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
2002-05-08
2004-10-12
Huff, Mark F. (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
C430S311000, C430S313000, C430S326000, C430S271100, C430S286100, C430S287100, C430S905000, C430S907000, C430S909000, C430S910000, C430S914000
Reexamination Certificate
active
06803171
ABSTRACT:
BACKGROUND
The present invention relates generally to photoimageable compositions. In particular, the present invention relates to photoimageable silsesquioxane compositions.
Photoresists are photosensitive films used for transfer of images 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.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable agents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For positive-acting photoresists, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. In general, photoresist compositions include at least a resin binder component and a photoactive agent.
More recently, chemically-amplified type resists have been increasingly employed, particularly for formation of sub-micron images and other high performance applications. Such photoresists may be negative-acting or positive-acting and generally include many crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In the case of positive chemically-amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain “blocking” groups pendant from a photoresist binder, or cleavage of certain groups comprising a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,581; 4,810,613; and 4,491,628 and Canadian Patent Application 2,001,384. Upon cleavage of the blocking group through exposure of a coating layer of such a resist, a polar functional group is formed, e.g. carboxyl or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer. See also R. D. Allen et al.
Proceedings of SPIE
, 2724:334-343 (1996); and P. Trefonas et al.
Proceedings of the
11
th
International Conference on Photopolymers
(
Soc. of Plastics Engineers
), pp 44-58 (Oct. 6, 1997).
The increasing density of integrated circuits has created a need for higher resolution patterning capabilities. One method of improving resolution involves using a shorter wavelength light during pattern formation. Shorter wavelengths of approximately 200 to 280 nm may be obtained by using a deep UV (“DUV”) source such as a mercury/xenon (“Hg/Xe”) lamp with appropriate filters. Additionally, KrF (248 nm) or ArF (193 nm) excimer lasers may be used as exposure sources. However, at shorter wavelengths the depth of focus of the exposure tool, which may be an excimer stepper, or step and scan tool, may be adversely affected. The depth of focus (“DOF”) is an expression of the range of distances from the image focal plane through which the projected image remains in subjectively acceptable focus. DOF is related to wavelength and lens numerical aperture according to the formula: DOF &agr;&lgr;/2(NA)
2
where &lgr; is the wavelength of exposing light and NA is the numerical aperture of the lens. Generally, a depth of focus of 1 to 2 &mgr;m is required for an adequate lithographic process window, in order to accommodate variations in the thickness or height of the resist film.
In addition to using shorter wavelengths during exposure, it is also desirable to use a thinner layer of resist. However, the major drawback of using a thin layer of resist is that the variation of resist thickness over a diffusion step on a substrate and into an etched pattern increases as the pattern size becomes smaller. This variation means that the dimensions of any pattern being imaged in the resist will vary as the step geometry is traversed. Therefore, in a single layer resist system, the lack of dimensional control on the wafer can create different line widths throughout the resist which reduces the quality of the electronic package.
To improve dimensional control, bilayer (or bilevel or multilevel) resist systems are often utilized. In a typical bilevel system, a bottom resist is first applied to a substrate to planarize wafer topography. The bottom resist is cured and a second thinner imaging top resist is then applied over the bottom resist. The top resist is then soft baked, and patterned (or imaged) using conventional resist exposure and development, followed by etch transfer of the top pattern through the bottom resist using the top resist pattern as an etch mask. Positive resists are commonly used in bilayer applications and are typically based on novolac resins, which are condensation polymers of phenols or substituted phenols and formaldehyde.
Sugiyama et al.,
Positive Excimer Laser Resists Prepared with Aliphatic Diazoketones, Soc. Plastics Eng., Conference Proceedings
, pages 51-60 (November 1988), disclose a new class of alkali-developable positive excimer laser resists designed for DUV lithography. Such resists are two-component resists and contain &agr;-diazoacetoacetates blended with polyhydroxybenzylsilsesquioxane as a matrix resin.
U.S. Pat. No. 4,745,169 (Sugiyama et al.) discloses silicon-containing polymers for use in bilayer resist applications. The base soluble silsesquioxane polymer is synthesized by reacting trimethylsilyl iodide with polymethoxybenzyl-silsesquioxane to form aryl-O-trimethyl silyl groups. These trimethyl silyl groups are then hydrolyzed in water to form hydroxy groups. However, this reaction is not highly reproducible and often gives crosslinked polymer. Moreover, when these polymers are combined with diazonaphthoquinone-based photoactive compounds, exposure doses of >100 mJ/cm
2
at 365 nm are required to pattern the resist. Resists containing such photoactive compounds are too optically dense in the 200 to 280 nm region to be practical for DUV lithography. The optical density is greater than 0.5 for a 0.3 &mgr;m film of 20% photoactive compound in any polymer and the imaging dose is greater than 50 mJ/cm
2
in the DUV range. The optical density should be less than 0.3 or 0.4 &mgr;m for a single layer resist film in order to provide the most vertical wall profiles. For thinner films in a bilayer system the optical density should typically be less than or equal to 0.3 for a 0.3 to 0.4 &mgr;m film.
U.S. Pat. No. 5,338,818 (Brunsvold et al.) discloses certain acid sensitive polymers suitable for use in bilayer resist systems. Such polymers are copolymers of hydroxyphenyl- or hydroxybenzyl-silsesquioxane/RO-phenyl- or RO-benzyl-silsesquioxane, where R is selected from certain acid sensitive groups.
Conventional silicon-containing polymers, such as the above discussed silsesquioxane polymers, for use in bilayer resist systems have dissolution rates that are too high. Such high dissolution rates can negatively affect the lithographic performance of such bilayer resist systems. Such dissolution rate may be controlled by increasing the amount of blocking (or acid cleavable) groups in a positive photoresist system. However, such increased amount of blocking results in slower photospeeds and a reduced percentage of silicon in the resist. Such reduced silicon content may adversely affect the etch resistance of the resist.
There is thus a need for polymers suitable for use in bilayer resists that have controlled and/or lower dissolution rates than conventional bilayer resist polymers, wit
Barclay George G.
Gronbeck Dana A.
Kanagasabapathy Subbareddy
Linehan Leo L.
Xiong Kao
Corless Peter F.
Edwards & Angell LLP
Frickey Darryl P.
Huff Mark F.
Lee Sin J.
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