JPH0252241A - Surface defect inspection instrument - Google Patents

Abstract

PURPOSE:To improve the identifying ability for the size of a defect by using two lasers which differ in wavelength as the light source of a detection system, and performing detection by the other light source in an area wherein it is difficult to perform discrimination by one light source, and making them complement each other. CONSTITUTION:A carbon dioxide gas (CO2) laser 11 is provided as a 2nd light source in addition to an He-Ne laser 1 as a 1st light source. Further, two kinds of photodetectors are provided corresponding to the light sources, a photoelectron multiplier tube 6 is used for He-Ne laser light, and a PbS photodetector 13 is used for CO2 laser light. Then an Si wafer 3 to be inspected is irradiated by the respective diameters of the light sources. If there is a defect on the wafer 3, the laser light beams are scattered and entered into the detectors 6 and 13. The scattered light beams entered into the detectors 6 and 13 are converted into electric signals, which are sent to a signal processing system 15 to detect the size and position of the defect. Thus, the two light sources which differ in wavelength are used as the same time, so variation in scatter sectional area becomes larger by at least one light source in the entire range at all time for the defect diameter, and the defect diameter is accurately recognized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a surface defect inspection device that utilizes scattering of light due to defects.

(Prior Art) In the semiconductor industry, since the processing is minute, dust has a very large effect on the yield of product manufacturing, and inspection and control of dust are very important requirements.

A surface defect inspection device inspects the dust on the wafer, and usually measures the size and number of defects (dust, scratches, etc.).

Conventionally, there are several types of surface defect inspection apparatus of this type, and the configuration of their detection system is shown in FIG.

The detection system is usually housed in a dark box and consists of a light source and a light receiver. Laser light emitted from a He-Ne laser 1 as a light source passes through a mirror 2 and the like, and is irradiated onto a Si wafer 3, which is an object to be inspected. If there is no foreign matter 4 such as dust (defective in a broad sense) on the Si wafer 3, the laser light will be specularly reflected, but if there is foreign matter 4 such as dust, the laser light will be scattered.

The scattered light from the foreign object 4 passes through the optical fiber 5, enters the photomultiplier tube 6, is converted into an electrical signal, and is sent to the signal processing system via the preamplifier 7. The scattered light intensity (scattering cross section) indicates that the foreign object 4, the position of the foreign object 4 is detected from the synchronization with the scanning of the Si wafer 3 and the laser beam.

(Problems to be Solved by the Invention) However, in the conventional detection system as described above, since a He-Ne laser (λ-6328) 1 is used as a light source, light scattered from the foreign object 4 or from the substrate The reflected light interferes with the incident light, and as shown in Figure 4, approximately 0.5 to 2
Scattering cross section (scattered light intensity) for a μm-sized defect
There is a problem in that it is difficult to identify the size of foreign particles with a size of 0.5 to 2 μm.

The present invention eliminates the problem that it is difficult to identify the size of defects of 0.5 to 2 μm in the detection system using the He-Ne laser as a light source. An object of the present invention is to provide a surface defect inspection device with excellent identification ability.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a surface defect inspection apparatus that includes a first light source having a first wavelength and a second light source having a first wavelength.
a second light source having a wavelength of , a first photodetector for detecting the first wavelength, and a second photodetector for detecting the second wavelength; In the defect diameter low sensitivity range of the system, the second wavelength detection system is used to detect defects.

(Function) According to the present invention, as described above, by using two lasers with different wavelengths as the light sources of the detection system, areas whose sizes are difficult to identify are made different, and in the areas where it is difficult to identify,
By performing detection using the other light source, the sizes of defects of all sizes can be appropriately identified in a mutually complementary manner.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a surface defect inspection apparatus according to the present invention.

In the figure, 1 to 7 are the same as those of the conventional device described above, and their explanation will be omitted here. 11 is a CO2 laser, 12 is a mirror that applies the laser light emitted from the CO2 laser to the defect, 13 is a PbS photodetector, ]4 is the Pb
A preamplifier for amplifying the output signal from the S photodetector, 15
is the processing system for the amplified signal.

In this way, in addition to the He-Ne laser (λ-6328) 1 as the first light source, the carbon dioxide (Co) laser (λ-1.06324) 11 as the second light source.
will be established. Furthermore, two types of photodetectors are used depending on the light source. That is, a photomultiplier tube 6 is used for the He--Ne laser beam, and a PbS photodetector 13 is used for the CO□ laser beam.

Therefore, the Si wafer 3, which is the object to be inspected, is irradiated by separate light source systems. If there is a defect on the Si wafer 3, the laser light will be scattered and each photodetector 6.1
Enter 3. The scattered light incident on each photodetector 6.13 is converted into an electrical signal and sent to the signal processing system 15, and the size of the defect is determined from the scattered light intensity (scattered cross section) by scanning the Si wafer 3 and the laser beam. The position of the defect is detected from the synchronization with the

FIG. 2 shows the relationship between the defect diameter and the scattering cross section obtained by the surface defect inspection apparatus of the present invention.

As shown in this figure, two curves corresponding to the l-1e-N e laser 1 and the CO2 laser 11, which are light sources, are shown. That is, in the curve a corresponding to He-Ne laser 1, when the defect diameter is in the range of 0.5 to 2 μm (B-E), the change in the scattering cross section is small with respect to the change in defect diameter, making it difficult to accurately recognize the defect diameter. is difficult. But on the other hand, CO. Similarly, the curve corresponding to laser 11 has a range (D - G) in which the change in scattering cross section is small with respect to the defect diameter, but because the wavelength of the laser beam is different, its characteristics are different from that of He-Ne. Appears in a range of defect diameters different from that of laser 1, with defect diameters of 0.5 to 2.
In the μm range (C-D), the scattering cross section changes greatly, making it possible to accurately recognize and recognize the defect diameter. In this way, by using two light sources with different wavelengths at the same time, at least one light source always has a large change in the scattering cross section with respect to the defect diameter in all ranges, making it possible to accurately recognize the defect diameter. .

In this case, 0.5 μm or more (A-B) and 2 μm or more:
(E-F) detects defects with He-N c laser 1;
0.5-2 p m (C-D) By detecting defects using a CO2 laser, the defect diameter can be accurately recognized in all ranges.

It should be noted that the present invention is not limited to the two embodiments described above, and various modifications can be made within the spirit of the present invention, and these are not intended to be excluded from the scope of the present invention.

(Effects of the Invention) As described in detail in Section 2, according to the present invention, the size of defects can be identified by using one laser with a different wavelength as the light source of the detection system of the surface defect inspection device. By making the difficult regions different and complementing each other, it is possible to perform accurate size identification for defects of all sizes.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a surface defect inspection device according to the present invention;
The figure shows the relationship between the defect diameter and the scattering cross section by the surface defect inspection device of the present invention, FIG. 3 is a block diagram of a conventional surface defect inspection device, and FIG. FIG. 3 is a diagram showing the relationship between the diameter and the scattering cross section. 1- He-N e laser, 2.12...mirror, 3
S1 wafer, 4... foreign matter, 5... optical fiber, 6...
...Photomultiplier tube, 7,14...Preamplifier, 11.
...CO2 laser, 13...PbS photodetector, 15...
・Signal processing system. Patent applicant: Oki Electric Industry Co., Ltd. Representative Patent attorney Mamoru Shimizu (one other person) Tomokatsuri's Tsukasa Saru case N.
Yoshizu diagram

Claims (2)

[Claims] (1) (a) a first light source having a first wavelength; (b) a second light source having a second wavelength; and (c) a first photodetector that detects the first wavelength. and,(
d) a second photodetector for detecting the second wavelength; (e) in the defect diameter low sensitivity range of the first wavelength detection system, the second wavelength detection system is used to detect the defect; A surface defect inspection device characterized by detecting. (2) A He-Ne laser is used as the first light source, a CO_2 laser is used as the second light source, a photomultiplier tube is used as the first photodetector, and a PbS photodetection cell is used as the second photodetector. The surface defect inspection device according to claim 1.