JP2000258144A - Flatness and thickness measurement device for wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously and accurately measure the flatness and thickness of a wafer. SOLUTION: The wafer 1 and a reference plane panel 4 are held so as to make the planes vertical and the plane is irradiated with a laser beam 9 at a prescribed angle α while two-dimensionally performing scanning. Reflected light 14 generated on the plane at the time is converged so as to reduce the diameter and then branched into two optical paths 19 and 20 and a first optical path 19 is provided with a first detector 21 for detecting the incident position of the reflected light 14. Further, a second optical path 20 is provided with an fθ lens 22 and a second detector 23 provided with a detection surface on the focus position of the fθ lens 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for measuring flatness and thickness of a wafer.

[0002]

2. Description of the Related Art For example, as an apparatus for measuring the flatness of a wafer, a Fizeau interferometer (Fizeau interferometer) is used.
A flatness measuring device comprising a ferometer is known, and a capacitance-type thickness measuring device is known as a technique for measuring the thickness of a wafer.

[0003]

However, in the flatness measuring device utilizing the interference, since only one surface of the wafer is measured, its thickness cannot be directly measured, and the flatness cannot be measured within a certain range. In this case, the calculation is performed based on the flatness when the wafer is attracted to the chucking machine which is guaranteed, and the variation in thickness can only be obtained indirectly. In this flatness measuring apparatus, foreign matter may be interposed between the wafer and the chuck board, and the foreign matter often causes an error in the measured value. In addition, in a capacitance-type thickness measuring device, it is possible to indirectly determine the thickness based on the distribution of thickness such that when one surface is adsorbed to a perfect plane, the other surface has a predetermined flatness. And the flatness could not be directly measured. And, in this capacitance type thickness measuring device, the size of the sensor is limited,
The resolution in the plane direction of the wafer was not so good.

The present invention has been made in consideration of the above-mentioned matters, and has as its object to measure a flatness and a thickness of a wafer (hereinafter simply referred to as a flatness and thickness measuring device capable of simultaneously measuring the flatness and the thickness of the wafer with high accuracy). Measurement device).

[0005]

In order to achieve the above object, a measuring apparatus according to the present invention holds a wafer and a reference plane board such that their planes are vertical, and applies laser light to said plane. Irradiation is performed at a predetermined angle while performing dimensional scanning, and then the reflected light generated on the plane is converged so that its diameter becomes smaller, then branched into two optical paths, and the incident position of the reflected light on the first optical path. Lens is provided in the second optical path and the fθ lens and the fθ
A second detector having a detection surface at a focal position of a lens is provided, an output obtained from each of the detectors when a laser beam is applied to a front surface of the wafer and a reference surface of a reference plane board, and a back surface of the wafer and the reference surface. The flatness on both surfaces of the wafer and the thickness of the wafer can be simultaneously obtained based on the outputs obtained from the two detectors when the surface is irradiated with the laser beam (claim 1).

In the above configuration, the wafer and the reference flat board may be rotatable around a vertical axis.

In the measuring apparatus having the above-described structure, the flatness of both surfaces of the wafer can be easily measured, and these flatnesses can be measured.
The calculation is performed based on the inclination of the reference plane board corresponding to each plane, and the distance (thickness) between both planes is obtained. Thereby, the absolute value of the flatness and the thickness of the wafer can be simultaneously measured.

[0008]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a configuration of a measuring apparatus according to the present invention. In this figure, reference numeral 1 denotes a wafer to be measured, 1a and 1b denote front and back surfaces of a wafer 1 to be inspected, and a mirror surface. Has become. The wafer 1 has its planes 1a, 1b held by wafer holders 3 provided at a plurality of appropriate locations on a wafer stage 2.
Are held vertically. Reference numeral 4 denotes a reference flat plate which is vertically held by an appropriate holding member 5 so that the front surface 4a and the back surface 4b of the same surface as the wafer 1 are vertical in the same plane as the wafer 1, and is made of, for example, a transparent glass plate. 4a is a reflective surface formed by appropriately depositing aluminum and is formed on the reference surface, and the back surface 4b is a light transmitting surface.

The lower end of the wafer stage 2 is connected to a rotating mechanism 6 driven by a motor or the like.
The wafer 1 and the reference plane board 4 can be freely rotated in any direction about a vertical axis 7. That is, the wafer 1 and the reference plane board 4 are vertically held by the wafer stage 2 so that both surfaces thereof can be opposed to a light irradiation optical system 8 and a light reduction optical system 13 described below one by one. ing.

Reference numeral 8 denotes a light irradiation optical system for irradiating the laser beam 9 to the wafer 1 and the reference plane board 4 held as described above. The laser light source 10 and the laser beam 9 are applied to the wafer 1 and the reference plane board 4. On the other hand, it comprises a two-dimensional scanning mirror 11 for scanning at a predetermined angle α in the two-dimensional direction, and a lens 12 for irradiating the scanned laser beam 9 to the wafer 1 as parallel light.

As the two-dimensional scanning mirror 11, one mirror may be two-dimensionally vibrated, or a combination of two galvanometer mirrors may be one-dimensionally vibrated. It may be so.

Reference numeral 13 denotes a light reduction optical system for reducing the light 14 generated by reflecting the laser light 9 radiated on the wafer 1 and the reference plane board 4 by the light irradiation optical system 8 on the surface of the wafer 1. It comprises a lens 15 for reducing the diameter of the reflected light 14 and a lens 17 for converting the reduced light into parallel light 16.

Reference numeral 18 denotes a beam splitter provided at the subsequent stage of the optical reduction optical system 13 and composed of, for example, a half mirror. The beam splitter 18 splits the reduced parallel light 16 from the optical reduction optical system 13 into two optical paths 19 and 20. . The first optical path 19 is provided with a first detector 21 for detecting the position of the reduced parallel light 16. In the other optical path (second optical path) 20, an fθ lens 22 and a second detector 23 having a detection surface at a focal position of the fθ lens 22 are provided.

Each of the first detector 21 and the second detector 23 is, for example, a two-dimensional detector array in which CCDs are two-dimensionally arranged.
Light 1 is affected by the position of the reflection surface and its inclination.

As shown in FIG. 2, the fθ lens 22 has a property that incident light 24 to 26 forms an image on a plane 29 perpendicular to the optical axis 28 at a distance equal to the focal point f. Lights 24 and 25 parallel to the optical axis 28
Forms an image at the intersection 30 between the optical axis 28 and the surface 29,
Lights 26 and 27 that are not parallel to 8 have the property of forming an image on a point 31 on a plane separated from the point 30 by a distance h. At this time, the relationship h = fθ holds between the angle θ between the optical axis 28 and the lights 26 and 27 and the focal length f and the distance h.

Therefore, according to the second detector 23, since the focal length f is known in advance, if the distance h is known, the inclination of the reflecting surface can be obtained.

Referring again to FIG. 1, reference numeral 32 denotes an arithmetic unit such as a personal computer, which performs an arithmetic operation based on the outputs of the first detector 21 and the second detector 23 to determine the flatness of the surface of the wafer 1 and the like. This arithmetic unit 32
, A scanning signal to the two-dimensional scanning mirror 11 is input, and is associated with output signals of the detectors 21 and 23.

Next, the operation of the measuring apparatus will be described with reference to FIG.
This will be described with reference to FIG. First, as shown in FIG.
Surface 1a of wafer 1 and reference plane 4a of reference plane board 4
Are set so as to face the light irradiation optical system 8 and the light reduction optical system 13. In this state, the laser light 9 from the laser light source 10 is two-dimensionally scanned at a predetermined angle α using the two-dimensional scanning mirror 11 and at a predetermined interval on the wafer surface 1a and the reference surface 4a. Irradiate.
This scanning interval is appropriately set according to the required density of the measurement data.

The light 14 reflected on the wafer surface 1a and the reference surface 4a is reduced by an optical reduction optical system 13 so as to have a predetermined diameter, and the reduced light 16 is converted into two optical paths 19 by a beam splitter 18. , 20 and
Light traveling in the first optical path 19 enters the first detector 21,
The light traveling in the second optical path enters the second detector 23 via the fθ lens 22.

By two-dimensional irradiation of the laser light 9 on the wafer surface 1a and the reference surface 4a, signals (information) are output from the first detector 21 and the second detector 23, respectively. 9
Is recorded in association with the scanning position. Thereby, the first
The position on the detector of the light incident on each of the detector 21 and the second detector 23 is determined by the position and angle of the incident light reflected on the wafer 1, and the position on the second detector 23 is the incident light. Is determined by the accuracy of Hereinafter, this will be described with reference to FIG.

First, the information obtained from the second detector 23 is the inclination of the reflected light 14 on the wafer 1 from the optical relationship with the fθ lens 22 as described above. On the other hand, the information obtained from the first detector 21 also includes the position of the reflected light 14. Therefore, the position of the reflection point of the reflected light 14 is uniquely determined by calculating based on the information from the detectors 21 and 23. That is, the incident point (light spot) on the first detector 21
Are the same, the position or inclination of the reflection point is different if the inclination of the light is different. Conversely, if the inclination of the reflected light 14 and the position of the incident light 14 (assuming the inclination is constant) are known, the position and the inclination of the reflection surface can be known.

FIG. 3 schematically shows reflected light incident on the first detector 21. In FIG. 3, a parallel light 34 reflected at a reflection point 33 is reflected by a certain parallel light 32 on the first detector 21. It is assumed that the light enters the point 35. At this time, even if the light is incident on the same point 35, the light that is incident on the parallel light 34 and the point 35 is not parallel to the optical axis but is incident at an angle η instead of being reflected at the reflection point 33. The light 36 is reflected at a point 37 where the line 36 forming η and the light 32 intersect linearly extended.

Even if the parallel light 32 is reflected at the reflection point 33, if the reflection point 33 is inclined as shown by the imaginary line 33 ', the first detector 21 is located at a position different from the point 35. Incident.

As described above, the position of the reflection point of the reflected light 14 and the reflection point thereof are determined by the inclination of the reflected light 14 on the wafer 1 obtained from the second detector 23 and the position of the reflected light 14 obtained from the first detector 21. You can see the inclination of
Therefore, by irradiating the wafer surface 1a with the laser beam 9 while scanning it two-dimensionally, the height position and the inclination (the inclination of the wafer 1 in the XX direction in FIG. 1) on the wafer surface 1a can be determined. .

As described above, the laser light 9 is irradiated on the wafer surface 1a, and the reflected light 14 generated at that time is incident on the two detectors 21 and 23.
From the output of 23, the height state on the entire surface of the wafer surface 1a, that is, the flatness can be obtained. At this time, the flatness of the reference surface 4a is similarly measured.

Next, the rotation mechanism 6 is operated to set the wafer 1 and the reference flat board 4 such that their back surfaces 1b and 4b face the light irradiation optical system 8 and the light reduction optical system 13, respectively. Similarly to the above, the laser light 9 from the laser light source 10 is irradiated while being two-dimensionally scanned. At this time,
On the reference plane board 4, the laser light 9 is reflected on the first plane 4a. That is, in this case, the reference plane 4a is measured on the reference plane board 4 in the same manner as the measurement of the wafer surface 1a.

The back surface 1b of the wafer and the reference surface 4a
(Strictly speaking, the light 14 reflected on the back side of the reference surface 4a) is reduced by the light reduction optical system 13 so as to have a predetermined diameter, and the reduced light 16 is converted into a beam splitter 18
The light is branched into two optical paths 19 and 20, and the light traveling in the first optical path 19 enters the first detector 21, and the light traveling in the second optical path enters the second detector 23 via the fθ lens 22.

The first detector 21 and the second detector 21 obtained based on the irradiation of the laser
By processing the output of the detector 23 as described above, it is possible to obtain the height state on the entire surface of the wafer back surface 1b, that is, the flatness. Since the same reference plane 4a as that of the measurement of the wafer front surface 1a is measured for the reference surface 4a, the height of the reference surface 4a is used as a reference so that the front surface 1a and the back surface 1a of the wafer 1 are measured.
b can be compared based on the same criteria. That is, the thickness of the wafer 1 and its distribution can be obtained as an absolute value (accurately, it is shifted by the thickness of the deposited aluminum film constituting the reference plane 4a).

By the way, the smaller the angle (angle α in FIG. 1) of the laser beam 9 incident on the front surface 1a (or the back surface 1b) of the wafer 1, the lower the resolution in the two-dimensional direction and the higher the resolution in the height direction. Become. Conversely, when the angle α is large, the resolution in the two-dimensional direction increases, and the resolution in the height direction decreases. Therefore, it is necessary to determine the angle α of the laser light 9 incident on the front surface 1a (or the back surface 1b) of the wafer 1 according to the inspection purpose or application.

As described above, in the measuring apparatus of the present invention, the coherent laser beam 9 is irradiated two-dimensionally on the wafer 1, and the reflected light obtained at that time is detected by the two detectors 21 and 23. Then, by obtaining the position of the reflected light and the inclination with respect to the optical axis, the flatness on both surfaces 1a and 1b of the wafer 1, the thickness of the wafer 1, and the distribution thereof can be simultaneously obtained based on these data.

Since the flatness and thickness are measured in the above-mentioned measuring apparatus while the wafer 1 is held vertically, the influence of the bending of the wafer 1 due to its own weight is eliminated, and the measuring accuracy is reduced as compared with the conventional one. Significantly improved.

In the above embodiment, the detection of the inclination of the wafer 1 in the XX direction has been described. However, the present invention is not limited to this, and the present invention is not limited to this. The direction, that is, the inclination in the direction perpendicular to the paper surface of the wafer 1 can be detected in the same manner.

Further, PSDs are used as the detectors 21 and 23.
(Position Sensing Device
s) may be used.

In the above-described embodiment, both surfaces 1a and 1b of the wafer 1 are mirror surfaces. However, when these surfaces are rough surfaces, the reference flat plate 4 may be slightly flattened with ceramics or the like. The same measurement can be performed by using a material formed with a material having a rough surface and measuring moire fringes.

Further, in the above-described embodiment, the light irradiation optical system 8 and the light reduction optical system 13 are provided only on one surface side of the wafer 1 and the reference plane board 4.
Although the reference plane 4 is rotated, the optical diameters 8 and 13 may be provided on both sides of the wafer 1 and the reference plane 4.

[0036]

According to the measuring apparatus of the present invention, the flatness on both surfaces of the wafer and the thickness of the wafer can be simultaneously and accurately measured. According to the above-described measuring apparatus, the measurement can be performed by setting the resolution of the in-plane digital direction according to the required resolution.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an example of a configuration of a wafer flatness and thickness measuring apparatus of the present invention.

FIG. 2 is a diagram for explaining the function of an fθ lens used in the device.

FIG. 3 is a diagram schematically illustrating a measurement principle of the device.

[Description of Signs] 1 ... Wafer, 1a, 1b ... Plane of wafer, 4 ... Reference plane board, 4a, 4 ... Plane plane of reference plane board, 7 ... Vertical axis,
9 ... laser light, 14 ... reflected light, 19 ... first optical path, 20 ...
A second optical path, 21... A first detector, 22.
23 ... Second detector.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA03 AA19 AA24 AA30 AA35 AA47 AA51 BB03 BB25 CC19 DD00 FF61 FF65 GG04 HH03 HH12 JJ01 JJ05 JJ08 JJ16 JJ26 LL00 LL04 LL05 LL10 LL13 LL13 LL13 MM46 CA48 DH03 DH12 DH32 DH39 DJ02 DJ06

Claims (2)

[Claims] 1. A wafer and a reference plane board are held such that their planes are vertical, and the plane is irradiated with a laser beam at a predetermined angle while scanning the plane two-dimensionally. After converging the resulting reflected light so that its diameter becomes smaller, the light is branched into two optical paths, a first detector for detecting the incident position of the reflected light is provided on a first optical path, an fθ lens and an fθ lens are provided on a second optical path. A second detector having a detection surface at a focal position of a lens is provided, an output obtained from each of the detectors when a laser beam is applied to a front surface of the wafer and a reference surface of a reference plane board, and a back surface of the wafer and the reference surface. Simultaneously obtaining the flatness on both surfaces of the wafer and the thickness of the wafer based on the outputs obtained from the two detectors when the surface is irradiated with laser light. It was possible manner flatness and thickness measuring device wafer, comprising. 2. The wafer flatness and thickness measuring apparatus according to claim 1, wherein the wafer and the reference plane board can be rotated about a vertical axis.