JPH0310144A - Corpuscle measuring apparatus - Google Patents

Abstract

PURPOSE:To decrease the signal caused by a stray light component and to improve S/N by overlapping laser light beams having the same wavelength on a rotating wafer, and forming interference fringes. CONSTITUTION:The linearly polarized laser light emitted from a laser light source 1 is split into two luminuous fluxes through a beam splitter 2. Thereafter, the light beams are overlapped on a wafer 6 through mirrors 3 and 4 at an angle theta, and interference fringes having a constant interval are formed. At this time, scattered light whose intensity depends on the grain size is generated when a corpuscle 7 which is attached on the wafer 6 crosses the interference fringes at a velocity V. The electric signal corresponding to the intensity of the scattered light and the electric signal component corresponding to the stray light other than the light caused by the laser light and the scattered light caused by gas on the laser light path are overlapped, and the result is outputted from a photodetector 8. The signal is filtered through a filter 9 so as to pass the frequency component. Thus, the signal corresponding to the scattered light caused by the corpuscle 7 is measured in a processing part 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fine particle measuring device for detecting fine particles on a wafer.

[Conventional technology]

, FIG. 3 is an explanatory diagram showing a conventional inspection method and apparatus for inspecting foreign matter on a wafer surface disclosed in Japanese Patent Application Laid-Open No. 62-297747. In the figure, 21 is a sample stage, 22
is a wafer, 23 is an inspection light, 24 is a light source, 25 is an objective lens, 26 is a light-to-electric conversion means, 27 is scattered light or reflected light, 28 is a first signal line, 29 is a second signal line, 30 31 is a comparison section, 31 is a determination section, and 32 is a delay section.

Next, the operation will be explained.

By irradiating the light emitted from the light source 24 onto the wafer 22 rotated by the sample stage 21, the surface of the wafer is continuously scanned by the inspection light 23, and at this time, the inspection light 23 is applied to the surface of the object to be inspected. Scattered light generated from a predetermined area to be illuminated.

Alternatively, the reflected light 27 is incident on the photoelectric conversion means 26 via the objective lens 25. Then, the object to be inspected 22 generates the scattered light or reflected light 27 detected at the first time T.
If a foreign object is present in the region, the optical-to-electrical conversion means 26 detects a mixture of scattered light or reflected light 7 from the foreign object and stray light as a signal S, and the optical-to-electrical conversion is performed at the second time T2. Scattered light or reflected light 2 detected by means 26
If the signal S2 of No. 7 is only a signal of stray light, it will have the waveforms shown in FIGS. 4(a) and 4(Cb), for example. In FIG. 4, 41 is a signal from a foreign object, and 42 is a stray light signal.

In the comparator 30, a difference signal S between Sl and 32 is generated.

When the stray light component is canceled out, the signal from the foreign object contained in the scattered light or reflected light is detected in good contrast with the stray light component that could not be canceled out, as shown in FIG. 4(C).
Signals from foreign objects are clearly detected.

[Problem to be solved by the invention]

Since the conventional microparticle measuring device for detecting foreign matter on the wafer surface is configured as described above, the effect of canceling the stray light intensity is effective only for the time-invariant part of the stray light intensity.
There are problems in that as the foreign matter becomes smaller, the intensity of its scattered light becomes weaker than the time-varying component of the stray light intensity, and it becomes difficult to detect it in an environment where there is a lot of stray light.

This invention was made to solve the above-mentioned problems, and it is possible to measure fine particles even in process equipment, especially when the fine particles are small and their scattered light is weak, or when there is a lot of stray light. The purpose is to obtain equipment.

[Means for Solving the Problems] A fine particle measuring device according to the present invention superimposes two laser beams of the same wavelength on a rotating wafer to form interference fringes at regular intervals, and detects interference fringes on the wafer that cross the interference fringes. The scattered light from the fine particles has a certain frequency component, and the output of the photodetector is filtered to pass that frequency.

[Effect]

In this invention, two laser beams of the same wavelength are superimposed on the wafer to form interference fringes at regular intervals, and the distance between the fringes and the difference between the fine particles are determined by the scattered light from the fine particles on the wafer that crosses the interference fringes. It has a certain frequency component determined by the speed, and the output of the photodetector for detecting scattered light is filtered to pass at least f frequency components, and the output is signal-processed to detect fine particles. Therefore, signals due to stray light components can be reduced and the S/N ratio can be improved.

〔Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a fine particle measuring device according to an embodiment of the present invention. In the figure, l is a laser light source, 2 is a beam splitter, 3 and 4 are mirrors, and 5 is a rotary table for rotating a wafer. , 6 is a wafer, 7 is a fine particle attached to the surface of the wafer 6, 8 is a photodetector composed of, for example, a photomultiplier tube, and 9 is at least an electrical signal output from the photodetector 8. Filter that passes frequency components, 1
0 is a processing unit that performs signal processing on the output of the filter 9 to detect fine particles.

Next, the operation will be explained. A linearly polarized laser beam with a wavelength λ emitted from the laser beam at is split into two beams by a beam splitter 2, and then superimposed on the wafer by a mirror at an angle θ to form fine particles as shown in FIG. 2(a). Interference fringes 13 are formed at regular intervals in a direction that is not parallel to the moving direction 15 of the .

At this time, the angle between the interference fringes 13 and the moving direction 15 of the fine particles is φ, and when the fine particles 7 attached to the wafer cross the interference fringes at a speed of ■, as shown in FIG. 2(b), , scattering light whose degree depends on the particle size is generated.

Then, an electrical signal corresponding to the intensity of this scattered light, stray light other than that caused by the laser beam (for example, indoor illumination light incident from the outside), and electrical signal components corresponding to the scattered light due to gas on the laser beam optical path. are outputted from the photodetector 6 in an overlapping manner. Of these three signal components, the second one is not caused by fine particles. The third one has no frequency components. Therefore, if filtering is performed in the filter 9 to pass the frequency components, electronic signals corresponding to stray light other than that caused by the laser beam and light scattered by gas on the laser beam optical path are removed, and light scattered by the fine particles 7 is removed. Only the signals corresponding to the above are measured in the processing section 10. In this way, in this example, compared to the conventional example, a device having a high measurement ability even for fine particles having a smaller particle size can be obtained.

〔Effect of the invention〕

As described above, in a microparticle measuring device according to the present invention, laser beams of the same wavelength are superimposed on a rotating wafer to form interference fringes, and a specific frequency component is added to the light scattered by the microparticles attached to the wafer. At least f of the output of a photodetector that receives scattered light and converts it into an electrical signal.
Since the filter is configured to pass the frequency component and the obtained output is subjected to signal processing, the signal due to the stray light component can be reduced, and the signal-to-noise ratio can be improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a fine particle measuring device according to an embodiment of the present invention, FIG. 2(a) is a diagram showing interference fringes on a wafer, and FIG. 2(b) is an example of an output signal. 3 is a block diagram of a conventional inspection device, and FIG. 4 is a diagram showing an example of a signal waveform of the amount of scattered light or reflected light detected by the optical-electrical detection means. 1 is a laser light source, 2 is a beam splitter, 3.4 is a mirror, 5 is a rotating table, 6 is a wafer, 7 is a fine particle, 8 is a photodetector, 9 is a filter, 10 is a processing unit, 11 is a laser beam, 13 is an interference fringe, and 15 is a fine particle traveling direction.

Claims (1)

[Claims] (1) A microparticle measuring device that detects microparticles attached to the surface of a semiconductor device substrate includes a table that moves the wafer, and a laser beam that superimposes laser beams of the same wavelength on the wafer to form interference fringes. An irradiation mechanism, a photodetector that receives light scattered by fine particles attached to the wafer and converts it into an electrical signal, and a device that passes at least a specific frequency signal among the electrical signals output from this photodetector. A fine particle measuring device comprising: a filter that performs signal processing; and a signal processing section that performs signal processing on the output of the filter.