Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1999-02-05
2001-06-12
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S325000, C430S328000, C430S330000
Reexamination Certificate
active
06245491
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photolithographic techniques utilized in manufacturing semiconductor integrated circuits and, in particular, to a post exposure bake (PEB) technique for suppressing acid diffusion induced critical dimension changes in a chemically amplified photoresist process by reducing reaction activation energy to thereby reduce reaction time. Reaction activation energy is reduced by delivering energy required to overcome the reaction activation energy barrier directly into the chemical bonds involved in the reaction.
2. Discussion of the Related Art
Chemically amplified photoresists have been widely used in Deep UltraViolet (DUV) photolithography to manufacture integrated circuit devices with feature sizes smaller than 0.35 &mgr;m. With DUV photoresists, strong acids are generated upon DUV illumination, as shown in FIG.
1
A. In the subsequent post exposure bake (PEB) step, shown in
FIG. 1B
, the acids act as a catalyst, inducing chain-like chemical reactions that can change the dissolution properties of the resist. This process can result in a change A in the critical dimension, as shown in
FIG. 1C
, due to the isotropic characteristics of the acid diffusion.
The working principle of chemically amplified photoresists can be represented by the following equations (1) and (2):
At DUV exposure step,
Ph
3
S
+
X
−
+hv→X
31
H
+
+others (
1
)
At PEB step,
The diffusion of catalytic acids in chemically amplified resists has a strong influence on resist lithographic performance. On one hand, acid diffusion is necessary within the DUV exposed region in order to make chemical reactions occur. On the other hand, lateral diffusion of the acid, which can cause critical dimension change, is undesirable.
Ideally, the acid catalyzed chemical reactions should be completely acid diffusion controlled. That is, since the chemical reaction kinetics is much faster than the acid diffusion process, the overall chemical reaction rate may be determined by acid diffusion. In such a case, the time required to induce a certain amount of chemical reaction is minimized. Therefore, the lateral diffusion of the acid is also minimized.
In reality, the chemical reaction described by equation (2) above has a considerable “activation energy” barrier because not every collision between acid (H
+
) and the protected group (—COOC (CH
3
)
3
) results in chemical reaction, even at elevated PEB temperature (~130° C.). In fact, the probability of a successful collision that leads to chemical reaction is on the order of 10
−12
, if the activation energy is assumed to be 100 kJ/mol. This low successful collision probability results in a longer time being required to complete a certain amount of chemical reaction. Therefore the time available for acid (H
+
) diffusion is also extended, causing a larger change in the critical dimension.
Accordingly, there is a need for a technique for suppressing the impact of acid diffusion on critical dimension change in a chemically amplified photoresist process.
SUMMARY OF THE INVENTION
One way to suppress acid diffusion induced critical dimension change in a chemically amplified photoresist process is to reduce the required reaction time by lowering the reaction activation energy barrier. In accordance with the present invention, energy required to overcome the chemical reaction activation energy barrier is delivered directly into the chemical bonds that are involved in the chemical reactions, instead of providing energy solely by thermal heating. By this means, the chemical reaction rate is increased significantly without increasing acid diffusion. A preferred method of introducing energy directly to the chemical bonds is by InfraRed (IR) radiation.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description and accompanying drawings which set forth an illustrative embodiment in which the concepts of the invention are utilized.
REFERENCES:
patent: 4581321 (1986-04-01), Stahlhofen
patent: 5631120 (1997-05-01), Swirbel
Nakamura, et al.; Effect of Acid Diffusion on Resolution of a Chemically Amplified Resist in X-Ray Lithography; Japanese Journal of Applied Physics; vol. 30, No. 10; Oct. 1991 pp. 2619-2625.
Nakamura, et al.; Influence of Acid Diffusion on the Lithographic Performance of Chemically Amplified Resists; Japanese Journal of Applied Physics; vol. 31; Part 1, No. 12B; pp. 4294-4300; Dec. 1992.
Cronin, et al.; Investigation of Onium Salt Type Photoacid Generators in Positive DUV Resist Systems; SPIE vol. 2195; pp. 212-224.
G. Wallraff, et al; Thermal and Acid-Catalyzed Deprotection Kinetics in Candidates Deep Ultraviolet Resist Materials; American Vacuum Society; J. Vac. Sci. Technology B. 12(6); pp. 3857-3862; Nov./Dec. 1994.
Metz, et al.; Selectively Breaking Either Bond in the Bimolecular Reaction of HOD with Hydrogen Atoms; American Institute of Physics; J. Chem. Phys. 99(3); pp. 1744-1751; Aug. 1, 1993.
G. Marc Loudon; Organic Chemistry; Purdue University; pp. 1057-1058.
Ito, et al.; Chemical Amplification in the Design of Dry Developing Resist Materials; Polymer Engineering and Science; vol. 23, No. 18; pp. 1012-1018; Dec. 1983.
Duda Kathleen
National Semiconductor Corp.
Stallman & Pollock LLP
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