Solid Phase Crystallization Of Amorphous Silicon Research Articles

Impact of solid-phase crystallization of amorphous silicon on the chemical structure of the buried Si/ZnO thin film solar cell interface

The chemical interface structure between phosphorus-doped hydrogenated amorphous silicon and aluminum-doped zinc oxide thin films is investigated with soft x-ray emission spectroscopy (XES) before and after solid-phase crystallization (SPC) at 600C. In addition to the expected SPC-induced phase transition from amorphous to polycrystalline silicon, our XES data indicates a pronounced chemical interaction at the buried Si/ZnO interface. In particular, we find an SPC-enhanced formation of Si-O bonds and the accumulation of Zn in close proximity to the interface. For an assumed closed and homogeneous SiO2 interlayer, an effective thickness of (5+2)nm after SPC could be estimated.

Advanced Solid-Phase Crystallization of Amorphous Silicon on a Glass Substrate

Advanced Solid-Phase Crystallization of Amorphous Silicon on a Glass Substrate Thanh Nga Nguyen and Sungwook Jung School of Information and Communication Engineering, Sungkyunkwan University, Suwon 440-746 Junsin Yi School of Information and Communication Engineering and Department of Energy Science, Sungkyunkwan Unversity, Suwon 440-746 (Received 22 September 2008) We report the crystallization of an amorphous silicon (a-Si) lm by using advanced solid-phase crystallization (a-SPC). Solid-phase crystallization (SPC) is the most common method to obtain polycrystalline silicon (poly-Si). However, SPC requires a long annealing time to change from the a-Si phase to the poly-Si phase. The a-SPC method, which employs a high annealing temperature (above 700 C) but a short annealing time, is investigated to overcome this disadvantage. After dehydrogenating at 450 C for 2 hours, the a-Si lms on Corning EAGLE glass substrates are annealed by rapid thermal processing (RTP). The UV-Vis spectrum reveals that the poly-Si appears for heat-treatment at 750 C for 3 seconds. When the annealing time is increased until the critical point, at which the glass substrate bends, the crystalline fraction, as well as the quality of the poly-Si layer, improves. Raman spectroscopy con rms these results. The highest crystalline fraction is 96 % for an annealing time of 5 minutes. PACS numbers: 78.66.Jg

Inkjet Printing of Nickel Nanosized Particles for Metal-Induced Crystallization of Amorphous Silicon

We demonstrated for the first time single-crystal grain growth in the solid-phase crystallization of amorphous silicon (a-Si) film induced by inkjet-printed colloidal solution containing Ni nanosized particles. The electrostatic inkjet nozzle with a needle can print dots of Ni colloidal solution, whose size ranges from submicron order to a few ten micrometers, on the a-Si film surface by controlling the needle apex radius and the number of applied voltage pulses. The dependence of the crystallization behavior of a-Si on dot size is investigated by electron backscattering pattern (EBSP) analysis. Crystallization behavior is categorized into three modes: single-crystal growth, polycrystal growth, and lateral-crystal growth. Statistical analysis suggests that, when the dot size is 0.86 µm in diameter, a single-crystal grain is grown at the inkjet-printed sites with a probability of 0.62.

Comparative Study of Solid-Phase Crystallization of Amorphous Silicon Deposited by Hot-wire CVD, Plasma-Enhanced CVD, and Electron-Beam Evaporation

AbstractSolid-phase crystallization (SPC) rates are compared in amorphous silicon films prepared by three different methods: hot-wire chemical vapor deposition (HWCVD), plasma-enhanced chemical vapor deposition (PECVD), and electron-beam physical vapor deposition (e-beam). Random SPC proceeds approximately 5 and 13 times slower in PECVD and e-beam films, respectively, as compared to HWCVD films. Doping accelerates random SPC in e-beam films but has little effect on the SPC rate of HWCVD films. In contrast, the crystalline growth front in solid-phase epitaxy experiments propagates at similar speed in HWCVD, PECVD, and e-beam amorphous Si films. This strongly suggests that the observed large differences in random SPC rates originate from different nucleation rates in these materials while the grain growth rates are relatively similar. The larger grain sizes observed for films that exhibit slower random SPC support this suggestion.

Effects of elastic stress introduced by a silicon nitride cap on solid-phase crystallization of amorphous silicon

Effects of stress on solid-phase crystallization of amorphous silicon (a-Si) were studied by laser Raman spectroscopy. Compressive stress was introduced in a-Si with a Si3N4 cap. The speed of crystallization decreased with the increase of the stress while it increased again with an additional cap of SiO2 on a Si3N4 cap. A SiO2 cap introduced tensile stress in an a-Si film and relaxed compressive stress by a Si3N4 cap. The reason why crystallization of a-Si is suppressed is that the stress is elastic and that it does not relax with crystallization.

The Substrate Effects on Kinetics and Mechanism of Solid-Phase Crystallization of Amorphous Silicon Thin Films

The substrate effects on solid-phase crystallization of amorphous silicon (a-Si) films deposited by low-pressure chemical vapor deposition (LPCVD) using Si 2 H 6 gas have been extensively investigated. The a-Si films were prepared on various substrates, such as thermally oxidized Si wafer (SiO 2 /Si), quartz and LPCVD-oxide, and annealed at 600 °C in an N2 ambient for crystallization. The crystallization behavior was found to be strongly dependent on the substrate even though all the silicon films were deposited in amorphous phase. It was first observed that crystallization in a-Si films deposited on the SiO 2 /Si starts from the interface between the a-Si and the substrate, so called interface-induced crystallization, while random nucleation process dominates on the other substrates. The different kinetics and mechanism of solid-phase crystallization is attributed to the structural disorderness of a-Si films, which is strongly affected by the surface roughness of the substrates.

Activation of luminescence in polycrystalline silicon thin films by ultrasound treatment

A dramatic increase of infrared photoluminescence (PL) intensity by a factor of 2 orders of magnitude is observed after a few minutes at 250 °C of ultrasound treatment (UST) applied to polycrystalline silicon thin films on glass substrates. In films obtained by solid-phase crystallization of amorphous silicon at 550 °C, UST enhances the PL band intensity at 0.7 eV, and also activates a new luminescence maximum at about 0.9 eV. We prove that the 0.9 eV PL band is related to the amorphous fraction of poly-Si films. Due to similarities in spectral shape and temperature behavior, this UST activated luminescence is attributed to a ‘‘defect’’ PL band previously observed in hydrogenated amorphous Si. This conclusion is confirmed by using a set of films with controlled fractions of the amorphous to crystalline phase. A mechanism of ultrasound stimulated hydrogen detrapping followed by hydrogen diffusion and passivation of nonradiative centers (e.g., dangling bonds) in polycrystalline and amorphous Si films is discussed.

Polycrystalline Silicon Films Formed by Solid-Phase Crystallization of Amorphous Silicon: the Substrate Effects on Crystallization Kinetics and Mechanism

AbstractThe substrate effects on the solid-phase crystallization of amorphous silicon (a-Si) have been extensively investigated. The a-Si films were prepared on two kinds of substrates, a thermally oxidized Si wafer (SiO2/Si) and a quartz, by low-pressure chemical vapor deposition (LPCVD) using Si2H6 gas at 470 °C and annealed at 600 °C in an N2 ambient for crystallization. The analysis using XRD and Raman scattering shows that crystalline nuclei are faster formed on the SiO2/Si than on the quartz, and the time needed for the complete crystallization of a-Si films on the SiO2/Si is greatly reduced to 8 h from ˜15 h on the quartz. In this study, it was first observed that crystallization in the a-Si deposited on the SiO2/Si starts from the interface between the a-Si film and the thermal oxide of the substrate, called interface-induced crystallization, while random nucleation process dominates on the quartz. The very smooth surface of the SiO2/Si substrate is responsible for the observed interface-induced crystallization of a-Si films.

Stress Induced During the Solid-phase Crystallization of Amorphous Silicon Deposited by LPCVD

AbstractThe Solid Phase Crystallization (SPC) of amorphous silicon films deposited by Low Pressure Chemical Vapor phase Deposition (LPCVD) using pure silane at 550'C was studied by in-situ monitoring the film conductance. The saturation of the conductance at the end of the crystallization process is found transient. The conductance decreases slowly after the onset of the saturation. This degradation is also observed from other analyses such as ellipsometry spectra, optical transmission and Arrhenius plots of the conductivity between 250 and 570K. Hall effect measurements show that the degradation is due to a decrease of the free carrier concentration n and not to a decrease of the mobility. This indicates a constant barrier height at the grain boundaries. The decrease of n is then due to a defect creation in the grain. Hence, whatever the substrate used, an optimum crystallization time exists. It depends on the amorphous quality film which is determined by the deposition techniques and conditions and on the crystallization parameters.

Axially Controlled Solid-Phase Crystallization of Amorphous Silicon

The crystallization behavior of a-Si films has been investigated as a function of the annealing temperature Ta (530-1100°C) and time (0-72 h) by means of X-ray diffraction, transmission electron microscopy (TEM) and Raman scattering. The a-Si films were deposited by low-pressure chemical vapor deposition (LPCVD) onto poly-Si films with a strong <110> texture prepared by plasma-enhanced CVD (PECVD) [poly-Si(P)], and onto fused quartz substrates [poly-Si(Q)]. Poly-Si(P) films were crystallized maintaining the same strong <110> texture as the PECVD poly-Si substrate, over the entire Ta range. However, poly-Si(Q) films exhibited a weak <111> texture. The final grain size estimated by TEM for poly-Si(P) films was independent of Ta, but became 7-8 times larger than that for the poly-Si substrate. The crystallization mechanism of poly-Si(P) films was discussed in comparison with that of poly-Si(Q) films.