JPH0854346A - Method and device for inspecting object for foreign matter - Google Patents

Abstract

PURPOSE:To provide a foreign matter-inspecting device which can detect with high sensitivity foreign matters adhering to the surface of an object which reflects incident light in multiple ways. CONSTITUTION:The foreign matter inspecting device is provided with an He-Ne laser oscillator 4 which can make a laser beam 3 incident on an SOI wafer 1 which reflects incident light 10 in multiple ways at a variable incident angle theta, a light receiving camera 6 which receives reflected light 5 from the wafer 1, a photomultiplier 9 which receives scattered light 8 and an incident angle controlling section 11 which is electrically connected to the oscillator 4 and camera 6, detects the minimum point of the intensity of the reflected light 5 which periodically changes in accordance with the variation of the incident angle theta, and fixes the incident angle theta from the oscillator 4 at the minimum point. The photomultiplier 9 catches the scattered light 8 and detects foreign matters 7 adhering to the surface of the wafer 1 at the minimum point of the intensity of the reflected light 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection method and a foreign matter inspection apparatus for optically detecting foreign matter adhering to the surface of an object to be inspected.

[0002]

2. Description of the Related Art In recent years, with the aim of achieving high speed and high integration of semiconductor integrated circuits, reduction of device parasitic capacitance by realization of a complete element isolation structure, improvement of α-ray soft error resistance by elimination of active parasitic effects, etc. In order to improve the device characteristics, or to improve the degree of integration by forming devices three-dimensionally, the technology of forming an integrated circuit using a semiconductor wafer with an SOI (Silicon On Insulator) structure has been put into practical use. Has been done.

Even in a semiconductor wafer having such an SOI structure (hereinafter referred to as "SOI wafer"), the foreign matter adhering to the surface can be removed by a cleaning technique as a pre-stage of device formation to prevent a decrease in yield. Has been done. Therefore, the technique of detecting foreign matter adhering to the surface of an SOI wafer after cleaning has its role not only for forming a device having desired performance, but also for locating the source of foreign matter and taking appropriate measures. Is becoming more important.

Here, as an example in which the technique for detecting adhered foreign matter is described in detail, for example, published by the Japan Society for Precision Engineering,
"Journal of Precision Engineering", Vol. 55, No. 2 (issued in February 1989),
Some of them are introduced under the title of "Semiconductor foreign matter inspection technology" in P52 to P56. The technique is to irradiate a wafer with a laser spot having a wavelength of about 10 to 100 μm, effectively collect weak scattered light from a foreign substance with a large number of optical fibers or integrating spheres, and convert it into an electric signal with a photoelectric element. It is intended to optically detect the adhering foreign matter.

[0005]

However, the object to be inspected is S
In the case of the OI wafer 21, this is S as shown in FIG.
A Si layer (silicon layer) 2 is formed on the main surface of the i substrate (silicon substrate) 21a via a SiO ₂ film (silicon oxide film) 21b.
1c is formed, part of the laser light emitted from the laser oscillator is detected as specular reflection light 25a reflected on the surface of the Si layer 21c, but the other part is detected as the Si layer 21.
c and the SiO ₂ film 21b, and the Si layer 21c and SiO
The interface between the ₂ films 21b or SiO ₂ film 21b and Si,
It is detected as so-called multiple reflection light 25b, 25c which is repeatedly reflected at the interface with the substrate 21a.

When the phases of the specularly reflected light 25a and the multiple reflected lights 25b and 25c which are background noises are modeled as shown in FIG. 4 (a), they are combined and represented. The reflection intensity increases as shown in FIG. That is, when the phases of the three waves having the amplitude A are respectively shifted by π / 3, the amplitude becomes 2A.

As described above, depending on the phase difference of the reflected light 25, the detection of weak scattered light is hindered and the detection sensitivity is lowered.

Therefore, an object of the present invention is to provide a technique capable of detecting foreign matter adhering to the surface of an object to be inspected such as an SOI wafer in which incident light is multiply reflected with good sensitivity.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0010]

The typical ones of the inventions disclosed in the present application will be outlined below.

That is, the foreign matter inspection method according to the present invention is
Prepare an inspected object that multiple-reflects incident light, irradiate the inspected object with light while changing the incident angle, and monitor the reflected light whose reflection intensity changes periodically due to the change of the incident angle. When the light reflection intensity becomes minimum, the scattered light is captured to detect foreign matter attached to the surface of the inspection object.

Further, the foreign matter inspection apparatus according to the present invention includes a light source in which an incident angle of light with respect to an object to be inspected in which incident light is multiple-reflected is variable, and reflected light detection for receiving reflected light by light emitted from the light source. Section, a scattered light detection section that receives scattered light due to light emitted from a light source, and a light source and a reflected light detection section that are electrically connected to each other It has an incident angle control unit that detects the minimum point and fixes the incident angle from the light source at this minimum point, and the scattered light detection unit captures the scattered light at the minimum point of the reflection intensity of the reflected light, and the object to be inspected. The foreign matter adhering to the surface of is detected. In this case, the object to be inspected may be a semiconductor wafer having an SOI structure.

[0013]

According to the above-mentioned means, by changing the irradiation angle of the light source, the incident angle control section monitors the reflection intensity of the reflected light composed of the regularly reflected light and the multiple reflected light, which changes periodically. This reflection intensity can be minimized by detecting the minimum point and fixing the irradiation angle of the light source at the minimum point.

Therefore, in this state, by capturing the scattered light with the scattered light detecting portion, it is possible to detect the foreign matter on the object to be inspected with good sensitivity which is not affected by the background noise due to the multiple reflected light. It will be possible.

[0015]

Embodiments of the present invention will now be described in more detail with reference to the drawings.

FIG. 1 is a cross-sectional view of a main part of a foreign matter inspection apparatus according to an embodiment of the present invention, and FIG. 2A shows a model of phases of respective reflected lights reaching a light receiving camera of the foreign matter inspection apparatus. It is a graph figure, (b) is a graph figure which combined each light of (a).

As shown in FIG. 1, the foreign matter inspection apparatus of the present embodiment has a wafer stage 2 on which an SOI wafer (inspection object) 1 is mounted and a laser beam (light beam) on the SOI wafer 1 at a predetermined incident angle θ. ) 3 for irradiating the He-Ne laser oscillator (light source) 4 and the He-Ne laser oscillator 4 that is provided so as to face the He-Ne laser oscillator 4, and the specular reflection light 5a and the multiple reflection light 5b of the laser beam 3 irradiating the SOI wafer 1 , 5c for receiving the reflected light 5 (reflected light detection unit) 6
And is provided above the SOI wafer 1 and the SOI wafer 1
It comprises a photomultiplier tube (scattered light detection section) 9 which receives scattered light 8 scattered by the foreign matter 7 and transmits a detection signal to a foreign matter display section (not shown).

The SOI wafer 1 mounted on the wafer stage 2 is formed of, for example, a 500 nm thick SiO 2 film on the main plane of a 0.5 mm thick Si substrate 1a serving as a base by utilizing chemical bonding force.
_{The 2} μm thick Si layer 1c formed with the ₂ film 1b is joined by a so-called bonding method.
The I structure is formed. The SOI wafer 1
Can also be formed by an ion implantation insulating layer separation method, a zone melting method, or the like. In addition, Si substrate 1a, SiO ₂
The thicknesses of the film 1b and the Si layer 1c are not limited to the above numerical values and can be set to arbitrary values.

The He-Ne laser oscillator 4 is movable in an arc with respect to the SOI wafer 1 so that the incident angle θ of the laser beam 3 to be irradiated on the SOI wafer 1 can be set to an arbitrary angle. There is. Further, the light-receiving camera 6 receives the incident light 10 by moving the He-Ne laser oscillator 4.
It is configured to be movable in an arc shape in association with the change of the incident angle θ of 1 to receive the reflected light 5 from the SOI wafer 1. Further, the He—Ne laser oscillator 4 and the light receiving camera 6 are rotatable around the central axis of the wafer stage 2.

He-Ne laser oscillator 4 and light-receiving camera 6
Are electrically connected to the incident angle control unit 11. The incident angle control unit 11 detects the minimum point of the reflection intensity from the change in the reflection intensity of the multiple reflection lights 5b and 5c received by the light receiving camera 6 due to the change in the incident angle θ, and determines the incident angle θ as the minimum point. The He-Ne laser oscillator 4 is fixed as described in 1.

That is, a part of the laser beam 3 emitted from the He-Ne laser oscillator 4 is reflected by the surface of the Si layer 1c as the specular reflection light 5a and is captured by the light receiving camera 6, but the other part is Si. The Si layer 1c and Si are transmitted through the layer 1c.
As the multiple reflected light 5b reflected one after another at the interface with the O ₂ film 1b, another part of the light also passes through the SiO ₂ film 1b and becomes S.
The light is received by the light-receiving camera 6 as multiple reflection light 5c that is successively reflected at the interface between the iO ₂ film 1b and the Si substrate 1a. Therefore, the reflected light 5 captured by the light receiving camera 6 is
The specular reflection light 5a and the multiple reflection lights 5b and 5c overlap each other, and the reflection intensity I is given by the following equation.

[0022]

[Equation 1]

I ₀ is the intensity of the incident light 10 and R is Si
The reflectance of the layer 1c, δ, is the phase difference of one wave in the multiple reflected lights 5b, 5c with respect to the immediately preceding wave. This phase difference δ is given by the following equation.

[0024]

[Equation 2]

Note that n'is the refractive index of the Si layer 1c and h is S
The thickness of the i layer 1c, λ is the wavelength of the incident light 10, and α is the refraction angle.

From Equation 2, the phase difference δ of one wave with the multiple reflected lights 5b and 5c with respect to the immediately preceding wave is given by the following equation in consideration of the phase shift π at the time of reflection.

[0027]

(Equation 3)

Therefore, when considering two consecutive waves,
At δ = 2πm, when m is an integer, the phase difference δ of the two waves becomes zero and they overlap each other, and the reflection intensity I becomes maximum. On the other hand, when m is a half integer, the phase difference δ becomes π and the two waves cancel each other, and the reflection intensity I becomes minimum.

Here, the incident angle θ of the incident light 10 when the light is refracted at the boundary between the atmosphere and the Si layer 1c is given by the following formula according to Snell's law.

[0030]

[Equation 4]

Note that n ₀ is the refractive index of the atmosphere.

Therefore, the incident angle θ of the laser beam 3 at which the reflection intensity I becomes minimum can be obtained by the equations 3 and 4. And, this means that the reflection intensity I changes periodically depending on the incident angle θ of the laser beam 3.

In the present embodiment, based on the above, the specular reflection light 5a and the multiple reflection lights 5b and 5c are extracted as a model, and as shown in FIG.
When the phases of a, 5b and 5c are shifted by 2π / 3,
As shown in (b), they should cancel each other and the reflection intensity should become minimum (zero). However, since the multiple reflected lights 5b and 5c actually captured by the light receiving camera 6 are more and absorbed, the reflection intensity does not become zero in this way. However, as the incident angle θ of the laser beam 3 is changed, the reflected intensity I actually changes periodically. Therefore, the incident angle control unit 11 monitors the reflected light 5 to detect the minimum point of the reflected intensity. It will be possible. Then, as described above, if the irradiation angle of the He—Ne laser oscillator 4 is fixed at the minimum point detected by the incident angle control unit 11, the background noise due to the reflected light 5 is minimized.

As described above, according to the foreign matter inspection apparatus of the present embodiment, by changing the irradiation angle of the He-Ne laser oscillator 4, the regular reflection light 5a and the multiple reflection lights 5b and 5c which change periodically. The reflection intensity of the reflected light 5 consisting of and is monitored by the incident angle control unit 11 to detect the minimum point, and the irradiation angle of the He-Ne laser oscillator 4 is fixed at the minimum point. Can be minimized. Therefore, in this state, by capturing the scattered light 8 with the photomultiplier tube 9, the foreign matter 7 on the SOI wafer 1 can be detected with good sensitivity.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, He-N shown in this embodiment.
The e-laser oscillator 4, the light receiving camera 6, and the photomultiplier tube 9 are examples of a light source, a reflected light detection unit, and a scattered light detection unit, respectively, and are not intended to be limited to these.

Further, in the above description, the case where the invention made by the present inventor is mainly applied to the technique of detecting foreign matter adhering to an SOI wafer, which is the field of application which is the background of the invention, has been described. However, it is also possible to apply, for example, a photomask for forming a circuit element, glass, a lens, a crystal, or the like as the inspection object.

[0038]

The effects obtained by the typical ones of the inventions disclosed in this application will be briefly described as follows.

(1). That is, according to the foreign matter inspection technique of the present invention, by changing the irradiation angle of the light source,
By detecting the local minimum point by monitoring the reflection intensity of the reflected light composed of the regular reflection light and the multiple reflection light that changes periodically, the minimum point is detected, and by fixing the irradiation angle of the light source at this minimum point, It is possible to minimize the reflection intensity.

(2) Therefore, by capturing the scattered light in this state by the scattered light detector, the foreign matter on the object to be inspected can be detected with good sensitivity without being affected by the background noise due to the multiple reflected light. Can be detected.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing a foreign matter inspection device that is an embodiment of the present invention.

FIG. 2A is a graph showing a model of phases of respective reflected lights detected by a light receiving camera of the foreign matter inspection apparatus;
(B) is a graph diagram in which the respective lights of (a) are combined.

FIG. 3 is a cross-sectional view showing reflected light when an SOI wafer is irradiated with light by a conventional foreign matter inspection apparatus.

4A is a graph showing a model of the phase of each reflected light detected by the reflected light of FIG. 3, and FIG. 4B is a graph obtained by combining the lights of FIG.

[Explanation of symbols]

1 SOI wafer (inspection object) 1a Si substrate 1b SiO ₂ film 1c Si layer 2 Wafer stage 3 Laser beam (light) 4 He-Ne laser oscillator (light source) 5 Reflected light 5a Regular reflected light 5b Multiple reflected light 5c Multiple reflected light Light 6 Light receiving camera (reflected light detection part) 7 Foreign matter 8 Scattered light 9 Photomultiplier tube (scattered light detection part) 10 Incident light 11 Incident angle control part θ Incident angle 21 SOI wafer 21a Silicon substrate 21b Silicon oxide film 21c Silicon layer 25 reflected light 25a specular reflected light 25b multiple reflected light 25c multiple reflected light

Claims (3)

[Claims] 1. An object to be inspected in which incident light is multiple-reflected is prepared, and light is irradiated from the light source to the object to be inspected while changing the incident angle, and the reflection intensity changes periodically with the change of the incident angle. A foreign matter inspection method comprising monitoring light and detecting scattered light at the time when the reflection intensity of the reflected light becomes minimum to detect foreign matter adhering to the surface of the object to be inspected. 2. A light source having a variable incidence angle of light with respect to an object to be inspected in which incident light is multiply reflected, a reflected light detection unit for receiving reflected light of light emitted from the light source, and an irradiation from the light source. And a scattered light detection unit that receives scattered light due to the light that is electrically connected to the light source and the reflected light detection unit,
An incident angle control unit that detects a minimum point of the reflection intensity of the reflected light that periodically changes due to a change in the incident angle, and fixes the incident angle from the light source at this minimum point, and reflects the reflected light A foreign matter inspection apparatus, characterized in that the scattered light detecting section captures scattered light at a minimum intensity point to detect foreign matter adhering to the surface of the object to be inspected. 3. The foreign matter inspection apparatus according to claim 2, wherein the inspection object is a semiconductor wafer having an SOI structure.