Sil_~Ge~ films deposited by very low pressure chemical vapor deposition (VLPCVD), with and without plasma enhancement, and by low-pressure CVD (LPCVD) were studied to explore the effects of Ge on various properties of polySi~_=Ge~ films. As the Ge content increases, growth rates increase for thermal and plasma-deposited polycrystalline and amorphous films. The transition temperature for poly-to-amorphous deposition is lower, and the crystallization of amorphous films is faster. Enlarged grain sizes are achieved with Ge in films grown thermally, with plasma enhancement, and by solid-phase crystallization, with grain sizes as large as 1.3 ~m in films of 1000 A thickness. Increased n-type and p-type Hall mobilities and decreased p-type resistivities are achieved as functions of Ge content in poly-Si~_=Ge~ films with x -< 0.20. The Hall mobility in an n-type poly-Si080Ge0.f0 film is 50 cmf/V-s, the highest value reported to date for poly-Si~_~ Ge~ materials. Poly-Si~ =Gex thin-film transistors (TFTs) have been fabricated and evaluated, leading to a proposal of a poly-Si-capped Si~_=Gez TFT structure.

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Results of strained layer Si1−xGex heteroepitaxy on patterned oxide silicon substrates using a very low pressure chemical vapor deposition reactor are presented. Patterned oxide wafers were in situ cleaned at 700 °C using an Ar/H2 plasma. Undoped Si1−xGex strained layers at 625 and 700 °C along with in situ doped p and n-type Si1−xGex strained layers at 625 °C were deposited using SiH4, GeH4, B2H6, and AsH3 with H2 as a carrier gas. Alternating layers of Si1−xGex and Si were formed by switching the inlet gases. Scanning electron microscope showed a smooth surface morphology for Si1−xGex strained layers deposited with GeH4/SiH4 gas ratios &lt;7.5%. Cross-sectional transmission electron microscope revealed a sharp transition between the Si1−xGex and Si layers with dislocation densities below the detection limit of 105 cm−2. Defect etching confirmed the low defect density at the surface. For epitaxial windows smaller than 50×50 μm, no defects were observed. Germanium solid mole fraction, boron and arsenic chemical dopant concentrations, and interfacial carbon and oxygen contamination were measured by secondary ion mass spectrometry. Undoped, B2H6, and AsH3 in situ doped Si1−xGex strain layers with germanium content up to 23% were demonstrated. The Ge incorporation was controlled by the GeH4/SiH4 gas ratio and the Si1−xGex growth rate decreased with increasing Ge solid mole fraction. The addition of B2H6 did not affect the Si1−xGex growth rate and modulation of the boron chemical incorporation was possible by controlling the B2H6 gas concentration. On the other hand, AsH3 severely degraded the Si1−xGex growth rate and varying the AsH3 gas concentration did not change the arsenic chemical incorporation. Lastly, selective AsH3 doped Si1−xGex heteroepi

Si1−xGex thin films on oxide-coated Si substrates have been formed by plasma-enhanced very-low-pressure chemical vapor deposition. Two modes of deposition, thermal and plasma enhanced, were studied using SiH4 and GeH4 at temperatures ≤600 °C. In both cases, growth rates and grain sizes increase with Ge content, and the polycrystalline-to-amorphous transition temperature is lower for Si1−xGex than Si. Compared to thermal growth of polycrystalline Si1−xGex, plasma-enhanced deposition of poly-Si1−xGex promotes higher growth rates, smaller grain sizes, and direct deposition onto oxide, as well as improved structural properties such as a smoother surface and a more columnar grain texture. Plasma deposition of amorphous-Si1−xGex films followed by a crystallization anneal at 600 °C results in an even smoother surface morphology with grain sizes enhanced by an order of magnitude compared to plasma-deposited poly-Si1−xGex films.

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