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EMULSITONE COMPANY
19 Leslie Court
Whippany, New Jersey 07981
TEL. (973)386-0053
FAX (973)503-0256
SILICAFILM WITH PHOSPHOROUS
PHOSPHOROSILICAFILM FOR GLASSIVATION
GLASS FORMING SOLUTION 306
These solutions have been available for some time and there has been some
confusion on the use of and the difference between these products. In addition, there has
been a question concerning the fact that there is usually a reference to the Co
of the solutions even though they are not used as diffusion sources. With regard to the
latter, the Co is specified as a simple way to indicate the phosphorous content
of the glass. Since the determination of the phosphorous concentration in the solution is
not a straightforward chemical analysis procedure and since all of us have diffusion
facilities, it is a simple matter to specify the doping capability of the film to indicate
the phosphorous content of the glass.
With this in mind we list the difference between the aforementioned formulations:
| Film Thickness in angstroms at 2000 RPM spin speed | Co atom/cm3 in Si after 15 min diffusion |
|
| SILICAFILM with Phosphorous | 2000 | 1 x 1019 |
| PHOSPHOROSILICAFILM for Glassivation | 2000 | 5 x 1019 |
| GLASS FORMING SOLUTION 306 | 3500 | 5 x 1019 |
As to applications and the reason for three different formulations:
Silicafilm with Phosphorous, the first of this family was intended to be applied as a
phosphorous containing SiO2 layer after emitter diffusion when one had problems
with photo resist adherence to a highly phosphorous doped thermal oxide. One simply
removed the phosphorous rich layer and deposited this film which contained less
phosphorous to achieve good resist adhesion. However the practice of applying a glass
layer over a metallized IC demonstrated that Silicafilm with Phosphorous was inadequate
for the purpose. The film cracked over the steep steps provided by the metallization.
Phosphorosilicafilm for Glassivation was then developed which does not crack over the
metallization steps. While the phosphorous content is sufficient to provide a sodium
barrier, in this instance this is not a necessary requirement of this film. The film is
intended to provide scratch protection for the underlying metal. However the phosphorous
content is such that surface is not hygroscopic and no phosphorous etching of the aluminum
occurs in high relative humidity.
The last product Glass Forming Solution 306 is similar to Phosphorosilicafilm for
Glassivation in its phosphorous content. However, it was developed originally as a
diffusion mask for zinc in III-V diffusion. Since it was required that the film be thicker
than the first two films, several firms found that Glass Forming Solution 306 may be used
in place of Phosphorosilicafilm for Glassivation and one can obtain a thicker glassivation
with the same number of applications.
All these solutions are applied in the same way. Spin-densify at 400oC for 1
hour, spin a second coat and densify at 400oC for 1 to 2 hours. The layers will
be very uniform in thickness, they will etch uniformly in dilute HF solution and with
automatic spinners, you can achieve a faster through put than with CVD. With the volume
discount, this process eliminates the high capital investment in CVD equipment. After all,
the $40,000 to $100,000 needed for CVD could earn, at 9 or 10%, the cost of our solutions,
and you will have no rejects due to overetched aluminum or open circuits where the glass
was not completely removed. Nor will your firm be noted in the Wall Street Journal because
of phosphorous problems.
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