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
2002-07-30
2004-10-19
Thornton, Yvette C. (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
C430S322000, C430S323000, C430S905000, C430S907000
Reexamination Certificate
active
06806027
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a chemically amplified photoresist that is particularly suitable for exposure with light having a wavelength of 157 nm, and to a process for structuring substrates, especially silicon wafers.
In order to raise the calculating speed of processors and the capacity of memory elements, and to reduce the costs of the components, the semiconductor industry is developing chips having ever smaller features and hence an ever increasing density of components. One particular challenge is reducing the minimum feature size. In optical lithography, these requirements have been met to date through the transition to ever shorter wavelengths. However, at a feature size of 100 to 70 nm, the existing processes, which use wavelengths as short as 193 nm, approach the limit of their resolution. Consequently, the development of new processes is needed. Particularly good prospects for industrial use are possessed by optical lithography where exposure is carried out using radiation with a wavelength of 157 nm, since in this case the chip manufacturers are able to continue utilizing their extensive knowledge of optical lithography. A key difficulty in the use of an exposure radiation having a wavelength of 157 nm is the insufficient transparency of the presently used materials. For industrial application, the transparency of the base polymer in these high-resolution resists must be as high as possible, while the photochemicals with which, for example, an acid is produced in the resist must have a high quantum yield.
Some of the resists presently used for the manufacture of microchips operate with what is known as chemical amplification. In such resists, exposure in a photoreaction changes the chemical structure of the resist. In the case of a positive-working chemically amplified resist, for example, exposure generates a strong acid that brings about catalytic conversion or cleavage of the resist in a subsequent heating step. As a result of this chemical reaction, the solubility of the polymer in a developer is drastically changed, so that a marked differentiation between exposed and unexposed areas is possible.
The structured (i.e. patterned) photoresists can be used as masks for further operations, such as dry etching operations, for instance. Where the photoresist is used to structure an underlying organic-chemical medium, such as in two-layer resists, the topmost photoresist layer is required to have a high etch resistance. To this end, either the photoresist may contain corresponding etch-resistant groups in the polymer chain, such as silicon-containing groups, or the photoresist is reinforced in terms of its etch resistance in the step following the structuring of the photoresist. For this purpose, the polymer must contain reactive groups as anchor groups. These groups then react with a suitable reactive group of an amplifying reagent, which acts as a linking group, to form a chemical bond. In this way, silicon-containing or aromatic groups can be introduced subsequently into the polymer. The etch resistance of aromatic and organosilicon compounds in an oxygen plasma is much higher than that of aliphatic organic hydrocarbon compounds. Especially for structured resists with a low layer thickness, therefore, subsequent amplification of the resist structures is advantageous. The reaction incorporating organosilicon compounds is often referred to as silylation, the incorporation of aromatic compounds as aromatization.
A process for consolidating structured resists is described, for example, in commonly-owned European Patent EP 0 395 917 B1, which corresponds to U.S. Pat. Nos. 5,234,794 and 5,234,793. In that process, the photoresists used for an exposure wavelength of 248 and 193 nm following their structuring, are chemically reinforced in terms of their etch resistance by incorporating organosilicon groups to form a sufficiently stable etch mask. Where the layer thickness of the resist is sufficient, the structures of the resist can be widened by lateral growth and in that way it is possible to obtain an improvement in the resolution.
As already mentioned, the low transparency of the known photoresists at a wavelength of 157 nm poses a key difficulty in the development of the 157 nm technology. With the existing photoresists, layer thicknesses of approximately 50 nm can be realized. Presently, photoresists are being developed in which fluorination improves the transparency of the polymer at a wavelength of 157 nm. See Patterson et al., Proc. SPIE, 3999 (2000). However, these polymers still have an absorption that is about 50 times higher than that of the polymers commonly used at present in the resists used in industry for exposure with radiation having a wavelength of 193 or 248 nm. Even with these highly fluorinated polymers, layer thicknesses of only about 200 nm are achieved.
Besides high transparency at a wavelength of 157 nm, in order to be useful industrially the resists must meet further requirements, such as, for example, high contrast, good film-forming properties and good developability in conjunction with low basic solubility (dark erosion). Furthermore, the photoresist polymers ought to be very easy to prepare, in order to prevent complex preparation processes that increase the costs of the photoresist.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide chemically amplified photoresist and process for structuring substituents using transparency enhancement of resist copolymers for 157 nm photolithography through the use of fluorinated cinnamic acid derivatives that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that provide photoresists having high transparency at a wavelength of 157 nm, high contrast, good film-forming properties and good developability in conjunction with low basic solubility (dark erosion). Furthermore, the photoresist polymers should be very easy to prepare and not require complex preparation processes that increase the costs of the photoresist.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a chemically amplified photoresist including a polymer, a photoacid generator, and a solvent. The polymer contains acid-labile groups that are eliminated under the action of an acid and that liberate polar groups that increase the solubility of the polymer in aqueous alkaline developers. The polymer has first repeating units derived from cinnamic acid or cinnamic esters that are at least monofluorinated and/or substituted by fluoroalkyl groups.
Through the introduction of a first repeating unit derived from an at least partly fluorinated and/or fluoroalkyl-substituted cinnamic acid or cinnamic ester into the polymer, the transparency of the photoresist of the invention is significantly increased; this permits higher layer thicknesses of the photoresist. The aryl units of the cinnamic acid groups considerably raise the etch resistance in the plasma etch operation. Furthermore, with the carboxyl group of the cinnamic acid, a reactive group is introduced at the same time into the polymer. The carboxyl group allows subsequent modification of the photoresist. The incorporation of an at least partly fluorinated cinnamic acid or an at least partly fluorinated cinnamic ester allows a plurality of functions to be introduced into the polymer. In turn, this makes it possible to circumvent the often complicated copolymerization of monofunctional monomers whose copolymerizability with one another is poor. Through the introduction of an at least partly fluorinated and/or fluoroalkyl-substituted cinnamic acid into the photoresist polymer, the following advantages are gained.
a) Fluorination raises the transparency of the photoresist at an exposure wavelength of 157 nm.
b) The introduction of aryl groups into the polymer raises the resistance of the resist toward an etch plasma.
c) The introduction of a carboxyl group, which may also be esterified, provides a group that is able to
Eschbaumer Christian
Hohle Christoph
Rottstegge Jörg
Sebald Michael
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