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Patterning of Cathode Element Arrays by Reactive Ion Etching

IP.com Disclosure Number: IPCOM000045705D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 16K

Publishing Venue

IBM

Related People

Krongelb, S: AUTHOR

Abstract

Cathode element arrays can be patterned with good edge definition as required for their use in cathode ray display tubes. The use of reactive ion etching avoids the patterning limitations and environmental problems of wet chemical processing. This is a process for patterning a multilayer structure of Ti/Mo/W (by reactive ion etching) compatible with the requirements of an electron-emitting cathode, to produce good pattern definition and highly insulating moats between required parts of the pattern. Conditions for forming an appropriate nickel stencil and for carrying out the reactive ion etch process so as to achieve the desired results are described.

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Patterning of Cathode Element Arrays by Reactive Ion Etching

Cathode element arrays can be patterned with good edge definition as required for their use in cathode ray display tubes. The use of reactive ion etching avoids the patterning limitations and environmental problems of wet chemical processing. This is a process for patterning a multilayer structure of Ti/Mo/W (by reactive ion etching) compatible with the requirements of an electron-emitting cathode, to produce good pattern definition and highly insulating moats between required parts of the pattern. Conditions for forming an appropriate nickel stencil and for carrying out the reactive ion etch process so as to achieve the desired results are described.

Fabrication of an array of cathode elements requires patterning a multilayer thin film structure consisting of layers of Ti, Mo and possibly W. Final dimensions in the pattern range between 5 and 10 Mum. It is extremely difficult to achieve these dimensions and maintain good edge definition by the traditional wet chemical approach, especially in the presence of the electrochemical effects which arise from the presence of three different layers of metallurgy (1). Wet chemical processing has environmental problems of use and disposal of liquid reagents. This process uses reactive ion etching to pattern elements and teaches critical steps necessary to carry out the process.

Fabrication of cathode elements typically requires etching a multilayer structure consisting of 120 nm Ti, 800 nm Mo and 80 nm Ti, all on a sapphire substrate. Alternatively, it may be required to etch 200 nm Ti, 100 nm Mo and 390 nm W on the same substrate. A constraint is that materials used in the process must not be detrimental to cathode electron emission.

The above materials can be etched by reactive ion etching in a CF plasma, and using permalloy (80:20NiFe) as a mask (2). However, the Fe from the permalloy has deleterious effects on the cathode. Ni, which is compatible with the cathode, is an effective mask, and its etching behavior and masking capabilities in a CF plasma are similar to that of permalloy.

Previous work (2) on the use of a permalloy etch mask used samples cooled by thermally bonding them to the water-cooled cathode with a Ga-In mixture. This approach cannot be used to make cathode elements since residual traces of Ga or In may adversely affect electron emission from the cathode and/or leakage across the moat. This process does not use thermal bonding of the sample to the cathode to improve cooling.

The conditions and procedures necessary to achieve the desired results in the absence of substrate cooling are disclosed and explained in the following process steps: (a) Mask Formation.

First, the desired mask pattern is formed by lift-off evaporation. The appropriate pattern is formed in photoresist which has been treated ith chlorobenzene, as aught by Hatzakis, et al. 3J) and a layer of i of the desired thickness is evaporated. The phot...