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One-Mask Polysilicon Resistor

IP.com Disclosure Number: IPCOM000051947D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Leas, JM: AUTHOR [+3]

Abstract

This article describes a technique to make high valued P type resistors with low temperature and voltage coefficients in any bipolar process technology using only one mask per resistor implant type. The process is also found to give a resistor uniformity of +/-10% up to 30 K omega/ and is readily implementable in any 2 mu epitaxial bipolar technology. The structure fabricated with the process is shown in the figure.

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One-Mask Polysilicon Resistor

This article describes a technique to make high valued P type resistors with low temperature and voltage coefficients in any bipolar process technology using only one mask per resistor implant type. The process is also found to give a resistor uniformity of +/-10% up to 30 K omega/ and is readily implementable in any 2 mu epitaxial bipolar technology. The structure fabricated with the process is shown in the figure.

There is a need for very high valued resistors for large-scale integration of semiconductor circuits. The present practice of making high valued resistors in single crystal silicon cannot be used for fabricating very high valued resistors. For such resistors, the required boron doping becomes comparable to the background epi doping (~10/16/) and the resistor tolerances become unacceptable to circuit operations. For a 4 K omega/square resistor, the resistor tolerances become +/-14%, and for K omega/square ion-implanted sheet resistances the tolerance is +/-18%. Mor the temperature coefficient of the single crystalline resistors in general is high, affecting circuit performance. For example, the TCR value amounts to as much as 0.5%/ degrees C for a 4 K omega/square implant and 0 for a 6 K omega/square implant. A 0.5%/ degrees C temperature coefficient for a resistor means a 30% tolerance value on the resistor values at 85 degrees C.

After initial oxide growth of about 500 nm, a P type isolation diffusion of about 50 omega/square is made, followed by a recessed oxide growth of about 1000 nm. After an appropriate reach-through diffusion of about 20 to 30 ohms/square, a base dif...