Silicon Wafer Processing | Everything You Need to Know about Polysilicon


August 30, 2019

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Single-crystal silicon isn’t the only type of silicon you can use for silicon wafer processing, there’s also what we call polycrystalline silicon or better known as polysilicon. Polysilicon is widely used in MOS applications, like MOS transistor gate and MOS circuits, and more. If you’re curious about polysilicon, then here’s everything you need to know about it:

What is Polysilicon?

In silicon wafer processing, thin films of Polysilicon or also known as polycrystalline silicon or Poly-Si are commonly used in MOS applications. It is also utilized as a resistor and in assuring ohmic contacts for hollow junctions. In gate electrode applications, poly-Si combined with a metal or metal silicide can enhance conductivity. It is also reliable and known to work well in high-temperature processing and junctions admirably with thermal SiO2. Heavily-doped polysilicon thin films are also widely used in emitter systems in bipolar circuits. While lightly-doped polysilicon films are used as resistors.

How is it Installed?

Polysilicon is normally deposited by high thermal decomposition of silane at 580-650 degrees Celsius. As the temperature increases, so does the rate of deposition. The deposition rate is also influenced by the pressure of silane, which converts to silane concentration. Variables such as dopant concentration and pressure are also important in a polysilicon deposition.

What is its Purpose?

Doping plays an important role when it comes to the electrical properties of polysilicon. A polysilicon thin film that has been heavily doped has lower resistivity. Polysilicon is also known to be more resistive compared to single-crystal silicon. Common dopants for polysilicon are boron, arsenic, and phosphorous. The dopants are introduced after deposition. Polysilicon can be doped 3 ways: in-situ doping, diffusion, and ion implantation.

  • In-situ doping involves adding of dopant gases to the CVD reactant gases throughout the epi deposition development.
  • Diffusion doping involves depositing a substantially-doped silicon glass over the undoped polysilicon. This process takes place at high-temperatures ranging from 900—1000 degrees Celsius.
  • Ion implantation involves blasting a polysilicon layer with high-energy ions directly.
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High-quality wafers go through high-quality silicon wafer processing. At Wafer World, we can provide you with high-quality wafers at the best price possible. Call us for inquiries or purchase wafers online!

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