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Diffused Resistor Underpass Combinations

IP.com Disclosure Number: IPCOM000090670D
Original Publication Date: 1969-Jun-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Craig, WJ: AUTHOR

Abstract

An additional diffusion opening during an isolation diffusion in the fabrication of integrated circuits can be used to alter the resistance value of diffused resistors. This is effected without changing the resistor configuration. Drawing A shows P type substrate 10 into which N+ subcollector layer 11 is diffused and on which N type epitaxial layer 12 is grown. Heavily doped P+ type isolation areas 14 are provided by diffusing boron or another acceptor impurity through openings 16 in SiO(2) layer 18. Additional opening 20 is provided for the diffusion of P+ area 22. This serves to alter the value of resistor 24, drawing B, subsequently diffused at least partially over area 22. After diffusion of resistor 24, the configuration of drawing B is obtained, with area 22 acting as a shunt over part of resistor 24.

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Diffused Resistor Underpass Combinations

An additional diffusion opening during an isolation diffusion in the fabrication of integrated circuits can be used to alter the resistance value of diffused resistors. This is effected without changing the resistor configuration. Drawing A shows P type substrate 10 into which N+ subcollector layer 11 is diffused and on which N type epitaxial layer 12 is grown. Heavily doped P+ type isolation areas 14 are provided by diffusing boron or another acceptor impurity through openings 16 in SiO(2) layer 18. Additional opening 20 is provided for the diffusion of P+ area 22. This serves to alter the value of resistor 24, drawing B, subsequently diffused at least partially over area 22. After diffusion of resistor 24, the configuration of drawing B is obtained, with area 22 acting as a shunt over part of resistor 24. The P type diffused resistor 24 normally has a resistivity of about 200 ohms per square, while P+ area 22 has a much lower resistivity, typically about 2.5 ohms per square, due to the higher doping levels in area 22. The integrated circuit is completed by the deposition of SiO(2) passivating layer 26 and aluminum conducting lines 28 which make contact to resistor 24 through via holes 30. The value of resistor 24 can be altered over a wide range by altering the size of opening 20 through which P+ area 22 is diffused. This technique allows resistor values in integrated circuits to be changed with only a single mask change...