Process to Increase the Inverse Gain of an NPN Transistor
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
When a transistor is operated in the inverse direction, holes are injected into the epitaxial region because of the low epitaxial dopant concentration. These holes essentially lower the injection efficiency of the inverse device. An N+ guard ring is therefore incorporated to increase the injection for an NPN transistor. The process for making such a high inverse gain NPN transistor is as follows: 1. Form the conventional junction isolation structure, as shown in Fig. 1, wherein the N+ subregion 10 and P+ junction isolation region 12 are in substrate 14, and silicon dioxide layer 16 and silicon nitride layer 18 are located upon the substrate surface. 2. Open the base area in the mask 16, 18 and undercut the layer 16. 3. Deposit molybdenum metal 20 and lift off the metal, leaving the Fig. 2 structure. 4.