Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-06-15
2004-03-16
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S326000, C430S926000
Reexamination Certificate
active
06706461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to new photoresist compositions especially for deep U.V. (particularly 248 nm) and I-line (365 nm) exposures and having the capability of forming highly resolved features.
2. Background Art
Photoresists are photosensitive films for transfer of images to a substrate. They form negative or positive images. After coating a photoresist on a substrate, the coating is exposed through a patterned photomask to a source of activating energy such as ultraviolet light to form a latent image in the photoresist coating. The photomask has areas opaque and transparent to activating radiation that define a desired image to be transferred to the underlying substrate. A relief image is provided by development of the latent image pattern in the resist coating. The use of photoresists is generally described, for example, by Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York (1975), and by Moreau, Semiconductor Lithography, Principals, Practices and Materials, Plenum Press, New York (1988).
An important property of a photoresist is image resolution. A developed photoresist image of fine line definition, including lines of sub-micron and sub-half micron dimensions and having vertical or essentially vertical sidewalls is highly desirable to permit accurate transfer of circuit patterns to an underlying substrate. However, many current photoresists are not capable of providing such highly resolved fine line images.
For example, 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 variations in the radiation intensity in the photoresist during exposure, 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 give rise to resolution-limiting reflection problems. Any image on a substrate can cause impinging radiation to scatter or reflect in various uncontrolled directions, affecting the uniformity of photoresist development. As substrate topography becomes more complex with efforts to design more complex circuits, the effects of reflected radiation become more critical. For example, metal interconnects used on many microelectronic substrates are particularly problematic due to their topography and regions of high reflectivity.
With recent trends towards high-density semiconductor devices, there is a movement in the industry to shorten the wavelength of exposure sources to deep ultraviolet (DUV) light (300 nm or less in wavelength) including excimer laser light (ca. 248 nm) and ArF excimer laser light (193 nm). The use of shortened wavelengths of light for imaging a photoresist coating has resulted in greater penetration of the photoresist layer and increased reflection of the exposing energy back into the photoresist layer. Thus, the use of the shorter wavelengths has exacerbated the problems of reflection from a substrate surface.
Many existing exposure tools are designed for imaging with relatively longer wavelengths, e.g. I-line (ca. 365 nm) wavelengths. However, advanced resists designed for imaging at shorter wavelengths such as 248 nm often can not be effectively exposed with an I-line exposure because the resist's photoactive component is not activated at 365 nm or other higher wavelengths. This requires design and supply of additional resist compositions that can be effectively imaged at selected wavelengths.
It thus would be desirable to have new photoresist compositions that could provide highly resolved fine line images, including images of sub-micron and sub-half micron dimensions. It would be further desirable to have such new photoresist compositions that could be imaged with deep U.V. radiation as well as other wavelengths, particularly 365 nm. It would be particularly desirable to have such photoresists that reduce undesired reflections of exposure radiation.
SUMMARY OF THE INVENTION
The present invention provides new photoresist compositions that in general comprise a resin binder, a photoactive component, particularly a photoacid generator compound, and a relatively low molecular weight dye material that contains an anthracene group.
We have surprisingly found that the dye compounds of photoresists of the invention can significantly reduce or even eliminate undesired reflections of exposure radiation, particularly deep U.V. exposure radiation such as 248 nm. Use of the dye compounds also provides significantly enhanced resolution and masking linearity of developed resist images. See, for instance, the results and comparative data disclosed in Example 4 which follows.
It also has been found that dye compounds of the invention function as I-line sensitizer compounds, enabling effective imaging of the resists at higher wavelengths, particularly I-line exposures, whereas the resists are not photoactivated and do not form acceptable relief images in the absence of the dye compound. See, for instance, the results of Example 5 which follows. While not being bound by theory, it is believed the anthracene dye compound can effectively absorb 365 nm radiation, and then transfer that energy in a form effective to activate a deep U.V. photoactive component.
It also has been found that preferred dye compounds of the invention as formulated in a photoresist are surprisingly resistant to undesired sublimation during resist processing conditions. More particularly, it has been found that many anthracene monomers can sublime out of a photoresist coating layer during pre-exposure softbake step, decreasing the anthracene concentration in the resist coating layer in an uncontrolled manner, which can compromise lithographic performance. In contrast, preferred dye compounds of the invention do not significantly sublime during resist processing such as pre-exposure soft-bake and post-exposure bake steps. See, for instance, the results of Example 6 which follow.
It also has been found that preferred dye compounds of the invention, particularly compounds that are reaction products of a phenyl compound such as phenol and an anthracene monomer, exhibit substantially greater absorbance of 248 nm radiation relative to use of a simple anthracene monomer such as 9-anthracenemethanol. See, for instance, the results of Example 6 below. Thus, dye compounds of the invention can be used in relatively low concentrations, which can provide enhanced lithographic results such as less potential occurrence of residues and scumming after development.
As used herein, the term “dye compound”, “anthracene dye compound” or other similar term refers to the compound whether it functions to reduce undesired reflections of exposure radiation, or to sensitize a resist to higher wavelength exposure wavelengths such as 365 nm.
Preferred dye compounds of resist compositions of the invention are non-polymeric molecules that have a molecular weight about less than 1,500 or 1,000 daltons, more preferably a molecular weight of less than about 800 or 500 daltons. Generally preferred dye compounds include those that are a reaction product of an optionally substituted anthracene compound (e.g. haloalkylanthracene, alkanolanthracene or other reactive anthracene compound) and another optionally substituted aromatic compound such as an optionally substituted phenolic compound. Even more preferred are such anthracene dye compounds that have one or more hydroxyl groups, preferably 1 to about 3 hydroxyl groups that can facilitate formation of a homogenous photoresist solution.
The invention further provides methods for forming photoresist relief images and novel articles of manufacture comprising substrates such as a microelectro
Sinta Roger F.
Zydowsky Thomas M.
Chu John S.
Corless Peter F.
Edwards & Angell LLP
Frickey Darryl P.
Shipley Company L.L.C.
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