SU1509694A1 - Device for detecting defects on the surface of objects having round shape - Google Patents

Abstract

The invention relates to instrumentation technology and can be used to detect defects on the surface of circular objects, such as semiconductor wafers, optical lenses, and the like. The purpose of the invention is to improve the accuracy of the registration of defects by increasing the reliability of determining the edges of the object being monitored. To do this, in a device containing a light source, a scanning unit, a photodetector, an object edge detection unit, an output connected to the first key input connected to a defect counter, a photodetector connected to the second key input, and the object edge detecting unit contains a phase shifter 90 °, the first and a second absolute value selection unit, respectively, connected to the first and second inputs of the comparator, the output of which is the output of the edge determining unit. The first absolute value selection unit of the signal through the phase shifter is connected to the vertical scanning output of the scanning unit, to the horizontal output of which a second absolute absolute signal separation unit is connected. 1 il.

Description

The invention relates to instrumentation technology and can be used to detect defects on the surface of circular objects, such as semiconductor wafers, optical lenses, and the like.

The purpose of the invention is to improve the accuracy of registration of defects by increasing the reliability of the determination of the monitored object.

The drawing shows the block diagram of the device, 1 mA.

The device contains a source of 1 light, for example, a laser installed according to

the beam, scanning unit 2, a photodetector 3 placed above the object to be monitored 4, block 5 of determining the edge of the object, an output connected to the first input of the key 6 connected to the defect counter 7. The unit 5 of determining the edge of an object consists of a phase shifter 8 by 90 °, blocks 9 and 10 of selecting the absolute value of the signal, designed to determine the modulus of the variable electrical signal, and comparator II, you

the stroke of which is the output of block 5 of determining the edge of the object. Second

ate

ABOUT

;about

Od

from 4;

the input of the key 6 is connected to the photodetector 3, the input of the block 9 through the phase shifter 8 is connected to the first output (output To frame scan), the scanning unit 2, to the second output (output C horizontal), which is connected to the input of the block 10, the outputs of blocks 9 and The 10 absolute magnitudes of the signal are connected respectively to the first and second inputs of the comparator 11,

The device works as follows.

The beam of light from source 1 is deflected by scanning unit 2 in two mutually perpendicular directions (in line and frame) and hits Object 4. The light scattered by defects is perceived by the photodetector 3, which converts it into an electrical signal. the input of the key 6 is fed to the counter 7 defects. The scanning unit 2 forms a square raster with the side of the square equal to the diameter of the object 4, and the object is inscribed in the raster.

Frame scanning is carried out in the sinusoidal order given by the frame scanning voltage.

to

(0., t

9694

jg 5 20 25

f (t) is a function of time.

The deviation of the beam from the center of the raster in the direction of the line, due to the voltage U., has the form

Y - | -f (t).

The flow 5 of determining the edge of the object works as follows

From the output of the frame sweep, the signal U | j is fed to the phase shifter 8 and the block 9 of the absolute value c

and.

signal, after which it converts

and;, and.

For a

positive values and. “J - n-costo t. The specified signal is fed to the first input of the comparator. 1 1, From the output of the horizontal scan, the signal Up is fed to the block 10 of the absolute value of the signal and

converted to u values,

and:

:and;

For positive j (.Up A f (t). The specified signal is fed to the second input of comparator 11, since at time t the signals are U Af (), ir, A-cosco tcpae, TO A f (tcppg) A coso t pjjg. The position of the beam on the object at this time point is determined by the corresponding signals u and Ujl and is determined from the deviation of the beam from the center of the raster:

in frame direction x in line direction y

-2 ctepa - | -CO brc.

 where A is the signal amplitude;

frame rate;

current time When choosing a coordinate system with the center coinciding with the center of the raster, the deviation of the beam from the center of the raster in the frame direction, caused by the voltage UM, has the form

X -T- SincO t,

where a is the size of the raster side (diameter of the object being monitored) Line scanning is carried out according to any periodic law set by the horizontal scanning voltage

and A.f (t),

where A is the signal amplitude, is equal to

frame voltage amplitude;

Consequently, the coordinates of the beam at the time of the operation of the comparator 11 are

cosQ tcpoe

X - sino3Rtcpo (6 ..

The resulting system of equations is a parametric record of a circle and characterizes all the positions of the beam on the object at which the comparator is triggered. Moreover, this circle is inscribed in a square raster and corresponds to the edges of the object being monitored. The device works in the same way if the first output of the scanning unit corresponds to a line scan, and the second to a frame one,

From the output of the comparator 11 to the input

Key 6 receives a signal that opens the key when the scanning beam is inside the circle (within the object) and the closing key is npi {1505 15096946

walking the beam out of it (on the Carrier nor connected to the first key entry,

the output of which is connected to the register is jTopy, different

five

surface on which the object is located). As a result, the recorder 7 (defect counter) receives signals detected by the photoreceiver when the beam is located only inside a circular controlled area, i.e. in fact at the facility itself.

by that

that, in order to improve the registration accuracy by increasing the reliability of determining the edge of the object being monitored, the photodetector is connected to the second key input, the definition unit

The device allows you to increase the point of the edge contains the phase shifter by 90

defect detection by increasing the reliability of determining the edge of an object and eliminating false triggering if there are defects outside the object on the bearing surface, since the counter of defects 7 receives only signals received from the object being monitored, and signals of surface delays ;, on which the object is placed are excluded from consideration.

Claims (1)

Invention Formula A device for detecting defects on the surface of circular objects, containing a light source, a scanning unit, a photodetector, a key, a recorder and an object edge detection unit, with its output the output of which is connected to the register- copying, different by that that, in order to improve the registration accuracy by increasing the reliability of determining the edge of the object being monitored, the photodetector is connected to the second key input, the definition unit the first and second blocks of absolute magnitude of the signal and the comparator whose output is the output of the edge determining unit, with the input of the first The absolute value block of the signal is connected via the phase shifter to the first output of the scanning unit, to the second output of which the input of the second block of the absolute signal magnitude is connected, while the output of the first and second blocks of the absolute magnitude of the signal is connected to the first and second inputs of the comparator, and the scan is implemented with the ability sinusoidal from the skairov time, neither in the coordinate corresponding to its first output, and any periodic scanning in the coordinate corresponding to its second output.