JPS6111714A - Automatic focus adjuster of microscope - Google Patents

Abstract

PURPOSE:To adjust the focus of a microscope having an image pickup device on a real image plane over a wide range in a short period with good accuracy and simple constitution by maximizing the inclination of the edge signal of the video signal having a line width obtd. from the image pickup device in the focusing position. CONSTITUTION:The movement of an optical system is fed in the 1st section 30 at the pitch shorter than the pitch of the 2nd section 31 and the first judgement of whether the video signal attains a lower slice level 28 or not is made. The movement of the optical system enters the 2nd section 31 where the optical system moves at the pitch shorter than the length 33 from the point Z2 up to the focusing position Z4 upon ending of the 2nd judgement after the video signal attains an upper slice level 29. The optical system enters the 3rd section 32 of the movement and is fed at the pitch smaller than the focal depth of the lens system up to the travel limit Z3 of the optical end at the end of the 3rd section which is so set as to pass by the focusing position Z4. The address therebetween and the quantity W3 of W1-W2 are stored together with the address and the min. value of the quantity W1-W2 and the focusing position Z4 are selected among the quantity W3 of the address W1-W2 at the travel limit of the optical path. The position of the optical system is thus determined at the position Z4. The automatic focusing is thus executed with good accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is useful for automatic measurement of the track width of a magnetic head or minute line width such as a vapor deposition pattern using a microscope equipped with an imaging device, and for automatic observation of surface conditions. This invention relates to a focus adjustment device.

Conventional configurations and their problems In general, minute line widths such as magnetic head track widths and vapor deposition patterns are magnified 100 to 1000 times by optical equipment, and line width video signals are shown in Figure 1 ( 1a is a blur signal), and the edge portion has a characteristic that a slope is observed depending on the resolution of the optical system, and the slope is maximum at the in-focus position. When performing line width measurement using this video signal 1, it is necessary to obtain an accurate video signal every time, and submicron precision is required for focal position accuracy because the depth of focus of the lens system is shallow. It is. Conventionally, an automatic focus adjustment device that performs focus detection using only the slice level/v1b length information 2 at one location of the video signal 1 is shown in FIG.
Graph of changes in length information 2 due to movement of the optical system in the focal direction)
As shown in , if W is the length information 2, υ is the movement of the optical system in the focal direction, then the change curve 3 is obtained, so the focus adjustment range is narrow between 4 and 5. In addition, the entire stroke of the focal range is sent at a minute pitch, the length information 2 of the video signal 1 at the current point is set to A, the length information 2 of the video signal 1 at the next sent point is set to B, and the person <B Because the robot was stopped at point 6, which occurs due to the influence of vibrations, the focus position was reached at abnormal point 6, which is caused by the influence of vibration, etc., and not only was the accuracy of measurement poor because an accurate focus position could not be obtained, but the entire stroke was moved at a minute pitch. This has disadvantages in that focus adjustment time is long and productivity is not improved.

Purpose of the Invention The present invention solves the above-mentioned drawbacks of the conventional technology, and is capable of achieving high accuracy in a short time with a simple configuration when measuring an object with a minute line width using a microscope having an imaging device on the real image surface. An object of the present invention is to provide an automatic focus adjustment device that can perform focus adjustment over a wide range.

Composition of the Invention The apparatus of the present invention is such that when measuring a subject having a minute line width, in a microscope having an imaging device on the real image plane, an edge signal of a line width video signal obtained from the imaging device is at a focused position. Based on the characteristic that the slope is maximum, the video signal is divided into a plurality of bits in the length direction, and a frame memory that divides the bits into bits and stores them as a grayscale image in the brightness direction, and a frame memory that stores the optical system position of the microscope in the focal direction. The upper slice level is set at a position where the peak value of the video signal at the time of focusing is 10% or more above the upper part of the frame memory in the brightness direction. , a lower slice level is set below the upper slice level, and the optical system is moved in the direction of the focus position until a first section where the number of bits in the length direction of the video signal at the lower slice level is greater than 0. 2, the number of bits of the video signal at the upper slice level is greater than 0, and the difference between the number of bits of the video signal at the upper slice level and the number of bits of the video signal at the lower slice level is , until the second section where the optical system position reaches a value set in advance so that it is several micrometers before the in-focus position, the optical system position is shorter than the distance between the end position of the second section and the in-focus position. The drive mechanism is driven at a pitch, and the drive mechanism is driven at a minute pitch that is less than the depth of focus of the lens system to drive a third section preset to pass the in-focus position from that position, and the section is stored as an address and corresponds to the address. a difference in the number of bits of the video signal between the upper and lower slice levels, and after driving the section, controls and drives the drive mechanism to an address where the difference in the number of bits is the smallest.
Since the state of the video signal is effectively determined based on the upper and lower slice levels, automatic focus adjustment can be performed over a wide range. In addition, focus information requires only a small amount of data around the focus area, and micro-focusing only needs to be done around the focus area, so automatic focusing can be performed with high accuracy in a short time, and simple processing of video signals and edge cams can be performed. A simple drive mechanism consisting of a pulse motor can effectively provide an automatic focus adjustment device.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 3 to 6. FIG. 3 is a block diagram showing one embodiment of the present invention. 8 is a sample stage, 8 is an object having a line width placed on the specimen stage 7, 9 is an objective lens for enlarging the object 8, 10 is an optical system lens barrel having the objective lens 9, etc., 11
12 is an intermediate lens that magnifies the image of the subject 8 magnified by the objective lens 9; 12 is a linear image sensor 11;
3 is an imaging device having a linear image sensor 12 that outputs an enlarged image of the subject 8 as a video signal;
4 is a guide portion that supports the lens barrel 1o and is slidable in the vertical direction (focal direction of the optical system), 15 is an end cam, and 16 is a pulse motor 116 that rotates the end cam! L is an end cam 15 attached to the rotating shaft of the pulse motor 16, and an origin plate 17 with a slit in a part of its outer circumference moves the lens barrel 1o up and down.
18 is a photo sensor that detects the origin of the pulse motor and is arranged so that the light beam passes through the slit of the origin plate 161L; 19 is the subject 8; A sample stand 7 on which a clay figure was placed,
Objective lens 9. A lens barrel 10 having an intermediate portion 11, etc., and a lens barrel 1
0, an imaging device 13 having a linear image sensor 12 connected to the guide portion 14, and an end cam 15. Origin board 16! A drive unit 17 consisting of a pulse motor 16 with an L handle, and a stage 20 on which a photosensor 18 is arranged.
2 is a frame memory for storing a video signal obtained from the imaging device 13; 21 is a drive circuit for the pulse motor 16;
2 is a pulse motor 16 that processes the video signal and adjusts the focus of the optical system to the in-focus position in relation to the subject 8.
This is a control unit that gives commands to and controls the drive circuit. Fig. 4 is a positional relationship diagram of the subject 8 and the objective lens 9 at the start of automatic focus adjustment, where 23 is the focal position of the optical system, 24 is the work distance, and in Fig. 4, the subject 8 is at the focal position 23. However, when setting it within the work distance 24, the optical system's feeding direction is moved from top to bottom in Fig. 4, but it should be set so that it moves from bottom to top. It is necessary to set the origin of the end cam of the drive section 17 by shifting the origin plate 16a. FIG. 6 is a diagram of a video signal obtained from the imaging device 13, in which brightness is shown vertically and line width is shown horizontally. 26 is a video signal at the in-focus position, 26 is a blurred video signal C127 is a blurred video signal D (
(described later in the automatic focus adjustment method), this video signal is digitally divided into bits in both the brightness direction and length direction and is stored in the frame memory 20. 28 is the lower slice level, 29 is the upper slice level set so that the video signal when in focus is 10% higher in the brightness direction, Wl is the amount of line width length at the lower slice level 1v28, Wl is the amount of line width length at V29 (upper slice rep). FIG. 6 shows the amount W3 of w and -w2 vertically, and the movement Z of the optical system horizontally. Since the automatic focus adjustment method can be explained using a change graph of the amount WS of w and -w2, the automatic focus adjustment method will be explained below with reference to FIG. Zo is the origin, zl is the first judgment end point, z2 is the second judgment end point, z3
is the optical system travel limit, Z4 is the focus position, 30 is the first section of optical system movement, 31 is the second section of optical system movement, 32 is the third section of optical system movement. The first section of the optical system is moved at a shorter pitch than the second section of the optical system movement, and the fifth section is
A first judgment is made as to whether the video signal has reached the lower slice level (lower slice level) v28 shown in the figure. The state of the blurred video signal 026 in FIG. 5 is the state of the first judgment end point Z1. Next, the optical system movement enters the second section, and the video signal reaches the upper slice level 1V29 as shown in FIG.
Until the value of W4 in the figure is reached, the second judgment end point) Z
2 to the focal position Za1 at a pitch shorter than the length 33 at 1.

Next, the optical system enters the third section of movement, and performs pitch feed below the lens system focal depth at the optical system travel limit Z3 at the end of the third section, which is set to pass the focus position Z4, and between The address and the amount Wl-Wl are stored together with the address, and the minimum value of the amount Wl-Wl, the so-called focusing position Z4, is selected from the address and the amount W3 of wl-Wl at the optical system limit. The optical system is positioned at the focus position z4. In this way, the focus position is selected from the video signal near the focus position, and in addition to being able to perform automatic focus adjustment with high precision, the third section of the optical system movement is quantitative, but
Since the first section can operate until the video signal reaches the lower slice level, a wide range can be achieved, and the automatic focus adjustment range can naturally be wide, and the first and second sections of optical system movement can be sent at a relatively large pitch. This allows for high-speed automatic focus adjustment.

As described above, in the present invention, when measuring an object having a minute line width, in a microscope having an imaging device on the real image plane, the edge signal of the line width video signal obtained from the imaging device is at the in-focus position. Based on the characteristic that the slope is maximum, the video signal is divided into a plurality of bits in the length direction, and the bits are divided into bits in the brightness direction as a grayscale image, and a frame memory is stored and the optical system position of the microscope is focused. The upper slice level is set at a position where the peak value of the video signal at the time of focusing is 10% or more above the brightness direction of the frame memory. Then, set a downward shift and slice level below the upper slice level, and move the optical system in the direction of the focus position until the first section where the number of bits in the length direction of the □ video signal at the lower slice level is greater than 0. The operation is performed at a pitch shorter than a second section described later, and the number of bits of the video signal at the upper slice level is greater than 0, and the number of bits of the video signal at the upper slice level and the bit number of the video signal at the lower slice level. The driving mechanism is moved between the end position of the optical system and the in-focus position until the second section where the difference in number becomes a value set in advance so that the optical system position is several μm before the in-focus position. The driving mechanism is driven at a pitch shorter than the distance, and the driving mechanism is driven at a minute pitch that is less than the depth of focus of the lens system in a third section that is set in advance so as to pass through the in-focus position from that position, and the section is stored as an address and then The difference in the number of bits of the video signal between the upper and lower slice levels corresponding to the address is memorized, and after the driving of the section is completed, the control unit controls the drive mechanism to the address where the difference in the number of bits is the smallest. It is controlled and driven.

Therefore, according to the present invention, it is possible to provide an automatic focus adjustment device that has a simple configuration and can perform accurate adjustment in a short time.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a conventional video signal processing method, FIG. 2 is a graph of the width change of a line width video signal as the microscope moves in the focal direction, and FIG. 3 is a block diagram of an embodiment of the present invention. Figure 4 is a positional relationship between the subject and the objective lens according to the same embodiment at the start of automatic focus adjustment, Figure 5 is an explanatory diagram of the video signal obtained from the imaging device, and Figure 6 is Wl-W.
It is a graph of changes in the amount W5 of l. 1.25...Video signal at focus position, 7...
... Sample stage, 8... Subject, 9...
Objective lens, 1o,. ... Lens barrel, 11... Intermediate lens, 13...
...Imaging device, 14...Guide section, 17...
・・・・Drive part, 18・・kawa・ho) SEFU-IJ--1
19...4... Stage, 20-... Frame memory, 22... Control unit, 23... Focus position of optical system, 24... work distance,
26. River...Blurred video signal C127...Blurred video signal D128...Lower slice level, 29.
・River/upper slice level, 30...First section of optical system movement, 31...Second section of optical system movement,
32...Third section of optical system movement. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3

Claims (1)

[Claims] When measuring an object having a minute line width, in a microscope having an imaging device on the real image plane, based on the characteristic that the edge signal of the line width video signal obtained from the imaging device has a maximum slope at the focused position, A frame memory that divides the video signal into a plurality of bits in the length direction and stores the divided bits as a density image in the brightness direction, and an end cam and a pulse motor that control and drive the position of the optical system of the microscope in the focal direction. a drive mechanism comprising: a video signal peak value of 10% or more at the time of focusing at the upper part of the frame memory in the brightness direction;
An upper slice level is set at a position above the upper slice level, a lower slice level is set below the upper slice level, and up to a first section where the number of bits in the length direction of the video signal at the lower slice level is greater than 0. The optical system is operated in the direction of the focus position at a pitch shorter than a second interval described later, and the number of bits of the video signal at the upper slice level is greater than 0, and the number of bits of the video signal at the upper slice level is equal to the number of bits of the video signal at the lower slice level. The difference in the number of bits of the video signal at the slice level is such that the optical system position is several μm from the focus position in advance.
The driving mechanism is driven at a pitch shorter than the distance between the end position of the second interval and the in-focus position until the second interval reaches the set value so that the optical system position is closer to the front, and the in-focus position is moved from that position. The drive mechanism is driven at a minute pitch below the depth of focus of the lens system through a third section that has been set in advance to pass through, and the section is used to store addresses and to record video signals at the upper and lower slice levels corresponding to the addresses. The difference in the number of bits is memorized, and after the driving of the section is completed,
An automatic focus adjustment device for a microscope, comprising a control section including a microprocessor or the like, which controls and drives a drive mechanism to an address having the smallest difference in the number of bits.