Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1998-11-06
2001-04-03
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S330000, C430S945000
Reexamination Certificate
active
06210868
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a method for forming a pattern on a chemical sensitization photoresist and, more particularly, to a method for forming a pattern on a chemical sensitization photoresist to obtain a photoresist mask used as an etching mask or an ion-implantation mask on a semiconductor substrate.
(b) Description of the Related Art
A higher integration and a higher-speed operation have been achieved in the field of semiconductor devices by obtaining finer patterns for device element using a photolithographic technique. The conventional semiconductor devices using a design rule of 0.5 &mgr;m are fabricated by g-line lithography using an exposure wavelength of 436 nm, whereas semiconductor devices using a design rule of 0.5 to 0.35 &mgr;m are fabricated by i-line lithography using an exposure wavelength of 365 nm.
Next generation semiconductor devices to be developed in the near future may be fabricated in a design rule of 0.30 to 0.18 &mgr;m. A KrF excimer laser lithography using an exposure wavelength of 248 nm is expected to provide such a finer design rule.
Conventional photolithographic techniques generally provided patterns of respective design rules larger than the exposure wavelength used in the photolithographic techniques. On the other hand, the KrF excimer laser is expected to provide a pattern in a finer design rule of 0.18 &mgr;m which is smaller than the wavelength 248 nm of the KrF excimer laser. In such a case, problems of insufficient resolution and depth of focus should be considered.
The resolution R and the depth of focus (DOF) are represented as follows:
R=k
1
·&lgr;/NA,
and
DOF=k
2
·&lgr;/(
NA
)
2
,
wherein &lgr; and NA are exposure wavelength and numerical aperture, respectively, of the exposure system, and k
1
and k
2
are constants.
In the above formulae, the resolution R can be improved by employing a smaller exposure wavelength and a larger numerical aperture, whereas the DOF suddenly decreases along with the smaller exposure wavelength and the larger numerical aperture. That is, the resolution R and DOF in the exposure system are tradeoffs.
In addition, it is generally difficult in a KrF excimer laser lithography to use a positive type photoresist, obtained as a compound of novolac resin and naphthoquinone-diacido, which has been used in the g-line and i-line lithographies. This is because novolac resin has a large optical absorption for light having wavelength of 248 nm, and cannot provide a suitable profile having a sharp vertical edge.
In view of the above, active researches have been conducted to obtain a new type photoresist that is called chemical sensitization photoresist. The chemical sensitization photoresist is made from a base resin, an acid generator which generates acid during exposure thereof, and a compound having a protective group which changes solubility of the compound for a developing solution depending on the amount of acid. The base resin is generally selected from phenolic resins having a high transmission factor to light having a 248 nm wavelength.
As one of the techniques for forming a finer pattern using a chemical sensitization photoresist that exceeds the conventional patterning technique, Patent Publication JP-A-4-364021 proposes a method for heating the photoresist up to around the softening point thereof after the patterning thereof to swell the photoresist to obtain a finer pattern.
In the proposed technique, however, the heating of the photoresist up to the softening point thereof causes problems of degradation in the profile and insufficient controllability of the dimensions in the resultant photoresist pattern.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a method for forming a pattern on a chemical sensitization photoresist, which is capable of providing an excellent profile and excellent controllability of the dimensions.
The present invention provides a method for forming a pattern on a chemical sensitization photoresist film comprising the consecutive steps of exposing a photoresist film through a mask pattern, developing the exposed photoresist film to form a photoresist pattern, separating a protective group from the photoresist pattern, and heat treating the photoresist pattern.
In accordance with the method of the present invention, providing the step of separating the photoresist group from the photoresist pattern separately from heat treating the photoresist pattern to swell the photoresist pattern can achieve improvement of the resolution and controllability of the dimensions. The present invention is based on the finding that the heating of the chemical sensitization photoresist up to the softening temperature thereof causes simultaneous separation of protective group and swelling of the photoresist, which degraded the resolution and controllability of the photoresist in the conventional technique.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.
REFERENCES:
patent: 5385809 (1995-01-01), Bohrer et al.
patent: 5580695 (1996-12-01), Murata et al.
patent: 0524759A1 (1993-01-01), None
patent: 4-364021 (1992-12-01), None
patent: 6-275514 (1994-09-01), None
patent: 9-160259 (1997-06-01), None
patent: 10-246959 (1998-09-01), None
patent: 10-333341 (1998-12-01), None
Duda Kathleen
Hayes, Soloway, Hennessey Grossman & Hage, P.C.
NEC Corporation
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