JP4922583B2 - Friction force correction method of stylus type step gauge for surface shape measurement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frictional force correction method for a stylus type step gage for measuring a surface shape capable of compensating frictional force generated by a frictional situation in a fulcrum portion, a change in a contact condition or the like to generate stylus pressure. <P>SOLUTION: In this frictional force correction method for the stylus type step gage attached with a probe in one end of a support body attached swingably to a fulcrum, attached adjacently to the one end with a magnetic substance core for a displacement sensor for detecting a vertical-directional displacement of the probe, attached with a magnetic substance core for the stylus pressure generator for applying the stylus pressure to the probe in the other end of the support body, and for measuring the surface shape of a sample captured by the probe, by the displacement sensor due to rotational motion around the fulcrum of the support body, the stylus pressure generator is operated to measure an acceleration when the probe is lowered, so as to find force in the lowering, an acceleration when the probe is elevated reboundingly by a lower stopper or the like after lowered is measured to find force in the elevation, and a current flowing in the stylus pressure generator is controlled to apply a half of the sum of the force in the lowering and the force in the elevation onto the probe, when measuring actually the surface shape. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a friction force correction method for a stylus type step gauge for measuring the surface shape of a sample.

  In the present specification, the term “surface shape of the sample” is meant to include the concept of the step, film thickness, and surface roughness of the sample.

Conventionally, this type of step gauge has a probe whose tip contacts the sample surface, a needle pressure generator that contacts the sample surface with a constant load, and a probe that vibrates in a direction perpendicular to the load direction. Known to have a structure with a device that reciprocates the needle in parallel with the sample surface and a detection device that detects the magnitude of vibration corresponding to the frictional force of the probe against the sample when vibration is applied. (See Patent Document 1).
JP-A-3-87737

  The present inventor previously proposed a stylus-type step gauge for surface shape measurement in Japanese Patent Application No. 2005-199337. As shown in FIGS. 1 to 6 of the accompanying drawings, this stylus type step gauge has a rod-shaped first support member 1, and the first support member 1 has both left and right sides at its intermediate portion. A fulcrum needle attachment member 2 extending in the lateral direction is provided, and two fulcrum needles 3 are attached to both ends of the fulcrum needle attachment member 2. These two fulcrum needles 3 are supported by two fulcrum receiving members 4 (FIG. 6), whereby the first support member 1 is supported by the fulcrum receiving member 4 in a freely swingable manner. . At one end of the first support member 1, a measuring element of the displacement sensor 5, that is, a core 6 is attached. The displacement sensor 5 comprises a differential transformer that generates an electrical signal in accordance with the vertical displacement of the probe, and includes a coil 7.

  The other end of the first support member 1 is provided with a core 9 of a needle pressure generator 8 that applies a needle pressure to the probe, and the needle pressure generator 8 includes a coil 10. The core 9 is made of a high magnetic permeability member arranged at a position shifted in the axial direction from the center of the coil 10.

  A holder in which two magnets 11 are embedded in the lower surface of the first support member 1 around the line connecting the two fulcrum needles 3 at both ends of the fulcrum needle mounting member 2 of the first support member 1. 12 is attached. As shown in FIG. 3, the holder 12 is provided with a longitudinal groove 13 having a trapezoidal cross section, and both side walls of the longitudinal groove 13 are tapered downward to form an inclined surface with respect to a horizontal plane. Yes. The two magnets 11 embedded in the holder 12 are arranged so that the polarities are opposite to each other as shown in FIG. The holder 12 containing the two magnets 11 is made of carbon in order to reduce the weight.

  In FIG. 1, FIG. 2, FIG. 4 and FIG. 6, reference numeral 14 denotes a rod-like second support member. A probe 15 is attached to the tip of the second support member, and the other end is formed of a high permeability member 16. Yes. Guide protrusions 17 extending upward are formed at both ends in the longitudinal direction of the high magnetic permeability member 16, and opposing side surfaces of these guide protrusions 17 are formed as inclined surfaces that open upward. The inclined surfaces of the high permeability member 16 together with the inclined surfaces of the both side walls of the longitudinal groove 13 in the holder 12 ensure the mutual positioning when the second support member is attached to the first support member and also serve as a guide. Plays. The high permeability member 16 at the other end of the second support member 14 is fitted in the groove 13 of the holder 12 in the first support member 1, and at that time, the high permeability at the other end of the second support member 14. The member 16 is configured to contact the bottom surface of the groove of the holder 12 and not to contact the two magnets 11. In addition, the groove and the high permeability material part are provided with inclined surfaces as shown in FIG. 2 to ensure mutual positioning and serve as a guide during mounting.

 The first support member 1 and the second support member 14 are made of light carbon in order to reduce the moment of inertia. On the other hand, the high permeability member 16 in the second support member 14 having a high density and a large mass and the magnet 11 in the holder 12 in the first support member 1 are close to the fulcrum in order to reduce the moment of inertia around the fulcrum. It is arranged.

  Further, as shown in FIG. 3, a plate-like member 18 is provided below the high-permeability member 16 in the second support member 14, and this plate-like member 18 has a high permeability material in order to enhance the magnetic field shielding effect. The plate-like member 18 allows the replacement part to be placed in the correct position even if it is tilted and brought close to the groove 13 of the holder 12 in the first support member 1.

 As described above, the magnet 11 embedded in the holder 12 in the first support member 1 is arranged so that the polarity is reversed, so that the magnetic field created in the place where the magnetic dipole is separated becomes small. 5. The magnetic field in the needle pressure generator 8 and the sample can be reduced. Further, due to this arrangement, the magnetic lines of force pass through the high permeability member 16 in the second support member 14 below the magnet 11, so that the magnetic field in the sample below and at the probe position is reduced.

  FIG. 5 shows an enlarged structure of the fulcrum receiving member 4 that receives the fulcrum needle 3. As shown in the drawing, the fulcrum receiving member 4 has a concave surface 4a for receiving the fulcrum needle 3. The concave surface is formed in an inverted conical shape so that the fulcrum needle 3 is positioned and received with high accuracy.

  FIG. 6 shows a state in which the stylus type surface shape measuring instrument shown in FIG. 1 is incorporated in the frame body 19, and the two fulcrum receiving members 4 are fixed to the lower frame member 19 a of the frame body 19. The movable part on the fulcrum is housed in the frame body 19, and a panel (not shown) is attached to the outside of the frame body 19k so as to prevent vibrations caused by wind and temperature changes. The coil of the displacement sensor 5, the fulcrum receiving member 4, and the coil 10 of the needle pressure generator 8 are fixed to the frame body 19 in the frame body 19. In FIG. 6, the coil of the displacement sensor 5 and the coil 10 of the needle pressure generator 8 are omitted for easy viewing. These two types of coils are covered with the coils from above and fixed to the frame 10 with screws or the like. A portion including the displacement sensor 5 including the frame body 19 of FIG. 6, the needle pressure generator, and other movable parts on the fulcrum is referred to as a sensor head. In order to monitor the probe 15 obliquely from above with a camera, the probe 15 protrudes from the frame 19 and is a rod-shaped body that supports the probe 15, that is, a thin windbreak cover that is shaped along the second support member 14 (see FIG. (Not shown) is attached to the front of the frame 19. Stoppers (not shown) are provided above and below the tip of the second support member 14 to limit the range of movement of the probe 15.

  The illustrated stylus type surface shape measuring instrument configured as described above includes a displacement sensor 5 and a needle pressure generating device 8 at both ends, and is supported by two fulcrum receiving members 4 via a fulcrum needle 3 so as to be swingable. The second support member 14 provided with the probe 15 and the high magnetic permeability member 16 at both ends is fixed to the holder 12 of the first support member 1 by magnet attracting force. In this case, the second support member 14 is formed by the inclined surfaces of both side walls of the longitudinal groove 13 in the holder 12 and the opposed inclined surfaces of the guide protrusions 17 in the high permeability member 16 of the second support member 14. The support member 1 can be easily positioned by being accurately positioned at a predetermined position with respect to the holder 12.

  Then, by applying a predetermined current to the coil 10 of the needle pressure generator 8, a force is generated according to the magnitude of the current, and the core 9 of the needle pressure generator 8 is drawn into the center of the coil 10 by this force. It is. As a result, the first and second support members 1 and 14 swing via the fulcrum needle 3 and press the probe 15 against the sample. By scanning the sample or the detection system, the probe 15 traces the surface of the sample, and the first and second support members 1 and 14 rotate slightly around the fixed fulcrum according to the surface shape. Then, the displacement of the core 6 of the differential transformer 5 is detected, and the displacement of the core 6 is converted into the displacement of the probe tip of the probe 15 to measure the surface shape and level difference of the sample.

By the way, in this type of step gauge, the force at the probe, that is, the needle pressure is measured as follows. When the current flowing through the coil 10 of the needle pressure generator 8 is 0, the probe 15 is raised upward due to the weight balance of the movable part on the fulcrum, and is stationary against the stopper. When an appropriate current is passed through the coil 10 of the needle pressure generator 8, the probe 15 is lowered by the generated force. The needle pressure can be obtained by measuring the time change of the needle tip displacement at that time and obtaining the acceleration by second-order differentiation with respect to time. For example, in the region of several tens mgf, the force and acceleration are measured by measuring the force at the needle tip with an electronic balance, obtaining the relationship between the coil current and the force, and measuring the acceleration at this coil current. The relationship between force and acceleration is obtained. Since force and acceleration are in a proportional relationship, a proportionality constant is obtained, and a force value corresponding to the value can be calculated from an arbitrary acceleration value. That is, the probe needle pressure is F, the z-direction position of the probe tip is z, the moment of inertia around the fulcrum is I, the distance from the fulcrum to the tip is r, and the equation of motion around the fulcrum is the rotation angle. If the deformation is made with a small value, the following equation is obtained.

F = I / r ² d ² z / dt ²

That is, it can be regarded as the motion of the mass point of mass I / r ^{2 in} the field where the force F is applied. In other words, the proportionality constant of the aforementioned means I / r ^2.

When the probe needle pressure y is the vertical axis, the current x flowing through the coil of the needle pressure generator is the horizontal axis, and a, b, and c are constants, the current x flowing through the coil and the probe needle pressure y Is expressed by a function y = ax ² + bx + c, and when measuring the surface shape, after setting the probe needle pressure y ₁ , the measurement is started, the value of c is automatically read, and x becomes y ₁ = a x ₁ determined from the function may be adapted to control the current flowing to output x ₁ to the coil of the needle pressure generator.

  In the calibration of the relationship between the current and force flowing through the coil of the needle pressure generator, the force at the probe is calculated from the acceleration measured at the tip of the probe, but depending on the wear and contact conditions of the fulcrum part, friction at the fulcrum The power may not be negligible. In this case, since the force calculated by the above method includes a force due to dynamic friction at the fulcrum, the force due to the original coil current is not correctly calculated. Therefore, the correct relationship between the force y and the coil current x cannot be obtained, and the correct force cannot be generated.

  Therefore, the present invention compensates for frictional forces that may occur due to the wear state of the fulcrum portion, changes in contact state, etc., and generates a probe force, that is, a needle pressure with an accuracy of the order of 0.01 mgf. The object of the present invention is to provide a friction force correction method for a step gauge.

In order to achieve the above object, according to the first aspect of the present invention, a probe is attached to one end of a support that is swingably attached to a fulcrum, and the probe is positioned in the vertical direction adjacent to the one end. A magnetic core of a displacement sensor that detects displacement is attached, and a magnetic core of a needle pressure generator that applies needle pressure to the probe is attached to the other end of the support, and the surface shape of the sample captured by the probe is supported. In the friction force correction method of the stylus type step gauge that measures with a displacement sensor by the rotational movement around the fulcrum of
Measure the acceleration when lowering the probe by operating the needle pressure generator to determine the force when descending,
Probe is determined to force at elevated by measuring the acceleration at the time of rising bounce at the bottom stopper chromatography provided at the tip vicinity of the supporting member of the rod-like body for supporting the probe,
When the surface shape is actually measured, the current flowing through the needle pressure generator is controlled so that a force that is half the sum of the downward force and the upward force is applied to the probe.

In the method according to the first aspect of the present invention, the current x and the force y flowing in the coil of the needle pressure generator are obtained by using a force that is half of the sum of the descending force and the ascending force obtained by measurement. A current x flowing through the coil of the needle pressure generator corresponding to the force set using the relational expression y = ax ² + bx + c is calculated.

According to the second aspect of the present invention, a probe is attached to one end of a support that is swingably attached to a fulcrum, and a magnetic body of a displacement sensor that detects a vertical displacement of the probe adjacent to the one end. A magnetic core of a needle pressure generator that applies needle pressure to the probe is attached to the other end of the support, and the surface shape of the sample captured by the probe is measured by a rotational motion around the support fulcrum. In the friction force correction method of the stylus type step gauge measured with
Generate a force to lower the probe by the coil current of the needle pressure generator,
Measure the acceleration when lowering the probe to find the force when descending,
Probe is determined to force at elevated by measuring the acceleration at the time of rising bounce at the bottom stopper chromatography provided at the tip vicinity of the supporting member of the rod-like body for supporting the probe,
When actually measuring the surface shape, subtract the half of the difference between the downward force and the upward force from the current flowing through the needle pressure generator, Seeking a correct relationship with such forces,
The coil current corresponding to the force to be set is calculated from the relationship.

  In the first and second inventions of the present invention, since only the force due to the original coil current can be detected, excluding the force caused by the friction at the fulcrum portion, the current and force flowing through the coil of the needle pressure generator The correct relationship between the two is obtained, so that the correct amount of force can be generated on the probe. As a result, the influence of the dynamic friction force and static friction force generated at the fulcrum portion is removed, and the surface shape can be measured with a small force up to about 0.01 mgf.

  In addition, even if the fulcrum part wears and the frictional force there increases, the original force excluding the frictional force can be measured, and the original force can be output when measuring the surface shape, so the life of the fulcrum part is increased. Will be able to.

  In the second aspect of the present invention, since the force resulting from the friction at the fulcrum can be measured, it can be determined whether the fulcrum portion has reached the end of its life.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 7, 8 and 9 of the accompanying drawings. In addition, as a stylus type level difference meter, the thing of the structure shown previously in FIGS. 1-6 is used.

  FIG. 7 shows how the position z of the probe tip changes with time after the current flowing through the coil of the needle pressure generator is changed from 0 to 24.8 mA. The probe stopped at the upper stopper is lowered to the position of the lower stopper by the force generated by the current flowing through the coil of the needle pressure generating device, looks back there, and then vibrates. Usually, z is second-order differentiated with respect to time at the position A in FIG. 4 to obtain acceleration and calculate force, but the value may include force due to friction at the fulcrum. Since the measurement target range of z in this sensor head is from −0.15 mm to +0.15 mm, acceleration and force are obtained within the range.

  In FIGS. 7A and 7C, the frictional force works upward (z is a positive direction), and in B works downward (z is a negative direction). Therefore, if the force measured at B is FB and the force at C is FC, (FB + FC) / 2 is the original force due to the coil current, and (FC−FB) / 2 is caused by friction at the fulcrum. It becomes the magnitude of power. The frictional force does not necessarily depend on the speed, but since the probe speeds at B and C are approximately the same, it is better to handle the measured values at B and C. The drag due to air resistance can also be removed.

  In the example shown in FIG. 7, the force obtained from B was −0.1048 mgf, and C was −0.0762 mgf. From these, the force due to the original coil current is [(−0.1048) + (− 0.0762)] / 2 = −0.0905 mgf, and the magnitude of the frictional force is [ (−0.0762) − (− 0.1048)] / 2 = 0.0143 mgf. The force obtained from A is the same as the value at C.

Therefore, from the measurement result of the force at A, an attempt is made to obtain the relationship y = ax ² + bx + c (a is negative, and b and c are positive constants) as shown in FIG. The value of c in the relational expression is about 0.0143 mgf larger than the original value. Since the sign of the downward force is negative and the absolute value of the force measured at A is smaller than the original value, y shifts in the positive direction in the above relational expression and shifts to the larger value of c. In FIG. 8, the original correct relationship is indicated by a solid line, and the incorrect relationship due to the influence of friction at the fulcrum is indicated by a dotted line.

  Using this erroneous relational expression, for example, when it is desired to measure the surface shape of the sample with the force y1, x2 is output where the current x1 should be output as shown in FIG. Therefore, the absolute value of the force due to the coil current is larger than that of y1. In the above example, the absolute value of the force due to the coil current is increased by 0.0143 mgf. In FIG. 7A, the dotted line relationship in FIG. 8 holds, but the relationship does not naturally hold when measuring an arbitrary surface shape. Therefore, the surface shape cannot be measured with a correct force. Measurement of a soft sample requires measurement at 0.05 mgf or 0.03 mgf, and the error c in the above relational expression cannot be ignored.

(FB + FC) / 2 is the original force due to the coil current. Using these measurement results, a relational expression y = ax ² + bx + c between the coil current y and the force x is obtained. It is possible to output correctly with an accuracy of 0.01 mgf. As a result, the surface profile can be measured with a very small force as this kind of step gauge of about 0.01 mgf, and measurement with less damage on a softer sample is possible. The basis for this will be described below.

An example in which the force resulting from the frictional force at the fulcrum is measured is shown in FIG. In this example, the probe is repeatedly moved up and down, and the frictional force changes due to the wear of the fulcrum and the change of the contact state. The speed of the probe tip | dz / dt | is 3 to 6 × 10 ⁻⁴ m / s and about 6 × 10 ⁻³ m / s. The frictional force at 6 × 10 ⁻³ m / s (indicated by ● in FIG. 9) is the force at B and C after the probe is lowered from the upper stopper to the lower stopper as shown in FIG. It is a value calculated from

When the center of gravity of the movable part on the fulcrum is below the fulcrum, if the force that lowers the probe is generated by the coil current of the needle pressure generator and the movable part is balanced on the fulcrum, the movable part will vibrate as a real pendulum . That is, in FIG. 7, when z is positive, force acts in the negative direction, and when z is negative, force acts in the positive direction, and the probe tip position z oscillates around z = 0. The amplitude is attenuated by friction and air resistance at the fulcrum and gradually decreases. FIG. 9 shows the results with squares when | dz / dt | is 3 to 6 × 10 ⁻⁴ m / s when the amplitude decreases and z = 0 is crossed. As described above, the value is half the difference in force between when the probe is raised and when it is lowered. At this time, there was a measurement error, and the upper limit of the measured frictional force was indicated by ■. It takes one minute or more from the state of FIG. 7 to reach such a value of | dz / dt |. The amplitude at that time is about 200 μm. The vibration period can be changed by adjusting the position and mass of the balance weight attached to the movable part on the fulcrum.

When the relative speed between the probe and the sample at the time of actual surface shape measurement is about 1 × 10 ⁻⁴ m / s, the angle of the probe tip is about 60 degrees. The speed to do is about 1 × 10 ⁻⁴ m / s at the fastest. 9 corresponds to that shown in FIG. 9 and, therefore, it can be seen from FIG. 9 that the force resulting from the friction of the fulcrum at the time of measuring the surface shape is as small as 0.005 mgf or less. Therefore, it can be said that the surface shape measurement at about 0.01 mgf is possible.

  When measuring the relationship between the coil current and the force, measurement at B and C in FIG. However, in such measurement, the frictional force may be as large as 0.015 mgf as indicated by ● in FIG. The physical meaning of the difference in frictional force due to the difference | dz / dt | is unclear. In the experiment shown in FIG. 9, the static frictional force was sufficiently small, 0.01 mgf or less.

In order to obtain the relationship between the coil current and force of the needle pressure generator in a short time, the frictional force is measured with a large value such as a speed | dz / dt | of about 6 × 10 ⁻³ m / s, and the friction By subtracting the force to obtain the correct relationship between the coil current and the force, and calculating and outputting the coil current corresponding to the force to be set from the relationship, the correct force can be generated and the relative speed between the probe and the sample is 1 In the surface shape measurement of about × 10 ⁻⁴ m / s, even if | dz / dt | is large, it is about 1 × 10 ⁻⁴ m / s. At that time, the influence of the dynamic friction force generated at the fulcrum is at the probe position. Therefore, the surface shape can be measured with a small force up to about 0.01 mgf.

 By the way, in the illustrated embodiment, the first support member has been described based on an apparatus having a structure in which the first support member is supported at two points. can do. In addition, the present invention can be equally applied to a stylus type surface shape measuring instrument in which the positional relationship between the measuring element of the displacement sensor provided at both ends of the first support member and the core of the needle pressure generator is reversed.

The schematic of the structure of the stylus type surface shape measuring device which is implementing this invention. The schematic diagram which looked at the principal part of the stylus type surface shape measuring instrument in FIG. 1 from the bottom. The expanded partial sectional view which shows the structure of the holder part of the stylus type surface shape measuring device in FIG. The expanded partial sectional view along the AB line which shows the structure of the holder part of the stylus type surface shape measuring device in FIG. The expanded sectional view which shows the structure of the fulcrum part of the stylus type surface shape measuring device in FIG. The schematic perspective view which shows the structure which incorporated the stylus type surface shape measuring device in the frame. The graph which shows how the position z of a probe tip changes with time when the electric current sent through the coil of a needle pressure generator is changed from 0 to 24.8 mA. The graph which shows the relationship between the electric current sent through the coil of a needle pressure generator, and force. A measurement example showing the relationship between the number of times the probe is moved up and down and the frictional force.

Explanation of symbols

1: first support member 2: fulcrum needle mounting member 3: fulcrum needle 4: fulcrum receiving member 5: displacement sensor 6: measuring element or core 7: coil 8: needle pressure generator 9: needle pressure generator 8 Core 10: coil 11 of needle pressure generator 8: magnet 12: holder 13: longitudinal groove 14: second support member 15: probe 16: high permeability member 17: guide protrusion 18: plate-like member 19: Frame 19a: lower frame member

Claims (3)

A probe is attached to one end of a support that is swingably attached to a fulcrum, and a magnetic core of a displacement sensor that detects the vertical displacement of the probe is attached adjacent to this end, and the other end of the support is attached to the other end of the support. Frictional force of a stylus profilometer that attaches a magnetic core of a needle pressure generator that applies needle pressure to the probe and measures the surface shape of the sample captured by the probe with a displacement sensor by rotational movement around the fulcrum of the support In the correction method,
Measure the acceleration when lowering the probe by operating the needle pressure generator to determine the force when descending,
Probe is determined to force at elevated by measuring the acceleration at the time of rising bounce at the bottom stopper chromatography provided at the tip vicinity of the supporting member of the rod-like body for supporting the probe,
When actually measuring the surface shape, the current flowing through the needle pressure generator is controlled so that half of the sum of the descending force and the ascending force is applied to the probe. Frictional force correction method for needle type step gauge. A relational expression y = ax ² + bx + c (a, b, 2. The method of correcting a frictional force of a stylus step meter according to claim 1, wherein a current x flowing through a coil of a needle pressure generator corresponding to a force set using c is a constant. A probe is attached to one end of a support that is swingably attached to a fulcrum, and a magnetic core of a displacement sensor that detects the vertical displacement of the probe is attached adjacent to this end, and the other end of the support is attached to the other end of the support. Frictional force of a stylus profilometer that attaches a magnetic core of a needle pressure generator that applies needle pressure to the probe and measures the surface shape of the sample captured by the probe with a displacement sensor by rotational movement around the fulcrum of the support In the correction method,
Generate a force to lower the probe by the coil current of the needle pressure generator,
Measure the acceleration when lowering the probe to find the force when descending,
Probe is determined to force at elevated by measuring the acceleration at the time of rising bounce at the bottom stopper chromatography provided at the tip vicinity of the supporting member of the rod-like body for supporting the probe,
When actually measuring the surface shape, subtract the half of the difference between the downward force and the upward force from the current flowing through the needle pressure generator, Seeking a correct relationship with such forces,
A method for correcting the frictional force of a stylus type step gauge, wherein a coil current corresponding to a force to be set is calculated from the relationship.

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