JP3418133B2 - Scanning electron microscope - Google Patents

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, and more particularly to a scanning electron microscope having a function of measuring a pattern on a sample surface.

[0002]

2. Description of the Related Art When a scanning electron microscope is used as a length measuring device, it is necessary to devise a method for preventing vibration from being transmitted to a sample or an electron gun. The factors that vibrate the sample and the like are roughly classified into vibrations generated by the apparatus itself and vibrations generated outside the apparatus.

Of these, the vibrations generated by the apparatus itself include, for example, vibrations associated with sample transport and sample supply, vibrations of a vacuum pump for exhausting the sample chamber, and vibrations generated outside the apparatus. Is, for example, vibration associated with floor vibration caused by a person walking around the device, or vibration caused by a person touching the device.

Among them, as a method for reducing the vibration generated outside the apparatus, for example, as described in Japanese Utility Model Laid-Open No. 168556/1987, a load plate is placed on a mount via a vibration-proof mount. Then, there was a method of installing an electron microscope fixedly on the load plate.

Regarding the vibration generated by the apparatus itself, on the other hand, in the length measurement in the prior art, (1) the sample to be measured is conveyed to the sample chamber, vacuum exhaust is performed, and then the length measurement is performed. (2) When the planned length measurement is completed, the sample is discharged from the sample chamber, a new sample is transferred to the sample chamber, and the next length measurement is performed after evacuation. Since it is performed in this step, the length measurement is inevitably performed when the sample is not transported or vacuum exhaust is not performed, and it is not necessary to mitigate the vibration generated by the apparatus itself.

[0006]

When the sample is a mass-produced product such as a semiconductor wafer, it is required to measure many lengths in a short time, and in order to perform the length measurement efficiently and in a short time,
To provide a loader chamber connected to the sample chamber via a gate valve, to convey the next sample to the loader chamber while measuring the length of one sample in the sample chamber, and to make the loader chamber vacuum It is necessary to perform parallel control such as exhausting air.

At this time, since the loader chamber and the transfer device are integrated with the sample table, the electron gun, etc., the vibration isolating member or the like for blocking the external vibration against the vibration generated from them is useful. However, this vibration may adversely affect the length measurement value.

Further, the environmental problem that adversely affects the length measurement value is not limited to vibration, and the electron beam is deflected by a change in the magnetic field around the lens barrel, which adversely affects the length measurement value.

An object of the present invention is to solve the above-mentioned problems, to provide a scanning electron microscope capable of performing length measurement efficiently and having a length measuring function which is not adversely affected by vibration or change in magnetic field. Especially.

[0010]

In order to solve the above problems, the present invention is characterized in that a scanning electron microscope having a function of measuring the surface of a sample is provided with the following means. is there. (1) A means for interrupting the length measurement by detecting that the sample transport mechanism of the scanning electron microscope is in operation is provided.

According to the above configuration (1), since the length measurement is performed only when the scanning electron microscope is not vibrating, an accurate length measurement result can always be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIG.

The electron beam 2 emitted from the electron gun 1 is
It is converged by the converging lens 4 and the objective lens 5, and is irradiated onto the surface of the sample 3 placed on the sample stage 43.
The electron beam 2 scans the surface of the sample 3 by a deflection lens (not shown) incorporated in the objective lens 5.

A secondary signal 6 such as secondary electrons and reflected electrons generated from the surface of the sample 3 by the irradiation of the electron beam 2 is detected by a detector 7, and the detected signal is amplified by an amplifier 8 and then arithmetic means. It is input to 44, and the calculation result is output to CRT 9. On the CRT 9, the measurement value, which is the calculation result, is displayed together with the observation image.

A beam blanking deflection coil 10 connected to a beam blanking power source 11 is provided between the converging lens 4 and the objective lens 5, and the power source is supplied based on a signal from a comparator 26 described later. When the electron beam 11 is energized, the electron beam 2 is deflected by the deflection coil 10, and the electron beam 2 is no longer irradiated on the sample (blanking).

The electron gun 1, the converging lens 4, the objective lens 5,
The deflection coil 10 for beam blanking is the lens barrel 3
The sample chamber 12 is provided inside the lens barrel 3 and is provided below the lens barrel 33. The sample chamber 12 and the loader chamber 15 are partitioned by a gate valve 14, the sample chamber 12 is evacuated by a vacuum pump 13, and the loader chamber 15 is evacuated by a vacuum pump 16.

A gate valve 21 is provided in a portion of the loader chamber 15 facing the gate valve 14, and from the gate valve 21, samples 3 taken out one by one from a sample case 22 that is lifted and lowered by a loader mechanism 23. Will be introduced.

A load lock mechanism 20, which will be described later in detail with reference to FIG. 5, is provided in the loader chamber 15, and two sample 3 can be stored in the loader chamber 15.

The lens barrel 33, the sample chamber 12, and the loader chamber 15 are supported by a load plate 17, and the load plate 1
7 is mounted on a pedestal 19 via a vibration proof mount 18, and the loader mechanism 23 is directly mounted on the pedestal 19.

On the other hand, an accelerometer 24 is provided on the load plate 17.
a, 24b (not shown), and 24c (not shown) are attached so that vibration measurement in the X direction, Y direction, and Z direction can be performed, and the output signals of the accelerometers 24a, 24b, and 24c are comparators. It is input to one of the input terminals of 26. The database 25 is connected to the other input terminal of the comparator 26.

The accelerometer 24 is installed at the load plate 1
The sample 3 and the electron gun 1 are not limited to the above.
The location may be the upper surface or the side surface of the lens barrel 33 as long as the vibration of at least one of the above can be detected.

The database 25 stores a reference signal corresponding to the vibration in which the shake of the observed image exceeds the length measurement resolution of the scanning electron microscope, and the comparator 26 stores the reference signal in each of the accelerometers 24a, 24b and 24c. The output signal is compared with the reference signal from the database 25, and the beam blanking power supply 11 is energized according to the comparison result.

The operation of the load lock mechanism 20 for introducing and discharging the sample will be described with reference to FIG. In the figure, for simplification of description, a gate valve 1 provided between the loader chamber 15 and the sample chamber 12 is provided.
4 is omitted.

As shown in FIG. 3A, the load lock mechanism in the loader chamber 15 is mainly composed of two sample mounting tables 40a, 4a.
0b and the mounting table 40a, 40b coupling member 4
And the sample mounting table 40a, 40b
Rotates about the central axis 42. Sample 3 is sample chamber 1
The sample is placed on the sample stage 43 in 2 and measured.

In FIGS. 5A to 5H, the sample 3 marked with "not" is the unmeasured sample, the sample 3 marked with "done" is the sample that has been measured, and "medium" The attached sample 3 shows the sample being measured.

A state in which no sample is introduced [FIG.
From (a)], after the sample 3 is first introduced into the mounting table 40a,
After rotating the coupling member 41 by 180 ° about the central axis 42, the sample 3 is further introduced onto the mounting table 40b [FIG.
(b)], where the sample chamber 12 and the loader chamber 15 are evacuated.

Next, the sample 3 on the mounting table 40a is mounted on the sample stage 43, and the length measurement is started [(c) in the figure]. When the length measurement is completed, the length-measured sample is placed on the placing table 40a in the loader chamber 15 again [(d) in the figure].

Then, after rotating the coupling member 41 by 180 ° [(e) in the figure], this time, the sample 3 on the mounting table 40b is mounted on the sample stage 43 in the sample chamber 12 and the length measurement is started. Then, the length-measured sample 3 on the mounting table 40a is discharged from the loader chamber 15 [(f) of the same figure].

Next, a new sample is introduced on the mounting table 40a [(g) in the figure] and evacuated, and a sample whose length has been measured is further mounted on the mounting table 40b [(h) in the figure].

Thereafter, similarly to the above, the steps (e) to (h) are repeated to measure the length.

According to the scanning electron microscope having such a structure, it becomes possible to efficiently exchange samples, and it is possible to measure many samples in a short time.

The load lock mechanism applied to the present invention is not limited to such a structure, and may be a load lock mechanism capable of simultaneously mounting three samples or more samples. .

In this embodiment, vibration is generated during the length measurement shown in (f) and (g) above, because the sample is introduced into the loader chamber 15, discharged, and evacuated by the vacuum pump. . The vibration is detected by the accelerometers 24a, 24b, 24c, and a detection signal is output to the comparator 26.

The comparator 26 includes a reference signal level stored in the database 25 and the accelerometers 24a, 24a.
The output signal levels of b and 24c are compared, and when the output signal level of either accelerometer exceeds the reference signal level, the beam blanking power supply 11 is activated to irradiate the sample 3 with the electron beam 2. Prohibit and interrupt measurement.

When the vibration is stopped, each accelerometer 24a, 24a
When both the output signal levels of b and 24c fall below the reference signal level, the comparator 26 stops energizing the beam blanking power supply 11 and restarts the length measurement.

According to the present embodiment, since the length measurement is not performed when the vibration that affects the length measurement is detected, the exhaust,
In a length measuring system that enables efficient length measurement by performing work involving vibration such as sample transportation and the length measurement in parallel, accurate length measurement is always possible.

Moreover, since the electron beam is not irradiated on the sample while the length measurement is not performed, the sample can be prevented from being damaged.

Although the deflection coil is used as the blanking coil in this embodiment, the same effect can be achieved by using the electrostatic blanking coil.

Further, in this embodiment, the accelerometer is used as the load plate 17
Although it is provided above, it may be provided above the sample chamber 12 or on the surface of the lens barrel 33.

FIG. 2 is a schematic configuration diagram of a scanning electron microscope which is a second embodiment of the present invention, and the same reference numerals as those in FIG. 1 represent the same or equivalent portions.

In this embodiment, the magnetic field measuring device 2 is placed on the sample chamber 12.
7 is provided, and the output signal thereof is input to one input terminal of the comparator 26.

The database 25 in this case stores a reference signal corresponding to an external magnetic field in which the shake of the observed image exceeds the length measurement resolution of the scanning electron microscope. The comparator 26 compares the output signal level of the magnetic field measuring device 27 with the reference signal level from the database 25. When the output signal level exceeds the reference signal level, the beam blanking power supply 11 is energized and the electronic beam is emitted. Blanking is performed so that the sample 2 is not irradiated with the sample 2.

According to this embodiment, since the amount of change in the magnetic field in the vicinity of the lens barrel is small and the length measurement is performed only when accurate length measurement is possible, an accurate length measurement result can always be obtained.

By the way, the permissible range of blurring of the observed image naturally depends on the length measurement range. That is,
The permissible range differs depending on whether the unit of measurement is the nm order or the μm order.

Therefore, if the reference signal level output from the database is changed according to the observation magnification or the measurement range, etc., an unnecessarily high level is not required for vibration or change in magnetic field.

In the above description, the case where only one of the accelerometer 24 and the magnetic field measuring device 27 is installed has been described as an example, but both may be installed together.

FIG. 3 is a schematic configuration diagram of a scanning electron microscope which is a third embodiment of the present invention, and the same reference numerals as those in FIG. 1 or 2 represent the same or equivalent portions.

In the figure, the gate valves 14, 21,
From devices such as the vacuum pumps 13 and 16 and the load lock mechanism 20 that generate vibrations that adversely affect the length measurement value, a control signal indicating whether or not each part is operating is provided by the control device. Is output to 32.

The control device 32 checks the input control signal, and if any of the above devices is in operation, energizes the beam blanking power source 11 to blank the electronic beam.

According to the present embodiment, since the length measurement is not performed during the period when a large vibration is likely to occur, accurate length measurement can always be performed.

FIG. 4 is a schematic configuration diagram of the fourth embodiment of the present invention, and the same reference numerals as those in FIG. 3 represent the same or equivalent portions.

In this embodiment, in addition to the structure shown in FIG. 3, a robot 28 mainly composed of a hand 29, an arm 30, and a main body 31 is further installed, and the robot 28 is installed.
Conveys the sample case 22, and stores the sample case 22 in the loader mechanism 23.

In the scanning electron microscope having such a configuration, when the robot 28 stores the sample case 22 in the loader mechanism 23, the vibration caused thereby causes the pedestal 19 and the vibration proof mount 18.
Will be transmitted to the load plate 17 via.

Therefore, in this embodiment, a signal is output when the robot 28 stores the sample case 22 in the loader mechanism 23, that is, when the hand 29 is opened, and the signal is also input to the control device 32. .

According to the present embodiment, similarly to the above, since the length measurement is not performed during the period when a large vibration may occur,
Accurate measurement is always possible.

Although not specifically shown in the above description, in order to cope with the change in the magnetic field described with reference to FIG. 2, the scanning electron microscope equipped with the vibration detecting means as described with reference to FIG. It is also possible to apply the above-mentioned means, or one or both of these means to each of the embodiments described with reference to FIGS.

Further, in each of the above-described embodiments, it is described that the electron beam is blanked to suppress the damage of the sample to the minimum when the measurement is interrupted when the vibration amount is large. The lens is controlled to reduce the convergence of the electron beam so that the spot diameter of the electron beam on the sample becomes large, and at that time, the calculation for obtaining the length measurement value is not performed. If so, the same effect as described above can be obtained.

Further, if it is not necessary to consider the damage of the sample, the electron beam is irradiated onto the sample in the same manner as during the length measurement, and only the calculation for obtaining the length measurement value is not performed. May be.

[0059]

As is apparent from the above description, according to the present invention, since the length measurement is performed only when there is no vibration or change in the magnetic field that influences the length measurement value, accurate measurement is always performed. Enables length measurement.

Further, when the measurement is interrupted, the electron beam is blanked, or the convergence of the electron beam is relaxed to increase the spot diameter, whereby the damage to the sample can be minimized. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a scanning electron microscope which is an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a scanning electron microscope that is a second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a scanning electron microscope which is a third embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a scanning electron microscope which is a fourth embodiment of the present invention.

FIG. 5 is a diagram for explaining a load lock mechanism.

[Explanation of symbols]

3 ... Sample, 10 ... Deflection coil, 11 ... Beam blanking power supply, 12 ... Sample chamber, 13, 16 ... Vacuum pump, 1
4, 21 ... Gate valve, 15 ... Loader chamber, 17 ... Load plate, 18 ... Anti-vibration mount, 19 ... Frame, 20 ... Load lock mechanism, 24 ... Accelerometer, 25 ... Database, 26
... Comparator, 33 ... Lens barrel, 43 ... Sample stage, 4
4 ... Calculation means

Claims (5)

(57) [Claims] 1. A scanning having a function of detecting an electron obtained when an electron beam emitted from an electron gun is converged and scanned on a sample, and measuring a pattern formed on the sample. In an electron microscope, a sample chamber in which a sample stage for arranging a sample to be irradiated with an electron beam is provided, a loader chamber for exchanging a sample with the sample chamber without breaking the vacuum of the sample chamber, and the loader chamber a gate valve for introducing a sample from the outside to the scanning electron microscope, characterized in that it comprises a means for interrupting the measurement at least when the gate valve is operating. 2. A scanning having a function of detecting an electron obtained when an electron beam emitted from an electron gun is converged and scanned on a sample, and measuring a pattern formed on the sample. In an electron microscope, a sample chamber in which a sample stage for arranging a sample to be irradiated with an electron beam is provided, a loader chamber for exchanging a sample with the sample chamber without breaking the vacuum of the sample chamber, and the loader chamber A scanning electron microscope comprising: a vacuum pump for evacuating the vacuum pump; and a means for interrupting the length measurement at least when the vacuum pump is operating. 3. A scan having a function of detecting an electron obtained when an electron beam emitted from an electron gun is converged and scanned on a sample, and measuring a pattern or the like formed on the sample. In an electron microscope, a sample chamber in which a sample stage for arranging a sample to be irradiated with an electron beam is provided, a loader chamber for exchanging a sample with the sample chamber without breaking the vacuum of the sample chamber, and the sample chamber A load lock mechanism including a moving mechanism that moves a sample table on which a plurality of samples to be carried in or out of the sample chamber can be moved, and means for interrupting the length measurement at least when the load lock mechanism is operating And a scanning electron microscope. 4. A beam blanking means for deflecting the electron beam so as not to irradiate the surface of the sample with the electron beam is provided, and when the length measurement is interrupted, the electron beam is emitted by the beam blanking means. beam claims 1 to scanning electron microscopy of the mounting serial to any one of 3, characterized in that it is blanking. 5. The method according to claim 1, further comprising convergence relaxation means for relaxing convergence of the electron beam, wherein the convergence relaxation means relaxes the convergence of the electron beam when the length measurement is interrupted. < 3 > The scanning electron microscope according to any one of < 3 >.