JPH0338647Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention scans the irradiated light onto the surface of the object by swinging a mirror (reflector), and detects surface defects based on the light reflected from the surface of the object. The present invention relates to a surface defect measuring device for detecting surface defects.

[Conventional technology]

Conventionally, in such a surface defect measuring device,
A mirror is positioned between the light source and the surface of the object and is supported, and the inclination of the reflective surface (hereinafter referred to as
It is called the deflection angle. ), the irradiation light is scanned back and forth on the same straight line on the surface of the object to be examined, and the object is moved in a direction perpendicular to this scanning direction, thereby scanning the surface of the object at a predetermined position. An apparatus is known that measures defects by scanning an area with irradiation light. The mirror drive signal D that controls the deflection angle θ of the mirror in such a device has a triangular waveform as shown in FIG. 2b, and the amplitude D _A corresponds to the length of one scanning line.
The period D _T corresponds to the scanning time of one round trip. Therefore, the zero level of signal D corresponds to the center position of the scanning width, and the peak corresponds to both end positions of the scanning width, and the phase of signal D corresponds to the scanning position of the irradiation light (more precisely, the target scanning position). Therefore, as shown in Fig. 2d, if reflected light (hereinafter referred to as measurement data) is captured based on the timing signal TP at predetermined intervals synchronized with signal D, it can be made to correspond to the scanning position. measurement data can be obtained. Note that the period _T1 shown in FIG. 2d is the time required to reverse the scanning direction at both ends of the scanning width and to move the subject one pitch, and _T2 is the time corresponding to the effective scanning width.

[Problem that the invention attempts to solve]

However, the deflection angle θ of the mirror driven and controlled by the above signal D does not follow the signal D due to friction and inertia of the sliding part of the mirror drive system, and as shown in Fig. 2c. As shown by the solid line in the figure, with respect to the target deflection angle shown by the dashed line in the figure,
There is a delay of T ₃ hours when scanning in one direction, either round trip. Therefore, if measurement data is captured at the same timing based on the mirror drive signal D,
There will be a shift in the scanning position between the forward and reverse scanning directions, and if one of the scanning directions is used as a reference, the measurement data for scanning in the reverse direction will contain an error in the scanning position. There was a drawback. Incidentally, when actually measured, the delay time _T3 was 0.78 msec, and the positional deviation on the scanning plane was 1 mm.

The purpose of this invention is to control the mirror deflection angle regardless of whether or not there is a delay in controlling the mirror deflection angle due to the interaction of mirror deflection directions.
It is an object of the present invention to provide a surface defect measuring device that improves the precision of the positional relationship between the measured position on the surface of an object and measured data.

[Means for solving problems]

In the present invention, a half mirror that reflects part of the irradiated light is arranged between the mirror and the surface of the subject, and two light receiving elements that receive the reflected light from the half mirror are arranged perpendicular to the scanning direction of the reflected light. The two light-receiving elements are placed adjacent to each other symmetrically with respect to the reference line so that the reflected light when the mirror is positioned at the center of the mirror deflection angle passes through the reference line, and the light-receiving signals output from these two light-receiving elements are compared. A scanning center point detector is provided that outputs a scanning center point detection signal when the signal levels match, and scanning of a measurement data string that is divided and stored for each scanning line is performed based on this scanning center point detection signal. The characteristic configuration is to correct the center point position.

[Effect]

According to the present invention having such a configuration, the scanning center point of the actual irradiation light is detected, and based on this, the measurement point position of the measurement data string corresponding to one scanning line is corrected. It is possible to improve the positional accuracy of measurement data by eliminating the delay in control of the deflection angle due to differences in the deflection directions of the mirrors.

〔Example〕

Hereinafter, the present invention will be explained based on an embodiment to which the present invention is applied.

FIG. 1 shows an overall configuration diagram of an embodiment of the present invention. As shown in FIG. 1, light 2 emitted from a light source 1 such as a laser oscillator is irradiated onto the surface of a subject 4 via the reflective surface of a mirror 3, and the reflected light 5 is incident on a light receiving element 6. It is becoming more and more like this. The mirror 3 is attached to a rotating shaft rotated by a mirror drive device 7, and its rotation is controlled to a deflection angle θ according to the value of the mirror drive signal D, so that the irradiation light is directed at the same direction on the surface of the subject 4. It is designed to scan along a line. The subject 4 is moved by a subject driving device 8 in a direction perpendicular to the scanning direction. The reflected light 5 incident on the light-receiving element 6 is converted into electrical quantity measurement data, further converted into a digital signal by an A/D converter 9, and then taken into a memory 10.

The mirror drive signal generator 11 counts the clock pulses CP shown in FIG. 2a outputted from the clock pulse generator 12, and performs addition/subtraction counting in order to form a triangular wave mirror drive signal D shown in FIG. 2b. A D/A converter converts the digital output of this adder/subtracter into analog, and a filter that shapes the waveform of the output of this D/A converter. Note that the zero level of the mirror drive signal D corresponds to the center of the scanning width, and its amplitude D _A corresponds to the scanning width. This mirror drive signal D is input to the mirror drive device 7.

The timing signal generator 13 is formed by including a frequency divider, etc., and receives an input clock pulse.
Based on the CP, n measurement points (for example,
As shown in FIG. 2d, a measurement data acquisition timing signal TP consisting of n pulses is generated and outputted in synchronization with the scanning position of _P1 to _P0 . Also, this timing signal TP
Fig. 2 e
A subject drive timing signal TW as shown in FIG. 1 is generated and output to the subject driving device 8. As a result, the subject 4 is moved by a predetermined pitch in a direction perpendicular to the scanning direction by the mirror 3.

Further, a half mirror 14 is provided in the optical path of the irradiated light reflected by the mirror 3, which transmits most of the irradiated light and reflects a part of the irradiated light. The reflected light reflected by this half mirror 14 is made to be incident on a light receiving element 15 formed by two light receiving elements 15A and 15B arranged adjacent to each other. As shown in FIG. 4, the light-receiving surfaces of the light-receiving elements 15A and 15B are arranged symmetrically adjacent to a reference line perpendicular to the scanning direction of the irradiation light (arrow 20 in the figure), and the mirror deflection angle θ=0°. The reflected light of the irradiation light (that is, the light that irradiates the center position of the set scanning width) is placed on the reference line. Then, each light receiving element 15A, 15B receives a light receiving signal (ψ _A , ψ _B ) at a level corresponding to the amount of light received.
It is designed to be output to a scanning center position detector 16. That is, when the reflected light of the irradiation light is scanned in the direction from position a to positions b and c in FIG. 4, the light reception signals output from the light receiving elements 15A and 15B are as shown in FIGS. 5a and 5b. The levels of ψ _A and ψ _B are changed. The scanning center point detector 16 is located at position b in FIG.
In other words, when the irradiation light is positioned at the center point of the scanning width, ψ _A = ψ _B , so this is detected and the scanning center point position detection signal Pc of the pulse signal shown in Figure 5c is stored in the memory. It is designed to output to 10. The memory 10 divides the captured measurement data into measurement data strings corresponding to one scanning line.
For example, the data is stored in consecutive addresses, and when the scanning center point detection signal Pc is input, the detection signal Pc is stored in another bit at the same address as the address of the measurement data that is input and stored at the same time. It's becoming like that. In this way,
The measurement data string for each scanning line is stored together with scanning center point position information. Then, the determination device 17 reads out the measurement data in the memory 10 as appropriate, and determines the presence or absence of a defect based on the measurement data of each measurement point whose position has been corrected in correspondence with the scanning center point as a reference. ing.

Regarding the operation of the embodiment configured in this way,
This will be explained next.

First, the inclination of the mirror 3 is initially set so that the irradiation light irradiates the center position of the desired scanning width on the surface of the subject 4 (point P ₀ in FIG. 3). When the device is started in this state, the deflection angle θ of the mirror 3 is increased at a constant rate in proportion to the mirror drive signal D.
The irradiation light is scanned from the point P ₀ shown in FIG. 3 to the left in the same figure. When the scanning position reaches the point corresponding to measurement point _P1 , the object drive timing signal TW is output.
As a result, the subject 4 is moved upward by a predetermined amount in FIG. The direction of deflection of the mirror 3 is reversed within a fixed time T ₁ determined corresponding to the time required for this transfer and the time for the mirror 3 to be reversed.
At this time, the actual deflection angle θ of the mirror 3 is determined by the drive signal D in the reverse direction, as shown in FIG. 2c.
(also indicated by the dashed line in the figure) has a time delay of T ₃ hours. Therefore, the center of the measurement data string consisting of n measurement data sequentially taken in by the timing signal TP is the mirror 3.
In the forward and reverse directions, the center position of the scanning width P ₀
It has become something out of place.

The measurement data string imported in this way is
It is stored in the memory 10 in association with the scanning center point detection signal Pc output from the scanning center point detector 16. In addition, the scanning center point detection signal is sent along with the measurement data to the address that stores the measurement data of the measurement point that is input when the detection signal Pc is input.
Remember PC. The determination device 17 reads measurement data from the memory 10 in units of measurement data strings, sets the measurement point containing the scanning center point detection signal Pc as the scanning center point, and determines the positions of other measurement points in correspondence with this. , determine the presence or absence of defects.

[Effect of idea]

As explained above, according to the present invention, it is possible to correct the positional deviation of the measurement data due to the delay in controlling the deflection angle due to the difference in the deflection direction of the mirror, and it is possible to improve the positional accuracy of the measurement data. .

[Brief explanation of the drawing]

Figure 1 is an overall configuration diagram of one embodiment of the present invention, Figure 2
The figure is an operation waveform diagram of each part of the example, Figure 3 is a measurement point array diagram for explaining the operation of the example, Figure 4 is an explanatory diagram of the configuration of the light receiving element of the example, and Figure 5 is a diagram showing the structure of the light receiving element. FIG. 3 is an operation waveform diagram of the scanning center point detector. DESCRIPTION OF SYMBOLS 1... Light source, 3... Mirror, 4... Subject, 7... Mirror drive device, 10... Memory, 11... Mirror drive signal generator, 13... Timing signal generator, 14...
Half mirror, 15... Light receiving element, 16... Scanning center point detector.

Claims (1)

[Scope of utility model registration request] A mirror is pivotally supported at a position where the light emitted from the light source is reflected and irradiated onto the surface of the subject, and the mirror is swung around the axis in accordance with an input drive signal.
a mirror drive device that reciprocally scans the irradiated light on a straight line located on the surface of the object; and a drive signal having a vibration waveform that has a value proportional to the deflection angle of the mirror and causes the mirror to swing in a constant angular width and at a constant cycle. a mirror drive signal generator that generates a signal and outputs it to the mirror drive device; a timing signal generator that generates a timing signal for capturing measurement data at predetermined intervals in synchronization with the drive signal; The measurement data of the reflected light from the surface of the object to be inspected is made to correspond to the scanning position of the irradiation light determined from the timing signal and the drive signal,
A surface defect measuring device comprising a memory that stores measurement data as a row of measurement data divided for each scanning line; The half mirrors are arranged adjacent to each other in line symmetry with respect to a reference line perpendicular to the scanning direction of the reflected light of the half mirror, and such that the reflected light passes through the reference line when the mirror is positioned at the center of the deflection angle. two light receiving elements that receive the reflected light; a scanning center point detector that compares the light reception signals output from the two light receiving elements and outputs a scanning center point detection signal when the signal levels match; A surface defect measuring device comprising: a correction means for correcting a scanning center point position of a measurement data string stored separately for each scanning line based on the scanning center point detection signal.