1. A silicon dioxide (SiO2) layer is
grown on a p-doped silicon wafer.
2. A positive photoresist layer is
applied to the SiO2.
3. A photomask is created with opaque
and clear areas, patterning the clear areas in locations where
windows in the SiO2 are to be formed. The photomask image is
transferred onto the positive photoresist, which becomes polymerized
in the areas where it is not exposed to the UV light (opaque areas in
the photomask).
4. The resist is developed, and the
unpolymerized areas dissolve, forming a window that exposes the SiO2.
5. The silicon dioxide is etched away
in the photoresist windows, exposing the silicon wafer.
6. The photoresist is removed.
7. Using phosphorus as the dopant, an
n-type region in the p-type silicon base is created by diffusion.
8. A new layer of silicon dioxide is
grown on the surface of the n-region, and steps (2) through (6) are
repeated to create a new window in the SiO2.
9. A second diffusion creates the
p-type region in the n-type base by using boron as the dopant.
10. Silicon dioxide (SiO2) is again
grown over the exposed silicon wafer, and the photoresist is applied
over the SiO2.
11. The photomask, containing the two
clearances for the emitter and base, is placed over the positive
photoresist, and steps (2) through (6) are repeated.
12. The structure is now ready for
metallization. An aluminum film is deposited over the entire surface,
followed by a coating of positive photoresist.
13. The photomask, with the emitter and
base areas opaque, is placed over the photoresist and exposed to UV
light.
14. The photoresist is developed,
leaving the resist over the emitter and base areas.
15. The exposed metallization is etched
away, followed by the removal of the resist over the emitter and base
areas.
16. A passivation layer of silicon
nitride is applied to the circuitry, leaving the bond pads exposed.
17. The silicon planar bipolar
transistor is now complete.
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