JP2018116006A - Contactless surface height measurement method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contactless surface height measurement method and device therefor, which allow for making rapid and accurate surface height measurement by continuously scanning a work under measurement with a laser probe.SOLUTION: A zero level of a bisected sensor is detected while rapidly moving a focus changing optical system to rapidly change a focal position of an objective optical system, thereby enabling rapid and accurate measurement of a surface height profile of a work under measurement. Accurate measurement is possible even when return light of a laser probe is weak at some measurement points such as tips.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-contact surface height measuring method and apparatus.

  Laser probe type non-contact surface height measuring devices using laser autofocus are used to measure the surface height of precision parts. In other words, while the autofocus control by the laser probe is applied to the upper surface of the measurement workpiece to be measured, the measurement workpiece is scanned horizontally at a predetermined pitch, and the objective lens in the autofocus optical system moves in the focus direction. Measurement data on the surface height of the workpiece is obtained from the quantity.

  The objective lens is controlled so that the return light of the laser probe is received at the center of the two-divided sensor as disclosed in Japanese Patent No. 2125498 (Patent Document 1). In other words, the measurement workpiece is sent at a predetermined pitch, the objective lens moves by feedback control, and when the return light from the measurement workpiece is received at the center of the two-divided sensor, it is determined as the focal position, and the amount of movement of the objective lens is The detected height information of the surface of the workpiece can be measured from the amount of movement.

  Further, as disclosed in Japanese Patent No. 5585140 (Patent Document 2), even if the measurement workpiece is continuously scanned and the laser probe is deviated from the focal position to a certain extent, the differential output of the two-divided sensor The speed of measurement can be increased by estimating the offset amount from the focal position based on the above.

Japanese Patent No. 2125498 Japanese Patent No. 5854140

  However, in such related technology, the S / W of the return light that reaches the two-divided sensor via the objective lens due to scattering of the surface, such as a measurement workpiece having an inclined surface or a surface with unevenness finer than the beam of the laser probe When the N intensity is weak, the differential output level also decreases. Therefore, in an autofocus system that converges the focal position while feeding back the differential output, it may be difficult to specify the on-focus position of the surface where the laser is scattered.

  The present invention has been made by paying attention to such a related technology, and can perform high-speed and accurate surface height measurement while continuously scanning the laser probe with respect to the measurement work even on the surface where the laser is scattered. It is an object of the present invention to provide a contact surface height measuring method and apparatus.

  A non-contact surface height measurement method according to the present invention is a non-contact surface height measurement method for measuring the surface height of a measurement workpiece while continuously scanning in the first direction of the surface of the measurement workpiece. The surface of the measurement workpiece is irradiated with the laser probe through the optical system, and the return light of the laser probe from the surface of the measurement workpiece is received by the two-divided sensor, and the objective is provided between the objective optical system and the two-divided sensor. Changing the focal position of the optical system The high-speed reciprocation of the focus-changing optical system along the optical axis of the objective optical system to change the focal position of the objective optical system at high speed, and the varying focal position of the objective optical system is measured Detecting the coincidence with the workpiece surface by detecting the differential output of the two-divided sensor to the zero position, and measuring the surface height of the workpiece in the optical axis direction based on the focal position corresponding to the zero position detection. detection Characterized in that it comprises a Rukoto, the.

  Instead of the autofocus method that converges the focal position by feedback control of the objective optical system as in the past, while moving the focal position of the objective optical system at high speed by reciprocating the movable part of the lightweight focus changing optical system at high speed Since the zero position detection method for detecting the timing and level (height) at which the differential output becomes zero is employed, it is possible to detect the surface height at high speed and accurately even for a scattering surface. Further, even when the intensity of the return light is small at a measurement point such as a tip, a zero position is always generated while the focal position is rapidly changed, so that the zero position can be reliably detected.

Schematic which shows the non-contact surface height measuring apparatus which concerns on embodiment of this invention. The conceptual diagram which shows the high-speed scan of a laser probe. The conceptual diagram showing the positional relationship of the high-speed scan by a laser probe, and the spot of the return light in a two-divided sensor. The conceptual diagram showing the relationship between the measurement workpiece | work surface and the high-speed scan of a laser probe. The conceptual diagram which shows the example of the other movable part of a focus change optical system.

  1-5 is a figure which shows embodiment of this invention. In the figure, XY is two directions orthogonal to each other on a horizontal plane, and Z is a vertical direction orthogonal to the horizontal plane.

  FIG. 1 is a conceptual diagram of a non-contact surface height measuring device 1, and this non-touch surface height measuring device 1 is combined with a stage 30 as a “scanning device” that is slidable in the X and Y directions. . The measurement workpiece 2 is fixed on the stage 30, and the measurement workpiece 2 can be slid in the X direction and the Y direction with respect to the non-contact surface height measurement device 1 by the stage 30. A driver for moving the stage 30 in the first direction, that is, the X direction or the Y direction is built in the controller 20, and the stage 30 is controlled and driven by the controller 20. The position of the stage 30 in the X direction or Y direction can be detected by a linear scale (not shown).

  An objective lens (objective optical system) 4 is fixed above the measurement work 2. The objective lens 4 itself moves and does not participate in the focus change, but the position is fixed.

  Above the objective lens 4, a focus changing optical system 12 including a concave lens (first optical system) 13 and a convex lens (second optical system) 14 is provided. The concave lens 13 and the convex lens 14 are each smaller in diameter and lighter than the objective lens 4, and both are arranged vertically along the vertical optical axis K. The optical axis K is defined in a second direction intersecting the first direction (X or Y), typically parallel to the Z axis.

  The concave lens 13 and the convex lens 14 are each connected to a linear actuator (driving means) 5. Of the concave lens 13 and the convex lens 14, only the concave lens 13 is a “movable part” that can reciprocate at high speed along the optical axis K, and the concave lens 13 moves to change the distance between the concave lens 13 and the convex lens 14. be able to.

  Changing the distance between the concave lens 13 (having a negative focal length) and the convex lens 14 (having a positive focal length) by the linear actuator 5 is proportional to changing the focal length of the objective lens 4. For example, a piezo actuator that can be driven at high speed can be used as the linear actuator 5. The linear actuator 5 is also controlled by the controller 20. The position of the concave lens 14 is detected by a position sensor (not shown), and the position information is also input to the controller 20.

  A beam splitter 10 is disposed above the objective lens 4 and the focus changing optical system 12. The beam splitter 10 has a function of transmitting 50% of light and reflecting 50%.

  Laser irradiation means 11 is disposed on the side of the beam splitter 10. Laser light (semiconductor laser) serving as the laser probe L is irradiated from the laser irradiation means 11 in the horizontal direction. The laser beam is reflected by the beam splitter 10 in a direction parallel to the optical axis K, passes through the focus changing optical system 12 and the objective lens 4, and strikes the surface T of the measurement workpiece 2 as a laser probe L. The optical center of gravity of the cross section of the beam of the laser probe L passes through a position offset in the X direction from the center of the optical axis of the objective lens 4.

  The laser probe L that has passed through the objective lens 4 is reflected by the surface T of the measurement workpiece 2, and its return light L ′ passes again through the objective lens 4, the focus changing optical system 12, and the beam splitter 10, and passes through the imaging lens 7. Light is received by the two-divided sensor S. The two-divided sensor S is composed of two photosensors a and b that are closely arranged in the X direction. In the drawing, the return light L 'is a light beam reflected by the surface T of the measurement workpiece 2 by the laser probe L, but is represented by a representative optical path L' for convenience.

  The two-divided sensor S is configured so that the outputs of the two sensors a and b are balanced and the differential output of the differential amplifier 21 becomes zero when the center of gravity of the spot of the return light L ′ coincides with the center. The differential output of the operational amplifier 21 is also input to the controller 20.

  In FIG. 2, the neutral position of the concave lens 13 is Zb, the optical path of the laser probe L at this time is Lb, and the focal position of the objective lens 4 is Fb. When the concave lens 13 is raised from this position (in the B direction) to increase the distance between the lenses, the optical path of the laser probe L passes through the outside of the objective lens 4 as indicated by La and is above the reference focal position Fb. Crosses the optical axis K at the focal position Fa. This is equivalent to shortening the focal length of the objective lens 4.

  When the concave lens 13 is lowered from the reference position (direction A), the distance between the lenses is shortened, the optical path of the laser probe L passes through the inside of the objective lens 4 as indicated by Lc, and is below the reference focal position Fb. Crosses the optical axis K at the focal position Fc. This is equivalent to an increase in the focal length of the objective lens 4.

  In FIG. 3, (II) in the center is a focus state in which the focal position F of the objective lens 4 and the surface T of the measurement workpiece 2 irradiated with the laser probe L coincide with each other, and (I) is the surface T in front of the focal position F. A certain state (III) shows a state in which the surface T is ahead of the focal position F.

  FIG. 4 schematically represents a part of the surface height distribution in the scanning direction (X direction) of the measurement workpiece 2. Since the measurement workpiece 2 moves at a constant speed in the X direction by the stage 30, it is continuously scanned with respect to the laser probe L. Accordingly, the horizontal axis represents time t and the corresponding position X (t), and the vertical axis represents the height information Z of the surface T and the fluctuation range d of the focal position of the laser probe L.

  The focus change optical system 12 detects the zero position of the differential output of the two-divided sensor S while changing the amplitude of the focus position of the objective lens 4 in the optical axis K direction at a high speed with a predetermined period τ and fluctuation width d. The height Z (t) of T is acquired. In particular, since the light concave lens 13 instead of the objective lens 4 is reciprocated in the vertical direction, the focal position can be changed at high speed. In this embodiment, the fluctuation width d is 30 μm and the period τ is 1 ms, but the present invention is not limited to this. In FIG. 4, the period τ is shown in an enlarged manner for easy understanding.

  Since the zero position is detected in the continuous variation of the focal position, a zero cross (zero position) is always generated even when the return light L ′ becomes weak due to scattering, so that the height Z ( t) can be captured.

  By detecting the position of the concave lens 13 at the timing at which the differential output of the two-divided sensor S becomes zero among the positions of the concave lens 13 that reciprocates up and down at high speed in this way, the equivalent focal position of the objective lens 4 is determined. The height information at each measurement point on the surface T of the measurement workpiece 2 as a target can be detected. Therefore, the three-dimensional shape of the surface T of the measurement workpiece 2 can also be measured by measuring the height of the measurement workpiece 2 in the X direction while gradually shifting it in the Y direction.

  In the present embodiment, in order to change the distance between the concave lens 13 and the convex lens 14, only the concave lens 13 is reciprocated as a movable part, but only the convex lens 14 may be used as the movable part. Further, as shown in FIG. 5, both the concave lens 13 and the convex lens 14 may be moved at high speed by the linear actuator 5 so as to move toward and away from each other while being synchronized in mutually opposite directions. When moving in directions opposite to each other, a reaction such as an impact accompanying the acceleration movement of the concave lens 13 and the convex lens 14 is canceled with each other, so that no vibration is generated.

  As described above, in this embodiment, the stage 30 is used as a scanning device, and the measurement work 2 placed on the stage 30 is moved in the X direction or the Y direction with respect to the non-contact surface height measuring device 1. Is provided on the non-contact surface height measuring device 1 side, and the entire non-contact surface height measuring device 1 is moved in the anti-X direction or the anti-Y direction with respect to the measurement work 2 whose position is fixed. 2 may be moved relative to the laser probe L in the X or Y direction.

1 Non-contact surface height measuring device 2 Measurement work 4 Objective lens (objective optical system)
5 Linear actuator (drive means)
DESCRIPTION OF SYMBOLS 11 Laser irradiation means 12 Focus change optical system 13 Concave lens (1st optical system: Movable part)
14 Convex lens (second optical system)
20 controller 30 XY stage (scanning device)
a, b Photosensor S Two-part sensor L Laser probe L 'Return light K Optical axis T Surface of workpiece F Focus position

Claims (4)

A non-contact surface height measuring method for measuring the surface height of a measurement workpiece while continuously scanning in the first direction of the surface of the measurement workpiece,
Irradiating the surface of the measurement workpiece with the laser probe via the objective optical system and receiving the return light of the laser probe from the surface of the measurement workpiece by the two-divided sensor;
A focal point changing optical system that is provided between the objective optical system and the two-divided sensor and changes the focal position of the objective optical system is reciprocated at high speed along the optical axis of the objective optical system to change the focal position of the objective optical system at high speed. And
Detecting that the foci of the objective optical system fluctuate with the surface of the workpiece by detecting the differential output of the two-divided sensor to zero.
Detecting the height of the surface of the measurement workpiece in the optical axis direction based on the focal position corresponding to the zero position detection;
A non-contact surface height measuring method comprising: A non-contact surface height measuring device that is used in combination with a scanning device and measures the surface height of a measurement workpiece while continuously scanning a laser probe in the first direction of the surface of the measurement workpiece by the scanning device. And
An objective optical system having an optical axis in a second direction perpendicular to the first direction and having a fixed position;
Laser irradiation means for irradiating the surface of the measurement workpiece with a laser probe via the objective optical system;
A two-divided sensor that receives the return light of the laser probe from the surface of the measurement workpiece and has a differential output of zero when the focal position of the objective optical system coincides with the surface of the measurement workpiece;
It is arranged between the objective optical system and the two-divided sensor, and is composed of a movable part that is lighter than the objective optical system and movable along the optical axis of the objective optical system. A focus changing optical system for changing the focal position of the objective optical system;
Driving means for reciprocating the movable part of the focus changing optical system at high speed;
A controller that detects the zero position of the two-divided sensor and detects the height of the surface of the measurement workpiece in the optical axis direction based on the focal position corresponding to the zero position detection;
A non-contact surface height measuring device comprising:   The focal point changing optical system includes a first optical system and a second optical system having different positive and negative focal points, and the driving means uses either the first optical system or the second optical system as a movable part in the optical axis direction of the objective optical system. 3. The non-contact surface height measuring device according to claim 2, wherein the non-contact surface height measuring device is reciprocated at a high speed.   The focus changing optical system includes a first optical system and a second optical system having different positive and negative focal points, and the driving means is synchronized in the optical axis direction of the objective optical system using both the first optical system and the second optical system as movable parts. 3. The non-contact surface height measuring device according to claim 2, wherein the non-contact surface height measuring device is reciprocated at high speed in opposite directions in the state.

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