Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2000-09-15
2002-11-05
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S306000, C250S309000, C250S311000
Reexamination Certificate
active
06476390
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a pattern inspection device and a pattern inspection method for semiconductors and the like, and, more particularly, to a pattern inspection device and a pattern inspection method which are capable of high-speed inspection of semiconductors and the like.
BACKGROUND OF THE INVENTION
In a semiconductor manufacturing process, a number of pattern formation steps are repeated. In the respective steps, if manufacturing conditions are not optimized, abnormalities such as foreign substances and defects and the like occur in a circuit pattern of a semiconductor device formed on a substrate. Accordingly, in the manufacturing process, it is necessary to detect the occurrence of an abnormality at an early stage and feed it back to the process.
Generally, in the manufacturing process for an VLSI or the like, as a number of chips having the same circuit pattern are obtained from one sheet of semiconductor substrate, a pattern abnormality is detected by comparing identical circuit patterns of different chips. In an inspection device to inspect a circuit pattern of a semiconductor wafer by using an electron beam, as it takes an enormous amount of time to inspect the entire wafer with the electron beam, a method to compare identical circuit patterns of different chips, by a construction having two electron-optic systems is especially disclosed in Japanese Published Unexamined Patent Application No. Sho 59-6537.
As is well-known in the art, if a difference signal of detection signals, obtained from identical circuit patterns of different chips, exceeds a reference value, it is determined that a pattern abnormality exists. However, in this construction, although it can be determined that an abnormality exists in one of the chips, the chip having the abnormal pattern cannot be determined. In the abnormality determination, comparison with another pattern obtained from another chip is necessary. For this purpose, all the image data of the two chips is stored into an image memory, then the inspection moves to another chip, the electron beam is emitted on the corresponding same pattern, and a determination is made. Accordingly, a large capacity image memory is required, and further, there is a possibility that the stability of the system is impaired with the lapse of time during movement to the other chip.
Further, to improve the throughput of the inspection time, it is necessary to emit a fine electron probe beam of large current on a sample. For this purpose, the brightness of an electron beam source must be high, so that a field-emission type electron source is indispensable as the electron beam source. Note that to operate the field-emission type electron beam source in a stable manner, the degree of vacuum around the electron beam source must be suppressed to the order of 10
−7
Pa. However, in the conventional construction, it is difficult to closely arrange plural electron-optic systems with maintaining a high vacuum degree in the electron beam guns. For example, in the above-described well-known art, an area around the electron beam source is evacuated from a sample chamber. Further, in a conventional technique described in “Journal of Vacuum Science and Technology B14(6)”, page 3776, the entire electron-optical system is placed in one chamber, as shown in FIG.
12
. Accordingly, in this construction, to evacuate the area around the electron beam source to a very high degree of vacuum, the sample chamber must be also evacuated to a very high degree of vacuum. However, since a wafer coated with chemical material, such as a resist, emits a large amount of gas, and the structure of a stage to control movement of the wafer is complicated, it is practically impossible to evacuate the sample chamber to a very high degree of vacuum. Generally, the degree of vacuum is merely improved to about 10
−5
Pa. Even if a very high degree of vacuum in the sample chamber can be realized, as the degree of vacuum in the sample chamber is lowered upon exchange of a sample, the period to evacuate the sample chamber after the sample exchange to the very high degree of vacuum is e.g. equal to or longer than one hour. Thus, it is impossible to inspect a large number of wafers within a short period,
Further, in a construction as shown in
FIG. 13
where an electron beam gun chamber
101
and a sample chamber
103
are respectively evacuated by independent vacuum pumps, a large number of vacuum pumps must be provided, with the result that a large number of spaces for placement of vacuum pumps must be provided. For example, in
FIG. 13
, to provide a vacuum pump for the central electron-optical system, a close arrangement is impossible.
Further, in general detection means, if the electron-optical systems are closely arranged, it is difficult to hold secondary electrons and reflected electrons
302
obtained by emitting an electron beam on a sample within the same electron-optical system. That is, as means for detecting the secondary electrons and reflected electrons
302
in plural electron-optical systems, a method for detection by providing detectors
13
on the rear surfaces of final stage lenses, as shown in
FIG. 15
, is disclosed in the “Journal of Vacuum Science and Technology B14(6)” page 3775. In this construction, it is difficult to hold the secondary electrons and reflected electrons
302
within the same electron-optical system, and so the secondary electrons and reflected electrons
302
are easily attracted by the detector
13
in the adjacent electron-optical system; as a result, precise pattern inspection cannot be made. Further, Japanese Published Unexamined Patent Application No. Hei 2-142045 discloses a method for detecting secondary electrons, accelerated by application of a negative voltage to a sample, that have passed through an objective lens. However, there is no specific construction to improve the efficiency of secondary electron detection.
SUMMARY OF THE INVENTION
The present invention has the following construction as means for solving the above problems. That is, at least three electron-optical systems are provided, and detection signals from identical circuit patterns of different chips are compared with each other. If three or more images are obtained at the same time, the position of a pattern defect can be simultaneously determined. Further, in a case where a stage is continuously moved, the same pattern repeatedly exists within the chip, and images continuously obtained by the respective electron-optical systems are sequentially compared, the throughput of the inspection period is improved in proportion to the number of electron-optical systems.
Further, in accordance with the present invention, as shown in
FIG. 14
, to maintain a high degree of vacuum in an area around the electron source
1
, three or more electron-optical systems are provided in one mirror body representing a same column or chamber, and a common vacuum pump evacuates an area around the electron source
1
or an area around an intermediate chamber
102
provided between the electron source
1
and the sample chamber
103
, so that the electron-optic systems can be closely arranged. That is, since the areas around the plural electron sources
1
are connected to the area around the sample chamber via fine openings through which electron beams pass, and the areas around the electron sources are evacuated independently of the area around the sample chamber
103
, a high degree of vacuum in the areas around the electron sources
1
can be maintained.
Further, to independently detect secondary electrons and reflected electrons, produced in the plural electron-optical systems, in the respective electron-optical systems, the secondary electrons and reflected electrons
302
, generated from the sample are accelerated toward the electron source side in the direction of the electron beam axis
9
so that they can be detected by a detector provided toward the electron source side from an objective lens, without colliding against a counter electrode
19
, as shown in
Hasegawa Masaki
Kuroda Katsuhiro
Murakoshi Hisaya
Nozoe Mari
Shinada Hiroyuki
Lee John R.
Vanore David A.
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