JP3841719B2 - Shape measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a shape measuring apparatus that can detect the edge of a measurement object in a shape measurement apparatus that measures the shape (flatness or the like) of the measurement object such as a semiconductor wafer using an interferometer.
[0002]
[Prior art]
In general, in a semiconductor wafer (hereinafter referred to as a wafer), the flatness at the center is sufficiently secured, but the flatness tends to deteriorate toward the edge. On the other hand, in recent years, in order to increase the number of semiconductor chips obtained from one wafer as much as possible, high flatness is required up to a portion closer to the edge of the wafer. At this time, the distance from the edge is used as an index representing the effective range that satisfies the required flatness in the entire wafer range. That is, it indicates that the inner side of the distance from the indicated edge is the effective range.
2. Description of the Related Art Conventionally, a shape measuring apparatus that measures the shape of a wafer based on an interference fringe image obtained by an interferometer that measures reflected light of light irradiated toward the measurement surface of the wafer has been widespread. In order to express the effective range by the distance from the edge of the wafer based on the shape data obtained by the shape measuring apparatus using such an interferometer, it is necessary to detect the edge of the wafer.
[0003]
[Problems to be solved by the invention]
However, as shown in FIG. 5, in the vicinity of the edge S, which is the tip of the end face of the wafer 1, a champ part 1c that gradually curves from the wafer 1 surface to the edge S is formed. For this reason, in the shape measurement using the conventional interferometer, the light irradiated on the champ part 1c is reflected in a direction completely different from the surface of the wafer 1, and no interference fringes are observed. It was not possible to detect which position of the edge S.
In the case where the surface shape is measured while moving the measuring needle from the inside of the wafer 1 toward the edge S using a stylus type shape meter that measures the shape by bringing the measuring needle into contact with the surface of the wafer 1. However, in the stylus type shape meter having the accuracy of the order of 0.1 μm required for the shape measurement of the wafer 1, the edge S cannot be detected because the measurement range is exceeded in the middle of the champ part 1c. In order to solve this problem, “M. Kimura et al., Jpn. J. Appl. Phys. Vol. 38 (1999)” (prior reference) describes the shape of the wafer 1 and the shape of the wafer 1 using a stylus shape meter. A method for detecting the edge S is shown.
In the edge detection method disclosed in the prior art document, the surface shape of the wafer 1 is measured by a stylus type shape meter, and a square block member is formed on the edge S which is the end of the wafer 1 as shown in FIG. 51, and the shape of the surface 51b (change in surface displacement) perpendicular to the surface 5a of the block member 51 contacting the wafer 1 is measured while moving the stylus 52 in the direction toward the wafer 1. The position where the measured value changes suddenly is detected as the edge of the wafer 1. Thus, the distance from the edge S representing the effective range can be obtained based on the detected edge S of the wafer 1 and the surface shape of the wafer 1 measured simultaneously.
However, when a stylus type shape meter is used, there is a problem that contamination such as scratches may occur on the surface of the wafer 1 due to the needle pressure. Furthermore, high accuracy flatness is required for the check table on which the wafer 1 is placed, and the processing accuracy of the check table and the trapping of dust between the wafer 1 and the block member 51 affect the measurement accuracy. There was also a problem.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a shape measuring apparatus capable of measuring the surface shape of an object to be measured and its edge in contact with high accuracy. .
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises an interferometer for measuring reflected light of light irradiated toward the measurement surface of the object to be measured, and the object to be measured based on an image obtained by the interferometer. In the shape measuring apparatus for measuring the shape of the object, light parallel to the reflected light is irradiated from the opposite side of the measurement surface of the object to be measured, and the irradiated light is incident on the interferometer as background light of the object to be measured. Background light irradiation means configured as described above, and edge detection means for detecting a boundary between the background light area and the other area as an edge of the object to be measured based on an image obtained by the interferometer. It is a shape measuring device characterized by being formed.
As a result, the surface shape of the object to be measured and its edge can be optically contacted and measured with high accuracy using an interferometer, and the object to be measured is not contaminated such as scratches. Further, the dust trapping does not affect the measurement accuracy as in the case of performing edge detection by bringing a measurement block member into contact with the object to be measured.
As the edge detection means, one that detects a boundary between the background light region and the other region based on one or both of luminance information and color information of the image obtained by the interferometer is conceivable.
[0005]
The interferometer may be a grazing incidence interferometer. That is, the interferometer measures reflected light reflected in an oblique direction with respect to the measurement surface of the object to be measured. The reflected light and the background light measured by the interferometer and the detection target. What is necessary is just to comprise so that the tangent of a direction parallel to the said measurement surface in the edge of the said to-be-measured object may become substantially parallel seeing from the direction perpendicular | vertical to the measurement surface of the to-be-measured object.
As a result, even if the direction of the background light is oblique to the surface of the object to be measured, the background light has a boundary line at the end (ie, edge) of the end of the object to be measured (ie, the champ It becomes background light.
[0006]
Further, a back side interferometer for measuring the shape of the back side of the measurement surface of the object to be measured is provided, and the irradiation light on the back surface of the object to be measured in the back side interferometer is outside the object to be measured. It is also conceivable that the background light irradiating means is configured by passing the light beam through the interferometer on the measurement surface side.
As a result, when measuring the shape of the front and back surfaces of the object to be measured with an interferometer, it is not necessary to provide a separate light source for edge detection.
[0007]
Further, the background light irradiation means has a reflection surface close to the opposite side of the measurement surface of the object to be measured, and out of the object to be measured out of the light irradiated toward the measurement surface of the object to be measured. It may be configured to irradiate the background light by reflecting light passing through the reflecting surface.
As a result, when measuring the shape of only one side of the object to be measured, there is no need to provide a separate light source on the back side.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments and examples of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. It should be noted that the following embodiments and examples are examples embodying the present invention, and do not limit the technical scope of the present invention.
Here, FIG. 1 is a configuration diagram of the shape measuring apparatus X according to the embodiment of the present invention, and FIG. 2 shows paths of measurement light in the two interferometers included in the shape measuring apparatus X according to the embodiment of the present invention. FIG. 3 is a schematic diagram, FIG. 3 is a diagram schematically showing an example of an image obtained by an interferometer included in the shape measuring apparatus X according to the embodiment of the present invention, and FIG. 4 is an embodiment of the present invention. FIG. 5 is a diagram schematically showing a cross-sectional shape near the edge of the wafer, and FIG. 6 is a conventional edge detection method using a stylus type shape meter. FIG.
[0009]
The configuration of the shape measuring apparatus X according to the embodiment of the present invention will be described with reference to FIG.
The shape measuring apparatus X includes an oblique incidence interferometer 10 and 20 provided on each of the main surface 1a side and the back surface 1b side of the wafer 1 which is an example of an object to be measured, and the oblique incidence interferometers 10 and 20, respectively. And an arithmetic unit 31 for inputting the obtained image. Here, one surface of the wafer 1 is the main surface 1a (corresponding to the measurement surface) and the opposite surface is the back surface 1b, which is referred to as such for the sake of convenience. It does not mean that aspect.
[0010]
The two oblique incidence interferometers 10 and 20 respectively emit the measuring beams 12 and 22 to the wafer 1 and send the measuring beams 12 and 22 to the surface of the wafer 1 (main surface 1a). The collimator lenses 14 and 24, which are parallel beams oblique to the rear surface 1b), and triangular prisms 15 and 25 having reference planes 15a and 25a that transmit part of the parallel beams 12 and 22 and reflect part of them. , A CCD camera or the like that receives the measurement light reflected by the surfaces 1a and 1b of the wafer 1 through the reference planes 15a and 25a (the triangular prisms 15 and 25) and the collimator lenses 14 'and 24'. And piezo actuators 17 and 27 for moving the triangular prisms 15 and 25 in a direction substantially perpendicular to the surface of the wafer 1. These two oblique incidence interferometers 10 and 20 are composed of the light emitter 21 on the back surface 1b side and the light receiver 16 on the main surface 1a side, and the light emitter 11 on the main surface 1a side and the The light receiver 26 on the back surface 1b side is configured to face each other. The reflected light from the reference planes 15a and 25a and the reflected light from the surfaces 1a and 1b of the wafer 1 are optical path differences corresponding to the distance between the reference planes 15a and 25a and the surfaces 1a and 1b. Therefore, this optical path difference is observed as interference fringes formed by both reflected lights in the light receivers 16 and 26. The triangular prisms 15 and 25 are arranged so that the reference planes 15a and 25a are close to the back surface 1b of the wafer 1 (for example, at a distance of about 0.1 mm). As the measurement lights 12 and 22, for example, a HeNe laser (λ = 633 nm) or a coherent light such as a semiconductor laser is used. The triangular prisms 15 and 25 may be a reference plate such as a wedge prism used for Fizeau interference.
[0011]
2 (a), 2 (b), and 2 (c) respectively show the front surface (the same surface as FIG. 1) side, the side surface side, and the upper surface side of the shape measuring apparatus X (perpendicular to the surfaces 1a and 1b of the wafer 1). FIG. 6 is a diagram schematically showing a path of measurement light passing through the two triangular prisms 15 and 25 when viewed from a different direction.
2A, the measurement light 12 on the main surface 1a side of the wafer 1 is reflected by the main surface 1a after passing through the triangular prism 15, and the back surface 1b side of the wafer 1 is reflected. The measurement light 22 is configured to be parallel to the measurement light 22a that has passed through the triangular prism 25. When viewed from the side, the two triangular prisms 15 and 25 are arranged so as to protrude outward from the edge S of the wafer 1 as shown in FIG. As a result, the measurement light 22a that has passed through the triangular prism 25 on the back surface 1b side passes through the outside of the wafer 1 through the triangular prism 15 and the collimator lens 14 ′ on the main surface 1a side, and the wafer 1 Is incident on the light receiver 16 on the main surface 1a side as background light 22a '. Since the reflected light 12b on the main surface 1a and the background light 22a ′ are parallel, they also enter the collimator lens 14 ′ on the main surface 1a side in parallel. Further, as shown in FIG. 2 (c), wherein the reflected light 12b and the background light 22a 'in the main surface 1a, a direction parallel to the main surface 1a of the edge S to be detected of the wafer 1 The tangent line SS is configured to be substantially parallel when viewed from a direction perpendicular to the surfaces 1 a and 1 b of the wafer 1. Thereby, even if the direction of the background light 22a ′ is oblique with respect to the surface of the wafer 1, the background light 22a ′ uses the front end (that is, the edge S) of the end portion of the wafer 1 as a boundary line. It becomes background light (the champ part 1c does not become a boundary line).
[0012]
The interference fringe images obtained by the two light receivers 16 and 26 are input to the calculator 31 (an example of the edge detection means) such as a personal computer having image input means, and based on the input interference fringe images. Thus, the surface shapes (height distribution) of the main surface 1a and the back surface 1b of the wafer 1 are calculated.
Interference fringe images from the two interferometers 10 and 20 are obtained by the triangular actuators 15 and 25 (that is, the reference planes 15 a and 25 a) and the wafer 1 of the measuring beams 12 and 22 by the piazo actuators 17 and 27. Are moved to positions in consideration of the incident angle θ on the surfaces 1a and 1b, for example, 0 (predetermined reference position), λ / 8 / conθ, 2λ / 8 / cosθ, and 3λ / 8 / cosθ. , The luminance data of the interference fringe image at each position is taken into the calculator 31. By performing predetermined unwrap processing on the phase data obtained from the luminance data, the distance between the main surface 1a and its reference plane 15a and the distance between the back surface 1b and its reference plane 25a can be calculated. As the calculation method, a known method may be applied, and the description thereof is omitted here.
[0013]
FIG. 3 is a diagram schematically illustrating an example of the interference fringe image input to the calculator 31. In the figure, the E portion where the interference fringes appear is the main surface 1a portion of the wafer 1, the black B portion outside the champ portion 1c, and the relatively bright A portion outside thereof is the outside of the wafer 1. (That is, the portion of the background light 22a ′). In the image of FIG. 3, FIG. 4 is a graph of luminance information at the position indicated by the white line segment CD (and its extension line). In the graph of FIG. 4, the vertical axis represents the luminance, and the horizontal axis represents the line segment CD and the position on the extension line. As can be seen from this graph, the outer side of the wafer 1 receives the background light 22a ′, and thus has higher brightness than the other parts, but suddenly on the way to the inner side (D side) of the wafer 1. There is a position to go down. This position is a boundary between the area (A part) of the background light 22a ′ and other areas (the part (B part) of the champ part 1c, etc.), and the position at which the brightness rapidly decreases is calculated by the calculator 31. Is calculated as the position of the edge S of the wafer 1.
As a result, the distance between the outermost position (for example, position D) and the edge S in the effective range having the flatness allowed as the surface shape of the wafer 1 can be obtained by contact. . In addition, in a conventional shape measuring apparatus that measures the shape of the front and back surfaces of the wafer using two interferometers, the arrangement of the light emitters 11 and 21 and the light receivers 16 and 26 is taken into consideration in the arithmetic unit 31. Since it can be realized simply by adding an arithmetic processing program, it is easy to apply.
[0014]
【Example】
The shape measuring apparatus X includes two oblique incidence interferometers 10 and 20 on both the front and back sides of the wafer 1, but is not limited to this, and the main surface 1a side and the back surface 1b of the wafer 1 are not limited thereto. Each of the sides may be another interferometer (for example, a Fizeau interferometer or a Michelson interferometer) that irradiates light substantially perpendicularly to the surface of the wafer 1. In this case, two interferometers may be arranged opposite to each of the main surface 1a side and the back surface 1b.
Of course, the present invention may be applied to a shape measuring apparatus having only one interferometer for measuring the shape of one surface of the wafer 1 (for example, the main surface 1a). In this case, light emitting means for irradiating light in the same direction as the measurement light 22a that has passed through the triangular prism 25 on the back surface 1b side (that is, parallel to the reflected light 12b on the main surface 1a) (for example, in FIG. The light emitter 21, the collimator lens 24, and the triangular prism 25) may be provided on the back surface 1b side. At this time, in the case of using an interferometer that irradiates light substantially perpendicularly to the surface of the wafer 1, light emitting means that irradiates light substantially perpendicularly to the back surface 1b from the back surface 1b side of the wafer 1 is provided. It goes without saying.
Further, when applied to a shape measuring apparatus having only one interferometer for measuring the shape of one surface of the wafer 1 (for example, the main surface 1a), the wafer 1 approaches the back surface 1b of the wafer 1 substantially in parallel. A reflection plate having a reflecting surface is provided, and the background light is irradiated by reflecting light passing through the outside of the wafer 1 out of the light irradiated toward the main surface 1a of the wafer 1 by the reflecting surface. You may comprise. This results in a very simple configuration.
Furthermore, a plurality of interference fringe images are acquired by changing the distance between the reflecting surface and the back surface 1b of the wafer 1 by supporting the reflecting plate or the like with a piezo actuator, and the surface of the wafer 1 is obtained by a so-called phase shift method. If the interference intensity I _kyodo is obtained from the plurality of interference images as in the case of measuring the shape, the portion of the background light 22a ′ (A portion in FIG. 3) compared to the _champ portion 1c (B portion in FIG. 3). since) is towards increased much the interference intensity I _Kyodo, the boundary line where the interference intensity I _Kyodo suddenly changes may be determined as an edge S. Here, the interference intensity I _kyodo is, for example, the luminances I ₀ , I ₉₀ , and I ₁₈₀ in each interference image when the position of the reflecting surface is moved in four steps for every 90 ° phase of the light irradiating the wafer 1 _. , I ₂₇₀ based on the following equation.
I _kyodo = ((I ₉₀ -I ₀ ) ² + (I ₂₇₀ -I ₁₈₀ ) ² ) ^1/2
Thereby, it is possible to more clearly (accurately) detect a boundary line (that is, an edge) between the champ portion 1c (B portion in FIG. 3) and the background light 22a ′ portion (A portion in FIG. 3). It becomes. Of course, the method for obtaining the interference intensity I _kyodo is not limited to the method in which the reflecting surface is moved in four steps for each 90 ° phase, and may be another known phase shift method.
[0015]
Further, in the shape measuring apparatus X, the boundary between the region of the background light 22a ′ and the other region is obtained based on the luminance information of the image data obtained by the interferometer. The illumination light (background light) has a color different from that of the measurement light used in the interferometer on the main surface 1a side, and the boundary is obtained based on color information of image data obtained by the interferometer. It is also possible to do.
In the embodiment, the two reference planes 15a and 25a are moved by the piezoelectric actuators 17 and 27 in four steps for each 90 ° phase, but other phase shift methods (for example, wavelength sweeping) are used. Etc.). Further, the wafer 1 may be moved by an actuator instead of moving the two reference planes 15a and 25a.
[0016]
【The invention's effect】
As described above, according to the present invention, the surface shape of an object to be measured and its edge can be optically contacted and measured with high accuracy using an interferometer. As a result, contamination such as scratches does not occur on the object to be measured, and dust trapping has an effect on the measurement accuracy as in the case of edge detection with a measurement block member in contact with the object to be measured. It does not occur.
In addition, when a back surface side interferometer for measuring the shape of the back surface of the object to be measured is provided, the irradiation light to the back surface of the object to be measured in the back surface side interferometer passes outside the object to be measured. Thus, it is not necessary to provide a separate light source for edge detection by being configured to be incident on the interferometer on the measurement surface side.
In addition, when measuring the shape of only one side of the object to be measured, a reflective surface is provided close to the opposite side of the measurement surface of the object to be measured, and the object to be measured out of the light irradiated toward the measurement surface of the object to be measured If the light passing through the outside of the object is reflected by the reflecting surface, it is not necessary to provide a separate light source on the back surface side, and edge detection can be performed more easily and at a low cost.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a shape measuring apparatus X according to an embodiment of the present invention.
FIG. 2 is a diagram schematically showing a path of measurement light in two interferometers included in the shape measuring apparatus X according to the embodiment of the present invention.
FIG. 3 is a diagram schematically illustrating an example of an image obtained by an interferometer included in the shape measuring apparatus X according to the embodiment of the present invention.
FIG. 4 is a graph showing an example of measurement data obtained by the shape measuring apparatus X according to the embodiment of the present invention.
FIG. 5 is a diagram schematically showing a cross-sectional shape near the edge of a wafer.
FIG. 6 is a diagram for explaining a conventional edge detection method using a stylus type shape meter.
[Explanation of symbols]
10, 20 ... Oblique incidence interferometers 11, 21 ... Light emitters 12, 22 ... Measuring light 14, 14 ', 24, 24' ... Collimator lenses 15, 25 ... Triangular prisms 15a, 25a ... Reference planes 16, 26 ... Light receivers 17, 27 ... Piezo actuator 31 ... Calculator 1a ... Main surface 1b of wafer ... Back surface of wafer

Claims (5)

In a shape measuring apparatus comprising an interferometer that measures reflected light of light irradiated toward the measurement surface of the object to be measured, and measuring the shape of the object to be measured based on an image obtained by the interferometer,
A background light irradiation means configured to irradiate light parallel to the reflected light from the opposite side of the measurement surface of the object to be measured, and the irradiated light is incident on the interferometer as background light of the object to be measured;
Edge detection means for detecting a boundary between the area of the background light and the other area as an edge of the object to be measured based on an image obtained by the interferometer;
A shape measuring apparatus comprising:   2. The shape measurement according to claim 1, wherein the edge detection unit detects a boundary between the background light region and another region based on one or both of luminance information and color information of an image obtained by the interferometer. apparatus. The interferometer measures reflected light reflected in an oblique direction with respect to the measurement surface of the object to be measured;
The reflected light and the background light measured by the interferometer, and the tangent line in the direction parallel to the measurement surface at the edge of the measurement object to be detected are perpendicular to the measurement surface of the measurement object The shape measuring apparatus according to claim 1, wherein the shape measuring apparatus is configured to be substantially parallel when viewed from above. A back side interferometer for measuring the shape of the back side of the measurement surface of the object to be measured;
The background light irradiation is configured such that irradiation light on the back surface of the object to be measured in the back surface side interferometer passes through the outside of the object to be measured and enters the interferometer on the measurement surface side. The shape measuring apparatus according to claim 1, comprising means.   The background light irradiation means has a reflection surface close to the opposite side of the measurement surface of the object to be measured, and passes outside the object to be measured among the light irradiated toward the measurement surface of the object to be measured. The shape measuring device according to claim 1, wherein the shape measuring device is configured to irradiate the background light by reflecting light to be reflected by the reflecting surface.

Images