D. Bielle-Daspet

Super Large Grain Polycrystalline Silicon Obtained from Pyrolysis of Si2H6 and Annealing

Polycrystalline silicon films on SiO2 are formed by Low Pressure Chemical Vapor Deposition from disilane at 450°C and subsequent annealing at 600°C. Homogeneity performances of the deposition are given, which compares with those of Si deposition from SiH4. The structure of the polysilicon material obtained after annealing is shown. The resulting grain size is much larger than the one that could be obtained by Si deposition from SiH4 and annealing. An optical evaluation of the film is given, confirming the potential of Si2H6 for the fabrication of high field effect mobility thin film transistors.

Characteristics of the thermal oxidation of heavily boron-doped polycrystalline silicon thin films

Abstract Dry oxidation kinetics were compared for 2 × 10 20 cm −3 boron-implanted and in-situ doped films deposited at temperatures ranging between 520 and 620 °C. The characteristics of the thermal oxidation of these films have been studied over the oxidation temperature range of 750 to 1 050 °C and for durations of 10 min to 26 h. High values of both the surface oxidation rate k s and the oxide diffusion coefficient D are evidenced as typical of the in-situ doped films. In addition to the well-known effect that heavy doping increases the rate of oxidation similar to what is observed in single-crystal silicon, it is also shown specially, for the in-situ boron-doped films compared with 2 × 10 20 cm −3 in-situ phosphorus-doped ones, that the greatest oxidation rate is observed at high oxidation temperatures ( T ox > 1 000 °C ). This enhancement is related to some specific factors of these materials, such as grain boundary structures, defects, texture and electrical properties related to the segregation and supersaturation phenomenon which occur at these levels of doping.

Structural and technological properties of heavily in situ phosphorus-doped low pressure chemically vapour deposited silicon films

Abstract Films of 100–200 nm thickness doped with 10 21 P cm −3 were isothermally deposited at temperatures ranging from 520 to 620°C from an SiH 4 -PH 3 -H 2 gas mixture. The structure (as deduced from transmission electron microscopy observations of sample plane views and cross-sections) and electronic properties (ultraviolet reflectance, resistivity, wet etching and oxidation rate) of the films showed specific features which are associated with nucleation and crystal growth mechanisms occurring at the gas-film interface during the deposition of the films.

Material and electronic properties of boron-doped silicon films deposited from SiH4BCl3N2 mixtures in an industrial low pressure chemical vapour deposition furnace

Abstract Heavily boron-doped polycrystalline silicon (p-Si) films were deposited in the 520–605°C temperature range using an industrial low pressure chemical vapour deposition (LPCVD) reactor equipped with gas injectors. The simulation of the film deposition rates and the theoretical calculations of the distribution of gaseous species along the reactor load showed that, in all the cases studied, the wafer position in the process load had only a small effect on the local deposition parameters for the films. From characterization by transmission electron microscopy of plane view and cross-section, reflection high energy electron diffraction patterns and Raman spectroscopy, the polycrystalline character of the boron-doped silicon films appears to result from heterogeneous crystal nucleation and growth occurring at the gas-film interface during deposition at temperatures Td≤520°C. The increase in the number of crystalline Si(c-Si) nuclei is responsible for the smaller grain size of the silicon films deposited at Td≥560°C. Correlations between deposition parameters and surface roughness, polarization properties at 405 nm and electrical resistivity of the films were established. Comparisons with the microstructure and properties of undoped and in situ phosphorus-doped LPCVD silicon films were also carried out.

Microstructure of boron-doped silicon layers prepared by low pressure chemical vapour deposition

Abstract The microstructures of silicon layers 0.55–0.60 μm thick with boron contents of about 1017 or 1020 atoms cm-3, prepared by low pressure chemical vapour deposition at 570 or 620°C on thermally oxidized silicon wafers, were characterized in the as-grown condition and after chemical thinning. The microstructural characteristics obtained from transmission electron microscopy examination on cross-sections, reflection high energy electron diffraction patterns, Raman spectrometry at 488 nm and UV absolute reflectance measurements as well as the optical and mechanical roughness of the sample surfaces were compared. The results showed the following. 1. (i) The layers are polycrystalline throughout their depth, with an external region of columnar character, intense twinning and 〈110〉 texture, and with a near-interface zone 50–100 nm thick of randomly oriented grains of size not greater than 10nm. 2. (ii) The thickness of the interfacial zone decreased as the deposition temperature increased. In the external region the texture became more developed as the level of boron doping and the deposition temperature increased, whereas the twinning, dislocation density, vacancy and/or impurity concentrations (from Raman results) and excess volume fraction (from absolute reflectance results) appear to be enhanced by increases in doping and decreased by increases in temperature. 3. (iii) The surface roughness was also clearly higher for layers with lower boron contents.

Crystallization of amorphous thin LPCVD Si films : in situ TEM measurement of nucleation and grain growth rates

Abstract The influence of deposition conditions on the solid phase crystallisation of as-deposited amorphous Si layers obtained by low pressure chemical vapor deposition has been investigated by “in situ” isothermal annealing in a transmission electron microscope. Both nucleation and grain growth rates have been determined. Growth process was found to be linear with an activation energy of 2.4 eV. Nucleation kinetics have been calculated from both the size of the crystallites and the grain growth rates. Final grain size has been shown to depend on deposition procedure.

Recombination Activity in Directly Bonded High Resistivity Silicon Wafers Measured by the Photoconductance Decay Method

Characterisation of bonded high-resistivity silicon wafers by the microwave photoconductance decay (?PCD) technique has been performed. Bonding is shown to drastically alter the bulk recombination activity of the wafers. The technique allows to separate between bulk and interface recombination and appears as a powerful tool to evaluate the quality of the bonded interface.

Conductivity of boron-implanted polycrystalline thin silicon films

Sub-micron thin films of polycrystalline silicon obtained by low-pressure chemical vapor deposition, boron-implanted (amount varying from 1012 to 1016 cm−2), and annealed at 760 °C for 26 h under an oxygen ambient (dry O2) have been characterized in terms of structural and electrical properties. The results obtained are correlated first with the Hall-effect measurements, which gives the resistivity p, the concentration of the free carriers p and the mobility μ, and in the second part with the observations of transmission electron microscopy (TEM), which gives the size of grains. The variations of p, p and μ have been studied as a function of the dopant concentration. A low rate of activation has been measured (40%) and a very low value of the mobility μ has been noted (3 cm2 V−1 s−1) as well as small grain size. These results have been discussed both qualitatively and quantitatively, based on the existence of phenomena of carrier trapping and dopant segregation at the grain boundaries.

Feasibility and electrical properties of 600°C thermal silica layers for thin film transistor applications

Abstract The electrical properties of 600 °C thermal oxide layers on crystalline silicon are reported together with the influence of this oxidation step on the morphology of non-crystalline low pressure chemical vapour deposition silicon films. It is concluded that such an oxide 5–10 nm thick is convenient for a pad oxide in thin film application.

Second-oxidation properties of thin polysilicon films grown by LPCVD and heavily in situ boron-doped

Abstract In this work, we present a comparative study between first- and second-thermal-oxidations properties of low pressure chemical vapor deposition (LPCVD) thin polysilicon films. These films are heavily in situ boron-doped with a concentration level of around 2×10 20 cm −3 . The first- and second dry oxidations experiments are systematically conducted under the same conditions. Their properties are analysed using electrical and structural characterization means. The thermal-oxidation processes are performed on submicron layers of 200 nm deposited at temperatures T d ranged between 520 and 605°C and thermally-oxidized in dry oxygen ambient at temperatures T ox =945 , 1000, and 1050°C. As presented in a previous study, the first-oxidation of these layers is known to have an enhanced oxidation rate compared to similar undoped, boron-implanted layers, and single crystal silicon. In the used range of the deposition temperature T d , we have found that the second-oxidations present a completely different behaviour compared to what is observed in the first ones. The second-oxidation rate becomes too weak and seems to be dependent of the first-oxidation time t ox1 . Furthermore, if the first dry oxide is etched off and a second dry oxide is grown, it is found that the second oxide contains less dopant than the first one. Obviously, the loss of the oxidation rate is comprehensively discussed if we assume that the film structure is subjected to a deep modification at the first stage of the oxidation process. These results will be also correlated with other specific phenomena that we have evidenced in a previous work.