JPH06102189A - Foreign substance detector - Google Patents

Abstract

PURPOSE:To obtain a foreign substance detector capable of inspecting foreign substance of a sample with film with high reliability by intensifying the scattered light regardless of film thickness. CONSTITUTION:A laser beam 14 is irradiated to a Si wafer 11 with film at an arbitrary angle in a foreign substance inspection device 1 inspecting foreign substance 25 by detecting scattered light from the foreign substance deposited on the Si wafer. The irradiation angle of the laser beam 14 is adjusted according to the film thickness of the Si wafer with film so that the intensity of the interference synthetic wave of incidence light and reflection light of the laser beam 14 is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign substance inspection apparatus for inspecting foreign substances attached to a film-coated wafer, for example.

[0002]

2. Description of the Related Art Generally, there are mainly two types of foreign matter inspection devices used in semiconductor process steps. One is a foreign matter inspection device for bare (mirror surface) wafers, and the other is a pattern.
This is a foreign matter inspection device for wafers with a wafer. An apparatus that can be used in an intermediate stage, that is, an exclusive apparatus that can inspect foreign matter attached on a film-coated wafer is not generally known.
Therefore, until now, the inspection apparatus for bare wafers has been mainly used as the inspection apparatus for film-coated wafers. As for the detection technique, the technique of detecting foreign matter adhering to a bare wafer is directly used for detecting foreign matter on a film-coated wafer.

However, a technique disclosed in, for example, Japanese Patent Laid-Open No. 63-226937 is known for detecting foreign matter for a wafer with a deposition film. That is, the foreign matter inspection apparatus described in Japanese Patent Laid-Open No. 63-226937 is provided with a means for switching the wavelength of the incident beam, and a good detection S can be performed on wafers with deposition films of various thicknesses and materials. Achieve the / N ratio.

[0004]

However, when the bare wafer inspecting apparatus and the inspecting technique are used as they are for a film-coated wafer, there is no signal uniformity and stability, and the reproducibility of measurement is further improved. There is no.

That is, in the case of a film-coated wafer, the film thickness is
This is an important parameter that influences the intensity (signal) of scattered light from a foreign substance, and when the film thickness changes, a signal of different intensity can be obtained from a foreign substance having the same diameter (size). If the inspection apparatus for bare wafers is simply used to detect the foreign matter on the film-coated wafer, it is not possible to deal with the change in the film thickness, and the reliability of the inspection is low.

On the other hand, in the inspection device described in Japanese Patent Laid-Open No. 63-226937, the wavelength of the incident beam is switched, but the detection sensitivity also changes with the switching of the wavelength. Therefore, even in this type of inspection device, there is no uniformity and stability of measurement and reliability is low.

It is an object of the present invention to provide a foreign substance inspection apparatus capable of increasing the scattered light intensity regardless of the film thickness and inspecting foreign substances in a film-coated sample with high reliability.

[0008]

In order to achieve the above object, the present invention provides a foreign matter inspection apparatus for irradiating a sample with inspection light and detecting scattered light from the foreign matter adhering to the sample to inspect the foreign matter. In the above, the inspection light is applied to the sample with the film at an arbitrary angle, and the irradiation angle of the inspection light is increased so that the intensity of the interference combined wave of the incident light and the reflected light of the inspection light increases based on the film thickness of the sample. To adjust. By doing so, the present invention aims to increase the scattered light intensity and improve the reliability of the foreign matter inspection of the film-coated sample.

[0009]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 shows a first embodiment of the present invention.
Reference numeral 1 in the drawing indicates a foreign matter inspection apparatus. The foreign matter inspection device 1 is provided with a laser oscillator 2, a beam expander 3, a reflection mirror 4, and a condenser lens 5. The light projecting unit 6 is configured by these devices.

Further, the foreign matter inspection device 1 includes an attenuator 7,
A photomultiplier 8, a wafer mounting stage 9, and a film thickness measuring unit 10 are provided. Of these,
The attenuator 7 absorbs and attenuates specularly reflected light from a film-coated Si wafer (hereinafter referred to as a wafer) 11 as a sample. Further, the photomultiplier 8 collects and detects scattered light from a foreign matter.

The wafer mounting stage 9 is an orthogonal stage 12
And a rotary stage 13. And
The wafer 11 is mounted on the rotating stage 13 with the film facing upward.

In the light projecting section 6, the laser beam 14 as the inspection light emitted from the laser oscillator 2 is expanded by the beam expander 3 and reflected by the reflection mirror 4 to be collected. Go to the optical lens 5. In addition, laser beam 14
Is condensed by the condenser lens 5 and is applied to the surface of the wafer 11 mounted on the wafer mounting stage 9. Wafer 1
The laser beam 14 irradiated on the laser beam 1 is reflected by the wafer 11 and then enters the attenuator 7. And this laser
The diaphragm 14 is absorbed and attenuated by the attenuator 7.

When foreign matter adheres to the wafer 11, the laser beam 14 is scattered by the foreign matter. This scattered light is condensed on the photomultiplier 8. And
When this scattered light is detected, the presence of foreign matter is detected.

The reflection mirror 4 of the light projecting portion 6 arbitrarily moves along the traveling direction of the laser beam 14 as shown by arrows A and A in the figure. The reflection mirror 4 rotates in a direction intersecting with the traveling direction of the laser beam 14 as shown by an arrow B. Further, the condenser lens 5 has arrows C and C.
As shown by, the object moves while drawing an arcuate locus within a range of approximately 90 °. Then, the position of the condenser lens 5 changes from directly above the wafer 11 to the same plane as the surface of the wafer 11.

That is, the traveling direction of the laser beam 14 is adjusted by the reflecting mirror 4 and the condenser lens 5, and the laser beam 14 is incident on the surface of the wafer 11 at an arbitrary angle. Note that various general devices can be adopted as a mechanism for moving or rotating the reflection mirror-4 and the condenser lens 5.

As shown in FIG. 2, the film thickness measuring unit 10 includes an infrared semiconductor laser 15, a collimator lens 16, a polarization beam splitter 17, a quarter wavelength plate 18, and a photodetector 1.
9 and a window 20 are provided. Infrared semiconductor ray
The laser 15 emits laser light 21. This laser light 21 is converted into parallel light, reflected by the polarization beam splitter 17, and guided to the quarter-wave plate 18. Further, this laser light 21 passes through the window 20 after passing through the quarter-wave plate 18, and is irradiated onto the wafer 11.

Further, the laser light 21 is reflected by the wafer 11 and again passes through the window 20 and the quarter-wave plate 18 to produce a polarized light beam.
Reach Musplitter 17. And this laser light 21
Passes through the polarization beam splitter 17, enters the photodetector 19, and is converted into an electric signal. The output of the photodetector is amplified and then input to a calculator (not shown).

The signal output from the photodetector 19 is a periodic signal, and a maximum and a minimum appear repeatedly in this signal.
The number of maximum and minimum of this signal corresponds to the thickness of the film formed on the wafer 11. Then, the film thickness is obtained based on the number of maximum and minimum signals. Here, as the film thickness measuring unit 10, various general devices for measuring the film thickness can be adopted. Next, an inspection method performed by the above-described foreign matter inspection device 1 will be described.

First, the wafer 11 is mounted on the wafer mounting stage 9
It is mounted on the wafer 1 and then the film thickness measuring unit 10 is mounted on the wafer 1.
The thickness of the film formed in 1 is measured. Measured film thickness d
Is taken into the computer, and the optimum incident angle θ of the laser beam 14 with respect to the film thickness is determined by the computer.
Is required.

The angle .theta. Is adjusted by adjusting the incident angle .theta. Of the laser beam 14 in the interference region in the film formed on the wafer 11 and by the following equation (1). It is the incident angle when it is satisfied.

[0022]

[Equation 1]

That is, as shown in FIG. 3, when the laser beam 14 is incident on the wafer 11, the laser beam 14 is incident.
The (incident light) and the specularly reflected light interfere with each other, and the interference regions 22 and 23
(Hatched portion) is formed. This interference area 22, 23
Is divided into, for example, an interference region 22 in the air and an interference region 23 in the film 24.

Reference numeral 25 in FIG. 3 indicates a foreign substance attached to the film 24. The foreign matter 25 exists in the interference area 22. When the foreign matter 25 adheres to the film 24 in this way, the laser beam 14 hits the foreign matter 25 and scatters to generate scattered light. Then, this scattered light is detected by the photomultiplier 8 in FIG.

The scattered light and the combined wave intensities of the interference regions 22 and 23 have a correlation, and when the combined wave strength increases, the scattered light strength also increases. Therefore, if the intensity of the composite wave is increased, strong scattered light can be obtained, and the accuracy of detecting scattered light can be improved.

The intensity distribution of the composite wave in the interference regions 22 and 23 is shown in the graph on the right side of FIG. This composite wave is a standing wave, and the strength of this standing wave depends on the air and the film 24.
Changes at the boundary with. The standing wave has a large amplitude in the air and a small amplitude in the film 24. Furthermore, the interference areas 22, 2
When analyzing the intensity distribution of the composite wave in 3, the following (a),
The concepts shown in (a) and (c) are basic.

(A) In general, when an electromagnetic wave enters from a medium having a density to a dense medium, fixed-end reflection occurs at the boundary surface, and the phase shifts by a half wavelength (180 °). Therefore, the phase of the laser beam 14 (s-polarized light) of this embodiment is shifted by a half wavelength when the laser beam 14 enters the film 24 from the air without depending on the incident angle. Also, the laser beam 14
The phase shifts by half a wavelength even when is incident on the wafer 11 from the inside of the film 24.

Therefore, on the surface 26 of the film 24, the incident light and the reflected light interfere with each other to produce dark fringes. Further, also on the surface 27 of the wafer 11, the incident light and the reflected light interfere with each other to generate dark stripes.

(A) Next, the inside of the film 24 will be considered.
Assuming that the refractive index of the film 24 is n ₁ , the wavelength in the film 24 is λ.
/ N ₁ and the irradiation light angle θ ′ is expressed by the following equation (2).

[0030]

[Equation 2] The interval x of the interference fringes shown in FIG. 4 is expressed by the following equation (3).

[0031]

[Equation 3]

That is, in the film 24, the fringe spacing x depends on the incident angle. This is the same in the air. Here, the black dots in FIG. 4 indicate dark stripes, and the white dots indicate bright stripes.

(C) Generally, the refractive index of the wafer 11 is set to n ₂
The refractive index of the film 24 is n ₁ , the outer medium (air in this embodiment)
The film 24 is an antireflection film if the relationship of n ₀ <n ₁ <n ₂ is satisfied, where n ₀ is the refractive index of the film. In addition, the intensity of the reflected light R | R | ² It is known that there is the following relationship between and the wavelength λ. That is, if the phase difference between the reflected light from the surface 26 of the film 24 and the reflected light from the surface 27 of the wafer 11 is δ, δ is expressed by the following equation (4).

[0034]

[Equation 4] (A) When δ = 2 mπ, that is, when the following expression (5) is established, the reflectance becomes maximum, and | R | ² Is also maximal.

[0035]

[Equation 5] (B) When δ = (2m + 1) π, that is, the following equation (6)
, Then the reflectance becomes a minimum and | R | ² Is also minimal.

[0036]

[Equation 6] Substituting equation (3) above into equation (5), the following equation (7) is obtained. d = mx (7)

Here, FIG. 5 shows the difference in fringe spacing and combined wave intensity when the incident angle changes. The left side of the figure shows the waveform and the stripe interval x ₁ when the reflected light intensity is small, and the right side shows the waveform and the stripe interval x ₂ when the reflected light intensity is large.

From the above (a), (a) and (c), the film 2
If the thickness of No. 4 is known, the incident angle θ is changed as shown in FIG. 5, the fringe spacing x is adjusted, and Expression (7) is satisfied, the intensity | R | ² Is maximum (maximum). Then, the intensity of the scattered light from the foreign matter 25 is also sufficiently increased.

That is, in the foreign matter inspection apparatus 1 of the present embodiment, the thickness of the film 24 is measured by the film thickness measuring section 10, and the incident angle of the laser beam 14 is determined by the intensity of the interference synthetic wave. Adjusted to maximize. Then, high-intensity scattered light is obtained, and this scattered light is detected to determine the presence of the foreign matter 25.

Therefore, the foreign matter adhering to the film-coated wafer 11 can be easily detected with high sensitivity, and the film 24 having an arbitrary thickness can be provided as long as the relationship of d> λ / 2n ₁ is satisfied. It is possible to detect foreign matter attached to the wafer 11 having

Furthermore, since the thickness of the film 24 is measured by the film thickness measuring unit 10, the thickness of the film 24 can be known in advance. Therefore, even when wafers having different film thicknesses are used as samples, the incident angle of the laser beam 14 can be set in consideration of the difference in film thickness. Therefore, high intensity scattered light can be obtained with good reproducibility, and the reliability of inspection can be improved.

Since it is not necessary to switch the wavelength according to the film thickness, the change in the detection sensitivity of scattered light is small. Therefore, it is possible to improve the uniformity and stability of the measurement,
The reliability of inspection can be improved.

In this embodiment, the photomultiplier 8 is used to detect scattered light, but various general detectors (such as photoelectron amplifying tubes) as means for detecting scattered light. Can be adopted.

Although the foreign matter inspection of the film-coated wafer 11 is described in the present embodiment, the present invention is not limited to this and can be applied to the foreign matter inspection of various samples. Further, specifically, it can be applied to, for example, inspection of foreign matter attached to a transparent electrode film of a liquid crystal display. Next, a second embodiment of the present invention will be described based on FIG. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 5 shows a second embodiment of the present invention,
Reference numeral 31 in the drawing is a foreign matter inspection device. In this foreign matter inspection apparatus 31, the light projecting section 6 including the laser oscillator 2 is L
It is housed in a character-shaped optical tube 32. Further, the foreign matter inspection device 31 is provided with an angle adjusting mechanism section 33, and the angle adjusting mechanism section 32 has a fixed section 34 and a movable section 35. An arc-shaped guide hole 36 is formed in the fixed portion 34, and movable protrusions 37, 37 are provided in the movable portion 35. Then, the movable projections 37, 3 of the movable portion 35
7 is engaged with the guide hole 26 of the fixed portion 34.

The optical barrel 32 is mounted on the movable portion 35 of the angle adjusting mechanism 33 and rotates together with the movable portion 35. The rotational displacement of the optical barrel 32 is caused by the engagement protrusions 37, 37.
And the guide hole 37. Further, the rotation range of the optical barrel 32 is approximately 90 as indicated by an arrow D in FIG.
It is set to °.

That is, the foreign matter inspection device 31 changes the incident angle of the laser beam 14 by rotationally displacing the entire light projecting portion 6. Therefore, even if the incident angle of the laser beam 14 is changed, the optical axis of the light projecting unit 6 does not shift, and the alignment of the light projecting unit 6 is unnecessary. Next, a third embodiment of the present invention will be described based on FIG. The same parts as those in the above-described embodiments are designated by the same reference numerals,
The description is omitted.

FIG. 6 shows a third embodiment of the present invention.
Reference numeral 41 in the figure denotes a foreign matter inspection device. In the foreign matter inspection device 41, the light projecting section 42 has a plurality of condenser lenses 5 ...
Are provided, and these condenser lenses 5 are arranged in a line in an arc shape. The reflection mirror-4 is indicated by an arrow A,
As shown by A, the laser beam 14 moves in a direction along the traveling direction of the laser beam 14, and as shown by an arrow B, it rotates in a direction intersecting with the traveling direction of the laser beam 14.

That is, the foreign matter inspection device 41 moves only the reflection mirror 4 to guide the laser beam 14 to the respective condenser lenses 5 ... And changes the incident angle of the laser beam 14. Therefore, it is not necessary to move each condenser lens 5.

[0050]

As described above, according to the present invention, in a foreign matter inspection apparatus for inspecting a foreign matter by irradiating the sample with the inspection light and detecting scattered light from the foreign matter adhering to the sample, the inspection light with a film is attached. While irradiating the sample at an arbitrary angle, the irradiation angle of the inspection light is adjusted based on the film thickness of the sample so that the intensity of the interference combined wave of the incident light and the reflected light of the inspection light is increased. Therefore, the present invention has the effect of increasing the scattered light intensity and improving the reliability of the foreign matter inspection of the film-coated sample.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a film thickness measurement unit.

FIG. 3 is an explanatory diagram showing an interference region formed by incident light and reflected light of inspection light.

FIG. 4 is an explanatory diagram showing an interval of interference fringes.

FIG. 5 is an explanatory diagram showing a state in which the incident angle is changed and the fringe spacing is adjusted.

FIG. 6 is a configuration diagram showing a second embodiment of the present invention.

FIG. 7 is a configuration diagram showing a third embodiment of the present invention.

[Explanation of symbols]

1 ... Foreign matter inspection device, 4 ... Reflective mirror, 5 ... Condensing lens,
8 ... Photomultiplier, 10 ... Film thickness measuring unit, 11 ...
Si wafer with film (sample with film), 14 ... Laser beam (inspection light), 25 ... Foreign material.

Claims (1)

[Claims] 1. A foreign matter inspection device for inspecting the foreign matter by irradiating the sample with the inspection light and detecting scattered light from the foreign matter adhering to the sample, wherein the inspection light is applied to the film-coated sample at an arbitrary angle. With irradiation, based on the film thickness of the sample,
A foreign matter inspection apparatus, wherein an irradiation angle of the inspection light is adjusted so that an intensity of an interference combined wave of the incident light and the reflected light of the inspection light is increased.