Structural properties of polycrystalline silicon films prepared at low temperature by plasma chemical vapor deposition

Abstract

Evolution with thickness of the structure of the polycrystalline silicon (poly-Si) films prepared at 300 °C has been studied by plasma decomposition of SiF4/SiH4/H2 source gases. The poly-Si films with varied thickness are characterized mainly by Raman spectroscopy, x-ray diffraction (XRD), and supplementarily by reflection high-energy electron diffraction, transmission electron microscopy, Fourier-transform infrared (FT-IR) spectroscopy, electron-spin resonance (ESR), and secondary-ion-mass spectroscopy (SIMS) measurements. The crystalline fraction of the film was calculated to be 87% by deconvoluting the Raman spectra. The grains indicated a strong 〈110〉 preferred orientation by XRD. The thickness (d) dependence of the diffracted (220) intensity is divided into three regions: an incubation region (d<200 nm, region 1), a linear region (200 nm ≤d<300–500 nm, region 2) where the deposition parameter (SiF4 flow rate, substrate temperature, and rf power) dependence is weak, and a linear region with steeper (or more moderate) slopes (300–500 nm≤d, region 3) where the deposition parameter dependence is large. The measurements of the angular distribution of the 〈110〉 grains reveal that they contain slanting ones by more than 4° in region 2, while they disappear in region 3. The FT-IR and SIMS measurements for typical samples (Ts = 300 °C, 300 Pa) indicate that the grain boundaries are passivated by hydrogen in the bonding configurations of Si—Hn (n=1–3) and its concentration is approximately 3 at. %. The residual fluorine in the film is found to be much fewer (6×1019 cm−3) than hydrogen. It is found that the density of unpassivated dangling bonds indicates a low value of 1.1×1017 cm−3 for the film with d=280 nm by ESR measurements. The origin of the preferred orientation is also discussed on the basis of a model in which nucleation, ledge formation, and etching processes are considered.

Thickness dependence of properties of excimer laser crystallized nano-polycrystalline silicon

“…23 Different energy densities result in different grain sizes, which further complicates the analysis, since the absorption coefficient changes too. 24 ␥ has been calculated to be between 0.8 and 0.9, the most widely used value being 0.8 for mixed phase silicon, especially for excimer laser crystallized silicon. 23,25,26 For this analysis too, ␥ was taken to be 0.8.…”

UV irradiation and H2 passivation processes to classify and distinguish the origin of luminescence from thin film of nc-Si deposited by PECVD technique

“…They have found that the (1 1 0) orientation occurs at high H 2 pressure and Si 3 H 8 flow rate at T d below 560°C, but turn to (1 0 0) above T d of 575°C [24]. Kakinuma et al [25] have investigated the structural properties of poly-Si thin films with different thickness deposited at T d of 300°C by PECVD method using SiH 4 -SiF 4 -H 2 gas mixture. They have found that the grains are strongly (1 1 0) oriented in good agreement with the present work.…”

Determination factor of <110> direction growth in microcrystalline silicon thin film deposition

“…Regarding the mechanism of the crystalline growth in the b110> direction, we have proposed that dimeric radicals play a key role for the bridge formation between the dangling bond rows with the space of two Si atoms on the (110) facet in order to enhance the lateral growth along these dangling bond rows (ledge formation [17]) by monomeric radicals [9,10]. We also proposed that the crystalline growth in the b110> direction is enhanced by the increased bridge formation on the (110) facet resulting from the increase of dimeric radicals in a gas phase.…”