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Phosphorofilm is an aqueous solution of a polymer containing phosphorous which may be applied to silicon wafers either by spraying or spinning.

Physical Characteristics
Viscosity 7 cp @ 25oC
Density 1.01

Contaminant Limits
Na, Fe, Zn, Cu, Au, Mn, Ni < 1 ppm

Application Notes
Films may be deposited either by spinning or spraying. Spinning at 3000 rpm will yield a film about 3200 angstroms thick. Film deposited by spraying will exhibit excellent leveling characteristics. Film thickness obtained by spraying will depend upon such variable as the liquid flow rates, determined by liquid pressure, and rate of travel of the substrates under the spray nozzle. Typical conditions are as follows:

Orifice size...............0.3 mm
Liquid flow rate...........5 cm3/minute
Height of nozzle above wafers................8-10 cm.
Wafer Traverse under spray gun...............30 cm/minute

Films deposited by spinning are ready for diffusion. Films deposited by spraying should be heated to 40-50oC to insure drying.

Diffusion is carried out in nitrogen atmosphere with 1-2% oxygen. Typical results for one hour diffusion are as follows:

Temperature Rs (ohms/sq.) Xj (microns)
850oC 45 0.05
875oC 35 0.1
900oC 30 0.5
950oC 20 0.7

After diffusion films which remain on the wafer surface are readily etched away in dilute HF solution.

All apparatus used with this solution may be cleaned in warm water.

Safety Considerations The solution is essentially non-flammable. The phosphorous concentration is such that the material should not be ingested. Eye protection should be used, since the solution is acidic. During the diffusion process, in addition to CO2, oxides of phosphorous will be evolved. At room temperature the only volatile is H2O. Since no toxicity studies have been carried out with this product, it should be treated with care as with any laboratory chemical.

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