JP2002139309A - Optical characteristics measuring device, film thickness measuring device, polishing end point determining device and polishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical characteristics measuring device, capable of surely and completely removing the diffracted lights of not less than first order. SOLUTION: A Koehler illumination light is formed, by arranging a condenser lens 7, so that a light source image position of a light source unit 1 is positioned in the vicinity of a front focus of the condenser lens 7 to illuminate an inspection object surface S of an inspection object 8, arranged in the vicinity of a rear side focal surface of the condenser lens 7. An opening area fixed or variable aperture diaphragm member 6 is arranged in the vicinity of the light source image position to control the size (NA of the illumination light) of a light source image. Since the extent of the diffracted light formed by the inspection object surface S becomes narrow, by restricting the opening half angle of the Koehler illumination light, the diffracted light of not less than the first order can be removed surely by a pinhole diaphragm member 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the optical characteristics of an object by irradiating the surface of the object with illumination light and measuring the reflected light with a photodetector, and a film thickness measurement using the same. The present invention relates to a polishing apparatus having at least one of an apparatus, a polishing end point determining apparatus, and a film thickness measuring apparatus and a polishing end point determining apparatus.

[0002]

2. Description of the Related Art As an optical characteristic measuring device for measuring optical characteristics such as reflectance and spectral reflectance of an object, the surface of an object to be measured is illuminated with predetermined light, and the reflected light is directly measured by a photodetector. In general, an apparatus for measuring with a photodetector after passing through a spectroscope is generally used.

A part of the present inventor and his colleagues have proposed a method of measuring a film thickness to prevent first-order or higher-order diffracted light and scattered light out of reflected light from entering a light receiver, and a method of determining a polishing end point in a polishing apparatus. Was invented. The invention is disclosed in JP-A-2000-18.
No. 6918 (hereinafter referred to as “prior art”).

FIG. 4 shows an embodiment of the prior art. Light from a xenon lamp 51, which is a light source, is converted into a parallel light beam by a lens 52, passes through an illumination area control slit 53, and is condensed on a beam splitter 55 by a lens 54. The light that has passed through the beam splitter 55 is again converted into a parallel light beam by the lens 56 and is irradiated on the surface of the wafer 57 to be measured. In the present embodiment, the xenon lamp 51, the lens 52, the illumination area control slit 53, the lens 54, and the lens 56 constitute light irradiation means.

The reflected light from the wafer to be measured 57 is again focused on the beam splitter 55 through the lens 56. In the beam splitter 55, the reflected light is 90 °
The direction is changed, and a parallel light beam is formed by the lens 58.
Then, the light is reflected by the mirror 59, and the slit 60 is a light shielding unit having an opening for selecting only the zero-order light by the lens 60.
The light is focused on 1. Then, noise components such as scattered light and diffracted light are removed, and are projected via a lens 62 onto a diffraction grating 63 serving as a spectral unit, and are separated. The split light is
The light enters the linear sensor 64, which is a photoelectric conversion element, and the spectral intensity is measured.

In this optical system, a xenon lamp 51
Is formed on the beam splitter 55, and the image forming position is located at the front focal point of the lens 56. Therefore, the surface of the wafer to be measured 57 is illuminated uniformly and almost vertically by parallel light.

[0007] The slit 61 is provided for the wafer 57 to be measured.
It is provided at the condensing position of the vertical reflected light from the camera. Therefore, by adjusting the diameter of the opening, the N of the reflected light is adjusted.
A, that is, the reflection angle of light passing through the opening can be adjusted. Therefore, the assumed wafer to be measured 57
By selecting the aperture diameter such that the first or higher order diffracted light generated from the pattern on the surface cannot pass through the opening of the slit 61, only the zero order light can be measured.

As described above, if the prior art is used, only the zero-order light can be selected and guided to the optical system after the lens 62, so that the measurement error caused by the first-order or higher-order diffracted light is eliminated. Accurate measurement becomes possible.

[0009]

However, also in the prior art, the light beam incident on the surface of the object to be measured is not limited to a parallel light beam incident vertically. That is, rays emitted from one point of the light source in each direction are parallel to each other, but lights emitted from different points are not parallel. Therefore, when the cross-sectional area of the light emitted from the light source is large, light incident at various angles is mixed, and accordingly, the spread of the angle at which the diffracted light is emitted (referred to as “spread of the diffracted light”) ) Increases.

FIG. 5 shows a case where light I ₀ is obliquely incident on the wafer 57 to be measured. In FIG. 5, diffracted light I _d1 is generated in the reflected light other than the 0th-order reflected light I ₀ ′, and the traveling direction of the diffracted light I _d1 is almost the same as the optical axis O of the vertically reflected light from the wafer 57 to be measured. is there. In this case, in FIG. 4, the diffracted light I _d1
Passes through the slit 61. Therefore, it may be difficult to completely remove the first or higher order diffracted light only with the slit 61 in FIG.

Further, the optical system as shown in FIG. 4 requires a slit 61 and a lens 62, and has a problem that the arrangement of the optical system is complicated.

The present invention has been made in view of such circumstances, and an optical characteristic measuring device capable of reliably removing first-order or higher order diffracted light, an optical characteristic measuring device in which the arrangement of the optical system is simpler, Another object of the present invention is to provide a film thickness measuring device and a polishing end point determining device using the same, and a polishing device having at least one of the film thickness measuring device and the polishing end point determining device.

[0013]

A first means for solving the above problems is to irradiate the surface of the object with illumination light and measure the reflected light with a photodetector to measure the optical characteristics of the object. An apparatus that uses Koehler illumination light as the illumination light, condenses the reflected light with an optical system, and provides an aperture at or near the converging point to generate a primary light generated on the surface of the object. In the above-mentioned device having a function of removing the diffracted light from the measurement light received by the photodetector, it may have an aperture area fixed or variable aperture for controlling the NA of the light beam of the Koehler illumination light. This is a characteristic optical characteristic measuring device (claim 1).

This means has an aperture having a fixed or variable aperture area for controlling the NA of the light beam of the Koehler illumination light, which is the illumination light. N of luminous flux in Koehler illumination
When A is determined, all the illumination light is composed of light rays having an inclination within an opening half angle determined by NA with respect to the optical axis. Therefore, the spread of the diffracted light formed on the surface of the object to be measured also becomes narrow, so that the aperture provided at or near the condensing position of the reflected light surely increases the intensity of the diffracted light.
It is possible to remove diffracted light of the next order or more. "Nearby"
This means that the position of the aperture may be shifted in the optical axis direction from the accurate light-converging point position within a range where the first-order or higher-order diffracted light can be reliably removed.

The aperture for controlling the NA may be a fixed aperture when the direction of emission of the generated diffracted light does not change much depending on the object to be measured. However, when the change is large, the aperture area is made variable and the opening half angle is changed. It is preferable to make it variable. The aperture for controlling the NA may be provided anywhere as long as the function can be exhibited.

In the description of the present means and other means, and in each claim, the "photodetector" means not only a single optical sensor but also a spectroscope or other optical system. The concept also includes the one that finally detects light with an optical sensor.

A second means for solving the above-mentioned problem is as follows.
An apparatus for measuring the optical characteristics of an object by irradiating the surface of the object with illumination light and measuring the reflected light with a photodetector, wherein Koehler illumination light is used as the illumination light, and the reflected light is used as an optical system. An optical characteristic measuring apparatus having a function of condensing light on or near an end face of an optical fiber and detecting light emitted from the other end face of the optical fiber by the photodetector. ).

In this means, one end face of the optical fiber is arranged at a position where an aperture for blocking the first or higher order diffracted light in the prior art is provided, that is, at or near a position where reflected light is condensed by the optical system. Let me. The light incident on the optical fiber is determined by the area of the end face of the optical fiber, and the end face is located at a position where the reflected light is condensed by the optical system, so that the optical fiber plays a role in determining the NA of the reflected light. .

The light incident on the optical fiber is emitted from the other end of the optical fiber and detected by the photodetector. Therefore, according to the present means, the aperture and the optical system provided thereafter as in the prior art are not required, and the arrangement of the optical system can be made simple and flexible.

As in the case of the first means, the term "near the vicinity" refers to a range in which the first or higher order diffracted light can be surely removed, and the position of the end face of the optical fiber is more accurate than the position of the converging point. Indicates that it may be shifted in the axial direction.

A third means for solving the above problem is as follows.
The second means is characterized in that it has an aperture having a fixed or variable aperture area for controlling the NA of the light beam of the Koehler illumination light (Claim 3).

In the second means, the end face of the optical fiber is made to function as an aperture. However, the dimensions of the optical fiber are determined by the standard, and it is difficult to freely change it. Therefore, in this means, an aperture having a fixed or variable aperture area for controlling the NA of the light beam of the Koehler illumination light is provided. This makes it possible to control the spread of the diffracted light as described in the description of the first means, so that the disadvantage of the second means can be eliminated.

In this means, similarly to the first means, the aperture for controlling the NA may be provided anywhere as long as its function can be exhibited.

A fourth means for solving the above-mentioned problem is:
A film thickness measuring device for measuring a film thickness of a thin film formed on a surface of an object by measuring an optical characteristic of the object.
The optical characteristic of the object is measured by using any one of the above means.

A film thickness measuring apparatus for measuring the film thickness of a thin film formed on the surface of an object by measuring the optical characteristics of the object has been widely used, for example, as described in JP-A-11-33901. Are known. In this means, in any of these film thickness measuring devices, any one of the first to third means is used as an optical characteristic measuring device, so that a pattern or the like formed on the surface of an object to be measured can be used. Even if diffracted light is generated, its influence can be reliably removed, and accurate film thickness measurement can be performed.

A fifth means for solving the above problem is as follows.
The polishing apparatus according to claim 1, wherein the polishing end point is determined by measuring an optical characteristic of the object to be polished. Using the optical property measurement device of
The optical characteristic of the object is measured (claim 5).

In the polishing apparatus, many examples of the polishing end point determining apparatus for determining the polishing end point by measuring the optical characteristics of the object to be polished, such as those described in JP-A-11-33901, are known. It has become. In this means, in the polishing end point determination device, the first
Since any one of the above-mentioned means to the third means is used as an optical characteristic measuring device, even if diffracted light is generated due to a pattern or the like formed on the surface of the object to be measured, it is necessary to surely remove the influence. This makes it possible to accurately determine the polishing end point.

Sixth means for solving the above-mentioned problems is as follows.
A polishing apparatus comprising at least one of the fourth means and the fifth means (claim 6).

In a polishing apparatus used for polishing a thin film formed on the surface of an object to be polished to a flat and predetermined thickness, for example, as described in JP-A-11-33901, The apparatus is provided with at least one of a device and a polishing end point judging device. In particular, a film thickness is measured while polishing is in progress (in-situ), and a polishing end point is determined. In this means, in the polishing apparatus, the film thickness measuring device and the polishing end point judging device are the fourth device.
Since the means according to the fifth means and the fifth means are used, the film thickness of the object to be polished can be accurately controlled.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a first example of an optical characteristic measuring device according to an embodiment of the present invention.

The apparatus shown in FIG. 1 irradiates part or all of the test surface S with light while polishing the test surface S of the test object 8 with a polishing device (not shown), and reflects reflected light from the test surface. This is a polishing end point determination device for detecting and analyzing to detect the end of the polishing process.

The light emitted from the light source unit 1 is converted into parallel light by the collector lens 2,
After the luminous flux diameter is determined by the fixed or variable aperture stop 3 disposed near the rear focal plane of
After passing through the optical path dividing member 4 (half mirror or the like), a light source image is formed by the relay lens 5.

The Koehler illumination light is formed by arranging the condenser lens 7 such that the light source image position is located near the front focal point of the condenser lens 7, and the test object arranged near the rear focal plane of the condenser lens 7. Object 8
Is illuminated. In the present embodiment,
As the “aperture fixed or variable aperture controlling the NA of the light beam of Koehler illumination light” which is a feature of the present invention, a fixed or variable aperture stop member 6 having an aperture area fixed near the light source image position is provided. The size (NA of illumination light) can be controlled. Here, since the test surface S and the field stop member 3 are conjugate, the irradiation area of the test surface S with the illumination light can be controlled by the opening area of the field stop member 3.

The light reflected by the surface S to be measured passes through an optical path partially common to the incident light, is converted into parallel light by the condenser lens 7 and the relay lens 5, and the component reflected by the optical path splitting member 4 is converted to a detection system. The light is condensed on the photodetector 13 by the relay lens groups 9, 11, and 12. At this time, the pinhole aperture member 10 is arranged near the rear focal plane of the first detection system relay lens 9, that is, near the focal point of the reflected light. Since the diameter of the light beam at this position corresponds to the angle of the reflected light on the surface S to be measured, the pinhole aperture member 10 can control the angle (NA) of the reflected light.

Although the diffraction angle increases as the periodic pattern structure of the object surface becomes finer, patterns having different roughness may exist on the actual object surface. In order to shield the emitted first-order or higher order diffracted light, it is preferable that the aperture area of the pinhole diaphragm member 10 be as small as the sensitivity of the photodetector 13 allows.
With the above configuration, high-order diffracted light can be removed, and only zero-order light can be selected.

In the present embodiment, the aperture stop member 6
As a result, the opening half angle of the Koehler illumination light is restricted, and as described in the description of the first means for solving the problem, the spread of the diffracted light formed on the test surface S also becomes narrow. . Therefore, by the pinhole aperture member 10,
The first or higher order diffracted light can be reliably removed.

Here, when the conjugate relationship is arranged, the light source unit 1, the aperture stop member 6, the pinhole stop member 10, and the photodetector 13 are conjugate, and the field stop member 3 and the test surface S are conjugate. The aperture stop 6 does not necessarily need to be provided at the position as shown in FIG. 1, and may be provided anywhere near the position where the light source image is formed.

FIG. 2 is a view showing a second example of the optical characteristic measuring apparatus according to the embodiment of the present invention. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals.

The embodiment shown in FIG. 2 is different from the embodiment shown in FIG. 1 in that it does not have a pinhole aperture member 10 and detection system relay lenses 11 and 12, but has an optical fiber 14 instead. That is the point. Therefore, the operation of the embodiment shown in FIG. 2 is the same as that of the embodiment shown in FIG. 1 up to the point where the reflected light from the test surface S is collected by the first detection system relay lens 9. Therefore, the description is omitted.

In this embodiment, the optical fiber 1
The fourth end surface 14a plays the same role as the pinhole stop member 10 in the embodiment shown in FIG. 1, and plays a role of blocking the first-order or higher-order diffracted light formed by the pattern on the test object. Therefore, in selecting an optical fiber diameter, it is necessary to select a diameter that can sufficiently exhibit this function.

However, since the diameter of the optical fiber 14 is determined by the standard, it is not always possible to use an optical fiber having an optimum diameter. In the present embodiment,
By adjusting the aperture stop 6, the spread of the illumination light can be adjusted, and at the same time, the opening angle of the reflected light can be adjusted, so that the conditions for selecting the optical fiber 14 are eased. That is, the aperture for adjusting the NA of the illumination light may be provided anywhere as long as the function can be exhibited. Of course, if the first-order or higher order diffracted light can be sufficiently removed only by selecting the optical fiber 14, the aperture stop 6 is unnecessary.

The light incident on the optical fiber 14 is transmitted to the photodetector 13 through the optical fiber 14. Therefore, there is no need to guide the light to the photodetector 13 by an optical system such as a lens, and these optical systems can be omitted, and the optical fiber 14 can be freely bent to some extent. Constraints are relaxed.

The above embodiments relate to the most frequently used vertical incidence, vertical reflection type optical characteristic measuring apparatus, but the present invention is not limited to such an apparatus. It is determined based on the matters described in the claims. For example, a configuration may be adopted in which Koehler illumination light is incident obliquely and specularly reflected light is received. 1 and 2, the photodetector 13
Although an example in which light is directly incident on the optical detector 13 is shown, an example in which light is incident on the photodetector 13 through another optical device such as a spectroscope or a filter is also included in the scope of the present invention. Needless to say.

Here, the conjugation relationship can be summarized as follows: light source unit 1, aperture stop 6, fiber surface 14a, photodetector 13
Are conjugate, and the field stop 3 and the test surface S are conjugate.

FIG. 3 is a diagram showing an example of a film thickness measuring device, a polishing end point determining device, and a polishing device according to an embodiment of the present invention. In FIG. 3, reference numeral 21 denotes a polishing object holding portion (hereinafter, referred to as a polishing object holding portion)
22 is a wafer, 23 is a polishing plate, 24 is a polishing body, 25 is a polishing liquid supply section, 26 is a polishing liquid, 27 is a film thickness measuring device and polishing end point judging device, 28 is a light source, and 29 is an optical path splitter. A member, 30 is a photodetector, and 31 is a cover.

The polishing apparatus comprises a holder 21, a polishing plate 23, a polishing body 24 attached to the polishing plate 23, and a polishing liquid supply unit 25. Then, a wafer 22 to be polished is attached to the holder 21, and the polishing liquid supply unit 25 supplies a polishing liquid 26.

As the polishing body 24, a sheet-like polishing pad made of foamed polyurethane or a non-foaming resin polishing pad having a groove structure on its surface is used. The holder 21 is rotated about the axis A in the direction of arrow a by appropriate means, and the polishing plate 23 is rotated about the axis B in the direction of arrow b by appropriate means. Further, the axis B swings linearly approaching or moving away from the axis A as indicated by an arrow c. In these processes, the polishing surface of the wafer 22 (the surface in contact with the polishing body 24) is polished by the action of the polishing liquid 26 and the polishing body 24.

In the above polishing process, the spectral reflectance of light is measured to determine whether the polished surface of the wafer is polished by a predetermined amount and sufficiently flattened, that is, to determine the polishing end point and measure the film thickness of the film on the wafer. Further, a film thickness measuring device and a polishing end point determining device 27 for performing these measurements are provided.
The film thickness measurement device / polishing end point determination device 27 is installed above the wafer 22. In order to prevent the polishing liquid from scattering to the film thickness measuring device / polishing end point judging device 27, the film thickness measuring device / polishing end point judging device 27 is almost covered with a cover 31.

In the figure, a light source 28 and an optical path dividing member 2 are used as constituent elements of the film thickness measuring device and polishing end point judging device 27.
9, only the photodetector 30 is shown, and details are omitted, but the actual optical system of the film thickness measuring device and polishing end point determining device 27 shown in FIG. 1 or 2 is used. As the photodetector 30, a detector having a spectroscope and detecting a change in spectral characteristics as shown in JP-A-11-33901 is used. Then, the spectral reflectance is measured based on the principle described in the publication, and from this, the film thickness measurement and the determination of the polishing end point are performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of an optical characteristic measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a second example of the optical characteristic measuring device according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a film thickness measuring device, a polishing end point determining device, and a polishing device according to an embodiment of the present invention.

FIG. 4 is a diagram showing an example of an embodiment of the prior art.

FIG. 5 is a diagram showing how light travels when light is obliquely incident on a wafer to be measured.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source unit, 2 ... Collector lens, 3 ... Field stop member, 4 ... Optical path dividing member, 5 ... Relay lens, 6 ... Aperture stop member, 7 ... Condenser lens, 8 ... Test object,
9: detection system lens, 10: pinhole aperture member, 11,
Reference numeral 12: detection system lens, 13: photodetector, 14: optical fiber, 14a: end face of the optical fiber, 21: holder (holder) for polishing object, 22: wafer, 23: polishing plate, 24 ...
Polishing body, 25: Polishing liquid supply unit, 26: Polishing liquid, 27: Film thickness measuring device and polishing end point determining device, 28: Light source, 29: Optical path dividing member, 30: Photodetector, 31: Cover, S: Covered Inspection

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H01L 21/304 622 H01L 21/304 622S (72) Inventor Yoshikazu Sugiyama 3-2 Marunouchi, Chiyoda-ku, Tokyo No. 3 Nikon Corporation (72) Inventor Motoo Koyama 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Stock Company Nikon Corporation (72) Kajiro Shio 3-2-2, Marunouchi Chiyoda-ku, Tokyo Stock Company F term in Nikon Corporation F term (reference) 2F065 AA30 CC00 DD04 FF42 FF44 FF46 GG01 HH13 JJ01 JJ09 LL02 LL04 LL28 LL30 LL46 2G051 BA20 BB07 BB09 CA07 CB01 CC07 CC15 CC17 EA17 2G019 EJ01 BB08 EJ01 BB08 KK01 KK03 NN01

Claims (6)

[Claims] 1. An apparatus for irradiating illumination light onto a surface of an object and measuring the reflected light with a photodetector to measure the optical characteristics of the object, wherein Koehler illumination light is used as the illumination light, The reflected light is condensed by an optical system, and by providing an aperture at or near the condensing point, the first-order or higher-order diffracted light generated on the surface of the object can be measured from the measurement light received by the photodetector. An optical characteristic measuring device having a function of removing light and having an aperture having a fixed or variable aperture area for controlling the NA of the light beam of the Koehler illumination light. 2. An apparatus for irradiating illumination light to a surface of an object and measuring optical characteristics of the object by measuring reflected light thereof with a photodetector, wherein Koehler illumination light is used as the illumination light, An optical system for collecting reflected light at or near the end face of the optical fiber by an optical system and detecting light emitted from the other end face of the optical fiber by the photodetector; apparatus. 3. The optical characteristic measuring apparatus according to claim 2, further comprising a fixed or variable aperture area aperture for controlling the NA of the light beam of the Koehler illumination light. apparatus. 4. The thickness of a thin film formed on the surface of an object
A film thickness measuring device for measuring by measuring optical characteristics of the object, wherein the film thickness measuring device is an optical characteristic measuring device.
4. A film thickness measuring device, comprising: measuring an optical characteristic of the object by using the optical characteristic measuring device according to claim 3. 5. A polishing end point judging device for judging a polishing end point by measuring an optical characteristic of an object to be polished, wherein the optical characteristic measuring device is any one of the optical characteristic measuring device. An apparatus for determining the end point of polishing, wherein the optical property of the object is measured using the optical property measuring apparatus according to claim 1. 6. A polishing apparatus comprising the film thickness measuring device according to claim 4 or the polishing end point determining device according to claim 5.