Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1999-03-08
2001-11-13
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S950000
Reexamination Certificate
active
06316165
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to compositions that reduce reflection of exposing radiation from a substrate back into an overcoated photoresist layer. More particularly, the invention relates to antireflective coating compositions that can be applied as coating layers that are planarizing with respect to an underlying substrate.
2. Background Art
Photoresists are photosensitive films used for transfer of an image to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate. Photoresist compositions in general are known to the art and described e.g. by Deforest,
Photoresist Materials and Processes
, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau,
Semiconductor Lithography, Principles, Practices and Materials
, Plenum Press, New York, ch. 2 and 4.
A major use of photoresists is in semiconductor manufacture where an object is to convert a highly polished semiconductor slice, such as silicon or gallium arsenide, into a complex matrix of electron conducting paths, preferably of micron or submicron geometry, that perform circuit functions. Proper photoresist processing is a key to attaining this object. While there is a strong interdependency among the various photoresist processing steps, exposure is believed to be one of the more important steps in attaining high resolution photoresist images.
Reflection of activating radiation used to expose a photoresist often poses limits on resolution of the image patterned in the photoresist layer. Reflection of radiation from the substrate/photoresist interface can produce spatial variations in the radiation intensity in the photoresist, resulting in non-uniform photoresist linewidth upon development. Radiation also can scatter from the substrate/photoresist interface into regions of the photoresist where exposure is not intended, again resulting in linewidth variations. The amount of scattering and reflection will typically vary from region to region, resulting in further linewidth non-uniformity. Variations in substrate topography also can give rise to resolution-limiting reflection problems.
It thus would be desirable to have new antireflective coating compositions.
SUMMARY OF THE INVENTION
We have found that antireflective coatings generally function optimally at a quarter wave thicknesses over a reflective surface. Accordingly, in many instances, conformal antireflective coatings will be preferred.
However, in certain applications, a conformal coating will be less preferred. For example, where wafer or other substrate topography has vertical steps, the desired quarter wave coating layer thickness can not be maintained. In that situation, use of a planarizing antireflective coating composition will be preferred as it will enable of no variation of resist thickness over the vertical step feature. Such uniform resist thickness will minimize CD variations and potentially enhance available depth of focus by placing all of the resist at the same height. Moreover, use of a planarizing ARC over such topographies enables relatively uniform exposure to the etch process, rather than having the trench center exposing to the antireflective etch during clearing of the sidewalls.
The present invention provides new radiation absorbing compositions suitable for use as antireflective coating compositions (“ARCs”) with photoresist compositions. The ARCs of the invention can be highly planarizing and thus will be useful in applications such as those described above.
In a first aspect of the invention, antireflective compositions are provided that comprise a resin binder component that contains a relatively low molecular weight polymer, e.g. a polymer having an M
w
of about 8,000 daltons or less, more preferably an M
w
of about 7,000, 6,000 or 5,000 daltons or less. Polymers or oligomers having a M
w
of about 4,000, 3000 or 2,000 daltons or less also will be useful in the planarizing ARCs of the invention. Generally, in this aspect of the invention, the low molecular weight resin will have a M
w
of at least about 1,000 or 1,500 daltons. Resins containing acrylate units are often preferred.
It has been found that ARCs of the invention with such low molecular weight resin components can exhibit good planarizing properties upon application to a substrate surface. For example, ARCs of the invention can coat substantial topography such as vertical and sloping steps quite to provide a uniform, planar surface thereover.
In a further aspect of the invention, planarizing ARCs are provided that comprise a relatively low molecular weight plasticizer compound. Preferred plasticizer compounds of ARC compositions of the invention include non-polymeric compounds, although various oligomers also can be employed. Plasticizers for use in the ARCs of the invention typically have a molecular weight of about less than 2,000 or 1,500 daltons, more preferably a molecular weight of less than about 1,000, 800 or 500 daltons. Preferred plasticizers also have sufficient molecular weight to be relatively non-volatile during lithographic processing, e.g. a molecular weight of at least about 150 or 200 daltons, and/or having a boiling point in excess of about 160° C., more preferably in excess of about 180° C. or about 200° C.
For example, suitable plasticizers include anthracene compounds, particularly phenyl or benzyl substituted compounds, e.g. 9-(2′, 4′-dihydroxy-3-methylbenzyl)anthracene; compounds having multiple aryl substitution, particularly multiple phenyl or other carbocyclic aryl substitution such as (3-hydroxypheny;)[bis(3-cyclohexyl-4-hydroxy-6-methylpheny;)]methane; phenolic compounds that may have additional carbocyclic aryl substitution such as 2,6-bis(2′, 4′-dihydroxybenzyl)4-methylphenol; alkyl phthalate compounds such as di(C
2
-C
16
alkyl) phthalate compounds e.g. dioctyl phthalate; and the like. Exemplary oligomers include acrylate oligomers such as oligomers of ethylacrylate/glycidyl acrylate, and the like.
It has been found that ARCs of the invention that contain such a plasticizer compound can exhibit good planarizing properties upon application to a substrate surface, including substrate surface with significant topography such as vertical and sloping steps.
Planarizing ARCs are also provided that combine both such aspects of the invention, i.e. that contain a low molecular weight resin as well as a plasticizer compound.
Crosslinking ARCs of the invention are often preferred. In a crosslinking system, one or more components are capable of some type of reaction that crosslinks or otherwise hardens the applied ARC coating layer. Such crosslinking-type compositions preferably comprise an acid or acid generator compound (e.g. a thermal acid generator) to induce or promote such crosslinking of one or more components of the ARC. Generally preferred crosslinking antireflective compositions comprise a separate crosslinker component such as an amine-based material. The invention also includes antireflective compositions that do not undergo significant cross-linking during intended use with a photoresist composition.
In yet further aspect of the invention, methods for provided for application of planarizing ARC compositions. These methods in general include application of an ARC composition on a substrate, heating the applied ARC coating layer to provide flow of the composition and hence enhanced planarization. The photoresist then can be applied over the ARC layer.
In these methods, if the ARC composition is a crossl
Adams Timothy G.
Barclay George G.
Coley Suzanne
DoCanto Manuel
Pavelchek Edward K.
Corless Peter F.
Duda Kathleen
Edwards & Angell LLP
Frickey Darryl P.
Shipley Company L.L.C.
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