JPH0254494B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for inspecting defects occurring on a substantially flat surface.

BACKGROUND ART In semiconductor manufacturing processes, electron tube manufacturing processes, and the like, various irregular defects occur on objects having substantially flat surfaces, which greatly affect the production rate of the process.

For this reason, in conventional production lines, visual inspection using an optical microscope has been performed in order to discover and remove such defects immediately after they occur.
In particular, in order to detect minute defects, light from an incandescent lamp is incident obliquely, the scattered light from the defect is detected, and the existence and size of the defect can be determined from changes in the amount of light.

In this visual inspection, there are large individual differences because it is an inspection with the naked eye, the amount of light scattered by defects is small because there is no strong light source, and there are many oversights, and if the defect has a directionality, the direction of viewing (inspection) However, this method has drawbacks such as a high risk of overlooking unexpected major defects.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a highly reliable defect inspection device that eliminates the above-mentioned drawbacks.

According to the present invention, a plurality of coherent light beams are used to illuminate the object, and each beam is irradiated onto a predetermined position on the surface of the object from different directions. Preferably, these beams are irradiated with respect to the surface of the object. It is incident at an angle of several degrees.

FIG. 1 shows an embodiment of the present invention. In the figure, 1 is a test object with a nearly flat surface;
For example, silicon wafers. A subject 1 is placed on a table 2, and the table 2 is connected to a rotating mechanism 3.
It is configured to be rotated in the direction of arrow A by the movement mechanism 4, and moved in the direction of arrow B by the movement mechanism 4. At one point P on the surface of the object 1, laser beams 10 1 , ₁₀ from laser light sources 5 ₁ , 5 ₂ , 5 ₃
10 ₂ and 10 ₃ are irradiated. Each laser beam is reflected at point P and becomes reflected light 20 ₁ , 20 ₂ , 20 ₃ . However, at point P, scattered light is generated. The scattered light is guided to a photodetector 7 via a lens system 6. In this embodiment, the optical axis of the lens system 6 is set perpendicular to the subject 1.

Here, the reason why the photodetector 7 does not receive the specular reflection component of the laser beam is that the (scattered light) signal from the surface defect is weak, and the degree of modulation of the defect signal with respect to the specular reflection component is very small. This is because the S/N ratio is poor.

Moreover, each laser beam 10 ₁ , 10 ₂ , 10 ₃ is incident on point P from mutually different directions. The wavelengths of each laser beam may be different or the same.

The rotation mechanism 3 and the movement mechanism 4 are mechanisms for scanning the entire surface of the subject 1, and these mechanisms cause the beam irradiation point P to scan the surface of the subject 1 in a spiral shape. It turns out.

Next, the usefulness of irradiating coherent light beams from multiple directions will be explained using FIG. 2. Second
Figure a is a front view of the object 1, in which a lint-like defect 100 is present. FIG. 2b is a sectional view thereof. For such a defect 100, an arrow 101
Scattered light when irradiated from the direction of arrow 10
Naturally, there is more scattered light when the light is emitted from the direction of the arrow 102 than when the light is emitted from the direction of the arrow 102.
This is because the scattering cross section of the defect 100 with respect to the illumination beam is larger from the direction of arrow 102 than from the direction of arrow 101.

Furthermore, FIGS. 2c and 2d show a state in which there is a concave defect 103 on the surface of the object 1. In FIG. 2d, arrows 104, 105, and 106 each indicate the direction of incidence of the illumination beam. Scattered light from this type of defect is primarily due to scattering at the edges of the recess. Therefore, the beam 104 that is incident perpendicularly to the defect 103 is
It is clear that a directional illumination beam is more advantageous for detection.

Figure 3 shows the experimental results. The figure shows an experiment using a single laser beam to determine the dependence of the irradiation angle on detecting dielectric convexities of several micrometers. The vertical axis shows (defect + surface scattered light photoelectric output)/(surface scattered light photoelectric output), and the horizontal axis shows the angle (irradiation angle) with respect to the surface of the object. The reason why there is no data when the irradiation angle is 1° or less is because the beam thickness makes it impossible to irradiate the surface of the object below this value. From the figure, it can be seen that the smaller the irradiation angle is, the greater the detection ability is. That is, it is desirable that the laser beams 10 ₁ , 10 ₂ , 10 ₃ in FIG. 1 be incident on the surface of the subject 1 at an angle of approximately 1° to 3° parallel to the surface of the subject 1 .

As described above, according to the present invention, various defects occurring in an object having a substantially flat surface can be detected with high reliability. In particular, as shown in Figure 1, since defect information is obtained on the optical axis of the photoelectric detection system, the influence of aberrations in the optical system is small, making it possible to construct a high-performance inspection device using inexpensive optical elements. . Furthermore, the optical system used in the present invention obtains defect information from a direction substantially perpendicular to the inspection light beam without using the regular reflection component from the object to be inspected, so it is possible to inspect the object while rotating it. . That is, by performing spiral scanning using a combination of rotation and horizontal shift of the object, defect inspection over a large area can be easily performed. Such spiral scanning is superior in maintainability and reliability, and can also eliminate the influence of shading that occurs in the output signal when the inspection beam itself is scanned. Furthermore, since all the optical systems used in the present invention may be fixed, there is an advantage that adjustment is easy. In addition, illuminating the defect from many spatial directions also has the meaning of realizing incoherent illumination with effectively high brightness.

Now, suppose we were to perform scanning in the two-dimensional X-Y direction instead of the spiral scanning using rotational movement and horizontal movement as described above. It will be due to. When looking at this in the waveform of the detection output of the sensor, a trailing phenomenon almost always occurs in the detection output due to the response characteristics of the sensor 7 provided in the device and the characteristics of the amplifier (not shown). If it appears in the same direction, its size etc. can be determined by considering the trailing portion. However, if this phenomenon appears in both directions, it is difficult to determine whether the detection output is from the actual defective part or from the tailing phenomenon, and the size of the defect cannot be accurately determined, or the tailing that appears on the left and right There is also a possibility that the pulled part may be mistakenly determined to be another newly generated defect. In this case, the more the sensitivity of the sensor provided in the inspection device is increased, the slower the response becomes, so erroneous judgments become more noticeable.

It is also possible to perform this two-dimensional scanning by scanning the same position twice and performing a blank scan in the opposite direction, but such a method would require a considerable amount of time for inspection. ineffective. Therefore, as mentioned above, spiral scanning is the best scanning in terms of inspection accuracy and inspection time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIGS. 2a to 2d and 3 are diagrams for explaining the effects of the present invention. DESCRIPTION OF SYMBOLS 1...Object, 2...Table, 3...Rotation mechanism, 4...Movement mechanism, ₅₁ , ₅₂ , ₅₃ ...Laser light source, 6...Lens system, 7...Photodetector.

Claims (1)

[Scope of Claims] 1. A light source that irradiates a light beam onto a subject having a substantially flat surface; A defect inspection apparatus includes a light receiving means for receiving light scattered by a defect on the surface of an object to be inspected, and a defect inspection apparatus for detecting the defect using the light receiving means, a holding means for holding the object to be inspected, and a holding means for holding the object to be inspected; What is claimed is: 1. A defect inspection apparatus comprising a scanning means for spirally scanning an object to be inspected, and inspecting the defect while the light source and the light receiving means are fixed. 2. The light source emits a plurality of light beams, at least one of which is incident on the surface of the subject at a small angle. defect inspection equipment.