JPH0521421B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention optically detects defects (microholes, chips, attached foreign matter, microprotrusions, etc.) on the surface of an object to be inspected that has polishing marks on the surface. Regarding surface inspection equipment,
More specifically, the present invention relates to a surface inspection device that can be applied to inspect surfaces with polishing marks, such as the surface of a magnetic disk substrate.

[Prior Art] Conventionally, a surface inspection device for inspecting the surface of a magnetic disk substrate (before or after surface coating treatment) irradiates a light beam almost perpendicularly to the surface of the object to be inspected. , scattering or diffracted light in a direction at an angle of 30 to 40 degrees with respect to the surface of the object to be inspected is incident on a photoelectric conversion element, and defects on the surface of the object to be inspected are detected based on the photoelectric conversion signal. It's summery.

[Problems to be Solved] With such conventional surface inspection equipment, defects of approximately 5 μm are the detection limit. If the detection sensitivity is increased to detect defects down to about 3 μm, the noise component in the photoelectric conversion signal will increase, leading to detection errors.

Furthermore, it was not possible to distinguish between convex defects such as adhered foreign matter and minute protrusions, and concave defects such as minute holes (pits), chips, and scratches.

[Object of the Invention] The specific invention and related invention in this patent application were made in view of the problems of the prior art, and the main purpose thereof is to solve the problems of the prior art. It is an object of the present invention to provide a surface inspection device which is suitable for surface defect inspection and is capable of detecting even smaller defects than conventional ones.

[Means for Solving the Problems] The surface inspection apparatus of the specific invention of this application for achieving the above object is characterized by detecting defects on the surface while scanning the surface of the object to be inspected with a light beam. A surface scanning device for detecting a surface, which includes a means for irradiating a surface with a light beam for scanning the surface, and a means for receiving diffracted light due to polishing marks on the surface as well as scattered light of the light beam due to foreign matter defects or convex defects on the surface. It is equipped with an optical system for inputting the scattered light to the photoelectric conversion element, and the angle at which the optical system receives the scattered light is set in the range of 0 degrees to 5 degrees in the direction perpendicular to the surface. be.

Furthermore, the surface inspection apparatus of the related invention is characterized in that, in addition to the optical system, a second optical system having a spatial filter is provided to detect concave defects as well.

[Function] FIG. 7 is an explanation of the relationship between the light receiving angle and the detection signal of the optical system for detecting foreign matter defects or convex defects in the magnetic disk substrate of the detection system 18 shown in FIGS. 1 and 2, which will be described later. It is a diagram.

From the characteristics shown in this figure, the angle at which the optical system 18 receives the scattered light is set in the range of 3 degrees or less, especially 1 degree or less in the direction perpendicular to the surface, even if there are polishing marks. It can be seen that it is possible to detect foreign objects and convex defects on the surface of the object to be inspected.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic perspective view showing the overall structure of an embodiment of a surface inspection apparatus according to the present invention. The surface inspection apparatus shown in this figure performs a surface inspection by scanning the surface of a disk-shaped object 12, such as a substrate of a magnetic disk, in a spiral manner with a laser beam. For the spiral scanning, a rotational movement mechanism 14 that rotates and moves the inspected object 12 in the radial direction (R direction) and a laser irradiation system 16 that irradiates the surface of the inspected object 12 with a laser beam are provided. ing. Further, a detection system 18 for detecting a convex defect or a foreign substance defect on the surface of the object to be inspected, and a detection system 20 for detecting a concave defect such as a microhole, a chip, or a scratch are provided.

The rotational movement mechanism 14 moves a moving table 30 in the radial direction (R direction) by a motor 32 via a ball screw, and a rotary spindle 34 rotatably supported by the moving table 30 is fixed to the moving table 30. It is configured to be rotated by a motor 36 via a timing belt 38. At the upper end of the spindle 34, there is an object 1 to be inspected.
2 is fixed horizontally. The rotating spindle 34 also includes a rotary encoder 40 for detecting its rotation angle.
are connected. In addition, R of the moving table 30
A linear encoder for detecting directional position is also provided, but not shown.

The laser irradiation system 16 includes a He-Ne laser oscillator 5
The laser beam emitted from the laser beam enters the elliptical expander 54 via the dichroic mirror 52 to form an elliptical laser beam, which is then passed through the lens 5.
6 and includes the normal to the inspected object 12
The configuration is such that an elliptical spot is formed by irradiating the surface of the object 12 to be inspected along a straight line path that makes an angle of approximately 20 degrees with respect to the normal line on the plane of the direction. Furthermore, slits 58 and 60 having elliptical openings are disposed between the lens 56 and the surface of the object to be inspected to prevent stray light.

This laser irradiation system 16 is stationary, and as the object 12 to be inspected moves in the R direction, the irradiation spot of the laser beam moves in the radial direction on the surface of the object to be inspected.
Since the object 12 to be inspected is moved and rotated at the same time, the surface of the object to be inspected is scanned in a spiral manner by the laser beam.

FIG. 2 is a schematic enlarged side view of the detection system 18.
As shown in this figure, the detection system 18 includes an optical system 72 for receiving scattered light due to a foreign defect or a convex defect on the surface of the object to be inspected, and the light received by this optical system 72 is incident on the detection system 18. A photomultiplier 74 serves as a photoelectric conversion element that outputs a photoelectric conversion signal.
It consists of

The optical system 72 receives only the scattered light from such foreign defects or convex defects, and receives stray light from sources other than the laser beam irradiation spot on the surface of the object to be inspected, and diffracted light from polishing marks and concave defects within the laser beam irradiation spot. In order to avoid receiving specularly reflected light, the surface of the object to be inspected is transmitted through the variable slit 76 and the condenser lens 78 from a direction forming a sufficiently small angle, for example, about 1 degree or less, to the surface of the object to be inspected. The optical image of the laser beam irradiation spot is formed on a pinhole 80 placed in front of the imaging surface of the photomultiplier 74. In addition, in order to limit the amount of light incident on the photomultiplier 74, an ND (Neutral Density) filter 82 is connected to the pinhole 80 and the photomultiplier 7.
It is located between 4 and 4.

This detection system 18 is stationary, but the optical system 72
The angle between the optical axis of the
It can be adjusted within a range of degrees. The adjustment mechanism for this purpose is omitted in the figure. This angle is adjusted to be smaller as the surface of the object to be inspected becomes rougher.
The detection sensitivity increases as this angle increases, but
Since the angle is easily affected by polishing marks, etc., the angle is adjusted to a sufficiently small angle of, for example, 1 degree or less when inspecting magnetic disk substrates, which are currently common. In this way, a photoelectric conversion signal of scattered light due to a foreign defect or a convex defect is obtained.

Figure 7a shows the angle (light reception angle on the horizontal axis) taken when facing the surface of a magnetic disk substrate (as the object to be inspected 12) that has polishing marks in the vertical direction and the scattering intensity (vertical light receiving angle). Figure c shows the relationship between the light receiving angle and the S/N ratio (vertical axis).

In the characteristic graph of (a), the policy (Gac)
is the detection signal (AC component) when polishing marks are detected
Polishing (Gbc) is the DC level signal (board itself) when polishing marks are detected.
It is. Particle DVB (6.4 μm) (S) is a characteristic of a detection signal when a standard particle of 6.4 μm is attached to a magnetic disk substrate as a measure against foreign matter or convex defects. Note that FIG. b explains the mutual relationship when these signals are observed on an oscilloscope.

As can be understood from these characteristics, within the adjustment range of 0 to 5 degrees, the acceptance angle is from 3 degrees to 0 degrees.
The characteristics are reversed over time, and the particle DVB (6.4 μm)
It can be seen that (S) is higher than the polish (Gac) signal. This means that in this range, the signal of foreign matter or convex defects is higher than that of polishing marks.

It can also be understood from this that foreign matter and convex defects can be sufficiently detected in the polishing marks of the magnetic disk substrate even if there are actual polishing marks, provided that the polishing marks are 1 degree or less. Moreover, as shown in Figure c, the S/N ratio is also good for the light receiving angle from 0 degrees to 5 degrees. Note that the characteristic value can be obtained even at the lower limit of the light receiving angle of 0 because the light is received not at a single central point but over an area.

In general, when there are polishing marks left on the surface of an inspected object such as a magnetic disk substrate or an optical disk medium whose surface has been polished to a highly polished state with high flatness, the diffracted light from there is Almost the same characteristics as shown in can be obtained. Therefore, as mentioned earlier, when inspecting magnetic disk substrates, etc., it is appropriate to increase the angle to 1 degree or less, and if the acceptance angle is set in this way, the influence of polishing marks will be reduced. I almost never get it.

However, as described above, the light receiving angle of the detection system 18 is determined by the relationship between the surface roughness of the object to be inspected and the detection sensitivity. As can be understood from the fact that the example in FIG. 7 is inverted from 3 degrees, it is almost certain that one angle within the range of 0 degrees to 5 degrees is more universally selected.

FIG. 3 is a schematic enlarged front view of the other detection system 20. With reference to this figure and FIG. 1, the detection system 20
Explain.

This detection system 20 includes a photomultiplier 90 as a photoelectric conversion element, and an optical system for receiving diffracted light due to a concave defect in a laser beam irradiation spot on the surface of an object to be inspected and making it incident on the photomultiplier 90. Consists of 92.

The light incident on the optical system 92 is converted into parallel light by a lens 94 whose optical axis substantially coincides with the optical axis of specular reflection of the laser beam irradiated from the surface of the object to be inspected. The components of this received light are specularly reflected light from the surface of the object to be inspected, specularly reflected light and diffracted light due to concave defects (pits, chips, scratches), and specularly reflected light and diffracted light due to polishing marks. Compared to such main components, the scattered light components due to foreign matter defects or convex defects are much smaller.

The incident light that has passed through the lens 94 is directed by a mirror 96 to a mirror 98 as parallel light.
However, a small mirror 100 provided between the mirrors 96 and 98 extracts the specularly reflected light component in the incident light. This specularly reflected light component is the lens 1
02 and pin photodiode 10
4 and is being monitored.

Here, the diffracted light due to the concave defect is generated centering on the specularly reflected light, and the diffraction pattern is a pattern perpendicular to the longitudinal direction of the concave defect. The intensity of the diffracted light decreases as it moves away from the specular optical axis. Detection system 9
2 is a photomultiplier 9 that converts the diffracted light due to the concave defect.
0 and detects the concave defect based on the photoelectric conversion signal. Therefore, in order to receive the diffracted light due to the concave defect as efficiently as possible, the optical axis of the lens 94 is aligned approximately with the optical axis of the specular reflection light. This means that they are consistent. Because of this relationship, the incident light includes a specularly reflected light component, so as described above, the small mirror 100
The specularly reflected light component is removed by

The incident light from which the specularly reflected light component has been removed as described above is reflected by the mirror 98 toward the perforated mirror 106 while remaining in a parallel beam state. A spatial filter 108 is arranged between the mirrors 98, 106. This spatial filter 108 is for removing a diffracted light component due to polishing marks on the surface of the object to be inspected from the incident light, and is constructed by plating a fine stripe pattern of chromium or the like on a glass plate, for example.

Here, diffraction due to polishing marks will be explained with reference to FIG. 4. A disk-shaped object to be inspected, such as a magnetic disk substrate, may be polished concentrically or linearly in one direction.

On the surface of the object to be inspected which has undergone concentric polishing, concentric polishing marks A are left as shown in FIG. 4a.
This polishing mark A produces a diffraction pattern in the direction a shown in the figure, centering on the specularly reflected light. Since the surface of the object to be inspected is scanned in a spiral manner, this diffraction pattern becomes a fixed pattern.

On the other hand, on the surface of the object to be inspected which has been linearly polished in one direction, linear polishing marks B as shown in FIG. occurs in Since it is a spiral scan, the direction b rotates as the object to be inspected rotates.

In order to remove the diffracted light component from the polishing marks on the surface of the inspected object subjected to such linear polishing, the spatial filter 108 is configured to be able to rotate in synchronization with the rotation of the inspected object 12. . For this synchronous rotation, a rotating shaft 110 that is rotationally driven by a timing belt 38 is provided so as to pass through a center hole 113 of the perforated mirror 106, and a spatial filter 108 is fixed to the tip of the rotating shaft 110. .
Note that a clutch 11 is located in the middle of this rotating shaft 110.
2 (FIG. 1), and when it is not necessary to rotate the spatial filter 108 synchronously, that is, when inspecting a concentrically polished object, by disengaging this clutch 112, The spatial filter 108 can be stopped.

The incident light that has passed through the spatial filter 108 is redirected by 90 degrees by the perforated mirror 106 and passed through another spatial filter 114 . This spatial filter 114 is for removing a diffracted light component due to polishing marks on the surface of the inspected object that has undergone concentric polishing, that is, a diffraction pattern component in the R direction.
Similar to spatial filter 108, but fixed.

The incident light that has passed through the spatial filter 114 is passed through a lens 116, a pinhole 118 for removing stray light, and
The light passes through the ND filter 120 sequentially and enters the photomultiplier 90, where it is photoelectrically converted. In this way, a photoelectric conversion signal corresponding to the diffracted light due to the concave defect can be obtained, with the influence of polishing marks sufficiently removed.

As explained so far, in this example, noise components related to polishing marks are sufficiently small.
A photoelectric conversion signal consisting of a signal component related to a foreign substance defect or a convex defect and a photoelectric conversion signal consisting of a signal component related to a concave defect can be obtained by the photomultipliers 74 and 90. As will be described later, defects on the surface of the object to be inspected are detected by determining the levels of these photoelectric conversion signals. Therefore, according to this embodiment, even if there are concentric or unidirectionally linear polishing marks on the surface of the object to be inspected, it is possible to detect even minute defects than in the past.

Furthermore, since photoelectric conversion signals for each type of defect can be obtained, defects can be detected for each type based on each photoelectric conversion signal.

Although not shown in FIG. 1, the surface inspection apparatus 10 includes a control processing section that controls motors and the like, determines photoelectric conversion signals, and stores data on detected defects. FIG. 5 is a schematic block diagram showing the control processing section with some parts omitted;
This will be explained below.

In FIG. 5, 150 is a microprocessor, 152 is a memory for storing programs and data, and 154 is an interface circuit.
These are interconnected by bus. 156 and 158 are amplifiers for amplifying the output signals (photoelectric conversion signals) of the photomultipliers 74 and 90, respectively. Comparators 160 and 162 respectively compare the output signals of amplifiers 156 and 158 with predetermined threshold values, and the comparison result signals are input to microprocessor 150 through interface circuit 154.

A drive circuit 164 drives the clutch 112 and is controlled by the microprocessor 150 via an interface circuit 154. 166
is a drive circuit for the motors 32 and 36, which is controlled by a microprocessor 150 via an interface circuit 154. Microprocessor 15
0 also includes a rotary encoder 40 and a linear encoder 41 (omitted in FIG. 1).
, an output signal from limit switch 172 (not shown in FIG. 1), and a key operation signal from operation panel 170 are input via interface circuit 154 .

Next, the operation of this surface inspection apparatus 10 will be explained. FIG. 6 is a schematic flowchart of the operation, and the step numbers in parentheses in the following explanation correspond to the processing step numbers in the flowchart.

Prior to inspection, an object to be inspected is set on chuck 12. If the object to be inspected 12 has been linearly polished in one direction, the polishing direction is set to match the R direction. Note that at the end of the inspection, the spindle 34 is stopped in a fixed direction.

Next, after the type of the inspected object 12 is specified by the keys on the operation panel 170, such as whether the inspected object 12 is concentrically polished or unidirectionally linearly polished, the inspection start key on the operation panel 170 is pressed. is pressed. The pressing signal of the inspection start key is input to the microprocessor 150 as an interrupt signal, and the processing of the main program (program for processing other than the surface inspection of each object to be inspected) that is being executed is interrupted, and the inspection process is started. Execution of the program 152A begins, and the following control and processing are executed.

First, the N counter 152C on the memory 152,
Initialization such as clearing of the N1 counter 152D, N2 counter 152E, input buffer, etc. is performed (step 200). Next, inspection object designation information from the operation panel 170 is read (step 205).
Then, it is determined whether the inspection object specification information specifies an inspection object for unidirectional linear polishing (step 210), and if the judgment result is YES, the clutch 1
12 is issued to the drive circuit 164, and the clutch 112 is closed (step 215). If the determination result is NO, step 215 is skipped,
Clutch 112 remains disengaged.

Next, a scanning start instruction is issued to the drive circuit 166, which drives the motors 32 and 36, and the laser beam begins to spirally scan the surface of the object to be inspected (step 220). Furthermore, at the end of the inspection,
The moving table 30 is positioned at a predetermined starting position.

The output signals (2-bit defect determination signal) of the comparators 160 and 162 are sampled at fixed time intervals (step 225). This defect determination signal is handled by the microprocessor 150 as a 2-bit binary code. If there is no defect at the scanning point at the sampling time, the input signals of the comparators 160 and 162 are at a lower level than their respective threshold values, so the code of the defect determination signal becomes "00". If there is a foreign object defect or a convex defect at the scanning point, the input signal level of the comparator 160 exceeds its threshold, so the code of the defect determination signal becomes "01". Conversely, if there is a concave defect at the scanning point, the input signal level of the comparator 162 exceeds its threshold, so the code of the defect determination signal becomes "10".

In other words, if the code of the defect determination signal is "00", no defect will be detected at the scanning point.
"01" means that a foreign object defect or a convex defect has been detected, and "10" means that a concave defect has been detected.

Next, the code of the defect determination signal is determined (step 230). If the code is "00" (no defect detected), the process returns to step 223. If the code is “01”, the N1 counter is incremented by 1 (step 240), and if the code is “10”, the N2 counter is incremented by 1 (step 240).
The counter is incremented by 1 (step
245), and then the N counter is incremented by 1 (step 250). In other words, the N counter is a counter that counts the number of all types of defects, and N1
The counter is a counter that counts the number of foreign matter defects or convex defects, and the N2 counter is a counter that counts the number of concave defects.

Defect detection is performed in this manner, and when the moving table 30 moves to a predetermined end position, the limit switch 172 outputs a scan end signal. The generation of this scanning end signal is checked in step 223, and when it occurs, the defect detection process is ended and the process proceeds to pass/fail determination process in step 260.

Here, the value of the N counter is less than or equal to the judgment threshold T, and
If the value of the N1 counter is below the judgment threshold T1 and the value of the N2 counter is below the judgment threshold T2, a pass indication is displayed on the display provided on the scanning panel 170 (step 265). If any of the three conditions are not met, a failure message will be displayed (step
270).

Note that failure may be displayed separately for each cause of failure, that is, for each condition that is not satisfied among the three conditions described above.

Thereafter, the motor 36 is controlled to stop the spindle 34 in a predetermined direction (step
275), then the motor 32 is controlled to return the moving table 30 to the starting position (step 275).
280). Finally, the clutch 112 is released to complete the test process and return to main program processing.

Note that the angle detection system, laser irradiation system, rotational movement mechanism of the object to be inspected, etc. may be modified as appropriate without departing from the gist of the specific invention and related inventions.

Regarding the contents of the inspection process, for example, data such as the number of detected defects may be saved on a floppy disk, the number of defects may be evaluated in multiple stages, and the threshold value for determining the level of the photoelectric conversion signal may be set. It may be made variable, or furthermore, the position information of detected defects may be collected. Such processing may be realized by hardware.

Furthermore, the object to be inspected to which this specified invention and related inventions can be applied is not limited to the substrate of a magnetic disk, but the specified invention and related inventions can be similarly applied to defect inspection on the surface of optical disk media, etc. Of course.

[Effects of the Invention] As is clear from the above description, according to this specific invention and related inventions, it is possible to detect even smaller defects on the surface of an inspected object with polishing marks than before,
Highly accurate surface scanning becomes possible. Further, according to this related invention, foreign object defects or convex defects and concave defects can be detected separately.

As described above, according to this specific invention and related inventions, it is possible to solve the conventional problems and realize a surface inspection apparatus capable of detecting defects with higher precision.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of an embodiment of a surface inspection device according to the specified invention and related invention, FIG. 2 is a schematic enlarged side view of one detection system, and FIG. 3 is a schematic enlarged front view of the other detection system. 4a and 4b are explanatory diagrams of polishing marks and their diffraction patterns, FIG. 5 is a schematic block diagram of the control processing system of the surface inspection device, FIG. 6 is a schematic flowchart of the surface inspection operation, and FIG. 7 FIG. 2 is an explanatory diagram of the relationship between a detection signal and a light receiving angle of an optical system for detecting a foreign substance defect or a convex defect in a magnetic disk substrate. 10...Surface inspection device, 12...Object to be inspected, 1
4...Rotation movement mechanism, 16...Sequence irradiation system, 18, 20...Detection system, 30...Movement table, 32...Motor, 34...Rotation spindle,
36...Motor, 38...Timing belt, 7
2...Optical system, 74...Photomultiplier, 9
0...Photomultiplier, 92...Optical system, 1
08,114... Spatial filter.

Claims (1)

[Scope of Claims] 1. A surface inspection device that detects defects on the surface of an object to be inspected, the surface of which has been polished, while scanning the surface with a light beam, the surface inspection device comprising: means for irradiating the surface, a photoelectric conversion element, and a means for receiving diffracted light due to polishing marks on the surface as well as scattered light of the light beam due to a foreign defect or a convex defect on the surface and making it incident on the photoelectric conversion element; an optical system, wherein the angle at which the optical system receives the scattered light is set to a certain value in the range of 0 degrees to 5 degrees in a direction perpendicular to the surface. Inspection equipment. 2. The object to be inspected has a polished surface with high flatness precision, such as a magnetic disk substrate or an optical disk medium, and the angle at which the optical system receives the scattered light is set relative to the surface. The surface inspection device according to claim 1, wherein the vertical direction is set to a certain value of 1 degree or less. 3 A surface inspection device that detects defects on the surface of an object to be inspected having polishing marks on the surface while scanning the surface with a light beam, the surface inspection device irradiating the surface with a light beam for scanning the surface. and the means to
a first and a second photoelectric conversion element; and a first
a first optical system for making the light incident on the photoelectric conversion element; and a second optical system for receiving the scattered light including the diffracted light of the irradiated light beam due to the concave defect on the surface and making it incident on the second photoelectric conversion element. an optical system, the angle at which the first optical system receives the scattered light is set to a certain value in the range of 1 degree to 5 degrees in the direction perpendicular to the surface; A surface inspection apparatus characterized in that the system is provided with a spatial filter for removing a component of diffracted light due to polishing marks on the surface from the received light. 4. The object to be inspected is a magnetic disk substrate, and the angle at which the first optical system receives the scattered light is perpendicular to the surface.
The second optical system includes a spatial filter for removing components of diffracted light due to polishing marks formed on the surface from the received light, and a hole in the center that receives the light that has passed through the spatial filter. A perforated mirror and a rotating shaft inserted through the hole of the perforated mirror are provided, and the light reflected by the concave defect of the light beam irradiated on the surface is transmitted through the spatial filter and the perforated mirror. The surface according to claim 3, wherein the spatial filter is rotated in synchronization with the rotation of the magnetic disk substrate via the rotating shaft. Inspection equipment.