Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1998-08-13
2001-06-12
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S330000, C430S394000
Reexamination Certificate
active
06245492
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to methods and resist compositions for increasing the resolution of photolithographic patterns and more specifically to an improved double-exposure technique for increasing photolithographic resolution.
2. Description of the Related Art
In optical lithography, the aerial image becomes degraded due to diffraction, especially with sub-half micron patterning. This limits the ultimate resolution of the lithography system. If the resolution of the aerial image is improved or sharpened, the process window can be widened and much smaller features can be formed.
The size reduction of features formed on wafers is limited by the resolution of the aerial image projected on the wafers. To improve resolution, conventional efforts were devoted to manipulating the illumination systems (e.g., off-axis and annular illumination) or to manipulating the masks (e.g., phase shift mask). However, manipulation of the illumination systems has disadvantages, such as loss of intensity and pattern distortion and/or artifacts. Similarly, phase-shift approaches impose stringent conditions on the circuit design, require the printing of high resolution sub-features and demanded special feature size and shape management, making the phase shift mask approach difficult and expensive.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a structure and method for increasing resolution using a double-exposure technique. More specifically, the invention changes the optical and/or physical properties of the exposed area, which then acts as in-situ mask for a subsequent low dose blanket exposure (e.g., double-exposure). Changing the optical and/or physical properties in this manner improves the aerial image of the final pattern.
The first exposure of the specially formulated resist creates optical and physical changes in the inventive resist. For example, as explained in greater detail below, the optical property change includes, but is not limited to, a change in optical density upon the first exposure of the inventive photoresist of the exposed areas of the photoresist with a chemical- or photo-bleachable resist system. The physical property change includes, but is not limited to, manipulating the resist film thickness of upon the first exposure of the inventive photo resist. One way to introduce a change in the physical property is by inducing a reduction of the film thickness upon exposure, using a shrinkable resist system.
The second blanket exposure of the inventive double-exposure enhances the overall aerial image and improves the resolution capabilities of the resist system; i.e., with better defined aerial images, the resolution limits can be pushed further, extending the imaging capability of the optical system when compared with capabilities of conventional optical systems.
More specifically, the invention comprises a system and method of forming a pattern comprising supplying a resist, forming a mask having the pattern over the resist, a first step of exposing the pattern on the resist, removing the mask, heating the resist, and a second step of exposing the resist. The invention also includes steps of reducing a thickness of, chemically bleaching or photo-bleaching exposed regions of the resist prior to the second exposure step.
The supplying step comprises steps of supplying a shrinkable resist, a chemically bleachable resist or a photo-bleachable resist. The step of supplying a shrinkable resist preferably comprises a step of supplying a resist having at least one of partially protected phenolic resins with, tertiary butyl carbonate (t-BOC), ethers, acetals or ketals functional group, or acrylate, methacrylate and cyclic olefin polymers with alkyl or aryl carboxylic esters. The step of supplying a chemically bleachable resist preferably comprises a step of supplying a resist having aryl vinyl ether (R—O—C═C—Ar). The step of supplying a photo-bleachable resist preferably comprises a step of supplying a resist containing a diazonaphthoquinone.
During the second exposing step, unexposed regions of the resist act as a second mask for the exposed regions of the resist. The first exposing step is preferably insufficient to make exposed regions of the resist selectively removable from unexposed regions of the resist and a combination of the first exposing step and the second exposing step is sufficient to make the doubly exposed regions selectively removable from the regions receiving only the second exposure.
In both the shrinkable and bleachable resist systems, the first exposing step may have a higher dosage than the second exposing step. In the photo-bleachable resist system, the first exposing step uses a radiation having a first wavelength and the second exposing step preferably uses a radiation having a second wavelength different than the first wavelength.
REFERENCES:
patent: 4142107 (1979-02-01), Hatzakis et al.
patent: 4548896 (1985-10-01), Sabongi et al.
patent: 4745042 (1988-05-01), Sasago et al.
patent: 4816115 (1989-03-01), Horner et al.
patent: 4927732 (1990-05-01), Merrem et al.
patent: 5229258 (1993-07-01), Sezi et al.
patent: 5434026 (1995-07-01), Takatsu et al.
patent: 5468595 (1995-11-01), Livesay
patent: 5631120 (1997-05-01), Swirbel et al.
patent: 5698377 (1997-12-01), Seino
patent: 5876904 (1999-03-01), Uetani
patent: 0 227 851 (1985-12-01), None
patent: 0 601 887 B1 (1994-06-01), None
T. Murakami, “Multilayer Circuit Fabrication Using Double Exposure of Positive Resist”, IBM Technical Disclosure Bulletin, vol. 36, No. 10, Oct. 1993, pp. 423-424.
Kunze, et al., “Bleachable Dyed-Resist—Investigation of Its Process Latitude In Comparison With Standard Resists”, Microelectronic Engineering 25, 1994, pp. 3-18.
Huang Wu-Song
Katnani Ahmad D.
Kwong Ranee W.
Martinek Kathleen H.
Capella, Esq. Steven
Huff Mark F.
International Business Machines - Corporation
McGinn & Gibb PLLC
Mohamedulla Saleha R.
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