Diffusion Furnaces: A Guide to Advanced Thermal Processing

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Diffusion Furnaces: A Guide to Advanced Thermal Processing

Diffusion furnaces exploit a complex form of advanced thermal processing to assist the upward trajectory of the semiconductor industry. Since the invention of the silicon (Si) transistor and subsequently the integrated circuit (IC) in the 1950s, the semiconductor market has grown into a new titan of industry worth more than $400 billion. Diffusion furnaces have proven instrumental to that success, which has brought about a host of technological advancements and developments in modern electronics.

Having written several posts on the topic of diffusion furnaces, we decided to put together a brief guide to advanced thermal processing of modern semiconductors.

Purpose of Diffusion Furnaces

Understanding what a diffusion furnace does requires a basic understanding of semiconductor manufacturing.

Semiconductors are a novel family of materials with electrical conductivities between those of conductors and insulators. They also tend to display dissimilar temperature coefficients of resistance (α) to metals, with electrical resistance (Rn°) decreasing proportionally to elevated temperatures. Manufacturers can exploit and fine-tune these electrical properties by deliberately introducing what are known as ‘dopants’ into the semiconductor’s crystal lattice.

Diffusion furnaces are primarily – but not exclusively – used in semiconductor doping, where an intrinsic semiconductor is heated to a setpoint temperature and exposed to a vapor-phase material. This causes solid-state diffusion; the process of gaseous molecules mixing with a host solid at an atomic scale and becoming immobilized within the semiconductor’s crystal lattice. Both n- and p-type semiconductor doping can be accomplished using diffusion furnaces.

Additional thermal processing methods conducted using diffusion furnaces include:

  • Dry and wet oxidation
  • Inert gas annealing in air or nitrogen (N2)
  • Low-temperature curing
  • High-temperature drive-in
  • Low-pressure chemical vapor deposition (LPCVD)

Diffusion Furnace Types

The architecture of a diffusion furnace is typically centered around a cylindrical heating chamber that ensures optimal thermal uniform for circular semiconductor wafers. These may be arranged horizontally or vertically depending on the application specifications. Key components in a diffusion furnace include:

  • Heating elements which are ideally comprised of a heavy gauge, helically-wound wire with ceramic interlocking spacers.
  • Insulation; most often formed of lightweight refractory ceramic fibers.
  • A shell, which often consists of an inner stainless steel liner with an aluminum outer shell and integrated cooling systems.
  • Seals and gaskets, which are generally installed into load-ends or vestibules and may be engineered as collars, discs, or blocks.

Read our previous blog post, Ceramic Heating Elements for Semiconductor Heat Treatment, to learn more about the components available for advanced thermal processing of electrical components from Thermcraft.

Applications of Diffusion Furnace Thermal Processing

Diffusion furnaces are best-known for producing n- and p-type semiconductors for end-use in a range of advanced electronics markets. Since the early development of diffusion thermal processing, semiconductors have permeated everyday life and become ubiquitous components in various products. These include:

  • Light-Emitting Diodes (LEDs) and Organic LEDs (OLEDs) for next-generation lighting and display applications, replacing conventional incandescent light sources.
  • Photovoltaics (PVs) which form the primary active component of hetero- and multi-junction solar cells.

Diffusion Furnaces from Thermcraft

Thermcraft is one of the world’s leading designers and manufacturers of thermal processing equipment that exceeds customer expectations in challenging sectors. If you need any more information about the capabilities or applications of our diffusion furnaces, read our previous blog posts: Why Use a Diffusion Furnace? and Using an Industrial Furnace for Semiconductor Device Fabrication.

Otherwise, contact us directly with any queries.