JP5103253B2 - Charged particle beam equipment - Google Patents

Description

  The present invention relates to a charged particle beam apparatus that includes an optical microscope and images a foreign substance on a bare wafer.

  2. Description of the Related Art A charged particle beam apparatus is used for inspection for irradiating a substrate such as a semiconductor wafer or a photolithography mask with a charged particle beam such as an electron beam to detect a defect on the substrate or observe the defect. There is also known a charged particle beam apparatus equipped with an optical microscope for measuring the position of a substrate, that is, alignment and the height of the substrate in advance (see, for example, Patent Document 1).

  On the other hand, the foreign matter on the surface of the bare wafer that is a semiconductor wafer before the circuit pattern is formed is irradiated with a laser beam to detect the reflected light from the foreign matter and obtain the coordinates of the foreign matter. It is used. The charged particle beam device finds a foreign material based on the coordinates of the foreign material acquired by the foreign material inspection device, and irradiates the charged particle beam to take an enlarged image of the foreign material. can do. However, the magnification of the charged particle beam device is very high, and it cannot be easily found even if it tries to find the foreign particle with the charged particle beam device based on the coordinates of the defect detected by the foreign particle inspection device. There was a problem.

  Therefore, an optical microscope for alignment and height measurement is used to first detect defects detected by a foreign substance inspection apparatus using an optical microscope, and an enlarged image is captured using a charged particle beam apparatus based on the coordinates. It has been broken. This utilizes the fact that the optical microscope has a lower magnification and a wider field of view than the charged particle beam apparatus.

  However, since the surface of the bare wafer has almost no unevenness and the material is uniform, there is a problem that focusing when acquiring an image is very difficult. Therefore, the bare wafer is moved to the coordinates of the foreign material sent from the foreign material inspection device, the height is measured with a height sensor using the reflection of light, and the optical microscope is focused on the basis of the height, Search for foreign matter, record the coordinates when found, and move the bare wafer to the next foreign matter coordinates, repeat the process of searching for all foreign matters or the specified number of foreign matters, Acquisition of an image of a foreign object is performed by a procedure of starting a process of capturing a magnified image of the foreign object using a charged particle beam apparatus. In this case, since it reciprocates between the height sensor and the optical microscope, it takes a long time just to move the stage on which the bare wafer is placed, and the operating time per bare wafer of the charged particle beam apparatus becomes long. There was a problem that the throughput decreased.

JP 2007-235033

  An object of the present invention is to provide a charged particle beam apparatus capable of preventing a decrease in throughput when capturing an image of a foreign substance on a bare wafer.

  In order to solve the above object, an embodiment of the present invention defines a virtual mesh on a bare wafer, measures the height for each virtual mesh, and determines the height based on the height value for each virtual mesh. The optical microscope is focused on all virtual meshes having the value of, and the optical microscope detects the foreign matter based on the coordinate data of the foreign matter sent from the foreign matter inspection device, defines the coordinates, and the charged particle beam optical system Provided is a charged particle beam apparatus having a configuration for imaging a foreign object for all of the coordinates based on coordinates in which columns are defined.

  ADVANTAGE OF THE INVENTION According to this invention, when taking the image of the foreign material of a bare wafer, the charged particle beam apparatus which can prevent the fall of a throughput can be obtained.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Electron beams and ion beams are known as charged particle beams. In the case of an electron microscope using an electron beam, the current density of the electron beam, the voltage reached on the sample, the strength of the electromagnetic lens or electrostatic lens, etc. are adjusted according to the type of sample, and applied to the inspection device. can do. In the case of an ion beam, it can be used as an inspection apparatus, just like an electron microscope, except that the sign of the energy is different from the intensity. In this embodiment, a scanning electron microscope that scans a sample with an electron beam, detects secondary electrons and reflected electrons generated from the sample, and forms an image will be described as an example.

  FIG. 1 is a perspective view of a scanning electron microscope. The electron optical system column 1 includes an electron gun, a condenser lens, a diaphragm, an objective lens, a scanning deflector, and a detector (not shown), and the inside is kept in a vacuum. The electron gun generates an electron beam, and the electron beam is converged by the condenser lens and the objective lens and irradiated onto the bare wafer 2. Since the electron beam is narrowed down, the image acquisition range on the bare wafer 2 is scanned by the scanning deflector. The secondary electrons 3 emitted from the bare wafer 2 by the irradiation of the electron beam are detected by the detector 4, imaged by the image processing device 5, and a secondary electron image is displayed on the display. The above-described control of each device is operated by a command from the control device 10 including a microprocessor and a storage device.

  By irradiating the bare wafer 2 with the electron beam narrowed down to the minimum, it is possible to obtain an image with high focus and no blur, so the height of the bare wafer 2 can be accurately measured. The lens conditions must be controlled. As one method for measuring the height of the bare wafer 2, a height sensor using reflected light can be used. Light is emitted obliquely from the height sensor light emitting unit 61 to the bare wafer 2, and the reflected light is detected by the height sensor light receiving unit 62. Calibration is performed in advance using the standard position of the bare wafer 2 as a reference. When the height of the bare wafer 2 changes, the light receiving position of the height sensor light receiving unit 62 goes up and down, so that the change in height can be measured. The height of the bare wafer 2 can be obtained from the reference value and the change value.

  The timing of light emission of the height sensor light emitting unit 61 is determined by a command signal sent from the control device 10. A height change signal from the height sensor light receiving unit 62 is sent to the control device 10 and stored in an internal storage device.

  The foreign matter inspection of the bare wafer 2 is executed by detecting the coordinates of the foreign matter with the foreign matter inspection device 7. The coordinate data 8 of the foreign matter is sent to the control device 10. The coordinate data 8 of the foreign matter acquired by the foreign matter inspection apparatus 7 has low coordinate accuracy, and it is often impossible to find a foreign matter with a high-magnification and narrow-field device such as a scanning electron microscope. Therefore, first, the control device 10 moves a bare wafer by moving a stage (not shown) so that the coordinates of one foreign substance are located below the electron optical system column 1. Even when an image is taken in this state, the foreign matter often deviates from the field of view of the image. Next, the height of the bare wafer under the electron optical system column 1 is measured using a height sensor, and the value and the coordinates of the stage at the measured position are stored in the storage unit of the control device 10. The control device 10 moves the bare wafer 2 so that the position where the height is measured is located under the optical microscope 9. The control device 10 sends the stored value of the height of the bare wafer to the optical microscope 9. The optical microscope 9 focuses on the basis of the height value of the bare wafer, acquires an image, and sends it to the image processing apparatus 5. Since the optical microscope 9 has a low magnification and a wide field of view, it can detect foreign matter based on the coordinate data 8 of the foreign matter. When the foreign matter displayed on the display of the image processing apparatus 5 is not at the center of the field of view, the operator moves the stage to position the foreign matter at the center of the field of view, and the center of the field of view is set as the stage coordinates of the foreign matter. As described above, when there is an error between the coordinate data 8 and the detected coordinates of the foreign substance stage, the coordinate correction value of the foreign substance is stored in the storage device of the control device 10.

  Although the optical axis of the electron optical system column 1 and the optical axis of the optical microscope 9 are difficult to coincide with each other in structure, the coordinates of the stage are common. There will be no error between. Accordingly, the foreign matter positioned at the center of the field of view of the optical microscope 9 can be positioned in the field of view even in the electron optical system column 1.

  The optical microscope 9 can be either a bright field or a dark field, and any of these may be used. However, since the dark field method using the deflection characteristics of laser light can detect fine foreign materials, A dark-field optical microscope is used.

  The coordinate data 8 includes the coordinates of many foreign objects. If the height measurement, optical microscope image acquisition, coordinate correction, and electron optical system column image acquisition are repeated for each coordinate, the stage movement time is repeated. As a result, a more efficient foreign object detection method is required.

  2, 3, and 4 are screen diagrams showing examples of screens displayed on the display of the image processing apparatus 5. The control device 10 assumes a virtual mesh 11 on the bare wafer 2 and displays this schematic diagram on a display. The pitch of the virtual mesh 11 can be set arbitrarily.

  Next, the control device 10 detects the height of the bare wafer 2 at the center position of each virtual mesh 11 of the virtual mesh 11 with a height sensor, stores the height value, and as shown in FIG. A height map of the bare wafer 2 is created. Next, the control device 10 collates individual coordinates of the foreign matter coordinate data 8 sent from the foreign matter inspection device 7 with the data of the height map shown in FIG. Assign and memorize individual coordinates. When there is a virtual mesh to which the foreign object coordinate data 8 is not assigned, as shown in FIG. 4, only the virtual mesh 12 to which the foreign object coordinate data 8 is assigned is measured for height. Thus, the time can be shortened.

  Next, the optical microscope 9 focuses on one virtual mesh based on the height value of the virtual mesh, and based on the individual coordinates of the foreign object coordinate data 8 assigned to the virtual mesh, Image foreign objects. If the foreign object is off the center of the field of view, the operator moves the foreign object to the center of the field of view and registers it as the stage coordinates. Alternatively, in the case of a dark-field optical microscope, foreign objects are displayed as light spots in a field with almost no light, so light is automatically detected by image processing technology, and the position of the light is staged. Can be registered as coordinates. Then, the control device 10 can calculate coordinate correction values between the coordinates of the stage and the individual coordinates of the foreign object coordinate data 8. This is executed for all virtual meshes or virtual meshes to which foreign object coordinates are assigned. Subsequently, the electron optical system column 1 acquires secondary electron images of individual foreign substances based on the registered stage coordinates. The operations from the creation of the virtual mesh to the acquisition of the secondary electron image can be continuously and automatically executed.

  When measuring the height of a bare wafer, detecting a foreign object with an optical microscope, and acquiring a secondary electron image with an electron optical system column alternately for each foreign object, movement between the optical microscope and the electron optical system column However, as in the embodiment of the present invention, since all of the foreign matters to be detected are executed before moving to the next process, the moving distance of the stage is shortened. The required time can be shortened, and the throughput can be prevented from decreasing.

  Next, using the updated coordinates of the foreign matter, the scanning electron microscope can be used to observe and analyze the foreign matter and to take an electron microscopic image of the foreign matter under high magnification conditions. Moreover, it can be operated continuously according to the coordinate position where the foreign object should be.

  Conventionally, for each foreign object, the detection of the height direction position with the Z sensor attached to the electron microscope and the detection with the dark field optical microscope are alternately performed, It became very fast and accurate.

  When focusing with the optical microscope 9, instead of using the center height value of the virtual mesh 11 as a reference, as shown in FIG. An approximate curve of the height of the bare wafer is created from the value, and the height value of the position corresponding to each coordinate of the foreign matter coordinate data 8 is used as a reference, so that the height of one virtual mesh can be calculated. The error can be reduced, and the focusing time of the optical microscope 9 can be further shortened.

  As described above, according to the present invention, when a foreign material on a bare wafer is imaged with a scanning electron microscope, a virtual mesh is defined on the bare wafer, a height is measured for each virtual mesh, and each virtual mesh is measured. Foreign matter is detected with an optical microscope, and then a secondary electron image of the foreign matter is taken, so that the focusing time of the optical microscope can be shortened, and the bare wafer between the columns of the optical microscope and the scanning electron microscope Therefore, it is possible to provide a charged particle beam apparatus that can prevent a decrease in throughput.

The perspective view of a scanning electron microscope. The screen figure which shows an example of the screen displayed on the display of an image processing apparatus. The screen figure which shows an example of the screen displayed on the display of an image processing apparatus. The screen figure which shows an example of the screen displayed on the display of an image processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electron optical system column 2 Bare wafer 5 Image processing apparatus 7 Foreign material inspection apparatus 8 Coordinate data 9 Optical microscope 10 Control apparatus 11, 12 Virtual mesh 61 Height sensor light emission part 62 Height sensor light reception part

Claims (6)

The charged particle beam apparatus that acquires an image of the foreign substance by irradiating the charged particle beam to the foreign matter on the bare wafer that is detected by the foreign substance inspection apparatus,
A control device for defining a virtual mesh on the bare wafer;
A height sensor that measures the height of the bare wafer for each virtual mesh of the virtual mesh;
After the measurement of the height value for each virtual mesh by the height sensor for all virtual meshes assigned at least the coordinate data of the foreign matter output from the foreign matter inspection apparatus is measured for each virtual mesh. was based on the height value, performs focusing for all virtual mesh having a value of the height, the charged particle detecting the foreign object based on the coordinate data of the foreign object sent from the foreign substance inspection apparatus An optical microscope that defines the coordinates of the foreign matter on the line device;
After the coordinates of each foreign matter on the charged particle beam device are defined for all foreign matters using the optical microscope, the coordinates of the foreign matter are determined based on the coordinates of the foreign matter on the charged particle beam device . A charged particle beam apparatus comprising: a charged particle beam optical system column that images the foreign matter for all.   The charged particle beam device according to claim 1, wherein the control device creates a map of the height of each virtual mesh and displays the map on a display.   2. The charged particle beam apparatus according to claim 1, wherein the height sensor measures the height only for a virtual mesh including coordinate data of the foreign matter.   2. The control device according to claim 1, wherein the control device creates an approximate curved surface of the height of the bare wafer from a height value measured by the height sensor, and the optical microscope performs focusing based on the approximate curved surface. A charged particle beam device characterized by combining.   The charged particle beam device according to claim 1, wherein a pitch of the virtual mesh can be arbitrarily set.   2. The height sensor according to claim 1, wherein the height sensor measures a height at a center position of the individual virtual mesh, and the optical microscope measures a foreign matter contained in the individual virtual mesh at the center position. A charged particle beam apparatus characterized in that focusing is performed based on a height value.

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