JP2006317428A - Face position detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect a face position even of an object having backside reflection. <P>SOLUTION: The face position detector comprises projection optical systems 13, 14 and 3 for irradiating an inspected object with light from a light source 11, a first optical path dividing member 12 that is disposed in the projection optical systems, shields part of a light flux from the light source, and reflects light from the inspected object, a second optical path dividing member 15 for dividing the light from the inspected object that is reflected by the first optical path dividing member into two optical paths, a first light receiving means 16 that has a plurality of light receiving sections and receives the light in one optical path divided by the second optical path dividing member, first position detecting sections 17 and 7 for detecting the face position of the inspected object based on the light quantity received by the plurality of light receiving sections detected by the first light receiving means, a second light receiving means 19 for receiving light having transmitted through a pinhole 18 disposed in the other optical path divided by the second optical path dividing member, second position detecting sections 20 and 7 for detecting the face position of the inspected object based on the light quantity received by the second light receiving means, and a moving means for altering the relative position between the projection optical systems and the inspected object. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface position detection device, and more specifically, a surface position that is used for height measurement in a measuring machine, surface shape measurement, and autofocus control of a microscope or a measuring machine, and detects the position of the surface of a test object. The present invention relates to a detection device.

  For the purpose of non-contact positioning of the optical system at a certain relative distance with respect to the surface of the object to be tested, for example, an autofocus device that positions the lens barrel of the microscope at the focus position, or measurement that determines the step or shape from the driving amount As a machine, one using a knife edge method is known. For example, there is a detailed description of the knife edge method in the prior art column of JP-A-11-72311.

The light receiving position of the auxiliary light is deviated by a change in the relative distance between the object surface and the optical system, and this is detected by the photoelectric conversion element and electrically processed to obtain a fixed position (focal point). Position). Some photoelectric conversion elements use photodiodes (two-divided sensors) that are divided into two regions with a narrow gap. A difference signal A-B between the signal in the A area and the signal in the B area is taken, and a certain position (for example, the focal position) where this signal becomes 0 is detected. Alternatively, positioning is performed by relatively driving the object surface and the optical system with the position of 0 as a target. Some photoelectric conversion elements, such as PSDs (semiconductor position detection elements) and CCD line sensors, detect not the light amount difference but the position of the light spot image itself.
Japanese Patent Laid-Open No. 11-72311

  The knife edge method as described above has an advantage that a pull-in range far wider than the depth of focus can be obtained, and the detected signal is a zero-cross signal in which the direction of blur is known, so that a follow-up operation is possible.

  However, the knife edge method has the following problems. The wide pull-in range, which is an advantage of the knife-edge method, may lead to false detection in the case of reflection of the back surface of a transparent body or a milky-white body in which spots are blurred by using a secondary light source. For example, in a glass substrate or the like, there are cases where the sensor receives both reflected light from the front surface and reflected light from the back surface, and zero-crosses at a weighted average position of the light amounts of both. In the milky white body, since the test object becomes a secondary light source and the light spot spreads and spreads, not only the reflected light from the original surface but also the position to which the influence of the blurred light spot is added may be detected.

  An object of this invention is to provide the surface position detection apparatus which can detect a surface position accurately even if it is a target object with back surface reflection.

In order to solve the above-described problem, the surface position detection device of the present invention includes:
A projection optical system for irradiating the object with light from the light source;
A first optical path dividing member that is provided in the light projecting optical system, shields a part of a light beam from the light source, and reflects light from the test object;
A second optical path splitting member that splits light from the object reflected by the first optical path splitting member into two optical paths;
A first light receiving means having a plurality of light receiving portions and receiving one light divided by the second optical path dividing member;
A first position detection unit that detects a surface position of the test object based on a light amount received by the plurality of light receiving units detected by the first light receiving unit;
A pinhole or slit provided in the optical path of the other light split by the second optical path splitting member;
Second light receiving means for receiving light transmitted through the pinhole or slit;
A second position detecting unit for detecting a surface position of the test object based on the amount of light received by the second light receiving means;
It has a moving means which changes the relative position of the projection optical system and the test object.

  According to the present invention, even when reflected light from both the front surface and the back surface is received, the surface position can be detected with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram illustrating a configuration of a surface position detection apparatus according to the present embodiment. The surface position detection device 1 includes a sensor unit 2, an objective lens 3, an imaging device 4, a stage 5 on which a test object is placed, an encoder 6 that detects the amount of movement of the sensor unit 2, and a control unit 7. The sensor unit 2, the objective lens 3, and the imaging device 4 are attached to the support column 8 via a drive mechanism (not shown), and the relative position with respect to the test object can be obtained from the amount of movement detected by the encoder 6.

  FIG. 2 is a diagram showing the configuration of the sensor unit 2. The inside of the broken line in FIG. The light beam emitted from the laser diode 11 is shielded by the knife edge 12 at half of the circular light beam, and the light beam having a semicircular cross section passes through the auxiliary lens 13 and the dichroic mirror 14 through the left half of the paper surface of the objective lens 3, Irradiate the surface of the test object O. The light beam that has passed through the objective lens 3 forms a light spot image at the focal position of the objective lens 3. FIG. 2 shows a case where the object O surface and the focal position of the objective lens 3 coincide. The light reflected by the object O passes through the right half of the objective lens 3 on the paper surface, is reflected by the dichroic mirror 14, passes through the auxiliary lens 13, is reflected by the mirror surface of the knife edge mirror 12, and is guided to the half mirror 15. It is burned. The light transmitted through the half mirror 15 forms a light spot image on the two-divided sensor 16 composed of the two-divided light receiving elements a and b. The light reflected by the half mirror 15 forms a light spot image on the surface of the pinhole 18 and is received by the light receiving element 19. In FIG. 2, the laser diode 11, the test object O, the two-divided sensor 16, and the pinhole 18 are arranged at conjugate positions. When the relative position between the test object O and the sensor unit 2 changes in the optical axis direction of the objective lens 3 and the surface position of the test object O deviates from the focal position of the objective lens 3, the light on the two-divided sensor 16. Since the point image is blurred, the amount of light received by the light receiving element b increases. Further, when the surface position of the test object O deviates from the focal position of the objective lens 3, the light spot image deviates from the surface of the pinhole 18, so that the amount of light passing through the pinhole becomes small. By utilizing such a change, the surface position of the test object O with respect to the position of the sensor unit 2 can be detected.

  In the surface position detection apparatus of the present embodiment, the light transmitted through the half mirror 15 is received by the light receiving elements a and b while the sensor unit 2 is moved in the optical axis direction of the objective lens 3 by a moving mechanism (not shown). The laser diode 11 is modulated and driven, and the light receiving elements a and b demodulate in synchronism with this to obtain a light receiving signal. Here, the output signal level from the region of the light receiving element a of the two-divided sensor 16 is A, and the output signal level from the region on the light receiving element b side is B. Output signals from the two light receiving elements are input to the first position detector 17. The first position detector 17 obtains a difference signal level S (described later) from the difference between the output signal levels from the two light receiving elements a and b, and detects the in-focus position by the knife edge method. Further, the first position detector 17 obtains the received light amount signal level (A + B) from the sum of the two output signal levels. The values (A−B) and (A + B) obtained by the first position detection unit 17 are output to the control unit 7. The control unit 7 feedback-controls the light emission amount of the laser diode 11 so that the received light amount signal level (A + B) is substantially constant.

Next, the operation of the knife edge method using the light receiving elements a and b will be described. In the control unit 7, the difference signal level S is obtained by the following equation.
S = (A−B) / (A + B)
The sensor unit 2 is moved in the optical axis direction (Z direction) of the objective lens 3. The change of the difference signal level S with respect to the amount of movement in the Z direction is as shown in FIG. As the position in the Z direction changes, the difference signal level S goes from negative to zero and becomes a positive value. At this time, the Z-direction position passing through zero (zero cross position) and the in-focus position are matched. Drive the sensor unit 2 at a constant speed in the Z direction,
S = (A−B) / (A + B) = 0
A + B> T
(That is, when (A + B) is larger than a predetermined level and the difference signal level S becomes zero), the control unit 7 determines the height position (Z direction position) of the sensor unit 2 at that moment as the encoder 6. Read location information from. Then, the height is measured. Alternatively, the focusing operation is performed by positioning and driving the sensor unit 2 with the height position as a target value. Alternatively, by performing feedback driving with the target of 0 of the difference signal level S itself, the focusing operation is performed, or the height position is measured as the stop position.

  Further, in the knife edge method, the feedback drive with the difference signal level S of 0 as the target is continuously performed, and the object to be scanned is scanned in the direction orthogonal to the height direction (Z direction). (Nuus AF) and continuous cross-sectional shape measurement.

  Next, position detection using a pinhole (pseudo confocal method) will be described. Similar to the knife edge method, the laser diode 11 is modulated and driven, and the light receiving element 19 demodulates in synchronism with this to obtain a light receiving signal. An output signal from the light receiving element 19 is input to the second position detector 20. The output signal level from the light receiving element 19 obtained by the second position detector 20 is C. The value of the signal level C is output to the control unit 7. As described above, the control unit 7 feedback-controls the light emission amount of the laser diode 11 so that the received light amount signal level (A + B) is substantially constant.

Next, the operation of the pseudo confocal method using the light receiving element 19 will be described.
In the control unit 7, the signal level C is obtained by the following equation.
I = C / (A + B)
The sensor unit 2 is moved in the optical axis direction (Z direction) of the objective lens 3. And the control part 7 detects the Z direction position where the value of I peaks. That is, the position in the height direction of the sensor unit 2 is detected by reading the position information from the encoder 6 at the time when I reaches a peak. For example, when the test object is a glass substrate for liquid crystal, the light intensity signal level C from the light receiving element 19 is detected with two peaks as shown in FIG. This is because the peak p1 caused by the reflected light from the surface of the glass substrate and the peak p2 caused by the reflected light from the back surface are detected separately.

  In this embodiment, the value of the signal level C corresponding to the amount of light received by the light receiving element 19 is normalized by the sum signal (A + B) corresponding to the amount of light received by the light receiving elements a and b. Even when the reflectance of the surface of the object is not uniform or the light amount fluctuates, the light amount peak can be detected with high accuracy.

  As described above, the surface position detection apparatus according to the present embodiment can perform autofocus, height measurement, tracking operation, and continuous scanning measurement with a highly versatile knife edge method, and the test object can be a transparent body or a milky white body. Even in such a case, the surface can be detected with high accuracy by the operator selecting the pseudo confocal method.

  In addition, since both surface detection methods of knife edge method and pseudo confocal method are provided, during single AF that detects the position of one surface, the operation is the knife edge zero cross signal, and the height detection is the confocal peak. It is basically based on the use of a signal, and it is possible to selectively use a knife edge during copying AF.

  For example, in single AF (height measurement), both types of detection results may be read, and the average value may be used as a height measurement value (or in-focus position / and in-focus position) for autofocus driving. Or, instead of using the average value, give the condition according to the test object or detection point, such as whether to adopt the highest value (front surface reflection) or the lower value (back surface reflection). Therefore, it is possible to reliably detect the target surface position.

(Second Embodiment)
The present embodiment is applied when single AF (height measurement) is performed while moving the sensor unit 2 in a direction in which the sensor unit 2 is moved closer to the test object. Within the knife edge method pull-in range, one point of focus position is detected by the knife edge method, and when two or more focus positions are detected by the pseudo confocal method, one point detected by the knife edge method is detected. It is determined as an error, and the first point of the pseudo confocal point is determined as the surface of the test object, and the second point is determined as the back surface. It is also possible to obtain the thickness of the test object from two points of the pseudo confocal method. Such determination of the detected point is performed by preparing and selecting a plurality of determination programs in the control unit according to the type of the test object.

(Third embodiment)
In this embodiment, a slit is provided instead of the pinhole 18 of the sensor unit 2 shown in FIG. In general, it is difficult to adjust the beam waist through the pinhole. Unlike the original confocal point, this method not only blurs the light spot but also spreads while shifting the position before and after the focal point. Therefore, a peak signal can be obtained even if a slit perpendicular to the light spot shift direction is used instead of the pinhole. Although the influence of ambient light is inferior to that of a pinhole, the conjugate adjustment with the in-focus position requires only a shift in one direction, and thus has the advantage of being very simple.

  It is desirable that the light receiving elements a and b, the pinhole (or slit) 18 and the laser diode 11 of the light source are accurately adjusted. In addition to having a mechanism for finely adjusting the position of each light receiving element mechanically, it is also possible to correct the offset of the knife edge method and the pseudo confocal method by preparing a correction value in the control unit. For example, each method is determined from a value detected based on the contrast obtained by placing the subject at the reference position and imaged by the imaging device 4, a value detected by the knife edge method, and a value detected by the pseudo confocal method. The correction value at the time of detection in (1) is held in the control unit, and the measurement data is corrected.

It is a block diagram of the surface position detection apparatus of 1st Embodiment. It is a block diagram of the sensor unit of the surface position detection apparatus of 1st Embodiment. It is a figure which shows the position detection signal in a knife edge system. It is a figure which shows the position detection signal in a pseudo-confocal system.

Explanation of symbols

1: surface position detection device, 2: sensor unit, 3: objective lens, 4: imaging device, 5: stage, 6: encoder, 7: control unit, 8: support, 11: laser diode, 12: knife edge mirror, 13: Auxiliary lens, 14: Dichroic mirror, 15: Half mirror, 16: Two-divided sensor (light receiving elements a and b), 17: First position detector, 18: Pinhole, 19: Light receiving element, 20: Second Position detector.

Claims (3)

A projection optical system for irradiating the object with light from the light source;
A first optical path dividing member that is provided in the light projecting optical system, shields a part of a light beam from the light source, and reflects light from the test object;
A second optical path splitting member that splits light from the object reflected by the first optical path splitting member into two optical paths;
A first light receiving means having a plurality of light receiving portions and receiving one light divided by the second optical path dividing member;
A first position detection unit that detects a surface position of the test object based on a light amount received by the plurality of light receiving units detected by the first light receiving unit;
A pinhole or slit provided in the optical path of the other light split by the second optical path splitting member;
Second light receiving means for receiving light transmitted through the pinhole or slit;
A second position detecting unit for detecting a surface position of the test object based on the amount of light received by the second light receiving means;
A surface position detection apparatus comprising: a moving unit that changes a relative position between the projection optical system and the test object. The surface position detection apparatus according to claim 1,
A surface having selection means for selecting one of a position of the test object obtained by the first position detection unit and a surface position of the test object obtained by the second detection unit. Position detection device. In the surface position detection apparatus according to claim 1 or 2,
A sum signal of the respective light amounts received by the plurality of light receiving portions of the first light receiving means is obtained, a light amount control signal for controlling the light emission amount of the light source is output based on the sum signal, and the first light receiving means A surface position detecting apparatus comprising: an arithmetic unit that normalizes the amount of light received by the second light receiving means and the amount of light received by the second light receiving means using the sum signal.

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