JP2006154358A - Automatic focusing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focusing device which performs follow up focusing operation while transferring an observation object and a processing object, preliminarily restricts distance between an objective lens and the objects within a certain range, shortens distance for performing the final focusing operation after standstill to shorten focal time. <P>SOLUTION: The automatic focusing device has a projection means 30A for projecting two pin holes 7A, 7B with different distance in the optical axis direction and in the direction perpendicular to the optical axis direction on a flat surface of an object 1 to be measured via an objective lens 2 and an operation means 11 for calculating difference between focal positions of projected images on the side of the object to be measured based on level difference of the two pin holes 7A, 7B and magnification of the objective lens 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an autofocus device used for observing a film forming state of a liquid crystal or a semiconductor member.

  A microscope is used for an observation and processing apparatus after pattern formation of a liquid crystal or a semiconductor. In this case, it is necessary to obtain a good contrast in the image of the actual object. For this reason, the microscope is moved to the focus position of the microscope. In a normal operation, the focus operation is performed after moving to the observation target point after the observation movement.

  However, in the above method, since the positional relationship in the height direction with respect to the objective lens and the object after movement is unknown, the best image point is searched from above in consideration of the maximum height difference from the movement start point to the movement end point. It was necessary and the focus operation took a long time. Particularly in the liquid crystal field, it is important to increase the production efficiency and reduce the cost by shortening the inspection time and the processing time by increasing the size of the glass.

  The present invention has been made to solve the above-mentioned conventional drawbacks, and its purpose is to perform a tracking-type focusing operation while moving an observation object or a processing object and to set a distance between the objective lens and the object in advance. It is an object of the present invention to provide an autofocus device that is limited to the inner distance, shortens the distance for performing a final focus operation after being stopped, and shortens the focus time.

  Therefore, the autofocus device according to the first aspect projects the two pinholes 7A and 7B having different distances in the optical axis direction and the direction perpendicular to the optical axis direction onto the flat surface 1a of the object 1 to be measured via the objective lens 2. And means 30 and calculation means 11 for calculating the difference in focus position of the projected image on the object side based on the step between the two pinholes 7A and 7B and the magnification of the objective lens 2. It is said.

  In the autofocus device according to a second aspect, the projection means 30 has two CCD cameras 8 and 9, and one CCD camera 8 is used for the coarse focus for tracking at the time of relative movement with respect to the objective lens 2, and the other The CCD camera 9 is characterized by a fine adjustment focus at the time of stationary relative to the objective lens 2.

  In the autofocus device according to a third aspect, the projection means 30 has one CCD camera, and when the two pinhole illumination devices are turned on, it becomes a coarse focus for tracking at the time of relative movement with respect to the objective lens 2, and When the observation illumination of the measurement object 1 is turned on, it becomes a fine adjustment focus at the time of stationary relative to the objective lens 2.

  The autofocus device according to a fourth aspect is characterized in that a moving mechanism is provided for changing the relative positions of the two pinholes 7A and 7B along the optical axis direction.

  According to the autofocus device of the first aspect, when the pinhole image is formed on the measured object side through the objective lens, the two pinhole images are formed between the objective lens and the measured object. The size and brightness change depending on the distance. For this reason, if the intermediate point of the pinhole in the optical axis direction is conjugate with the surface to be measured, a position where the size of about two pinholes is equal can be regarded as an approximate focal point. That is, when two pinholes are used, it can be confirmed in which direction the objective lens is displaced with respect to the in-focus point from the difference in size between the two. For this reason, it is possible to easily perform focusing to the in-focus point.

  According to the autofocus device of the second aspect, one CCD camera is used for a coarse focus for tracking when moving relative to the objective lens, and the other CCD camera is used for a fine adjustment focus when stationary relative to the objective lens. For this reason, follow-up focus operation is performed on the object to be measured, the distance between the objective lens and the object is limited within a certain range in advance, and the distance for the final focus operation after stationary is shortened, the focus time Can be shortened.

  According to the autofocus device of the third aspect, the same effect as that of the autofocus device of the second aspect can be exhibited with one CCD camera. In addition, since there is only one CCD camera, it is possible to reduce the size and cost of the apparatus.

  According to the autofocus device of the fourth aspect, since the moving mechanism for changing the relative position of the two pinholes along the optical axis direction is provided, the pinhole of the pinhole is adjusted according to the magnification of the objective lens and the amount of deflection of the surface to be measured. The difference (step) can be changed. Thereby, it can respond to various to-be-measured objects, and can aim at the improvement of the work efficiency of observation in the test | inspection etc. which use this apparatus.

  Next, specific embodiments of the autofocus device of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a simplified diagram of this autofocus device. FIG. 1 shows an optical configuration of the autofocus device. This autofocus device includes, as an optical system, an infinity-corrected microscope objective lens 2 for observing an image of a target object (object to be measured) 1, an illumination device 4 for the target object 1, an imaging lens 5, and the like. Further, the beam splitters 3A, 3B, 3C, and 6 for dividing the optical path into two, the follow-up coarse focus CCD camera 8, the final fine focus CCD camera 9, and the pinhole (step pinhole) 7A , 7B illumination device (pinhole illumination) 10.

  In this case, the projection means 30 for projecting the two pinholes 7A and 7B having different distances in the optical axis direction and the direction perpendicular thereto onto the flat surface 1a of the object to be measured 1 through the objective lens 2, and the above two pieces The calculation means 11 for calculating the difference in the focus position of the projected image on the measured object side based on the step (difference) between the pinholes 7A and 7B and the magnification of the objective lens 2 is provided.

  That is, the projection unit 30 includes the illumination device 10, the follow-up coarse focus CCD camera 8, the beam splitters 3A and 6, the imaging lens 5, the beam splitter 3B, the objective lens 2, and the illumination device 4. A beam splitter 3C and a CCD camera 9 for final fine focus. At this time, the camera CCD surface, the intermediate position of the step pinholes 7A and 7B in the optical axis direction, and the focus surface (object) of the objective lens 2 are arranged optically conjugate. The images of the step pinholes 7A and 7B form two images with different focus states on the CCD surface as the objective lens 2 is moved up and down. In FIG. 1, reference numeral 13 denotes a Z-axis control driver described later.

  In the autofocus device configured as described above, the autofocus optical system can be incorporated into a normal microscope optical system via a beam splitter in the microscope optical system. That is, the step pinholes 7A and 7B are illuminated by the pinhole illumination 10, and the bright spots of the two pinholes 7A and 7B are the beam splitter 3A, the beam splitter 6, the imaging lens 5, the beam splitter 3B, and the objective lens 2. Is projected onto the surface of the DUT 1 via. At this time, the difference ΔX in the focus position of the projected image on the surface to be measured is determined by the step ΔS of the step pinholes 7A and 7B and the magnification of the objective lens 2. Specifically, for example, in the case of the objective lens 2 of about 5 times and the step ΔS10 mm, it is about ΔX400 microns, and the focus follow-up range is thereby determined.

  Therefore, for the gentle measurement surface (flat surface) 1a having no sudden step, the integrated objective lens 2 is focused on the measurement surface 1a while the XY stage 15 (see FIG. 2) is being driven. As described above, the calculation unit 11 and the control unit 12 can control the video of the CCD camera 8. The XY stage 15 is a stage that can move in the X-axis direction and the Y-axis direction orthogonal thereto.

  The calculation means 11 can calculate a change in position of the objective lens 2 with respect to the object based on a change in the size and brightness state of the two images of the pinholes 7A and 7B. Further, even while the object is moving with respect to the objective lens 2, the pinhole image is localized at a fixed position of the CCD image, and the arithmetic processing can be easily performed. As shown in FIG. 2, the control means 11 includes a CPU 16 having an algorithm for controlling autofocus using two pinhole images and its peripheral circuits. Here, the peripheral circuit includes a driver circuit 17, a pulse generator 18, a video signal input circuit 19, an A / D converter 20, a memory circuit 21, a communication unit 22, and the like.

  That is, in the arithmetic means 11, the video signal is converted into digital data by the AD converter 20 through the video signal input circuit 19, and enters the memory circuit 21 as digital data. The data is processed by the CPU 16 to calculate the Z-axis drive amount, and the drive signal is sent from the Z-axis control driver 13 (see FIG. 1) to the Z-axis stage 14 via the pulse generator 18 and the driver circuit 17. The control means 12 can display drive data by having the CPU and the communication unit 23. Further, the final focus drive amount by the image processing by the control means 12 after being stationary is sent to the calculation means 11 via the communication unit 23.

  And after the XY stage 15 stops, after turning off the pinhole illumination 10, the light source device 4 is turned on. At this time, it is possible to focus at a high speed using a narrow range of images, that is, a small number of captured pattern images, with the image capture board 24 of the image capture board in which the images of the CCD camera 9 are incorporated in the control means 12. .

  Next, a method for measuring the DUT 1 using this apparatus will be described. First, during the XY stage operation, images of the step pinholes 7A and 7B are formed on the surface to be measured 1a. The image is captured by the CCD camera 8 and the focus control is performed by the stage control in the height direction (the Z-axis direction orthogonal to the X-axis direction and the Y-axis direction), that is, the focus control by the Z-axis control driver 13 while detecting the in-focus position. Performing focus adjustment. That is, when the images of the step pinholes 7A and 7B are formed on the measured surface 1a through the microscope objective lens 2, the size and brightness of the two pinhole images vary depending on the distance between the microscope objective lens 2 and the measured surface 1a. change. Further, if the intermediate point of the step pinholes 7A and 7B in the optical axis direction is conjugate with the surface to be measured 1a, the positions where the sizes of the two pinholes 7A and 7B are approximately equal to the focal point. Can be considered. Therefore, using such two pinholes 7A and 7B, it is possible to recognize in which direction the objective lens 2 is deviated from the focal point due to the difference in size between the two.

  If the illumination device 4 of the target object 1 is turned off, only the pinhole image is acquired by the two-dimensional CCD camera. Therefore, if the surface to be measured 1a can be regarded as a plane in the microscope field of view, two points are connected at substantially the same position. Therefore, it is only necessary to perform processing at a specific position of the CCD camera image, and it is not necessary to perform complicated processing such as pattern processing. Further, even when there is a base pattern on the surface to be measured 1a, this apparatus can remove the influence by inclining the angle of the two-dimensional CCD with respect to the pattern direction. In addition, the wavelength threshold value and polarization component of the light to be projected can be changed by an intermediate optical system or light source depending on the type of object.

  According to the autofocus device, by installing this device in an optical system including a microscope, a focus follow-up operation is performed while the microscope and the object to be measured are relatively moved in the XY direction to the measurement target point. Thus, the Z position range of the focus position can be tracked and processed after processing in a narrow range of video, that is, a small number of captured pattern images, and focusing to the focal point can be performed in a short time. That is, during the movement of the microscope, using the images of the stepped pinholes 7A and 7B to narrow the palm range, and after resting, the pinhole illumination 10 is turned off, and the illumination device 4 of the target object (object to be measured) 1 is turned on. The autofocus time can be shortened by focusing at high speed using the image of the final fine focus CCD camera 9.

  By the way, the step of the pinholes 7A and 7B can be made variable. However, if the step of the pinholes 7A and 7B is made variable, the pin is pinned according to the magnification of the objective lens 2 and the surface deflection of the surface 1a to be measured. The steps of the holes 7A and 7B can be changed. Thereby, it can respond to the various to-be-measured objects 1, and can aim at the improvement of the work efficiency of observation in the test | inspection etc. which use this apparatus. The structure in which the level difference between the pinholes 7A and 7B is variable can be configured by providing a moving mechanism (not shown) that changes the relative positions of the two pinholes 7A and 7B along the optical axis direction.

  In the autofocus device shown in FIG. 1, two CCD cameras are used. However, one CCD camera may be used. That is, one CCD camera is used as a coarse focus for tracking at the time of relative movement with respect to the objective lens 2 when the illumination device (pinhole illumination) of the two pinholes 7A and 7B is turned on. When the observation illumination is turned on, it may be used as a fine adjustment focus at the time of stationary relative to the objective lens 2, and the focus operation at the time of driving the XY stage and at the time of stationary may be performed by branching the image.

  As described above, even when one CCD camera is used, the same function as that using two CCD cameras can be exhibited. In addition, since there is only one CCD camera, it is possible to reduce the size and cost of the apparatus.

  Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention. For example, switching between the pinhole illumination 10 and the device illumination 4 and switching between the CCD camera 8 for moving focus and the CCD camera 9 for stationary focus are performed. It is also possible to eliminate the illumination switching by providing the wavelength dependence.

1 is a simplified perspective view showing an embodiment of an autofocus device of the present invention. It is a simplified diagram of the control circuit of the autofocus device.

Explanation of symbols

  1 .... Target object (object to be measured), 1a ... Flat surface (surface to be measured) 2 .... Objective lens, 7A, 7B ... Pin pole, 8,9 ... CCD camera, 11 .... Calculation means, 30 ..Projection means

Claims (4)

  Projection means for projecting two pinholes (7A) and (7B) having different distances in the optical axis direction and the direction perpendicular thereto onto the flat surface (1a) of the object to be measured (1) via the objective lens (2). (30) and a calculation means (11) for calculating the difference in the focus position of the projection image on the measured object side based on the step between the two pinholes (7A) and (7B) and the magnification of the objective lens (2). ).   The projection means (30) has two CCD cameras (8) and (9), and one CCD camera (8) is used for a coarse focus for tracking at the time of relative movement with respect to the objective lens (2). 2. The autofocus device according to claim 1, wherein the CCD camera (9) is used as a fine adjustment focus at the time of stationary relative to the objective lens (2).   The projection means (30) has one CCD camera, and when the lighting device of the two pinholes (7A) (7B) is turned on, it becomes a coarse focus for tracking at the time of relative movement with respect to the objective lens (2). 2. The autofocus device according to claim 1, wherein when the observation illumination of the object to be measured (1) is turned on, it becomes a fine adjustment focus at the time of stationary relative to the objective lens (2).   The autofocus device according to any one of claims 1 to 3, further comprising a moving mechanism that changes the relative positions of the two pinholes (7A) and (7B) along the optical axis direction.