JP5043476B2 - Shape measuring apparatus and method - Google Patents

Description

  The present invention relates to a shape measuring apparatus for measuring a surface shape in the vicinity of an end portion of a circular plate-like sample such as a semiconductor wafer and a measuring method thereof.

In general, a semiconductor wafer having a circular plate shape (hereinafter referred to as a wafer) has a sufficiently flatness at the center, but the flatness in the vicinity of the end (circumferential part) is not sufficient (so-called sagging). Is often formed).
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. For this reason, it is important to measure the surface shape near the edge of the wafer with high accuracy.
For example, in Patent Document 1 and Non-Patent Document 1, a block member is brought into contact with the edge edge of a wafer, and the position of the surface of the block member in contact with the wafer is used as a reference while moving a stylus shape meter. A technique for measuring the surface shape of a wafer is shown.
Here, sagging occurs in the radial direction of the wafer, and the surface shape hardly changes in the circumferential direction.
In contrast, Patent Document 2 discloses a technique for measuring the sagging of a wafer with high accuracy by measuring a plurality of surface shapes in the radial direction of the wafer over a predetermined range in the circumferential direction and averaging the measured values. It is shown.

Further, Patent Document 2 discloses a technique for measuring a two-dimensional surface shape (surface height distribution) of a wafer by a phase shift method using an interferometer (also called a fringe scanning method or a fringe scanning method). It is shown.
As shown in Patent Document 2, in the shape measurement by the phase shift method, a plurality of interference fringe images obtained by the interferometer are obtained by changing the position of the reference surface of the interferometer or the position of the sample (wafer) in the optical axis direction. The surface shape value of the wafer is calculated from the luminance data of the plurality of interference fringe images.
A technique for measuring the two-dimensional surface shape of a sample by a spatial carrier frequency method using an interferometer is known. In shape measurement by the spatial carrier frequency method, the reference plane or sample of the interferometer is tilted to increase the number of interference fringes obtained by the interferometer, and the number of interference fringes is regarded as the spatial carrier frequency, and Fourier transform is performed. And the two-dimensional surface shape value of the sample is calculated by performing inverse Fourier transform.
JP 2000-14669 A JP 2004-184194 A M. Kimura etc., "A New Method for the Precise Measurement of Wafer Roll off of Silicon Polished Wafer", Jpn.J.Appl.Phys.Vol.38 (1999)

However, the stylus-type shape measurement shown in Patent Literature 1 and Non-Patent Literature 1 and the shape measurement by the phase shift method shown in Patent Literature 2 (a method of observing a plurality of interference fringe images) are very useful for measurement. There was a problem that it took time.
In addition, the shape measurement by the spatial carrier frequency method described above requires a process of extracting a specific Fourier spectrum after Fourier transformation separately from other Fourier spectra. The process is similar to the low-pass filter processing for the spatial frequency of the interference fringes. This is because the background intensity distribution of the interference fringes and the amplitude of the change in brightness change gradually, that is, the surface shape of the sample. It is assumed that the changes in are very gradual. For this reason, the spatial carrier frequency method has a problem in that a surface shape that changes relatively greatly in the radial direction, such as the edge of a wafer, cannot be measured with high accuracy.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to form a surface shape that changes relatively greatly in the radial direction, such as an end portion of a wafer, with high accuracy and in a short time. An object of the present invention is to provide a shape measuring apparatus and a measuring method thereof that can be measured.

In order to achieve the above object, the present invention provides a surface shape of a region (hereinafter referred to as a measurement region) extending from an end to a predetermined range inside a circular plate-like or substantially similar sample (a semiconductor wafer is a typical example). Is a shape measuring device that measures the above and includes the components shown in the following (1) to (6).
(1) Imaging means for capturing an image of interference fringes formed in output light of an interferometer that observes the measurement region.
(2) Direction changing means for changing the direction of a reference surface (surface that reflects reference light) or the surface of the measurement region in the interferometer.
(3) By controlling the orientation changing means, the image of the interference fringes obtained by the imaging means is an axis parallel to the radial direction of the sample (hereinafter referred to as a reference) in an area excluding the end in the measurement area. Interference fringe image adjusting means for adjusting the image so as to form a plurality of fringe images formed extending in a direction parallel to or nearly parallel to the axis).
(4) Luminance data recording means for recording luminance data of the interference fringe image obtained by the imaging means after adjustment by the interference fringe image adjusting means.
(5) Spatial periodic waves (waves whose luminance values periodically change in a direction orthogonal to the reference axis) represented by the luminance data column in a direction orthogonal to the reference axis at each position of the reference axis Phase calculating means for calculating the phase of
(6) Surface shape value calculating means for calculating a surface shape value in the reference axis direction in the measurement region based on the phase calculated by the phase calculating means.

As described above, a semiconductor wafer (a typical example of a circular plate-like sample) has a sag in its radial direction, and hardly changes its surface shape in the circumferential direction. Therefore, after adjustment by the interference fringe image adjusting means, the luminance data of the interference fringe image obtained through the interferometer and the imaging means is at each position in the direction of the reference axis (axis parallel to the radial direction of the sample). When viewed as a data string in a direction orthogonal to the reference axis, the data string represents a periodic wave having a predetermined spatial frequency (the spatial periodic wave). The phase of each of the spatial periodic waves at each position on the reference axis represents a change in the surface shape in the reference axis direction. Therefore, according to the present invention, it is possible to optically measure (calculate) the surface shape value (profile) of the sample in the reference axis direction based on the phase calculated by the phase calculating means.
In addition, since the surface shape in the reference axis direction can be measured (calculated) by measuring the interference fringe image once, measurement in a short time is possible.

Here, as a specific example of the phase calculation means, for example, a sin wave (sine wave) and a cosin wave (cosine wave) whose spatial frequency is substantially equal to the spatial periodic wave in the region excluding the end of the measurement region. It is possible to calculate the phase by orthogonal detection processing based on data representing each.
In addition, the shape measuring apparatus according to the present invention may further include the components shown in the following (7) to (9).
(7) A spot for focusing the output light of the interferometer to form two spot images on which the object light and the reference light superimposed on the output light of the interferometer are focused on the imaging means. Imaging lens.
(8) An imaging state switching unit that switches a first state in which the image of the interference fringe is formed on the imaging unit and a second state in which the two spot images are formed by the spot imaging lens.
(9) The interference fringe image adjusting means is provided, and the positional relationship between the two spot images obtained by the imaging means by being switched to the second state by the imaging state switching means is determined in advance. Spot image adjusting means for controlling the direction changing means so as to be in a relationship (that is, according to a deviation in both positional relationships).
If the surface shape of the measurement region of each sample to be measured is not significantly different, the interference fringes obtained by the interferometer are determined by the relative relationship between the orientation of the reference surface of the interferometer and the orientation of the surface of the measurement region. The general content of the image is determined.
Similarly, the positional relationship (relative position) of the two spot images is generally determined by the relative relationship between the orientation of the reference surface in the interferometer and the orientation of the surface of the measurement region.
Therefore, the orientation of the reference surface in the interferometer is such that the positional relationship between the two spot images is a standard positional relationship when an image of an interference fringe suitable for measuring the shape of the sample is obtained. By setting (adjusting) the relative relationship with the direction of the surface of the measurement region, an image of interference fringes suitable for measuring the shape of the sample can be obtained. Thereby, in the adjustment of the interference fringe image by the interference fringe image adjusting means, the adjustment is easier than the adjustment based only on the interference fringe image (by image processing alone).
Moreover, this invention can also be grasped | ascertained as the shape measuring method which performs the execution content of each means with which the shape measuring apparatus which concerns on this invention mentioned above is equipped.

  According to the present invention, the surface shape value (profile) of the sample in the reference axis direction (direction parallel to the radial direction) can be measured (calculated) optically with high accuracy using an interferometer. In addition, since the surface shape in the reference axis direction can be measured by measuring the interference fringe image once, measurement in a short time is possible.

Embodiments of the present invention will be described below with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: It is not the thing of the character which limits the technical scope of this invention.
Here, FIG. 1 is a schematic configuration diagram of a shape measuring apparatus Z according to an embodiment of the present invention, FIG. 2 is a flowchart showing a shape measuring procedure by the shape measuring apparatus Z, and FIG. FIG. 4 is a diagram showing an optical path and an output image in an interferometer when performing, FIG. 4 is a diagram showing an example of data obtained in the course of carrier wave phase calculation processing (orthogonal detection processing) by the shape measuring apparatus Z, FIG. Is a graph showing data obtained in the process of carrier wave phase calculation processing (orthogonal detection processing) by the shape measuring device Z, and FIG. 6 is a graph showing carrier wave phases and surface shape values calculated by the shape measuring device Z. It is.

First, the configuration of the shape measuring apparatus Z will be described with reference to FIG.
As shown in FIG. 1B, the shape measuring apparatus Z according to the embodiment of the present invention has an end portion (sample edge we) in a semiconductor wafer (hereinafter referred to as a sample w) having a circular plate shape or a shape close thereto. Is a device for measuring the surface shape of a region (hereinafter referred to as a measurement region wa) over a predetermined range inside. Note that the symbol wo shown in FIG. 1B represents the center position of the sample w.
Hereinafter, in the measurement region wa, the coordinate axis in the direction parallel to the radial direction of the sample w is defined as the X axis (corresponding to the reference axis), and the coordinate axis in the direction orthogonal thereto is defined as the Y axis.
As shown in FIG. 1, the shape measuring apparatus Z includes a laser light source 1, an interferometer 30, a spot imaging lens 7, a rotary lens holder 8, a lens switching motor 9, a CCD camera 10, a computer 11, a rotary stage 12, The elevating stage 13, the displacement type sample support parts 21 and 22, the displacement devices 21 a and 22 a, the fixed type sample support part 23 and the like are configured.
The interferometer 30 is a Fizeau interferometer, and includes a first lens 2, a beam splitter 3, a second lens 4, a reference glass 5, and an interference fringe imaging lens 6.

The light supplied from the laser light source 1 to the interferometer 30 is converted into parallel light having a diameter of, for example, about 40 mm by the first lens 2 and the second lens 4 and enters the reference glass 5.
Then, a part of the parallel light incident on the reference glass 5 is reflected by the reference surface 5a which is the lower surface of the reference glass 5, and the reference light which is the reflected light again passes through the reference glass 5 and the second lens 4. It passes in the opposite direction and reaches the beam splitter 3.
On the other hand, the remaining part of the parallel light incident on the reference glass 5 passes through the reference glass 5 and irradiates the region including the measurement region wa of the sample w, and the object light that is the reflected light is again emitted from the reference glass 5. Then, the light passes through the second lens 4 in the reverse direction and overlaps with the reference light to reach the beam splitter 3.
The interference light in which the reference light and the object light overlap is reflected by the beam splitter 3, passes through the interference fringe imaging lens 6, and is input to the CCD camera 10. Here, the interference fringe imaging lens 6 forms an image of the interference fringe on the CCD camera 10 by adjusting the diameter of the output light of the interferometer 30 to a size corresponding to the light detection unit of the CCD camera 10. It is a lens.
The CCD camera 10 is a camera (imaging means) that captures an image of interference fringes formed in the output light of the interferometer 30 that observes the measurement area wa of the sample.

FIG. 4A is an example of an interference fringe image of the measurement region wa obtained by the CCD camera 10 in the shape measuring apparatus Z.
In the shape measuring apparatus Z, as shown in FIG. 4A, the interference fringe image obtained by the CCD camera 10 is parallel to the radial direction of the sample w in the region excluding the end portion we in the measurement region wa. The surface shape (surface height distribution) in the X-axis direction is adjusted after adjusting to a state (hereinafter referred to as a parallel stripe formation state) of a plurality of stripes formed extending substantially parallel to ).
As described above, the sample w (semiconductor wafer) is sagging in the radial direction (X-axis direction in the measurement region wa), and the surface shape hardly changes in the Y-axis direction.
Therefore, in the parallel stripe formation state, the luminance data of the interference fringe image obtained through the CCD camera 10 is predetermined when viewed as a data string (luminance data string) in the Y-axis direction at each position in the X-axis direction. The data string represents a periodic wave (spatial periodic wave) having a spatial frequency of. Hereinafter, the spatial periodic wave represented by the data string in the Y-axis direction is referred to as a carrier wave.
The phase of each carrier wave at each position on the X axis represents a change in the surface shape in the X axis direction. Therefore, if the phase of each carrier wave at each position on the X axis (the distribution of the carrier wave in the X axis direction) is calculated, the surface shape value (profile) in the X axis direction of the measurement region wa is optically calculated based on the phase. Therefore, it can be measured (calculated) with high accuracy. In addition, since the surface shape in the X-axis direction can be measured (calculated) by measuring the interference fringe image once, measurement in a short time is possible.
The example shown in FIG. 4A shows an image of interference fringes in which six stripes (six shades) are formed in the Y-axis direction at each position on the X-axis.
Here, in order to obtain the interference fringes in the parallel fringe formation state as shown in FIG. 4A, the reference surface 5a of the reference glass 5 and the surface of the measurement region wa are arranged in a predetermined direction in which they are non-parallel. Must be set to relationship.

In the shape measuring apparatus Z, in order to be able to adjust the orientation relationship between the reference surface 5a of the reference glass 5 and the surface of the measurement region wa, the sample w is supported as follows.
That is, the sample w is composed of two displacement sample support portions 21 and 22 configured to be displaceable in the vertical direction (position adjustment is possible) independently by the displacement devices 21a and 22a, and the fixed sample support portion 23. Supported at 3 locations (supported at 3 points). The displacement devices 21 a and 22 a are configured by, for example, Peltier elements, and the displacement position (height) is controlled by the computer 11.
The displacement devices 21a and 22a change the direction of the surface of the sample w, that is, the direction of the surface of the measurement region wa, by displacing the two displacement-type sample support portions 21 and 22 that support the sample w. Yes (an example of orientation changing means).
As described above, in this embodiment, the orientation of the surface of the measurement region wa is changed by a mechanism that independently displaces two of the three sample support portions 21 to 23 that support the sample w at three locations. .
In the example shown in FIG. 1B, the tilt of the surface of the measurement region wa in the X-axis direction is adjusted by one displacement device 21a, and the tilt of the surface of the measurement region wa in the Y-axis direction is adjusted by the other displacement device 22a. Is configured to be adjusted.

Further, the elevating stage 13 and the rotary stage 12 constitute an apparatus for changing the position of the measurement region wa in the sample w.
Here, the raising / lowering stage 13 raises / lowers the rotary stage 12 in accordance with a control command from the computer 11.
The rotary stage 12 is lifted by the lifting stage 13 so that the upper surface (supporting portion) is above the sample supporting portions 21 to 23, thereby supporting the sample w (hereinafter referred to as a sample supporting state). ) The rotating stage 12 changes the position (light irradiation position) of the measurement region wa in the sample w by rotating and stopping the upper surface (supporting portion) in accordance with the control command from the computer 11 in the sample supporting state. After changing the position of the measurement region wa, the elevating stage 13 lowers the rotary stage 12 in accordance with a control command from the computer 11 to return the sample w to the state supported by the sample support portions 21 to 23.

On the other hand, when the spot imaging lens 7 is disposed in front of the CCD camera 10, the object light and the reference light superimposed on the output light of the interferometer 30 are collected by condensing the output light of the interferometer 30. Is a lens that forms two focused spot images P1 and P2 on the CCD camera 10. Hereinafter, a state in which the spot imaging lens 7 is disposed in front of the CCD camera 10 is referred to as a spot imaging state, and a state in which the interference fringe imaging lens 6 is disposed in front of the CCD camera 10 is a loose stripe imaging state. That's it.
In the shape measuring apparatus Z, the interference fringe imaging lens 6 and the spot imaging lens 7 are held by a rotary lens holder 8. Furthermore, the lens switching motor 9 controlled by the computer 11 rotates the rotary lens holder 8 and positions it at a predetermined position, whereby the interference fringe imaging state (corresponding to the first state), The spot imaging state (corresponding to the second state) can be switched (an example of imaging state switching means).

FIG. 3A is a diagram illustrating an optical path in the interferometer 30 when the orientation of the sample w is adjusted in the spot imaging state, and FIG. 3B is a diagram illustrating an output image of the interferometer 30. FIG.
In the spot imaging state, when object light is not generated (a state where the sample w is not disposed opposite to the reference glass 5 or a state where a light absorbing member is disposed between the reference glass 5 and the sample w), As shown in FIG. 3B, the CCD camera 10 obtains an image that appears only in the spot image P1 of the reference light.
On the other hand, in the spot imaging state, when object light is generated (a state in which the sample w is disposed opposite to the reference glass 5), the reference surface 5a of the reference glass 5 and the surface of the measurement region wa are not parallel. Is set, as shown in FIG. 3A, a deviation occurs between the optical path R1 of the reference light and the optical path R2 of the object light. For this reason, as shown in FIG. 3C, an image in which both the spot image P1 of the reference light and the spot image P2 of the object light appear is obtained by the CCD camera 10.

Here, if the surface shape of the measurement region wa of each sample w to be measured is not greatly different, the interference fringes obtained by the interferometer 30 depending on the relative relationship between the orientation of the reference surface 5a and the orientation of the measurement region wa. The general content of the image is determined.
Similarly, the positional relationship (relative position) between the two spot images P1 and P2 is generally determined by the relative relationship between the orientation of the reference surface 5a and the orientation of the surface of the measurement region wa.
Therefore, the positional relationship between the two spot images P1 and P2 is a standard when an image of interference fringes suitable for measuring the shape of the sample w (the above-described parallel fringe formation state as shown in FIG. 4A) is obtained. If the orientation (tilt) of the surface of the sample w is adjusted so as to achieve a general positional relationship, an image of an interference fringe suitable for measuring the shape of the sample w can be obtained in the interference fringe imaging state. It becomes a state.

On the other hand, the computer 11 stores a CPU (an example of a processor) that executes various arithmetic processes and control processes by executing a predetermined program, and a hard disk drive that stores programs executed by the CPU and various data. And a computer equipped with an information input device such as a keyboard and a mouse and an information output device such as a liquid crystal display.
Further, the computer 11 includes a signal input / output interface for inputting image information (brightness data) from the CCD camera 10 and outputting control signals to the various drive devices 9, 12, 13, 21a, and 22a. Yes.
Hereinafter, each process described as being executed by the computer 11 is realized by a CPU included in the computer 11 executing a predetermined program.

Next, the shape measurement procedure by the shape measuring apparatus Z will be described with reference to the flowchart shown in FIG. S1, S2,... Shown below represent identification codes of processing procedures (steps).
[Steps S1 to S5]
First, the computer 11 controls the lens switching motor 9 to set the spot imaging state (a state where the spot imaging lens 7 is disposed in front of the CCD camera 10) (S1, imaging state switching procedure). Example).
Next, in the spot imaging, the image obtained by the computer 11 with the CCD camera 11 (only the spot image P1 of the reference light) is formed in a state where the sample w is not disposed (a state where no object light is generated). (B) image) brightness data is recorded (obtained and stored in the storage unit) (S2).
Next, the computer 11 detects the position of the spot image P1 of the reference light (for example, the center position of an area having a predetermined luminance or higher) from the luminance data obtained in step S2, and stores this as the standard position of the spot image P1. (S3).
Next, in a state where the sample w is placed on the sample support portions 21 to 23, the computer 11 controls the elevating stage 13 and the rotary stage 12 to set the measurement area wa (the desired measurement area wa It is arranged at the irradiation position) (S4).
Next, with the measurement area wa set, the computer 11 controls the displacement devices 21a and 22a, so that the direction of the sample w (that is, the height of each of the displacement type sample support portions 21 and 22) is predetermined. The initial state is set (S5).

[Steps S6 to S11]
Next, the computer 11 records the luminance data of the image obtained by the CCD camera 11 (the image of FIG. 3C in which the two spot images P1 and P2 of the reference light and the object light are formed) (S6). .
Next, the computer 11 detects the respective positions of the reference light spot image P1 and the object light spot image P2 from the luminance data obtained in step S6 (S7). Here, the computer 11 determines the spot of the reference light that has a position within the predetermined range with respect to the standard position of the spot image P1 detected in step S3, out of the two spot images extracted from the luminance data. It is determined that the image is P1.
Next, the difference between the positional relationship (relative position) between the two spot images P1 and P2 detected by the computer 11 in step S7 and the target positional relationship stored in advance in the storage unit of the computer 11 (hereinafter referred to as spot position). Is calculated), and it is determined whether or not the spot position difference is within a predetermined error range (S8).
Here, the target positional relationship is a standard positional relationship when an image of interference fringes suitable for measuring the shape of the sample w (the above-described parallel fringe formation state as shown in FIG. 4A) is obtained. Yes, it is information that is acquired in advance experimentally (or by simulation calculation or the like).
Here, if the calculator 11 determines that the spot position difference is not within the predetermined error range, the sample w is changed according to the spot position difference (difference in the X-axis direction and difference in the Y-axis direction). The correction value (that is, the correction value of the displacement position of each of the displacement devices 21a and 22a) is calculated (S9). Furthermore, the computer 11 corrects the direction of the sample w by controlling the displacement devices 21a and 22a based on the correction value (S10), and then executes the above-described steps S6 to S8 again.
The computer 11 executes the processes of steps S6 to S10 to obtain 2 obtained by the CCD camera 10 when the lens switching motor 9 is switched to the spot imaging (second state) (S1). Displacement devices 21a and 22a (an example of orientation changing means) are controlled so that the positional relationship between the two spot images P1 and P2 is a predetermined target positional relationship (spot image adjusting means and a procedure thereof) .
When the computer 11 determines that the spot position difference is within a predetermined error range by the processing in steps S6 to S10, the computer 11 controls the lens switching motor 9 to control the interference fringe imaging state (interference fringe). The imaging lens 6 is switched to a state in which the imaging lens 6 is disposed in front of the CCD camera 10 (S11, an example of an imaging state switching procedure).

[Steps S12 to S16]
Next, in the interference fringe imaging state, the computer 11 records luminance data of an image (an image on which an interference fringe image is formed) obtained by the CCD camera 11 (S12). Here, since the orientation adjustment of the sample w is almost completed by the processing of steps S1 to S10, the interference fringe image obtained in step S12 is the image of the parallel fringe formation state shown in FIG. Or an image close to that.
Next, the computer 11 detects the number of fringes in the interference fringe image based on the luminance data recorded in step S12 (S13). Here, since the interference fringe image to be detected is substantially the image in the parallel fringe formation state, the number of fringes can be determined by a simple process of detecting the number of repetitions of the luminance density in the Y-axis direction in the luminance data. Can be detected.
Next, the computer 11 determines whether or not the number of fringes detected in step S13 is a predetermined target number (S14).
Here, when the calculator 11 determines that the number of stripes is not the target number, the correction value of the direction of the sample w (that is, the displacement position of each of the displacement devices 21a and 22a) according to the difference between the number of stripes and the target number. Correction value) is calculated (S15). Furthermore, the computer 11 corrects the direction of the sample w by controlling the displacement devices 21a and 22a based on the correction values (S16), and then executes the above-described steps S12 to S14 again.
The computer 11 controls the displacement devices 21a and 22a (an example of direction changing means) by executing the processes of steps S6 to S16 described above (S10 and S16), and the interference fringes obtained by the CCD camera 10 are controlled. The image is adjusted so as to be an ideal image in the parallel stripe formation state shown in FIG. 4A (an example of interference fringe image adjusting means and its procedure).
Note that immediately before it is determined in step S14 that the number of fringes is the target number, the latest luminance data recorded in step S12 (an example of the luminance data recording procedure) by the computer 11 is the interference fringe image adjustment process ( This is the luminance data of the interference fringe image obtained by the CCD camera 10 after the adjustment in steps S6 to S16).

[Step S17]
Next, the computer 11 calculates the phase Φ of each carrier wave (spatial periodic wave represented by a column of luminance data in the Y-axis direction) at each position on the X-axis based on the latest luminance data recorded in step S12. Calculation is performed by quadrature detection processing (an example of phase calculation means and its procedure).
Hereinafter, the calculation process of the phase Φ by the quadrature detection process executed by the computer 11 will be described.
In general, in quadrature detection, a time-domain signal f (t) to be processed is branched, and for each of the branched signals, a cosin wave signal (cosωt) and a sin wave signal (sinωt) that are substantially equal in frequency to the branched signal. Further, the signal is subjected to low-pass filter processing for each signal after the multiplication, and arctan (tan ⁻¹ ) calculation of the processed signal is performed. Thereby, the phase of the signal f (t) to be processed can be detected.
On the other hand, in step S <b> 17, the computer 11 performs orthogonal detection processing in the space region (y) in the Y-axis direction, not orthogonal detection processing in the time domain.

In the process of step S <b> 17, the calculator 11 first calculates the spatial frequency (gray frequency in the Y-axis direction) of the carrier wave (spatial periodic wave) in the region excluding the sample end portion we of the measurement region wa. For example, the average value of the spatial frequencies of the carrier waves at a plurality of positions in the X-axis direction is calculated.
Next, the computer 11 generates data representing each of the cosin wave and the sin wave having the spatial frequency of the carrier wave (the spatial frequency is equal). Here, the value of data representing each of the cosin wave and the sine wave is a value corresponding to the luminance obtained through the CCD camera 10. Hereinafter, they are referred to as cos luminance data and sin luminance data, respectively.
FIGS. 4B and 4C show cos luminance data and sin luminance data generated by the computer 11 as images, respectively.

Next, the calculator 11 calculates a product (multiplication value) of each value of the cos luminance data and the sin luminance data for each pixel (for each position). Hereinafter, the calculated data is referred to as cos luminance product data and sin luminance product data, respectively.
4D and 4E show the cos luminance product data and the sin luminance product data calculated by the computer 11 as images, respectively.
Further, the computer 11 performs a Gaussian distribution weighting process (Gaussian filter process) in the Y-axis direction for each of the cos luminance product data and the sin luminance product data. This is a process for weighting the low-pass filter process (the following addition process or average process), and may be omitted.
FIGS. 4F and 4G show cos luminance product data and sin luminance product data after being subjected to Gaussian filter processing by the computer 11 as images. Hereinafter, the images shown in FIGS. 4F and 4G are referred to as an image f and an image g, respectively.

Next, the computer 11 adds (accumulates) or averages all the luminances in the Y-axis direction for each position of the X-axis with respect to the luminance data of the images f and g. This corresponds to low-pass filter processing. Hereinafter, the luminance data for each position on the X-axis obtained by this addition or averaging is assumed to be c (x) (corresponding to cos luminance data) and s (x) (corresponding to sin luminance data), respectively.
FIG. 5 is a graph showing data c (x) and s (x). Note that the X-axis coordinate is converted into a distance from the edge of the sample w, and the luminance data is normalized in a range of ± 50.
Next, the computer 11 calculates the phase Φ (x) of the carrier wave for each position on the X axis by performing arctan calculation of the data c (x) and s (x) [Φ (x) = tan ^-1 (s (x) / c (x))].
FIG. 6 shows an example of a graph of the phase Φ calculated by the calculator 11. Note that the X-axis coordinate is converted to a distance from the edge of the sample w.
As described above, in step S17, the computer 11 is based on data representing a sine wave and a cosin wave having the same spatial frequency as the carrier wave (spatial periodic wave) in the region excluding the end portion we of the measurement region wa. The phase Φ (x) of the carrier wave is calculated by the quadrature detection process (an example of phase calculation means and its procedure).

[Step S18]
Next, the calculator 11 calculates the surface shape value h (x) in the X-axis direction in the measurement region wa based on the phase Φ (x) calculated in step S17 (phase calculation procedure), and stores the calculation result. (S18, an example of surface shape value calculating means and its procedure).
As shown in FIG. 6, the phase Φ (x) of the carrier wave is folded back at a period of 2π and is in a discontinuous state. On the other hand, the change in the surface shape of the sample w is continuous (smoothly changes).
Therefore, on the assumption that the change in the surface shape of the sample w is continuous in Step S18, the computer 11 performs the connection process (so-called unwrap process) of the phase Φ (x), so that the X of the measurement region wa The surface shape value h (x) (profile) in the axial direction is calculated.
Here, when the interferometer 30 is a Fizeau interferometer, the distance between the “bright part” and the “bright part” of the interference fringe (wavelength of the carrier wave) is the wavelength λ of the irradiation light (output light of the laser light source 1). Is equivalent to 1/2 of the length. Therefore, the calculator 11 calculates the surface shape ground h (x) by multiplying the phase Φ ′ (x) after the phase connection (unwrapping process) by (λ / 4π).
FIG. 6 shows an example of a graph of the surface shape ground h (x) calculated by the calculator 11. Note that the X-axis coordinate is converted to a distance from the edge of the sample w.

[Steps S19 and S20]
Next, the calculator 11 applies the evaluation value of the edge of the sample w by applying the surface shape value h (x) of the sample w calculated in step S19 to a predetermined evaluation formula (evaluation value calculation formula). The calculation is performed and the calculation result is output (output to the display unit or output to the external device) (S19).
As the evaluation value, for example, the surface shape value h (x) at the innermost position (center side of the sample w) in the measurement region wa is used as a reference, and a difference in the surface shape value h (x) with respect to the reference is a predetermined value. A position that falls within the maximum allowable value (position on the X-axis) or the like is conceivable.
Further, the computer 11 determines whether or not a predetermined measurement end condition (e.g., completion of the shape measurement of all the measurement areas wa planned) is satisfied for the set sample w (S20).
Here, when it is determined that the measurement end condition is not satisfied, the computer 11 executes a setting process for a new measurement area wa (S21), similarly to step S4 described above, and the new measurement area. For wa, the processes of steps S12 to S20 described above are repeated. In the second and subsequent steps S12 to S20 for the same sample w, the sample w orientation correction (S15, S16) is not executed (a proper interference fringe image can be obtained without correction). It is thought that there are many cases.
On the other hand, when it is determined that the measurement end condition is satisfied, the computer 11 ends the shape measurement process for the set sample w.

In the embodiment described above, an example in which a Fizeau interferometer is employed as the interferometer 30 is shown. However, the present invention is not limited to this, and other examples such as an oblique incidence interferometer, a Michelson interferometer, and a Twiman Green interferometer are used. It is also possible to employ an interferometer.
In the above-described embodiment, an example in which the Gaussian weighting process and the addition process (integration process) are employed as the low-pass filter process has been described. However, an embodiment in which the Gaussian weighting process is omitted in the above-described embodiment or weighting is performed. It is also possible to adopt other processes such as various averaging processes and low pass filter processes using FFT.
In the above-described embodiment, an example in which a mechanism for independently displacing two of the sample support portions 21 to 23 that support the sample w at three points has been described. However, the same support mechanism is adopted as a support mechanism for the reference glass 5 that is a member on which the reference surface 5a of the interferometer 30 is formed, and the orientation of the surface of the sample w is fixed (fixed support mechanism). It doesn't matter.

  INDUSTRIAL APPLICABILITY The present invention can be used for a shape measuring apparatus that measures the surface shape near the end of a circular plate-like sample such as a semiconductor wafer.

The schematic block diagram of the shape measuring apparatus Z which concerns on embodiment of this invention. The flowchart showing the shape measurement procedure by the shape measuring apparatus Z. The figure showing the optical path and output image in an interferometer at the time of adjusting the direction of a sample by the shape measuring apparatus Z. The figure which represented as an image an example of the data obtained in the process of the phase calculation process (orthogonal detection process) of the carrier wave by the shape measuring apparatus Z. The graph showing the data obtained in the process of the phase calculation process (orthogonal detection process) of the carrier wave by the shape measuring apparatus Z. The graph showing the phase and surface shape value of the carrier wave calculated by the shape measuring apparatus Z.

Explanation of symbols

Z ... shape measuring apparatus 1 ... laser light source 2 ... first lens 3 ... beam splitter 4 ... second lens 5 ... reference glass 6 ... interference fringe imaging lens 7 ... spot imaging lens 8 ... rotary lens holder 9 ... lens Switch motor 10 ... CCD camera 11 ... Computer 12 ... Rotary stage 13 ... Elevating stages 21, 22 ... Displacement type sample support parts 21a, 22a ... Displacement device 23 ... Fixed type sample support part 30 ... Interferometer P1 ... Spot image of reference light P2 ... Spot image S1, S2 ... of object light ... Processing procedure (step)

Claims (6)

A shape measuring device for measuring the surface shape of a measurement region ranging from an end of a substantially circular plate-shaped sample to a predetermined range inside thereof,
Imaging means for imaging an image of interference fringes formed in the output light of an interferometer that observes the measurement region;
Orientation changing means for changing the orientation of the reference surface or the surface of the measurement region in the interferometer;
By controlling the orientation changing means, the image of the interference fringes obtained by the imaging means extends substantially parallel to a reference axis parallel to the radial direction of the sample in a region excluding the end portion in the measurement region. Interference fringe image adjusting means for adjusting so as to be an image of a plurality of stripes formed by,
Luminance data recording means for recording luminance data of the interference fringe image obtained by the imaging means after adjustment by the interference fringe image adjusting means;
Phase calculation means for calculating the phase of each spatial periodic wave represented by the row of luminance data in the direction orthogonal to the reference axis at each position of the reference axis;
Surface shape value calculating means for calculating a surface shape value in the reference axis direction in the measurement region based on the phase calculated by the phase calculating means;
A shape measuring apparatus comprising:   The phase calculation means calculates the phase by quadrature detection processing based on data representing sine waves and cosine waves having spatial frequencies substantially equal to the spatial periodic wave in the region excluding the end of the measurement region. The shape measuring apparatus according to claim 1. A spot imaging lens that focuses the output light of the interferometer to form on the imaging means two spot images in which the object light and the reference light superimposed on the output light of the interferometer are condensed. When,
An imaging state switching unit that switches a first state in which the image of the interference fringe is formed on the imaging unit and a second state in which the two spot images are formed by the spot imaging lens; And
The interference fringe image adjusting unit is switched to the second state by the imaging state switching unit, and the orientation is changed so that a positional relationship between the two spot images obtained by the imaging unit becomes a predetermined positional relationship. 3. The shape measuring apparatus according to claim 1, further comprising spot image adjusting means for controlling the means. A shape measuring method for measuring a surface shape of a measurement region ranging from an end portion of a substantially circular plate-shaped sample to a predetermined range inside thereof,
An interference fringe imaging procedure for capturing an image of an interference fringe based on the irradiation light to the measurement region obtained by an interferometer;
The interference fringe image obtained by the interference fringe imaging procedure is controlled by controlling the direction changing means for changing the orientation of the reference surface in the interferometer or the orientation of the surface of the measurement region. An interference fringe image adjustment procedure for adjusting to an image of a plurality of stripes formed extending substantially parallel to a reference axis parallel to the radial direction of the sample in a region excluding
Luminance data recording procedure for recording luminance data of the interference fringe image obtained by the interference fringe imaging procedure after adjustment by the interference fringe image adjustment procedure;
A phase calculation procedure for calculating a phase of each of the spatial periodic waves represented by the row of luminance data in a direction orthogonal to the reference axis at each position of the reference axis by a predetermined processor;
Based on the phase calculated by the phase calculation procedure, a surface shape value calculation procedure for calculating a surface shape value in the reference axis direction in the measurement region by a predetermined processor;
A shape measuring method comprising:   The phase calculation procedure is a procedure for calculating the phase by quadrature detection processing based on data representing a sine wave and a cosine wave having spatial frequencies substantially equal to the spatial periodic wave in the region excluding the end of the measurement region. The shape measuring method according to claim 4. A first state in which the image of the interference fringe is formed on the imaging means, and object light superimposed on the output light of the interferometer by focusing the output light of the interferometer with a predetermined lens and reference An imaging state switching procedure for switching between a second state in which two spot images each of which light is condensed is formed on the imaging means;
When the interference fringe image adjustment procedure is switched to the second state by the imaging state switching procedure, the positional relationship between the two spot images obtained by the imaging unit becomes a predetermined positional relationship. 6. The shape measuring method according to claim 4, further comprising a spot image adjusting procedure for controlling the orientation changing means.

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