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Process to Improve Electrical Properties of Metal Oxide Capacitor Materials

IP.com Disclosure Number: IPCOM000051584D
Original Publication Date: 1981-Feb-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 74K

Publishing Venue

IBM

Related People

Howard, JK: AUTHOR

Abstract

High density memory programs may require a capacitor structure with an E ratio of 0.04 or greater (Ta(2)O(5), E=23, where E=dielectric constant; t/t/= 625 angstroms oxide thickness). The capacitance/area valve should be 3.5 f/f/mu/2/ (718 pF for a(9)20 mil. dot); the leakage current should be less than or equal to 10 amps at 1 volt. It is important that these properties be maintained during device processing; the maximum temperature is approximately 350 degrees C for glassing and chip reflow. However, the maximum working temperature for Ta(2)O(5) (and other dielectric materials) is 200 degree Temperatures above 200 degrees C cause irreversible increases in capacitance, dissipation factor, temperature coefficient of capacitance, and, most importantly, DC leakage current (M. H. Rotterman, et al., Proc.

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Process to Improve Electrical Properties of Metal Oxide Capacitor Materials

High density memory programs may require a capacitor structure with an E ratio of 0.04 or greater (Ta(2)O(5), E=23, where E=dielectric constant; t/t/= 625 angstroms oxide thickness). The capacitance/area valve should be 3.5 f/f/mu/2/ (718 pF for a(9)20 mil. dot); the leakage current should be less than or equal to 10 amps at 1 volt. It is important that these properties be maintained during device processing; the maximum temperature is approximately 350 degrees C for glassing and chip reflow. However, the maximum working temperature for Ta(2)O(5) (and other dielectric materials) is 200 degree Temperatures above 200 degrees C cause irreversible increases in capacitance, dissipation factor, temperature coefficient of capacitance, and, most importantly, DC leakage current (M. H. Rotterman, et al., Proc. 27th Electronic Components Conf., 1977, page 462). Ta(2)O(5) capacitors can be fabricated, which are stable to 350 degrees C, by adding approximately 20-25 at % nitrogen to the oxide. However, nitrogen addition causes a decrease in capacitance density (dielectric constant) by 20-25% approximately, and is therefore undesirable where E/(t) >/- 0.04 requires a large E valve.

A process is described here to extend the temperature region of capacitor stability from 200 degrees C to >/~ 350 degrees C.

A Ta(2)O(5) layer 500 angstroms thick was deposited by reactive sputtering. The cross-section is shown in Fig. 1.

The average capacitance after deposition was 864+/-62 pF; the leakage current was approximately 10/-10/ amps at 1 volt. The effect of annealing this structure in an inert environment (forming gas, argon, vacuum, etc.) is shown in Fig. 2. The average capacitance (20 samples) increases during annealing at 300 degrees C and 350 degrees C (c > 1000 pF). Howev the leakage current is 1.5 X 10/-7/ amps at 1 volt following the 350 degrees C anneal (1(/N) spec is 10/-9/ amps at 1 volt).

This process yields data similar to that found i...