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Borofilm type B is a polymer solution containing boron which is applied to silicon wafers by spinning. When the silicon wafer coated with Borofilm type B is subjected to diffusion temperatures, the polymer film decomposes to yield CO2, H2O and B2O3. The B2O3 is the source of boron for the diffusion.

Specifications for Borofilm Type B

Viscosity 115cp at 25oC
Boron Content 5.5% as B2O3
Metallic Impurities Na < 1 ppm
  Fe < 1 ppm
  Cu < 1 ppm
  Mn < 1 ppm


Wafer treatment prior to spinning.
While Borofilm type B is not particularly sensitive to surface condition of the wafer, more uniform results will be obtained with a hydrophillic surface as is obtained by treating the wafer with hot
H2SO4 + H2O2 or hot nitric acid etch prior to coating.

The recommended spin speed for coating the wafer is 6000 thick films will exhibit cracking at the diffusion temperatures. Should such cracking be observed, higher spin speed which produces a thinner film should be employed.

After spinning the wafer should be bake at 150 - 200oC in air.


Borofilm type B is intended for applications requiring a rpm. Excessively deep diffusion with low sheet resistivity and high C0. Diffusion temperatures are in the range of 1200 to 1300oC.

A typical diffusion process is as follows:

Diffusion temperature 1250
Ambient N2:O2 97%-3%
Time 16 hours

Results: Rs 0.5 ohms/square
Xj 42 microns

After diffusion the films are removed in conc HF solution. Should a boron stain be exhibited, this may be avoided by use of a thinner film, or by increasing the oxygen content of the ambient during diffusion.

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