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Resist hardening process having improved thermal stability
| Details |
Inventors: Shibata, Tsuyoshi;
Assignee: Kabushiki Kaisha Toshiba (Kawasaki, JP)
Primary Examiner: McPherson; John A.
Assistant Examiner:
Attorney, Agent or Firm: Banner & Witcoff, Ltd.
The present invention is directed to a method of hardening a photoresist formed on a patterned layer during photolithograpy, without causing undesirable shrinkage of the resist features. The patterned layer is disposed on a semiconductor substrate, and the photoresist layer is disposed on the patterned layer in a conventional manner. The photoresist layer is irradiated and developed in a conventional manner to have the desired pattern formed therein. The larger features of the developed photoresist layer are irradiated without heat to thereby harden these features, without irradiating the smaller features. The hardening may be performed by screening the smaller features from the radiation applied to the photoresist layer, or by scanning a beam across only the larger features. The radiation may be UV light or an electron beam. Alternatively, all of the features of the photoresist may be hardened by exposure to a basic atmosphere immediately before, during or immediately after irradiation with UV light. In both cases, the features are hardened without shrinkage. After the features are hardened, the photoresist and patterned layer are etched in a conventional manner to transfer the pattern to the patterned layer. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS.
7a-b, a method for hardening photoresists according to the present invention will be described.
It has been determined that photoresist features may be sufficiently hardened against profile degradation by application of UV irradiation without heat.
Further, application of UV irradiation in the absence of heat results in only minimal pattern shrinkage because as explained further below with reference to FIGS.
9-10, the deblocking and volatization of the protection group OR found in the photoresist material is minimized.
It is this deblocking which is responsible for the pattern shrinkage.
In FIG.
7a, UV radiation is applied so as to cover the entire surface area of the developed photoresist.
However, mask 6 which is opaque to UV radiation is disposed to cover the smaller resist features 3a.
Mask 6 does not block large feature 3b.
The ambient temperature of the substrate and layers disposed thereon is not raised, that is, the photoresist is not subjected to heat which would cause it to undergo thermal flow.
The temperature is maintained below 90.
degree.
C.
, and preferably at room temperature.
Accordingly, large feature 3b of the resist pattern is hardened against thermal flow and rapid volume reduction by irradiation with UV light without application of heat.
However, without application of heat, large feature 3b will undergo only minimal pattern shrinkage because excessive pattern shrinkage due to the deblocking and volatization of the protection group is minimized.
For features having a width of 1 .
mu.
m or greater, the shrinkage will be less than 5% of the width.
It has been determined that large features 3b will be provided with sufficient thermal stability with this minimal shrinkage if the intensity of the applied UV light is at least 120 mW/m.
sup.
2, at a wavelength of less than 400 nm.
In a preferred embodiment, the wavelength of the UV will be less than 300 nm.
FIG.
7b shows the result of the etching process
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Manufacturing Materials 
