Radiation imagery chemistry: process – composition – or product th – Registration or layout process other than color proofing
Reexamination Certificate
1999-12-17
2002-04-23
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Registration or layout process other than color proofing
C430S030000, C430S296000, C430S942000
Reexamination Certificate
active
06376136
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a charged beam exposure method and charged beam exposure apparatus, and, more particularly, to a charged beam exposure method and charged beam exposure apparatus for use in aligned exposure.
A typical alignment method to be used in exposure using a charged beam, for example, an electron beam is to scan a mark formed on the base substrate with a fast-accelerated electron beam and detect back-scattered electrons or secondary electrons from the mark. This mark for alignment is formed in a step structure or formed of materials with different back-scattered electron emission efficiencies.
Recently, studies are being made on exposure with a low-energy electron beam of 1 to 2 kV because it provides enhanced resist sensitivity and lower proximity effect and is difficult to cause charge-up (see, for example, J. Vac. Sci. Technol. 10 (1992) 2743, “Arrayed miniature electron beam columns for high throughput sub-100 nm lithography” by H. P. Chang et al.). Such a low-energy electron beam however has a poor penetration capability.
The problem that arises from mark detection using a low-energy electron beam will be discussed below referring to FIG.
1
. As shown in
FIG. 1
, a sample has a lamination structure of an Si substrate
21
, an Si oxide film
22
and a resist
24
. An alignment mark
12
is formed on the Si substrate
21
deep from the surface of the resist
24
. When a low-energy electron beam
10
is used, the electron beam
10
does not reach the alignment mark
12
formed deep from the surface of the resist
24
, so that a back-scattered electron signal cannot be acquired. While there has been proposed provision of separate electron beam sources respectively for mark detection and exposure (e.g., Jpn. Pat. Appln. KOKAI Publication No. Hei 2-37710, Jpn. Pat. Appln. KOKAI Publication No. Hei 7-169665 and Jpn. Pat. Appln. KOKAI Publication No. Sho 63-263720), this approach makes the exposure apparatus complex.
As a solution to the problem that a back-scattered electron signal cannot be acquired, a mark detection method as illustrated in
FIG. 2
is proposed. As shown in
FIG. 2
, this method scans only a resist surface
182
with the electron beam
10
to charge up the resist surface
182
so that the image of the alignment mark
12
is seen as secondary electrons
183
.
This method utilizes the fact that there is a contrast between a capacitance
184
applied to the insulating film above the mark
12
differs from that in the other region, which makes the secondary electron emission efficiency directly above the mark
12
different from that on the other region.
FIGS. 3A and 3B
show the pattern image and waveform of the alignment mark
12
detected by this method.
FIG. 3A
is a top view of the pattern image of the alignment mark
12
, and
FIG. 3B
shows the detected waveform of the pattern image. Although this method has been discussed with reference to an example wherein the resist film is used as the insulating film, an Si oxide film or the like may be used as the insulating film without changing the effect.
This mark detection method however has the following shortcomings. In a case of performing electron beam exposure on an insulating film like a resist, charge-up may cause misalignment of the beam. Conventionally, to eliminate this charge-up, a conductive film
201
was formed under (or on) the resist
24
as shown in FIG.
4
. Here, the conductive film
201
, like the Si substrate
21
, is grounded to an earth
7
. In such a case, no charge-up occurs, thus ensuring electron beam exposure without misalignment. Because the whole conductive film
201
has the same potential, however, there is no capacitance contrast between a region above the alignment mark
12
and the other region. This makes it difficult to detect the image of the alignment mark
12
.
Further, inclination of a sample to the objective lens lowers the precision of alignment.
FIG. 5
is a diagram for explaining this problem.
FIG. 5
shows a case where a sample
2
is tilted with respect to, for example, an objective lens
211
at the time a voltage is applied to the sample
2
. In this case, an electric field
212
between the sample
2
and the objective lens
211
become non-uniform, changing the traveling path of the electron beam
10
.
As apparent from the above, the conventional exposure method using a low-energy electron beam suffers a low penetration capability of the electron beam, which makes it difficult to ensure high-precision alignment exposure with a simple system structure. With regard to the mark detection scheme which utilizes the capacitance contrast, when a conductive film is formed on or under the resist to prevent charge-up of the resist, the alignment mark cannot be detected. When the traveling direction of the electron beam deviates from the inclination of the surface of the sample, it is difficult to perform high-precision alignment.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a charged beam exposure method which can accomplish high-precision alignment and pattern exposure with a simple structure.
It is another object of this invention to provide a charged beam exposure apparatus which can accomplish high-precision alignment and pattern exposure with a simple structure.
According to a first aspect of the invention, there is provided a charged beam exposing method comprising the steps of: applying a first voltage for accelerating a charged beam, emitted toward a sample by a charge-particle irradiating section, more than is accomplished by application of a reference exposure voltage to the sample and scanning an alignment mark formed in the sample with the charged beam to thereby acquire a position of the alignment mark; and applying the reference exposure voltage to the sample to carry out pattern exposure with the charged beam emitted from the charge-particle irradiating section.
According to a second aspect of the invention, there is provided A charged beam exposing method comprising: a first step of applying a voltage different from a reference exposure voltage to a sample; a second step of scanning the sample with a charged beam to thereby detect a position of an alignment mark formed in the sample; a third step of changing an applied voltage to the sample; a fourth step of detecting an amount of change in the position of the alignment mark caused by a change in the applied voltage; and a fifth step of adjusting a tilt of the sample based on the amount of change in the position of the alignment mark.
According to a third aspect of the invention, there is provided A charged beam exposing apparatus comprising: an charge-particle irradiating mechanism irradiating a charged beam to a sample; a voltage applying mechanism selectively applying a voltage for accelerating the charged beam to the sample at a time of alignment exposure; and a mark position detecting mechanism detecting charge particles from the sample generated by irradiation of the charged beam in the alignment exposure to thereby detect a position of an alignment mark formed in the sample.
According to this invention, an acceleration electric field is generated on the surface of a sample by applying a voltage to the sample and an alignment mark is detected using the accelerated charged beam. Even if a low-energy charged beam is used, therefore, the mark located deep from the sample surface can be detected. Further, even in which case where a conductive film is formed under the resist, high-precision detection of the alignment mark is possible which was difficult according to the conventional alignment method using a low-energy electron beam. Further, as charged beam exposure is carried out at a slower acceleration than mark detection, it brings about such advantages as suppression of the proximity effect by the slow-accelerated charged beam exposure apparatus and prevention of charge-up. Furthermore, alignment with the fast-accelerated beam and exposure with slow-accelerated beam can be switched from one to
Abe Hideaki
Nakasugi Tetsuro
Yamazaki Yuichiro
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Young Christopher G.
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