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Effecting a High Collector Doping Gradient

IP.com Disclosure Number: IPCOM000093442D
Original Publication Date: 1967-Sep-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Collins, TW: AUTHOR

Abstract

This transistor fabrication process provides a high doping gradient at the collector junction. The resulting transistor has a higher F(T) by virtue of the reduced base width spreading. In Step 1 a semiconductor wafer is prepared having a background N-type doping level as shown. A P-type dopant is then predeposited in Step 2 on the surface of the wafer in a conventional manner.

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Effecting a High Collector Doping Gradient

This transistor fabrication process provides a high doping gradient at the collector junction. The resulting transistor has a higher F(T) by virtue of the reduced base width spreading. In Step 1 a semiconductor wafer is prepared having a background N-type doping level as shown. A P-type dopant is then predeposited in Step 2 on the surface of the wafer in a conventional manner.

Heat is applied in Step 3 to drive the predeposited P dopant into the wafer. The time and temperature of the diffusion, together with the nature of the drive-in, are selected to obtain a more or less even doping level for a given depth with an abrupt drop off as shown for Step 3. Ion implantation can also be used to obtain a profile such as this.

The emitter diffusion of N-type dopant is then performed as in Step 4. The relatively higher concentration of N-type impurity near the surface of the wafer results in a net N-type doping to provide the emitter region as shown in the profile for the final device. The N-type concentration decreases with the depth into the wafer. At some point the P-type impurity predominates to create the emitter- base junction.

The emitter diffusion extends to a depth greater than the emitter-base junction, even though the P-type base impurity concentration is greater and therefore predominates. Still further below the surface, the concentration of the P-type base drops quite sharply. The collector-base junction is created...