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Process for Fabricating Small High Value Capacitors

IP.com Disclosure Number: IPCOM000036402D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Leas, JM: AUTHOR

Abstract

Process techniques are shown in the formation of capacitor dielectric by chemical vapor deposition (CVD) pyrolysis of titanium isopropoxide or the pyrolytic spray deposition of titanium isopropoxide.

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Process for Fabricating Small High Value Capacitors

Process techniques are shown in the formation of capacitor dielectric by chemical vapor deposition (CVD) pyrolysis of titanium isopropoxide or the pyrolytic spray deposition of titanium isopropoxide.

Capacitor size is key in determining the number of dynamic random-access memory cells on a chip since capacitors are the largest user of chip area, requiring about ten times the area of each transistor. By using a high dielectric constant insulating material in a single layer format, or in combination with other layers, a reduction in chip area can be realized and result in a more dense cell configuration.

The dielectric constant of TiO2 (80 along one axis and 180 along a perpendicular axis) is an order of magnitude higher than that of SiO2 (3.9) or Si3N4 (7) and significantly higher than Ta2O5 (22). The dielectric strength of TiO2 is comparable to that of SiO2 and Si3N4 . In addition to amorphous TiO2, there are three crystalline phases: anatase, brookite and rutile. The material can be deposited crystalline, polycrystalline or amorphous. The rutile form of crystalline TiO2 has the highest dielectric constant which varies from 80 to 180, depending upon orientation. Polycrystalline has an intermediate dielectric constant of 110. Rutile is a stable crystal; the other two crystalline phases are not.

A key problem with TiO2 is that if it is deposited in a somewhat reduced state, it acts not like an insulator but like a conductor or a semiconductor. To form a good insulator, TiO2 must be in a highly oxidized state with the proper 1:2 stoichiometric ratio between titanium and oxygen. Reduced and conductive TiO2 is easily detected because it absorbs light and is blue/black in color, while a fully oxidized TiO2 is transparent. The only color is that due to interference in a thin film. Many of the current deposition techniques have the TiO2 deposited in a reduced state which requires a subsequent 900 to 1000@C anneal in a pure oxygen ambient to reoxidize the TiO2 . The anneal has the undesirable effect of growing a layer of SiO2 under the TiO2 which reduces device capacitance due to the series capacitance formed.

When the capacitor dielectric is formed by CVD pyrolysis of titanium isopropoxide, a uniform and pinhole-free layer of TiO2 in a highly oxidized state results. The liquid, titanium isopropoxide, can be vaporized or atomized prior to deposition on the wafer at high temperature. The high purity liquid can be vaporized by heating it and allowing evaporation into a carrier ga...