Borosilicafilm
Co=1x1020 yields an SiO2
layer doped with boron in sufficient concentration to yield a surface
concentration in silicon of 1x1020 atoms for diffusion
penetrations up to 5 microns. Thereafter, the source no longer adds
additional boron to the silicon and further diffusion into the silicon
proceeds via a Gaussian process. This situation holds for wafers which are
stacked vertically in the diffusion boat. when the wafers are coin stacked,
the diffusion process will be of the erfc type for penetrations up to 20
microns.
Borosilicafilm
Co=1x1020yields, after heat treating as
described below, a pure glassy film consisting only of B2O3:SiO2.
No surface pitting will be observed on the silicon or in the SiO2
layer which may be used as a diffusion mask. The glassy films will be very
uniform in thickness and of extremely low porosity. Diffusion fronts which
result will be flat with no diffusion spikes or non-uniformities. Under
proper processing conditions the sheet resistivity over the wafer surface
will be uniform to -2%. In addition, the silicon wafers when subjected to
suitable etches, will exhibit no slip lines or etch pits characteristic of
large concentrations of boron in silicon.
Processing Recommendations
When the solution is fresh it may be used without filtration. Should there
be an accumulation of particulate matter in the solution, it may be filtered
through a 1 micron membrane filter in the same manner as photo-resist is
filtered. However, caution is advised to be sure that the membrane filter is
insoluble in ethyl alcohol which is the solvent for the solution.
Borosilicafilm
Co=1x1020 is designed to be applied by
spinning. When spun at 3000 rpm and baked at 100oC for 1 hour, a
film will result which is approximately 2000 angstroms thick. After
diffusion in a non-oxidizing atmosphere a film thickness of 1200-1500
angstroms will result. While there is great latitude in the baking
temperature, after spinning it is best to subject the wafers to 100oC
heat treatment to prevent pinholes form appearing in the film. After
spinning the film will be soft and this mild heat treatment will remove the
solvent slowly and eliminate pinholes.
Diffusion
The diffusions should be carried out in nitrogen or argon with a few percent
of oxygen. The following diffusion results are typical of what will be
observed. The films were applied to 10 ohm cm."N" type silicon wafers
oriented 1-0-0, the spin speed was 3000 rpm, and the wafers were heated at
100oC for 1 hour in air prior to diffusion.
Temperature
oC |
Time |
Sheet
Resistivity |
Junction Depth |
1000 |
2 Hrs |
130
± 10
Ω/sq. |
0.5
µm |
1165 |
15 Min |
32
±
0.5
Ω/sq |
0.88
µm |
1165 |
1 Hr |
16
±
0.5
Ω/sq |
1.76
µm |
1200 |
15 Min |
21
±
0.5
Ω/sq |
2.1
µm |
1200 |
1 Hr |
10
±
0.2
Ω/sq |
4.2
µm |
Boron Back
Surface Field Using Spin-On Dopants by Rapid Thermal Processing![](icoLeaf.gif)
Application of semiconductor diffusants to
solar cells by screen printing![](icoLeaf.gif)
Spectroscopic Investigations of Borosilicate Glass and Its
Application as a Dopant Source for Shallow Junctions![](icoLeaf.gif)
If you don't find what you're looking for,
Contact Us.
We may have a suitable product that's not listed, or we may be
able to develop a material to fit your specific needs.
Tel : (02)2217-3442 / Fax : (02)2704-4070
|
|