Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
1999-07-28
2001-02-06
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S397000
Reexamination Certificate
active
06184526
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for successively inspecting a plurality of patterns provided on a surface of a sample such as a wafer or a mask by use of an electron beam and, more particularly, to a configuration for detecting at least one of secondary electrons, reflected electrons, and back-scattered electrons from the surface of the sample irradiated by the electron beam.
2. Related Background Art
With recent increase in integration of LSI, the detection sensitivity required for detection of defect on the surface of the sample such as the wafer or the mask is becoming higher and higher. For example, where 256M-DRAM is formed on the wafer of the line width 0.25 &mgr;m, the detection sensitivity necessary for this wafer is that enough to detect a defect in the dimension of 0.1 &mgr;m. Desires are also increasing for inspection apparatus satisfying the demand for increase in the inspection speed, as well as the increase in the sensitivity for detection of defect. In order to meet these demands, surface inspection devices (pattern inspection apparatus) utilizing the electron beam have been developed.
An example of the conventional pattern inspection apparatus using the electron beam is the inspection apparatus, for example, described in Japanese Laid-open Patent Applications No. Hei 5-258703 (U.S. Pat. No. 5,502,306) and No. Hei 7-249393 (U.S. Pat. No. 5,576,833).
FIG. 1
is a drawing to show the configuration of the conventional pattern inspection apparatus disclosed in above Japanese Laid-open Patent Application No. Hei 7-249393. This conventional pattern inspection apparatus is composed of a primary column
81
, the primary column
81
consisting of an electron gun having a rectangular cathode for generating a rectangular electron beam and a quadrupole lens system, and a projection type secondary electron detecting column (secondary column)
84
for detecting secondary electrons or reflected electrons from the sample surface (electron beam irradiation area
85
) being an inspected object. When the primary column
81
emits the electron beam (primary beam) to the electron beam irradiation area
85
on the sample
82
, the secondary beam
83
of secondary electrons or the like from the electron beam irradiation area
85
is guided to an electron incident surface of electron detector
86
by an electron lens system for beam shaping provided in the secondary column
84
. Then an electron image of the electron beam irradiation area
85
is taken as electric signals into detection signal processing circuit
87
. By this arrangement wherein the electron optical system is composed of the rectangular cathode and quadrupole lens system, the electron beam irradiation area
85
on the sample
82
irradiated by the primary beam can be shaped readily and arbitrarily. This conventional pattern inspection apparatus is characterized in that high detection sensitivity is achieved and the inspection time for scanning the entire surface of sample can be decreased largely, by generation of the rectangular electron beam with an appropriate aspect ratio.
Next, various detecting systems have been proposed as secondary electron detecting systems for detecting the secondary electrons from the electron beam irradiation area in the surface of sample. An example is a secondary electron detector comprised of MCP/fluorescent screen/linear image sensor.
FIG. 2
is a cross-sectional view to show the structure of the conventional secondary electron detector. The secondary electrons emitted from the electron beam irradiation area in the surface of sample travel through the secondary electron detecting column and then are multiplied by microchannel plate (MCP)
71
. A fiber optic plate (FOP) the input surface of which is coated with a fluorescent film
72
is located behind this MCP
71
. A group of electrons multiplied by the MCP
71
are converted to light by the fluorescent film
72
and thereafter the electrons are guided through the FOP
73
into MOS linear image sensor
74
to be further converted to electric signals.
SUMMARY OF THE INVENTION
The inventors examined the prior art described above and found the following problems.
Specifically, the conventional secondary electron detector uses the MCP, and the area where the secondary electrons generated in the surface of sample arrive also has such a high aspect ratio as to be long in a predetermined direction, similar to the cross-sectional shape of the electron beam emitted to the surface of sample. Therefore, the area of the electron incident region in the MCP being an electron multiplying means also becomes very small.
It is generally known that the MCP lowers its relative gain down to about 60% when the overall output charge per unit area becomes 0.1 C/cm
2
. Accordingly, the small use area of MCP (the area of the region where the electron beam from the surface of sample is incident) poses a problem that the lifetime of the MCP becomes shortened.
On the other hand, noting the inspection accuracy of defect in the surface of sample, consideration must be given to the possibility that the position of the sample could deviate while a stage with the sample mounted thereon is continuously moved. The positional deviation of the sample occurring during inspection will make the resultant sample image imperfect. No consideration is given to this problem in the conventional pattern inspection apparatus, which will hinder the inspection of patterns or the like on the wafer, for example.
The present invention has been accomplished mainly to solve the above problems and an object of the present invention is to provide an inspection apparatus and an inspection method in the structure that can increase the lifetime of the MCP while maintaining the high inspection accuracy.
The pattern inspection apparatus according to the present invention basically comprises a primary column including an illumination system for emitting an electron beam (primary beam) to a surface of a sample and a secondary column for guiding an electron beam (secondary beam) from the surface of the sample to an electron detecting system. The primary column comprises an electron gun for emitting the primary beam and a quadrupole lens system for guiding the primary beam to a predetermined area in the surface of the sample and for shaping a cross section of the primary beam, and the secondary column also comprises a quadrupole lens system for focusing an electron image, formed by the secondary beam, at a predetermined magnification on an electron incident surface of the electron detecting system. In the apparatus, the above primary column and secondary column can be incorporated by applying an electromagnetic prism such as a Wien filter for bending an orbit of the primary beam and letting the secondary beam travel straight as shown in
FIG. 3
; or, they can be constructed separately and independently of each other as shown in
FIG. 7
etc.
Specifically, the first embodiment of the pattern inspection apparatus according to the present invention is at least an apparatus for successively inspecting a plurality of patterns provided on a principal surface of a predetermined sample, which comprises an irradiation system for emitting an electron beam to a predetermined area (electron beam irradiation area) including an inspection target area in the surface of the sample, a stage capable of moving with the sample being mounted thereon, a position detecting system for detecting a position of the stage, and an electron detecting system for detecting at least either of secondary electrons, reflected electrons, and back-scattered electrons from the electron beam irradiation area on the sample irradiated by the electron beam.
The above electron detecting system has a microchannel plate (MCP) for multiplying at least either of secondary electrons, reflected electrons, and back-scattered electrons arriving thereat from the electron beam irradiation area, a fluorescent section for converting a group of electrons multiplied and outputte
Hamashima Muneki
Kohama Yoshiaki
Takemoto Shigeru
Foley & Lardner
Nguyen Kiet T.
Nikon Corporation
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