JP3526122B2 - Shape measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shape measuring apparatus and method, and more particularly to a shape measuring apparatus and method for measuring the shape of optical elements such as lenses and mirrors.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring the surface shape of an aspherical lens or the like, a method in which the surface of the object to be measured is scanned by a contact probe and the shape of the object to be measured is determined by the amount of movement of the probe is generally used. According to this measuring method, there is a problem that the surface of the object to be measured is scratched. Therefore, in the case of measurement in which damage to the surface of the object to be measured poses a problem, a non-contact measurement method using a non-contact probe has come to be used. In this non-contact measuring method, the object-to-lens provided on the non-contact probe is focused on the surface of the object to be measured, the surface to be measured is scanned, and the surface shape is measured from the amount of movement of the object-to-lens.

In the non-contact measuring method as described above, if dust or scratches are present on the surface to be measured, the light is scattered, the reflected light received is reduced, the focus is lost, and the focus state determination operation becomes impossible. It may happen. This not only makes the shape measurement impossible, but also creates the risk of the non-contact probe colliding with the object to be measured, and as a result of moving in the scanning direction, scratches, dust, etc. on the surface to be measured. Even if there is no light, there is a problem that it is impossible to return to the focus state and it becomes impossible to continue the measurement.

Therefore, in the invention disclosed in Japanese Patent Laid-Open No. 63-223513, when the focus pulling range is out of the range, the loop is automatically switched to the positioning servomechanism loop, and the autofocus microscope is locked at that position. The focus position of the lens is locked at the position just before passing through scratches, dust, etc., and in this state, the non-contact probe is scanned, and when it passes through scratches, dust, etc., it returns to the focus pull-in range again. By detecting this, it automatically returns to the autofocusing servo mechanism loop. In the focus state determination, the focus state is determined by the signal of the light receiving element being near the center of the light receiving element.

In the invention described in Japanese Patent Laid-Open No. 3-110406, it is assumed that the focus is out of focus due to a step that exceeds the focus pull-in range. The lens is held, the objective lens is moved up and down to search for the focus pull-in range, and the focus position is restored.

[0006]

As described above, in the case of returning to the focus pull-in range when the focus is out of focus, in the invention of Japanese Patent Laid-Open No. 63-223513, the focus position of the objective lens is scratched or dusted. It is locked at the position immediately before passing through the same, and in this state, the non-contact type probe is scanned, and when it passes through scratches, dust, etc., it returns to the focus pull-in range again. Since this is polar coordinate measurement by swivel scanning, in the minute scanning range,
The displacement of the measured surface in the focus direction is very small,
This is because it can be ignored.

On the other hand, in the orthogonal coordinate measurement by linear scanning, the displacement in the focus direction of the surface to be measured in the minute scanning range is not minute and cannot be ignored. Therefore,
As in the invention described in JP-A-63-223513, even if the objective lens is held at the position immediately before defocusing and moved in the minute scanning direction, it is not always possible to return to the focus state.

Further, in the invention disclosed in Japanese Patent Laid-Open No. 3-110406, it is assumed that the focus is out of focus due to a step that exceeds the focus pull-in range. Is held, and the objective lens is moved up and down to search for the focus pull-in range to return to the focus position, but when passing through the edge of the step, light is scattered at the edge,
Since the reflected light decreases, it is impossible to return to the focus pull-in range on the edge.

In view of the above problems, the invention of claim 1 is
Also in the orthogonal coordinate measurement by linear scan, when the focus is off, for the purpose of preventing the collision with the object to be measured, provides a shape measuring equipment capable of returning to the focus capture range Hisage <br/> It was made.

In addition to the out-of-focus caused by scratches, dust, and steps on the surface to be measured, the focus is not caused by the object to be measured, such as a disturbance such as vibration or a deviation of the end position due to an error in the scanning start position. There is a case where the lens is out of focus, and it may not be possible to return to the focus pull-in range even if the focus state return operation is performed. In such a case, in order to prevent runaway, the measurement is stopped, but at that time, the measurement has to be performed again, which takes time and labor.

According to a second aspect of the invention, there is provided a shape measuring apparatus which can use the shape measurement data up to that point without wasting it if the focus state cannot be restored even after the focus state returning operation. It was made for the purpose of providing.

With respect to the focus state determination means, in polar coordinate measurement by swivel scanning, the change in the inclination of the surface to be measured in the scanning direction is small and the change in the amount of received reflected light is small, so the focus state is determined by the amount of received light. ing. However, in the orthogonal coordinate measurement by linear scanning, the inclination of the surface to be measured in the scanning direction changes and the change in the amount of reflected light received cannot be ignored, and it is impossible to determine the focus state based on the amount of received light.

A third aspect of the present invention has been made for the purpose of providing a focus state discriminating means which is effective even in the measurement of rectangular coordinates by linear scanning.

[0014]

[0015]

According to a first aspect of the present invention, an optical displacement gauge is provided as a non-contact probe, and the non-contact probe is linearly scanned along the surface of the object to be measured to obtain the surface of the object to be measured. In a probe scanning type shape measuring device for measuring a shape, a first control means for controlling the objective lens of the non-contact probe by a position signal and a reflected light from the surface of the object to be measured are received. Second focus tracking control means for keeping the non-contact probe and the surface to be measured at a constant distance by pulling the objective lens of the non-contact probe into the focused state on the surface to be measured, and maintaining the retracted focus state. comprising means for linearly scanning the contact probe along the surface of the object to be measured, and a focus state determination means for determining whether the focus pull-state, pre-Symbol focus status determination Based on the item, if it is detected defocus signal, said maintaining non-contact probe to a position immediately before the focus deviates in that the fine distance in the scanning direction, by front and rear the objective lens in the focusing direction, It is characterized in that the focus pull-in operation is executed again to restore the focus pull-in state.

According to a second aspect of the present invention, in the shape measuring apparatus according to the first aspect, the means for storing the out-of-focus position, the means for storing the shape measurement data until the out-of-focus, and the error signal are generated. One of the means is provided.

According to a third aspect of the present invention, in the shape measuring apparatus according to the first aspect, the focus state determination means for determining whether or not the focus is in the pull-in state is based on the rate of change in the amount of light received by the light receiving element. It is characterized by determining the state.

[0018]

1 is a schematic configuration diagram for explaining an embodiment of the present invention (FIG. 1 (A) is a plan view, FIG.
(B) is a side view), in which 1 is an object to be measured, 2 is a non-contact probe, and the non-contact probe 2 is X,
There are three axes of Y and Z (3, 4, 5), and the DUT 1 and the non-contact probe 2 are arranged horizontally. Therefore, the Y-axis direction is the focus direction, and scanning is performed in the X or Z direction. Alternatively, the DUT 1 and the non-contact probe 2 may be arranged vertically (up and down), and the Z direction may be the focus direction and scanning may be performed in the X and Y directions. Also, focus direction and 1
Two axes in the scanning direction may be used. 6 is the DUT 1
It is a mounting jig.

The response to the displacement of the non-contact probe 2 is
An S-shaped curve as shown in FIG. 2 is drawn, b is the focus pull-in range, and the zero cross point a is the focus state. When measuring the shape of the object to be measured, position control sets a non-contact probe in the vicinity of the focus pull-in range and switches to focus tracking control. Scanning is started in this state. Thereby, the shape is measured by the position change of the non-contact probe and the focus signal.

As described above, during the measurement or in any other case, when the non-contact probe is moved in the scanning direction while the focus follow-up control is performed, some influence such as scratches, dust or steps on the surface to be measured is exerted. 2
FIG. 3 shows a processing flow when the focus pulling range shown in FIG.

This will be described with reference to FIGS. 3 and 4. Now, assuming that a focus error occurs at point c on the measured surface 1 in FIG. 4, the focus tracking control of the non-contact probe 2 outputs a focus defocus signal (S1), and switches the focus tracking control to the position control (S3). ), The non-contact probe 2 maintains the current position (Rc). This prevents the non-contact probe 2 from losing focus and running out of control and colliding with the object to be measured. In the scanning direction, the out-of-focus signal is received, and the scanning is temporarily stopped (S2) (Xc).

State in which the focus position is maintained (S4)
Then, move a small amount (ΔX) in the scanning direction (S5) (X
d). At this point, the change amount ΔR in the focus direction cannot be ignored, so the focus state pull-in operation is performed again (S6). The amount of change ΔR in the focus direction cannot be ignored, but is small, so the non-contact probe is located in the vicinity of the focus pull-in range. Therefore, it can be easily set to the focus state by changing it in the focus direction (S7) ( Rd).

The above is an example, and the scanning direction may not be stopped, but may be stopped after moving by a predetermined amount (a minute amount), or may be slowed down after decelerating and moving by a predetermined amount so that the focus can be pulled in. As described above, if it is possible to return to the focus state, the state is returned to the measurement mode by returning to the focus state (S8), focus tracking control is performed while scanning, and shape measurement is performed.

(Invention of Claim 2 ) As described above, even if the focus state returning operation is executed,
There are cases where it is impossible to return to the focus state. In that case, the measurement cannot be continued, an error signal (different from the out-of-focus signal) is output (S10), and the non-contact probe (focus direction) is locked (S11). The controller in the scanning direction receives the error signal, locks the scanning direction (S12), and at the same time stores and saves the position in the scanning direction immediately before defocusing and the measurement data (S13, S14). In this state, the shape measuring device is in a standby state (initial state) (S15). When the same object to be measured is measured again, the non-contact probe is moved to the saved position and the measurement is restarted from that point. As a result, it is possible to effectively use the measurement data until the focus is lost.

(Invention of Claim 3 ) Next, the above-mentioned focus state determining means will be described. FIG. 5 is a diagram showing the relationship between the response to the displacement of the non-contact probe and the amount of received light. For the response e to the displacement of the non-contact probe, the amount of received light is compared to f when the objective lens and the surface to be measured are perpendicular to each other. When there is a slope g, it is small.
Therefore, in polar coordinate measurement by swivel scanning, the inclination of the surface to be measured in the scanning direction is small and almost vertical, so the change in the amount of received light is small, and the threshold h is provided for the amount of received light to determine the focus state. However, in the orthogonal coordinate measurement by linear scanning, the inclination in the scanning direction changes and the change in the amount of received reflected light cannot be ignored, so it is impossible to determine the focus state based on the amount of received light. Therefore, the rate of change of the amount of received light is obtained during measurement, a predetermined value of the rate of change of the amount of received light is set as a threshold, and the focus state is determined.

[0026]

[0027]

[Effect of the Invention] According to the invention of claim 1, comprising an optical displacement gage as the non-contact probe, the non-contact probe by linear scanning along the surface of the object to be measured, the surface shape of該被measured measurement In the probe scanning type profile measuring device ,
First control means for controlling the objective lens of the non-contact probe by a position signal, and receives reflected light from the surface of the object to be measured and pulls the objective lens of the non-contact probe to the measured surface in a focused state, maintaining the focused state has been drawn, the a second focus tracking control means for maintaining a non-contact probe and the measurement surface at a constant distance, the linear scanning the non-contact <br/> probe along the surface of the object to be measured and means for, and a focus state determination means for determining whether the focus pull state, based on the previous SL focus state determination signal, when it is detected defocus signal, the focus is out of the non-contact probe The objective lens is moved back and forth in the focus direction at a point that is maintained at the position immediately before and moved a small distance in the scanning direction,
The focus pull-in operation is performed again to return to the focus pull-in state.When the out-of-focus signal is detected based on the focus determination signal, the non-contact probe is maintained at the position immediately before the focus is removed, and scanning is performed. The objective lens is moved back and forth in the focus direction at the point slightly moved in the direction, and the focus pull-in operation is executed again to restore the focus pull-in state. it is possible to prevent a collision with, and, straight
Small changes in the scanning direction in Cartesian coordinate measurement by line scanning
It is possible to recover the focus state by correcting the fluctuation of the focus direction due to the movement, and to continue the measurement. Also,
Even when the focus is out of focus due to a step or the like, it is possible to avoid the influence of light scattering due to the edge, return to the focus state, and continue the measurement.

According to a second aspect of the present invention, in the shape measuring apparatus according to the first aspect, means for storing the out-of-focus position, means for storing the shape measurement data until the out-of-focus, and an error signal are generated. Since any of the above means are provided, even if the focus state return operation is performed and the error cannot return to the focus state, even when re-measurement of the same DUT is performed, the position up to the position where the error occurred Since the measurement data is stored, it is sufficient to move the non-contact probe to the position where the error has occurred and start the measurement from that position, the measurement data until the focus is removed can be effectively used, and the time can be shortened.

According to the third aspect of the present invention, in the shape measuring apparatus according to the first aspect, the focus state is determined based on the rate of change in the amount of light received by the light receiving element in order to determine whether or not the focus is in the pull-in state. Therefore, the focus state can be determined even in the orthogonal coordinate measurement by linear scanning in which the inclination of the surface to be measured in the scanning direction changes and the change in the amount of received reflected light cannot be ignored.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a main part for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing a response to displacement of a non-contact probe.

FIG. 3 is a flowchart of a process when the focus is outside the pull-in range.

FIG. 4 is a detailed view of a main part for explaining the operation principle of the present invention.

FIG. 5 is a diagram showing the relationship between the response of the non-contact probe to the displacement and the amount of received light.

[Explanation of symbols]

1 ... Object to be measured, 2 ... Non-contact probe, 3, 4, 5 ... Shaft,
6 ... An object mounting jig.

Claims (3)

(57) [Claims] 1. A probe scan for measuring the surface shape of an object to be measured by linearly scanning the surface of the object to be measured by providing the optical displacement gauge as a non-contact probe. Type shape measuring apparatus , the first control means for controlling the objective lens of the non-contact probe by a position signal, and the objective lens of the non-contact probe on the surface to be measured by receiving the reflected light from the surface of the object to be measured. pull the focus state, to maintain the focused state has been drawn, and the second focus tracking control means for maintaining said non-contact probe and the measurement surface at a constant distance, the non-contact probe along the surface of the object to be measured comprising means for linearly scanning, the focus state determination means for determining whether the focus pull state, based on the previous SL focus state determination signal, defocus Shin The case of detecting, maintaining the position immediately before the focus of the non-contact probe is out, in that the minute distance in the scanning direction, wherein by back and forth objective lens in the focusing direction to perform focusing pull-in operation again, A shape measuring device characterized by returning to a focus retracted state. 2. The shape measuring device according to claim 1, wherein any one of a means for storing the out-of-focus position, a means for storing shape measurement data until the out-of-focus, and a means for generating an error signal. A shape measuring device comprising: 3. The shape measuring device according to claim 1, wherein the focus state determination means for determining whether or not the focus pull-in state is, determines the focus state based on a rate of change in the amount of light received by the light receiving element. Shape measuring device characterized by.