JP2003329414A - Shape measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a shape of a wafer (thickness distribution) with high accuracy without being affected by errors of flatness of a reference surface of an interferometer even when a main side of the wafer is mirror-finished and a back side of the wafer is coarse. <P>SOLUTION: A shape measuring device comprises two reference surfaces, i.e., a reference surface disposed on a main surface side 1a of a wafer 1 and a back surface side of the wafer, a main surface side interferometer 10 to acquire a first interference fringe image formed by each reflected light from the main surface 1a and the reference surface 15a on the main surface side, and a back surface side interferometer 20 to acquire a second interference fringe image formed of each reflected light from the back surface 1b and a reference surface 25a on the back surface side of the light 22 irradiated diagonally on the back surface 1b of the wafer 1, and acquires a third interference fringe image formed of reflected lights from the two reference surfaces 15a and 25a by the main surface side interferometer 10 with the wafer 1 removed therefrom, and calculates the thickness distribution of the wafer based on the first to third interference fringe images. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shape measuring apparatus for measuring the shape (thickness distribution) of a semiconductor wafer using an interferometer.

[0002]

2. Description of the Related Art A shape measuring device for measuring the thickness distribution of a wafer such as semiconductor silicon is disclosed in, for example, Japanese Unexamined Patent Publication No. 2001.
There is one proposed in Japanese Patent Laid-Open No. 241923 (Gazette 1). In the shape measuring apparatus disclosed in the publication 1, a Fizeau interferometer that makes parallel light incident perpendicularly to the surface of a wafer is arranged so as to face the main surface side and the back surface side of the wafer, and the thickness distribution of the wafer is measured. This is a measuring device. In the technique of the above-mentioned publication 1, based on the interference fringes formed by the reflected light from the main surface of the wafer and the reflected light from the reference plane on the main surface side of the wafer, the main surface of the wafer and the reference plane on the main surface side Distance to La
Based on interference fringes formed by the reflected light from the back surface of the wafer and the reflected light from the reference plane on the back surface side of the wafer, (x, y) is a distance Lb between the back surface of the wafer and the reference plane surface on the back surface side. (X, y) is an interference fringe formed by reflected light from one of the reference planes on the main surface side and the back surface side of the wafer with respect to one of the parallel rays, with the wafer removed from between the two reference planes. Based on the above, the distance Lt (x, y) between the two reference planes is obtained, and the wafer thickness T (x, y
y) is obtained by the following equation (1). T (x, y) = Lt (x, y) −La (x, y) −Lb (x, y) (1) As a result, for each position (x, y) of each of the two reference planes. Since the displacement (unevenness) is canceled out, even if the flatness of each of the two reference planes is not sufficient with respect to the required wafer measurement accuracy,
It becomes possible to perform highly accurate wafer shape measurement without depending on this. That is, at a predetermined position (x0, y0) viewed from the direction perpendicular to the front surface of the wafer, the reference planes on the main surface side and the back surface side are each Δ relative to the ideal plane.
Assuming that there are errors (concavities and convexities) of a and Δb, the measurement distances La0 (= La (x0, y0)), L at that position.
b0 (= Lb (x0, y0)), Lt0 (= Lt (x
0, y0)) is represented by the following equations, respectively. La0 = La0′−Δa Lb0 = Lb0′−Δb (2) Lt0 = Lt0′−Δa−Δb Here, La0 ′, Lb0 ′, and Lt0 ′ are La0 when two reference planes are ideal planes, It is a true distance corresponding to Lb0 and Lt0. When this equation (2) is applied to the equation (1), the errors Δa and Δb are canceled out, and the true thickness of the wafer with respect to the ideal plane is obtained.

[0003]

However, in the main semiconductor wafers (hereinafter simply referred to as wafers) currently used, the main surface is a mirror surface, but the back surface is scattered by etching treatment or sandblasting treatment. Surface (hereinafter referred to as a rough surface). If the Fizeau interferometer disclosed in the above publication 1 is used for such a rough surface (back surface), the reflectance of the irradiated parallel light becomes low, and there is a problem that sufficient interference fringes cannot be obtained for measurement. It was On the other hand, as a method for performing interference measurement on a rough surface, for example, Japanese Patent Laid-Open No. 2000-81321
A grazing incidence interferometer as shown in Japanese Patent Laid-Open Publication No. (Gazette 2) is known. The technique disclosed in the publication 2 obliquely irradiates a wafer surface with parallel light through a reference plane (reference surface) of a prism arranged close to the wafer, and reflects light from each of the wafer surface and the reference plane. The distance between the surface of the wafer and the reference plane is measured on the basis of the interference fringe image formed in. If this is used, it is possible to increase the reflectance even on a rough surface, and it is possible to obtain interference fringes sufficient for measurement. However, in the technique disclosed in the above-mentioned publication 2,
Since the parallel light is radiated obliquely to the wafer surface, the flatness of the reference plane of the prism affects the measurement accuracy. This will be described with reference to FIG.

FIG. 3A is a diagram schematically showing an optical path when the distance between the reference plane and the wafer is measured by the conventional oblique incidence interferometer Z. Consider a case where oblique incidence interferometers are arranged on the main surface 1a side and the back surface 1b side of the wafer 1 as shown in FIG. 3 (a). That is, the prisms 41 and 42 are arranged on the main surface 1a side and the back surface 1b side, respectively, so that the reference planes 41a and 42a are close to the main surface 1a and the back surface 1b, respectively. Now, the parallel light B obliquely irradiated on the back surface 1b of the wafer 1 passes through a predetermined emission position L on the reference plane 42a of the prism 42 and the back surface 1b of the wafer 1.
Let's go to. This light is reflected by the back surface 1b of the wafer 1 at a position M deviated from the emission position L when viewed from a direction perpendicular to the surface of the wafer 1 (as viewed from above or below in FIG. 3A). After that, the reference plane 42a is reached at a position N further deviated. Therefore, the optical path difference between the reflected light S from the back surface 1b of the wafer 1 and the reflected light R from the reference plane 42a is (distance between L and M) + (distance between M and N). Interference fringes are obtained. Therefore, if the flatness of the reference plane 42a is not sufficient and the position L and the position N of the reference plane 42a deviate from the ideal plane (if the surface has irregularities), the deviation causes a measurement error. Will end up. Here, if the reference plane 42a is sufficiently close to the back surface 1b of the wafer 1, the distance between the positions L to N becomes sufficiently small, and the measurement error due to the deviation of the positions L and M can be suppressed within the allowable range. This also applies to the main surface 1a side of the wafer 1. However, what is obtained on the basis of the interference fringes thus obtained is only the distance between the reference planes 41a and 42a and the surfaces 1a and 1b of the wafer 1, and there are two criteria for the required measurement accuracy of the wafer. If the flatness of each of the flat surfaces 41a and 42a is not sufficient, accurate shape measurement cannot be performed. Therefore, wafer 1
Reference planes 41 on the main surface 1a side and the back surface 1b side, respectively.
It is conceivable to apply the technique of the aforementioned publication 1 which removes (cancels) the influence of the flatness error of a and 42a.
For that purpose, the wafer 1 is provided with two reference planes 41a and 42a.
It is necessary to measure the distribution of the distance between the two reference planes 41a and 42a by removing the distance between the two reference planes 41a and 42a.

However, since the thickness of the wafer 1 is generally about 0.7 to 0.8 mm, the two reference planes 41
The distance between a and 42a needs to be at least about 1 mm. FIG. 3B is a diagram schematically showing an optical path when the distance between the two reference planes 41a and 42a is measured by the conventional oblique incidence interferometer Z. As shown in FIG. 3 (b), light passing through a predetermined incident position L'on the reference plane 42a and traveling toward the reference plane 41a is reflected on the reference plane 41a at a position M'shifted from the entrance position L '. After that, the reference plane 42a is reached at a position N'which is further deviated. The distance (shift) between the positions L ′ and N ′ at this time becomes about 10 mm. Generally, in the reference plane, the maximum flatness error (for example, with a spatial period (spacing) of about 10 mm (for example,
Since the grazing incidence interferometer disclosed in the publication 2 is replaced with the interferometer used in the technology disclosed in the publication 1, the maximum error of the flatness of the reference plane becomes a measurement error as it is. There was a problem that it would end up.
This cannot be applied when a measurement accuracy of 0.01 μm order is required. Therefore, the present invention has been made in view of the above circumstances, and its object is to:
Even if the main surface of the wafer is a mirror surface and the back surface is a rough surface, a shape measuring device capable of accurately measuring the wafer shape (thickness distribution) without being affected by the flatness error of the reference plane of the interferometer, and the same To provide a method.

[0006]

In order to achieve the above object, the present invention comprises a reference plane arranged on the main surface side of a wafer and a reference plane arranged close to the back surface side of the wafer.
Means for forming two reference planes, a main surface side light emitting means for irradiating the main surface of the wafer with parallel light substantially perpendicularly via the reference surface on the main surface side, and a parallel light by the main surface side light emitting means. Via a main surface side interference fringe image acquisition means for acquiring a first interference fringe image formed by reflected light from each of the main surface of the wafer and the main surface side reference plane, and the back surface side reference plane. Second interference fringe image formed by the back surface side light emitting means for obliquely irradiating the back surface of the wafer and the parallel light reflected by the back surface side light emitting means from the back surface of the wafer and the reference plane of the back surface side. Of the back surface side interference fringe image acquisition means and the wafer from which the wafer is removed from between the two reference planes, the parallel surface of the back surface side reference plane and the main surface side of the parallel light by the main surface side light emitting means. Shaped by reflected light from each reference plane A reference plane interference fringe image acquisition means for acquiring a third interference fringe image, and a shape calculation means for calculating a thickness distribution of the wafer based on the first to third interference fringe images. It is a shape measuring device characterized by the following.

Here, the shape calculation means calculates the thickness distribution T (x, y) of the wafer based on the first interference fringe image and the main surface of the wafer and a reference plane on the main surface side. La (x, y), a distance Lb (x, y) between the back surface of the wafer and a reference plane on the back surface, which is obtained based on the second interference fringe image, and the third interference fringe. The distance Lt (x, x,
Based on y), it can be calculated by the following equation. T (x, y) = Lt (x, y) -La (x, y) -Lb
(X, y) This makes it possible to arrange the interferometers suitable for the main surface (mirror surface) and the back surface (rough surface) of the wafer to measure the shapes of the main surface and the back surface of the wafer, as well as the interference on the main surface side. Based on the distance between the two reference planes on the main surface side and the back surface side, the displacement (concavity and convexity) of each position on each of the two reference planes is offset, so the required wafer measurement accuracy is obtained. On the other hand, even if the flatness of each of the two reference planes is not sufficient, it is possible to perform highly accurate wafer shape measurement without depending on this. further,
On the main surface side where the vertically incident light is used, the distance between the reference plane on the main surface side and the wafer can be secured. It is easy to insert and remove between two reference planes.

Further, the apparatus further comprises an absolute thickness measuring means for measuring an absolute thickness of at least one portion of the wafer, wherein the shape calculating means calculates the absolute thickness of the wafer based on the absolute thickness measured by the absolute thickness measuring means. The absolute thickness distribution may be calculated.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments and examples of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. It should be noted that the following embodiments and examples are merely examples embodying the present invention and are not of the nature to limit the technical scope of the present invention. Here, FIG. 1 is a configuration diagram of a wafer shape measuring apparatus X according to an embodiment of the present invention, and FIG.
FIG. 3 is a diagram schematically showing an optical path between a reference plane and a wafer and between two reference planes in a wafer shape measuring apparatus X according to an embodiment of the present invention. FIG. 3 is a reference by a conventional oblique incidence interferometer Z. It is the figure which represented typically the optical path between a plane and a wafer, and between two reference planes.

A wafer shape measuring apparatus X according to an embodiment of the present invention will be described below with reference to FIG. In the present wafer shape measuring apparatus X, two optical measuring systems 10 and 20 are arranged opposite to each other on both sides of the main surface 1a and the back surface 1b of the wafer 1 supported by the wafer supporting portion 30. The main surface 1
The a-side optical measurement system 10 is a Fizeau interferometer, and includes a main surface side light emitter 11 that emits the measurement light 12, a half mirror 13 that transmits the measurement light 12, and the measurement light 12 that has passed through the half mirror 13. Is a parallel beam perpendicular to the main surface 1a, a reference plate 15 having a main surface side reference plane 15a that transmits a part of the parallel beam and reflects a part of the parallel beam, the main surface 1a of the wafer 1. CC which receives the light reflected by the half mirror 13 through the reference plate 15 and the collimator lens 14
A main surface side light receiver 16 such as a D camera and a piezo actuator 17 for moving the reference plate 15 in a direction perpendicular to the surface of the wafer 1 are provided. Here, the reflected light on the main surface side reference plane 15a and the reflected light on the main surface 1a of the wafer 1 include the main surface side reference plane 15a and the main surface 1
Since there is an optical path difference corresponding to the distance to a, this optical path difference is observed as an interference fringe formed by both reflected lights in the main surface side light receiver 16.

On the other hand, the optical measurement system 20 on the back surface 1b side
Is an oblique-incidence interferometer, which includes a back-side light emitter 21 that emits the measurement light 22, a collimator lens 24 that makes the measurement light 22 a parallel beam in an oblique direction with respect to the back surface 1b, and a part of the parallel beam The triangular prism 25 having a back surface side reference plane 25a that transmits and reflects a part, and the measurement light reflected by the back surface 1b of the wafer 1 has the back side reference plane 25a.
a (the triangular prism 25) and the collimator lens 2
Piezoactuator 27 for moving rear surface side light receiver 26 such as CCD camera for receiving light passing through 4'and the like, and triangular prism 25 in a direction substantially perpendicular to the surface of wafer 1.
Is equipped with. The reflected light on the back surface side reference plane 25a and the reflected light on the back surface 1b of the wafer 1 are:
Since there is an optical path difference corresponding to the distance between the back surface side reference plane 25a and the back surface 1b, this optical path difference is observed in the back surface side light receiver 26 as an interference fringe formed by both reflected lights. The triangular prism 25 is arranged so that the back surface side reference plane 25a is close to the back surface 1b of the wafer 1 (for example, at a distance of about 0.1 mm).
As the measurement light 12 and 22, for example, coherent light such as an HnNe laser (λ = 633 nm) or a semiconductor laser is used. Further, the triangular prism 25 may use a reference plate such as a wedge prism used in Fizeau interference.

The interference fringe images obtained by the main surface side light receiver 16 and the back surface side light receiver 26 are input to a computing unit 31 (an example of the shape calculating unit) such as a personal computer having an image input unit, The surface shapes (height distribution) of the main surface 1a and the back surface 1b of the wafer 1 are calculated based on the input interference fringe image. Hereinafter, an interference fringe image formed by the reflected light of the main surface 1a of the wafer 1 and the main surface side reference plane 15a obtained by the main surface side light receiver 16 is obtained by the back surface side light receiver 26. An interference fringe image formed by reflected light from the back surface 1b of the wafer 1 and the back surface side reference plane 25a is defined as b.

In addition to the two interference fringe images a and b, the arithmetic unit 31 further includes interference fringes formed by reflected light from the main surface side reference plane 15a and the back surface side reference plane 25a. Image c is captured. The interference fringe image c shows the wafer 1 on the two optical measurement systems 10, 20.
The light emitter 1 on the main surface 1a side in a state of being removed from between
Reference planes 1 on the main surface side and the back surface side of the measurement light from 1
The reflected light at 5a and 25a is received by the main surface side photodetector 16 and observed. The arithmetic unit 31 uses the input interference fringe image c to determine the main surface side reference plane 15
The distribution of the distance between a and the back side reference plane 25b is calculated. Here, the main surface side light emitter 11 and the collimator lens 14 are an example of the main surface side light emitting means, the back surface side light emitter 21 and the collimator lens 24 are an example of the back surface side light emitting means, and the main surface side light receiving means. The device 16 is an example of the main surface side interference fringe image acquisition means and the reference plane interference fringe image acquisition means, and the back surface side light receiver 26 is an example of the back surface side interference fringe image acquisition means.

Next, referring to FIG. 2, the interference fringe images a ...
An optical path of the parallel light at the time of observing each of c will be described. At the time of observing the interference fringe image a (main surface), as shown in FIG. 2A, light traveling from the predetermined incident position Q of the main surface side reference plane 15a toward the main surface 1a of the wafer 1 is , Because it is irradiated in a direction perpendicular to the main surface 1a,
When viewed from a direction perpendicular to the surface of the wafer 1 (viewed from the upper side or the lower side in FIG. 2A), after being reflected on the main surface 1a of the wafer 1 at the same position M ′ as the incident position Q, It returns to the incident position Q of the main surface side reference plane 15a. In this way, since the light emitted from the emission position Q returns to the original position, it is not affected by the flatness (unevenness) of the main surface side reference plane 15a. On the other hand, when observing the interference fringe image b (back surface), as shown in FIG. 2A, the light traveling from the predetermined incident position L of the back surface side reference plane 25a to the back surface 1b of the wafer 1 is: Since the back surface 1b is obliquely irradiated, when viewed from a direction perpendicular to the surface of the wafer 1, it is reflected at a position M deviated from the incident position L and then at a position N deviated further from the back surface side. The reference plane 25a is reached. Here, as described above, since the back surface side reference plane 25a is close to the back surface 1b of the wafer 1,
The deviation between the positions L and N is sufficiently small so that no problem occurs in measurement accuracy. As described above, in general, the maximum flatness error is likely to occur in the reference plane with a spatial period (spacing) of about 10 mm.
When a is brought closer to the back surface 1b of the wafer 1 by about 0.1 mm, the deviation between the positions L and N becomes about 1 mm, and the influence of the flatness error of the reference plane can be suppressed to a negligible level. Further, at the time of observing the interference fringe image c (between two reference planes), as shown in FIG.
The light traveling from the incident position Q of the main surface side reference plane 15a toward the main surface 1a of the wafer 1 is viewed from a direction perpendicular to the surface of the wafer 1 (from the upper side or the lower side in FIG. 2B). (Seeing), after being reflected by the back surface side reference plane 25a at the same position P as the incident position Q, the main surface side reference plane 15
It returns to the said incident position Q of a. In this way, since the light emitted from the emission position Q returns to the original position, it is not affected by the flatness (unevenness) of the main surface side reference plane 15a. Therefore, the position M ′ on the main surface 1a side of the wafer 1 is
Considering that and the position M on the back surface 1b side are positions having a front-back relationship, the respective deviations of the positions L, P, N on the back surface reference plane 25a are caused by the flatness error of the back surface reference plane 25a. Can be kept small enough to ignore the effect of. Further, on the back surface 1b side of the wafer 1, the back surface side reference plane 25a and the wafer 1
However, on the side of the main surface 1a of the wafer 1, since the distance between the main surface side reference plane 15a and the wafer 1 can be secured, the wafer 1 is placed between the two reference planes 15a and 25a. It is easy to handle by inserting and removing it.

Using the interference fringe images a to c obtained by the above measurement, the calculator 31 performs the following calculation. First, based on the interference fringe image a, a distance La (x, between the main surface side reference plane 15a and the main surface 1a is set.
y), the distance Lb (x, y) between the back surface side reference plane 25a and the back surface 1b based on the interference fringe image b, and the main surface side reference plane 15a and the above based on the interference fringe image c. Distance Lt (x, y) from the back side reference plane 25a
Is required. The interference fringe image a by the optical measurement system 10 on the main surface 1a side is displayed by the piezo actuator 17 on the reference plate 15 (that is, the main surface side reference plane 15).
a) is, for example, 0 (predetermined reference position), λ / 8, 2λ
/ 8, 3λ / 8 (where λ is the wavelength of the measurement light) to move the interference fringe image luminance data I ₀ (x, y), I ₉₀ (x, y), I ₁₈₀ (x,
y) and I ₂₇₀ (x, y) are taken into the arithmetic unit 31. Based on this luminance data, the interference fringe image a
The phase φa (x, y) of is calculated by the following equation (2). φa (x, y) = arctan {(I ₀ −I ₁₈₀ ) / (I ₉₀ / I ₂₇₀ )} (2) The φa (x, y) thus obtained is subjected to a predetermined unwrapping process (after processing). , The distance La (x, y) is obtained by the following equation (3). La (x, y) = (φa ′ (x, y) / 2π) × (λ / 2) (3) The distance Lc (x, y) is also the same as the distance La (x, y). Desired. Similarly, for the interference fringe image b by the optical measurement system 20 on the back surface 1b side, similarly, the triangular prism 25 (that is, the back surface side reference plane 25a) is moved by the piezo actuator 27 to the wafer 1 of the measurement light 22. Position considering the incident angle θ to the back surface 1b of
For example, 0 (predetermined reference position), λ / 8 / con θ, 2
It is moved to each position of λ / 8 / cos θ and 3λ / 8 / cos θ, and is taken into the arithmetic unit 31 as the luminance data of each interference fringe image. Further, the phase φb ′ (x, y) of the interference fringe image b after the unwrap processing is obtained from the luminance data in the same manner as the φa ′ (x, y) is obtained. Then, by the following equation (4), the distance L
b (x, y) is calculated. Lb (x, y) = (φb ′ (x, y) / 2π) × (λ / 2 × 1 / cos θ) (4) Then, the three distances La (x, y) and Lb (x,
Based on y) and Lt (x, y), the thickness distribution T (x, y) of the wafer 1 is obtained by the equation (1). The thickness distribution T of the wafer 1 thus obtained
As described in paragraph 0014 of the publication 1, the displacement (concavity and convexity) of (x, y) is offset for each position (x, y) of the two reference planes 15a and 25a. It is a value that does not depend on the flatness (planar shape) of the main surface side reference plane 15a and the back surface side reference plane 25a.
That is, according to the wafer shape measuring apparatus X, it becomes possible to measure the thickness distribution of the wafer with high accuracy without depending on the flatness of the reference plane. Thereby, the main surface 1a of the wafer 1 is
Even if the mirror surface is a mirror surface and the back surface 1b is a rough surface, the shape (thickness distribution) of the wafer 1 can be accurately measured without being affected by the error in the flatness of the two reference planes 15a and 25a.
Further, since the two reference planes 15a and 25a do not necessarily have to be ideal planes, the cost of the device can be reduced.

[0016]

[Embodiment] Wafer shape measuring apparatus X according to the above embodiment
The thickness distribution T (x, y) of the wafer 1 obtained by the above equation contains an unknown amount of Offset. Therefore, if a thickness measuring device (corresponding to the absolute thickness measuring means) for measuring the thickness of the wafer 1 at an arbitrary position is provided, and the obtained thickness measured value t is input to the arithmetic unit 31, The absolute thickness distribution of the wafer 1 can be obtained based on the measured thickness value t. That is, in the thickness distribution T (x, y), the thickness distribution T (x, y) is set so that the value at the measurement point of the thickness measurement value t matches the thickness measurement value t. Each value of can be translated. Further, in the above-described embodiment, the two reference planes 15a and 25a are moved by four steps for each 90 ° phase by the piezo actuators 17 and 27, but other phase shift methods (for example, wavelength sweeping). Etc.). Furthermore, instead of moving the two reference planes 15a and 25a, the wafer 1 may be moved by an actuator. Further, in the above embodiment, a Fizeau interferometer is used as the optical measurement system 10 on the main surface 1a side of the wafer 1, but other interferometers that irradiate the surface of the wafer 1 with light substantially perpendicularly ( For example, a Michelson interferometer) may be used.

[0017]

As described above, according to the present invention,
Interferometers suitable for the main surface (mirror surface) and the back surface (rough surface) of the wafer are arranged to measure the shapes of the main surface and the back surface of the wafer. 2 based on the distance between the two reference planes on the back side
Displacement (concavo-convex) at each position of each of the two reference planes
Since the amount is canceled out, even if the flatness of each of the two reference planes is not sufficient for the required wafer measurement accuracy, it is possible to perform highly accurate wafer shape measurement without depending on this. Becomes In addition, since the distance between the main surface side interferometer where the vertically incident light is used and the wafer can be secured, the wafer can be placed between two reference planes as compared with the case where the oblique incidence interferometer is placed close to both sides of the wafer. It is easy to insert and remove.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a wafer shape measuring apparatus X according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing an optical path between a reference plane and a wafer and between two reference planes in a wafer shape measuring apparatus X according to an embodiment of the present invention.

FIG. 3 is a diagram schematically showing an optical path between a reference plane and a wafer and between two reference planes by a conventional grazing incidence interferometer Z.

[Explanation of symbols]

1 ... Wafer 10 ... Optical measurement system on the main surface side (Fizeau interferometer) 11 ... Main surface side light emitter 12 ... Measuring light (main surface side) 13 ... Half mirror 14, 24, 24 '... Collimator lens 15 ... Reference plate 15a ... Main surface side reference plane 16 ... Main surface side light receiver 17, 27 ... Piezo actuator 20 ... Optical measurement system on the back side (oblique incidence interferometer) 21 ... Back side light emitter 22 ... Measuring light (back side) 25 ... Triangular prism 25a ... Back side reference plane 26 ... Back side light receiver 30 ... Wafer support 31 ... Calculator

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Claims (3)

[Claims] 1. A means for forming two reference planes, a reference plane arranged on the main surface side of the wafer and a reference plane arranged in proximity to the back surface side of the wafer, and a reference plane on the main surface side. Through the main surface side light emitting means for irradiating the main surface of the wafer with parallel light substantially perpendicularly, and the reflection of the parallel light by the main surface side light emitting means from the main surface of the wafer and the reference plane on the main surface side. A main surface side interference fringe image acquiring means for acquiring a first interference fringe image formed by light, a back surface side light emitting means for obliquely irradiating the back surface of the wafer via the reference plane on the back surface side, and the back surface. The back side interference fringe image acquisition means for acquiring the second interference fringe image formed by the reflected light of the parallel light by the side light emitting means from the back surface of the wafer and the reference plane on the back surface side, and With removed from between the two reference planes, Reference plane interference fringe image acquisition means for acquiring a third interference fringe image formed by reflected light from the reference plane on the back surface side and the reference plane on the main surface side of the parallel light by the main surface side light emitting means, And a shape calculation unit that calculates the thickness distribution of the wafer based on the first to third interference fringe images. 2. The shape calculating means calculates a thickness distribution T (x, y) of the wafer between a main surface of the wafer obtained based on the first interference fringe image and a reference plane on the main surface side. La (x, y), the distance Lb (x, y) between the back surface of the wafer and the reference plane on the back surface, which is obtained based on the second interference fringe image, and the third interference fringe image. The shape measuring device according to claim 1, which is calculated by the following equation based on the distance Lt (x, y) between the two reference planes obtained by T (x, y) = Lt (x, y) -La (x, y) -Lb
(X, y) 3. An absolute thickness measuring means for measuring an absolute thickness of at least one portion of the wafer, wherein the shape calculating means calculates the absolute thickness of the wafer based on the absolute thickness measured by the absolute thickness measuring means. The shape measuring device according to claim 1, wherein an absolute thickness distribution is calculated.