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EMULSITONE COMPANY
19 Leslie Court
Whippany, New Jersey 07981
TEL. (973)386-0053
FAX (973)503-0256
PHOSPHOROSILICAFILM
Phosphorosilicafilm is a dopant formulation designed to produce
phosphorous diffused layers in semiconductor wafers. Phosphorous diffused layers may be
produced routinely with sheet resistance profiles over the wafer surface flatter than
1-2%. Similar reproducibility from wafer to wafer and from run to run is easily achieved.
When applied by spinning or spraying, a film forma which consists of silica with
phosphorous dissolved in it. This phosphorous doped silica layer provides an erfc source,
and the sheet resistance decreases linearly with the square root of the diffusion time.
Phosphorous concentrations required for emitters with high emitter efficiency in high
frequency transistors and integrated circuits are obtained with films about 2000 angstroms
thick. For high voltage devices requiring deep penetration and low sheet resistances less
than 1 ohm/square, sprayed-on films are used.
Phosphorosilicafilm contains ethyl alcohol as solvent. In addition to ethyl alcohol,
methanol or isopropyl alcohol may be used as diluents if it is desired to dilute the
"as-received" formulation.
Phosphorosilicafilm is hygroscopic and for extended storage, the container should be
securely fastened to prevent access of water vapor. The bottle may be left open for
reasonable periods of time with no deleterious effects. After films have been applied by
spinning or spraying, the wafers may be processed directly. However, if it is desired to
store the wafers for extended periods of time after film application and prior to
diffusion, the films should be hardened so that the layer is insoluble in water, and the
wafers may be stored with no loss in doping characteristics. If it is desired to
photo-etch Phosphorosilicafilm, higher temperature or longer heat soak is necessary for
good adhesion of the photo-resist and to prevent leaching of phosphorous from the glass
film.
For special application where higher sheet resistance and lower Co's are
required, formulations yielding Co's as low as 1016 are available
from stock.
Application
The viscosity of Phosphorosilicafilm is quite low, and the material wets readily to
silicon surface. One or two drops are sufficient to cover a 1 1/2" wafer. For shallow
penetrations where the source is not depleted, the sheet resistance obtained is
independent of spin speed. A spin speed should be selected which minimizes the lip which
builds up at the edge of the wafer. In 10 to 15 seconds of spinning, the film will be
formed. For spraying, the material should be diluted to yield a film less than 10,000
angstroms thick. A thicker film will develop cracks on drying.
Diffusion
Typical diffusion results are obtained as shown in the table following.
| Spin Speed (rpm) | Diffusion Temperature (oC) |
Time (min.) | Ambient | Rs (ohms/square) | Co (Atoms/cm.) |
| 3000 | 1050 | 20 | N2:O2 4:1 | 5 | 1021 |
| 3000 | 1200 | 60 | N2:O2 4:1 | 2 | 1021 |
| Sprayed-on 6000 angs. | 1200 | 480 | N2:O2 1:1 | 0.5 | 1020 |
Surface Condition
Phosphorosilicafilm will yield no surface damage or deposits. The phosphorous doped silica
film is easily removed in dilute HF solution.
"LOW Co" PHOSPHOROSILICAFILM
"LOW Co" Phosphorosilicafilm formulations, which yield surface
concentrations less than solid solubility, are similar to the standard formulations with
the exception that the phosphorous concentration in the SiO2 layer is reduced.
The Low Co materials are applied in the same way as the standard materials.
Diffusion Process
The surface concentration and sheet resistance realized with these materials will depend
upon the atmosphere in which the diffusions are carried out. In an oxidizing atmosphere,
the growth of SiO2 at the silicon surface will eventually prevent the access of
dopant atoms from the doped oxide to the silicon. As a standard for reference, the Low Co
Phosphorosilicafilm materials, except for the 1017 to 1016 range are
evaluated by diffusion in N2 at 1200oC. Films are applied at 3000
rpm to silicon wafers of 10 ohm cm. resistivity. The diffusion time is fifteen minutes.
Surface concentration is estimated from the sheet resistance and junction depth,
determined by angle lapping and staining. For the materials in the lowest Co
range, 1017 to 1016, the ambient is N2:O2 5:1,
with the same temperature, 1200oC, for 15 minutes.
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