by a millisecond Flash-assisted RTA technique while preventing undesirable effects in the SiGe channel, such as within-wafer statistical performance variation.

SPM Characterization of Titanium Disilicide Nanostructures Grown on a Ni-Modified Si(100) Substrate

The paper presents our recent investigations of the early stage growth of titanium silicides on a modified Si(100) substrate. The substrate was modified by deposition of a minute amount of Ni atoms, and the subsequent flash annealing. This process led to the creation of parallel defect lines on the Si(100) surface. We expected TiSi2 to form elongated structures on top and/or between the defect lines. Though this idea failed, stable nanostructures were observed and characterized using scanning probe microscopy (scanning tunneling microscopy and atomic force microscopy) methods.

Highly scaled (Lg ∼ 56 nm) gate-last Si tunnel field-effect transistors with ION > 100 μA/μm

Planar band-to-band tunneling FETs (TFETs) have been fabricated on silicon-on-insulator (SOI) substrates using conventional CMOS technologies with a highly scaled sub-60nm gate length (effective gate length [Lg]∼40nm due to an overlap between the source and gate) and different anneal sequences. The optimal anneal sequence including spike and flash annealing resulted in a drive ON current (ION))>100μA/μm with ION/IOFF>105 at a drain bias of −1V. The devices exhibited negative differential resistance and non-linear subthreshold temperature dependencies, consistent with the band-to-band tunneling mechanism. Simulations using a 2-D TCAD simulator, MEDICI, agreed with experimental data, demonstrating the possibility of Si tunnel transistors in logic applications.

Self-assembled strontium ferrite on Au nano-dot arrays using rapid thermal annealing

The self-assembled SrM dot array on Au nano-dots has been prepared by using DC magnetron sputtering system without any substrate heating. Then, flash annealing was carried out to crystallize the SrM film. C-axis oriented SrM perpendicular to the films can be observed only at annealing temperature of 800 °C for annealing time of 7 min. The coercivity and remanent squareness ratio in perpendicular direction are 2.8 kOe and 0.72, respectively. The reversal magnetization of SrM on patterned Au nano-dots is closer the Stoner-Wohlfarth model compared to continuous films. The peak of ΔM of SrM film deposited on patterned Au nano-dots is lower compared to SrM deposited on continued Au films.