Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-04-29
2001-08-21
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06277527
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to masks employed in photolithography processes used to make microelectronic components and, in particular, to a phase shift mask for such photolithography.
2. Description of Related Art
In producing microelectronic contacts and wiring on wafers using photolithographic processes, a major concern is how to print the smallest lines onto the wafer using optics.
Chrome or other light blocking materials used on masks have limitations at the line width where conventional resolution is lost, and may not be used below these line widths, presently about 0.2 microns. Moreover, the masks are sensitive to defects therein.
Phase shift masks have been well known wherein etching and/or additive methods have been used to impart a phase shift to light passing through the mask, for example, in U.S. Pat. Nos. 5,342,713 and 5,549,995. However, such phase shift masks have not been used to create images without use of chrome or other blocking material.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a photolithographic mask which has improved capability to produce printable images at or below the limit of optical resolution of the photolithographic process.
It is another object of the present invention to provide a photolithographic mask which is not subject to the limitations of imaging conventional chrome blocking layers.
A further object of the invention is to provide a simplified phase shift mask and method of making such mask which is less sensitive to mask defects.
It is yet another object of the present invention to provide a photolithographic mask which is of simpler design.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a photolithographic mask comprising a first plurality of image segments imparting a predetermined phase shift with respect to electromagnetic radiation of a predetermined frequency and a second plurality of image segments imparting a phase shift of 180° more or less than the phase shift of the first plurality of image segments with respect to the predetermined electromagnetic radiation. The first and second segments are disposed on a substrate and positioned such that an intersection of the predetermined electromagnetic radiation passing through the segments causes printable images to be created below the substrate when exposed to the predetermined electromagnetic radiation. Preferably, the first and second plurality of image segments are etched into a surface of the substrate at different levels below the surface. In one embodiment, the first plurality of image segments impart a phase shift of 90° with respect to the electromagnetic radiation of a predetermined frequency and the second plurality of image segments impart a phase shift of 270° with respect to the electromagnetic radiation of a predetermined frequency.
In another aspect, the present invention provides a photolithographic mask comprising a substrate adapted to permit transmission of electromagnetic radiation therethrough, the substrate having a surface, a first region on the substrate at a level below the surface adapted to impart a predetermined phase shift with respect to the electromagnetic radiation, and a second region on the substrate at a different level below the surface adapted to impart a phase shift of 180° more or less than the phase shift of the first region with respect to the electromagnetic radiation. The second region is adjacent the first region and forms a desired configuration such that, upon transmission of the electromagnetic radiation through the substrate and the first and second regions, the radiation interferes so as to cause printable images corresponding to the configuration to be created below the substrate when exposed to the electromagnetic radiation. Preferably, the first region imparts a phase shift of about 90° with respect to the electromagnetic radiation and the second region imparts a phase shift of about 270° with respect to the electromagnetic radiation.
The first and second segments or regions may be positioned directly adjacent each other on the substrate and may also contact each other on the substrate. Preferably, the first and second segments or regions are positioned directly adjacent each other on the substrate without an intervening blocking material for the electromagnetic radiation of a predetermined frequency.
The mask may further include a blocking material for the electromagnetic radiation adjacent at least one of the first and second segments or regions. Such blocking material may be of a configuration adapted to cause a printable image to be created below the mask when exposed to the predetermined electromagnetic radiation. The first and second segments or regions may intersect along lines or points of a desired configuration such that the printable images conform to the lines or points, respectively.
In a related aspect, the present invention provides a method of producing a photolithographic mask comprising providing a substrate and creating in the substrate a first and second plurality of image segments. The first plurality of image segments imparting a predetermined phase shift with respect to electromagnetic radiation of a predetermined frequency and the second plurality of image segments imparting a phase shift of 180° more or less than the phase shift of the first plurality of image segments with respect to the predetermined electromagnetic radiation. The second segments being positioned adjacent the first segments such that printable images may be created below the substrate, when exposed to the predetermined electromagnetic radiation, at an intersection of the first and second segments.
Preferably, the method is performed by etching the first and second plurality of image segments into a surface of the substrate at different levels below the surface. More preferably, the first plurality of image segments are etched to impart a phase shift of 90° with respect to the electromagnetic radiation of a predetermined frequency and the second plurality of image segments are etched to impart a phase shift of 270° with respect to the electromagnetic radiation of a predetermined frequency.
In a further aspect, the present invention relates to a method of creating an image comprising providing a photolithographic mask having a first plurality of image segments imparting a predetermined phase shift with respect to electromagnetic radiation of a predetermined frequency and a second plurality of image segments imparting a phase shift of 180° more or less than the phase shift of the first plurality of image segments with respect to the predetermined electromagnetic radiation. The first and second segments are positioned adjacent each other on a substrate. The method then includes transmitting the predetermined electromagnetic radiation through the first and second image segments such that printable images are created at an intersection of the radiation below the substrate.
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Liebmann Lars W.
O'Grady David S.
DeLio & Peterson LLC
International Business Machines - Corporation
Reynolds Kelly M.
Rosasco S.
Walter, Jr. Howard J.
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