Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2001-12-27
2004-07-27
Wells, Nikita (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S492100, C250S492200, C250S492300
Reexamination Certificate
active
06768112
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of priority from the prior Japanese Patent Application No. 2000-400814, filed on Dec. 28, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an inspection system and a method for controlling the same. More specifically, the invention relates to a substrate inspection system for observing an integrated circuit pattern on a semiconductor wafer by using charged particle beams.
2. Description of the Related Art
With the high integration of LSIs, the detection sensitivity required to detect defects and foreign matters on wafers and masks are rising. It is said that the detection sensitivity must be generally ½ or less of a pattern wiring width in order to inspect pattern defects and foreign matters which cause critical failures. For that reason, in a defect inspection on a semiconductor wafer which has a design rule of 0.13 &mgr;m or less, the limitation of the pattern defect inspection based on optical systems is realized. Under such a background, pattern defect inspection systems using charged particle beams have been developed (Japanese Patent Laid-Open Nos. 5-258703, 6-188294, 7-249393, etc.). In order to achieve a high-speed processing in a semiconductor wafer pattern inspection system based on charged particle beams, it is expected that the construction of an electron optical system proposed by Japanese Patent Laid-Open No. 7-249393 is the most influential means. In order to realize it, there is an optical system proposed by Japanese Patent Laid-Open No. 11-132975.
Referring to
FIG. 3
, a technique described in Japanese Patent Laid-Open No. 11-132975 will be described as an example of a related art. Furthermore, the same reference numbers are given to the same portions in the respective figures, and the detailed descriptions thereof are omitted.
A substrate inspection system shown in
FIG. 3
uses electron beams as charged particle beams, and schematically comprises: an electron beam irradiation part, and a control part thereof; a stage
12
for mounting thereon a substrate
11
serving as a sample, and a control part thereof; a secondary, reflected and back-scattered electron beam mapping projecting optical part (which will be hereinafter simply referred to as a mapping projecting optical part), and a control part thereof; an electron image detecting part, and a control part thereof; and an electron beam deflecting part, and a control part thereof.
The electron beam irradiation part is arranged so as to be mechanically inclined with respect to the surface of the substrate
11
. On the other hand, the optical axis of the mapping projecting optical part is arranged so as to extend in a direction perpendicular to the surface of the substrate
11
. With this construction, electron beams (which will be hereinafter referred to as irradiation electron beams)
31
emitted from an electron gun enter the electron beam deflecting part in a direction inclined by a predetermined angle with respect to the surface of the sample, and the irradiation electron beams
31
are deflected by the electron beam deflecting part in a direction perpendicular to the surface of the substrate
11
to enter the substrate
11
. In addition, secondary electrons, reflected electrons and back-scattered electrons (which will be hereinafter referred to as secondary electrons and so forth), which are produced on the surface of the substrate
11
, are accelerated by the electric field on the surface of the substrate
11
in a direction perpendicular to the surface of the substrate
11
and enter the mapping projection optics.
The electron beam irradiation part comprises an electron gun and two-stage quadrupole lenses. The electron gun includes a lanthanum hexaboride (which will be hereinafter referred to as LaB
6
) cathode
1
having a rectangular electron emission surface with the size of 100 &mgr;m×10 &mgr;m, an Wehnelt electrode
2
having a rectangular opening, an anode
3
having a rectangular opening, and a deflecting system
4
for adjusting an optical axis. The accelerating voltage, emission current and optical axis for the irradiation electron beams
31
are controlled by control parts
7
,
8
and
9
, respectively. In order to form rectangular beams having a size of 100 &mgr;m×25 &mgr;m on the surface of the substrate
11
, two-stage electrostatic quadrupole lenses
5
and
6
, and a control part
10
thereof are provided. The accelerating voltage for the irradiation electron beam
31
is determined by the relationship between the resolution of the mapping projecting optical part and the incidence voltage to the substrate
11
.
The irradiation electron beams
31
are emitted from the LaB
6
cathode
1
to leave the electron beam irradiation part while being converged by the quadrupole lenses
5
and
6
, and enter the electron beam deflecting part
34
. The electron beam deflecting part
34
has a Wien filter (not shown). The trajectory of irradiation electron beams
31
is deflected by the Wien filter so as to be perpendicular to the surface of the substrate
11
, and then, the irradiation electron beams
31
leave the electron beam deflecting part
34
. Thereafter, the irradiation electron beams
31
are reduced by a rotationally symmetric electrostatic lens
14
to perpendicularly irradiate the substrate
11
. A voltage is applied to the electrostatic lens
14
by a power supply
15
.
A negative voltage is applied to the stage
12
by a power supply
13
, so that a negative voltage is applied to the substrate
11
. The movement of the stage
12
is controlled by a control part
13
. The value of the voltage applied to the substrate
11
is determined by the resolution performance of the mapping projecting optical part. In order to obtain a resolution of 0.1 &mgr;m or less, the voltage of electron beams of secondary ions (which will be hereinafter referred to as secondary electron beams)
32
require energy of about 5 keV, so that a voltage applied to the sample is preferably 5 kV. On the other hand, the energy of the irradiation electron beams
31
is determined by the difference between the voltage applied to the substrate and the incident voltage to the substrate. If the substrate
11
is a semiconductor wafer, the incident voltage to the substrate
11
is generally about 800 V or less to prevent the irradiation damage and charging. As a result, the voltage of the irradiation electron beams is 5.8 kV.
When the wafer is irradiated with the irradiation electron beams
31
, secondary electrons and so forth forming an electron image indicative of the shape, material, potential and so forth of the surface of the substrate are emitted from the surface of the substrate
11
. These electrons are accelerated by an accelerating field produced between the electrostatic lenses
14
and enter the electron beam deflecting part
34
while drawing a trajectory having a focal point at infinity by the electrostatic lens
14
. The electron beam deflecting part
34
is controlled on the conditions that the secondary electron beams
32
incident from the substrate
11
are caused to travel straight, and the secondary electron beams travel straight in the deflecting part
34
to enter a spectral means. Of energy of the secondary electron beams
32
produced from the substrate
11
, only secondary electron beams having energy of a predetermined value or more enter the mapping projecting optical part.
The mapping projecting optical part includes three-stage rotationally symmetric electrostatic lenses
16
,
18
and
20
. The secondary electron beams
32
are enlarged to be projected by the electrostatic lenses
16
,
18
and
20
to form an image on the electron image detecting part. The control parts
17
,
19
and
21
control the voltages of the electrostatic lenses
16
,
18
and
20
, respectively.
The electron image detecting part includes an MCP (Micro Channel Plate) detecting device
22
, a fluorescent
Miyoshi Motosuke
Yamazaki Yuichiro
El-Shammaa Mary
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Wells Nikita
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