JP2003166947A - Surface inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface inspection apparatus by which an inspection of high accuracy can be performed stably without being influenced by the film kind and the film thickness on the surface of a substrate. <P>SOLUTION: In the surface inspection apparatus, the surface of the substrate 5 is irradiated with a laser beam 2, scattering reflected light due to the laser beam is detected, and a foreign substance is detected. The inspection apparatus is provided with an irradiation optical system 7 whose light source part 12 comprises a plurality of light emitting sources and by which the surface of the substrate is irradiated with laser beams 2a, 2b from the respective light emitting sources in a state that reflection characteristics on the surface of the substrate are different. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection apparatus for inspecting fine foreign matters on the surface of a substrate such as a semiconductor wafer or fine scratches such as crystal defects.

[0002]

2. Description of the Related Art A surface inspection apparatus irradiates a laser beam on the surface of a substrate and detects scattered reflection light generated by a foreign substance or a scratch to detect the foreign substance or the scratch. Although a gas laser (He, Ar, etc.) has been generally used as a light emission source in the surface inspection apparatus, recently, a laser diode (LD) has been used for reasons such as easy handling, safety, and long life. It is used.

FIG. 11 shows a conventional irradiation optical system using a laser diode as a light emitting source.

A laser beam 2 emitted from a light emitting source 1 is collimated by a collimator lens 3 into a parallel light beam, and an image forming lens 4 forms a surface of a substrate 5 such as a wafer (the image forming lens 4).
It is irradiated so that it may be focused on a point (focus point f).
The laser beam 2 is incident on the substrate 5 at an angle of θ. A scattered / reflected light detector (not shown) detects scattered / reflected light from a position deviated from the reflected light axis of the laser beam 2, for example, a direction substantially perpendicular to the paper surface.

The detection sensitivity and detection accuracy are related to the wavelength and intensity of the laser beam 2 with which the surface of the substrate is irradiated. The detection sensitivity can be improved by shortening the wavelength or increasing the intensity. Further, by expanding the irradiation range while keeping the intensity uniform, it is possible to improve the detection accuracy while maintaining the detection sensitivity.

In recent years, the surface inspection apparatus is required to have further improved detection sensitivity and detection accuracy. For example, with the increase in density of semiconductor elements, the surface inspection apparatus is required to detect finer foreign matters and scratches on the wafer surface. You are required to do so.

As described above, the surface inspection apparatus detects foreign matters and scratches based on the detection of scattered reflected light. The scattered reflected light slightly changes depending on the properties of the substrate surface, that is, the film type and film thickness. . For example, in the case of a silicon oxide film (SiO2) formed on the surface of a silicon wafer, it is known that the reflectivity changes depending on the film thickness, and the change in the reflectivity changes periodically depending on the film thickness. It is also known that the change of is different depending on the wavelength.

FIG. 12 shows a silicon oxide film (S
In the case where iO2) is formed, the reflectance variation curve corresponding to the film thickness is shown by a laser beam of three wavelengths (488 nm, 680 nm).
nm, 780 nm).

The detection sensitivity of foreign matters and scratches has a substantial correlation with the reflectance of the substrate surface, and if the reflectance decreases and the amount of scattered reflected light decreases, the detection accuracy decreases. Therefore, in order to stably maintain the predetermined detection accuracy, it is necessary to select the wavelength of the laser beam to be applied according to the film type and the film thickness.

[0010]

In the above-mentioned conventional surface inspection apparatus, it is necessary to set the wavelength of the laser beam according to the film type and the film thickness, and the workability is poor. Further, the film thickness is not completely uniform over the entire surface of the substrate, and the reflectance may fluctuate depending on the site on the surface of the substrate, and the detection accuracy may fluctuate as the reflectance fluctuates.

In view of the above situation, the present invention provides a surface inspection apparatus that enables stable and highly accurate inspection without being affected by the film type and film thickness of the substrate surface.

[0012]

SUMMARY OF THE INVENTION The present invention is a surface inspection apparatus for irradiating a substrate surface with a laser beam and detecting scattered reflected light of the laser beam to detect foreign matter. The present invention relates to a surface inspection apparatus having a light source, and irradiating a laser beam from each light emitting source onto a substrate surface in a state where reflection characteristics on the substrate surface are different, and at least one of the plurality of light emitting sources. The present invention relates to a surface inspection device, one of which emits light at different wavelengths, and a surface inspection device provided with a polarizing member for changing the polarization state of at least one laser beam of the plurality of light emission sources, and one irradiation optical system. The present invention relates to a surface inspection apparatus having an image forming lens and an optical member which is provided corresponding to each light emitting source and makes a laser beam from the light emitting source enter the image forming lens. Those of the disposed surface inspection apparatus.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

An outline of the surface inspection apparatus will be described with reference to FIG.

In the figure, 5 is a substrate which is an object to be inspected, such as a wafer, and the surface inspection apparatus is mainly composed of a scanning drive mechanism section 6, an irradiation optical system 7 and a detection system 8.

Further, the scanning drive mechanism section 6 comprises a substrate holding section 9 for holding the substrate 5, the substrate holding section 9 is rotatably supported by a rotation driving section 10, and the rotation driving section 1
0 is adapted to be linearly moved in the radial direction parallel to the rotating surface of the substrate 5 by the linear drive mechanism section 11.

The irradiation optical system 7 is a deflection optical member 1 such as a light source section 12 for emitting a laser beam 2 as an inspection light, and a mirror for directing the laser beam 2 from the light source section 12 onto the substrate 5.
3, 14 and a lens group 15 for focusing the laser beam 2 on the surface of the substrate 5 and the like. The detection system 8 includes light receiving detectors 16 and 17 having a detection optical axis that intersects the optical axis of the laser beam 2 with which the surface of the substrate 5 is irradiated.

The surface inspection of the substrate 5 is performed by irradiating the laser beam 2 on the surface of the substrate 5 from the irradiation optical system 7 while the substrate 5 is rotated by the rotation driving unit 10, and further by the straight line. The rotation drive unit 10 is moved in the radial direction by the drive mechanism unit 11.

Thus, the irradiation point of the laser beam 2 is concentric circles by stepwise feeding at a required pitch for each revolution of the substrate 5 or by continuously feeding the rotary drive unit 10 at a predetermined speed. , Or while drawing a locus of a spiral circle, the substrate 5 moves from the center to the outer edge, and the entire surface of the substrate 5 is scanned by the laser beam 2.

During the process of scanning the surface of the substrate 5 by the laser beam 2, the laser beam 2 is scattered and reflected if there is a foreign substance or a scratch. The scattered reflected light is detected by the light receiving detectors 16 and 17 of the detection system 8 arranged at a predetermined position,
By processing the signals from the light receiving detectors 16 and 17 by an arithmetic processing unit (not shown), foreign matter and scratches are detected.

FIG. 2 shows the outline of the irradiation optical system 7 of the surface inspection apparatus of the present invention, and the deflecting optical members 13, 14 and the like are omitted in the figure.

The light source unit 12 includes two sets of light emitting sources 1a and 1b.
The light emitting sources 1a and 1b are capable of individually controlling the light emitting state and emit laser beams 2a and 2b having different wavelengths λ1 and λ2.

Laser beam 2 from the light emitting sources 1a and 1b
a and 2b are collimating lenses 3a and 3b, respectively.
Is formed into a parallel light beam by means of one imaging lens 4 and is condensed on the surface of the substrate 5. The optical axes of the collimator lenses 3a and 3b and the imaging lens 4 are parallel to each other, and the light emitting sources 1a and 1b are provided.
The laser beams 2a and 2b emitted from are focused on the same irradiation point 18 by the imaging lens 4.

Laser beams 2a and 2b having different wavelengths from the light emitting source 1a and the light emitting source 1b are focused and irradiated onto the same irradiation point 18 by the imaging lens 4.

When the laser beam of the light emitting source 1a and the light emitting source 1b alone is applied to the irradiation point 18, for example, the laser beam 2a of the wavelength λ1 is applied to the irradiation point 18 independently from the light emitting source 1a. When the film type is the silicon oxide film (SiO2) as described above, the reflectance of the scattered reflection light of the No. fluctuates periodically with respect to the change of the film thickness such as one predetermined wavelength in FIG. To do. Further, although not shown, when the laser beam 2b having the wavelength λ2 from the light emitting source 1b is applied to the irradiation point 18 alone, the light emitting source 1a emits light as shown by lines having different wavelengths in FIG. It changes periodically in response to the change in film thickness in a phase different from the case.

Next, when the laser beams 2a and 2b are simultaneously irradiated from the light emitting source 1a and the light emitting source 1b, the reflectances are out of phase with each other as shown in FIG. The rate is a combination of the reflectances of the laser beams 2a and 2b. That is, the laser beams 2a, 2
By combining the reflectances of b, the peak portions of the reflectances become substantially flat, and the reflectance fluctuation curve has a trapezoidal shape.

By simultaneously irradiating the same irradiation point 18 with the two kinds of laser beams 2a and 2b having wavelengths λ1 and λ2,
For example, since it is possible to reduce the drop-in portion of the reflectance at the predetermined two wavelengths in FIG. 12, the scattered reflection light due to foreign matter and scratches is stable and the detection accuracy is stable even when the film thickness changes. Does not change.

The laser beams of three or more wavelengths may be mixed and irradiated at the same irradiation point. In this case, the reflectance variation curve is a combination of the reflectances of the respective laser beams, and if the wavelength of the reflectance variation curve of each laser beam is shifted by an appropriate amount, the irradiation light intensity can be adjusted. , The flat part of the peak of the reflectance fluctuation curve becomes larger, and it becomes more stable against fluctuations in film thickness.

FIG. 5 shows an example of an irradiation optical system for mixing laser beams of three or more wavelengths.

FIG. 5 shows a second embodiment, and in the second embodiment, a case where a large number of light emitting sources 1a ... 1n are used is shown. .. 2n of different wavelengths are emitted from the light emitting sources 1a.

1n are linearly arranged, and collimating lenses 3a ... 3n are provided for the respective light emitting sources 1a ... 1n, and the collimating lenses 3a ... 3n are provided.
2n is a single imaging lens 4
3n, and the optical axes of the collimating lenses 3a ... 3n are parallel to the optical axis of the imaging lens 4.

In the present embodiment, all the laser beams 2a ... 2n having different wavelengths are condensed at one point of the irradiation point 18, the reflectances of the respective laser beams 2a ... 2n are combined, and the flat trapezoidal reflection is performed. A rate variation curve is obtained.

In the above embodiment, it has been described that the reflectance varies with the film thickness due to the different wavelengths.
It has been found that the polarization state of the laser beam 2 influences the reflectance as the angle θ of the laser beam 2 incident on the substrate 5 increases, as shown in FIG.

A third embodiment will be described with reference to FIG.

FIG. 6 shows an outline of the irradiation optical system 7 of the third embodiment. In the figure, the same parts as those shown in FIG. 2 are designated by the same reference numerals, and the detailed description thereof will be omitted. .

The light emission sources 1a and 1b can individually control the light emission state, and the laser beams 2a and 2b from the light emission sources 1a and 1b are individually collimated lenses 3a and 3b.
A parallel light beam is formed by 3b, and the surface of the substrate 5 is condensed and irradiated by one imaging lens 4. The optical axes of the collimating lenses 3a and 3b and the imaging lens 4 are parallel to each other, and the laser beams 2a and 2b emitted from the light emitting sources 1a and 1b are irradiated by the imaging lens 4 at the same irradiation point. It is designed to be focused on 18.

Polarizing members 19a and 19b are provided so that they can be inserted and removed with respect to the respective optical axes of the laser beams 2a and 2b. The wavelengths of the laser beams 2a and 2b emitted from the light emitting sources 1a and 1b may be the same or different, but the following description will be made as the same. The incident angle θ of the laser beam 2 with respect to the substrate 5 is an angle at which the polarization state of the laser beam 2 is reflected in the reflectance.

As the polarizing member, a polarizing plate, 1 / 2λ
Examples include a plate, a 1 / 4λ plate, a depolarizing plate (where polarized light is random polarized light), and the like.

In FIG. 6, for example, the laser beam 2a is used.
When the polarizing member 19a is inserted only with respect to the optical axis of
The polarization states of the laser beam 2a and the laser beam 2b change. Therefore, as shown in FIG. 3, there is a difference between the laser beam 2a and the laser beam 2b in the reflectance variation curve with respect to the variation of the film thickness, but the combined reflectance variation curve of the laser beams 2a and 2b is shown in FIG. Similarly, the peak value becomes flat when the film thickness is between 0.6 μm and 0.7 μm.

Thus, also in the third embodiment, even when the film thickness is changed, the scattered reflected light due to the foreign matter and the scratch is stable, and the detection accuracy is not stable.

By selecting a polarizing plate, a 1 / 2λ plate, a 1 / 4λ plate, and a depolarizing plate, the polarization state of the laser beam can be changed, and the reflectance fluctuation curve also changes. Therefore, by appropriately selecting the polarization members 19a and 19b to be inserted into the optical axes of the laser beam 2a and the laser beam 2b, it becomes possible to adjust the reflectance fluctuation curve of the laser beams 2a and 2b. .

Further, it goes without saying that the reflectance fluctuation curves of the laser beams 2a and 2b change by changing the wavelengths of the laser beams 2a and 2b. By appropriately selecting the wavelength and the polarization state, the adjustment range of the reflectance variation curve becomes large, and a more optimal reflectance variation curve can be realized.

FIG. 7 shows a fourth embodiment. In the fourth embodiment, the light emitting sources 1a and 1b are provided at separate positions, and the laser beams are mixed.

The light emitting source 1a and the collimating lens 3a provided corresponding to the light emitting source 1a are provided at a position intersecting with the optical axis of the imaging lens 4, for example, on an optical axis orthogonal to each other, and from the light emitting source 1a. The emitted laser beam 2a is reflected by the reflecting mirror 21a in parallel with the optical axis of the imaging lens 4 and guided to the imaging lens 4.

The light emitting source 1b and the collimating lens 3b are also arranged in the same manner, and the laser beam 2b emitted from the light emitting source 1b is reflected by the reflecting mirror 21b, and the imaging lens 4 is formed.
The light is incident on the imaging lens 4 in parallel with the optical axis of.

By the image forming lens 4, the light emitting sources 1a, 1
The laser beams 2a and 2b emitted from b are focused on the irradiation point 18.

In the fourth embodiment, when the number of light emitting sources 1 is three or more, the light source 1 and the collimating lens 3 may be arranged on the radiation centered on the optical axis of the image forming lens 4.

In the fourth embodiment, the light emitting source 1a,
1b changes the wavelength emitted, or the laser beams 2a, 2b
By inserting and removing the polarizing members 19a and 19b on the optical axis of
A reflectance fluctuation curve similar to that of the above-described embodiment can be obtained, and an optimum reflectance fluctuation curve can be realized.

FIG. 8 shows a fifth embodiment. In the fifth embodiment, as in the fourth embodiment, the light emitting sources 1a and 1b are provided at separate positions. This is a case where the laser beams 2a and 2b are mixed.

The light source section 12 has two sets of light emitting sources 1a and 1b provided apart from each other. The light emitting sources 1a and 1b are capable of individually controlling their light emitting states and have different wavelengths λ1,
The laser beams 2a and 2b of λ2 are emitted.

Laser beam 2 from the light emitting sources 1a and 1b
a and 2b are collimating lenses 3a and 3b, respectively.
To form a parallel light beam. A reflecting mirror 22 is arranged on the optical axis of the laser beam 2a, and a half mirror 23 is arranged at the intersection of the reflecting optical axis of the reflecting mirror 22 and the optical axis of the collimating lens 3b.

The laser beam 2a is reflected by the reflecting mirror 22 and the half mirror 23, and the half mirror 2
The laser beam 2b that passes through the laser beam 3 is focused on the irradiation point 18 of the substrate 5 on the optical axis of the imaging lens 4 and focused.

Also in the fifth embodiment, the wavelengths emitted by the light emitting sources 1a and 1b are changed, or the polarization members 19a and 19b are inserted and removed on the optical axes of the laser beams 2a and 2b. Then, a reflectance variation curve similar to that of the above-described embodiment can be formed, and an optimal reflectance variation curve can be realized.

In the fifth embodiment, the reflecting mirror 22 and the half mirror 23 are omitted, and the laser beam 2a from the light emitting source 1a is directly reflected by the deflection optical member 14 'and the imaging lens 4'. The irradiation point 18 is focused and irradiated, and the irradiation point 1
The laser beams 2a and 2b may be mixed at 8. In this case, the laser beam 2a and the laser beam 2b have different incident angles with respect to the substrate 5, and the reflection characteristics are also affected by the incident angle. Therefore, by switching the optical paths of the laser beams 2a and 2b, they differ. It is possible to obtain excellent reflection characteristics.

FIG. 9 shows an example of the optical path switching means.

A reflecting mirror 24 is provided on the optical axis of the laser beam 2a.
a and 25a, and the reflecting mirrors 24b and 25b can be integrally inserted into and removed from the optical axis of the laser beam 2b.
With 25a and the reflecting mirrors 24b and 25b inserted,
The laser beam 2a is reflected by the reflecting mirrors 24a, 25b to the optical axis of the laser beam 2b before the change, and the laser beam 2b is reflected by the reflecting mirrors 24b, 25a and the laser beam 2 before the change.
The optical path is changed to the optical axis of a.

FIGS. 10A and 10B show another example of the optical path switching means.

In the other optical path switching means, the light emitting sources 1a,
1b is rotatable integrally, and the light emitting sources 1a and 1b are
The optical path is switched by rotating 0 °.

In the embodiment shown in FIG. 5, the plurality of light emitting sources 1 are arranged in a straight line, but the plurality of light emitting sources 1 may be arranged in a required row and arranged in a matrix.

In the case of a matrix, the light intensity of the irradiation point can be adjusted as follows, although not particularly shown. This will be described with reference to FIG.

That is, for each row, the wavelength of the light emitting source 1 is changed, the polarizing member 19 is further inserted / removed as appropriate, and the reflectance of each laser beam is combined for the first row to obtain a flat trapezoidal reflectance. The condition is that a fluctuation curve can be obtained. Next, the second and subsequent columns are set in a state in which the same reflectance fluctuation curves as those in the first column can be obtained. The optical axis of the collimator lens 3 provided corresponding to each light emitting source is parallel to the optical axis of the imaging lens 4.

In this state, all the laser beams 2 are focused and irradiated on the irradiation point 18, and a flat trapezoidal reflectance fluctuation curve is obtained for each row, and the light intensity of each row is different. Light intensity will be added for the number of rows,
The amount of scattered reflection light obtained increases.

Since the detection accuracy is improved by increasing the irradiation light intensity, when the plurality of light emitting sources 1 are arranged in a matrix, the stability of the inspection accuracy of the surface inspection apparatus against the film thickness variation is improved. Improvement of inspection accuracy can also be obtained.

Further, it is effective even when the laser beam 2 cannot obtain a sufficient amount of light by itself, such as a blue laser diode.

The array of the plurality of laser beams 2 is not limited to the matrix, and may be circular or any other array. In short, the wavelength, polarization state, and light intensity of each light emitting source may be adjusted so that a flat reflectance variation curve can be obtained.

[0066]

As described above, according to the present invention, in the surface inspection apparatus for irradiating the surface of the substrate with the laser beam and detecting the scattered reflected light of the laser beam to detect the foreign matter, a plurality of light source units are provided. Of the light source, the laser beam from each light source is provided on the substrate surface, the irradiation optical system for irradiating the substrate surface in a state where the reflection characteristics on the substrate surface are different. It is less affected by the film thickness and exhibits excellent effects such as stable and highly accurate inspection.

[Brief description of drawings]

FIG. 1 is a skeleton view showing a basic configuration of a surface inspection device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an irradiation optical system of the surface inspection device.

FIG. 3 is a diagram showing a relationship between a change in film thickness and reflectance when a substrate surface is irradiated with a laser beam having a single wavelength.

FIG. 4 is a diagram showing the relationship between the change in film thickness and the reflectance when a single-wavelength laser beam with different polarization is applied to the substrate surface.

FIG. 5 is an explanatory diagram of an irradiation optical system of the surface inspection apparatus according to the second embodiment.

FIG. 6 is an explanatory diagram of an irradiation optical system of a surface inspection device according to a third embodiment.

FIG. 7 is an explanatory diagram of an irradiation optical system of a surface inspection device according to a fourth embodiment.

FIG. 8 is an explanatory diagram of an irradiation optical system of a surface inspection device according to a fifth embodiment.

FIG. 9 is an explanatory diagram showing an example of an optical path switching unit according to a fifth embodiment.

FIGS. 10A and 10B are explanatory views showing another example of the optical path switching means in the fifth embodiment.

FIG. 11 is an explanatory diagram showing an irradiation optical system of a conventional surface inspection device.

FIG. 12 is a diagram showing the relationship between the change in film thickness formed on the substrate surface and the reflectance of laser beams having different wavelengths.

[Explanation of symbols]

1 light source 2 laser beam 5 substrates 6 Scan drive mechanism 7 Irradiation optical system 8 detection system 12 Light source 15 lens groups 18 irradiation points 19 Polarizing member

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2G051 AA51 AB01 AB02 BA01 BA08                       BA10 BA11 BB01 BB09 BB20                       CA01 CB01 CB05                 4M106 AA01 BA05 CA41 CA46 DB08                       DB14

Claims (5)

[Claims] 1. A surface inspection apparatus for irradiating a laser beam on a substrate surface and detecting scattered reflected light of the laser beam to detect foreign matter, wherein a light source section has a plurality of light emission sources, and each light emission is performed. A surface inspection apparatus, comprising: an irradiation optical system that irradiates a laser beam from a source onto a substrate surface in a state where the substrate surface has different reflection characteristics. 2. The surface inspection apparatus according to claim 1, wherein at least one of the plurality of light emitting sources emits light at different wavelengths. 3. The surface inspection apparatus according to claim 1, further comprising a polarizing member that changes a polarization state of at least one laser beam of the plurality of light emitting sources. 4. The irradiation optical system has one image forming lens, and an optical member provided corresponding to each light emitting source to make a laser beam from the light emitting source incident on the image forming lens. Surface inspection device. 5. The surface inspection apparatus according to claim 1, wherein the light emission sources are arranged in a matrix.