NREL scientists have developed an optical processing furnace that combines photonic effects of light with heat to selectively induce reactions at far lower temperatures than they would be if caused by heat alone. In addition to saving energy for standard processing steps and producing devices with higher ohmic quality, this makes possible such new processes as:

  • Simultaneous fabrication of front and back electrical contacts for semiconductors;
  • Precise design of interfaces to either reflect or absorb light and to have either smooth or rough surfaces;
  • Transformation of low-cost fine-grain amorphous or multicrystalline silicon to a more highly crystalline structure; and
  • Growth of high-quality, low-cost thin-film silicon oxides for solar cells, computer memory chips, or other uses.

The mechanics of the NREL optical processing furnace are similar to those of a rapid thermal processing furnace. A bank of halogen lamps delivers heat and the targeted visible and near-infrared light that generates the photonic effect. A quartz muffle forms the inner chamber of the furnace, argon gas keeps out oxygen and contaminants (unless a reactive gas is part of the treatment), and a computer controls gas flow and intensity and duration of the light — typically 60 to 90 seconds. Control of light wavelength spectrum, intensity, and duration helps target particular portions of the treated device and produce the desired interaction.

Optical processing uses a phenomenon of light energy at interfaces to fabricate semiconductor devices at much lower temperatures than would otherwise be needed. The compact Optical Processing Furnace uses a bank of halogen lamps to preferentially deliver the optical energy.

Lower-temperature reactions are possible in the NREL furnace because the photonic effects of light energy cause a variety of phenomena, including generation of electric fields, creation of temperature gradients, enhancement of diffusivity, and reduction of melting temperatures. Consequently, processes such as sintering and alloying can be done at much lower temperatures, producing high-quality junctions such as low-resistance contacts. Most photonic effects occur at the interface between different materials, but some within the bulk of a material.

NREL's optical processing technology is covered by US patents (5,223,453; 5,304,509; 5,426,061; 5,429,985; 5,452,396; and 5,358,574; others pending). NREL welcomes licensing inquiries from companies interested in manufacturing furnaces for general semiconductor use or for developing specific equipment for particular operations or fields. NREL actively seeks partners to develop the furnace for growth of silicon oxides and fabrication of cobalt and titanium as well as aluminum electrical contacts. NREL also welcomes cooperative research programs to develop new uses for optical processing and can help design equipment and operating procedures for individual users.

The lead researcher in development of the optical processing furnace is Bhushan Sopori of the National Renewable Energy Laboratory. Inquiries concerning the patent status and availability of rights and licenses should be directed to NREL's Business Ventures Center; (303) 275-3009.

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Photonics Tech Briefs Magazine

This article first appeared in the April, 1998 issue of Photonics Tech Briefs Magazine.

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