Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
1999-12-14
2001-11-13
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
C033S551000, C033S555000, C033S558000, C033S558400, C033S561000
Reexamination Certificate
active
06314800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micro-geometry measuring device for precisely measuring surface geometry of LSI, semiconductor wafers, or the like.
2. Description of Related Art
Special devices are used for precisely measuring surface geometry of semiconductor wafers, etc. Published Japanese translation of PCT international publication for patent applications No. Hei 8-502357 and U.S. Pat. No. 5,309,755 are known as conventional examples of such device.
The conventional example has an arm rotatably supported by a frame through a flexural pivot (elastic hinge), an end of the arm having a stylus made of a diamond tip and the other end of the arm having a movable plate.
The movable vane (plate) moves between two parallel plates fixed to a base, the movable plate forming a bridge-electrode together with the parallel plates to be a pair of capacitor. When the arm pivotally moves, equilibrium of the bridge is lost and displacement of an end of the stylus is measured. Since the movable plate moves between the two parallel plates, the movable plate receives resistance of air and appropriate damping effect can be expected.
A lever arm is provided to a central portion of the arm. A tip provided at an end of the lever arm is controlled by a magnetic field of a biasing mechanism to keep a constant measuring force at a pointed end of a stylus. The control is conducted by feedback of displacement amount of stylus end.
Stabilization of the measuring force will be described below.
Without the feedback control by the biasing mechanism, since the arm is rotatably supported by the elastic hinge, the measuring force fluctuates in accordance with rotation angle of the arm as shown in solid line p in a graph of FIG.
7
. In other words, the measuring force differs according to a position of the stylus or a magnitude of irregularity of a workpiece, which causes error in detection result of surface position of the workpiece, and, when angle fluctuation is large, the measuring force can be so excessive as to effect bad influence on the surface of the workpiece.
Accordingly, the biasing mechanism is provided to the lever arm and magnetic force is applied therefrom, thereby conducting correction corresponding to measuring force fluctuating in accordance with the angle. If the correction results in a characteristic shown in dotted line Q in the graph of
FIG. 7
, the measuring force can be largely reduced from f
1
to f
2
at the arm rotation angle shown by D in the graph.
Incidentally, for correcting measuring force by the biasing mechanism of the above-described conventional example, the displacement amount of the stylus end is detected, which is fed back to magnetic intensity at the distal end of the lever arm.
However, in the conventional example, the measuring force working onto the stylus and the workpiece is not directly detected for control, but the position of the movable plate is detected for indirect control based on the position value. On account of the indirect control, the measuring force cannot be controlled (stabilized) precisely enough for the stylus to accurately follow the irregularity on the surface of the workpiece.
On the other hand, the measuring force itself may be increased for the stylus to accurately follow the surface of the workpiece. However, micro-geometry on the workpiece surface is likely to be damaged by the stylus in the above arrangement.
Further, since the measuring force is controlled by the distal end of the lever arm, mechanical rigidity between the stylus and the distal end of the lever arm is small in the conventional example, so that responsivity thereof cannot be improved.
Accordingly, the measuring force working between the stylus and the workpiece is fifty microgram-force (&mgr;gf) at the minimum, and measurement is difficult at a lower measuring force or with a faster arm movement.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a micro-geometry measuring device capable of reducing measuring force for avoiding damage on the micro-geometry of the workpiece surface and measuring at a high speed.
For attaining the above object, a vibrating stylus is used for a stylus mechanism having a stylus body, in which measuring force working between the vibrating stylus and the workpiece is directly measured.
More specifically, a micro-geometry measuring device according to the present invention includes: a pivotable arm; a stylus mechanism having a stylus body provided to the arm to be in contact with a workpiece; a measuring force adjusting mechanism for adjusting a measuring force working between the stylus body and the workpiece; a displacement sensor for detecting a position of the arm; and a measuring force controller for controlling the measuring force adjusting mechanism, the stylus mechanism including a holder provided to a part of the arm, the stylus body attached to the holder, a vibrator for resonantly vibrating the stylus body, and a detector for detecting vibration status to be changed when the stylus body touches the workpiece, and the measuring force controller conducting feedback control of the measuring force adjusting mechanism based on an output signal sent from the detector.
According to the present invention, the stylus body of the stylus mechanism abuts to the workpiece surface and the measurement is conducted while relatively moving along the surface.
When the stylus body relatively moves while following irregularity of the workpiece surface, the arm having the stylus body is pivotally moved. The position of the arm is detected by the displacement sensor and the displacement when the stylus body touches the workpiece, i.e. the surface position of the workpiece is measured.
The measuring force of the stylus body against the workpiece is adjusted by the measuring force adjusting mechanism. The measuring force adjusting mechanism is controlled by the measuring force controller for the stylus body to abut to the workpiece always at an appropriate measuring force.
In other words, when the vibrator of the stylus mechanism is driven, the stylus body resonantly vibrates at a predetermined vibration mode. When the stylus body abuts to the workpiece surface in the above condition, the vibration of the stylus body is restricted and the vibration change is detected by the detector.
Then, output signal from the detector is sent to the measuring force controller and a signal is sent to the measuring force adjusting mechanism for feedback control of the measuring force.
Since the stylus mechanism of the present invention is a vibrating stylus including the stylus body, the vibrator and the detector, the measuring force working between the stylus body and the workpiece can be directly detected. In other words, the stylus body is vibrated for contact detection by virtue of restriction of the vibration caused by the contact against to the workpiece, and the measuring force against the workpiece can be detected by the restriction of the vibration.
When the measuring force adjusting mechanism conducts feedback control based on the directly detected signal through the measuring force controller, measuring force fluctuation caused by the irregular surface of the workpiece can be set extremely low, thereby conducting accurate and high-speed measurement.
In the present invention, the stylus body of the stylus mechanism may be resonantly vibrated in an axial direction thereof, or alternatively, the stylus body may be flexurally vibrated (vibrating crosswise relative to the axis). However, the stylus body is preferably vibrated in the axial direction thereof.
Generally speaking, since the flexural natural frequency is lower than a natural frequency in the axial direction, the axially vibrating type of the stylus body has higher responsivity than the flexurally vibrating type, thereby accurately detecting the measuring force.
In the present invention, the stylus mechanism may preferably oppose the measuring force adjusting mechanism and the displacement sensor sandwiching the arm.
According t
Larkin Daniel S.
Mitutoyo Corporation
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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