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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