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
2000-11-16
2003-01-07
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
C430S905000, C430S907000
Reexamination Certificate
active
06503686
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to photoimaging and, in particular, the use of photoresists (positive-working and/or negative-working) for imaging in the production of semiconductor devices. The present invention also pertains to photoresists containing polymer compositions having high UV transparency (particularly at short wavelengths, e.g., 157 nm or 193 nm) which are useful as base resins in resists and potentially in many other applications.
2. Background
Polymer products are used as components of imaging and photosensitive systems and particularly in photoimaging systems such as those described in
Introduction to Microlithography, Second Edition
by L. F. Thompson, C. G. Willson, and M. J. Bowden, American Chemical Society, Washington, D.C., 1994. In such systems, ultraviolet (UV) light or other electromagnetic radiation impinges on a material containing a photoactive component to induce a physical or chemical change in that material. A latent image is thereby produced which can be processed into a useful image for semiconductor device fabrication.
Although the polymer product itself may be photoactive, generally a photosensitive composition contains one or more photoactive components in addition to the polymer product. Upon exposure to electromagnetic radiation (e.g., UV light), the photoactive component acts to change the rheological state, solubility, surface characteristics, refractive index, color, electromagnetic characteristics and/or other such physical or chemical characteristics of the photosensitive composition as described in the Thompson et al. publication supra.
For imaging very fine features at the submicron level in semiconductor devices, electromagnetic radiation in the far or extreme ultraviolet (UV) is needed. Positive working photoresists generally are utilized for semiconductor manufacture. Lithography in the UV at 365 nm (I-line) using novolak polymers and diazonaphthoquinones as dissolution inhibitors is a currently established chip technology having a resolution limit of about 0.35-0.30 micron. Lithography in the far UV at 248 nm using p-hydroxystyrene polymers is known and has a resolution limit of 0.35-0.18 nm. There is strong impetus for future photolithography at even shorter wavelengths, due to a decreasing lower resolution limit with decreasing wavelength (i.e., a resolution limit of 0.18-0.12 micron for 193 nm imaging and a resolution limit of about 0.07 microns for 157 nm imaging). Photolithography using 193 nm exposure wavelength (obtained from an argon fluorine (ArF) excimer laser) is a leading candidate for future microelectronics fabrication using 0.18 and 0.13 &mgr;m design rules. Photolithography using 157 nm exposure wavelength (obtained from a fluorine excimer laser) is a leading candidate for future microlithography further out on the time horizon (beyond 193 nm). There is a strong need for photoresist materials having sufficient transparency and other required properties at these very short wavelengths. The opacity of traditional near UV and far UV organic photoresists at 193 nm or shorter wavelengths precludes their use in single-layer schemes at these short wavelengths.
Photoresist compositions, also referred to herein as “resists”, suitable for imaging at 157 nm are presently unknown. The main reason for this current status of 157 nm resists is that all conventional resist materials absorb to a significant degree at this wavelength to preclude their use as component(s) in 157 nm resists.
There is a critical need for suitable novel resist compositions for use at 193 nm, and particularly at 157 nm, or lower wavelengths, that have not only high transparency at these short wavelengths but also suitable other key properties, including good plasma etch resistance, development characteristics, and adhesive properties.
SUMMARY OF THE INVENTION
In some embodiments, the invention is a photoresist comprising:
(a) a polymer comprising:
(i) a repeat unit derived from at least one ethylenically unsaturated compound containing a fluoroalcohol functional group having the structure:
—C(R
f
)(R
f
′)OH
wherein R
f
and R
f
′ are the same or different fluoroalkyl groups of from 1 to about 10 carbon atoms or taken together are (CF
2
)
n
wherein n is 2 to about 10; and
(ii) a repeat unit derived from at least one ethylenically unsaturated compound having the structure:
(H)(R
1
)C═C(R
2
)(CN)
wherein R
1
is a hydrogen atom or CN group; R
2
is C
1
-C
8
alkyl group, hydrogen atom, or CO
2
R
3
group, where R
3
is C
1
-C
8
alkyl group or hydrogen atom; and
(b) at least one photoactive component.
In other embodiments, the invention is a process for preparing a photoresist image on a substrate comprising, in order:
(A) applying a photoresist composition on a substrate to form a photoresist layer, wherein the photoresist composition comprises:
(i) a polymer comprising:
(a) a repeat unit derived from at least one ethylenically unsaturated compound containing a fluoroalcohol functional group having the structure:
—C(R
f
)(R
f
′)OH
wherein R
f
and R
f
′ are the same or different fluoroalkyl groups of from 1 to about 10 carbon atoms or taken together are (CF
2
)
n
wherein n is an integer ranging from 2 to about 10; and
(b) a repeat unit derived from at least one ethylenically unsaturated compound having the structure:
(H)(R
1
)C═C(R
2
)(CN)
wherein R
1
is hydrogen atom or CN group; R
2
is an alkyl group of 1 to about 8 carbon atoms, hydrogen atom, or CO
2
R
3
group, wherein R
3
is an alkyl group of 1 to about 8 carbon atoms or hydrogen atom; and;
(ii) at least one photoactive component;
(B) imagewise exposing the photoresist layer to form imaged and non-imaged areas; and
(C) developing the exposed photoresist layer having imaged and non-imaged areas to form the photoresist image on the substrate.
Typically the photoresist composition is further comprised of a solvent, and the process (as given supra) further comprises, between steps (A) and (B), a step of drying the photoresist composition to substantially remove solvent and thereby form a photoresist layer on the substrate.
With respect to some specific embodiments of the photoresists and associated processes of this invention, the polymer (nitrile/fluoroalcohol-containing polymer) present as a component in the photoresists preferably has an absorption coefficient of less than 5.0 &mgr;m
−1
at a wavelength of 157 nm. In other certain embodiments, the (nitrile/fluoroalcohol-containing) polymer is further comprised of protected acid groups and/or aliphatic polycyclic functionality. In some embodiment(s), the photoactive component of the photoresists and associated processes is a photoacid generator. In still other certain embodiment(s), the photoresists and associated processes are further comprised of a dissolution inhibitor.
DETAILED DESCRIPTION OF THE INVENTION
A key characteristic of the polymers (and photoresists comprised of the polymers) of this invention is the cooperative combination in the polymers of repeat unit(s) containing a fluoroalcohol functional group with repeat units containing the cyano (CN) group. Another characteristic of the polymer is that it lacks amounts of functionality sufficient to cause the polymer to detrimentally absorb in the extreme and far UV. The presence of repeat units containing fluoroalcohol functional groups is desirable in order for the polymers to be sufficiently acidic to be developable in basic aqueous media while at the same time minimizing the need for having alternate functionality, such as carboxylic acid, present for developability, which may lead to too high absorptions in the deep UV for these materials to be used in resists at these low imaging wavelengths (e.g., 157 nm or 193 nm). The presence of repeat units containing cyano (CN) functionality in these polymers is desirable in order for the polymers to possess high optical transparency, i.e., to have low optical absorptions in the extreme and far UV, and improved etch resistan
Fryd Michael
Periyasamy Mookkan
Schadt, III Frank L
Chu John S.
E. I. du Pont de Nemours and Company
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