Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Processing feature prior to imaging
Reexamination Certificate
1998-12-04
2001-06-12
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Processing feature prior to imaging
C430S311000, C430S313000, C216S052000, C216S067000
Reexamination Certificate
active
06245493
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to reducing reflectivity of surfaces in order to facilitate lithography.
BACKGROUND OF THE INVENTION
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down device dimensions at submicron levels on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller feature sizes are required. This may include the width and spacing of interconnecting lines and the surface geometry such as comers and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Present techniques in optical projection printing can resolve images of sub-micron when photoresists with good linewidth control are used. However, reflection of light from substrate/resist interfaces produce variations in light intensity and scattering of light in the resist during exposure, resulting in non-uniform photoresist linewidth upon development.
Constructive and destructive interference resulting from reflected light is particularly significant when monochromatic or quasi-monochromatic light is used for photoresist exposure. In such cases, the reflected light interferes with the incident light to form standing waves within the resist. In the case of highly reflective substrate regions, the problem is exacerbated since large amplitude standing waves create thin layers of underexposed resist at the wave minima. The underexposed layers can prevent complete resist development causing edge acuity problems in the resist profile.
Antireflective coatings are known and used to mitigate the aforementioned problems, however, the use thereof presents additional problems such as, for example, introduction of particulate contamination, requirement of tight temperature tolerances during production, etc.
SUMMARY OF THE INVENTION
The present invention relates to a method of reducing reflectivity of an underlayer surface to be covered by a resist. The reflectivity of the surface is reduced by roughening (e.g., dulling) the surface so that it is less reflective. Reducing reflectivity of the surface mitigates destructive and constructive interference and standing waves resulting from light reflected therefrom. The surface roughening is accomplished via a plasma etch process to create a plurality of divots (or roughness profile) in the surface. The roughening of the surface makes the surface substantially less reflective. Light incident to the roughened surface is diffused to such a degree that the aforementioned problems associated with resist damage resulting from reflected light is mitigated. Furthermore, the present invention does not require the use of anti-reflective coatings, and thus avoids many of the problems associated with using anti-reflective coatings.
In accordance with one specific aspect of the invention, a method for creating a roughened surface on an underlayer material is provided. The method includes the steps of: roughening the surface of the underlayer via a plasma etch; subsequently forming a photoresist on the underlayer; and exposing the photoresist to light to form a pattern.
Another aspect of the invention relates to a method of mitigating damage to a photoresist formed on an underlayer. The method includes the step of: using an underlayer having a roughened surface which diffuses light incident to the underlayer, the incident light being diffused to such a degree that the diffused beams of light result in insubstantial damage to the photoresist.
Yet another aspect of the present invention relates to an underlayer which mitigates damage to a photoresist layer formed on the underlayer. The underlayer includes a reflective material; and a roughened surface formed on a surface of the underlayer, the roughened surface diffusing light incident to the underlayer so that the diffused light is of an intensity which results in minimal damage to the photoresist, the roughened surface formed via a plasma etch.
In accordance with another aspect of the present invention, a method for creating a roughened surface on an oxide layer is provided. The method includes forming an oxide layer over an underlayer material; creating a roughened surface on a surface of the oxide layer via a plasma etch process; subsequently forming a photoresist on the oxide layer; and exposing the photoresist to light to form a pattern.
Another aspect of the present invention relates to a method for creating a roughened surface on an oxide layer serving as an anti-reflective coating for an underlayer. The method includes the steps of: using a plasma etch process to form the roughened surface, the plasma etch process including using argon as a reactant gas, the roughened surface being tailored to diffuse light incident to the oxide layer such that the diffused light does insubstantial damage to a photoresist formed on the oxide layer.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
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“Limiting Reflectivity in Al-Cu Films”, IBM Technical Disclosure Bulletin, NN 79054832, abstract, May 1979.
Lyons Christopher F.
Rangarajan Bharath
Singh Bhanwar
Templeton Michael K.
Yedur Sanjay K.
Amin & Turocy LLP
Barreca Nicole
Huff Mark F.
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