研究目的
Investigating the chemical-vapor deposition conditions for the growth of pure boron (PureB) layers on silicon at temperatures as low as 400oC to optimize photodiodes fabricated with PureB anodes for minimal B-layer thickness, low dark current, and chemical robustness.
研究成果
For 450°C PureB deposition, conditions were found with which layers as thin as 3 nm with a 2-nm-thick roughness provided diodes with ideal I-V characteristics and low dark current. The B-coverage was so complete that it protected the underlying Si from being etched in TMAH. In-situ cleaning steps before the B-deposition were found to modify the Si surface structure, resulting in higher diode dark currents and more susceptibility to TMAH etching of the Si through the PureB.
研究不足
The study found that in-situ cleaning steps before the B-deposition modify the Si surface structure, resulting in higher diode dark currents and more susceptibility to TMAH etching of the Si through the PureB. The perfection of the B-coverage is degraded due to the extra cleaning steps.
1：Experimental Design and Method Selection:
The study involved the deposition of pure boron layers on silicon using a diborane precursor in a commercially-available Si epitaxial reactor at temperatures ranging from 400°C to 700°C. In-situ cleaning methods such as high-temperature baking in hydrogen and exposure to HCl were tested.
2：Sample Selection and Data Sources:
n-type Si (100) wafers with a resistivity of 1-10 Ω-cm were used. The wafers were immersed in a diluted HF solution to remove native oxide and H-passivate the surface before loading into the CVD reactor.
3：List of Experimental Equipment and Materials:
ASM Epsilon 2000 CVD reactor, ellipsometry, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and optical profiling.
4：Experimental Procedures and Operational Workflow:
The wafers were prepared with boron layer thickness from 2 nm to 7 nm. The as-grown thickness was evaluated directly after deposition by ellipsometry. Electrical test structures were fabricated to test the diode characteristics directly after deposition.
5：Data Analysis Methods:
The ellipsometry data was interpreted using a model with two regions: a compact homogeneous boron film and a surface region of incomplete boron coverage. XPS was used to study the composition of the layers.
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