JP2002352760A - Scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning electron microscope that does not need scanning stoppage, when a pre-evacuation chamber evacuated for the evacuation and the air leakage process and can steadily suppress deterioration of the throughput. SOLUTION: Two or more piezoelectric elements 4 are arranged between a base 17 and a sample chamber 1, and the sample chamber 1 is slanted, in response to the deformation of the sample chamber 1 caused by a vacuum evacuation and air leakage process, in the a pre-evacuation chamber 3. A lens- barrel 2 is slanted to the sample chamber 1 by its own weight, and the deviation of an irradiation position of the electron beam EB to the sample 7 can be suppressed. Since the scanning stoppage time caused by the evacuation and the air leakage process in the pre-evacuation chamber 3 is eliminated, throughput in the electron microscope is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope having a preliminary exhaust chamber, and more particularly to a scanning electron microscope suitable for use in inspection and observation in the field of semiconductor manufacturing.

[0002]

2. Description of the Related Art In recent years, in the field of manufacturing semiconductor devices,
Scanning electron microscope (SE) for observation and inspection of semi-finished products and products
M) has been widely used because the advantages of the high resolution characteristic and the deep depth of focus characteristic of the electron microscope are great.

Incidentally, the flow of processing in observation and inspection of a sample in a SEM, for example, a sample such as a silicon wafer, is generally as follows. First,
First, the wafer is taken out of the wafer cassette by the wafer transfer robot and carried into the preliminary exhaust chamber of the SEM.

Next, the pre-evacuation chamber is evacuated by a vacuum pump, and when the chamber reaches a certain degree of vacuum, a valve (door) between the pre-evacuation chamber and the sample chamber of the SEM is opened, and the wafer is sampled. Transported to the room. The reason why the preliminary exhaust chamber is provided is that a large amount of processing time is required if the exhaust and air leak of the sample chamber having a considerably large internal space are performed each time the wafer is transferred.

The wafer transported into the sample chamber is further moved to a predetermined position in the sample chamber, where an electron beam is irradiated on the wafer surface and scanned (scanned). Then, the secondary electrons generated thereby are detected, and image data such as a pattern on the wafer surface is taken in. The wafer is inspected by processing the image data.

While the wafer is being inspected in the sample chamber, the evacuated preliminary exhaust chamber is returned to the atmospheric pressure by air leaking, and the uninspected wafer (the next wafer to be inspected) is transported therein. After evacuation, after the inspection is completed, the inspected wafer and the uninspected wafer are exchanged in the preliminary evacuation chamber, the uninspected wafer is loaded into the sample chamber by the wafer transfer robot, and the inspected wafer is unloaded and transferred to the wafer cassette. Will be returned.

However, in such an SEM, a change in stress is given due to a pressure difference between the time of evacuation of the preliminary exhaust chamber and the time of air leak, and it is inevitable that deformation appears on the wall surface of the preliminary exhaust chamber. Here, this preliminary exhaust chamber is attached to the sample chamber. Therefore, if it is deformed, it also affects the sample chamber, and as a result, particularly, the sample chamber supporting the lens barrel of the electron microscope. There is a risk that the top plate will be deformed.

For this reason, in the SEM according to the prior art, if the pre-evacuation chamber is evacuated and air leaked during the inspection of the wafer, the irradiation position of the electron beam on the wafer surface deviates from a predetermined measurement point, and the observation screen is displayed. The wafer image inside is, for example, 1
Although it is a very small ratio of about 00 to 200 nm / 10 s, it shifts with a change in pressure.

This is a major cause of a decrease in inspection accuracy, especially in the case of a scanning electron microscope for length measurement (length-measuring SEM) for inspecting the dimensions of fine patterns, since it takes several seconds to capture an image. I will. Further, even if the image is not being captured, if the wafer image moves after the positioning, an erroneous inspection that another adjacent pattern is inspected occurs.

Therefore, for example, Japanese Patent Application Laid-Open No. HEI 3-156493.
In the prior art described in Japanese Patent Application Laid-Open Publication No. H11-260, the scanning of the electron beam is stopped at the time of the exhaust processing of the preliminary exhaust chamber and the air leak processing, and
After the positioning, the exhaust of the preliminary exhaust chamber and the air leak are not performed until the measurement scan is completed.

[0011]

The above prior art does not take into account the fact that the time during which scanning is stopped and the time required for stopping the exhaust and leak of the preliminary exhaust chamber are wasted. However, there is a problem that the throughput is reduced. Here, it is not necessary to say that this decrease in throughput is nothing but an obstacle to improving productivity.

Here, for example, 45 sheets per hour
If a dead time is 5 seconds in a length measuring SEM capable of inspecting (80 seconds per wafer) wafers, the number of measured sheets per hour is reduced to 41 due to the presence of the dead time. SUMMARY OF THE INVENTION An object of the present invention is to provide an SEM that solves these problems and does not require scanning to be stopped at the time of evacuation of the preliminary evacuation chamber and at the time of air leak, thereby reliably suppressing a decrease in throughput. .

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a scanning electron microscope in which a lens barrel is provided upright on a sample chamber having a pre-evacuation chamber on the side. Means are provided to control the inclination of the sample chamber due to its own weight appearing in the lens barrel by the inclination of the sample chamber, so that the correction of the irradiation position of the electron beam on the sample surface is achieved. At this time, the driving unit may be controlled when the preliminary exhaust chamber deforms due to a change in internal pressure, a deformation appears in the sample chamber, and the direction of the lens barrel changes.

Further, at this time, the driving means is disposed between the sample chamber and a base supporting the sample chamber at substantially the same angle with respect to the center axis of the lens barrel and at substantially the same distance. May be composed of at least three piezoelectric elements,
At least three motor-driven wedge-type moving mechanisms disposed between the sample chamber and a base supporting the sample chamber at substantially the same angle with respect to the center axis of the lens barrel and at substantially the same distance. You may comprise.

At this time, control means for controlling the driving means is provided, and the control means grasps in advance the relationship between the deformation amount of the sample chamber and time and determines the operation amount of the driving means. The driving means may be controlled. Further, at this time, a control unit for controlling the driving unit and a distortion detection unit for detecting the deformation of the sample chamber are provided, and the control unit determines a relationship between the amount of distortion measured by the distortion detection unit and time. The operation amount of the driving unit may be calculated to control the driving unit.

Here, there are provided control means for controlling the driving means, and inclination detecting means attached to the top plate of the sample chamber, wherein the controlling means comprises: an inclination amount measured by the inclination detecting means; The operation amount of the driving unit may be calculated from the relationship of time, and the driving unit may be controlled, and a control unit for controlling the driving unit and a pressure detecting unit attached to the preliminary exhaust chamber are provided. The control means may calculate an operation amount of the drive means from a relationship between the pressure amount measured by the pressure detection means and time, and control the drive means.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an SEM (scanning electron microscope) according to the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 shows an embodiment of the present invention. In the drawing, main constituent members are a sample chamber 1, a lens barrel 2, a preliminary exhaust chamber 3, and a piezoelectric element 4, which are all on a base 17 as a whole. The base 17 is mounted on the vibration isolator 26.
It is installed on a predetermined place by being held on the installation base 6 via the.

The sample chamber 1 forms a closed space, and is provided with an exhaust system 9 so that the inside can be maintained at a high vacuum. The lens barrel 2 is provided on the top plate, and the preliminary exhaust chamber 3 is provided on the side wall. Are mounted, and a sample stage 10 is provided inside.

First, the lens barrel 2 is, as shown in FIG.
Is made of a tubular member having no bottom and communicating with the inside, and is provided with a filament 5 serving as an electron source near the top of the inside, and an electron beam E generated from this is provided.
B is deflected and focused so that a predetermined region on the surface of the sample 7 such as a wafer placed on the sample stage 11 can be irradiated.

Then, electrons generated from the sample 7 by irradiation of the electron beam EB, that is, secondary electrons SB are detected by the secondary electron detector 8, and the secondary electrons detected by the secondary electron detector 8 are detected. An enlarged image of the surface of the sample 7 is displayed on an image display device (not shown) based on the signal. The lens barrel 2 is also provided with an exhaust system 27 so that the inside of the lens barrel 2 and the sample chamber 1 can be maintained at a high vacuum.

At this time, the sample stage 10 in the sample chamber 1 is positioned in a plane perpendicular to the central axis of the electron beam EB.
That is, it is configured to be able to move by an arbitrary amount in an arbitrary direction in a horizontal plane. Therefore, by mounting the sample stage 11 on which the sample 7 such as a wafer is mounted on the sample stage 10, the sample 7 is moved to an arbitrary position in the horizontal plane at the time of observation and inspection, and necessary for measurement. It can be positioned at a predetermined location.

The preliminary exhaust chamber 3 is attached to the side wall of the sample chamber 1 so as to communicate with the sample chamber 1 through a valve 12 serving as a door for entry and exit. Is provided so that the vacuum can be made higher or the pressure can be returned to the atmospheric pressure.

A sample 15 to be inspected next is loaded into the preliminary exhaust chamber 3 while being placed on the sample table 14, and the sample 7 already loaded into the sample chamber 1 is loaded. After the observation inspection of the above is completed, by opening the valve 12,
The sample 7 is replaced with the sample 15 together with the sample stage 11.

Here, the sample 1 is introduced into the preliminary exhaust chamber 3 from outside.
When carrying in 4, the inside of the preliminary exhaust chamber 3 is returned to the atmospheric pressure by air leaking by the leak valve 16 by the leak valve 16, and when opening the valve 12 between the sample chambers 1, the inside of the preliminary exhaust chamber 3 is kept at a vacuum. . By the way, the configuration described so far is a conventional SE.
M is the same, but in this embodiment, the sample chamber 1
A plurality of piezoelectric elements 4 are provided between and the base 17.

Here, these piezoelectric elements 4 function as actuators that expand and contract according to a control signal supplied from the control device 18, and are located between the sample chamber 1 and the base 17 with respect to the center axis of the lens barrel 2. The sample chamber 1 can be inclined in an arbitrary direction with respect to the base 17 by arranging and controlling the expansion and contraction of at least three at substantially the same angle and at substantially the same distance from each other.

Next, FIG. 2 shows a state of deformation of each part which occurs when the inside of the preliminary exhaust chamber 3 is evacuated. Here, as an example, the sample The top plate of the chamber 1 is mainly deformed, and the lens barrel 2 is
The right side of the figure shows a case where the tilt has occurred. Note that the degree of the deformation or the inclination is extremely small in practice, and is exaggerated in the drawings.

As described above, when the lens barrel 2 is tilted, the irradiation position of the electron beam EB deviates from the original position. This deviation is caused by the movement of the image of the sample 7 on the image display surface. In this case, as in the case of the related art, there is a risk of a decrease in inspection accuracy and an erroneous inspection.

However, even when the state shown in FIG. 2 is reached, according to this embodiment, the piezoelectric device 4 is controlled by the control device 18, and as a result, as shown in FIG.
Despite the tilt, the change in the irradiation position of the electron beam EB can be suppressed, and a state in which no deviation occurs on the surface of the sample 7 can be achieved.

Here, FIG. 3 shows that the height of the piezoelectric element 4 is individually controlled and the sample chamber 1 is tilted by a predetermined angle in a predetermined direction. The situation where the irradiation position of the electron beam EB is corrected by being tilted to the indicated position is shown. FIG. 3 also shows the same as FIG.
The deformation is exaggerated.

That is, in this embodiment, when the preliminary exhaust chamber 3 is deformed and the lens barrel 2 is tilted, the heights of the plurality of piezoelectric elements 4 are individually controlled to reduce the inclination appearing in the lens barrel 2. The sample chamber 1 is tilted in the opposite direction so that a gravitational moment acts on the top of the lens barrel 2 as shown by an arrow G in FIG. 3, so that the surface of the sample 7 is irradiated with the electron beam EB. The lens barrel 2 is tilted in the opposite direction so that the position does not change.

Next, the control of the piezoelectric element 4 by the control device 18 at this time will be specifically described. Note that, in the figure, since it can be expressed only by a two-dimensional cross section, the operation by the two piezoelectric elements 4 will be described.

First, the amount of image shift that appears when the interior of the preliminary exhaust chamber 3 is evacuated by the exhaust system 13 is determined by elapse of time from when the exhaust is started to when a predetermined degree of vacuum is reached and the exhaust is stopped. The piezoelectric element 4 necessary for compensating the image shift at that time and preventing the irradiation position of the electron beam EB from being changed on the surface of the sample 7.
Are stored as a function of time, for example, in a table.

The inside of the preliminary exhaust chamber 3 is provided with a leak valve 16.
Similarly, the amount of deviation of the image that appears when air leaks is also measured in response to the passage of time from the predetermined degree of vacuum to equilibrium with the atmospheric pressure, and at that time, the deviation of the image is compensated, The piezoelectric element 4 necessary to keep the irradiation position of the electron beam EB unchanged on the surface of the sample 7
Are stored as a function of time and are also tabulated.

The control unit 18 refers to the data in the above-mentioned table during the exhaust process and the air leak process of the preliminary exhaust chamber 3 and, based on time, each piezoelectric element 4.
, And a control signal (voltage) to be supplied to the piezoelectric element 4.

As a result, the change in the irradiation position of the electron beam EB on the surface of the sample 7 due to the inclination appearing in the lens barrel 2 is corrected during the evacuation processing and the air leak processing of the preliminary evacuation chamber 3. According to this embodiment, even if the exhaust processing and the air leak processing are executed in parallel with the inspection observation processing, it is possible to surely suppress the deterioration of the inspection accuracy and the occurrence of an erroneous inspection.

Next, another embodiment of the present invention will be described. First, FIG. 4 shows a linear movement mechanism using a motor 19 and a feed screw 20 and a wedge-type movement mechanism 22 driven by this linear movement mechanism as an actuator for tilting the sample chamber 1 with respect to the base 17. In one embodiment of the present invention, the wedge (wedge) body below the wedge-type moving mechanism 22 is moved horizontally by the nut 21 of the feed screw 20 and the wedge body above is moved up and down, and the sample chamber is moved. 1 is tilted, and the other configuration is the same as the embodiment described with reference to FIG.

In this embodiment, for example, a pulse motor may be used as the motor 19, and the control device 18
Is the rotation angle position of the feed screw 20 and the wedge-type moving mechanism 2
The motor 19 is controlled by referring to the above-mentioned tabulated data based on the relationship between the vertical movement positions of the motor 2. Therefore,
According to this embodiment, the exhaust processing and the air leak processing can be performed in parallel with the inspection observation processing. In this case, it is also possible to surely prevent the inspection accuracy from being lowered or the erroneous inspection from occurring. Can be.

Next, FIG. 5 also shows an embodiment of the present invention, in which a distortion detector 23 is provided on the top plate of the sample chamber 1, whereby the amount of deformation appearing in the sample chamber 1 is measured. Is supplied to the control device 18 and reflected in the control of the operation amount of the piezoelectric element 4 in a feedback control configuration.
Other configurations are the same as the embodiment of FIG.

In the case of the embodiment shown in FIG.
The amount of deformation of the sample chamber 1 due to exhaust and air leaks in the chamber and the change in the irradiation position of the electron beam EB on the surface of the sample 7 are previously tabulated. The amount of deformation of the sample chamber 1 is measured from time to time by the detector 19, and the piezoelectric element 4 is controlled by referring to the table based on the amount of change.

Therefore, according to the embodiment shown in FIG.
Exhaust processing and air leak processing can be performed in parallel with the inspection observation processing. In this case as well, it is possible to reliably suppress the reduction in inspection accuracy and the occurrence of erroneous inspections, and to perform feedback control. Therefore, it is possible to cope with a shift of the electron beam EB without reproducibility.

Next, FIG. 6 shows another embodiment of the present invention. In this embodiment, an electronic level 24 is used instead of the distortion detector 23 in the embodiment shown in FIG. In this embodiment, the inclination angle appearing on the top plate 1 is detected and the amount of deformation is measured. The other configuration is the same as that of the embodiment shown in FIG. In this case as well, it is possible to reliably suppress the deterioration of the inspection accuracy and the occurrence of an erroneous inspection, and in this case, the feedback control is performed. Beam EB
The same is true of the shifts that can be made.

Next, FIG. 7 also shows an embodiment of the present invention, in which a pressure gauge 25 is attached to the preliminary exhaust chamber 3 and the internal pressure is measured to estimate the amount of deformation appearing on the top plate of the sample chamber 1. It is like that. Here, the amount of deformation of the top plate of the sample chamber 1 depends on the amount of deformation of the preliminary exhaust chamber 3, and the amount of deformation of the preliminary exhaust chamber 3 depends on the internal pressure.
The amount of deformation of the top plate of the sample chamber 1 can be calculated from the pressure measurement value obtained by the measurement.

Therefore, according to the embodiment shown in FIG.
Exhaust processing and air leak processing can be performed in parallel with the inspection and observation processing. In this case as well, it is possible to reliably suppress the deterioration of inspection accuracy and the occurrence of erroneous inspections, and to perform feedback control. Therefore, the embodiment can cope with the shift of the electron beam EB without reproducibility, which is the same as the embodiment of FIGS.

[0044]

According to the present invention, since the change in the irradiation position of the electron beam on the sample surface due to the deformation of the sample chamber can be suppressed, there is no danger of the accuracy being reduced due to the exhaust processing in the preliminary exhaust chamber and the air leak processing. be able to. Therefore, according to the present invention, the evacuation and air leak of the preliminary exhaust chamber can be performed in parallel with the inspection and observation processing. As a result, the dead time associated with the stop of the inspection and observation processing is eliminated, and the throughput of the electron microscope is greatly increased. Can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a scanning electron microscope according to the present invention.

FIG. 2 is an explanatory diagram of a deformation state of a sample chamber in one embodiment of the present invention.

FIG. 3 is an explanatory diagram of a correction operation according to the embodiment of the present invention.

FIG. 4 is a sectional view showing a second embodiment of the scanning electron microscope according to the present invention.

FIG. 5 is a sectional view showing a third embodiment of the scanning electron microscope according to the present invention.

FIG. 6 is a sectional view showing a fourth embodiment of the scanning electron microscope according to the present invention.

FIG. 7 is a sectional view showing a fifth embodiment of the scanning electron microscope according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sample chamber 2 lens barrel 3 preliminary exhaust chamber 4 piezoelectric element 5 filament 6 mounting table 7 sample 8 secondary electron detector 9 exhaust system 10 sample stage 11 sample table 12 valve 13 exhaust system 14 sample table 15 sample, 16 leak valve 17 Base 18 Control device 19 Motor 20 Feed screw 21 Nut 22 Wedge type moving mechanism 23 Strain detector 24 Electronic level 25 Pressure gauge 26 Vibration isolator 27 Exhaust system EB Electron beam SB Secondary electron

Claims (8)

[Claims] 1. A scanning electron microscope in which a lens barrel is provided upright above a sample chamber having a preliminary exhaust chamber on a side thereof, wherein a driving means for inclining the sample chamber is provided. A scanning electron microscope, characterized in that the tilt is controlled by the tilt due to its own weight appearing in the lens barrel, so that the irradiation position of the electron beam on the sample surface can be corrected. 2. The invention according to claim 1, wherein the driving means is controlled when a preliminary exhaust chamber is deformed by a change in internal pressure, a deformation appears in the sample chamber, and a direction of the lens barrel changes. A scanning electron microscope characterized by the following: 3. The invention according to claim 1, wherein the driving means is substantially equiangular with respect to a center axis of the lens barrel between the sample chamber and a base supporting the sample chamber. so,
A scanning electron microscope comprising at least three piezoelectric elements arranged at substantially equal distances from each other. 4. The invention according to claim 1, wherein the driving means is substantially equiangular with respect to a center axis of the lens barrel between the sample chamber and a base supporting the sample chamber. so,
A scanning electron microscope comprising at least three motor-driven wedge-type moving mechanisms disposed at substantially equal distances from each other. 5. The invention according to claim 1, further comprising control means for controlling the driving means, wherein the control means grasps in advance the relationship between the deformation amount of the sample chamber and time, A scanning electron microscope, wherein an operation amount of the driving unit is determined to control the driving unit. 6. The invention according to claim 1, further comprising: a control unit that controls the driving unit; and a distortion detection unit that detects deformation of the sample chamber. A scanning electron microscope, wherein an operation amount of the driving unit is calculated from a relationship between a distortion amount measured by a detection unit and time, and the driving unit is controlled. 7. The invention according to claim 1 or 2, further comprising control means for controlling the driving means, and inclination detecting means attached to a top plate of the sample chamber. A scanning electron microscope, wherein an operation amount of the driving unit is calculated from a relationship between the amount of inclination measured by the inclination detecting unit and time, and the driving unit is controlled. 8. The invention according to claim 1 or 2, further comprising: a control unit for controlling the driving unit; and a pressure detection unit attached to the preliminary exhaust chamber. A scanning electron microscope, wherein an operation amount of the driving means is calculated from a relationship between a pressure amount measured by the means and time, and the driving means is controlled.