Boron Doped Silicon Wafer

A boron doped silicon wafer is used in the manufacture of semiconductors, such as microchips and solar cells. Boron is a common dopant in p-type silicon wafers, which have more holes than n-type wafers. The boron doping process increases the electrical conductivity of silicon, so it is often a key part of p-type silicon fabrication.

The doping concentration in a wafer is determined by the type of device it is intended for, and can range from parts per million to millions. In general, doping concentrations above about 1018 cm-3 are considered degenerate and must be tailored to produce the properties desired in the device that will be made from the silicon.

Generally, a thick boron-doped silicon film is needed in a semiconductor device to increase its electrical conductivity. For example, for a microchip that produces high-speed digital circuits, a 0.5mm-thick epitaxial layer is required.

This thick film requires a lot of time to grow, so it is important that the doping profile be precise. Plasma-enhanced chemical vapor deposition (PECVD) with low temperatures (175degC) is used to produce these thin boron-doped layers.

PECVD-grown boron-doped epitaxial silicon films were annealed to measure their carrier concentrations. Compared with as-deposited epitaxial layers, the boron concentrations in the annealed samples were much more concentrated. Additionally, they had a much sharper doping profile. This resulted in a very high efficiency of boron doping, which could be a major advantage when realizing p-n junctions. In addition, the annealing process results in a reduction of the epitaxial grain size and increases the thermal stability of the boron-doped layer.

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