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Browse Prior Art Database

Capacitor Structure for Bipolar Memory Device

IP.com Disclosure Number: IPCOM000052179D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Howard, JK: AUTHOR

Abstract

Some bipolar memory cells require a low-leakage high-capacitance densi capacitor. Described here is a capacitor structure to meet increased requirements of such cells.

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Capacitor Structure for Bipolar Memory Device

Some bipolar memory cells require a low-leakage high-capacitance densi capacitor. Described here is a capacitor structure to meet increased requirements of such cells.

The device requirements include N/+/ poly Si contact to the N+,emitter, as shown in Fig. 1. The N/+/ poly thickness is approximately 1500 Angstrom. The capacitor must be designed around this bottom poly Si electrode.

Next, hafnium (Hf) metal is evaporated or sputtered to coat the N+ poly, prior to reactive sputtering or RF sputtering of HfO(2) (hafnium dioxide), as shown in Fig. 2. The Hf layer is approximately 1000 Angstroms, and the HfO(2) is approximately 300-600 A thick. The top electrode Al or Au is deposited over the HfO(2) to complete the capacitor. The films are usually annealed in O(2) prior to Al (top electrode evaporation).

Experiments have shown that if the Hf film is not included in Fig. 2, oxygen diffuses through HfO and oxidizes the Npoly. This decreases the capacitance because of the low dielectric constant of SiO(2). The Hf layer also planarizes the Npoly surface which reduces the number of breakdown sites. A reactively sputtered HfO(2) film (540 Angstroms) over 1000 A of Hf yields an average capacitance of 640 picofarads, and leakage of less than 10/-12/ amperes up to 5 volts. Typical cell requirements would be 700 picofarads and 10/-9/ amperes up to 3-4 volts (aluminum electrodes). A 300 Angstroms HfO(2) film yields 904 picofarads and...