Structure Of Polycrystalline Silicon Films Research Articles

Structure of thin polycrystalline silicon films on ceramic substrates

The structure of polycrystalline silicon films with thickness of 10 μm, which were deposited by thermal chemical vapor deposition on ceramic substrates, was investigated. In this article we report results of silicon films deposited on SiAlON, mullite, and alumina substrates. The type of substrate strongly influences the stress and the texture of the films. In the silicon films deposited on SiAlON substrate tensile stress is observed, while in the films deposited on mullite and alumina substrates compressive stress is present. In all deposited films the observed stress is higher than the thermal stress, which has been determined from the differences in the thermal expansion coefficients of the film and substrate materials. We observe in the films grown on SiAlON substrate that the total stress decreases with increasing deposition temperature, which implies a reduction of the intrinsic stress in the films. We ascribe the reduction of the intrinsic stress to a lower defect formation at higher deposition temperature. The silicon films exhibit a preferential texture, which becomes more random at higher deposition temperatures. We also observe that at higher deposition temperatures the grain size is larger and the crystal growth is columnar. We propose that the observed structural coherence between the alumina substrate and the silicon film results in an epitaxial growth that is responsible for a good adhesion of the film to the substrate.

Raman line profile in polycrystalline silicon

Raman spectroscopy is applied to the study of the structure of polycrystalline silicon films. The analysis of the transversal optical phonon Raman line shows its complex structure consisting of two dominant contributions, centered at about 519 and 517 cm−1 and attributed to two dominant groups of grains with different size. The profile of this Raman line is demonstrated to give deeper information about the film morphology, directly influenced by the deposition temperature in terms of the ratio of amorphous to crystalline phases, as well as the grain-size distribution, and the film stress.

Temperature Effects on the Structure of Polycrystalline Silicon Films by Glow-Discharge Decomposition Using SiH4/SiF4

Polycrystalline silicon (poly-Si) films were prepared on glass substrates by the plasma- enhanced chemical vapor deposition method using SiH4/SiF4 mixtures as a function of deposition temperature, Td, from 150 to 400°C, and the structural properties were investigated. In addition, the effects of addition of H2 to the SiH4/SiF4 gas were also examined. The crystallinity and grain size of Si films with added were found to have maximum values at around Td = 250–300°C. However, poly-Si films without H2 addition contain numerous microvoids, and exhibit easy O contamination, and their crystallinity monotonically increased with Td. The change in the SiH and SiH2 bond density with H2 addition was consistently interpreted in terms of this model. As a result, H2 addition at low Td was suggested to suppress O contamination and improve the crystalline quality. By contrast, H2 addition at high Td is likely to deteriorate crystalline quality. The results were discussed in terms of fluorine and hydrogen chemistry.

Structure of polycrystalline silicon films deposited at low temperature by plasma CVD on substrates exposed to different plasma

Polycrystalline silicon (poly-Si) films were deposited on glass substrates (corning 7059) at 300°C by a plasma enhanced chemical vapor deposition (PECVD) from a SiH 4/SiF 4 mixture. All poly-Si films were prepared under the same deposition conditions on the substrates subjected to nitrogen, hydrogen and/or CF 4 plasma with different gas pressures, just before deposition of the poly-Si films. Effects of such pretreatments for substrates on the structural properties of the resultant poly-Si films have been investigated. The Si film deposited on the substrates without any pretreatments was amorphous. However, formation of a strong 〈110〉 preferentially oriented poly-Si with improved crystallinity was obtained for the films deposited on the glass substrate after plasma pretreatments, which exhibit smoother surfaces. This result was interpreted in terms of a removal of weak Si–Si bonds during nucleation and the subsequent grain growth.

Effect of total deposition pressure on the structure of polycrystalline-silicon films

The effect of total deposition pressure on the structure of chemically vapor deposited polycrystalline-silicon films was examined over the pressure range from 10–600 Torr using thermal decomposition of SiH4 in a hydrogen carrier gas in the 625–675 °C temperature range in a cold-wall, lamp-heated reactor. The temperature and deposition rate were kept constant for each set of experiments to isolate the effect of hydrogen on the surface diffusion of the silicon species. Both the amorphous-to-polycrystalline transition and the dominant crystal orientation depend on the total deposition pressure; however, the dependence is only moderate. Differences in gas purity and system integrity between different reactors also play a strong role in controlling the structure.

Study of Polycrystalline and Amorphous LPCVD Silicon Films by Atomic Force Microscopy

The surface topography and structure of low-pressure chemical vapour-deposited silicon films grown on the thermal oxide of (100) silicon substrates have been investigated using atomic force microscopy. The measurements have been performed on undoped as-grown samples with deposition temperatures between 550 and 630°C and after ex situ phosphorus doping for samples deposited at 620°C. The transition from amorphous to polycrystalline deposition of the silicon film takes place in the temperature range 570-600°C. At 570°C a small number of crystallites are embedded in an amorphous matrix. With increasing temperature the number of crystallites grows rapidly and at 600°C the deposited film is polycrystalline. Doping from a POCl 3 source and subsequent annealing of films deposited at 620°C causes complete recrystallization. For the first time it has been possible to investigate the topography and the grain structure of polycrystalline silicon films using a scanning probe technique only. Our clear distinction between these two features allows controversial results from different characterization methods to be clarified.

高周波スパッタ蒸着法による多結晶Siの低温成膜に関する研究 (第2報)

Structure of polycrystalline silicon films was investigated by X-ray diffraction, reflection electron diffraction and transmission electron microscopy. Furthermore, electric-al and optical properties of the films were studied with the measurements of IR absorption, optical absorption, electron spin resonance and electrical conductivity. The films were prepared by rf planar magnetron sputtering, in which process atomic hydrogen radicals were utilized in order to make the polycrystalline silicon films on the substrate at low temperature. It was shown from X-ray diffraction, reflection electron diffraction and transmission electron microscopy that most of crystal silicon grains grew with a [100] texture, and that the grain sizes were 10 - 20nm. The results obtained from IR absorption and optical absorption measurements were as follows; hydrogen content decreased with the increase of hydrogen partial pressure (PH2) in the range of 2 ≤ PH2 ≤ 7mTorr, which was caused by the formation of Si Si bonds, and in the range of 7 ≤ PH2 ≤ 12mTorr, however, hydrogen content increased gradually with PH2, which suggested that dangling bonds in the silicon films were more terminated in the higher hydrogen partial pressure. These facts were also explained by the electrical conductivity measurement, and it was found that the polycrystalline silicon film prepared under the highest hydrogen partial pressure had the lowest hopping site density in the films observed in this work.

Microcrystalline structure of poly-Si films prepared by cathode-type r.f. glow discharge

X-ray diffraction (XRD) and spectroscopic ellipsometry measurements have been performed to study the crystalline structure of polycrystalline silicon films deposited by cathode-type r.f. glow discharge. Ratios of XRD peak intensities are used to describe the degree of crystallinity of samples. For ellipsometric data analysis, a multilayer structure model is used based on the effective medium approximation. It is found that the crystalline fractions of the deposited films increase with the increase of power density and substrate temperature. The film compositions of as-deposited samples are compared with those of annealed samples and films prepared by thermal pyrolysis of silane. The crystallinity estimated from the ellipsometric measurements compares well with that obtained from XRD measurements.

Structure of polycrystalline silicon films by ultraviolet pulse laser annealing

AbstractSilicon films deposited by low‐pressure chemical vapor deposition (CVD) technique was crystallized by ultraviolet (UV) pulse laser annealing and its crystallinity was evaluated by X‐ray diffraction and transmission electron microscopy.Although the average grain size of laser‐annealed Si films was smaller than that of Si films annealed at 600°C for 24 hr, in the former film, the density of defects was lower and the grain size was more uniform. In both laser annealed and thermally annealed films, most of the defects in the grains were twin defects whose twin faces were oriented in < 111 > direction and went across the entire grain. In the depth direction, two layers were observed: one had large grains and the other had small grains below. For Si films 330 nm in thickness and for laser intensity of 200 mJ/cm2, crystallization seemed to be initialized not only from the surface but also from the Si‐SiO2 interface.The texture of the films was either random (111) or textured (110), depending on the film deposition temperature and laser intensity. The laser absorption coefficient depended on the crystallinity of the film prior to laser illumination and the threshold energy for laser crystallization was larger for polysilicon films than for originally amorphous films.

The simultaneous growth of monocrystalline and polycrystalline silicon films with controlled parameters

The influence of the temperature of deposition of nucleation layers on the structure of polycrystalline silicon films which grow locally during the epitaxial growth of monocrystalline films was investigated. The structure of polycrystalline films grown in the high temperature chloride process has been found to depend on the deposition mode of the nucleation layer. For temperature changes in the range 800–860°C, the grain sizes in polycrystalline silicon increase by more than one order of magnitude. It was shown that heat treatment of films of small grain size in an atmosphere of oxygen leads to a decrease in their resistance owing to recrystallization of the grains, whereas during the annealing of films of large grain size the oxidation of intergrain boundaries is the dominant process resulting in an increase in the resistance. The possibility of using polycrystalline films fabricated under specific technological conditions for the isolation of integrated circuit elements was demonstrated.