Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
2002-06-07
2004-03-09
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S296000, C430S270100, C430S281100, C430S910000, C430S926000, C430S326000, C430S324000, C430S330000, C430S921000, C430S923000
Reexamination Certificate
active
06703190
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a process for producing negative resist structures.
In microelectronics, resists known as chemical amplification resists (CAR) are widely used for a variety of lithographic technologies (see Solid State Technology, vol. 39 (1996), No. 7, pages 164 to 173). The principle of chemical amplification is employed both for wet-developable single-layer resists and for two-layer resist systems which can be developed wholly or partly under dry conditions. The resists may operate in accordance with the principle of acid-catalytic cleavage. In the case of positive-working resists, in a heating step (heat treatment) a polar carboxylic acid group is formed from an apolar chemical group, such as a tert-butyl carboxylate group, in the presence of an acid generated photolytically. Further examples of “blocked” groups of this kind are tert-butoxycarbonyloxy groups (t-BOC groups) and acetal groups. In the case of development in an aqueous-alkaline developer, the change in polarity is then used for selectively dissolving the exposed (polar) areas.
In the case of negative chemical amplification resists that can be developed in aqueous alkalis, exposure likewise produces a strong acid, from a photoacid generator. In this case, however, in the heating step that follows exposure, the acid that is produced serves not to eliminate “blocked” groups (as in the case of the positive resists) but instead for the acid-catalyzed cross-linking of the resist base polymers, commonly in the presence of suitable cross-linking agents. Acid-cleavable “blocked” groups on the polymer are therefore not needed with these resists.
A negative chemical amplification resist that does not operate on the basis of cross-linking is known from U.S. Pat. No. 4,491,628. In this case a resist system is used which is composed of the same components as the positive chemical amplification resists described above. The negative image of the mask is brought about by using, instead of the aqueous-alkaline developer that dissolves out the polar areas of the resist, an organic developer that selectively dissolves out the apolar (unexposed) areas. A disadvantage here exists, however, in the use of organic solvents as developers (toxicity, flammability, disposal). Developers of this kind are not accepted in semiconductor applications.
Otherwise, like negative chemical amplification resists, the positive chemical amplification resists have been known for a long time (see, for example: Advanced Materials for Optics and Electronics, vol. 4 (1994), pages 83 to 93).
One specific variant of a positive resist is known from Published, Non-Prosecuted German Patent Application DE 42 26 464 A. This dry-developable resist is based on the chemical combination of a photobase generator with a thermoacid generator, as a result of which the unexposed areas of the solid resist film are modified in that, in a chemical reaction step following exposure, silicon molecules can be installed in the near-surface area of the resist film. In the processing operation, the otherwise customary wet-chemical developing step is omitted. Instead, the latent structures produced in the course of exposure are generated by direct siliconization and subsequent etching in an oxygen plasma (top surface imaging, TSI). A disadvantage here is that, owing to acid-base diffusion processes within the resist and also by diffusion of the siliconizing agent, the edges of the structure following siliconization are not clearly defined. After the final oxygen etching process, this results in high edge roughness and in particular to a limitation on the resolving power. Future lithographic generations with a required resolution of <150 nm can therefore not be realized in this way.
In a process known from European Patent EP 0 395 917 B for widening photoresist structures, a specific kind of positive resist system is used which can be developed by aqueous alkali. In this case the base polymer used in the resist contains reactive groups. These groups allow the developed resist structure to be after treated with appropriate reagents. In the course of the after treatment, the structures are “widened” (chemical amplification of resist lines, CARL) and the resist valleys and holes are narrowed.
In accordance with a process known from U.S. Pat. No. 5,234,793, the after treatment is utilized for siliconization in a two-layer resist system (Si-CARL). However, this kind of after treatment cannot be carried out if the polymer matrix is cross-linked in the developed resist structure. Negative resists that operate on the basis of cross-linking are therefore unsuitable for this system. For the patterning of defined levels in semiconductor fabrication, however, negative resist systems with the stated type of after treatment are needed.
Particularly with the conventional negative resists that can be developed by aqueous alkalis, the problem exists of what is known as swelling. Although in principle the exposed areas of resist are made insoluble toward the developer by the polymer cross-linking which takes place during the heating step, the marginal areas of the structures are problematic. In these areas, in fact, owing to a weaker light irradiation intensity and also to diffusion processes, fewer protons are available for cross-linking. As a result, cross-linking is unable to take place to the same extent as is the case in the center of the structures. Although the marginal areas are insoluble in the developer, they may nevertheless swell up in the course of development and falsify the profile of the structure. This can be attributed to the reduced extent of polymer cross-inking, as a result of which the structures in the marginal area are mechanically less stable than in the core area. Especially in the case of structures of continually reduced size, this is a great problem, since in this case the fraction of the marginal areas (edges) becomes ever greater in comparison to the actual volume of structure. Using conventional negative resist systems, therefore, faithful reproduction of very fine structures is very difficult, if not impossible, to achieve.
Conventional resist systems utilize only one single photoactive component for the actual patterning. Other additives are not aimed directly at the structurability, but instead merely compensate the disruptive lateral diffusion of the photoactive component. Published, European Patent Application EP 0 425 142 A, on the other hand, discloses a photoresist system wherein patterning takes place by combined production of acids and bases. In this way it is possible to convert a negative-working resist into a positive-working resist. This system, however, has the same disadvantages as the positive resist known from Published, Non-Prosecuted German Patent Application DE 42 26 464 A, namely high edge roughness and limited resolving power.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for producing resist structures which overcomes the above-mentioned disadvantages of the prior art methods of this general type, in which the resist, developable by aqueous alkali, is not structured by cross-linking and hence an after-treatment is possible after the developing step, and which solves the problem of edge roughness and of limited resolution. Moreover, the process should be suitable for use both for optical lithography and with direct writing processes (using laser, electron or ion beams) and also with electron projection lithography (EPL) and ion projection lithography (IPL).
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for producing negative resist structures. The process includes providing a substrate and applying a chemical amplification resist to the substrate. The chemical amplification resist contains a polymer that changes polarity when exposed to an acid and the ploymer includes carboxylic anhydride groups, a compound functioning as a thermoacid generator from which an acid is released by w
Elian Klaus
Hien Stefan
Richter Ernst-Christian
Sebald Michael
Chacko-Davis Daborah
Huff Mark F.
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