Magnetically patterned etch mask

Details Magnetically patterned etch mask Magnetically patterned etch mask

1998-05-14

2001-01-16

Gulakowski, Randy (Department: 1746)

Etching a substrate: processes

Masking of a substrate using material resistant to an etchant

Resist material applied in particulate form or spray

C427S547000

Reexamination Certificate

active

06174449

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to etch masks and their formation, and more particularly to etch masks for formation of emitter tips for field emission displays.
BACKGROUND OF THE INVENTION
In the microelectronics industry, there is a movement toward creating flat panel displays. These displays have the advantage of being significantly more compact than cathode ray tube displays, e.g., conventional computer monitors. There are different types of flat panel displays, such as liquid crystal displays (“LCDs”), gas-plasma displays, thin film transistor (“TFT”) displays, and field emission displays (“FEDs”). FEDs are particularly well-suited to applications requiring high resolution, low power, wide viewing angle, and environmental robustness.
FEDs are able to achieve high resolution owing in part to the presence of a significant number of emitter tips concentrated in a small space. These emitter tips, or cold cathode field emitter tips, and their formation are described in U.S. Pat. Nos. 5,391,259, 5,358,908, 5,151,061, among others.
Owing to recent advancements in photolithography and microlithography (hereinafter collectively referred to as “lithography”), many emitter tips may be formed within a given area, which allows for increased resolution capabilities of FEDs.
However, this increased resolution is not without a price. Lithography, especially at or below a one micron topographic structure dimension, requires expensive equipment and process steps. These steps often include using a reticle or pattern to form a patterned mask layer on a substrate. This patterning is conventionally achieved by exposing the reticle to energy to transfer a reticle image onto layer of resist on the substrate. Owing to the costly nature of the above-described “resist formed mask” step, it would be desirable to avoid it.
One approach to avoid a resist mask step is found in U.S. Pat. No. 4,407,695 entitled “Natural Lithographic Fabrication of Microstructures Over Large Areas” to Deckman et al. (“Deckman et al. '695”). Deckman et al. '695 describes forming a mask by depositing a monolayer of colloidal particles on a substrate. The particles may be arranged in the monolayer as an array. The array serves as a lithographic mask for etching the substrate. As the balls or particles are packed together, they form emitter tips in the substrate when etched. However, gaps between particles may not always be uniform, so resulting emitter tips will not be uniform.
Another approach to avoid a resist mask step for forming field emitter tips is found in U.S. Pat. No. 5,399,238 entitled “Method of Making Field Emission Tips Using Physical Vapor Deposition of Random Nuclei As Etch Mask” to Kumar (“Kumar '238). Kumar '238 describes vapor deposition of randomly located, discrete nuclei. The nuclei are deposited on a emitter tip material, and form a discontinuous etch mask thereon. Using an ion etch, the emitter tips are formed with aid of the nuclei etch mask. However, such deposition does not preclude agglomeration of nuclei, and so resulting emitter tips will not be uniform.
Therefore, it would be desirable to provide a method of non-lithographically forming an etch mask, which does not produce significant non-uniformity in the subsequent formation of emitter tips.
SUMMARY OF THE INVENTION
The present invention includes processes for forming an etch mask, and is particularly suited for use in defining field emission tips for a field emission display. In such a process, a plurality of masking objects in combination with a matrix medium are disposed on a substrate assembly. The matrix medium facilitates maintaining the masking objects on the substrate assembly, as well as reducing unwanted movement of the masking objects with respect to one another. In other words, movement of the masking objects is restricted by a matrix medium. Moreover, the masking objects may sink in, be suspended in, or float on the matrix medium. The masking objects and the matrix medium are then subjected to a magnetic field. The magnetic field causes agglomeration or clustering of the masking objects to be reduced. This reduction in clustering facilitates forming a discrete structure under each masking object, and in particular, forming discrete emitter tips for a field emission display. Importantly, the above-described process of forming a mask may be done in a non-lithographic manner. By non-lithographic it is meant that masking objects are dispensed on a substrate assembly and moved about thereon without any microlithographic and/or photolithographic step.


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