Post-deposition Thermal Processing Research Articles

Effect of post-deposition annealing on atomic layer deposited SiO2 film for silicon surface passivation

We have investigated the passivation performance of atomic layer deposited silicon dioxide (ALD-SiO2) films on crystalline silicon surface with various post-annealing temperatures. A maximum effective lifetime of 2157 μs can be achieved at the optimized annealing temperature of 650 °C on 3 Ω cm n-type silicon wafers. The improved passivation quality can be attributed to the low interface defect density and extremely high positive fixed charge density. Especially, the high positive fixed charge density of over 4 × 1012 cm-2 can be observed after annealing at high temperature. Therefore, it is inferred that the passivation mechanism for ALD-SiO2 films is based on not only chemical passivation but also field-effect passivation, which is more similar with the ALD-Al2O3 films rather than the thermally grown SiO2 films. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and thermal effusion measurement revealed the variation of elements content and distribution of silicon, oxygen, hydrogen and carbon during the post-deposition thermal treatment process, indicating that the rearrangement and release of these elements create more oxygen vacancies and result in the improvement of interface quality and positive fixed charge density of ALD-SiO2 films.

Cu2ZnGeS4 thin films deposited by thermal evaporation: the impact of Ge concentration on physical properties

In this work, the processing of Cu2ZnGeS4 (CZGS) thin films by a thermal evaporation technique starting from CuS, GeS and ZnS precursors, and post-deposition thermal processing, is discussed. Batches of films with GeS layers of varying thicknesses are deposited in order to study the role of Ge concentration on the structural, morphological, optical and electrical properties of CZGS films. The formation of the CZGS compound with a tetragonal phase and a kesterite structure is confirmed for all samples using XRD and Raman studies. An improvement in crystallite size for Ge-poor films is also observed in the XRD analysis, which is in good agreement with the grain size observed in the cross section SEM image. Furthermore, it is found that the band-gap of CZGS film can be tailored in the range of 2.0–2.23 eV by varying Ge concentration. A comprehensive electrical characterization is also performed which demonstrates that slightly Ge-poor samples are described by the lowest grain boundary defect densities and the highest photosensitivity and mobility values. A study of the work function of CZGS samples with different Ge concentrations is also presented. Finally, a theoretical evaluation is presented, considering, under ideal conditions, the possible impact of these films on device performance. Based on the characterization results, it is concluded that Ge-poor CZGS samples deposited by thermal evaporation present better physical properties for device applications.

Vacuum coated Sb2S3 thin films: Thermal treatment and the evolution of its physical properties

In this work, we report a detailed study of the post-deposition thermal processing and material properties of Sb2S3 thin films deposited by thermal evaporation under vacuum. The effect of the annealing temperature on the structural, morphological, optical, opto-electronic, spectroscopic, and electrical properties of the films was investigated using various tools such as XRD, AFM, UV–vis spectroscopy, Raman spectroscopy, Ellipsometry, photoconductivity, Seebeck effect, and Kelvin probe. The annealing temperature had an interesting influence on the grain growth, and morphology of the films; in a small temperature window of 10°C, the change in grain size and shape was striking. The annealing temperature of 325°C was identified as a critical point at which the grain size is smallest and the morphology is exceptionally homogeneous. Two highly noticeable features were the change in morphology and photosensibility. The photosensibility increased from 0.6 for the as-deposited film to 132 after annealing at 400°C.

Effect of Thermal Budget on the Electrical Characterization of Atomic Layer Deposited HfSiO/TiN Gate Stack MOSCAP Structure.

Metal Oxide Semiconductor (MOS) capacitors (MOSCAP) have been instrumental in making CMOS nano-electronics realized for back-to-back technology nodes. High-k gate stacks including the desirable metal gate processing and its integration into CMOS technology remain an active research area projecting the solution to address the requirements of technology roadmaps. Screening, selection and deposition of high-k gate dielectrics, post-deposition thermal processing, choice of metal gate structure and its post-metal deposition annealing are important parameters to optimize the process and possibly address the energy efficiency of CMOS electronics at nano scales. Atomic layer deposition technique is used throughout this work because of its known deposition kinetics resulting in excellent electrical properties and conformal structure of the device. The dynamics of annealing greatly influence the electrical properties of the gate stack and consequently the reliability of the process as well as manufacturable device. Again, the choice of the annealing technique (migration of thermal flux into the layer), time-temperature cycle and sequence are key parameters influencing the device’s output characteristics. This work presents a careful selection of annealing process parameters to provide sufficient thermal budget to Si MOSCAP with atomic layer deposited HfSiO high-k gate dielectric and TiN gate metal. The post-process annealing temperatures in the range of 600°C -1000°C with rapid dwell time provide a better trade-off between the desirable performance of Capacitance-Voltage hysteresis and the leakage current. The defect dynamics is thought to be responsible for the evolution of electrical characteristics in this Si MOSCAP structure specifically designed to tune the trade-off at low frequency for device application.

Improved Silicon Surface Passivation of APCVD Al2O3 by Rapid Thermal Annealing

Short-duration post-deposition thermal treatments at temperatures above those normally used for annealing activation have the potential to further improve the already excellent passivation of crystalline silicon (c-Si) achieved by Al2O3, but have so far received little attention. In this work we investigate the influence of rapid thermal annealing (RTA) on the surface passivation of c-Si by Al2O3 deposited by atmospheric pressure chemical vapour deposition (APCVD) as a function of RTA peak temperature between 500 and 900°C, and for Al2O3 deposition temperatures between 325 and 440°C. The saturation current density J0 of undiffused p-type surfaces is observed either to increase or decrease following RTA depending on the Al2O3 deposition temperature and the RTA peak temperature. The optimum deposition temperature depends on the post-deposition thermal processing to be applied. Films deposited at lower temperatures provide worse passivation after low temperature heat treatment, but maintain this passivation better at higher RTA temperatures. An exceptionally low J0 of 7 fA cm−2, due to the combination of a very low interface state density Dit and unusually high negative fixed charge density Qf, is achieved by the use of a short 500–550°C RTA combined with optimised deposition conditions.

Structural, morphological and spectroscopic ellipsometry studies on sputter deposited Sb2S3 thin films

In this work we are discussing RF magnetron sputter deposition of Sb2S3 thin films, postdeposition thermal processing, and the material characterization. After thermal treatment at 300 °C in N2/S environment, films were crystallized in orthorhombic structure, which was determined by XRD and Raman spectroscopy. Crystallite size, lattice parameters, strain, texture coefficient and degree of preferred orientation are reported. AFM and SEM images of the annealed films revealed a compact and uniform surface, composed of grains of large-size in the order of micrometers and well-defined rhombic geometry. Elemental analysis by EDXS showed a slight sulfur excess in the films. Optical properties and electronic band to band transitions were determined by spectroscopic ellipsometry. The dielectric function of Sb2S3 films was well represented by a Tauc–Lorentz and Lorentz oscillator models collection. Optical constants n and k revealed notable differences caused by thermal treatment, which are consistent with amorphous (as deposited) and polycrystalline (annealed) film properties, such as increase in E g and lowering of n and k values. The optical band gap of the annealed films from the ellipsometric measurements was in the range of 1.63–1.7 eV with an absorption coefficient larger than 104 cm−1 in the above band gap region. The films showed p-type conductivity and photo-response.

ZnO Nanorod Arrays as Electron Injection Layers for Efficient Organic Light Emitting Diodes

Nanostructured oxide arrays have received significant attention as charge injection and collection electrodes in numerous optoelectronic devices. Zinc oxide (ZnO) nanorods have received particular interest owing to the ease of fabrication using scalable, solution processes with a high degree of control of rod dimension and density. Here, vertical ZnO nanorods as electron injection layers in organic light emitting diodes are implemented for display and lighting purposes. Implementing nanorods into devices with an emissive polymer, poly(9,9‐dioctyluorene‐alt‐benzothiadiazole) (F8BT) and poly(9,9‐di‐n‐octylfluorene‐alt‐N‐(4‐butylphenyl)dipheny‐lamine) (TFB) as an electron blocking layer, brightness and efficiencies up to 8602 cd m−2 and 1.66 cd A−1 are achieved. Simple solution processing methodologies combined with postdeposition thermal processing are highlighted to achieve complete wetting of the nanorod arrays with the emissive polymer. The introduction of TFB to minimize charge leakage and nonradiative exciton decay results in dramatic increases to device yields and provides an insight into the operating mechanism of these devices. It is demonstrated that the detected emission originates from within the polymer layers with no evidence of ZnO band edge or defect emission. The work represents a significant development for the ongoing implementation of ZnO nanorod arrays into efficient light emitting devices.

Structural Evolution of Multilayer SnS/Cu/ZnS Stack to Phase-Pure Cu2ZnSnS4 Thin Films by Thermal Processing

In this work, thin films of phase-pure Cu2ZnSnS4 (CZTS) were developed from a stack of binary metal sulfides by post-deposition thermal processing. The precursor stack SnS/Cu/ZnS was grown by sequential electrodeposition of SnS and Cu layers followed by thermal evaporation of ZnS layer. The transformation from binary/ternary composition to phase-pure CZTS was studied using different experimental tools such as X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The TEM images revealed the formation of tetragonal crystals with interplanar spacing 0.312 nm. Raman spectra of the films confirmed that annealing at 550°C for 30 min under N2/S ambient resulted in the formation of phase-pure CZTS film. The bandgap estimated from the optical transmittance and reflectance spectra showed a direct transition at 1.59 eV. The films are photosensitive and the photo electrochemical measurements showed the p-type conductivity of the films.

Impact of Pulse Thermal Processing on the Properties of Inkjet Printed Metal and Flexible Sensors

We report on the low temperature processing of environmental sensors employing pulse thermal processing (PTP) technique to define a path toward flexible sensor technology on plastic, paper, and fabric substrates. Inkjet printing and pulse thermal processing technique were used to realize mask-less, additive integration of low-cost sensors on polymeric substrates with specific focus on temperature, humidity, and strain sensors. The printed metal line performance was evaluated in terms of the electrical conductivity characteristics as a function of post-deposition thermal processing conditions. The PTP processed Ag metal lines exhibited high conductivity with metal sheet resistance values below 100 mΩ/□ using a pulse width as short as 250 μs. The flexible temperature and relative humidity sensors were defined on flexible polyimide substrates by direct printing of Ag metal structures. The printed resistive temperature sensor and capacitive humidity sensor were characterized for their sensitivity with focus on future smart-building applications. Strain gauges were printed on polyimide substrate to determine the mechanical properties of the silver nanoparticle films. The observed electrical properties of the printed metal lines and the sensitivity of the flexible sensors show promise for the realization of a high performance print-on-demand technology exploiting low thermal-budget PTP technique.

Thin films of SnO2:F by reactive magnetron sputtering with rapid thermal post-annealing

Thin films of fluorine-doped tin oxide (FTO) are transparent conducting oxide (TCO) layers that exhibit excellent corrosion and mechanical resistance and are typically produced by high temperature (>400°C) spray pyrolysis. Magnetron sputtering is another industry relevant method for large area FTO deposition where a low temperature process can be used although the electrical properties of sputtered FTO are currently inferior to those of spray pyrolysis. Here reactive sputtering of FTO is investigated in order to optimize the sputter and post-treatment parameters for achieving high quality TCO layers. FTO layers are deposited by reactive DC magnetron sputtering of metallic tin targets in an atmosphere of Ar/O2/CF4 or CHF3. Post-deposition rapid thermal processing (RTP) for a short annealing time of less than 5min at 450°C is sufficient to lower electrical resistivity down to ~2×10−3Ωcm as a result of the increased carrier concentration and mobility while keeping the average optical transmittance above 79%. The free carrier concentration can be controlled by changing the fluorine doping via the CF4/CHF3 flow, as determined by Rutherford backscattering spectrometry and elastic recoil detection analysis. The electrical activation of the fluorine dopant is found to be low, on the order of 4%. Based on temperature-dependent Hall measurements we show that the electrical conductivity in RTP-annealed FTO is primarily limited by ingrain scattering.

SiO2/TiO2 distributed Bragg reflector near 1.5 μm fabricated by e-beam evaporation

The authors report on the fabrication and characterization of SiO2/TiO2 distributed Bragg reflector (DBR) mirrors operating at the eye safe and optical communication wavelength window, λ = 1.5 μm. Our experimental results demonstrated that SiO2/TiO2 DBR mirrors with reflectivity exceeding 95% at λ = 1.5 μm can be achieved using e-beam evaporation in conjunction with postdeposition thermal annealing process in ambient air. It was found that the postdeposition annealing process transformed the crystal structure of the as-deposited TixOy to TiO2, leading to a significant reduction in optical absorption. Erbium doped III-nitride semiconductors incorporating DBR mirrors at 1.5 μm emission may open up many novel applications, including infrared emitters, optical amplifiers, and high power infrared lasers.

Enhanced charge generation of the ZnO nanowires/PZT hetero-junction based nanogenerator

We fabricated an alternative nanogenerator device with distinguished structure. Representative piezoelectric materials of ZnO nanowires and PZT thin films were tried to be combined to form a hetero-junction structure for fabrication of an alternative nanogenerator device to possibly obtain a synergy effect and then improved performance. The ZnO nanowires were grown by a hydrothermal synthesis technique and then PZT thin films were deposited on the surface of the ZnO nanowires by rf magnetron sputtering process. The PZT thin films were annealed to be crystallized with different conditions for post-deposition thermal treatment process. The hetero-junction structure was polarized by a Corona poling process to obtain a unidirectional orientation of dipole moments to enhance their piezoelectric property. Structure and morphology of the grown ZnO nanowires were investigated to achieve appropriate characteristics to achieve performance improvement for the resulting nanogenerator device. To confirm effect of the hetero-junction structure on improvement of power generation performance of the resulting nanogenerator device, current generating properties were comparatively investigated with those of nanogenerator device with only ZnO nanowires or PZT thin films as active piezoelectric component, respectively. The nanogenerator device with a hetero-junction structure of ZnO nanowires/PZT revealed distinctively improved average currents of 270nm, which is quite higher than those of the nanogenerator devices with pristine ZnO nanowires, or with pristine PZT thin films, respectively. Possible factors contributed to improvement of the current generation properties were discussed for the presented nanogenerator device.

Fabrication and Characterization of Low-Cost, Large-Area Spray Deposited Cu2ZnSnS4 Thin Films for Heterojunction Solar Cells

ABSTRACTLarge-area Cu2ZnSnS4 (CZTS) thin films were deposited by low-cost spray pyrolysis technique on Mo-coated soda-lime glass (SLG) substrates at varied substrate temperatures of 563-703°K. Deposition conditions were optimized to obtain best quality films and effect of post deposition thermal processing of the as-deposited films under H2S ambient were investigated. Structural, morphological, and compositional characterization of as-deposited and H2S treated CZTS absorber layers were carried out by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX). Optical and electrical properties were measured by UV-Vis spectroscopy, van der Pauw, and Hall-effect measurements. Films grown at ∼360°C substrate temperature showed superior optoelectronic properties, improved stoichiometry and smoother morphology compared to films grown at much higher or lower temperatures. Film properties were significantly improved after the H2S processing. Our results show that large area high quality CZTS films can be fabricated by low-cost spray pyrolysis technique for high throughput commercial production of CZTS based heterojunction solar cells.

Nanoassembly control and optical absorption in CdTe-ZnO nanocomposite thin films

The spatial distribution of CdTe nanoparticles within a ZnO thin-film matrix was manipulated using a dual-source, sequential radio-frequency (RF)-sputter deposition technique to produce nanocomposite materials with tuned spectral absorption characteristics. The relative substrate exposure time to each sputtering source was used to control the semiconductor phase connectivity, both within the film plane and along the film growth direction, to influence the degree of photocarrier confinement and the resulting optical transition energies exhibited by the CdTe phase. Significant changes (up to ΔE ≈ 0.3 eV) in the absorption onset energy for the CdTe nanoparticle ensemble were produced through modification in the extended structure of the semiconductor phase. Raman spectroscopy, cross-sectional transmission electron microscopy, and x-ray diffraction were used to confirm the phase identity of the CdTe and ZnO and to characterize the nanostructures produced in these composite films. Isochronal annealing for 5 min at temperatures up to 800 °C further indicated the potential to improve film crystallinity as well as to establish the post-deposition thermal processing limits of stability for the semiconductor phase. The study highlights the significance of ensemble behavior as a means to influence quantum-scale semiconductor optical characteristics of import to the use of such materials as the basis for a variety of optoelectronic devices, including photosensitized heterojunction components in thin film photovoltaics.

Atomic Layer Deposition and Characterization of Amorphous ErxTi1-xOy Dielectric Ultra-Thin Films

Er1-xTixOy dielectric thin films were deposited on Si(100) substrates by atomic layer deposition (ALD) using tris(methylcyclopentadienyl)erbium [(CpMe)3Er] and tetrakis(diethylamino)titanium [TDEAT] as metal precursors, and O3 as oxidant. The deposition temperature dependence of both Er2O3 and TiO2 film growths showed the overlapping ALD window of 175–250°C. Compositional tunability of Er1-xTixOy films was obtained through deposition process control. Carbon and nitrogen impurities in as-deposited films were found to be below X-ray photoelectron spectroscopy detection level. Glancing incidence X-ray diffraction and phase-shifting interferometry results showed that ErxTi1-xOy films with ALD cycle ratios (Er2O3/TiO2) of 1:8 or higher have a good thermal stability and remain amorphous with unchanged surface roughness after post-deposition rapid thermal processing (RTP) at 700°C in O2. Electrical measurements showed that optimized amorphous Er1-xTixOy films after RTP exhibited a dielectric constant of ∼36, a hysteresis voltage of less than 10 mV, and a leakage current density of 10−8 A/cm2 at −1 MV/cm; such properties compare favorably with the properties of other reported amorphous titanium-based ternary dielectrics on Si. The sizable reduction of leakage current density of Er1-xTixOy found in our study suggests that amorphous Er1-xTixOy thin films are promising future dielectrics in Si integrated circuit technology.

Remote plasma-deposited GeO 2 with quartz-like Ge- and O-local bonding: Band-edge state and O-vacancy comparisons with SiO 2

X-ray absorption spectroscopy (XAS) and many-electron theory are combined to describe symmetries and degeneracies for intrinsic bonding defects in remote plasma-deposited (rpd-) non-crystalline (nc-), rpd-nc-GeO 2 and rpd-nc-SiO 2, hereafter simply GeO 2 and SiO 2. GeO 2 is emerging as an alternative gate dielectric for nano-CMOS devices. High resolution O-vacancy spectral features in O K pre-edge spectra for SiO 2 have been assigned to multiplet transitions and negative ion states based on an extended d 2 equivalent model, including both weaker singlet and as well the stronger triplet transitions discussed in previous publications. This has revealed predominantly mid-gap Ge and Si singlet and triplet bonding arrangements for the electrons in O-vacancy sites. These have been examined as a function of post deposition rapid thermal annealing in Ar ambients for GeO 2 deposited at 300 °C on both Si and Ge substrates, identifying different post-deposition thermal budget processing windows for low defect density GeO 2 on Si and Ge substrates. For ultra thin nitrided SiO x , x < 2 interfacial layers on Si, this is at least 700 °C, but on Ge, independent of surface processing it less than 600 °C.

RF-Sputtered ZnO Thin Films: The Tailoring of Structural, Electrical and Optical Properties

ABSTRACTWe report on the influence of radio-frequency magnetron sputtering variables (working pressure and deposition atmosphere) and post-deposition thermal treatment processing upon the structural, optical and electrical properties of c-axis highly textured ZnO thin films. The films’ crystallinity increased progressively with argon pressure for the inert atmosphere experiments and with the oxygen dilution in the working atmosphere (up to 10%) for the reactive atmosphere experiments. The post-deposition annealing treatment at 450°C/1h in air reduced the strain in the ZnO films and enhanced their crystallinity and texturing. The ZnO films had an average transmittance of ∼90% in visible range and an average band-gap of ∼3.4 eV, regardless of the sputtering variables used. The samples prepared at the higher argon pressure (0.45 Pa) had a resistivity with one order of magnitude smaller than the samples prepared at the lower pressures.

Monoclinic textured HfO2 films on GeOxNy/Ge(100) stacks using interface reconstruction by controlled thermal processing

The authors used x-ray absorption spectroscopy of the O K edge to investigate the nanocrystalline structure of thin HfO2 films deposited by remote plasma enhanced chemical vapor deposition on Ge(100). Postdeposition thermal process induced the interfacial reconstruction and the crystallization of the HfO2 in the monoclinic structure driven by the Ge(100) substrate. The substrate templating of the HfO2 crystallization is an evidence that the processing used here removes the undesired the interfacial layer and has the potential to yield interfaces with low density of defects.

Chemical bonding and graded interfacial transition regions at transition metal, Hf(Zr), /high- k gate dielectric, Hf(Zr)O 2, interfaces

One of the most significant and challenging process integration issues for high- k dielectrics is the replacement of poly-Si gates in CMOS devices with either dual metal gates, or a single mid-band gap metal. The issue is the stability of the metal gate/high- k gate dielectric interface with respect to post-deposition thermal processing. Ab initio quantum chemistry calculations address this issue, and two questions have been resolved, providing results that are consistent with the experiment. The interface between a metal gate electrode and a high gate electrode and oxide dielectric cannot be atomically abrupt after post-deposition thermal processing. Instead there must be a chemically-graded interfacial transition region that mitigates some of the benefits of replacing dual poly-Si gates by metals, except for gate-last processing. However, electrical stress and heating during device operation will be significant driving force atomic motion, and the formation of an interfacial transition region.

Increase in pyrolytic carbon optical anisotropy and density during processing of coated particle fuel due to heat treatment

Measurements of pyrolytic carbon optical anisotropy and density have been made on a series of tri-isotropic (TRISO) coated particles prepared for the United States Department of Energy’s Advanced Gas Reactor Fuel Development and Qualification (AGR) program. These measurements show the effect of varying the deposition conditions, especially the deposition temperature, on the density and optical anisotropy of the carbon layers. Additional heat treatment studies of the coated particles at various stages illustrate the strong effect of post-deposition thermal processing on these two pyrolytic carbon properties. Such post-deposition heat treatment occurs during SiC deposition and fuel compact firing, resulting in increased anisotropy and density of the pyrolytic carbon layers.