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
1999-07-12
2002-08-20
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
C430S296000, C430S323000
Reexamination Certificate
active
06436605
ABSTRACT:
TECHNICAL FIELD
The present invention relates to radiation sensitive resist compositions which exhibit enhanced resistance to plasma and especially to Cl
2
/O
2
plasma used in reactive ion etching. The present invention is concerned with the compositions as well as their use in lithography. For instance, the materials of the present invention are suitable for use in device and mask fabrication on optical, e-beam, x-ray and ion-beam lithography tools.
BACKGROUND OF INVENTION
In the manufacture of patterned devices and especially microelectronic devices, the processes of etching different layers which constitute the finished product are among the most crucial steps involved. One method widely employed in the etching process is to overlay the surface to be etched with a suitable mask.
The mask is typically created by imagewise forming a pattern of resist material over those areas of the substrate to be shielded from the etching. The resist is normally formed of a polymeric organic material. The pattern is formed by imagewise exposing the resist material to irradiation by lithographic techniques. The irradiation employed is usually x-ray, UV radiation, or electron beam radiation.
Radiation sensitive materials and/or compositions are either positive-acting (i.e. radiation solubilizable) or negative-acting (i.e. radiation insolubilizable or crosslinkable). Positive-working sensitive compositions are rendered soluble (or developable) by exposure to radiation (UV light, x-ray or electron-beam) and can be removed using selective developing solutions leaving unexposed areas intact. Negative-working sensitive compositions are those which become insoluble upon exposure to actinic radiation. Selected solutions can dissolve and remove the unexposed areas of the composition while leaving the exposed portions intact. Development of such exposed materials yields negative tone images.
The production of binary masks includes pattern definition by exposure of electron beam resists on, for instance, a chrome coated glass plate. The image is then developed and the pattern is etched into chrome by either aqueous based wet etching or by reactive ion etching with a chlorine based plasma (see U.S. Pat. No. 3,236,413).
With the advent of shrinking dimensions, the photomask of nX enlargement (n-4-10X) is also shrinking to less than 400 nm in dimensions. Because wet etching causes undercutting or undesired enlargement, reactive ion etching (RIE) has been utilized (see Tsai et al U.S. Pat. No. 3,412,149). In RIE>50% of the resist film can be eroded away. The particular resists that have been used for electron beam exposure are polymers that undergo main chain degradation. The primary examples are derived from a positive resist such as polymethylmethacrylate (PMMA) described in U.S. Pat. No. 3,535,137 and polybutene sulfone described in U.S. Pat. No. 3,935,332. Improved contrast developers for PMMA can be found such as amyl acetate as described, for example, in U.S. Pat. No. 3,931,435 and a mixture of methyl isobutyl ketone and water as described in U.S. Pat. No. 4,078,098. All of these resists and copolymers are described in W. Moreau,
Semiconductor Lithography
, Plenum Press, 1989, Chapter 3. These resists, however, are not RIE etch resistant and thus the pattern cannot be transferred by an RIE process.
For reactive ion etching, a commercial resist identified as ZEP manufactured by Nippon Zeon (see U.S. Pat. No. 3,236,397) has been used. ZEP is composed of a copolymer of alpha-chloromethacrylate and alpha-methyl styrene (PCMMS). Copolymers of polyalpha-chloromethacrylate are described in U.S. Pat. Nos. 4,359,481, 4,011,351 and 4,454,222. A preferred example is described in U.S. Pat. No. 4,259,407 which is directed to a copolymer of poly(alpha-chloroacrylate-alpha-methylstyrene), commercially available from Nippon Zeon as ZEP 7000 electron beam resist. U.S. Pat. No. 4,259,407 discusses a developer of a ketone such as 3 pentanone mixed with another ketone. In U.S. Pat. No. 4,454,222, a developer comprising MIBK (4 methyl-2-butanone) and isopropanol or a mixture with 2 butanone is suggested for a trifluoromethyl alpha-chloroacrylate-methacrylic acid copolymer in a spray development mode. U.S. Pat. No. 4,414,313 describes a mixture of dimethylacetamide and toluene as a developer for a poly(alpha-chloroacrylate-methacrylic acid) copolymer. The disclosures of U.S. Pat. Nos. 4,359,481, 4,011,351, 4,454,222, 4,259,407 and 4,414,313 are incorporated herein by reference.
The ZEP resist uses a commercial developer preferably consisting of the following compositions: ZED 300-methyl ethyl ketone/anisole 93/7 by weight, ZED 400-diglyme/methyl ethyl ketone 20/80 by weight, and ZED 500-diethyl ketone/diethyl malonate 50/50 by weight.
In addition to using ZEP type resists for chrome mask fabrication, other masks, substrates or direct exposure of silicon wafers could also be exposed and developed with the resist, exposure tools, and developer modes used in semiconductor fabrication.
After the resist is developed forming the desired mask, the substrate and mask can be immersed in a chemical solution which attacks the substrate to be etched while leaving the mask intact. These wet chemical processes suffer from the difficulty of achieving well-defined edges on the etched surfaces. This is due to the chemicals undercutting the mask and the formation of an isotropic image. In other words, conventional chemical wet processes do not provide the resolution considered necessary to achieve optimum dimensions consistent with current processing requirements.
Moreover, such wet etching processes are undesirable because of the environmental and safety concerns associated therewith.
In view of the various drawbacks associated with wet chemical development, various so-called “dry processes” have been suggested to improve the process from an environmental viewpoint, as well as to reduce the relative cost of the etching. Furthermore, these “dry processes” have the potential advantage of greater process control and higher aspect ratio images. Also, when fabricating patterns having feature sizes below 350 nm, dry etching processes are necessary.
Such “dry processes” generally involve passing a gas through a container and creating a plasma in this gas. The species in this gas are then used to etch a substrate placed in the chamber or container. Typical examples of such “dry processes” are plasma etching, sputter etching, and reactive ion etching.
Reactive ion etching provides well-defined, vertically etched sidewalls.
One of the challenges in the fabrication of microelectronic devices and masks is to develop a resist which exhibits good lithographic performance as well as high dry etch resistance for subsequent pattern transfer into an underlying substrate. The dry etch chemistries include O
2
currently used for antireflective coatings, Cl
2
/O
2
currently used for chrome etching in mask fabrication, Cl
2
based plasma for polysilicon etch, and fluorocarbon based plasmas such as CF
4
for oxide etching. These plasmas are examples only and are not meant to limit the scope. Conventional novolak/diazonapthoquinone resists used for i-line lithography have to date exhibited the best dry etch resistance. ZEP is an e-beam resist which has been adopted by the industry for advanced mask making to replace the conventional wet etch polybutenesulfone (PBS) process. Although ZEP provides significant improvement over the PBS process, its dry etch resistance to Cl
2
/O
2
is marginal (etch rate of 1.95 nm/s). Novolac is 1.4 nm/s.
There is a need to develop radiation sensitive compositions that provide improved dry etch resistance for use in mask fabrication (binary, attenuating phase shift masks, alternating phase shift masks) and for device fabrication.
The use of silicon and germanium has been intended to impart O
2
etch resistance to certain resist materials. For example, see U.S. Pat. Nos. 4,764,247, 4,935,094 and 5,733,706 and
Microelectronic Engineering
3, 279 (1985). However, these do not suggest masking against Cl
2
/O
2
reactive ion etc
Angelopoulos Marie
Aviram Ari
Babich Edward D.
Brunner Timothy Allan
Faure Thomas Benjamin
Chu John S.
Connolly Bove Lodge & Hutz
Morris Daniel P.
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