Yasuo Kunii

Solid‐phase lateral epitaxy of chemical‐vapor‐deposited amorphous silicon by furnace annealing

A single‐crystalline silicon‐on‐insulator structure has been fabricated with solid‐phase lateral epitaxy. Chemical‐vapor‐deposited amorphous silicon (CVD a‐Si) deposited on a SiO2 stripe is crystallized by furnace annealing. A new CVD technique (clean CVD) has met the conditions required for solid‐phase epitaxy; clean interface and reduction of impurities and microcrystallites in the a‐Si film. In the case of a 4‐μm‐wide SiO2 stripe parallel to the 〈100〉 direction, the entire deposited layer grows epitaxially by low‐temperature furnace annealing (550∼650 °C). In the case of a 10‐μm‐wide SiO2 stripe, the whole surface region also grows epitaxially, although the deep region partially becomes polycrystalline in areas distant from the open substrate surface. The grown‐layer crystallinity is improved by subsequent high‐temperature annealing.

Amorphous‐Si/crystalline‐Si facet formation during Si solid‐phase epitaxy near Si/SiO2 boundary

Amorphous‐Si (a‐Si)/crystalline‐Si (c‐Si) interface facet formation was found during Si solid‐phase epitaxy (SPE) near the Si/SiO2 boundary. A (110) facet is formed during (010)b‐[100]SPE (SPE growth in the [100] direction and near the (010) boundary between a‐Si and SiO2). A (111) facet is formed during (011)b‐[100]SPE. The facet formation is explained with an atomistic model wherein an a‐Si atom must complete at least two undistorted bonds to attain SPE growth, and the boundary condition wherein an a‐Si atom cannot form undistorted bond to Si/SiO2 boundary.

Si Surface Cleaning by Si2H6–H2 Gas Etching and Its Effects on Solid-Phase Epitaxy

Si surface cleaning with Si2H6–H2 was studied for lateral solid-phase epitaxy (L-SPE) of CVD a-Si films. The cleaning was performed at 850°C, which is considerably lower than the previously-reported H2-cleaning temperature (1100°C). This is because etching of native oxide is enhanced by a reaction between oxide and Si-atoms dissociated from Si2H6. The effects of Si2H6-cleaning on L-SPE were studied using a Si (100) wafer with SiO2 stripes. After Si2H6-cleaning or H2-cleaning at 850°C, CVD a-Si films are deposited on the wafers, then crystallized by annealing (575°C). An H2-cleaned sample showed imperfect L-SPE because of a residual native-oxide layer at the a-Si / substrate interface. In the Si2H6-cleaned sample, the native-oxide layer was removed, and L-SPE growth was observed uniformly in the wafer. Si2H6-cleaning at 850°C is applicable for substrates with abrupt impurity distribution.

Solid-Phase Epitaxy of CVD Amorphous Si Film on Crystalline Si

The authors demonstrate that CVD amorphous Si crystallizes epitaxially on a (100)Si substrate with furnace annealing at temperatures of 600°C or below. Cleaning the substrate surface and depositing amorphous film at a low temperature with a high deposition rate are essential to this procedure. After loading the substrate into a CVD reactor, the substrate surface is first etched with H2 to remove native oxide at 1100°C, and then with HCl to prevent foreign atom adsorption up to a low deposition temperature of 550°C. The low temperature prevents microcrystallite formation, and the high deposition rate hinders foreign atom inclusion during deposition. With the appropriate cleaning and deposition conditions, the resultant epitaxial layer crystallinity has been proven to be good through Rutherford backscattering and reflection electron diffraction measurement.

Multiple SOI Structure Fabricate by High Dose Oxygen Implantation and Epitaxial Growth

A triple SOI (Silicon crystal On Insulator) structure has been fabricated on (100) and (111) Si substrates, utilizing three SIMOX (Separation by IMplanted OXygen) cycles. The SIMOX process consists of high-dose oxygen implantation followed by annealing and epitaxial growth of silicon, and provides good surface morphology. The top Si layer of the present triple SOI is single crystalline, which is confirmed by reflection electron diffraction and Rutherford backscattering measurement.

Effects of Substrate-Surface Cleaning on Solid Phase Epitaxial Si Films

The effects of two substrate-surface cleaning procedures were studied for solid-phase epitaxy of chemical vapor deposited amorphous Si (a-Si) films with respect to crystalline quality. These a-Si films were deposited on Si (100) wafers after surface cleaning by HF-dipping or in-reactor gas etching. The a-Si films were then crystallized by furnace annealing. The film quality was estimated using several techniques, such as etch-pit density measurements. For the samples etched by HF-dipping, the film crystallinity became worse with increasing film thickness owing to a residual oxide layer at the deposited-film/substrate interface. As a result, the electron mobility decreases with increasing deposited film thickness. For in-reactor gas-etched samples, the residual at the interface was negligible, and the crystallinity of a SPE film was as good as that of bulk Si.

High-Resolution Electron Microscope Study of Silicon on Insulator Structure Grown by Lateral Solid Phase Epitaxy

Structural study of L-SPE grown (100)Si/SiO2 interface after high temperature annealing in Ar has been carried out using HRTEM. On an atomic scale the roughness at the (100)Si/ SiO2 interface is less than a few lattice planes (0.5 nm). When micro-twins are present in the L-SPE layer, almost all of them nucleate at the Si/SiO2 interface. This is evidence for the formation of {111} growth planes near the interface during the L-SPE growth. The twin/SiO2 interface is not parallel to the substrate and forms atomically sharp {111} facets. This fact indicates that the interfacial energy of the (111)Si/SiO2 interface is lower than that of the (100)Si/SiO2 in solid phase.

Lateral Solid-Phase Epitaxy of Vacuum-Deposited Amorphous Si Film over Recessed SiO2 Patterns

A single-crystal silicon-on-insulator structure had been fabricated by lateral solid-phase epitaxy (L-SPE) of vacuum-deposited amorphous Si (a-Si) film on Si (100) substrate with SiO2 patterns. It is essential in L-SPE of vacuum-deposited a-Si that the substrate surface be planarized by recessing SiO2 patterns. A 7µm-wide single-crystal area over irecessed SiO2 was grown by low temperature annealing (575°C, 20 h). Only a polycrystalline area was formed over the unrecessed SiO2 pattern. This is probably because of voids or the large stress field in a-Si film at the pattern edge step.

Characterization of roughness and defects at an Si/SiO2 interface formed by lateral solid phase epitaxy using high‐resolution electron microscopy

Using high‐resolution transmission electron microscopy, we have characterized on an atomic scale the interfacial roughness and the interfacial defects at the Si/SiO2 interface obtained by lateral solid phase epitaxial growth of Si on SiO2. At the matrix/SiO2 interface, the protrusions of Si with 2–3 Si(200) lattice planes make the interface indented. These images can be explained by the pyramid‐type or edge‐type pseudo Si(100)/SiO2 interface models composed of small {111} facets. Defects, mainly microtwins, are localized only within 50 nm from the interface, and are adjacent to the SiO2. It indicates that microtwins are interface‐related and are supposed to form from atomic scale indents of the original a‐Si/SiO2 interface.

Impact of In situ Postnitridation Annealing for Successful Fabrication of HfSiON Thin Film

For the successful integration of high-k gate dielectrics into advanced complementary metal–oxide–semiconductor (CMOS) processes, it is important to determine the stability of high-k materials during exposure to an ambient atmosphere. In this work, we investigated the effect of exposure to air on the nitrogen concentration in HfSiON films formed by sequentially combining HfSiO chemical vapor deposition (CVD), plasma nitridation, and postnitridation annealing (PNA). We observed that exposure to air after the nitridation step reduces the nitrogen concentration due to a reaction between the HfSiON surface and the constituents of atmospheric air. We also found that exposure to air for even a short time between nitridation and PNA leads to a significant loss of nitrogen concentration, indicating that in situ PNA is critical for achieving precise control of the nitridation. These results confirmed the importance of using clustered multichamber platforms for successful high-k fabrication.