D. Wolfe

Investigation of postoxidation thermal treatments of Si/SiO2 interface in relationship to the kinetics of amorphous Si suboxide decomposition

Interfacial Si suboxides (SiOx, x 500 °C initially there is a rapid segregation into amorphous Si (a-Si) surrounded by a SiO2 shell which acts as a diffusion barrier decelerating the reaction. Phenomenological modeling of kinetics with a one-dimensional Avrami–Erofe’ve treatment gives an upper limit for a-Si lateral growth rates of 1.2 A/s at 900 °C with an activation energy of 120 kJ/mol. PL, Raman, transmission electron microscopy and ellipsometry confirm this segregation model in the amorphous state. Due to the ra...

Study of SiOx decomposition kinetics and formation of si nanocrystals in an SiO2 matrix

The kinetics of the decomposition of silicon suboxides (SiO x , 0.7 < x< 1.3) was studied as function of post deposition annealing treatment. Amorphous Si:O:H alloys were deposited by remote plasma enhanced chemical vapor deposition and subjected to rapid thermal anneal. Extent of reaction was monitored by Fourier transform infrared analysis. For all compositions, it was found that there was a fast initial reaction associated with hydrogen loss, followed by a decelatory reaction that is described as 3-dimensional diffusion limited. However the reaction is strongly deceleratory at temperatures less than 900°C, thus SiO x stability is found through kinetic hindrance. Photoluminescence (PL) experiments showed that the decomposition reaction proceeds in the amorphous state with the observation of a-Si PL after high temperature anneals up to 800°C and H 2 plasma passivation.

THERMOCHEMICAL STABILITY OF SILICON-OXYGEN-CARBON ALLOY THIN FILMS : A MODEL SYSTEM FOR CHEMICAL AND STRUCTURAL RELAXATION AT SIC-SIO2 INTERFACES

Alloy thin films of hydrogenated silicon–oxygen–carbon (Si,C)Ox x<2, were deposited and analyzed in terms of changes in structure and bonding as a function of rapid thermal annealing between 600 and 1100 °C using a combination of Fourier transform infrared spectroscopy, Raman scattering and high-resolution transmission electron microscopy. Results showed that three structural/chemical transformations took place upon annealing. The initial reaction (600–800 °C) involved the loss of hydrogen bonded to both silicon and carbon. At intermediate temperatures (900–1000 °C) a Si–O–C type bond was observed to form, and subsequently disappear after annealing to 1050 °C. The formation of ordered amorphous-SiC regions, nanocrystalline-Si regions, and stoichiometric, thermally relaxed SiO2 accompanied the disappearance of the Si–O–C bond at the 1050 °C annealing temperature. Using this alloy as a model system, important information is obtained for optimized processing of SiC–SiO2 interfaces for device applications.

Plasma-assisted formation of low defect density SiC–SiO2 interfaces

The initial stages of SiC–SiO2 interface formation by low temperature (300 °C) remote plasma assisted oxidation (RPAO) on flat and vicinal 6H SiC(0001) wafers with Si faces have been studied by on-line Auger electron spectroscopy (AES). Changes in AES spectral features associated with Si–C and Si–O bonds are readily evident as oxidation progresses; however, there are no detectable AES features that can be attributed to C–O bonds. Initial oxidation rates as determined from AES data are greater for vicinal wafers than for flat wafers paralleling results for RPAO oxidation of Si. Devices fabricated on vicinal SiC wafers require an 1150 °C anneal in an H2 containing ambient to reduce defect densities from the 1013 to 1011 cm−2 range, consistent with termination of C atom step edge dangling bonds by H atoms. Devices prepared by thermal oxidation also require a 1150 °C anneal in H2 even though silicon oxycarbide regions with C–O bonds are formed in a transition region at the SiC–SiO2 interfaces.

Low-temperature (450 C) poly-Si thin film deposition on SiO{sub 2} and glass using a microcrystalline-Si seed layer

A low-temperature (450 C), remote plasma-assisted CVD process for deposition of poly-Si thin films on SiO{sub 2} and Corning 7059 glass in which interface formation is separated from bulk film growth has been developed. This approach is based on first depositing an ultra-thin (<100 {angstrom}) microcrystalline-Si seed layer onto the oxide in order to provide nucleation sites at which low-temperature poly-Si film growth can be initiated. Conditions for poly-Di film deposition were optimized by using a low-temperature, remote plasma process that had previously yielded epitaxial growth of Si thin films on crystalline Si substrates. Microstructural characterization was performed on poly-Si films grown with different seed layer thicknesses, and additionally with exposure of this seed layer to a predeposition hydrogen plasma treatment. Results demonstrated that the seed layer thickness and surface morphology played a significant role in promoting crystallinity in the poly-Si overlayer. For example using deposition conditions that yielded epitaxial film growth on Si substrates, films deposited on un-seeded oxide substrates were amorphous, whereas those deposited using a seed layer were polycrystalline. This indicated that interfacial nucleation was the rate limiting step in promoting the low-temperature deposition of poly-Si thin films.

Formation of nano-crystalline Si by thermal annealing of SiOx, SiCx and SiOyCx amorphous alloys: model systems for advanced device processing

Abstract Formation of Si with nanometer sized crystallites by thermal annealing of hydrogenated alloys of SiOx, SiCx, and SiOxCy (x,y∼0.1 to 0.2) amorphous alloys has been studied by infrared (IR) absorption spectroscopy, Raman scattering, and high resolution cross-section transmission electron microscopy (TEM) lattice imaging. The appearance of crystalline features in the Raman spectra, and TEM micrographs coincides with qualitative and quantitative changes in the IR spectra. Crystrallites appear in the SiOx alloys at an annealing temperature of ∼900°C, and at higher temperatures in the SiCx and (Si,C)Ox alloys, 950°C and 1050°C, respectively.

Low-temperature (<450 °C), plasma-assisted deposition of poly-Si thin films on SiO2 and glass through interface engineering

A low-temperature, two-stage process that employs interface engineering is investigated for deposition of poly-Si thin films on SiO2 and glass. In this two-stage process, film growth is separated into two regimes: (i) interface formation and (ii) bulk film growth. Interface formation (stage 1) was optimized for remote plasma enhanced chemical-vapor deposition (PECVD) of ultra thin (<100 A) μc-Si films on the oxide. This layer acts as a seed template, providing ordered growth sites for the next stage of film growth. Bulk Si film deposition (stage 2) was then initiated on the seed template using remote PECVD process conditions shown to produce low-temperature (<450 °C), epitaxial-Si films on crystalline silicon substrates, so as to drive a transition to larger grain growth off of the seed crystals. Results showed that the seed layer had a dramatic impact on bulk film crystallinity. Films deposited without a μc-Si seed layer were amorphous, whereas films deposited using a seed layer, in conjunction with the appropriate second stage conditions, were highly oriented (220) poly-Si.A low-temperature, two-stage process that employs interface engineering is investigated for deposition of poly-Si thin films on SiO2 and glass. In this two-stage process, film growth is separated into two regimes: (i) interface formation and (ii) bulk film growth. Interface formation (stage 1) was optimized for remote plasma enhanced chemical-vapor deposition (PECVD) of ultra thin (<100 A) μc-Si films on the oxide. This layer acts as a seed template, providing ordered growth sites for the next stage of film growth. Bulk Si film deposition (stage 2) was then initiated on the seed template using remote PECVD process conditions shown to produce low-temperature (<450 °C), epitaxial-Si films on crystalline silicon substrates, so as to drive a transition to larger grain growth off of the seed crystals. Results showed that the seed layer had a dramatic impact on bulk film crystallinity. Films deposited without a μc-Si seed layer were amorphous, whereas films deposited using a seed layer, in conjunction with the ...

A Study of Silicon Suboxide Thin Films by Photoluminescence

Note: IMT-NE Number: 290 Reference PV-LAB-CONF-1998-009 Record created on 2009-02-10, modified on 2017-05-10

Recrystallization of amorphous silicon deposited on ultra thin microcrystalline silicon layers

This study reports on a method to reduce the thermal crystallization time and temperature of amorphous silicon films by initially depositing an ultra thin {micro}c-Si:H seed layer. After rapid thermal annealing (RTA), films were characterized by means of Raman spectroscopy, x-ray diffraction, reflection high energy electron diffraction, atomic force microscopy, and dark and photocurrent. The results show that the microcrystalline particles in the seed layer act as nucleation centers, promoting crystallization of a-Si:H at lower temperatures and at shorter times, compared to a-Si:H films deposited without any seed layer. Additionally, it was found that the seed layer affects the orientation of the crystallized films. The dark current increases abruptly over 4 orders of magnitude in the first 15 second anneal, then decreases as the time increases, and tends to saturate. The photocurrent has an opposite behavior. These transport results can be understood in terms of a change in defect density and band gap shrinkage.