Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-05-26
2001-09-11
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
Reexamination Certificate
active
06288404
ABSTRACT:
TECHNICAL FIELD
The invention relates to a device used in lithography in microchip fabrication, and more particularly to a device which performs lithography by manipulating an electric field in close proximity to a resist.
BACKGROUND OF THE INVENTION
Microchip fabrication is a cornerstone of modern technology. As integrated circuits (“ICs”) have become staple items in devices in all areas, the fabrication process for ICs has developed rapidly. Central to the fabrication process is the patterning of a substrate in accordance with the configuration of a desired feature set.
Conventional patterning typically utilizes photolithography in the patterning process. Multiple forms of photolithography are commonly used. Each includes several similar basic steps. A photoresist film is applied to a substrate surface to be patterned. Photoresist is a light-sensitive material that has properties which change upon exposure to light. A mask is then aligned to the substrate. The mask contains a pattern of the desired pattern to be transferred to the substrate. The photoresist film is then exposed to light, where the mask obscures portions of the photoresist from the light. A developer or solvent is then applied to remove a portion of the photoresist, according to the reaction of the photoresist to exposure. An etchant is applied again to pattern the substrate through the holes formed in the photoresist. Finally, any remaining photoresist is stripped away, leaving a patterned substrate.
A significant limitation of photolithography is the resolution capability of optical photolithography. The smallest openings which are created are limited by the smallest areas which can be defined by the mask and exposure on the photoresist. Conventional photolithography is typically limited to about 125 to 200 micrometers. As resolution capability improves, the number of devices which may be included in a single IC increases, improving the efficiency and performance of the IC. In addition, improved resolution capability typically raises wafer yield.
Alternate forms of resist may be used in lithographic processes. Photoresist changes in response to exposure to light. Other resists change in response to different events. Some resists alter in response to an electric field applied to the resist.
Accordingly, the inventors have determined that it would be desirable to provide a device for lithography which has an improved resolution capability relative to conventional photolithography technology using modification of an electric field to alter a resist for lithographic patterning.
SUMMARY
A lithographic device of the preferred embodiment provides patterning of a resist through manipulation of an electric field at an evanescent field level.
One known way to alter an electric field is to illuminate a tip of a probe with a laser. The tip used is typically of a nanometer scale, or even better, atomically sharp. In an area near the tip, the electric field becomes stronger under illumination. The electric field is particularly strong within the near field of the tip, decaying rapidly with distance from the tip. Thus, a spatially very small electric field may be manipulated in this way.
In one embodiment, a nanometrically fine tip of a scanning probe is brought into close proximity of a surface of a resist to be patterned. The resist is sensitive to variations in electric fields, similar to a photoresist's sensitivity to light exposure. A laser illuminates the tip, creating a modified electric field in the evanescent field surrounding the tip. The modified electric field alters the resist's properties in the portion of the resist which coincides with the position of the modified electric field. The tip is moved across the surface of the resist according to a pattern, such that a desired portion of the resist is altered.
In another embodiment, a nanometrically fine tip of a scanning probe is brought into close proximity with an upper surface of a resist to be patterned. Again, the resist is sensitive to variations in electric fields. A laser permeates the resist from the lower side at an angle less than the critical angle, such that substantially no light penetrates the upper surface. A tunneling effect is created by the close proximity of the tip to the upper surface of the resist. The tunneling effect modifies the electric field in the evanescent field surrounding the tip. The modified electric field alters the resist's properties in the portion of the resist which coincides with the position of the modified electric field. The tip is moved across the surface of the resist according to a pattern, such that a desired portion of the resist is altered.
REFERENCES:
patent: 5464977 (1995-11-01), Nakagiri et al.
patent: 5743998 (1998-04-01), Park
patent: 6078055 (2000-06-01), Bridger et al.
Bridger Paul M.
McGill Thomas C.
California Institute of Technology
Fish & Richardson P.C.
Nguyen Kiet T.
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