Browse Prior Art Database

IMPROVED AL TO CR/SI/N CONTACT RESISTANCE

IP.com Disclosure Number: IPCOM000006632D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-17
Document File: 4 page(s) / 192K

Publishing Venue

Motorola

Related People

Tom Anderson: AUTHOR [+4]

Abstract

For several years thin film resistors composed of chromium, silicon and nitrogen (CrlSi/N) have been used in many Motorola devices. These thin tihn CrlSilN resistors were originally developed to produce sheet resis- tivity, following high temperature anneal, and TCR val- ues compatible with the manufacture of these devices.

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MOTOROLA INC. Technical Developments Volume 16 August 1992

IMPROVED AL TO CR/SI/N CONTACT RESISTANCE

by Tom Anderson, Keenan Evans, Don Warner and James R. Black

INTRODUCTION

  For several years thin film resistors composed of chromium, silicon and nitrogen (CrlSi/N) have been used in many Motorola devices. These thin tihn CrlSilN resistors were originally developed to produce sheet resis- tivity, following high temperature anneal, and TCR val- ues compatible with the manufacture of these devices.

  The primary electrical problems associated with these thin film resistors have been resistivity shis, noted on completed product, and resistivity drift under tempera- ture and bias test conditions. Yield losses of from 10 to 15 percent were estimated due to these problems. A testing procedure, referredf to as the "ZAP" test, which monitors resistor shift caused by contact bum-in after a 60 volt pulse for 500 msec., was therefore developed to contain the problem at final trim and test.

  The root cause for these electrical problems was defmed as a high aluminum to Cr/Si/N contact resist- ance. It was theorized that a layer of oxidized chromium formed on the surface of the Cr/Si/N, preventing good electrical contact to the Al.

  The following presentation describes a new method to remove this layer of oxidized Cr from the surface of the Cr/WN. The effectiveness of this treatment in reduc- ing the Al to Cr/Si/N contact resistance was confrmed via statistical evaluation of factorial experiments which compared previous treatments to the new treatment. Var- ious alternate processing combinations were also included in these experimental designs. These evaluations are discussed in the following presentation. The physical and chemical effects of this new treatment on the actual SW- face of the Cr/Si/N film were characterized and are also summarized.

EXPERIMENTAL

  The following experiments were performed to under- stand the nature of the contact resistance problem and determine the effectiveness of the new process.

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  1.) In order to determine the condition of typical Cr/Si/N fdms, Auger and SIMS characterizations were completed on samples of the CrlSilN fti prior to Al deposition.

  2.) Insofar as it was theorized that removal of a Cr based oxide from the surface of these flms would result in improved aluminum to Cr/SilN contact resistance, etches designed to etch another common Cr based resis- tor, in this case NiCr, were initially researched. The solu- tion chosen for investigation was an 8% acetic acid, 2200 ceric ammonium nitrate and 70% water mixture. Test wafers were used to study the effect of this etch on the initial sheet resistivity of the Cr/Si/N tihn. Five test wafers were fabricated with blanket Cr/Si/N thin Elms and their as deposited sheet resistivity determined. Each wafer was then exposed to the 8% acetic acid, 2200 ceric ammo- nium nitrate and 7000 water mixture for a period rang- ing from 10 to 60 sec. Their sheet resistivity was then...