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EMULSITONE COMPANY
19 Leslie Court
Whippany, New Jersey 07981
TEL. (973)386-0053
FAX (973)503-0256
GALLIUMSILICAFILM WITH BORON
Galliumsilicafilm with Boron is an ethyl alcohol solution of a silica
forming compound which yields on drying pure SiO2 doped with gallium and boron.
This solution is designed for use as an open tube diffusion source to replace the older
ampoule diffusions. By including boron in the SiO2 layer, one obtains in one
diffusion step, the high surface concentration of boron atoms (> 1020) and
the more rapid penetration of gallium to reduce the long diffusion times required for deep
penetrations.
Applications
Galliumsilicafilm with Boron is applied to the surface of the silicon wafer by placing
several drops of solution in the approximate center of the wafer and allowing the solution
to wet out over the surface. When the silicon surface is hydrophilic, a drop of the dopant
solution will spread in a uniform circle approximately one inch (1") in diameter.
Four drops will cover a two inch (2") wafer. The time required to spread over the
surface in 1-5 seconds. After the wafers are coated, the films may be hardened by heating
at 200oC for 10-15 minutes in air. If the wafer surface is not hydrophilic, it
may be made so by heating to temperatures in excess of 300oC for several
minutes, or by soaking the wafer in NH4OH:H2O2 or H2SO4:H2O2
for 10-15 minutes.
Diffusion
Diffusion is carried out in either N2 or argon. The wafers should be coin
stacked. It has been found that it is not necessary to coat both surfaces to achieve
boron-gallium diffusion into both sides of the wafers. The uncoated side in contact with
the coated surface will be doped by volatilization from the coated surface. Typical
diffusion results are illustrated in the table below which shows the penetration achieved
with Galliumsilicafilm with Boron compared with the penetration observed with
Galliumsilicafilm without boron and with Borosilicafilm Co=1x1021.
DIFFUSION RESULTS WITH VARIOUS SOURCES
| Diffusion Source | Temperature oC | Time (HOURS) | Ambient | Xj (MICRONS) | Rs (Ohms/Sq.) |
| Galliumsilicafilm with Boron | 1250 | 16 | N2 | 44 | 1.5 |
| Galliumsilicafilm | 1250 | 16 | N2 | 35 | 10.0 |
| Borosilicafilm Co=1x1021 |
1250 | 16 | N2 | 22 | 0.5 |
Removal of Films
After diffusion, the films may be removed with HF solution. If there is any boron
staining, this is removed by oxidizing the wafers for 10-15 minutes at 900oC or
higher to grow more SiO2. The boron stain is then removed in HF. Boron staining
may be prevented by replacing the nitrogen atmosphere with air or oxygen in the last hour
of the diffusion process.
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