Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2002-02-04
2004-05-25
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06740456
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-028553, filed Feb. 5, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method of correcting a photomask used for the manufacture of a semiconductor integrated circuit, and more particularly to a method of correcting a photomask by applying a focused ion beam (FIB) to a defect of the photomask to repair the defect.
2. Description of the Related Art
In correcting a defect of a photomask using a focused ion beam, one point drift correction is used in order to totally correct a drift of an image due to charge up, or a drift due to thermal expansion of a mask or a mask holder. In the one point drift correction, a pinhole is formed in a pattern of the photomask. The beam is moved to the portion to be corrected by using the pinhole as a reference point, thereby enhancing correction accuracy. A specific example of the one point drift correction will be described below with reference to
FIGS. 8
to
10
.
A focused ion beam
22
a
is applied to a part of a pattern
12
which is formed on a substrate
11
for a photomask, so that a pinhole
13
, which serves as a reference point, is formed. Then, an ion beam
22
b
is applied from an ion beam source
21
to a scan region
14
including the pinhole
13
. Secondary ions (secondary charged particles)
23
released from the portion where the pinhole
13
is formed are detected by a detector
24
, thereby recognizing (obtaining) the reference point. Then, the positional relationship between the detected position of the pinhole
13
(position of the reference point) and the portion to be corrected which is known in advance, is calculated. After re-confirming the position of the pinhole
13
, the ion beam is applied to the portion to be corrected, thereby correcting the defect. After that, by repeatedly performing the ion beam irradiation for confirming the reference point and the ion beam irradiation for correcting the defect, the defect correction is completed. In this way, by confirming the reference point immediately before the defect correction processing, the influence of a drift can be reduced to a minimum.
If defect correction is performed using the above-described one point drift correction, it is conventionally considered that a round shape is ideal as the shape of a planar pattern of the reference point (pinhole) (refer, for example, to Jpn. Pat. Appln. KOKOKU Publication No. 5-4660). From this point of view, the pinhole is conventionally formed by applying the ion beam to a square-shaped area with an equal number of dots in longitudinal and horizontal directions (e.g. 4×4 dots).
However, if a phase shift mask is used as a photomask, a proper phase shift operation (phase effect) cannot be obtained at the region where the pinhole is formed. Therefore, if the pinhole is large relative to the pattern, a region which affects a projected image is also large. If the pinhole is large, the scan region for detecting the pinhole needs to be large. Thus, the beam scan damages a wide area of the pattern. Therefore, if the pattern is small, the line size of the projected image is small, which is a problem. Further, in the case of correcting a pinhole mark, since a carbon film deposited for correction does not have a phase shift operation, the smaller the pattern, the wider the region which affects the projected image.
As shown in
FIG. 10
, in general, a detector
24
is disposed obliquely above the pinhole
13
. Thus, if the pattern of the pinhole has a square shape, the following problem will arise. Since the detector
24
is disposed obliquely above the pinhole
13
, the secondary ions
23
coming out of the pinhole
13
are considered to be blocked to some extent by a sidewall at the detector
24
side (the left sidewall in FIG.
10
). Therefore, the length of the pinhole
13
in the X direction shown in
FIG. 10
needs to be increased to a degree. In this case, if the pinhole
13
is a square pattern, the length of the pinhole
13
in the Y direction is equal to that in X direction. Regarding the X direction, the arrival of the secondary ions to the detector
24
is limited by the left sidewall (in FIG.
10
). Thus, the yield of the secondary ions is biased to the right region (in FIG.
10
), and a certain degree of positional accuracy can be obtained. However, since such a situation will hardly occur in the Y direction, the positional accuracy (recognition accuracy) of the pinhole in the Y direction cannot sufficiently be obtained. In actuality, as shown in
FIG. 11
, a secondary ion image
31
corresponding to the pinhole is a vertically elongated image in the Y direction.
Further, in the prior art, many secondary ions are blocked by a sidewall on the detector
24
side as described above. Thus, there is a problem that the secondary ions from the bottom portion of the pinhole, i.e., the exposed surface of the substrate, do not reach the detector with efficiency.
In the conventional method of correcting the photomask using one point drift correction, if the phase shift mask is used as a photomask, the region, where phase shift operation (phase effect) cannot be obtained, increases. Thus, a proper projected image cannot be obtained, which is a problem. There are also problems that the positional accuracy (recognition accuracy) of the reference pinhole is insufficient, and that the secondary ions (secondary charged particles) from the pinhole cannot efficiently be made incident on the detector.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a method of correcting a photomask, comprising: preparing a photomask substrate with a mask pattern including a phase shift pattern; forming a reference hole by removing a part of the mask pattern; applying an ion beam from an ion beam source to an area including the reference hole to allow secondary charged particles to be released from the reference hole; obtaining a position of the reference hole by detecting the secondary charged particles by a detector; calculating a positional relationship between the obtained position of the reference hole and a position of a defect of the mask pattern; and correcting the defect by applying an ion beam from the ion beam source to the defect, based on the calculated positional relationship, wherein a pattern of the reference hole, as viewed in a direction perpendicular to a top surface of the photomask substrate, is substantially rectangular, and a longitudinal direction of the rectangular pattern is parallel to a longitudinal direction of the phase shift pattern.
According to a second aspect of the present invention, there is provided a method of correcting a photomask, comprising: preparing a photomask substrate having a mask pattern; forming a reference hole by removing a part of the mask pattern; applying an ion beam from an ion beam source to an area including the reference hole to allow secondary charged particles to be released from the reference hole; obtaining a position of the reference hole by detecting the secondary charged particles by a detector, a charged particle incidence portion of the detector being disposed obliquely above the reference hole; calculating a positional relationship between the obtained position of the reference hole and a position of a defect of the mask pattern; and correcting the defect by applying an ion beam from the ion beam source to the defect, based on the calculated positional relationship, wherein a pattern of the reference hole, as viewed in a direction perpendicular to a top surface of the photomask substrate, is substantially rectangular, and a longitudinal direction of the rectangular pattern is parallel to a straight line obtained by projecting, on the top surface of the photomask substrate, a straight line linking the incidence portion of the detector and the reference hole.
Acc
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Rosasco S.
LandOfFree
Method of correcting a photomask and method of manufacturing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of correcting a photomask and method of manufacturing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of correcting a photomask and method of manufacturing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3256676