Growth Of μc-Si Research Articles

Growth of microcrystalline silicon by remote plasma chemical vapor deposition without hydrogen dilution

We have grown microcrystalline silicon by a remote plasma chemical vapor deposition technique using silane and helium only, without hydrogen dilution. The optimum growth temperature and rf power are 330 °C and 100 W, respectively. These results indicate that an atomic hydrogen environment on the growing surface is not always necessary to grow microcrystalline (μc-)Si at low temperatures. It is found that the exposure of He plasma on the growing surface of μc-Si etches the Si layer, explaining the growth of μc-Si by using only silane and He and no hydrogen.

Microcrystalline Silicon Thin film Growth and Simultaneous Etching of Amorphous Material

ABSTRACTAn investigation of silicon plasma deposition and etching using both a VHF plasma in dilute SiH4/H2 and the pulsed silane flow method is presented. It is possible to find preparation conditions at which simultaneous growth of µc-Si:H and etching of amorphous silicon (a-Si:H) on the same substrate is observed. The results clearly demonstrate that microcrystalline silicon growth proceeds via the preferential etching of amorphous tissue during film growth, and that observations of crystallization during hydrogen plasma treatment without etching are due to chemical transport of silicon within the reactor.

Surface controlled plasma deposition and etching of silicon near the chemical equilibrium

In this study we present investigations of silicon growth and etching in a dilute SiH4/H2 plasma near the partial chemical equilibrium in order to study nucleation processes at the growth surface in plasma CVD. μc-Si:H and a-Si:H deposited on Corning 7059 glass substrates was simultaneously exposed to an extremely diluted SiH4 in H2 VHF plasma at a frequency of 100 MHz. Under conditions used in our study simultaneous growth of μc-Si:H and etching of a-Si:H is observed. The results support the μc-Si:H growth model in which the net growth rate is the difference of a deposition and an etch rate.

Optical properties of μc-Si:H/α-Si:H layered structures: Influence of the hydrogen bonds, crystallite size, and thickness

Thin films of layered μc-Si:H/α-Si:H structures grown with rf magnetron sputtering have been studied with spectroscopic ellipsometry (SE) and Raman spectroscopy (RS). Analysis of the dielectric function spectra with the Si-centered tetrahedron model and deconvolution of the Raman spectra suggest that the silicon-hydrogen bonds are correlated with the microscopic voids in α-Si:H while the good quality α-Si:H films exhibit SiH3 bonds and small amount of SiH2 bonds. The quality of the surface and interface of the μc-Si:H/α-Si:H was analyzed by SE and transmission electron microscopy and the dependence of an interfacial amorphous layer at the initial stages of the μc-Si:H growth on the argon and hydrogen pressure was found. Furthermore, a correlation between the SE and RS results on μc-Si:H layers is shown and commented, while a dependence of the energy shift and the broadening of the interband transitions and the Raman transverse optical peak on the mean crystallite size has been found and discussed in view of the finite size and stress effects on the electronic structure of these materials. This analysis suggests that strain is one of the most important factors during the growth of μc-Si:H.

In situ studies of semiconductor processes by spectroellipsometry

Recent in situ applications of spectroscopic phase modulated ellipsometry (SPME), from 0.25 to 11 μm, to studies of thin-film semiconductor processes are reviewed. In the ultraviolet (UV) range, the ability of kinetic ellipsometry to perform fast real-time investigations is illustrated. Thus a 10 ms resolution is needed to perform a detailed analysis of the silicide formation during exposure of a Pd film to silane at 250°C. In the case of plasma enhanced chemical vapour deposition (PECVD), new insights into the complex growth mechanism of microcrystalline silicon (μc-Si) are presented. In particular, the importance of hydrogen etching during μc-Si growth is evidenced. The high sensitivity of infrared phase modulated ellipsometry (IRPME) is illustrated by the study of amorphous silicon (a-Si : H) air oxidation. Si-O-Si and (O n )Si-H stretching vibrations are identified at the film surface at the submonolayer level. The weak reactivity of a-Si : H with atmosphere is correlated with the presence of a hydrogen-rich thin layer at the top surface.

Ellipsometry Studies of (μc-Si:H/ZnO) and (μc-Si:H/a-Si:H) Interfaces in Magnetron Sputtering System

We have studied the microstructure of μc-Si:H/ZnO and μc-Si:H/a-Si:H interfaces in reactive magnetron sputtering (RMS) using in situ spectroscopic ellipsometry (SE). For (μc- Si:H deposited on ZnO, the real time ellipsometry trajectory shows that there is 20 volume % void apparent inside the first 100Å film. Then the film becomes densified, the initial void layer propagates as a surface layer, and its thickness decreases to 53Å when the bulk film reaches 200Å. Both unhydrogenated and hydrogenated silicon films deposited on ZnO show similar nucleation and coalescence behavior. This indicates that the atomic hydrogen rich plasma under μc-Si growth conditions doesn't reduce the ZnO substrate. For the μc-Si:H/a-Si:H study, we also observe the delayed crystallite nucleation after a ∼ 100Å high H content interface layer forms. Part of this layer results from H implanted into the a-Si:H substrate (∼ 45Å deep). The thickness of this interface layer decreases as the crystallite nucleation begins. This is the first direct experimental evidence showing sub-surface μc-Si:H formation.

Growth and Structure of Microcrystalline Silicon by Reactive DC Magnetron Sputtering

ABSTRACTWe have deposited microcrystalline silicon (μc-Si) at low temperature by reactive dc magnetron sputtering. The structure and crystallinity of the films are analyzed by in situ spectroscopie ellipsometry. μc-Si growth occurs at deposition conditions with substrate temperature between 150 – 300 °C and hydrogen partial pressure above 4 mtorr. We have also observed that the deposition rate strongly affects the interface structure. At a rate of 21 À/min, a 230 Å thick amorphous layer appears at the interface of film and glass substrate. The interface layer thickness decreases with deposition rate, and becomes undiscernible for growth rates ∼ 2 Å/min. The thickness of the interface layer is also found to depend on substrates.

Microcrystalline Silicon by Dc Magnetron Sputtering: Growth Mechanisms

ABSTRACTWe have used real-time, in situ spectroscopie ellipsometry (SE) and infrared reflectance (IR) to study microcrystalline silicon (μc-Si) formation in reactive magnetron sputtering (RMS). μc-Si growth occurs at high hydrogen partial pressures and moderate substrate temperatures. We use IR studies and SE studies of film growth on rough surfaces, respectively, to show that these conditions lead to high hydrogen coverage of the film surface and high effective surface diffusivity. The interface region is amorphous and its thickness decreases with deposition rate. For a fixed growth flux, we observe a 30% decrease in the deposition rate of μc-Si relative to the amorphous interface region. This could be due to increased etching or decreased sticking coefficients during microcrystalline growth.

Plasma Surface Interaction During the Growth of Semiconductor Thin Films Studied byin Situ Infrared Ellipsometry

ABSTRACTThe early stages of the growth of plasma deposited amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si) on glass substrates are investigated by in situ infrared phase modulated ellipsometry (IRPME) in the silicon-hydrogen stretching mode region. μc-Si are prepared by alternating SiH4 and H2 plasmas. New insights on the plasma-surface interactions during the growth of these films are given. During the deposition of the first 20 Å of a-Si:H, the hydrogen is incorporated as SiH2. During the further growth of a-Si:H the SiH2 bonds are located at the film surface inside a very thin hydrogen rich overlayer. During the deposition of the first 10–20 Å of μc-Si, the SiH2 bonds are predominantly removed by the H2 plasma, the material being amorphous. After this selective removal of the SiH2 groups, a transition from amorphous to microcrystalline growm is observed. A systematic hydrogen etching during the further growth of μc-Si is observed.

In situ investigation of the growth of microcrystalline silicon obtained by alternating deposition and hydrogen-etching sequences

The growth of μc-Si prepared by alternating layer deposition (in growth conditions of a-Si:H) and hydrogen plasma exposure is studied by in situ spectroellipsometry. The deposition and etching sequences are clearly identified in the real time trajectories. More generally the influence of the etching by the hydrogen plasma is emphasized, in contrast with previous results.

I n s i t u ellipsometry of thin-film deposition: Implications for amorphous and microcrystalline Si growth

Real-time ellipsometric characterization of the nucleation of hydrogenated amorphous silicon (a-Si:H) prepared by plasma-enhanced chemical vapor deposition (PECVD) on smooth, dense metal, and crystalline Si substrates is reviewed. The experimental results for photoelectronic quality a-Si:H from pure SiH4 on Mo and Cr are consistent with the Volmer–Weber nucleation mode, with a separation of 40–50 Å between nucleation centers. For c-Si substrates, a new interpretation suggests that nucleation occurs on the same scale, but the geometry in the first monolayer is disklike. A well-defined lobe and cusp in the data can be ascribed to surface smoothening by diffusion that results upon coalescence of these structures. For films from a pure SiH4 plasma, the rates of coalescence and relaxation of substrate-induced surface roughness on thick films are consistent with a diffusion length of ∼80 Å for the adsorbed precursors. For films prepared from a SiH4-depleted plasma, the average surface diffusion length is reduced by at least a factor of 2. New results for the growth of μc-Si:H on a-Si:H films reveal an induction period of several minutes for the nucleation of microcrystallites. During this period a structurally defective 40–80 Å amorphous layer is deposited. Such a layer is expected to influence the properties of photoelectronic devices and compositionally modulated materials that use thin μc-Si:H.