Semiconductor device manufacturing: process – Radiation or energy treatment modifying properties of... – Ionized irradiation
Reexamination Certificate
2000-10-26
2001-10-23
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Radiation or energy treatment modifying properties of...
Ionized irradiation
Reexamination Certificate
active
06306780
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of semiconductor devices, and, more particularly, to the manufacture of semiconductor devices using photoresist materials.
BACKGROUND OF THE INVENTION
In the semiconductor device manufacturing process, masks are commonly used to define a pattern on a substrate or layer. For example, a mask may be formed using a material that is resistant to etchants so that the underlying substrate or layer is removed during etching where there are gaps in the mask. Alternatively, a mask may be made using a photoresist material that is impervious to radiation (such as ions used during ion implantation) to prevent the areas of the substrate or layer covered by the mask from being penetrated by the radiation.
One particular problem associated with typical photoresist layers used for ion implantation is that they are subject to degradation as a result of high-current, high-dosage, high-energy implants. That is, during implantation bonds within the polymer used to form the photoresist layer are broken, which leads to gases such as H
2
, H
2
O, O
2
, and N
2
being released from the carbon chain and becoming trapped beneath carbonized photoresist material which is left behind. Stated alternatively, solvents and water present in the photoresist material may cause such gases to form under the carbonized photoresist material during the ion implantation. The formation of these gases results in bubbles which may cause blistering, peeling, lifting, and reticulation of the photoresist layer. Additionally, this problem may be particularly acute in thick photoresist layers, which are used for blocking high-current, high-dosage, high-energy ion implants, for example.
Typical methods for dealing with the above problem include performing an extended hardbake of the photoresist or using a hard mask instead of a photoresist layer. These methods may be disadvantageous because they require longer processing times and/or provide less desirable results than a photoresist layer. A method for enhancing heat resistance and plasma resistance of a photoresist layer is disclosed in U.S. Pat. No. 4,882,263 to Suzuki et al. entitled “Method for Treating Photoresists.” The method involves applying ultraviolet rays to a developed photoresist layer at lower than 1 atmosphere of pressure while filtering unwanted radiation from the photoresist to prevent the generation of gases in the photoresist. Yet, to implement such filtering and processing at desired pressure levels may be cumbersome and require additional processing time.
Another prior art method for addressing image flow problems encountered in reactive ion etching processes is disclosed in an article by Hiraoka, H. et al. entitled “UV Hardening of Photo- and Electron Beam Resist Patterns,” J. Vac. Sci. Technol., 19(4), November/December 1981, pp. 1132-1135. The article discloses the use of UV exposure or very low heating of resist patterns in air to render images resistant to image flow. Yet, the article fails to address how to alleviate the above-referenced gases to thereby reduce the occurrences of blistering, peeling, lifting, and reticulation.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the invention to provide a method for treating photoresist layers providing reduced blistering, peeling, lifting, or reticulation as a result of high-current, high-dosage, high-energy ion implantation.
This and other objects, features, and advantages in accordance with the present invention are provided by a method for making a photoresist layer including forming a photoresist layer adjacent a substrate and patterning the photoresist layer. The photoresist layer may include at least one of a solvent and water. The photoresist layer may then be heated and exposed to ultraviolet light during the heating to reduce at least one of the solvent and water therein. As a result, the formation of gases in the photoresist layer during ion implantation is reduced, which thus reduces damage to the photoresist layer from blistering, peeling, lifting, or reticulation, for example.
The photoresist layer may be formed to have a thickness greater than about 2 &mgr;m, for example, to block high-current, high-dosage, high-energy ion implantation. Exposing may include exposing the photoresist layer to ultraviolet light having a power density in a range of about 200 to 500 mW/cm
2
, and, more preferably, about 270 to 360 mW/cm
2
, and having a wavelength in a range of about 200 to 300 nm, for example. The photoresist layer may be heated for about 200 to 400 seconds and to a temperature in a range of about 150° C. to 250° C., and more preferably about 230° C. to 250° C. Furthermore, heating may include maintaining the photoresist layer at a high temperature for about 15 to 60 seconds.
The method may also include stabilizing the photoresist layer at a low temperature and exposing the photoresist layer to ultraviolet light during the stabilizing. The photoresist layer may be exposed to ultraviolet light during the stabilizing having a power density in a range of about 5 to 15 mW/cm
2
and having a wavelength in a range of about 200 to 300 nm, for example. Additionally, the stabilizing may be for about 15 to 60 seconds.
According to another aspect of the invention, a method for making a semiconductor device includes forming a photoresist layer adjacent a substrate, patterning the photoresist layer, and heating the photoresist layer. Furthermore, the method may also include exposing the photoresist layer to an ultraviolet light source during heating and exposing the photoresist layer to an ion source.
REFERENCES:
patent: 4882263 (1989-11-01), Suzuki et al.
patent: 5356758 (1994-10-01), Orvek
Hiraoka et al., UV hardening of photo-and electron beam resist patterns, J. Vac. Sci. Tech. 19(4), Nov./Dec. 1981, p. 1132-1135.
Bourdelle Konstantin K.
Roy Pradip Kumar
Agere Systems Guardian Corp.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Bowers Charles
Thompson Craig
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