U.S. patent application number 15/329468 was filed with the patent office on 2017-11-09 for charged particle beam device.
The applicant listed for this patent is Hitachi High-Technologies Corporation. Invention is credited to Shahedul HOQUE, Hideki ITAI, Hajime KAWANO, Wataru MORI, Kumiko SHIMIZU.
Application Number | 20170323763 15/329468 |
Document ID | / |
Family ID | 55217462 |
Filed Date | 2017-11-09 |
United States Patent
Application |
20170323763 |
Kind Code |
A1 |
ITAI; Hideki ; et
al. |
November 9, 2017 |
Charged Particle Beam Device
Abstract
The purpose of the present invention is to provide a charged
particle beam device with which it is possible to minimize the beam
irradiation amount while maintaining a high measurement success
rate. The present invention is a charged particle beam device
provided with a control device for controlling a scan deflector on
the basis of selection of a predetermined number n of frames,
wherein the control device controls the scan deflector so that a
charged particle beam is selectively scanned on a portion on a
sample corresponding to a pixel satisfying a predetermined
condition or a region including the portion on the sample from an
image obtained by scanning the charged particle beam for a number m
of frames (m.gtoreq.1), the number m of frames being smaller than
the number n of frames.
Inventors: |
ITAI; Hideki; (Tokyo,
JP) ; SHIMIZU; Kumiko; (Tokyo, JP) ; MORI;
Wataru; (Tokyo, JP) ; KAWANO; Hajime; (Tokyo,
JP) ; HOQUE; Shahedul; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi High-Technologies Corporation |
Minato-ku, Tokyo |
|
JP |
|
|
Family ID: |
55217462 |
Appl. No.: |
15/329468 |
Filed: |
July 27, 2015 |
PCT Filed: |
July 27, 2015 |
PCT NO: |
PCT/JP2015/071186 |
371 Date: |
January 26, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 2237/2806 20130101;
H01J 37/147 20130101; H01J 37/22 20130101; H01J 2237/221 20130101;
H01J 2237/2817 20130101; H01J 37/28 20130101; H01J 37/1474
20130101 |
International
Class: |
H01J 37/28 20060101
H01J037/28; H01J 37/147 20060101 H01J037/147 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2014 |
JP |
2014-155678 |
Jul 31, 2014 |
JP |
2014-155679 |
Jul 31, 2014 |
JP |
2014-155680 |
Claims
1. A charged particle beam device comprising: a scanning deflector
that performs scanning with a charged particle beam discharged from
a charged particle source; a detector that detects a charged
particle obtained based on the scanning with the charged particle
beam; and a control device that controls the scanning deflector,
based on selection of a predetermined number of frames n, wherein
the control device controls the scanning deflector so that scanning
with the charged particle beam is selectively performed on a
portion on a sample corresponding to a pixel satisfying a
predetermined condition or on a region including the portion on the
sample, from an image obtained by scanning with the charged
particle beam for the number of frames m (m.gtoreq.1) which is
smaller than the number of frames n.
2. The charged particle beam device according to claim 1, wherein
the control device performs selective scanning with the charged
particle beam on a frame subsequent to the number of frames m.
3. The charged particle beam device according to claim 1, wherein
the control device generates an image signal by integrating a
plurality of signals of the number of frames n.
4. The charged particle beam device according to claim 1, wherein
the control device controls the scanning deflector so that scanning
with the charged particle beam is selectively performed on a
portion on a sample corresponding to a pixel whose signal amount
shows a predetermined value or greater or on a region including the
portion on the sample, from an image obtained by scanning performed
on the number of frames m.
5. A charged particle beam device comprising: a scanning deflector
that performs scanning with a charged particle beam discharged from
a charged particle source; a detector that detects a charged
particle obtained based on the scanning with the charged particle
beam; and a control device that adjusts an irradiation condition of
the charged particle beam in at least two ways, wherein the control
device measures or inspects a pattern formed on the sample, based
on a signal obtained by scanning a first region on the sample with
a first charged particle, and wherein the control device scans a
second region including the first region with a second charged
particle beam whose dose amount is smaller than that of the first
charged particle beam, and specifies the first region, based on a
signal obtained by scanning with the second charged particle
beam.
6. The charged particle beam device according to claim 5, wherein a
scanning speed of the second charged particle beam is faster than
that of the first charged particle beam.
7. The charged particle beam device according to claim 5, wherein
the control device specifies a portion, an edge portion of a
pattern, or a position of a pattern on the sample whose signal
amount shows a predetermined value or greater, from a signal
obtained by scanning with the second charged particle beam, and
performs scanning with the first charged particle beam so as to
include the specified region.
8. The charged particle beam device according to claim 5, wherein
the control device evaluates quality of an image obtained by
scanning with the charged particle beam in which a scanning speed
and the number of scanning times are differently combined with each
other, and sets a combination between the number of scanning times
and the scanning speed whose evaluation result satisfies a
predetermined condition, as a beam condition of the first charged
particle beam.
9. A charged particle beam device comprising: a scanning deflector
that performs scanning with a charged particle beam discharged from
a charged particle source; a detector that detects a charged
particle obtained based on the scanning with the charged particle
beam; and a control device that adjusts an irradiation condition of
the charged particle beam in at least two ways, wherein the control
device measures or inspects a pattern formed on a sample, based on
a signal obtained by scanning a first region on the sample with a
first charged particle beam, and wherein the control device scans a
second region including the first region with a second charged
particle beam whose dose amount is smaller than that of the first
charged particle beam, and selects a scanning direction of the
first charged particle beam, based on a signal obtained by scanning
with the second charged particle beam.
10. The charged particle beam device according to claim 9, wherein
a scanning speed of the second charged particle beam is faster than
that of the first charged particle beam.
11. The charged particle beam device according to claim 9, wherein
the control device specifies an edge portion of a pattern or a
position of a pattern, from the signal obtained by scanning with
the second charged particle beam, and performs scanning with the
first charged particle beam so as to include the specified region.
Description
TECHNICAL FIELD
[0001] The present invention relates to a charged particle beam
device, and particularly relates to a charged particle beam device
which can properly set a scanning condition of a beam.
BACKGROUND ART
[0002] As a semiconductor pattern has been micronized, a slight
shape difference has affected operation characteristics of a
device. Accordingly, there is a growing need for shape management.
Therefore, a scanning electron microscope (SEM) used in inspecting
and measuring semiconductors requires higher sensitivity and higher
accuracy than those in the related art. When a sample is irradiated
with an electron beam, the SEM observes a shape of a surface by
detecting a secondary electron discharged from the sample. In this
case, the detected secondary electron has low energy, and is likely
to receive charging influence of the sample. Due to a recently
micronized pattern or use of a low dielectric constant material
such as low-k, the charging influence is noticeable. In some cases,
it becomes difficult to capture a signal from a place which
requires management. In addition, some patterns shrink due to beam
irradiation. Therefore, it is necessary to properly set an
irradiation condition.
[0003] PTL 1 discloses an electron microscope in which at the time
of frame integration, an image is formed by integrating image
signals obtained by selective scanning performed on a specific
pattern and by scanning performed on a region including the
specific pattern and a region other than the specific pattern. In
addition, PTL 2 discloses an electron beam device in which an image
is formed by performing beam scanning after selectively setting a
scanning region in a portion such as a pattern edge. In PTL 3, a
method is described in which a shape of a pattern is specified from
an electron beam image, and in which a scanning direction of an
electron beam is controlled so as to be perpendicular to an edge of
the pattern.
CITATION LIST
Patent Literature
[0004] PTL 1: JP-A-2010-272398
[0005] PTL 2: JP-A-2013-185852
[0006] PTL 3: U.S. Pat. No. 6,879,719
Summary of Invention
Technical Problem
[0007] As disclosed in PTL 1 or PTL 2, a beam irradiation amount
per unit area can be reduced by limiting a scanning region. As a
result, it is possible to restrain charging or shrinkage from
occurring. However, depending on a pattern workmanship, there is a
possibility that a pattern or pattern edge may not be formed at a
predetermined position. As a result, there is a possibility that
measurement may fail since a position of a scanning region whose
range is narrowed is different from a position of a desired
measurement target. Both PTL 1 and PTL 2 disclose that the charging
or the shrinkage can be restrained by reducing a total beam
irradiation amount, but give no consideration to whether there is
the possibility that the position of the scanning region and the
position of the measurement target may differ from each other. In
addition, according to the method disclosed in PTL 3, it is
necessary to separately perform beam scanning for specifying the
pattern shape and scanning in which the scanning direction of the
electron beam is controlled. Consequently, the beam irradiation
amount increases.
[0008] Hereinafter, a charged particle beam device will be
described. A first object thereof is to compatibly restrain a beam
irradiation amount and maintain high measurement success rate by
accurately aligning a position of a measurement target and a
position of a scanning region with each other even in a case where
beam scanning is performed while a scanning range is limited.
[0009] Hereinafter, a charged particle beam device will be
described. A second object thereof is to compatibly set a scanning
line direction to a proper direction and restrain a beam
irradiation amount.
Solution to Problem
[0010] As one aspect of a first configuration for achieving the
above-described first object, a charged particle beam device is
proposed herein. The charged particle beam device includes a
scanning deflector that performs scanning with a charged particle
beam discharged from a charged particle source, a detector that
detects a charged particle obtained based on the scanning with the
charged particle beam, and a control device that controls the
scanning deflector, based on selection of a predetermined number of
frames n. The control device controls the scanning deflector so
that scanning with the charged particle beam is selectively
performed on a portion on a sample corresponding to a pixel
satisfying a predetermined condition or on a region including the
portion on the sample, from an image obtained by scanning with the
charged particle beam for the number of frames m (m.gtoreq.1) which
is smaller than the number of frames n.
[0011] As one aspect of the first configuration for achieving the
above-described first object, a charged particle beam device is
proposed herein. The charged particle beam device includes a
scanning deflector that performs scanning with a charged particle
beam discharged from a charged particle source, a detector that
detects a charged particle obtained based on the scanning with the
charged particle beam, and a control device that adjusts an
irradiation condition of the charged particle beam in at least two
ways. The control device measures or inspects a pattern formed on
the sample, based on a signal obtained by scanning a first region
on the sample with a first charged particle beam. The control
device scans a second region including the first region with a
second charged particle beam whose dose amount is smaller than that
of the first charged particle beam, and specifies the first region,
based on a signal obtained by scanning with the second charged
particle beam.
[0012] As one aspect of a second configuration for achieving the
above-described second object, a charged particle beam device is
proposed herein. The charged particle beam device includes a
scanning deflector that performs scanning with a charged particle
beam discharged from a charged particle source, a detector that
detects a charged particle obtained based on the scanning with the
charged particle beam, and a control device that adjusts an
irradiation condition of the charged particle beam in at least two
ways. The control device measures or inspects a pattern formed on
the sample, based on a signal obtained by scanning a first region
on the sample with a first charged particle beam. The control
device scans a second region including the first region with a
second charged particle beam whose dose amount is smaller than that
of the first charged particle beam, and selects a scanning
direction of the first charged particle beam, based on a signal
obtained by scanning with the second charged particle beam.
Advantageous Effects of Invention
[0013] According to the above-described first configuration, it is
possible to compatibly restrain a beam irradiation amount and
maintain high measurement success rate. In addition, according to
the above-described second configuration, it is possible to
compatibly set a scanning line direction to a proper direction and
restrain a beam irradiation amount.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a view schematically illustrating a scanning
electron microscope.
[0015] FIG. 2 is a view schematically illustrating a coordinate
memory that stores abeam irradiation condition in pixel unit.
[0016] FIG. 3 is a flowchart illustrating an image integration
process which follows a limiting process of a scanning region.
[0017] FIG. 4 is a flowchart illustrating the limiting process of
the scanning region.
[0018] FIG. 5 is a view schematically illustrating the limiting
process of the scanning region.
[0019] FIG. 6 is a view schematically illustrating the limiting
process of the scanning region.
[0020] FIG. 7 is a view illustrating an example of a graphical user
interface (GUI) screen for setting a beam scanning condition.
[0021] FIG. 8 is a view illustrating a process of selecting a
region for performing a high dose scanning by recognizing a pattern
inside a low dose image.
[0022] FIG. 9 is a view for describing a method of determining a
scanning region.
[0023] FIG. 10 is a view illustrating an example of database for
recording an image quality evaluation value of each beam scanning
condition.
[0024] FIG. 11 is a view illustrating an example of a control
signal supplied to a scanning deflector and a blanking
deflector.
[0025] FIG. 12 is a view illustrating an example of selecting a
high dose scanning region inside a low dose image.
[0026] FIG. 13 is a view illustrating a relationship between a
pattern array within a beam scanning range and a scanning
speed.
[0027] FIG. 14 is a view illustrating a process of determining a
beam scanning pattern, based on measurement target pattern
information.
[0028] FIG. 15 is a view illustrating a process flow in forming an
image, based on an input of the measurement target pattern
information.
[0029] FIG. 16 is a view illustrating a process of determining a
scanning direction suitable for a vertical pattern.
[0030] FIG. 17 is a view illustrating a process of determining a
scanning direction suitable for a horizontal pattern.
[0031] FIG. 18 is a view illustrating a process of determining a
scanning direction suitable for a two-dimensionally arrayed
pattern.
[0032] FIG. 19 is a view illustrating a process of determining a
scanning direction suitable for a hole shape.
[0033] FIG. 20 is a view illustrating a process of determining an
edge direction, based on low dose scanning performed using a
scanning line in two directions.
[0034] FIG. 21 is a view illustrating an example in which one field
of view is divided into a plurality of scanning regions.
[0035] FIG. 22 is a view illustrating an example of scanning only a
location having a pattern.
[0036] FIG. 23 is a view illustrating a process of determining a
scanning region, based on pattern recognition using a template.
[0037] FIG. 24 is a view illustrating an example in which a field
of view is internally divided into a low dose region and a high
dose region.
[0038] FIG. 25 is a view illustrating an example of a scanning
pattern in accordance with the presence or absence of a
pattern.
[0039] FIG. 26 is a view illustrating an example of a scanning
pattern in accordance with an edge direction of a pattern.
DESCRIPTION OF EMBODIMENTS
[0040] FIG. 1 is a view schematically illustrating a scanning
electron microscope (SEM) which is one type of charged particle
beam devices. An electron beam 103 which is drawn out from an
electron source 101 by a lead electrode 102 and accelerated by an
acceleration electrode (not illustrated) is condensed by a
condenser lens 104 which is a form of focusing lenses. Thereafter,
the electron beam 103 is used in one-dimensionally or
two-dimensionally scanning a portion on a sample 109 by a scanning
deflector 105. The electron beam 103 is decelerated by a negative
voltage applied to an electrode incorporated in a sample stage 108,
condensed by a lens operation effect of an objective lens 106 and
is used in irradiating the portion on the sample 109.
[0041] If the sample 109 is irradiated with the electron beam 103,
an electron 110 such as a secondary electron and a backscattered
electron is discharged from the irradiated location. The discharged
electron 110 is accelerated in an electron source direction by an
accelerating operation effect based on a negative voltage applied
to the sample, and collides with a conversion electrode 112,
thereby generating a secondary electron 111. The secondary electron
111 discharged from the conversion electrode 112 is captured by a
detector 113. Depending on the amount of the captured secondary
electron, an output of the detector 113 varies. Luminance of a
display device (not illustrated) varies in accordance with the
output. For example, in a case of forming a two-dimensional image,
a deflecting signal to the scanning deflector 105 and the output of
the detector 113 are synchronized with each other, thereby forming
an image of a scanning region. In addition, the scanning electron
microscope illustrated in FIG. 1 includes a deflector (not
illustrated) for moving the scanning region of the electron beam.
The deflector is used in order to form an image of the same shape
pattern present at a different position. The deflector is called an
image shift deflector, and can move a position in a field of view
of the electron microscope without causing the sample stage to move
the sample. The image shift deflector and the scanning deflector
may serve as a deflector used in common. In this manner, an image
shift signal and a scanning signal may be superimposed on each
other so as to be supplied to the deflector.
[0042] Referring to an example in FIG. 1, an example has been
described in which the electron discharged from the sample is once
converted by the conversion electrode and detected. As a matter of
course, without being limited to this configuration, for example, a
configuration can be adopted in which an electron multiplier tube
or a detection surface of the detector is disposed on an orbit of
the accelerated electron. In addition, a blanking deflector (not
illustrated) is installed inside SEM 100. The blanking deflector is
a mechanism that blocks beam irradiation on the sample by
deflecting the beam out of a beam optical axis, and is controlled
in accordance with an operation parameter stored in a coordinate
memory (to be described later).
[0043] The present embodiment employs an electrostatic deflector as
the scanning deflector 105. Compared to an electromagnetic
deflector, high speed scanning can be performed. If the high speed
scanning is not required, the electromagnetic deflector may be
used.
[0044] A control device 120 controls each configuration of the
scanning electron microscope, and is provided with a function to
form an image, based on the detected electron and a function to
measure a pattern width of a pattern formed on a sample, based on
intensity distribution of the detected electron which is called a
line profile. In addition, the control device 120 internally
includes a SEM control device which mainly controls an optical
condition of SEM, and a signal processing device which performs
signal processing on a detection signal obtained by the detector
113. The SEM control device includes a scanning control device for
controlling a beam scanning condition. The scanning control device
performs beam scanning, based on information stored in a coordinate
memory as illustrated in FIG. 2. Each address of a coordinate
memory 200 stores time data, X-coordinate data, Y-coordinate data,
an operation parameter, and incorporated enable data. Data input to
"time" in the memory represents an irradiation time or an arrival
time in each address, and can be set in pixel unit. In addition, a
beam operation parameter (blanking on/off and direction) can also
be set in pixel unit. The irradiation time (scanning time) and the
blanking on/off can be controlled in pixel unit. Each address
corresponds to a pixel. The time data in the coordinate memory is
read by a timer. The data is read from the coordinate memory in
such away that an address counter counts up one coordinate data as
one unit. An update time of the address counter can be changed in
coordinate unit. Blanking enable data controls blanking of a
primary electron beam in coordinate unit. In addition, the
incorporated enable data controls writing on an image memory
included in the signal processing device.
[0045] For example, the image memory can store 256 gradations in a
depth direction with 1,024.times.1,024 pixels. Based on a signal
output from the SEM control device, the signal is written for each
address (pixel). An address signal corresponding to a memory
position of the image memory is synchronized with a beam
irradiation position, thereby aligning the beam irradiation
position and the written coordinate with each other. The signal
read corresponding to the address is converted into an analog
signal from a digital signal by a D/A converter, and is input to an
image display device after being subjected to luminance modulation.
The control device 120 performs an integration process of
integrating image data obtained based on scanning performed a
plurality of times. For example, the integration process is
performed in such a way that signals obtained by a plurality of
frames are additionally averaged for each pixel.
[0046] The control device 120 performs the following control, based
on information input to the coordinate memory 200.
Embodiment 1
[0047] According to the present embodiment, for example, in a
charged particle beam device such as the scanning electron
microscope, a scanning region of a primary electron beam for
obtaining an observation image having a high S/N ratio is limited
to only a desired pattern required for measurement or observation
within a range of a field of view during a process of acquiring the
observation image. In this manner, an irradiation amount of the
primary electron beam is restrained in a region other than the
desired pattern within the range of the field of view, and
shrinkage of the pattern is restrained.
[0048] Therefore, when the observation image is acquired, a
scanning region is limited by extracting a region having the same
signal amount as that of the desired pattern from the inside of the
image acquired during the acquiring process and by setting the
region or only the vicinity of the region to a subsequent scanning
target region. While this process is repeatedly performed, the
observation image of the desired pattern is acquired.
[0049] According to the above-described configuration, when the
observation image is acquired, the scanning region is limited by
extracting the region having the same signal amount as that of the
desired pattern from the inside of the image acquired during the
acquiring process and by setting the region or only the vicinity of
the region to the subsequent scanning target region. This process
is repeatedly performed until the observation image is completely
acquired. In this manner, the observation image of the desired
pattern within the range of the field of view which has the high
S/N ratio can be acquired while the irradiation amount of the
primary electron beam is continuously restrained.
[0050] FIG. 3 is a flowchart illustrating a process of forming an
integrated image. For example, the process (to be described later)
is performed in accordance with an operation recipe stored in a
storage medium incorporated into the control device 120.
[0051] First, the sample 109 is transported onto the sample stage
108 (Step 302). Since a high vacuum state is maintained in a sample
chamber 107, an atmosphere where the sample is present is brought
into a vacuum state by a preliminary evacuation chamber (not
illustrated). Thereafter, the sample is introduced into the sample
chamber. Next, the sample stage 108 is driven so that a beam
irradiation position of the sample 109 is irradiated with the
electron beam 103 discharged from the electron source 101 (Step
303). Next, based on a device condition stored in the operation
recipe, conditions such as the number of frames n which shows the
total number of sheets to be integrated or a method of limiting the
scanning region are set.
[0052] The control device 120 controls the scanning deflector 105
so as to perform beam scanning based on the set device condition,
and causes a frame memory to write a signal based on the detection
signal obtained by scanning, based on the enable data stored in the
coordinate memory illustrated in FIG. 2 (Step 304 and Step 305).
For example, in this stage, the enable data of all addresses is set
to allow writing on the memory. An analysis (to be described later)
is performed on an image formed based on the data written in this
way.
[0053] In Step 307, the scanning region is limited by using
information accumulated up to m (1.ltoreq.m<n) frames. Here, the
number of frames n is set so as to sufficiently obtain SN required
for desired measurement, and is set as a setting item of the
operation recipe of the scanning electron microscope. Based on the
set condition, the control device 120 performs beam scanning for
the number of frames. Details of this process will be described
later. In Steps 308 and 309, in a state where the scanning region
is limited, the beam scanning is performed. Beam scanning of a
selected region and data writing on a selected address are
performed, thereby forming an image. This process is performed at a
fixed frame interval .DELTA.f (1.ltoreq..DELTA.f<n). This frame
interval can be designated by an operator.
[0054] Image data formed as described above is stored in a
predetermined storage medium, and is used in measuring or
inspecting a pattern. After the image data is acquired, the sample
is transported from the sample chamber 107, and the sample is
measured, thereby completely inspecting the sample (Step 310).
[0055] FIG. 4 is a flowchart illustrating a specific process in a
scanning region limiting process performed in Step 307 in FIG. 3.
First, the image data obtained by scanning for a predetermined
number of frames (m) is acquired (Step 402). Next, signal data of
each pixel is acquired so as to determine whether or not a signal
amount satisfies a predetermined condition (Steps 403 to 405). In a
case of this example, it is determined whether or not the signal
amount is a predetermined value or greater. For example, signal
amount information of a pixel (X, Y) is extracted from signal
amount information accumulated up to the m-frame. In a case where
the signal amount of the pixel (X, Y) exceeds a threshold value st
of the designated signal amount, the pixel is set as a subsequent
frame scanning location. More specifically, in a case where the
signal amount of the pixel (X, Y) exceeds the threshold value st,
the time, the operation parameter, and the enable are set for a
corresponding address of the coordinate memory illustrated in FIG.
2. The pixel (X, Y) is used in acquiring a signal by means of beam
irradiation. Accordingly, the coordinate memory is set so as to
ensure a proper irradiation time and blanking-off, and to perform a
writing process.
[0056] On the other hand, a pixel which does not satisfy the
predetermined condition is not irradiated with the beam.
Accordingly, the coordinate memory is updated so as to ensure
blanking-on, and so as not to perform the writing process.
[0057] For example, the threshold value st of the signal amount can
be designated by using a method of setting a value of the signal
amount, for example, a luminance value or a percentage such as any
percentage from the largest signal amount in the entire image. This
value can be designated by using a method of automatically
calculating a value from a template image of a desired pattern, or
can be designated by a user setting the threshold value to a
numerical value.
[0058] Through the above-described process, the pixel (X, Y) is set
to a scanning target subsequent the next frame. As illustrated in
FIG. 3, when the observation image is acquired, Steps 306 and 307
are repeatedly performed for each frame. In this manner, while the
inner region in the field of view is scanned, a portion whose
signal amount increases due to noise is excluded from the scanning
region. Accordingly, it is possible to acquire an image whose S/N
ratio is high.
[0059] In addition, the number of integrated frames is determined
depending on image quality required by an operator of the electron
microscope. As the number of frames increases, the signal amount
increases. On the other hand, excessive beam irradiation induces
charging of the sample. Accordingly, it is necessary to set the
proper number of frames so as to satisfy accuracy required for
measurement and so as not to perform unnecessary beam irradiation.
According to the present embodiment, a portion having much signal
amount can be scanned for a predetermined number of frames.
Therefore, the signal amount of a portion serving as a measurement
reference during dimension measurement of a pattern, such as an
edge portion, can satisfy requested specifications. It is possible
to restrain only the irradiation amount of a portion other than the
edge which is not directly required for the measurement. Therefore,
it is possible to compatibly perform very accurate measurement in
compliance with the requested specifications and restrain charging
or shrinkage from occurring due to beam scanning.
[0060] FIG. 7 illustrates an embodiment of GUI used when an
operator sets scanning limitation within a range of a field of
view. A GUI 700 is installed in the image processing device inside
the control device 120. In accordance with an actuating command,
OSD is displayed on a display device (not illustrated). The GUI 700
in this embodiment is configured to include an image display region
710, a scanning region limiting unit 720, a signal amount
acquisition unit 740, and a scanning button 750.
[0061] The image display region 710 displays a template image of a
desired pattern which is acquired in advance, and an image acquired
when scanning is performed within the range of the field of view.
An operator can resize and move a signal amount acquisition cursor
711 displayed inside the image display region 710 by using an input
device of the image processing device.
[0062] The scanning region limiting unit 720 has a function to
input a setting value when scanning which limits the scanning
region is performed. A scanning frame setting text box 721 can set
the number of frames n for performing the scanning. A limitation
start frame setting text box 722 can set the number of frames m for
starting to limit the scanning region. A frame interval setting
text box 723 can set the number of interval frames .DELTA.f for
performing the process in Steps 306 and 307 in FIG. 3. A threshold
value setting area 724 of the signal amount can set the threshold
value st of the signal amount. A signal amount setting switch radio
button 725 can select whether to set the threshold value st of the
signal amount by using the signal amount or whether to set the
threshold value st of the signal amount by using a percentage such
as any percentage from the largest signal amount of the entire
image displayed in the image display region 710. In addition, an
algorithm setting unit 728 for determining the scanning region can
set how to determine the scanning region subsequent to the next
frame.
[0063] A signal amount acquisition amount setting unit 740 has a
function to display the signal amount by acquiring the signal
amount of the designated region from the image displayed in the
image display region 710. A cursor display / no display button 741
can control a signal amount acquisition cursor 711 to show
display/no display in the image display region 710. A signal amount
display form switch radio button 743 can select whether to display
a display form of the acquired signal amount information by using
the signal amount or whether to display a display form of the
acquired signal amount information by using a percentage such as
any percentage from the largest signal amount of the entire image
displayed in the image display region 710. A signal amount reading
button 742 can read the signal amount of the region surrounded by
the signal amount acquisition cursor 711 in the image display
region 710. The read signal amount matches the content selected by
the signal amount display form switch radio button 743. The minimum
value is displayed in a minimum signal amount text box 744, and the
maximum value is displayed in a maximum signal amount text box
745.
[0064] The scanning button 750 can perform scanning within the
region of the field of view, based on the content set by the
scanning region limiting unit 720.
Embodiment 2
[0065] In this embodiment, with regard to the process in Step S406
in FIG. 4 according to Embodiment 1, even in a case where a drift
occurs between the m-frame and the m+.DELTA.f-frame, the
observation target is set to the scanning target subsequent to the
next frame. In a case where the observation target is set to only
the scanning region subsequent to the m-frame of the pixel (X, Y),
the drift occurs due to some reasons between them-frame and the
m+.DELTA.f-frame. In a case where a position of the observation
target is offset, when the m+.DELTA.f-frame is scanned, there is a
possibility that a pattern may be out of the scanning region. In
contrast, as illustrated in FIG. 5, it is possible to correspond to
the pixel designated as the scanning target in Step 406 by setting
the pixel (X, Y) and 8 pixels in the vicinity {(X-1, Y-1) (X-1, Y)
(X-1, Y+1) (X, Y-1) (X, Y+1) (X+1, Y-1) (X+1, Y) (X+1, Y+1)} to the
scanning target. In addition, as a scanning target pixel, the pixel
(X, Y) and 4 pixels in the vicinity {(X-1, Y) (X, Y-1) (X, Y+1)
(X+1, Y)} may be used, but a configuration is not limited
thereto.
[0066] The GUI in FIG. 7 includes a scanning region algorithm radio
button 729 as an item for setting an algorithm for determining this
scanning region. The scanning region can be selected from only the
pixel within the threshold value, the pixel+4 pixels in the
vicinity within the threshold value, and the pixel+8 pixels in the
vicinity within the threshold value, and others.
[0067] In addition, in a case of shortening a time for the limiting
process of the scanning region, as illustrated in FIG. 6, a method
may also be used in which the vicinity in only the scanning
direction is acquired and only the pixels in the front and rear
which exceed the threshold value st of the signal amount are set to
the scanning region. In addition, in FIG. 6, it is also possible to
correspond to the drift by including one pixel in the front and
rear. This method is particularly effective in a case of a pattern
orthogonal to the scanning direction. In the GUI in FIG. 7, in a
case where "others" are selected as a selection item of the
scanning region algorithm radio button 729, a method of determining
the scanning region can be employed by using any optional algorithm
or reference prepared by a user. When the optional algorithm is
read, the optional algorithm is read by utilizing an algorithm
reading button 730.
Embodiment 3
[0068] With regard to the process in Step 405 in FIG. 4 according
to Embodiments 1 and 2, this embodiment solves a problem that an
observation target pattern does not necessarily have much signal
amount. Instead of the threshold value st, the signal amount for
determining the scanning region has a range (srmin, srmax) of the
signal amount. In the process in Step 405, it is determined whether
the pattern falls within the range (srmin, srmax) of the signal
amount designated in advance, and the process in Step 406 is
performed in only a case within the range. For example, in a case
where the generated image is subjected to image processing such as
brightness and contrast adjustment in a post process, the
adjustment does not match a portion having much signal amount.
Accordingly, this method is effectively used. In the GUI in FIG. 7,
in a case where the range of the signal amount is set in the
threshold value setting area 724 of the signal amount, the minimum
value can be set in a threshold value minimum setting text box 726
of the signal amount, and the maximum value can be set in a
threshold value maximum setting text box 727 of the signal
amount.
Embodiment 4
[0069] In this embodiment, information of the scanning region of
the n-.sup.th frame is utilized as outline information or
information for outputting the outline information. The scanning
region of the n-.sup.th frame is set to only a region which is
close to a pre-designated threshold value. For example, in a case
where the pre-designated threshold value shows a value having much
signal amount, the scanning region is close to the outline
information of a desired pattern. This information is output
together with the acquisition of the observation image in Step 309
in FIG. 3.
[0070] Hitherto, in the above-described embodiments, examples of
the scanning electron microscope relating to the charged particle
beam device and employed in measuring a sample or in observing a
structure have been described in detail. However, the present
invention is not limited to the above-described embodiments. As a
matter of course, the present invention can be modified in various
ways within the scope not departing from the gist.
Embodiment 5
[0071] Embodiments described hereinafter relate to a charged
particle beam device, and particularly relate to a charged particle
beam device which determines a scanning parameter of a high dose
beam used in irradiating a sample, based on sample information
obtained by low dose beam scanning.
[0072] In order to manage a dimension of a semiconductor device, a
critical-dimension scanning electron microscope (CD-SEM) which is
one of the scanning electron microscopes and which has high space
resolution is widely used. A measurement or inspection target
pattern has been more progressively micronized. On the other hand,
the number of measurement or inspection targets per one sheet of
wafer increases. Therefore, improved throughput of CD-SEM is
required. In a case of measuring or inspecting a pattern by using
CD-SEM, a peripheral region including the target pattern is scanned
in XY-direction (for example, from left to right in an X-direction,
and from above to below in a Y-direction), thereby acquiring a SEM
image.
[0073] However, according to this scanning method, an unnecessary
region other than the target pattern is scanned. That is, in order
to further improve the throughput or in order to restrain charging
of the wafer or shrinkage of the pattern, it is conceivable that a
necessary location is selectively scanned without scanning the
unnecessary region. However, in some cases, due to sample charging
or pattern deformation, an accurate beam scanning position cannot
be set at a location which has to be selectively scanned.
[0074] High speed scanning is an effective way to restrain sample
charging. However, if emission intensity or time of a scintillator
is not sufficient, a detection signal is insufficient. In addition,
in a case where a drift occurs due to charging, it is conceivable
to correct a shifted portion of the scanning region by recognizing
a pattern from the obtained image and extracting an edge. However,
if hundreds of sheets overlap each other, an enormous calculation
system is required.
[0075] In the present embodiment, in view of a charging phenomenon
occurring during the above-described electron beam irradiation or a
deformation possibility of a pattern formed on a sample, a charged
particle beam device will be described which sets a beam scanning
region at a proper position while a beam irradiation amount is
restrained. In particular, a charged particle beam device will be
described which sets a scanning region and a scanning speed in
accordance with a sample state.
[0076] Hereinafter, a scanning electron microscope will be
described which can determine a scanning parameter such as the
scanning region and the scanning speed, based on a viewpoint of
improved throughput, damage to a sample, and sample charging.
[0077] In the present embodiment, a scanning electron microscope
will be mainly described which includes an electrostatic scanning
deflector suitable for high speed scanning and which can control
the scanning speed so as to be variable. In order to determine a
measurement or inspection target location, high speed scanning is
first performed. That is, a first image is acquired by performing
scanning with a decreased dose amount per unit area. Subsequently,
a measurement or inspection target pattern is recognized from the
first image, thereby automatically determining the scanning
parameter such as the scanning region and speed. Thereafter,
scanning is performed at a lower speed than the speed used when the
first image is acquired. That is, the determined scanning region is
scanned with an increased dose amount per unit area, thereby
measuring or inspecting the target pattern.
[0078] More specifically, the following charged particle beam
device will be described. A first region is specified, based on a
signal obtained by scanning a second region which is a wider region
than a region (first region) scanned with a beam for measurement or
inspection, with a second beam whose dose amount is less than that
of a first charged particle beam for scanning the first region.
Based on the specified first region, scanning with the first
charged particle beam is performed.
[0079] According to the above-described configuration, it is
possible to realize measurement or inspection by which the
throughput is improved, damage to the sample is reduced, and the
sample charging is optimized.
[0080] Hereinafter, referring to a flowchart in FIG. 8, a process
of determining the scanning region and the scanning speed which are
suitable for an inspection or measurement target pattern will be
described. In the process, the scanning electron microscope as
illustrated in FIG. 1 is used, and one pattern is used from
patterns formed on the inside of a wafer surface with the same
layout.
[0081] First, the scanning region of a first image is determined
using design data of a semiconductor device (Step 801). The
scanning region of the first image is set so as to include a
measurement target pattern. The control device 120 is configured to
be accessible to the design data stored in an external storage
medium. The control device 120 converts the design data into
pattern layout data, and drives the sample stage 108 so that a
coordinate position of the wafer which corresponds to the set
scanning region is irradiated with a beam of the scanning electron
microscope.
[0082] The control device 120 performs beam scanning for acquiring
the first image after the scanning region of the electron beam is
located at a wafer position for acquiring the first image (Step
802). In this case, compared to the scanning speed of the beam
scanning for measurement or inspection (to be described later), the
scanning range determined in Step 801 is scanned at a higher speed
(speed a). In this way, the entire surface is scanned with a
decreased dose amount per unit area, thereby acquiring the first
image including pattern information of the measurement or
inspection target. In addition to the scanning at the higher
scanning speed, it is conceivable to limit a dose amount by
preparing apertures having openings with a plurality of sizes which
limit beam passage and decreasing the size of the opening. However,
a beam irradiation condition has to be changed. Accordingly, in
order to enable high speed measurement or inspection, it is
desirable to perform dose control using the higher scanning speed
without changing the irradiation condition of the beam itself.
[0083] In Step 803, a process of recognizing a pattern present
inside the first image is performed. For example, as illustrated in
FIG. 9, in this process, a profile waveform is extracted from the
first image so as to recognize a position (edge portion) whose
luminance value is a predetermined threshold value or greater or a
position of a region interposed between the positions whose
luminance value is the predetermined threshold value or greater
(pattern region interposed between edges). Specifically, a contrast
value (luminance value) in the X-direction (pixel X) is calculated
for each Y-line. For example, the profile waveform such as A and B
as illustrated in FIG. 9(c) is acquired, and a pixel position at
which the contrast value in the X-direction is maximized is
determined as the edge portion. A threshold value is provided for
the contrast value, and a position having a value equal to or
greater than the threshold value is recognized as a pattern
position. The reason is as follows. As illustrated by the contrast
of B in FIG. 9(c), a slight difference in the contrast value occurs
in a place having no pattern due to random noise. Accordingly, in
this manner, the maximum value is not erroneously detected as the
edge.
[0084] In Step S804, an edge width of the pattern is obtained. With
regard to the contrast value obtained in Step 803 as illustrated in
FIG. 9(d), a contrast difference in pixels X adjacent in the
leftward direction from the maximum value is calculated. A pixel
position where the changed amount is a preset threshold value or
smaller is determined as a background portion other than the
pattern. Similarly, a pixel position of the background portion is
also calculated in the rightward direction from the maximum value,
thereby determining the edge width. In this manner, a first
scanning region is determined.
[0085] In Step 805, with regard to the first scanning region
obtained in S4 as illustrated in FIG. 9 (d) , a second scanning
region is set so that the edge is reliably included in the scanning
region. The edge position obtained in Step 803 is a position
determined from an image acquired using the low dose electron beam.
Accordingly, there is a possibility that a detailed position of the
edge portion may be different from a real position. Therefore, in
order to avoid a case where edge information cannot be sufficiently
obtained, a constant value is added to the front and the rear in
the scanning region, if necessary. In this manner, the scanning
region may be expanded so as to serve as a second scanning
range.
[0086] In Step 806, a scanning sequence is determined so that the
position in the scanning region obtained in Step 804 and Step 805
can be scanned within the shortest time. If a beam moving distance
is most shortened, the scanning sequence is determined so that an
added value of the distance between a plurality of scanning regions
decreases to the minimum. On the other hand, for example, if it is
considered that the beam is affected by the charging of the sample
due to the scanning region irradiated with the beam, the first
scanning region may be scanned, and then, a third scanning region
separated from the first scanning region may be scanned.
Thereafter, it is preferable to scan a second scanning region
closer to the first scanning region than the third scanning region.
According to this scanning sequence, while the third scanning
region is scanned, the charging of the first scanning region is
eased to some extent. Accordingly, when the second scanning region
is scanned, it is possible to restrain the beam from being affected
by the charging of the first scanning region.
[0087] In Step 807, the scanning speed and the number of scanning
times at the same location, that is, the number of image
superimposition times is determined. A second image used for
measurement or inspection is acquired using a higher dose than that
used in acquiring the first image. Accordingly, scanning is
performed at a slower speed than the first scanning speed (speed
a). In this case, it is necessary to set an optimal scanning speed
in accordance with a sample state. The scanning speed is obtained
as follows. The second image is acquired, and S/N is evaluated
using a matrix as illustrated in FIG. 10, which shows different
speeds in several stages (for example, speeds b, c, d, and e,
however, a>b>c>d>e) and the number of scanning times in
several stages (for example, once, four times, and eight
times).
[0088] A condition for obtaining the fastest throughput is
determined as a scanning parameter from the scanning speed and the
number of scanning times which are equal to or greater than the
preset S/N. In addition, in a case where a plurality of target
patterns are present in the first image as illustrated in FIG. 9,
and in a case where each target pattern has a different scanning
parameter which is equal to or greater than the preset S/N, the
scanning parameter is set for each target pattern.
[0089] According to the above-described determining method, it is
possible to set a measurement condition which compatibly enables
high speed measurement and very accurate measurement. In order to
automatically determine a device condition of the above-described
scanning electron microscope, a storage medium of the control
device 120 may store an operation program. For example, for the
operation program, patterns disposed at different positions are
scanned with beams having different combinations of the number of
scanning times and the scanning speed. An image quality evaluation
value such as S/N or sharpness is obtained. A combination of the
number of scanning times and the scanning speed in which the image
quality evaluation value satisfies a predetermined condition (for
example, a combination whose image quality evaluation value is
greatest) is set as the device condition.
[0090] In addition, in view of a time so that the electrostatic
deflector rises so as to be linearly deflected as illustrated in
FIG. 11, in accordance with the scanning speed, a start position of
deflection scanning is set to be in front of a position obtained in
Step 804 or Step 805. In addition, in a case where it is necessary
to move the scanning region, a beam blanker performs blanking. In
this case, in view of response delay in blanking, blanking timing
is determined so that scanning can be performed from the scanning
range in Step 804 or Step 805.
[0091] In the example 1 in FIG. 12, the region including both side
edges of the target pattern is set as the scanning range. However,
in a case where the pattern width is wide as illustrated in the
example 2 in FIG. 12 and scanning can be sufficiently performed in
the linear region even if the rise of the deflector is considered,
the scanning range is determined so that scanning can be performed
by scanning one side edge and then moving to the opposite side edge
in a state where blanking is performed.
[0092] In the above-described manner, the scanning range, the
scanning speed, the scanning sequence, and the scanning parameter
are determined. If the SEM image having the same pattern on the
wafer surface is acquired by causing the scanning control device to
control the determined scanning parameter, the throughput can be
maintained, and measurement or inspection can be performed so as to
provide high S/N.
Embodiment 6
[0093] In a case where it is also necessary to obtain information
around the measurement or inspection target pattern, the scanning
range obtained in S4 or S5 is scanned under the scanning condition
obtained in S7. Others are scanned at the speed a used when the
first image is obtained or at a speed between the speed a and the
speed obtained in S7, thereby obtaining the SEM image. In this
case, as illustrated in FIG. 12, the scanning speed a cannot be
instantaneously changed to the speed obtained in S7 from the
viewpoint of responsiveness. Accordingly, the scanning speed is
changed stepwise. This speed change amount is determined by using
values obtained before and after the speed is changed.
Embodiment 7
[0094] An embodiment described hereinafter relates to an electron
microscope, an electron beam irradiation method, and a computer
program for the same, and particularly relates to a beam
irradiation method, an electron microscope, and a computer program
in which pattern detection scanning (hereinafter, referred to as
rough scanning) is performed so as to perform image scanning based
on a result of the pattern detection scanning.
[0095] As semiconductor devices are diversified, there is a growing
need to observe or measure a two-dimensional or three-dimensional
pattern. In the devices, in many cases, a pattern edge within an
observation field of view has multiple directions. Beam scanning
employs a method of scanning a sample with an electron beam in one
direction and moving the sample in the vertical direction, and a
method of moving the electron beam. According to this method,
particularly in a case of a charged sample, all pattern edges
arrayed two-dimensionally in various directions are less likely to
be imaged with the same degree of accuracy.
[0096] Therefore, the present embodiment proposes a method of
capturing an image by determining optimal scanning based on pattern
array information, and a charged particle beam device which
realizes the method. In some cases, a pattern formed on a sample
may be damaged or shrunk due to electron beam irradiation. In order
to reduce damage, it is conceivable to reduce an irradiation
current and the number of integrated frames. However, in this case,
an image S/N is degraded, and measurement accuracy is degraded. In
addition, if beam irradiation energy decreases, damage is reduced.
However, resolution becomes poor, thereby causing a problem of
degraded measurement accuracy. Therefore, the present embodiment
proposes a method of reducing a total irradiation dose applied to
the sample and reducing damage by selectively performing beam
irradiation on only a portion having a measurement target
pattern.
[0097] There is a scanning method of scanning a square or
rectangular region at a uniform speed by using a fixed triangular
waveform signal in order to deflect an electron beam. In contrast,
the present embodiment proposes a method of performing beam
irradiation by preparing a scanning waveform based on information
of an observation or measurement target pattern without using a
fixed scanning waveform. Hereinafter, the information for defining
the scanning is referred to as scanning data. In the present
embodiment, the scanning data becomes a function of the detection
target pattern, and can be defined as scanning data Fs=Fs
(detection pattern). An image forming flow based actual scanning
from the recognition of the measurement target pattern shows
pattern information acquisition.fwdarw.preparation of scanning data
Fs.fwdarw.scanning and image acquisition.
[0098] According to the above-described scanning method, charging
influence can be reduced, and observation or measurement accuracy
can be improved. In addition, in a case of a device greatly damaged
by beam irradiation, an optimized beam scanning region enables
reduced shrinkage and improved measurement accuracy. Furthermore,
since the scanning is optimized depending on a pattern, unnecessary
beam scanning is no longer needed, and a time required for
acquiring an image is shortened. Therefore, it is also possible to
realize high throughput (high speed) required for an in-line
SEM.
[0099] As illustrated in FIG. 14, as a mechanism for determining a
scanning condition from pattern information 1401 (.chi.) of an
observation target, the control device 120 is internally equipped
with a scanning condition conversion function preparation unit 1402
(unit that calculates a function Fs (.chi.) from the pattern
information (.chi.)) and a scanning data preparation unit 1403.
After being subjected to proper conversion (D/A conversion or
amplification), an output of the scanning data preparation unit
1403 becomes a signal for scanning performed by a control system
1404 using a beam deflecting system 1405 (for example, the scanning
deflector 105).
[0100] In order to obtain the pattern information (.chi.), beam
scanning in the scanning electron microscope is performed in two
stages. The first stage is rough scanning, and the second stage is
image scanning. In the rough scanning, an image is acquired using a
low dose so as to acquire a pattern array (edge direction) and size
information (.chi.). The low dose is realized by high speed
scanning, probe current changing, or combining both of these with
each other. However, as described above, if the probe current is
changed, an optical condition of the beam is also changed, thereby
causing a possibility that it may take time to switch the rough
scanning to the image scanning. Therefore, it is desirable to
perform beam switching between the low dose and the high dose by
switching the scanning speed.
[0101] Next, based on the direction of the pattern and the size
information .chi., the scanning data (Fs(.chi.)) is prepared. The
scanning data is input to the deflecting system, thereby performing
the image scanning.
[0102] As the pattern information .chi., pattern data (template)
can be used, and the rough scanning can be omitted. In this case,
the template .chi. and the scanning data F(.chi.) corresponding
thereto are recorded in a control unit in advance. In particular,
when observation or measurement is performed using a recipe, a
position of the observation pattern is specified by alignment and
addressing, thereby performing the image scanning based on the
template.
[0103] An image of the rough scanning and the image scanning can be
generated using a desired signal electron. For example, the image
of the rough scanning is generated using a secondary electron (SE)
having low energy, and the image of the image scanning can be
generated using a back-scattered electron (BSE). A certain
percentage of the SE image of the rough scanning is added to the
BSE image acquired by the image scanning. In this manner, it is
possible to emphasize an edge, for example. In general, as
illustrated in FIG. 15, it is conceivable that the image scanning
is performed based on rough scanning information .chi.1501 and a
certain percentage of the pattern information .chi. is added to the
obtained image so as to generate a final image 1505. Hereinafter,
an example will be described in which the pattern information .chi.
is detected and the scanning data Fs(.chi.) is prepared.
[0104] As illustrated in FIG. 16, in a case where the pattern is a
vertical line (a longitudinal direction of a pattern edge 1601
shows a pattern in a Y-direction), the direction of the image
scanning is set to a direction perpendicular to the edge direction
(Y). That is, in this case, the direction is set to a horizontal
direction (scanning line 1602 in an X-direction). As the image
scanning, the scanning data is conceivable in which scanning in the
+X direction, scanning in the -X direction, or scanning in the +X
and -X directions are alternately performed. In addition, the
alternate scanning in the +X and -X directions includes scanning
which reversely changes directions for each frame and scanning
which reversely changes directions for each line of y-direction.
The purpose of performing scanning by combining two .+-.X
directions with each other is to prevent right and left edges from
being asymmetrical with each other.
[0105] Since the rough scanning is performed using the low dose, an
image having low SN is obtained. However, in order to accurately
specify an edge from the image, a method of compressing the image
and image processing for removing noise are used in combination
with each other. As described above, as a result of acquiring the
roughly scanned image, when it is determined that a beam scanning
line direction for the rough scanning and a scanning line direction
for the image scanning are the same as each other (if it is not
necessary to change the scanning line direction when the rough
scanning is switched to the image scanning), a signal at the time
of the rough scanning may be incorporated as a portion of
integration data of the captured image. In addition, even when the
scanning line direction is changed, pixel signal of a necessary
portion which are pixel signals in regions superimposed before and
after the rotation in the scanning direction may be selectively
integrated.
[0106] According to the above-described configuration, a properly
set scanning direction can be realized while a beam irradiation
amount is restrained.
Embodiment 8
[0107] As illustrated in FIG. 17, in a case where a horizontal
(x-direction) pattern (pattern in which the longitudinal direction
of a pattern edge 1701 is the X-direction) is specified by
performing the rough scanning, scanning is performed by using a
scanning line 1702 in the vertical (y) direction. In addition,
similarly to the vertical pattern, in order to improve symmetry of
the upper and lower edges of the pattern, the image scanning is
alternately performed in the .+-. direction.
Embodiment 9
[0108] As illustrated in FIG. 18, in a case where edges are
detected in two directions in a field of view, the image scanning
is alternately performed in the directions perpendicular to the
respective edges. In the example in FIG. 18, an edge 1801 of a
pattern A shows a direction of 45.degree., and an edge 1802 of a
pattern B shows a direction of 0.degree.. In this case, in order to
clearly show the edge 1801 of the pattern A, scanning is performed
using a scanning line 1803 in the direction of -45.degree.. In
order to clearly show the edge 1802 of the pattern B, scanning is
performed using a scanning line 1804 in a direction of -90.degree..
Furthermore, in order to improve symmetry of the both edges of the
pattern, reciprocating scanning is performed in the above two
directions.
Embodiment 10
[0109] An edge 1901 of a hole pattern as illustrated in FIG. 19 has
edges in all directions of 0.degree. to 360.degree.. In this case,
the image scanning is performed by setting the scanning direction
to an interval of 90.degree./n. However, n is an integer of n=1, 2,
3, or more. In FIG. 19, scanning in the directions of 0 and
90.degree. at n=1 (scanning using a scanning line 1902 in two
directions) is alternately performed. In a case of n=2, the image
scanning is performed in the directions of 0.degree., 45.degree.,
and 90.degree.. In a direction having edges opposite to each other,
in a case where the two edges are asymmetrical with each other due
to charging, reciprocating scanning is performed in the
direction.
[0110] In addition, as illustrated in FIG. 20, the rough scanning
may be performed on a hole pattern 2001, and specified edges (2002
and 2003) may be selectively scanned with a beam having a high
dose. In a case where a direction of a measurement target edge is
specified, the rough scanning is performed on the measurement
target edge by means of beam scanning so that a scanning line is
formed in the direction perpendicular to the measurement target
edge. In this manner, it is possible to accurately specify a
position serving as the measurement target.
Embodiment 11
[0111] As illustrated in FIG. 21, in a case where two patterns are
detected in a field of view by performing the rough scanning, only
a region having the patterns is scanned in the direction
perpendicular to the pattern edge. A region including a pattern
A2101 is scanned using a scanning line A2103 in the X-direction,
and a region including a pattern B2102 is scanned using a scanning
line B2104 in the Y-direction. Charging can be reduced and damage
to the sample can be reduced by limiting the scanning region to a
portion of the measurement target pattern. In addition, since the
scanning region is narrowed, a time for imaging can be shortened,
and high throughput can be achieved.
Embodiment 12
[0112] In addition, in a case where there is only one pattern as
illustrated in FIG. 22, an image is captured by scanning only a
region having the pattern in the direction perpendicular to the
pattern edge.
Embodiment 13
[0113] In a case where the same patterns are periodically arrayed,
a template of periodical patterns is prepared in order to
selectively scan the plurality of pattern portions, and a position
specified by template matching is selectively scanned. In this
manner, a dose amount can be restrained, and necessary information
can be acquired. The template matching is performed by an image
processing device incorporated in the control device 120. The
template is stored in a predetermined storage medium inside the
control device 120.
[0114] In a case of this example, the template which is n-times
(n=real number) a pattern area is prepared. The scanning deflector
105 is controlled so as to scan a region superimposed on the
template with the beam.
[0115] As illustrated in the example in FIG. 23, a template 2301 is
prepared in advance so that a scanning width is set to horizontally
K1x and is set to vertically K2y for a pattern of a horizontal
width x and a vertical width y. In a case of a rough image as
illustrated in FIG. 23(b), 5 periodical patterns are present.
Accordingly, 5 image scanning regions 2302 can be specified from
the rough image by the template matching. Beam scanning is
selectively performed on the specified regions (rough image regions
superimposed on the template). In this manner, unnecessary scanning
can be restrained, and the region including the measurement target
pattern can be measured using an image whose S/N is high. A pattern
2303 includes edges in the vertical direction and the horizontal
direction. Accordingly, scanning in the vertical direction
(scanning for clearly showing the edge in the horizontal direction)
and scanning in the horizontal direction (scanning for clearly
showing the edge in the vertical direction) are alternately
performed on the respective scanning regions. In this manner, it is
possible to accurately evaluate a shape of the pattern 2303.
Embodiment 14
[0116] In a case of a two-dimensional pattern, there is a
possibility that an edge parallel to the rough scanning direction
cannot be detected due to the charging influence. In order to avoid
this possibility, the rough scanning is performed with a low dose
in two directions which are perpendicular to each other. As
illustrated in FIG. 20, in a case where the rough scanning is
performed on the hole pattern 2001 in the x-direction and the
y-direction, an edge such as an edge 2002 in FIG. 20(b) is detected
in which the vertical direction is further relatively emphasized
than the horizontal direction by the x-scanning, and an edge such
as an edge 2003 in FIG. 20(c) is detected in which the horizontal
direction is further relatively emphasized than the vertical
direction by the y-scanning. Based on two results thereof, it is
possible to determine that the observation target is circular.
Embodiment 15
[0117] According to the present embodiment, a pattern is detected
during the rough scanning, and depending on the presence or absence
of an edge, a scanning speed is changed during the image scanning.
A region having no edge is scanned at a high speed, and the
periphery including the edge is scanned at a relatively low speed.
The purpose of setting the slow scanning speed is to increase an
incident dose and to improve SN. A time for imaging can be
shortened by scanning a region which is not a measurement target at
the high speed. In addition, in a case of a sample which is likely
to be damaged, shrinkage is reduced.
[0118] As illustrated in FIG. 24(a), the pattern is detected during
the rough scanning. Based on an edge detection process, the pattern
is divided into a pattern region (B) and a region (A) which is not
the pattern region (B) as illustrated in FIG. 24(b). As the pattern
region, the front and rear portions of the edge are allowed to have
a width of n% of the edge width. However, n is n=real number. FIG.
24(c) illustrates an x-scanning waveform in a case where the
pattern in FIG. 24 is imaged by the x-scanning. If an inclination
in the region having no pattern is set to .theta. and an
inclination in the region having the pattern is set to .alpha., a
relationship of 0>.alpha. is satisfied.
[0119] In addition, FIG. 24(d) illustrates an example in which an
irradiation dose is changed depending on the presence or absence of
the pattern. An irradiation current is decreased in the region A,
and an irradiation current is increased in the region B having the
pattern.
Embodiment 16
[0120] When measuring the vertical (y) line pattern which is likely
to receive damage due to the electron beam irradiation, in order to
reduce shrinkage, a method is employed in which the x-scanning is
performed at a certain interval in the y-direction. As illustrated
in FIG. 25(a), however, in a case where the vertical line pattern
is discontinuous in the y-direction, there is a possibility that a
location having no pattern may be scanned. In order to avoid this
possibility, the discontinuous portion is specified during the
rough scanning (FIG. 25(b)), and the interval in the y-direction is
determined so as to avoid the portion (FIG. 25(c)).
Embodiment 17
[0121] In general, as illustrated in FIG. 26, data of the image
scanning is prepared for any pattern so that the image scanning is
always perpendicular to the pattern edge detected by the rough
scanning. As described above, the beam used in selectively scanning
the edge portion for the rough scanning is used in low speed
scanning for the rough scanning.
REFERENCE SIGNS LIST
[0122] 101 ELECTRON SOURCE
[0123] 102 LEAD ELECTRODE
[0124] 103 ELECTRON BEAM
[0125] 104 CONDENSER LENS
[0126] 105 SCANNING DEFLECTOR
[0127] 106 OBJECTIVE LENS
[0128] 107 SAMPLE CHAMBER
[0129] 108 SAMPLE STAGE
[0130] 109 SAMPLE
[0131] 110 ELECTRON
[0132] 111 SECONDARY ELECTRON
[0133] 112 CONVERSION ELECTRODE
[0134] 113 DETECTOR
[0135] 120 CONTROL DEVICE
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