Two-step Rapid Thermal Annealing Research Articles

Si tunnel junctions obtained by proximity rapid thermal diffusion for tandem photovoltaic cells

Low-resistance c-Si Esaki tunnel junctions (TJ) can be applied in two-terminal Si-based tandem solar cells to electrically connect two sub-cells. Proximity rapid thermal diffusion (PRTD) is an economical and facile method to fabricate the Si tunnel junctions with a damage-free surface. The p++/n++ Si TJ on (111)-oriented c-Si wafer produced by combining PRTD and photovoltaic industrial techniques is reported in this work. The adjustment of the n++ emitter by a two-step rapid thermal annealing effectively facilitates the realization of the p++/n++ TJ. The peak current density of a tunnel diode based on this TJ is within the range 140–192 A cm−2 with a peak to valley current ratio of 1.9–3.2. Such a p++/n++ TJ is implemented in III–V nanowires (NWs) on Si tandem solar cells. Despite the defectuosity of the NWs array, we demonstrate that an increase of the open-circuit voltage is observed compared with the sole single-junction Si solar cell. This kind of TJ can also be integrated with other top cell materials such as perovskites and copper indium gallium selenide. Low-cost and high-efficiency c-Si based tandem solar cells might be produced with the application of Si TJs obtained by PRTD.

Enhanced hole concentration in nonpolar a-plane p-AlGaN film with multiple-step rapid thermal annealing technique

An innovative multiple-step rapid thermal annealing (RTA) technique was developed for obtaining high hole concentration in the nonpolar a-plane Mg-delta-doped AlGaN films grown on semi-polar r-plane sapphire substrates with metal organic chemical vapor deposition. The structural, optical, and electrical properties of the nonpolar a-plane p-AlGaN epi-layers were characterized with high-resolution x-ray diffraction, photoluminescence spectra, and Hall effect measurement. The characterization results demonstrated that the dissociation efficiency of the Mg–H bonds in the nonpolar a-plane p-AlGaN films could be improved significantly with the multiple-step RTA process. In fact, a hole concentration as high as 1.9 × 1018 cm−3 was achieved with the multiple-step RTA technique, which was 35%, 9%, and 23% higher than those obtained with conventional one-step, two-step, and the recently renovated two-step RTA methods, respectively.

Dynamics of metal-induced crystallization of ultrathin Ge films by rapid thermal annealing

Though Ge crystallization has been widely studied, few works investigate metal-induced crystallization of ultrathin Ge films. For 2 nm Ge films in oxide matrix, crystallization becomes challenging due to easy oxidation and low mobility of Ge atoms. Introducing metal atoms may alleviate these problems, but the functions and the behaviours of metal atoms need to be clarified. This paper investigates the crystallization dynamics of a multilayer structure 1.9 nm Ge/0.5 nm Al/1.5 nm Al2O3 under rapid thermal annealing (RTA). The functions of metal atoms, like effective anti-oxidation, downshifting Raman peaks, and incapability to decrease crystallization temperature, are found and explained. The metal behaviours, such as inter-diffusion and defect generation, are supported with direct evidences, Al-Ge nanobicrystals, and Al cluster in Ge atoms. With these understandings, a two-step RTA process achieves high-quality 2 nm nanocrystal Ge films with Raman peak at 298 cm−1 of FWHM 10.3 cm−1 and atomic smooth interfaces.

Effects of the amount of Si rings on the phase separation and crystallization of silicon-rich SiO2 thin films

Si rich oxide (SRO) thin films were annealed by two-step rapid thermal annealing (RTA) to form SiO2-matrix silicon-nanocrystals (Si-NCs). The effects of the amount of Si rings in SRO thin films on the phase separation and crystallization processes of annealed thin films were investigated using Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Results showed that the amount of Si rings exerted little effects on the phase separation and the crystallization of SiO0.7 thin films. Moreover, the amount of Si rings significantly influenced the crystallization of SiO1.5 thin films. The crystalline fraction of 1000°C-SiO1.5 thin films firstly increased from 7% to 15% with increased of the amount of Si rings. The changes in crystallization processes were most possibly due to the different amount of SiO4 bond in the SRO thin films with different amount of Si rings. Our work indicated that the amount of Si rings could facilitate the crystallization of annealed thin films with higher O/Si atomic ratio.

Development of annealing process for solution-derived high performance InGaZnO thin-film transistors

Abstract The influences of the annealing process on solution-derived InGaZnO thin-film transistors (TFTs) were investigated. Operation characteristics of IGZO TFTs were obtained from high temperature processes: rapid thermal annealing (RTA) at 600 °C and conventional thermal annealing (CTA) at 500 °C. It is found that the RTA increases the on-current and off-current of TFTs. The CTA decreases off-current and improves the interfacial property. Meanwhile, a two-step annealing process, comprising RTA and CTA, increases on-current and decreases off-current and is considered as the optimal annealing procedure. Another two-step annealing process, comprising CTA and RTA, increases on-current but increases off-current, simultaneously.

Formation of pre-silicide layers below Ni1−xPtxSi/Si interfaces

The formation of a pre-silicide layer below Ni1−xPtxSi films is reported with structure and composition distinctly different from previously observed diffusion layers. It was found that during two-step rapid thermal annealing Ni interstitial diffusion can kinetically dominate over the formation of Ni silicide, which results in a metastable pre-silicide layer. Aberration corrected scanning transmission electron microscopy experiments have revealed Ni to occupy interstitial and substitutional sites in the pre-silicide layer. Rapid thermal annealing and Pt alloying determines the stoichiometry and thickness of the layer, while the point defect configurations give rise to lowering of the associated Schottky barrier heights. The pre-silicide layer effectively limits diffusion of Ni into the substrate and therefore allows for the low-temperature growth of Ni2Si and NiSi.

Formation and investigation of cobalt silicide ultrathin layers in Ti/Co/Ti-, TiN/Ti/Co-, and TiN/Co-on-silicon structures

The formation of ultrathin CoSi2 layers in Ti(8 nm)/Co(10 nm)/Ti(5 nm), TiN(18 nm)/Ti(2 nm)/Co(8 nm), and TiN(18 nm)/Co(8 nm) systems magnetron-sputtered on the Si(100) surface is studied. The systems are subjected to two-step rapid thermal annealing. In between the annealing steps, the “sacrificial” layer is chemically removed and the second and third systems are additionally covered by a 17-nm-thick amorphous silicon (α-Si) layer. In the course of the fabrication process, the structures are examined using time-of-flight secondary-ion (cation) mass spectrometry, Auger electron spectroscopy, and scanning electron microscopy combined with X-ray energy dispersion microanalysis. It is shown that the above complex of analytical investigation provides efficient physical control of ultrathin silicide layer formation.

Nickel Silicide Formation using Pulsed Laser Annealing for nMOSFET Performance Improvement

The formation of a uniform, high tensile stress and low silicide/Si interfacial resistance nickel silicide in nMOSFET by introducing pulsed laser annealing (PLA) is reported. This annealing approach facilitated the phase transformation of nickel silicide to Si-rich NiSix compounds using a low-thermal-budget process, improves the silicide/Si interface regularity and avoids familiar (111) NiSi2 facet formation at a laser energy of 1.5 J cm−2. By increasing laser energy density up to 2.3 J cm−2, the device performance and statistics junction leakage distribution were degraded due to the increased sheet resistance of silicide layer and the destroyed silicide/Si interface morphology. When the PLA with a laser energy density of 1.5 J cm−2 was employed for nickel silicidation on the p-type Schottky diodes, a 0.16 eV hole Schottky barrier height (SBH) increase from 0.52 to 0.68 eV was observed. In addition, the application of PLA for source/drain silicidation of nMOSFETs demonstrated an 8% enhancement in Ion−Ioff characteristic relative to that obtained through the conventional two-step rapid thermal annealing (RTA). This PLA method holds promise as a potential replacement for current nickel silicide annealing approaches toward extremely scaled-down transistors.

Denuded Zone Formation in Germanium Codoped Heavily Phosphorus-Doped Czochralski Silicon

The formation of a denuded zone (DZ) by conventional furnace annealing (CFA) and rapid thermal annealing (RTA) based denudation processing is investigated and the gettering of copper (Cu) atoms in germanium co-doped heavily phosphorus-doped Czochralski (GHPCZ) silicon wafers is evaluated. It is suggested that both a good quality defect-free DZ with a suitable width in the sub-surface area and a high density bulk micro-defect (BMD) region could be formed in heavily phosphorus-doped Czochralski (HPCZ) silicon and GHPCZ silicon wafers. This is ascribed to the formation of phosphorus-vacancy (P-V) related complexes and germanium-vacancy (GeV) related complexes. Compared with HPCZ silicon, the DZ width is wider in the GHPCZ silicon sample with CFA-based denudation processing but narrower in the one with two-step RTA pretreatments. These phenomena are ascribed to the enhancing effect of germanium on oxygen out-diffusion movement and oxygen precipitate nucleation, respectively. Furthermore, fairly clean DZs near the surface remain in both the HPCZ and GHPCZ silicon wafers after Cu in-diffusion, except for the HPCZ silicon wafer which underwent denudation processing with a CFA pretreatment, suggesting that germanium doping could improve the gettering of Cu contamination.

Structural Characterization of Sputtered Silicon Thin Films after Rapid Thermal Annealing for Active-Matrix Organic Light Emitting Diode

The microcrystalline phase obtained by adopting a two-step rapid thermal annealing (RTA) process for rf-sputtered silicon films deposited on thermally durable glass was characterized. The optical properties, surface morphology, and internal stress of the annealed Si films are investigated. As the thermally durable glass substrate allows heating of the deposited films at high temperatures, micro-polycrystalline silicon (micro-poly-Si) films of uniform grain size with a smooth surface and a low internal stress could be obtained after annealing at 750 °C. The thermal stress in the Si films was 100 times lower than that found in the films deposited on conventional glass. Uniform grains with an average grain size of 30 nm were observed by transmission electron microscopy (TEM) in the films annealed at 800 °C. These micro-poly-Si films have potential application for fabrication of uniform and reliable thin film transistors (TFTs) for large scale active-matrix organic light emitting diode (AMOLED) displays.

Size control of Si nanocrystals by two-step rapid thermal annealing of sputtered Si-rich oxide/SiO2 superlattice

Controllable size of silicon (Si) nanocrystals can be achieved by a two-step rapid thermal annealing technique consisting of rapid annealing at 1000°C in nitrogen ambient and rapid oxidation at 600–800°C of a radio frequency magnetron co-sputtered Si-rich oxide/SiO2 superlattice structure. The photoluminescence (PL) spectra related to Si nanocrystals were observed in the visible range (600–900 nm). After rapid oxidation, the size of the nanocrystals was reduced and the quality of the Si nanocrystal/SiO2 interface was improved, resulting in a blue shift and an increase of the PL peak intensity. Finally, annealing in air increases the PL intensity further.

Spike Annealing as Second Rapid Thermal Annealing to Prevent Pure Nickel Silicide From Decomposing on a Gate

To create a nickel-monosilicide (NiSi) film with superior electrical properties, two-step rapid thermal annealing (RTA) was optimized. Using <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> chemical dry cleaning and increasing initial RTA temperature makes it possible to macroscopically transform nickel into NiSi without causing oxygen contamination. Nevertheless, di-nickel silicide (Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si) remaining on the top surface of NiSi on p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -doped gate degrades the electrical properties of the NiSi film. This top-surface Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si is formed by decomposition of NiSi by conventional second RTA and appears as a disconnection of the NiSi film on the logic test device or agglomeration of silicon and nickel on the blanket NiSi film with activation energy of 2.92 eV. Using ldquospike RTArdquo with higher temperature suppresses the decomposition of NiSi and activates transformation of Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si to NiSi. It is concluded that the proposed two-step RTA significantly improves the uniformity of the electrical properties of NiSi in 65-nm-node logic devices.

Silicide Schottky-Barrier Phototransistor Integrated in Silicon Channel Waveguide for In-Line Power Monitoring

An in-line power monitor with a thin nickel silicide layer placed on a silicon channel waveguide for optical absorption is proposed. A two-terminal Schottky-barrier collector phototransistor configuration is used to amplify significantly the primary photocurrent, and the Ni silicide thickness is thinned down to ~5 nm using a two-step rapid thermal annealing procedure to reduce the insertion loss. The demonstrated in-line detectors exhibit ~24-mA/W responsivity around 1550 nm with the insertion loss of ~0.8-1.2 dB. The approaches to further increase the responsivity and simultaneously decrease the insertion loss are addressed.

Activation of Mg-doped P-GaN by using two-step annealing

One- and two-step rapid thermal annealing (RTA) for activating Mg-doped p-type GaN films had been performed to compare with conventional furnace annealing (CFA). The two-step annealing process consists of two annealing steps: the first step is performed at 750°C for 1min and the second step is performed at 600°C for 5min in pure O2 or air ambient. It is found that the samples annealed in air ambient exhibit poor electrical properties as compared to those annealed in pure O2. Compared to one-step RTA annealing and CFA annealing, the samples with two-step annealing exhibit higher hole concentration and lower resistivity. This means that the two-step annealing is a powerful method to enhance the electrical performance of Mg-doped p-type GaN films. Similar results were also evidenced by photoluminescence (PL) measurement. Possible mechanism was confirmed by secondary ion mass spectrometry analysis.

Reduction of Leakage and Low-Frequency Noise in MOS Transistors Through Two-Step RTA of NiSi-Silicide Technology

A two-step rapid thermal annealing (RTA) nickel salicidation process was employed to fabricate 0.1-mum gate length CMOS transistors. Excess salicidation, common in the conventional one-step RTA NiSi process, is effectively suppressed by this approach, which is confirmed by transmission electron microscopy (TEM) images. More improvements due to two-step NiSi are observed in NMOS than in PMOS transistors: The n+-p junction diode with two-step NiSi exhibits lower reverse leakage and higher breakdown voltage than the one-step silicided diode. For the first time, it is found that two-step NiSi NMOS exhibits significant reduction in off-state leakage (~5times) and low-frequency noise (up to two orders of magnitude) over one-step NiSi NMOS, although there is not much difference in PMOS transistors

Enhancement of Photoluminescence Intensity of GaInNAs/GaAsQuantum Wells by Two-Step Rapid Thermal Annealing

We investigate the effect of rapid thermal annealing on InGaNAs/GaAsquantum wells. At optimized annealing temperatures and times, thegreatest enhancement of the photoluminescence intensity is obtained bya special two-step annealing process. To identify the mechanismaffecting the material quality during the rapid thermal annealing,differential temperature analysis is applied, and temperature- andpower-dependent photoluminescence is carried out on the samplesannealed under different conditions. Our experiment reveals that somecomposition redistribution or other related ordering processes mayoccur in the quantum-well layer during annealing. Annealing at a lowertemperature for a long time primarily can remove defects anddislocations while annealing at a higher temperature for a short timeprimarily homogenizes the composition in the quantum wells.

Study of activation of beryllium implantation in gallium nitride

In this paper, post-implantation thermal activation of beryllium in GaN by rapid thermal annealing (RTA) or pulsed laser annealing (PLA) has been investigated. The result of a two-step RTA, in which the Be-implanted GaN sample was annealed first in forming gas (12% H 2, 88% N 2) and followed by annealing in pure nitrogen, showed slight p-type for Hall measurement, which was also confirmed by hot probe measurement. However, low activation efficiency and reproducibility was a problem in RTA. In PLA, by optimizing the laser fluence and annealing ambient, efficient activation of Be can be obtained using a 248 nm KrF excimer laser. The photoluminescence (PL) spectra revealed the presence of a Be-related transition level. The Hall measurement results showed that a hole sheet concentration of 2.56×10 13 cm −3 can be achieved with a single-pulse laser irradiation of 0.2 J/cm 2 in flowing nitrogen ambient.

Development of spectroscopic ellipsometry as in-line control for Co SALICIDE process

This work is aimed at in-line thickness and composition analysis of Co silicides by spectroscopic ellipsometry (SE). The silicides were formed by a two-step rapid thermal annealing (RTA) in nitrogen at different temperatures from initial Co layers deposited on Si (100) substrates and capped by a protective layer of TiN. The optical constants of Co, CoSi and CoSi 2 films were calculated in the wavelength range of 240–800 nm, describing the optical dispersions by harmonic oscillator models. These models were applied for in-line thickness and composition control of the main steps of Co SALICIDE process. The effects of the first RTA temperature and initial Co thickness on formation of silicide phases and their thickness were evaluated. For phase identification, additional methods (sheet resistance, Auger electron spectroscopy and X-ray diffraction) were used. Finally, the suitability of SE for layer thickness uniformity evaluation was demonstrated for the main steps of Co SALICIDE process.

Study on the Variations of Microstructures and Domain Structures of Bi3.35La0.85Ti3O12 Ferroelectric Thin Films Formed by Two-Step Rapid Thermal Annealing (RTA) Process Utilizing Piezoresponse Force Microscope (PFM)

Recently, La-substituted Bi4Ti3O12 (BLT) has been widely studied as a candidate material for FeRAM due to its superior properties like high fatigue endurance with relatively lower crystallization temperature. In this study, we attempted to examine ferroelectric properties of various BLT thin films that were made using two-step rapid thermal annealing (RTA) process. The microstructure of BLT thin film is appeared as a critical factor to maximize ferroelectric properties. We found that the 2nd annealing temperature in two-step RTA process played an important role in determining the crystalline orientation of BLT thin films. Grain orientations of the BLT thin films were interpreted based on x-ray diffraction (XRD) in conjunction with piezoresponse images that were obtained utilizing piezoresponse force microscope (PFM). In addition, the results were correlated with the hysteresis loops.

Effects of a two-step rapid thermal annealing process on Mg-doped p-type GaN films grown by metalorganic chemical vapor deposition

A two-step rapid thermal annealing (RTA) process is proposed in order to improve the electrical properties, the crystal quality, and the surface roughness of Mg-doped p-type GaN films. In the two-step RTA process, the first low temperature step (600 °C) with a long annealing time (5 min) was followed by the second high temperature (950 °C) step with a short annealing time. These results show that the two-step RTA process significantly improves electrical properties and reduces the surface roughness of p-GaN compared to the one-step RTA process.