JP2013084344A - Charged particle beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that noise is generated for a deflection signal and a detection signal between the control circuit of a charged particle beam device and a controlled apparatus, and a problem that maintenance is difficult in a sample chamber when the cable connecting the control circuit and the controlled apparatus is shortened in order to reduce noise, and to provide a charged particle beam device which can produce a high-quality image, in which the impact of noise is reduced, without sacrifice of maintainability.SOLUTION: The charged particle beam device comprises a column for irradiating a sample with a charged particle beam, a control unit for controlling the internal apparatus of the column, and a moving mechanism for moving the control unit. The control unit is located in the vicinity of the column when an image is acquired by irradiating a charged particle beam, and can move to recede from the column during maintenance.

Description

  The present invention relates to a charged particle beam apparatus that observes the microstructure of a sample using a charged particle beam such as an electron beam.

  In a charged particle beam apparatus such as a scanning electron microscope, a finely focused charged particle beam is scanned and deflected on a sample, and various signals generated from the sample are detected to generate an image. In recent years, the miniaturization of the structure of a semiconductor device has progressed, and a charged particle beam apparatus for observing a semiconductor device is required to have high resolution and high magnification. When the resolution is increased and the magnification is increased, there is a problem that the influence of noise such as electromagnetic waves and electric fields generated in the peripheral device and inside the device becomes remarkable, and the image quality of the generated image is lowered.

  In addition, the charged particle beam irradiated to the sample may cause a problem that the sample surface is charged (charged up) and the charged particle beam beam drifts due to the influence. Such charging scans the beam at high speed. Has been found to be reduced. The beam deflection method includes an electromagnetic method using a magnetic field generated by applying a current to a coil and an electrostatic method using an electric field generated by applying a voltage to an electrode. The electromagnetic method has poor response compared to the electrostatic method because the coil is an inductive load, and the electrostatic method is effective for high-speed scanning. However, the electrostatic method has a problem that it is susceptible to noise because of its responsiveness.

  In Japanese Patent Laid-Open No. 2003-197141 (Patent Document 1), a charged particle beam is scanned and deflected on a wafer on which a circuit pattern is formed, and secondary charged particles generated are detected to obtain an image. In an inspection apparatus using a charged particle beam for detecting the above, a technique for shortening a cable length by fixing an amplification unit (amplifier unit) of an electrostatic deflector to a column is disclosed.

JP 2003-197141 A

  In the invention described in Patent Document 1, the amplifying unit (amplifying unit) is fixed to the column to shorten the cable length to the deflector to reduce superimposed noise. No noise reduction is considered. The maximum output voltage of the amplifying unit is about ± 200 V, but the maximum signal voltage from the scanning signal generating circuit to the amplifying unit is about ± 10 V. From the viewpoint of noise resistance, it is necessary to reinforce noise countermeasures in this part. There is.

  As a countermeasure against noise from a control circuit such as a deflector to an amplification unit, the control circuit itself is fixed at a position close to a column including a control target device such as a deflector, and the control circuit is connected to the amplification unit and the control target device. The cable length should be shortened. However, if the cable length is shortened, the control circuit interferes with the column or the upper lid of the sample chamber during maintenance or the like in the sample chamber, and the maintainability is impaired.

  An object of the present invention is to provide a charged particle beam apparatus capable of obtaining a high-quality image with reduced influence of noise without impairing maintainability.

  In order to solve the above problems, a charged particle beam apparatus according to the present invention includes a column that irradiates a sample with a charged particle beam, a control unit that controls equipment inside the column, and a moving mechanism that moves the control unit. It is characterized by providing.

  According to the present invention, the control unit can be arranged near the column when observing the sample, and the control unit can be moved to a position where it does not interfere with the column or the like during maintenance. Therefore, maintainability is not impaired, and a high-quality image with reduced noise can be obtained.

It is a schematic block diagram of the scanning electron microscope for demonstrating a 1st Example. It is an example of the block diagram of a column control unit. It is a figure which shows the state at the time of the maintenance of the scanning electron microscope of a 1st Example. It is a schematic block diagram of the scanning electron microscope for demonstrating a 2nd Example. It is a figure which shows the state at the time of the maintenance of the scanning electron microscope of a 2nd Example.

  An embodiment in which the present invention is applied to a scanning electron microscope which is one of charged particle beam apparatuses will be described.

  FIG. 1 is a schematic configuration diagram of a scanning electron microscope for explaining the first embodiment, and shows a state of an apparatus when an electron beam is irradiated to observe a sample. The scanning electron microscope includes a main body 1 and a console 2. The main body 1 includes a column 10 that is an optical system for irradiating an electron beam, a sample chamber 20, a sample exchange chamber 24, and a storage unit 3 that stores a power source and a control circuit described later.

  The wafer 22 to be observed is held on the sample stage 23 in the sample chamber 20 via the sample exchange chamber 24 maintained in vacuum by the vacuum pump 25. The column 10 is installed in the upper part of the sample chamber 20, and the column 10 and the sample chamber 20 hold a vacuum by a vacuum pump 26 and an ion pump 27. The column 10 is irradiated and deflected with a charged particle beam such as an electron source 11 that generates an electron beam, a deflector 13 that deflects the electron beam, a detector 15 that detects a signal from the sample, and a lens that focuses the electron beam. Equipment for scanning, focusing and detection is installed. The column control unit 30 described later includes a deflection control circuit 31 and a signal capturing circuit 32. The column control unit 30 is connected to each device in the column by a cable, and outputs a signal for controlling the device included in the column to each device in the column based on a user instruction or a predetermined inspection condition. An electron source 11 connected to an electron gun power source 35 generates an electron beam 12. The electron beam 12 emitted from the electron source 11 in the column 10 is deflected by the deflector 13 and scans on the wafer 22 of the sample. The deflector 13 may be either an electromagnetic type or an electrostatic type. However, as described above, since the electrostatic type is weak against noise, the present invention is particularly effective. Accordingly, the following description will be made as an electrostatic deflector. Secondary electrons 14 generated by irradiating the sample with the electron beam 12 are converted into electrical signals by the detector 15. Although a detector that detects secondary electrons is shown here, a detector that detects reflected electrons may be used. A signal having sample information such as secondary electrons and reflected electrons is called a secondary signal. Hereinafter, it is assumed that the detector 15 includes all detectors that detect secondary signals. The signal output from the detector 15 is converted from an analog signal into digital data by the signal capturing circuit 32, and the image processing means provided in the overall control unit 36 associates this signal with the scanning position of the electron beam 12. To generate image data. The generated image data is stored in the image memory 37 of the overall control unit 36. The image data is transferred to the computer 38 and displayed on the display monitor 39.

  When noise is applied to the scanning signal to the deflector, the deflection position of the electron beam is shifted, so that the deflection position controlled by the deflection control circuit 31 is different from the position irradiated with the actual electron beam. Although the detector 15 detects the secondary signal generated at the position where the electron beam is actually irradiated, the image processing means erroneously assumes that this is the secondary signal generated at the deflection position controlled by the deflection control circuit 31. An image is generated in association with the selected position.

  In addition, if noise occurs before being input from the detector 15 to the signal capturing circuit 32, the amount of the actually detected secondary signal is erroneously input to the signal capturing circuit 32. Since the image processing means determines the brightness of the pixel based on the amount of the secondary signal, the brightness of the pixel is different from the original brightness.

  FIG. 2 is an example of a configuration diagram of the column control unit 30, which includes a deflection control circuit 31 and a signal capture circuit 32. The deflection control circuit 31 includes a scanning signal generation circuit 41, D / A converters 42 to 43, and deflection amplifiers 44 to 47. The scanning signal generation circuit 41 generates electron beam scanning data in response to a command from the overall control unit 36. The D / A converters 42 to 43 generate analog sawtooth waveforms, convert the digital scanning signal generated by the scanning signal generation circuit 41 into an analog scanning signal, and output the analog scanning signal to the deflection amplifiers 44 to 47. The scanning signal is amplified to a maximum of ± 200 V by deflection amplifiers 44 to 47 and output to the deflector 13 connected by a cable. The deflector 13 scans and deflects the electron beam 12 in accordance with the given scanning signal.

  The signal capturing circuit 32 included in the column control unit 30 includes an input amplifier 48, an A / D converter 49, and a buffer 50. The input amplifier 48 adjusts the level of the output signal from the detector 15 and amplifies the output signal from the detector 15. An A / D converter 49 converts the analog signal into digital data. The digital data is transferred to the image memory 37 of the overall control unit 36 via the buffer 50, and image data is generated by the overall control unit 36 by synchronizing with the scanning signal.

  As described above, the output voltage of the deflection amplifiers 44 to 47 is about ± 200 V at the maximum, whereas the signal voltage from the scanning signal generation circuit 41 to the deflection amplifiers 44 to 47 is about ± 10 V at the maximum. From the viewpoint of noise, it is necessary to strengthen noise countermeasures in this part. Therefore, the scanning signal generation circuit 41 and the deflection amplifiers 44 to 47 are made closer to each other, and the deflection control circuit 31 is configured by one substrate. Therefore, in consideration of noise with respect to the scanning signal from the deflection amplifiers 44 to 47 of the deflection control circuit 31 to the deflector, it is necessary to bring the deflection control circuit 31 itself closer to the deflector 13.

  In the signal acquisition circuit 32 as well, the signal is weak since it is weak until it is transmitted to the input amplifier 48 from the signal detected by the detector 15, and the input amplifier 48 is detected for noise reduction. It is necessary to approach the container 15.

  However, if the column control unit is disposed in the vicinity of the column including the deflector and the detector, the column control unit and the column and the upper lid of the sample chamber may physically interfere with each other during maintenance. This will be described below with reference to FIG.

  FIG. 3 is a diagram showing a state during maintenance of the scanning electron microscope. A maintenance operation is periodically performed to clean the sample chamber in order to keep the sample chamber clean and to lubricate the sample stage 23 to raise the sample chamber top lid 21. In this state, if the column control unit 30 is located near the column 10, for example, above the upper lid of the sample chamber, it interferes with the column 10 or the upper lid 21 of the sample chamber, so that the column control unit 30 collides with other equipment. Failure, or ease of maintenance by the user.

  Therefore, in this embodiment, a moving mechanism that allows the column control unit 30 to move is provided. Specifically, the column control unit 30 is mounted on the slide rail 33 as shown in FIG. The moving mechanism can move the column control unit 30 so as to change the distance between the column 10 and the column control unit 30.

  In a normal state where the sample is irradiated with an electron beam and the image is observed, the column control unit 30 is fixed at a position close to the column 10. The position close to the column means a position where the distance between the column 10 and the control unit 30 is closer than the distance at the time of maintenance described later. For example, the distance between the column 10 and the control unit 30 is the storage unit 3 and the column 10. It is shorter than the interval.

  Thereby, the cable length from the deflection amplifiers 44 to 47 of the deflection control circuit 31 to the deflector 13 can be shortened. Similarly, the cable length from the detector 15 to the input amplifier 48 of the signal capturing circuit 32 can be shortened. Specifically, the cable length can be shorter than the distance between the storage unit 3 and the column 10. Therefore, the deterioration of the deflection scanning accuracy of the electron beam 12 and the noise component of the detection signal can be reduced, and the image quality of the generated image can be improved.

  On the other hand, at the time of maintenance, the cable from the deflection amplifiers 44 to 47 to the deflector 13 and the cable from the detector 15 to the input amplifier 48 of the signal capturing circuit 32 are disconnected, and the column control unit 30 is moved away from the column 10. For example, it moves to the storage unit 3. The position away from the column 10 refers to a position farther from the column 10 than at least the distance between the column control unit 30 and the column 10 when the electron beam is irradiated. If the column control unit 30 is accommodated in the storage unit 3, safety is ensured because it does not interfere with other devices in the main body 1, but the movement destination is not limited to the storage unit 3, and the column or sample chamber top cover Any position that does not interfere is acceptable. The column control unit 30 can move on the slide rail without any restriction on the distance from the column 10 because the cable manufactured with the shortest length is removed during maintenance.

  Note that the cable is disconnected and the column control unit 30 is moved during maintenance, but the cable connecting the column control unit 30 and the overall control unit 36 transmits a digital signal that is resistant to noise, so that it has a sufficient length. Can remain connected. By providing the moving mechanism, the column control unit 30 can be moved safely without removing the cable connecting the column control unit 30 and the overall control unit 36.

  Thereby, the column control unit 30 does not interfere with the column 10 and the sample chamber upper lid 21, and the user can easily maintain the inside of the sample chamber.

  As described above, by making the column control unit that stores the charged particle beam deflection control circuit and signal acquisition circuit movable, it is arranged near the column when irradiating the electron beam, and during maintenance such as cleaning the sample chamber. It can be placed away from the column. As a result, it is possible to reduce noise generated in the transmission process from the column to the control circuit without impairing maintainability.

  Further, in Patent Document 1 shown above, the amplification unit is fixed to the column, and heat generation from the circuit is not taken into consideration. The amplification unit generates heat corresponding to the high-speed scanning, but heat is transmitted to the column when it is fixed to the column. When non-uniform thermal expansion occurs in the column, the axis adjustment of the charged particle beam shifts and image quality deteriorates.

  In contrast, in the present embodiment, the column control unit 30 is not directly fixed to the column 10 but connected by a cable, so that heat is not directly transmitted to the column.

  Moreover, the heat insulating material 34 is also installed around the storage unit 3 in which other control devices and power supplies are stored, so that heat generated by these is not transmitted to the column. Since the column control unit 30 of the present embodiment has a structure protruding from the storage portion 3 when irradiated with an electron beam, the column control unit 30 itself is further covered with a heat insulating material as shown in FIG. Thereby, the column control unit 30 and the column 10 are separated in temperature by the heat insulating material 34, so that the heat generated in the column control unit 30 is not easily transmitted by the column 10, and the axis of the electron beam is not shifted. .

  Next, a second embodiment will be described with reference to FIGS. The description of the same parts as those in the first embodiment is omitted.

  FIG. 4 is a schematic configuration diagram of a scanning electron microscope for explaining the second embodiment, and is a view of the state of the apparatus when irradiating an electron beam as viewed from above. The difference from the first embodiment is that the moving mechanism of the column control unit 30 is changed from the slide rail 33 to the hinge 53. Also in the present embodiment, the column control unit 30 is provided so as to protrude from the storage unit 3, so that the transmission cable from the column control unit 30 to the column can be shorter than the distance between the storage unit 3 and the column 10.

  FIG. 5 is a top view of the state of the apparatus during maintenance in the sample chamber. As shown in FIG. 5, the column control unit 30 is moved to the inside of the storage unit 3 by a rotation operation around the hinge 53. Since the cable is disconnected during maintenance, the column control unit 30 can be moved to a position where it does not interfere with other devices without worrying about the distance from the column. In this embodiment, the cost of the moving mechanism can be reduced by using the hinge 53 as compared with the slide rail 33.

  As mentioned above, although the embodiment in the scanning electron microscope has been described, the present invention is not limited to the scanning electron microscope, but a focused ion beam apparatus that processes a sample by irradiating a charged particle beam, and a pattern for measuring a semiconductor pattern. The present invention is applied to various charged particle beam apparatuses such as a measurement apparatus (CD-SEM), a defect inspection apparatus for inspecting defects on a sample, and a composite apparatus thereof. As a result, it is possible to meet the demand for higher resolution and higher magnification for the charged particle beam apparatus and contribute to the development of a semiconductor device having a fine structure.

DESCRIPTION OF SYMBOLS 1 Main body 2 Console 3 Storage part 10 Column 11 Electron source 12 Electron beam 13 Deflector 14 Secondary electron 15 Detector 20 Sample chamber 21 Sample chamber upper cover 22 Wafer 23 Sample stage 24 Sample exchange chamber 25, 26 Vacuum pump 27 Ion pump 30 column control unit 31 deflection control circuit 32 signal acquisition circuit 33 slide rail 34 heat insulating material 35 electron gun power source 36 overall control unit 37 image memory 38 computer 39 display monitor 41 scanning signal generation circuits 42 to 43 D / A converter 44 to 47 deflection amplifier 48 input amplifier 49 A / D converter 50 buffer 53 hinge

Claims (5)

In a charged particle beam apparatus that scans and deflects a charged particle beam to a sample, irradiates the sample, detects a secondary signal emitted from the sample, and generates an image.
A sample chamber having a sample stage for holding the sample therein;
A column including a charged particle beam source that generates the charged particle beam, a deflector that scans and deflects the charged particle beam, and a detector that detects the secondary signal;
A deflection control circuit for providing a deflection signal to the deflector;
A signal capturing circuit for capturing a signal from the detector;
A charged particle beam apparatus comprising: a moving mechanism for moving a control unit including the deflection control circuit or the signal capturing circuit. The charged particle beam apparatus according to claim 1,
The charged particle beam apparatus, wherein the moving mechanism is capable of moving the control unit to a position where the control unit does not interfere with the column in a state where an upper lid of the sample chamber is opened. The charged particle beam apparatus according to claim 1,
The charged particle beam apparatus according to claim 1, wherein the control unit can move closer to the column when capturing an image of the sample than when performing maintenance in the sample chamber. The charged particle beam device according to claim 2, further comprising:
A storage unit that stores the control unit when the upper lid of the sample chamber is opened,
The length of the cable connecting the deflection control circuit and the deflector, or the length of the cable connecting the signal capturing circuit and the detector is shorter than the distance between the storage unit and the column. Charged particle beam device. The charged particle beam apparatus according to claim 1,
The charged particle beam apparatus, wherein the control unit and the column are separated by a heat insulating material.