JPH037767Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention] This invention scans the irradiated light on 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.

[Background of the idea]

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. 4a, 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 and the scanning position of the irradiation light (more precisely, the target scanning position) are Therefore, as shown in Fig. 4c, if the reflected light (hereinafter referred to as measurement data) is captured based on the timing signal TP at a predetermined interval synchronized with the signal D, it will correspond to the scanning position. measurement data can be obtained. Note that the period T ₁ shown in FIG. 4c is the time required to reverse the scanning direction at both ends of the scanning width and move the subject one pitch, _and
is the time corresponding to the effective scanning width.

However, the deflection angle θ of the mirror driven and controlled by the signal D does not follow the signal D due to friction and inertia of the sliding parts of the mirror drive system, and as shown in FIG. The target deflection angle is delayed as shown by the solid line in the figure with respect to the target deflection angle shown by the dotted line in the figure. 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 backward 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 above-mentioned delay was 0.78 msec in time, and the positional deviation in the scanning plane was 1 mm.

[Purpose of invention]

An object of the present invention is to provide a surface defect measuring device that eliminates control delays when switching the scanning direction of a mirror and improves the positional accuracy of measurement data.

[Summary of the idea]

The present invention detects the reversal position of the deflection direction of the mirror drive signal in synchronization with the period corresponding to one of the deflection directions of the mirror drive signal, and synchronizes it with the period corresponding to one of the deflection directions. By subtracting and correcting the drive signal by a certain amount, the control delay of the deflection angle due to the difference in the deflection direction of the mirror is removed, and the position accuracy of the measurement data is improved.

[Example of idea]

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

FIG. 1A shows an overall configuration diagram of an embodiment, and FIG. 1B shows a detailed configuration diagram of main parts. As shown in Figure 1A,
Light 2 emitted from a light source 1 consisting of a laser oscillator or the like is irradiated onto the surface of a subject 4 via a reflective surface of a mirror 3, and the reflected light 5 is made incident on a light receiving element 6. 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/judgment device 10 including a memory. It's getting old.

As shown in FIG. 1B, the mirror drive signal generator 11 includes a basic signal generator 21, a correction amount setter 22,
It is formed to include an adder 23, a D/A converter 24, and a filter 25. The basic signal generator 21 is
It consists of an addition/subtraction counter that counts the clock pulses CP shown in FIG. 2a outputted from the clock pulse generator 12 and generates the triangular wave-like fundamental signal _D0 shown in FIG. 2b. The zero level of the basic signal D ₀ corresponds to the center of the scanning width, and its amplitude D _A corresponds to the scanning width. Further, the basic signal generator 21 detects the inflection point of the triangular wave and outputs a correction command signal synchronized with the phase section of the negative (or positive) slope. The correction amount setter 22 synchronizes with the input correction command signal,
A constant correction amount Δd shown in FIG. 2C is output. The basic signal D ₀ is subtracted and corrected by the correction amount Δd in the adder 23, converted into an analog signal by the D/A converter 24, and then waveform-shaped by the filter 25 to form the waveform shown in FIG. 2d. The mirror drive signal D is outputted 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,
Measurement data acquisition timing signal consisting of n pulses in synchronization with the scanning position of P ₁ to Pn)
It is designed to generate and output TP. Also,
In synchronization with the falling edge of the n-th pulse of the timing signal TP, a subject drive timing signal TW as shown in FIG. 2g is generated and output.

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.
Since the mirror drive signal D in the reverse direction has been corrected by the correction amount Δd, the control delay of the mirror drive system is compensated, and the deflection angle θ of the mirror 3 is as shown in Fig. 2e.
As shown in , it is similar to the basic signal D ₀ and is synchronized. Therefore, after T ₁ hour has elapsed, the scanning position of the irradiation light is at measurement point P ₁ , and the measurement data acquisition timing signal output at the same time
The data is captured and stored in the memory/judgment device 10 by the TP as measurement data of the measurement point _P1 . Subsequently, the measurement data corresponding to the measurement points P ₂ to Pn are stored in accordance with the timing signal TP that is sequentially output.

[Effect of idea]

As explained above, according to the present invention, the drive signal proportional to the amount of deflection of the mirror is subtracted and corrected by a certain amount in synchronization with the switching of the mirror scanning direction. You will be swayed sharply in that direction. This makes it possible to eliminate control delays when switching the scanning direction of the mirror due to friction and inertia of the sliding parts of the mirror drive system, which has the effect of improving the position accuracy of measurement data. be.

[Brief explanation of drawings]

FIG. 1A is an overall configuration diagram of an embodiment of the present invention, FIG. 1B is a detailed configuration diagram of its main parts, FIG. FIG. 4 is an operational waveform diagram of each part of a conventional example for explaining the background of the present invention. 1... Light source, 3... Mirror, 4... Subject, 7
...Mirror drive device, 10...Memory/determination device, 11...Mirror drive signal generator, 13...Timing signal generator, 21...Basic signal generator,
22...Correction amount setter, 23...Adder.

Claims (1)

[Scope of utility model registration request] A mirror is pivotally supported so as to reflect the light emitted from the light source and irradiate it onto the surface of the object to be examined, and the deflection angle of the mirror is controlled to scan the irradiated light on the same straight line located on the surface of the object to be examined. a mirror drive device; a mirror drive signal generator that generates a drive signal with a vibration waveform having a value proportional to the deflection angle of the mirror and swings the mirror in a constant angular width and at a constant cycle; A timing signal generator that generates a timing signal for capturing measurement data at intervals, and a memory that stores measurement data captured based on the timing signal in correspondence with a scanning position of irradiation light determined by the timing signal and the drive signal. In the surface defect measuring device, the correction means detects a reversal position of the deflection direction of the drive signal and subtracts and corrects the drive signal by a certain amount in synchronization with a period corresponding to one of the deflection directions. A surface defect measuring device characterized by being provided with.