Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-08-09
2001-04-24
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S322000, C430S311000
Reexamination Certificate
active
06221542
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates generally to the manufacture and use of a photomask used in photolithographic processes during the manufacture of integrated circuits. More particularly, the present invention is directed to a photomask offering controllable multiple radiation-absorption levels and to a method for manufacturing the photomask.
2. Description Of The Related Art
Certain integrated circuit fabrication processes require precise delimitation of areas to be affected by the fabrication process and of areas to be protected from the fabrication process. Photomasks are patterned masks used in photolithographical processes for selectively inhibiting the exposure to radiation, such as light, specific regions of a material to be patterned, while allowing radiation to act on other regions.
Conventional photomasks include a patterned layer of a light-blocking material, usually chromium, used to block transmission of the particular form of light used. Conventional chromium masks generally provide only one level of complete absorption—that is, light is either totally blocked by the chromium or transmitted in those regions from which the chromium has been removed. These “on-off” photomasks are referred to as binary intensity masks (BIM).
The exposure level of the photoresist, which is the material to be patterned using the photomask, can be controlled by raising or lowering the illumination level. This procedure causes all features defined by the photomask to receive approximately the same light exposure. To provide greater versatility in the exposure of photoresist patterns, particularly in the submicron regime, it would be desirable to have some features that receive relatively greater or less exposure than other features. For example, it is generally helpful if larger features receive less exposure than small features. Of course, it is possible to vary the exposure levels by using separate photomasks and repeating the exposure process. However, this repetitive process is impractical, requiring additional masks and additional exposure and development steps.
As an alternative to existing BIM photomasks, photomasks have been prepared which function to phase-shift the light energy. The basic principle of such masks is to use a phase-shifting material to interfere with the electric fields of light passing through adjacent open features and, thus, cause the annihilation of superimposed fields with opposite phases. One type of phase-shifting photomask, an attenuated phase-shifting mask (APSM), uses a film of a slightly transmissive absorber with a 180° phase shift. By controlling the thickness and optical properties of the mask, such as by changing the chemical content of the film, two levels of light-transmission can be achieved in a single mask.
However, phase-shifting systems provide only limited control of absorption levels and require complex manufacturing processes. Additionally, researchers of phase-shifting systems have encountered difficulties applying such systems to arbitrary mask patterns and obtaining accurate feature delineation.
In view of the problems described above, a need remains for a photomask which can be efficiently manufactured and which offers multiple absorption levels. Accordingly, there is provided herein a photomask and method of its use which allows different portions of the photoresist to be exposed simultaneously to various levels of exposure using a single exposure process.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided a semiconductor manufacturer mask. The mask includes a plurality of radiation-absorbing layers. At least one etch-stop layer is disposed between the radiation absorbing layers.
In accordance with another aspect of the present invention, there is provided a semiconductor manufacturer mask having multiple light-absorption levels. The mask includes a plurality of light-absorbing layers. At least one etch-stop layer is disposed between the light-absorbing layers.
In accordance with yet another aspect of the present invention, there is provided a method for manufacturing a photomask having multiple light-absorbing levels. A photomask substrate is provided. A plurality of alternating layers of a light-absorbing material and of an etch-stop material arc formed on the photomask substrate. The light-absorbing material and the etch-stop material are selectively etchable in relation to each other.
In accordance with still another aspect of the present invention, there is provided a method for manufacturing a photomask having multiple light-absorbing levels. A photomask substrate is provided. A first layer of a generally light-absorbing material is deposited onto the substrate. A second layer of a buffer material is formed onto the first layer. The second layer of buffer material is selectively etchable relative to the first layer. A third layer of a generally light-absorbing material is deposited. The third layer is selectively etchable relative to the second layer.
In accordance with a further aspect of the present invention, there is provided a method for patterning a semiconductor device. A photomask substrate is provided. A plurality of alternating layers of a light-absorbing material and of an etch stop material is formed on the photomask substrate. The layers are successfully patterned by removing at least a portion of at least one of the layers by selective etching process to form a photomask. A semiconductor wafer is provided. A photoresist is applied to at least a portion of the surface of the semiconductor wafer. The photomask is aligned over at least a portion of the photoresist. The photomask is exposed to light. The photoresist is developed.
In accordance with a still further aspect of the present invention, there is provided a method for manufacturing a semiconductor device. A photomask is provided. The photomask includes the plurality of selectively patterned light-absorbing layers. A semiconductor wafer under fabrication is provided. The wafer has a layer of photoresist at least partially over the wafer. The semiconductor wafer is exposed to light through the photomask. The photoresist is developed.
In accordance with a yet further aspect of the present invention, there is provided a method for patterning a semiconductor device. A photomask is provided. The photomask includes a substrate element. A first layer of a generally light-absorbing material is supported by the substrate. The first layer is over at least a first portion of the substrate. A buffer layer is over the first layer. A second layer of a generally light-absorbing material is supported over the buffer layer. The second layer is over a second portion of the substrate. The second portion is a substrate of the first portion. A semiconductor wafer under fabrication is provided. The wafer has a layer of photoresist at least partially over the wafer. The semiconductor wafer is exposed to light through the photomask. The photoresist is developed.
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A.K. Pfau et al., “Exploration of Fabrication Techniques for Phase-Shifting Masks,” SPIE, vol. 1463, Mar. 6-8, 1991, pp. 124-134 (Abstract also attached).
Burn J. Lin, “The Attenuated Phase-Shifting Mask,” Solid State Technology, vol. 35, No. 1, Jan. 1992, pp. 43-47. (Abstract also attached).
Alessandro Callegari et al., “Optical properties of hydrogenated amorphous-carbon film for attenuated phase-shift mask applications,” Journal of Vacuum Science & Technology B, Second Series, vol. 11, No. 6, Nov./Dec. 1993, pp. 2697-2699, (Abstract also attached).
Csepregi et al. “Fabrication of Silicon Oxynitride Masks for X-ray Lithography”, J. Vac. Sci. Technol. vol. 16 No. 6.
Fletcher Yoder & Van Someren
Micro)n Technology, Inc.
Rosasco S.
LandOfFree
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