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Borosilicafilm P-250 is a formulation designed to be used as a boron diffusion source to yield a high concentration of boron in the silicon lattice and a minimum concentration of dislocations usually observed with high boron doping. Borosilicafilm P-250 is supplied as a two component formulation labelled "A" and "B". Prior to use, the "A" and "B" components should be mixed in equal volumes. The mixture is ready for use as soon as the bubbles have settled out of the solution. This formulation is singularly free of contaminants such as sodium iron, etc. In addition, it will be noted that the silicon surface will be unstained or etched in any way by this diffusion source. When properly used, extremely uniform diffusion profiles will result. The uniformity in sheet resistivity will be at least within 1% of the mean, and junctions will be perfectly flat as evidenced by the extremely sharp Zener Knee observed when the junctions are biased to breakdown.

Suggested Process Specifications

A typical process for carrying out a boron diffusion with Borosilicafilm P-250 is as follows:

1. Spin Speed - 3000 rpm for approximately 10 seconds.

2. Bake wafers at 2000oC for 15 minutes in air.

3. Diffuse in N2 or argon.

The following diffusion results will be obtained:

TemperatureoC Time (Minutes) Sheet Resistivity (Ohms/Sq.) Junction Depth (Microns)
1200 15 5 +/- 0.5 2.2
1100 15 10 +/- 0.1 0.81
1000 15 40 +/- 0.5 0.25
900 15 147 +/- 2.0 0.11

The surface concentration exhibited by this diffusion source under the above conditions is estimated to be approximately 7-8x1020. The diffusion source behaves as an unlimited source for penetrations of 2-3 microns under the conditions described above. For very deep diffusions where it is desired to obtain lower sheet resistivities, thicker films should be applied and the wafers should be coin-stacked with the boron sides facing.

NOTE: The wafers should be heated to 200oC as soon as feasible after spinning. Should the films acquire a cloudy appearance on standing, this will disappear on heating with no deleterious results.

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