Rapid Photothermal Processing Research Articles

Annealing of silicon optical fibers

The recent realization of silicon core optical fibers has the potential for novel low insertion loss rack-to-rack optical interconnects and a number of other uses in sensing and biomedical applications. To the best of our knowledge, incoherent light source based rapid photothermal processing (RPP) was used for the first time to anneal glass-clad silicon core optical fibers. X-ray diffraction examination of the silicon core showed a considerable enhancement in the length and amount of single crystallinity post-annealing. Further, shifts in the Raman frequency of the silicon in the optical fiber core that were present in the as-drawn fibers were removed following the RPP treatment. Such results indicate that the RPP treatment increases the local crystallinity and therefore assists in the reduction of the local stresses in the core, leading to more homogenous fibers. The dark current-voltage characteristics of annealed silicon optical fiber diodes showed lower leakage current than the diodes based on as-drawn fibers. Photons in UV and vacuum ultraviolet (VUV) regions play a very important role in improving the bulk and carrier transport properties of RPP-treated silicon optical fibers, and the resultant annealing permits a path forward to in situ enhancement of the structure and properties of these new crystalline core optical fibers.

The Mechanism of Enhanced Diffusion of Phosphorus in Silicon During Rapid Photothermal Processing of Solar Cells

In this paper, we have presented the experimental results of phosphorus diffusion in silicon for the cases of rapid thermal processing (RTP) and rapid photothermal processing (RPP). In the case of the RPP, other than thermal energy, the vacuum ultraviolet photons are used as an additional source of energy. We have investigated the secondary-ion-mass-spectroscopy impurity profiles at different concentrations of P in Si. Based on our own experimental results and the data published in the open literature, we have provided an explanation of the enhanced diffusion both for the RTP and RPP cases. The thermal factor leads to the excitation (vibration) of atoms and quantum energy to the electron system excitation. As compared with the pure thermal process, the quantum-energy contribution provides a reduced activation energy and a higher diffusion coefficient.

Synthesis of nanostructured Al-doped zinc oxide films on Si for solar cells applications

Al-doped ZnO thin films have been prepared by a novel successive chemical solution deposition technique. The variation in morphological, structural, electrical, and optical properties of nanostructured films with doping concentration is investigated in details. It was demonstrated that rapid photothermal processing (RPP) improves the quality of nanostructured ZnO films according to the enhancement of resonant Raman scattering efficiency, and the suppression of the visible luminescence with the increase of RPP temperature. It was found from the I– V characteristics of ZnO/Si heterojunction that the average short-circuit current density is about 8 mA/cm 2. For 1%Al-doped ZnO/SiO 2/Si structure, the short-circuit current density is about 28 mA/cm 2. The improvement shown in the characteristics may be assigned partially to the reduction of the defect density in the nanostructured Al-doped ZnO films after RPP. The correlations between the composition, microstructure of the films and the properties of the solar cell structures are discussed. The successive chemically deposited Al-doped ZnO thin film offers wider applications of low-cost solar cells in heterojunction structures.

Nanostructured zinc oxide films synthesized by successive chemical solution deposition for gas sensor applications

Nanostructured ZnO thin films have been deposited using a successive chemical solution deposition method. The structural, morphological, electrical and sensing properties of the films were studied for different concentrations of Al-dopant and were analyzed as a function of rapid photothermal processing temperatures. The films were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron and micro-Raman spectroscopy. Electrical and gas sensitivity measurements were conducted as well. The average grain size is 240 and 224 Å for undoped ZnO and Al-doped ZnO films, respectively. We demonstrate that rapid photothermal processing is an efficient method for improving the quality of nanostructured ZnO films. Nanostructured ZnO films doped with Al showed a higher sensitivity to carbon dioxide than undoped ZnO films. The correlations between material compositions, microstructures of the films and the properties of the gas sensors are discussed.

Nanostructured zinc oxide gas sensors by successive ionic layer adsorption and reaction method and rapid photothermal processing

Undoped and Sn, Ni-doped nanostructured ZnO thin films were deposited on glass substrates using a successive ionic layer adsorption and reaction (SILAR) method at room temperature. The SILAR deposited zinc oxide films have been rapid photothermal processing (RPP) at various temperatures to study the effect of annealing on the sensing properties. Structural, electrical and sensing properties were investigated by means of X-ray diffraction (XRD), Energy Dispersive X-ray spectroscopy, scanning electron microscopy, electrical resistivity, and sensitivity measurements. Microstructures of the deposited films were studied for different concentrations of dopants and zinc-complex solution and temperatures. The results of influence of growth processes, doping, and RPP on phase structure, surface morphology, particles size and resistivity values are presented and discussed. The average grain size determined from XRD patterns was 240, 220 and 265 Å for ZnO, Sn–ZnO and Ni–ZnO films, respectively. Moreover, electrical characterization of the sensors prepared from SILAR deposited nanostructured zinc oxide thin film has been carried out. The variation in resisitivity of the ZnO film sensors was obtained with doping and post-deposition rapid photothermal processing in vacuum and N 2 ambient. Electrical resistivity measurements showed semiconducting nature with room temperature resistivity 1.5 × 10 5, 6.1 × 10 2, 70 Ω cm for as-deposited ZnO, 4 at.% Ni–ZnO and 4 at.% Sn–ZnO, respectively. These values decreased to 1 × 10 4, 2 × 10 2, 30 Ω cm for RPP annealed films. The types of doping and temperatures of RPP were found to have an important role in determining the sensitivity and resolution of the NO 2, NH 3 ZnO-based sensors. While the nanostructured ZnO sensor showed higher ammonia sensitivity than that of NO 2, an enhanced NO 2 sensitivity was noticed with the ZnO films doped with 4 at.% Sn and higher NH 3 sensitivity was obtained by 4 at.% Ni doping of zinc oxide thin films.

Nitrogen oxides and ammonia sensing characteristics of SILAR deposited ZnO thin film

Abstract Pure and Sn, Ni doped ZnO thin films were deposited on glass substrates using a novel successive ionic layer adsorption and reaction (SILAR) method at room temperature. Microstructures of the deposited films were optimized by adjusting growth parameters. The variation in resistivity of the ZnO film sensors was performed with rapid photothermal processing (RPP). The effect of rapid photothermal processing was found to have an important role in ZnO based sensor sensitivity to NO 2 , NH 3 . While the undoped ZnO film surface exhibited higher NH 3 sensitivity than that of NO 2 , an enhanced NO 2 sensitivity was noticed for the ZnO films doped with Sn and higher NH 3 sensitivity was obtained by Ni doping.

Synthesis and Characterization of Functional Nanostructured Zinc Oxide Thin Films

A novel aqueous relatively low-temperature thin film growth technique has been developed to fabricate a new generation of smart and functional nanostructured metal oxide thin film materials. This chemical synthetic route uses stable and inexpensive metal inorganic salts and environment-friendly solvents. The nanomaterials are obtained to analyze the physical and structural requirements of their applications in gas sensors and solar cells. The rapid photothermal processing at the 650 ºC of nanostructured zinc oxide leads to the suppression of deep-defect-level emission and improvement of near-band edge emission. The responses of the sensing elements when exposed to 100 ppm ammonia at temperatures between 20 ºC and 300 ºC have been assessed.

Novel NO 2 gas sensor based on cuprous oxide thin films

In this paper we present the results concerning the characterization of cuprous oxide thin films fabricated by chemical deposition and rapid photothermal processing (RPP) method. The growth kinetic effects and influence of the RPP temperature on the chemical deposited cuprous oxide thin films microstructures were investigated by scanning electron microscopy and energy dispersive X-ray spectrometry. The effect of the electrical resistivity change of Cu 2O thin film layer in the presence of NO 2 is used for gas sensing measurements. Cuprous oxide layers are used as NO 2 gas sensitive material in a novel gas sensor element. It can be shown from experimental results that chemical bath deposition and rapid photothermal processing not only allows green materials preparation but also improves the performance and reliability over conventional methods of the production of sensors for continuous environmental monitoring.

Sensing characteristics of tin-doped ZnO thin films as NO 2 gas sensor

NO 2 gas sensor was fabricated by successive ionic layer adsorption and reaction (SILAR) technique and rapid photothermal processing (RPP) of the Sn-doped ZnO film. The experimental results shows that tin doping of zinc oxide thin films improve the sensor element sensitivity to 1.5 ppm NO 2 in air and downshift the operating temperature. The influence of variation of Sn concentration in the chemical bath and the RPP temperature on NO 2 sensitivity of thin film sensor elements was investigated in this work. Higher sensitivity was obtained at 5–10 at.% tin concentration in the solution of ions and RPP temperature of 550–650 °C. Increasing the Sn concentration in doped ZnO samples more than 10 at.% as well as decreasing the oxygen partial pressure leads to the NO 2 gas sensitivity decrease. It looks promising to use the inexpensive tin-doped zinc oxide thin films obtained by SILAR method and RPP in smart gas sensing devices that are able to recognize gas species in low concentrations and are demanded for continuous environmental monitoring.

Properties of SiO 2 thin films prepared by anodic oxidation under UV illumination and rapid photothermal processing

Anodic oxidation under ultraviolet (UV) illumination and rapid photothermal processing technique used for high quality oxide preparation in terms of device surface passivation and gate or tunnel dielectrics are reported. A number of samples of SiO 2 thin films were prepared using this technique. It is shown that anodic oxidation under UV illumination followed by rapid photothermal processing (450 °C, 15 s) in the inert ambient yields the best optimization of the SiO 2 thin films properties. Avoiding high temperature process should result in a better performance of the semiconductor devices. Anodic oxidation under UV illumination at low temperature and post-oxidation photothermal processing can be a possible alternative to the furnace growth silicon oxide; not only because of the low temperature process, but also because this technology essential improves the oxides properties.

Prospects of manufacturing organic semiconductor-based integrated circuits

The driving force for developing organic thin-film transistor (OTFT)-based electronics is the fact that they are flexible, lightweight and have the prospect of low-cost manufacturing. Major barriers in the practical realization of OTFT-based electronic systems are the need for larger power supplies, lower gain, lower switching speeds and reliability problems. New directions leading to changes in the design of transistors, materials used in the fabrication, and processing techniques are warranted for developing process and equipment that can lead to the manufacturing of OTFT-based electronics. For developing dense OTFT-based electronics, the low thermal conductivity (as compared to silicon) of organic semiconductors is a fundamental problem. The use of nanodimension polymers with homogeneous microstructure, transistors operating in subthreshold region and the use of new materials (high and low dielectric constant dielectric materials as well as Cu as the conductor for interconnections) for fabricating transistors and a novel rapid photothermal processing technique for depositing thin films of organic semiconductors as well as for reducing the defects introduced during processing are some of the proposed directions that may lead to the manufacturing of OTFT based electronics.

Rapid photothermal processing as a semiconductor manufacturing technology for the 21st century

The interactions of photons below about 800nm provide thermal effects and quantum photo-effects. The performance of rapid thermal processing (RTP) techniques can be improved manifold by exploiting the use of quantum photo-effects in thermal processing. Photo excitations of species taking part in a chemical reaction or solid-state phenomena (e.g. annealing, solid-phase epitaxy etc.) lead to reduced activation energy. The quantum photo-effects dominated RTP is called rapid photothermal processing (RPP). At lower processing temperatures (compared to RTP), semiconductor devices with better performance, reliability and yields can be processed by RPP. Manufacturing of silicon integrated circuits (ICs) with dimension as low as 20nm feature sizes is expected to dominate the 21st century. The ultra small feature size coupled with 12in. (may be even 18in.) diameter wafers will force the IC manufacturers to reduce the processing temperature to the point that only RPP can provide the desired performance, reliability and yields. This new era of low processing temperature of silicon IC processing will provide new capabilities in the processing of compound semiconductors related electronic and optical devices. The low-processing temperature aspect of RPP coupled with high throughput also opens new doors for large area devices such as solar cells and flat panel displays. The major challenge is the development of commercial equipment for manufacturing of ICs, solar cells and flat panel etc.

A study of the effect of ultraviolet (UV) and vacuum ultraviolet (VUV) photons on the minority carrier lifetime of single crystal silicon processed by rapid thermal and rapid photothermal processing

Minority carrier lifetime is an efficient indicator of defect levels present in the starting material as well as process and equipment induced defects. By employing rapid thermal processing (RTP) and rapid photothermal processing (RPP) as the thermal processing techniques, we have studied the effect of ultraviolet (UV) and vacuum ultraviolet (VUV) photons on the bulk minority carrier lifetime of phosphorous doped and undoped single crystal silicon wafers. For both diffused and undiffused wafers, we have observed an enhancement in the minority carrier lifetime when UV and VUV photons are used in conjunction with the samples processed without the use of UV and VUV photons. The effect of ramp rates on the minority carrier lifetime and the significance of optimized thermal cycles have also been studied in this paper. A possible explanation based on the dependence of diffusion coefficient on the photo spectrum of light source is also given in this paper.

Importance of rapid photothermal processing in defect reduction and process integration

Importance of rapid photothermal processing in defect reduction and process integration

Changing from rapid thermal processing to rapid photothermal processing: what does it buy for a particular technology?

Rapid thermal processing (RTP) based on incoherent light as a source of energy has emerged as an alternate of furnace processing. In recent years, we have demonstrated that in addition to the high heating and cooling rates, quantum photoeffects play an important role in the operation of RTP. The quantum photoeffects can be fully exploited by using an incoherent light source as the source of optical energy (photons with wavelength less than 800 nm) and tungsten halogen lamps as the source of optical and thermal energy. The use of ultra violet (UV) or vacuum ultra violet (VUV) photons along with infrared photons is referred to as rapid photothermal processing (RPP). This paper addresses the issues involved as we move from RTP to RPP. The improved device performance results of diffusion, chemical vapor deposition (CVD), ohmic contact formation and metallization are described in detail. The manufacturing issues like stress, defects, reliability and yield are discussed in the context of RPP and the paper presents potential advantage of RPP for the manufacturing of microelectronics, solar cells, flat panel display and optoelectronics.

Sub-quarter micron silicon integrated circuits and single wafer processing

This paper describes the role of single wafer processing in the development of sub-quarter micron silicon integrated circuits (ICs). The issues related to device processing, choice of materials, performance, reliability, and manufacturing are covered. Single wafer processing based rapid photothermal processing (dominant photons with wavelength less than about 800 nm) is an ideal answer to almost all the thermal processing requirements of current and future Si ICs. For process integration, a new model for process optimization based on minimization of thermal stress is proposed. For breaking the sub-100 nm manufacturing barriers, high throughput lithography based on direct writing is a proposed solution.

Role of rapid photothermal processing in process integration

The smaller dimension devices and larger scales of integration are demanding constant reduction of the macroscopic and microscopic defects in the manufacturing of silicon integrated circuits. Increasing capital investment in manufacturing is forcing us toward processes and equipment that are effective not only in reduction of the cost of ownership but can also increase the effectiveness of equipment of current as well as future applications. Rapid thermal processing (RTP) based on incoherent light as the source of energy is playing an important role in the manufacturing of 300 nm and larger diameter wafers. The dominance of ultraviolet and vacuum ultraviolet photons in RTP results in rapid photothermal processing (RPP). The results presented in this paper show that the materials and devices processed by RPP are better than those processed by other thermal processes. This paper discusses the manufacturing science, operating principles of RPP and experimental results supporting its role in future process integration.

Dependence of activation energy of mass transport limited region on the photospectrum of photons participating in rapid photothermal assisted chemical vapor deposition

In this letter, we demonstrate the importance of high energy photons (λ<800nm) in reducing the activation energy and providing higher growth rates and low defect densities for the materials deposited by rapid photothermal processing assisted chemical vapor deposition (CVD). The dependence of growth rate, structural properties, and electrical properties of Y2O3/Si structure on the photospectrum reaching at the Y2O3/Si interface has been studied. The observation that high energy photons result in the reduction of activation energy of mass transport limited region has direct advantage of depositing various electronic materials by CVD at low processing temperatures.

Role of rapid photothermal processing in environmentally conscious semiconductor manufacturing

Compliance with the increasingly stringent environmental laws will force the phasing out of conventional methods for the manufacture of all semiconductor devices. Development of processes with the highest possible material and energy efficiencies is the heart of the present ecological preservation efforts. Besides other benefits, rapid isothermal processing (RIP) also uses less energy than furnace processing. Further increase of material and energy efficiencies is possible by using rapid photothermal processing. Central to this method is the use of quantum photoeffects in conventional RIP systems. This approach can be consolidated with advanced chemical vapor deposition methods that further lower the wastages leading to systems that can give significant improvements over those presently used. Key experimental results and possible future directions are presented.