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EMULSITONE COMPANY
19 Leslie Court
Whippany, New Jersey 07981
TEL. (973)386-0053
FAX (973)503-0256
BOROSILICAFILM II
Borosilicafilm II is designed for applications where the
surface concentration is required to be less than the solid
solubility of boron in silicon. The spun-on film is very thin--of
the order of 200 angstroms. Since the film is so thin, and the
boron concentration is limited, the surface concentration
obtained is sensitive to the ambient in which the heat soak is
carried out. The solubility of boron in SiO2 is such
that out-diffusion of boron from silicon into the SiO2
phase must be taken into account when using Borosilicafilm II as
a diffusion source. Lower sheet resistance is obtained in a
nitrogen atmosphere; higher sheet resistance is obtained in an
oxidizing atmosphere, the highest being obtained in oxygen or wet
oxygen where the growth of SiO2 during diffusion is
the most rapid.
In addition to offering a wide range of sheet resistance by
choice of ambient, Borosilicafilm II is formulated so that
removal of the boron doped oxide after diffusion is easily
carried out in mild HF solutions. In this way, the boron-doped
oxide is removed without disturbing the original SiO2
film used for masking. Borosilicafilm II contains no observable
sodium ions or other impurities which are mobile in SiO2.
The boron concentration introduced into the silicon is such that
the large concentration of dislocations observed when silicon is
saturated with boron will not be seen when the wafers are treated
with etches designed to reveal dislocations.
APPLICATION
Borosilicafilm II may be applied to the wafer surface with a dropper. Sufficient material should be applied so that the wafer is completely covered with solution prior to the start of spinning. After about 15 seconds of spinning, a thin glassy film will form which consists of SiO2 containing dissolved boron. The wafers may then be subjected to the diffusion cycle. If it is desired to store the wafers for extended periods, the wafers should be heated to 70o-80oC for 10 to 15 minutes to remove residual solvent. The surface concentration achieved will not be sensitive to spin speed for shallow penetrations. However, film thickness will determine the time in the diffusion cycle when the source is depleted and the proceeds as a Gaussian rather than an erfc diffusion. For most applications, spin speeds between 2000 to 6000 rpm will suffice.
DIFFUSION
To obtain reproducible results, the wafer surface or the
windows in the silicon dioxide must be clean and free of
unremoved oxide. Any oxide remaining in the windows will dilute
the Borosilicafilm deposited on the surface, resulting in lower Co.
Typical diffusion results are obtained as follows:
| Temperature--950oC | Time--15 minutes | ||
| Ambient | Spin Speed (rpm) | Rs (Ohms/square) | Co (atoms/cm3) |
| N2 | 3000 | 65 | 5X1019 |
| N2:O2 4:1 | 3000 | 145 | 2X1019 |
| O2 | 3000 | 7500 | 5X1018 |
| O2 | 5000 | 15000 | 1X1017 |
| Temperature--1200oC | Time--15 minutes | ||
| Ambient | Spin Speed (rpm) | Rs (Ohms/square) | Co (atoms/cm3) |
| N2 | 3000 | 25 | 5X1010 |
| N2:O2 4:1 | 3000 | 45 | 2X1010 |
| O2 | 3000 | 600 | 5X1018 |
Removal of Boron Doped Silicon Oxide Layer
For a film applied at 3000 rpm spin speed, the oxide layer is
completely removed in two minutes of etching in a buffered HF
solution consisting of 60 grams NH4F, 100 grams H2O,
and 16 grams 48% HF. This film was produced in an N2
ambient. In a more oxidizing atmosphere, the films are removed
more rapidly.
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