Growth and characterization of undoped and in situ doped Si1−xGex on patterned oxide Si substrates by very low pressure chemical vapor deposition at 700 and 625 °C

Abstract

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 <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