Diffusion Furnace Heating Elements for Semiconductor Processing

One of the most critical steps in semiconductor manufacturing is the introduction of deliberate impurities into the material’s molecular structure, which is known as doping. The unique electrical properties of semiconductors are utterly dependent on the number of free electrons and electron holes available in its atomic bands. Under stable thermal conditions, the concentrations of these are roughly equivalent. Dopants are introduced to increase the conductivity of semiconductors closer to that of a conventional conductor. For example, introducing an impurity such as boron (Bn), gallium (Ga), or phosphorous (P) into a silicon (Si) semiconducting wafer increases the number of free electrons available, thus reducing the material’s electrical resistivity.

Doping semiconductor materials is carried out using diffusion furnaces that can operate under either atmospheric or vacuum conditions. This blog post will explore the purpose of diffusion furnaces for semiconductor doping in more detail.

What is a Diffusion Furnace?

Diffusion furnaces comprise cylindrical heating chambers that can be arranged either vertically or horizontally. Each orientation enables operators to maximize thermal efficiency by offering a uniform distance between silicon wafers and the radiating surface of heating elements. This ensures that the solid-phase semiconductor is heated with a high degree of precision and good consistency across the full surface, which is integral for chemical vapor deposition (CVD) processes.

Diffusion of dopants into a heated semiconductor is typically achieved by introducing gas phase impurities into the heated atmosphere of a diffusion furnace. At elevated temperatures, gaseous molecules can permeate silicon substrates and diffuse through the solid, altering the chemical composition of the semiconductor. Modulating the electronic behavior of silicon with phosphorous, for example, can be carried out through diffusion of phosphine (PH3) at elevated temperatures. The precursor gas may be introduced with an inert carrier such as nitrogen (N) to eliminate unwanted impurities from the diffusion furnace atmosphere.

This process is typically carried out under vacuum or low-pressure conditions to further decrease the number of unwanted gas-phase reactions. Low-pressure chemical vapor deposition (LPCVD) is currently one of the leading techniques for producing intermediate semiconductors for use in solar cells, commercial displays, thin film structures, and more.

Diffusion Furnace Heating Elements from Thermcraft

Thermcraft has a wealth of experience in the design and manufacture of replacement heating elements for diffusion furnaces and semiconductor processing. We prepare tailor-made ceramic heating systems housed in cylindrical stainless steel casings; a technology that is based around our thermally-engineered FibercraftTM and DuracraftTM furnace elements. Unique design features are available upon request to suit your thermal processing applications, including: LPCVD; high-temperature oxidation; high-vacuum CVD; and more.

If you have any questions about our diffusion furnace heating elements for semiconductor manufacturing, read our previous blog post: Using an Industrial Furnace for Semiconductor Device Fabrication. Or contact us directly.

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