Atomic force microscopy and ellipsometry study of the nucleation and growth mechanism of polycrystalline silicon films on silicon dioxide

Abstract

The primary purpose of this research was to elucidate the mechanism of Si nucleation on SiO2 in a rapid thermal chemical vapor deposition (RTCVD) environment. To this end a combination of in situ real time ellipsometry and atomic force microscopy (AFM) to follow the RTCVD process in real time and measure key nucleation parameters was used. Real time ellipsometry data, in terms of Δ versus time, show significant changes as the deposition evolves from critical nuclei through coalescence to continuous film growth. From these data nuclei parameters such as the incubation time (tinc), coalescence point, nuclei density, and nuclei size are obtained from nucleation models. From the AFM images, nuclei parameters such as nuclei height, radius, and density were collected and compared across processing temperatures. It was found that kinetics rather than thermodynamics controls nuclei growth, and the mechanism depended upon the temperature regime (pressure not varied) due to the higher activation energy (212 kJ/mol) for vertical growth relative to lateral growth (167 kJ/mol). A transition temperature (∼600 °C) was identified where the size, shape, and density of the nuclei abruptly change from small numerous nuclei at temperatures less than 660 °C to large, sparse, disklike nuclei for temperatures greater than 660 °C. The temperature regime also affected the shape of the nuclei during growth with low temperature nuclei becoming flatter with time as the adatoms attached to the nuclei circumference, whereas high temperature nuclei grew taller with time. It is demonstrated that the RTCVD temperature regime dictates both the initial nuclei size and the nuclei growth mechanism with high temperature processes (i.e., highest adatom mobility), yielding the lowest nuclei density, largest nuclei, and roughest final Si film.

In Situ Selectivity and Thickness Monitoring During Selective Silicon Epitaxy Using Quadrupole Mass Spectrometry and Wavelets

“…Si nuclei are clearly visible in the remaining SEM micrographs. It is well known that nucleation on the insulator requires an incubation time for stable Si nuclei or islands (Volmer-Weber growth) to appear on the surface [27], [28]. Fig.…”

“…AFM is more sensitive than SEM and ellipsometry and can resolve atomic scale Si islands or nuclei on the oxide prior to continuous film formation [27]. Fig.…”

Growth Inhibitor To Homogenize Nucleation and Obtain Smooth HfB2 Thin Films by Chemical Vapor Deposition

“…In-situ spectroscopic ellipsometry (SE) experiments are performed with a fixed incident angle of 70° and a continuous spectrum of photon energies in the range 0.75–5.05 eV. SE is a sensitive and reproducible means to determine when initial islands have formed on the substrate. ,, However, because the initial morphology can be highly anisotropic, e.g., a sparse population of tall islands, it is not physically meaningful to fit the data to an effective medium theory. To estimate the order of magnitude of the optical response, we use a multilayer optical model, consisting of a thin HfB 2 film on the SiO 2 /Si substrate.…”

CVD‐Produced Polycrystalline Silicon Thin Film Prepared by Fluorine‐Mediated Crystal Growth on a Glass Substrate and its Thin Film Transistor Application

“…It can be clearly observed that nuclei have been formed by the RTCVD on the substrates in 30 s or less after the gas introduction, which is comparable to the case of poly-Si film deposition at 750 -C in a conventional rapid thermal CVD. [7] Flat nuclei spread over the substrate first. Then the nuclei assume a cone-like shape, which becomes predominant until the occurrence of coalescence of the nuclei (2-10 min).…”