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Borosilicafilm Type 5257 yields results similar to Borosilicafilm I except that the film is less sensitive to humidity and a silicon surface results after diffusion which is not pitted. Borosilicafilm Type 5257 is supplied as a two component product, "A" and "B". Equal volumes of "A" and "B" are mixed prior to use. The individual components have a six month shelf life while the mixture has a shelf life of 2 to 3 weeks.

Borosilicafilm Type 5257 is designed for use in IC production as a diffusion source for isolation diffusion and for base diffusion in the two step process. This diffusion source yields extremely uniform sheet resistivities well with +/-% over the wafer surface and the VI characteristics of the resultant p-n junction are close to ideal, with sharp breakdown voltage and low leakage current.

Process Details

Component "A" is mixed with Component "B" in equal volume. The mixture is allowed to stand for about 1/2 hour to allow air bubbles to settle out. The Borosilicafilm Type 5257 mixture exhibits a viscosity of 24-25 cp. at 25oC. Should this formulation prove too thick, the solution may be diluted with denatured ethyl alcohol. Dilution of the Borosilicafilm Type 5257 in equal volume with ethyl alcohol will yield a solution with a viscosity of 12 cp. and dilution of 1 part of Borosilicafilm Type 5257 to 2 parts of ethyl alcohol will yield a viscosity of 3 cp.

The mixture of Borosilicafilm Type 5257 is applied to the wafers by spinning. Spin speeds from 3000 rpm to 10,000 rpm may be used. After spinning, the wafers are baked at 150oC to remove all remnants of solvent. This may also be accomplished by letting the coated wafers which are stacked in the diffusion boat rest in the mouth of the furnace tube for 10-15 minutes prior to insertion in the hot zone. The ambient atmosphere for the diffusion process is N2:O2 4:1 or air. For very dilute solutions or very thin films, the ambient atmosphere should be N2 for the diffusion process.

Typical diffusion results with Borosilicafilm Type 5257 are shown below:

TemperatureoC Diffusion Time (Minutes) Rs (Ohms/sq) Xj(Microns)
900 15 110.00 <.1
1000 15 30.0 0.44
1100 15 12.0 0.66
1200 15 3.5 2.2

The effect of dilution on the sheet resistivity on a diffusion run at 1200oC for 1 hour in an ambient of 10% O2:90% N2 is shown:

Dilution Sheet Resistivity (Ohms/sq.)
Undiluted 2.4
1:1 Borosilicafilm 5257 A+B and Ethyl Alcohol 6.5
1:2 Borosilicafilm 5257 A+B and Ethyl Alcohol 11.0


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Borosilicafilm 5257 Part A MSDS
Borosilicafilm 5257 Part B MSDS