JPH08219752A - Shape measuring device - Google Patents

Abstract

(57) [Abstract] [Purpose] To suppress the fluctuation of the contact pressure of the probe and improve the measurement accuracy. [Structure] The speed of the probe is added as a feedforward element to a control system that feedback-controls the position of the slide unit so that the distance between the slide unit and the probe is kept constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shape measuring device for measuring a shape by bringing a probe into contact with an object to be measured.

[0002]

2. Description of the Related Art In recent years, with the high integration of semiconductors, ultra high precision and high speed measurement technology is required in the peripheral device industry field. Also in the field of the shape measuring device for measuring a three-dimensional shape, the number of measurement points is increased and the measurement time is increased in order to improve the measurement accuracy in the conventional point measurement method.

Therefore, in order to shorten the measuring time, a contact type shape measuring apparatus has been proposed in which a probe is brought into contact with an object to be measured and scanning is performed to measure the shape. FIG. 2 shows an example of the probe portion of the contact type shape measuring apparatus. The DUT 1 is placed on the tracing stage 2, and the probe 3 is brought into contact with the DUT 1 while moving in the tracing direction (Y-axis direction). The probe 3 is supported along the guide 4 and is movable in the probe direction (X-axis direction) orthogonal to the tracing direction. Further, a spring 6 is inserted between one end 3a of the probe 3 and the slide 5, and the probe 3 is pressed against the DUT 1 by this spring force.

In this contact type shape measuring apparatus, in order to improve the measurement accuracy, the contact force of the probe 3 is reduced,
Further, it is necessary to reduce the fluctuation of the contact force and surely bring the probe 3 into contact with the DUT 1. Therefore, the spring pressure inserted between the probe 3 and the slide 5 is reduced, and even if the probe 3 moves up and down along with the tracing operation, the interval between the slide 5 and the slide 5 is always kept constant. Is driven by an actuator (not shown) to perform position feedback control.

FIG. 3 is a control block diagram of a slide drive control system of a conventional contact type shape measuring apparatus. Slide 5
In the drive control system, the main loop is composed of a position feedback control loop and the minor loop is composed of a speed feedback control loop. The slide 5 is driven by the actuator 10, and the actuator 10
Is detected by the speed sensor 11. In the speed control loop, for example, PID calculation is performed by the speed controller 12 based on the deviation between the speed command and the slide speed feedback from the speed sensor 11, and a drive signal is output to the driver 13 to output the actuator 10
Is driven. In the position control loop, for example, PID calculation is performed by the position controller 15 based on the deviation between the probe position detected by the probe position sensor (not shown) and the slide position detected by the slide position sensor 14, and the speed control loop is entered. Speed command is output.

However, in the conventional shape measuring device,
Since the slide drive control system is composed of a position control and speed control feedback control system, a delay occurs in the slide drive control system when the probe is moved. In particular, there is a problem that a large control deviation occurs when the speed of the probe suddenly changes, the fluctuation of the contact force increases, and the shape measurement error increases.

An object of the present invention is to provide a contact type shape measuring apparatus which suppresses fluctuations in the contact pressure of the probe and improves the measurement accuracy.

[0008]

In order to achieve the above object, the invention of claim 1 is a probe which is attached to a slide part through an elastic body and which comes into contact with an object to be measured which is installed on a tracing stage. A slide driving means for driving the slide portion, a slide position detecting means for detecting the position of the slide portion, a probe position detecting means for detecting the position of the probe, the slide position detecting means and the probe position detecting means. On the basis of the position detected by the slide drive means of the slide part so as to keep the distance between the slide part and the probe constant when the profile stage is moved to measure the shape of the object to be measured. A feedback control system of the control means, which is applied to a shape measuring apparatus having a control means for feedback-controlling a position. Added the speed of the probe as a feedforward component. According to another aspect of the shape measuring apparatus of the present invention, the control means calculates the speed of the probe by differentiating the position detected by the probe position detecting means. The shape measuring apparatus according to claim 3, further comprising probe speed detecting means for detecting the speed of the probe, wherein the control means applies the speed detected by the probe speed detecting means to the feedback control system as a feedforward element. It was done like this. The shape measuring apparatus according to claim 4, further comprising probe acceleration detecting means for detecting acceleration of the probe,
The control means integrates the acceleration detected by the probe acceleration detection means to calculate the speed of the probe. The shape measuring apparatus according to claim 5, wherein the control means has a minor loop for feedback controlling the speed of the slide portion driven by the slide driving means, and the speed feedback control system uses the speed of the probe as a feedforward element. It is added to the speed command of. According to a sixth aspect of the shape measuring apparatus, the speed of the probe is low-pass filtered by the control means.

[0009]

The speed of the probe is added as a feedforward element to the control system that feedback-controls the position of the slide portion so that the distance between the slide portion and the probe is kept constant. As a result, the control deviation of the feedback control system is reduced, and the control accuracy and responsiveness in the slide position control are improved. As a result, the fluctuation of the contact pressure of the probe is suppressed and the measurement accuracy is improved.

[0010]

FIG. 1 is a control block diagram of a slide drive control system according to an embodiment. The same elements as those of the conventional drive control system shown in FIG. 3 are designated by the same reference numerals, and different points will be mainly described. The configuration of the probe portion of one embodiment is similar to that shown in FIG. 2, and this embodiment will be described with reference to FIG. As shown in FIG. 1, the slide drive control system of one embodiment is obtained by adding a feedforward loop 20 to the conventional drive control system shown in FIG. The feed forward loop 20 is for differentiating the probe position signal by a differentiating circuit 21 to obtain the speed of the probe 3 and adding it to the speed command signal of the speed feedback minor loop.

In this feedforward loop 20,
The low-pass filter 22 removes noise components from the probe velocity signal calculated by the differentiating circuit 21. It is desirable that the cutoff frequency of the low-pass filter 22 be set as high as possible within a range in which vibration due to noise does not adversely affect the measurement to improve the responsiveness to the speed fluctuation of the probe. The gain of the feedforward loop 20 is set by the gain setting circuit 23. In this embodiment, the optimum value of the gain K in the sense that the steady speed deviation is 0 is 1, but when the unit between the probe speed obtained by the differential operation and the speed command from the position controller 15 is different. Can be multiplied by a unit factor.

In the slide drive control system shown in FIG. 1, the control system is configured so that the distance between the probe 3 and the slide 5 becomes 0. However, an offset is added to the probe position signal or the slide position signal. By doing so, the interval can be controlled arbitrarily. The actuator 10 may be a DC motor, an AC motor, a servo motor, or the like, and the speed sensor 11 may be a tachogenerator, an encoder, or the like. The position sensor 14 and the probe position sensor (not shown) are respectively provided on the slide 5
And the corner cube of the laser interferometer is attached to the probe 3 to detect their positions with high accuracy. Also, position controller 15 and speed controller 1
2. The controller 30 including the feedforward loop 20 may be configured by software of a microcomputer or hardware by an analog device.

FIG. 4 shows a slide position control result according to the above-described embodiment. Now, as shown in (a), it is assumed that the probe 3 is scanning the object 1A having an extremely convex shape. (B) shows the position of the slide 5 driven and controlled by the slide drive control system. When the probe 3 rises from x1 to x2 at the position y1, the probe speed signal obtained by instantaneously differentiating the probe position by the feedforward loop is added to the speed command, and the probe speed signal from the position control loop operates to correct the delay of the speed command. . As a result, the position of the slide 5 rapidly rises from x1 'to x2'. here,
If the distance between the probe 3 and the slide 5 is L,

## EQU00001 ## x1 '= x1 + L and x2' = x2 + L. Further, when the probe 3 descends from x2 to x1 at the position y2, the probe speed signal obtained by instantaneously differentiating the probe position by the feedforward loop is added to the speed command, and the speed from the position control loop is increased, as in the case of the above-mentioned sudden increase. Operates to correct the command delay. As a result, the position of the slide 5 rapidly drops from x2 'to x1'.

FIG. 3 constructed by only a feedback control system
In the conventional slide drive control system shown in (b), as shown by the broken line in (b), the rising of the position of the slide 5 and the rising of the slide are delayed, and overshoot and undershoot occur to reach the target position. slow. On the other hand, in the slide drive control system of the embodiment in which the feed forward loop is added to the feedback control system, the rise of the position of the slide 5 at the time of ascent and descent is fast, the overshoot and the undershoot are small, and the target position is reached. Reach fast

FIG. 5 shows another slide position control result according to the above-described embodiment. Now, as shown in (a), it is assumed that the probe 3 is scanning the trapezoidal object 1B to be measured. (B) shows the position of the slide 5 driven and controlled by the slide drive control system. DUT 1 in which probe 3 is trapezoidal
While scanning the slope B, the probe 3 moves in the X-axis direction at a constant speed. This state is equivalent to a state in which a so-called lamp input is added to the slide drive control system. Normally, in the type 1 feedback control system by PID control, when the target input is a ramp input with a constant speed V, a steady speed deviation Ev appears, and a control delay occurs with respect to the target input as shown by a broken line in (b). . Here, when the transfer function of the control system is G (s), the steady speed deviation Ev is

Ev = V / Kv where Kv = lim (s
→ 0) s · G (s). That is, the steady speed deviation Ev in the type 1 feedback control system can be obtained from the speed V of the lamp input and the constant Kv obtained from the transfer function G (s) of the control system. Since the constant Kv can be calculated by determining the control system, the steady speed deviation Ev can be estimated if the speed V is known.

Therefore, in this embodiment, the position of the probe 3 detected by the probe position sensor is used as the differentiating circuit 21.
The velocity V of the probe 3 is obtained by differentiating with
And the preset constant Kv are substituted into Equation 2 to estimate the steady speed deviation Ev of the type 1 feedback control system, and the steady speed deviation estimated value Ev is subtracted from the speed command signal of the speed feedback minor loop. As a result, even when the shape of the trapezoidal object to be measured 1B as shown in (a) is measured by the slide drive control system of the embodiment, the steady speed deviation Ev is significantly reduced, and the thick line is shown in (b). Thus, the position control characteristic close to the target input can be obtained. That is, the position control accuracy is improved, the fluctuation of the contact pressure of the probe is suppressed, and the measurement accuracy is improved. The position where the estimated value Ev of the steady speed deviation is subtracted may be any position in the position loop by adjusting the gain. Further, the gain K of the speed V of the feedforward loop 20 can be experimentally obtained by measuring the input speed and the steady speed deviation at that time.

As described above, since the feedforward loop of the probe speed is added to the feedback control system of the slide position and speed, the speed control deviation of the feedback control system is reduced, and the overshoot and undershoot in the slide position control are suppressed. In addition, the response speed becomes faster, the fluctuation of the contact pressure of the probe is suppressed, and the measurement accuracy is improved. In addition, even when measuring a trapezoidal object to be measured in which the probe moves at a constant speed, the steady speed deviation is greatly reduced and the position control accuracy is improved.
Fluctuations in the contact pressure of the probe are suppressed and measurement accuracy is improved. Furthermore, the contact pressure itself can be reduced by the amount that the fluctuation of the contact pressure of the probe is reduced, and damage to the object to be measured can be reduced, and a force other than the X-axis direction acts on the probe to incline it. Can be prevented.

Although the position signal from the position sensor is differentiated to calculate the probe speed in the above-described embodiment, a speed sensor may be provided to detect the probe speed directly. Alternatively, an acceleration sensor may be provided to detect the acceleration of the probe, and the probe acceleration may be integrated to calculate the probe speed. Further, although feedforward is added to the speed command of the minor loop in the above-described embodiment, it may be added to the slide position command or the position controller. In this case, the optimum value of the feedforward gain K depends on the characteristics of the position controller.

In the construction of the above embodiment, the spring 6 constitutes an elastic body, the driver 13 and the actuator 10 constitute a slide driving means, the position sensor 14 constitutes a slide position detecting means, and the controller 30 constitutes a control means.

[0020]

Since the speed of the probe is added as a feedforward element to the control system that feedback-controls the position of the slide portion so as to keep the distance between the slide portion and the probe constant, the control deviation of the feedback control system is increased. Can be reduced, overshoot and undershoot in the slide position control can be suppressed, the response speed can be increased, the fluctuation of the contact pressure of the probe can be suppressed, and the measurement accuracy can be improved. Even when measuring a trapezoidal object to be measured in which the probe moves at a constant speed, steady-state speed deviation is greatly reduced, position control accuracy is improved, and fluctuations in the contact pressure of the probe are suppressed. Accuracy is improved. Furthermore, the contact pressure itself can be reduced by the amount that the fluctuation of the contact pressure of the probe is reduced, and damage to the object to be measured can be reduced.
It is possible to prevent the probe from tilting due to a force other than in the X-axis direction.

[Brief description of drawings]

FIG. 1 is a control block diagram of a slide drive control system according to an embodiment.

FIG. 2 is a diagram showing a probe portion of the shape measuring apparatus.

FIG. 3 is a control block diagram of a slide drive control system of a conventional shape measuring apparatus.

FIG. 4 is a diagram showing a control result of a slide drive control system according to an embodiment.

FIG. 5 is a diagram showing a control result of another slide drive control system according to an embodiment.

[Explanation of symbols]

 1 Object to be Measured 2 Tracing Stage 3 Probe 4 Guide 5 Slide 6 Spring 10 Actuator 11 Speed Sensor 12 Speed Controller 13 Driver 14 Position Sensor 15 Position Controller 20 Feedforward Loop 21 Differentiation Circuit 22 Low Pass Filter 23 Gain Setting Circuit 30 Controller

Claims (6)

[Claims] 1. A probe which is attached to a slide part through an elastic body and which comes into contact with an object to be measured which is installed on a tracing stage, a slide drive means for driving the slide part, and a position of the slide part is detected. Slide position detecting means, probe position detecting means for detecting the position of the probe, and based on the positions detected by the slide position detecting means and the probe position detecting means, the tracing stage is moved to perform the measurement. A shape measuring apparatus comprising: a control unit that feedback-controls the position of the slide unit by the slide driving unit so as to keep the distance between the slide unit and the probe constant when measuring the shape of an object. The speed of the probe is added as a feedforward element to the feedback control system of Shape measuring apparatus according to claim and. 2. The shape measuring apparatus according to claim 1, wherein the control unit calculates the speed of the probe by differentiating the position detected by the probe position detecting unit. . 3. The shape measuring device according to claim 1, further comprising probe speed detecting means for detecting the speed of the probe, wherein the control means feeds the speed detected by the probe speed detecting means. A shape measuring device characterized by being added to the above feedback control system as. 4. The shape measuring apparatus according to claim 1, further comprising a probe acceleration detecting means for detecting an acceleration of the probe, wherein the control means integrates the acceleration detected by the probe acceleration detecting means. A shape measuring device characterized by calculating the speed of a probe. 5. The shape measuring device according to claim 1, wherein the control unit has a minor loop that feedback-controls the speed of the slide unit driven by the slide driving unit, A shape measuring apparatus, wherein the speed of the probe is added to a speed command of the speed feedback control system as a feedforward element. 6. The shape measuring apparatus according to claim 1, wherein the control unit performs a low-pass filter process on the speed of the probe.