JPS63279147A - Surface defect inspector - Google Patents

Abstract

PURPOSE:To achieve a highly accurate measurement of a surface roughness eliminating effect due to vibration of an object to be inspected, by detecting several reflected beams of beams irradiating different positions of the surface of an object to be inspected from several light sources to determine a distance therebetween. CONSTITUTION:Two laser beams L1 and L2 from a laser light source are made to irradiate vertical to the surface of an object 2 to be inspected such as magnetic disc through a polarized beam splitter 1 at an interval of a distance l. Reflected beams R1 and R2 on the surface of the object 2 being inspected of the beams L1 and L2 are reflected with the splitter 1 to be incident respectively into brightness position detectors 3a and 3b such as PSD. Then, the reflected beam R1 is checked to deviate in the incident position from a reflected beam R01 with no deffect due to a defect on the surface of the object 2 being inspected, hence detecting a surface defect. Thus, a difference between the positional deviation thus obtained and that of the other reflected beam R2 is detected with a comparator 4, thereby enabling the removal of effect due to vibration of the object 2 being inspected.

Description

Detailed Description of the Invention (Industrial Application Field) This invention is a surface defect inspection method for automatically inspecting defects such as scratches on the surface of an object to be inspected such as a magnetic disk substrate. Regarding equipment.

(Conventional technology and its problems) The quality of products such as substrates for magnetic disks for computers and semiconductor wafers is greatly affected by defects such as slight scratches on the surface. In addition to ultra-precise processing to a similar level, it is necessary to inspect the substrate for surface defects after processing.

Traditionally, such defect inspections have been carried out visually by inspectors, and skilled inspectors can not only identify defects on the submicron order, but also detect harmless dust and other particles that can be removed through subsequent cleaning processes. and defects that may affect the product. Based on this, it is determined whether the object to be inspected can be sent to the subsequent process or whether it should be disposed of as a rejected item.Furthermore, depending on the type of defect, an abnormality in the surface processing equipment can be sensed and appropriate H7ffi measures taken. It is also being done.

However, as mentioned above, visual inspection by inspectors requires a wide range of abilities, so it is not easy to train inspectors, and due to differences in inspection ability among inspectors,
There is a problem that the quality of products is not necessarily uniform.

Therefore, various surface defect inspection apparatuses have been proposed to replace such visual inspection by inspectors. For example, JP-A-60-69
539, this device irradiates a spot light onto an object to be inspected such as a magnetic disk, receives reflected light from the surface of the object to be inspected, and detects the change and direction of the received light level and light receiving position. However, the presence or absence of a defect on the surface of the object to be inspected and the type of the defect are determined based on the determination results obtained by comparing these values with predetermined reference values.

Conventional surface defect inspection apparatuses, including the above-mentioned surface defect inspection apparatus, are based on the premise that the positional relationship between the measurement apparatus (particularly the optical system) and the object to be measured remains unchanged. However, in reality, the positional relationship (interval) between the object to be measured and the device changes over time due to various external vibrations. In order to prevent this, a large, high-performance vibration isolating table must be provided, which limits the installation location of the device. Furthermore, if the object to be measured moves slightly up and down depending on the straightness of a mechanism (for example, a slide mechanism) for moving the object for scanning, this vibration will be reflected in the measurement results.

For this reason, when measuring nanometer-order roughness, in reality, the distance between the surface to be measured and the measurement system changes due to various vibrations, making it difficult to perform high-precision roughness measurements. The problem was that it was difficult.

In addition, signal processing such as filtering can be performed to remove signal components due to the influence of vibration, but even with this method, the signal due to the surface defect of the object to be inspected and the signal due to the influence of vibration may be out of phase.

When the periods are almost the same, there is a problem in that it is almost impossible to accurately discriminate between these two signals.

(Object of the Invention) The object of the present invention is to solve the problems of the above-mentioned prior art, and to provide a surface defect inspection device that can perform a surface defect inspection of an object to be inspected with high accuracy without being affected by vibrations during inspection. The goal is to provide the following.

(Means for Achieving the Object) In order to achieve the above-mentioned object, a surface defect inspection apparatus according to the present invention (first and second light fi! The influence of vibration is removed by irradiating each with a beam of light, detecting the first and second reflected lights from the surface of the object to be inspected, and determining the difference between the two.

(Embodiment) FIG. 1 is a schematic configuration diagram of a surface defect inspection apparatus which is an embodiment of the present invention. In the figure, two laser beams Ll are emitted from a laser light source (not shown).

L2 is irradiated perpendicularly to the surface of an object to be inspected 2 such as a magnetic disk through a polarizing beam splitter (half mirror) 1 at intervals of a distance l. These laser beams L1.
L2 is reflected by the surface of the object to be inspected 2 and becomes reflected light R1, R2.
becomes.

These reflected lights R1 and R2 are each reflected by a polarizing beam splitter 1 and sent to bright spot position detectors 3a and 3b such as PSD.
leading to. Of these, if there is no defect as shown in the figure on the surface of the object to be inspected 2, the reflected light R1 follows the path of the specularly reflected light R81 as shown by the broken line in the figure.
When the deviation Δ×1 of the incident position of the reflected light R1 on the bright spot position detection 153a exceeds a predetermined reference position, a surface defect on the object to be inspected 2 can be detected.

However, as shown in FIG. 2(a), the signal S1 of the deviation Δx1 detected by the actual bright spot position detector 3a is heavily influenced by vibration, so It is difficult to extract only the signal component reflecting the surface defect (in the example of FIG. 2, it occurs at scanning positions P1 to P2).

Therefore, the signal S2 (FIG. 2(b)) of the incident position deviation ΔX2 of the specularly reflected light R82 detected by the bright spot position detector 3b where the reflected light R2 is incident and the reflected light R2 is also detected, and both signals 8
1.82 in the next stage comparator 4, and by taking the difference between the two, it is possible to extract a signal S3 reflecting only the surface defects of the object to be inspected 2, as shown in FIG. 2(C). This is because if the rigidity of the inspected object 2 is high, the signal components due to the influence of vibration included in the signals 81 and 82 can be considered to have the same phase and the same amplitude.

Note that the signal S1. If both S2 contain a signal component that reflects a surface defect on the object to be inspected 2, it will be difficult to detect the defect position, but since the frequency of surface defects on the object to be inspected 2 is low, this is a practical problem. There isn't.

Further, as shown in FIG. 3, the same effect can be obtained by changing the incident angle of the laser beam by -2.

However, it is necessary to accurately adjust the range between the deviation signals 81 and 82. (Advantages of the Invention) As explained above, according to the present invention, the first and second reflected lights are detected, Since the influence of vibration is removed by determining the difference between the two, it is possible to inspect the surface defects of the object to be inspected with high precision even if imaging occurs during inspection.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a surface defect inspection apparatus that is an embodiment of the present invention, FIG. 2 is a graph showing signal changes at the surface defect detection gi position of FIG. 1, and FIG. 3 is a diagram of another embodiment of the present invention. FIG. 1 is a schematic configuration diagram of a surface defect inspection apparatus according to an embodiment. 2...Object to be inspected, 3...Bright spot position detection device, 4...Comparator, Ll, L2...Laser beam, R1, R2...Reflected light

Claims (1)

[Claims] (1) In a surface defect inspection device that optically inspects surface defects existing on the surface of an object to be inspected, a first and a second
A light beam is irradiated from a light source to different positions on the surface of the object to be inspected, the first and second reflected lights from the surface of the object to be inspected are detected, and the difference between the two is determined. A surface defect inspection device characterized by eliminating the influence.