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ZINCSILICAFILM 306

Zincsilicafilm 306 is a formulation designed for use as a diffusion source in GaSb and GaAs, for the production of Light Emitting Diodes by open tube diffusion. Zincsilicafilm 306 does not require a Silicafilm intermediate layer between the source and the semiconductor substrate. Zincsilicafilm 306 may be applied directly to GaSb or GaAs wafers. This makes it simple to use yielding high doping levels. In addition, Zincsilicafilm 306 offers advantages over the process in which a Silicafilm coated wafer is diffused in a two furnace process where zinc vapor is passed over the wafer.

Process details:

Coating GaSb or GaAs
Zincsilicafilm 306 will not wet GaAs orGaSb unless the wafer surfaces have been conditioned prior to application. The wafer conditioning is quite simple. The wafers are heated at 350oC or 400oC for a few minutes in air. The wafers are cooled and are then ready for coating. Proper surface conditioning is evidenced when a drop of the Zincsilicafilm 306 mixture is placed on the surface of the wafer and proceeds to wet out over the wafer surface. Improper conditioning is evidenced when the drop remains stationary with no wetting or spreading.

After conditioning the wafers are ready for coating. The wafers may be coated by spinning, or in the case of odd size or bowed wafers, the solution may be diluted with alcohol and the solution may be applied by painting. For spinning, spin speeds of 2000-3000 rpm or of such magnitude so as to yield a minimum lip on the edge of the wafer may be used. After spinning the wafers should be heated in air for 10-15 minutes at 100-120oC. Higher temperatures may be employed, but care should be exercised not to bring the wafers up to temperature too rapidly to prevent the formation of holes in the film due to solvent evaporation.

Diffusion

Diffusion may be carried out in N2 or argon. Slight traces of oxygen in the ambient will cause no difficulty. Diffusion temperature of 850oC is optimum. Lower temperatures require long diffusion time, and higher temperatures may result in excessive dissociation of the semiconductor. The following typical results are obtained withGaSb of the type commonly used for Light Emitting Diodes.

Diffusion temperature
(oC)
Diffusion time (min.) Rs (ohms/sq.) Xj (microns)
850 15 35 1
850 60 17 2



Removal of Zincsilicafilm 306
After diffusion the Zincsilicafilm may be removed by etching in 10% HF. A clean specular surface will result.

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