Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2001-07-20
2003-09-02
Tran, Huan (Department: 2861)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S397000, C250S307000
Reexamination Certificate
active
06614022
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a substrate manufacturing apparatus including circuit patterns such as semiconductor devices and liquid crystal and particularly to the technique for inspecting the patterns of substrate in the course of the manufacture using SEM.
A pattern inspecting apparatus using the electron beam of the related art is described, for example, in the official gazette of Japanese Laid-Open Patent Application No. 258703/1993. An example of the pattern inspection apparatus using electron beam described in the above cited reference is illustrated in FIG.
1
. An electron beam
2
emitted from an electron beam source
1
is deflected with a deflector
3
in the X direction, this electron beam irradiates an object substrate
5
via an objective lens
4
, the secondary electron
7
(including the secondary electron and reflected electron generated from a sample through irradiation of the primary electron beam) emitted from the object substrate
5
is simultaneously deflected with an E×B deflector (hereinafter referred to as only E×B)
13
while a stage
6
is continuously moved in the Y direction, this secondary electron beam
7
is detected with a detector
8
as an electric signal and it is then amplified with a pre-amplifier
14
, thereafter the detected signal is A/D-converted with an A/D converter
9
to obtain a digital image, this image is then compared with a digital image at the area which may be expected as to be identical in an image processing circuit
10
, thereby an area generating a difference is detected as a pattern defect
11
to identify the defective area. The object substrate
5
is kept at a negative potential with the retarding voltage and therefore an acceleration voltage can easily be changed on the object substrate
5
by changing the retarding voltage
12
.
In the apparatus of the related art as illustrated in
FIG. 1
, the secondary electron
7
has been detected with convergence to one detector
8
. However, a degree of convergence of the secondary electron is restricted with various conditions. As the restricting conditions, it is possible to consider (1) degree of freedom of the electro-optical system (retarding voltage, current of primary beam, electric field of the area near the sample, etc. for controlling the acceleration voltage of the primary electron incident to the sample), (2) deflection of the electron beam
2
with the deflector
3
for scanning the sample, (3) allowance of setting, (4) contamination of surface of the detector
7
generated with collision of electron beam and (5) various aberrations in the electro-optical system, or the like.
Although depending on the practical design of the electro-optical system, the conditions (4) and (5) contribute to the degree of convergence of secondary electron and the minimum degree may be estimated as about 1 mm under the condition of the electro-optical system, that is, under the condition that the retarding voltage, current of primary beam and field at the area near the sample which control the acceleration voltage of the primary electron incident to the sample is fixed to only one condition. Moreover, the influence on the degree (2) of convergence of the secondary electron due to the scanning of the deflector
3
with the electron beam
2
appears as the movement of the converging position of about 0.5 mm, although depending on the scanning width and magnifying factor for the secondary electron. Moreover, in regard to the degree of freedom (1) of the optical system, a degree of convergence is changed for about 1 mm by the defocusing, although depending on the other conditions, when the retarding voltage
12
, for example, is changed.
Moreover, in actual, since the optical axis of the secondary electron optical system is deviated, it can be estimated that the converging position is shifted by about 0.5 mm. When these factors are added, the diameter of about 3 mm is required for the effective light receiving surface of the detector to detect the secondary electron and when the allowance of setting (3) is considered, the diameter of 4 mm will be required for the effective light receiving surface of the photosensor.
Meanwhile, the frequency characteristic of detector is inversely proportional to the area of the detector. For example, in the case of the detector having the diameter of 4 mm, the cut-off frequency is only 75 MHz even when the design condition and operating condition are improved. On the other hand, when the diameter of detector is set to 2 mm, the cut-off frequency becomes about 150 MHz. However, as explained above, since the detector of the related art requires a diameter of 4 mm, response is possible only for 15 Msps (sps: sample per second) of the sampling frequency corresponding to the cut-off frequency of 75 MHz and it has been impossible to respond to the higher frequency.
SUMMARY OF THE INVENTION
The present invention can provide an inspection apparatus using SEM which can sufficient detect the secondary electron even at the sampling frequency higher than 150 Msps which has been difficult in the structure of the related art to sufficiently cover the detection of secondary electron.
The first means for embodying the present invention is illustrated in FIG.
2
.
Here, the structure for solving the problems will be explained, for easier understanding, for detection at the 400 Msps rate under the assumption that a size of detector is 4 mm square (in above example, the diameter is set to 4 mm, but here the detector has the size of 4 mm square), cut-off frequency is 75 MHz and the cut-off frequency is inversely proportional to only the area. Of course, the numerical values also change depending on the internal structure and material of sensor, but these are not explained here. The contents explained above is the essential factors for the case where the target of speed is set to 400 Msps or more. Moreover, the number of detectors is set, for example, to four, but it is selected as the typical value of a plurality of detectors and the present invention is never limited only to the numerical value 4.
The first means is composed of an electron source
1
for generating the electron beam
2
, a deflector
3
for deflecting the electron beam
2
, an objective lens
4
for converging the electron beam
2
on the object substrate
5
, a stage
6
for holding the object substrate
5
to apply the retarding voltage
12
for the scanning and positioning, E×B
13
for deflecting the secondary electron
7
emitted from the object substrate
5
, a 4-split detector
20
of 2 mm square each for detecting the secondary electron
7
deflected with the E×B
13
, preamplifiers
21
a
to
21
d
having the bandwidth of 200 MHz or higher connected to each detector, an A/D converter
22
of 400 Msps for adding and A/D-converts outputs of the preamplifiers
21
a
to
21
d
to obtain the digital image and an image processing circuit
10
for detecting, from the digital image, an area generating difference as a defect
11
through comparison with the digital image of the area intrinsically providing expectation for the matching of images.
In above structure, the electron beam
2
from the electron source
1
is deflected in the X direction with the deflector
3
, this electron beam
2
irradiates the object substrate
5
via the object lens
4
, the secondary electron
7
from the object substrate
5
is bent with E×B
13
for detection with the 4-split detector
20
while the stage
6
is continuously moved in the Y direction, the signal is A/D-converted to obtain the digital image after the signal of each split detector into voltage with the preamplifiers
21
a
to
21
d
and the signals are added with the A/D converter and the image processing circuit
10
detects the area generating difference as the defect
11
through comparison with the digital image of the area intrinsically providing expectation for the matching of images. In this case, the secondary electron
7
can be expanded only to the maximum area of 4 mm square even whe
Gunji Yasuhiro
Hiroi Takashi
Kuni Asahiro
Shinada Hiroyuki
Shishido Chie
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Tran Huan
LandOfFree
Pattern inspection method and apparatus using electron beam does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pattern inspection method and apparatus using electron beam, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pattern inspection method and apparatus using electron beam will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3085413