JP2002005640A - Optical shape-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical shape-measuring apparatus which can accurately measure shape, e.g. flatness and thickness, of a thin planar sample, especially a wafer. SOLUTION: The optical shape-measuring apparatus comprises optical measuring means 10, 20 provided with two reference planar substrates 15, 25 disposed opposite on the major surface 1a side and the rear surface 1b side of a wafer 1 held substantially vertically via an edge part, and transparent rigid plates 19, 29 disposed between the referential planar substrates 15, 25 and the wafer 1 in the proximity of the wafer, while forming a parallel gap with respect to the wafer 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to thin glass, mirrors,
The present invention relates to an optical shape measuring apparatus for measuring the shape, such as flatness and thickness, of a thin plate-shaped subject such as an aluminum magnetic disk, a glass disk, and a wafer. In the following, for ease of understanding, description will be made by taking an optical shape measurement of a wafer as an example.

[0002]

2. Description of the Related Art As a method for measuring the flatness, thickness, and the like of a wafer, a method proposed in, for example, JP-A-11-260873 is known.

[0003] In the wafer optical shape measuring device proposed in the above publication, as shown in FIG. 5, two optical measuring systems 10 and 20 are opposed to each other on both sides of a wafer 1 held vertically at an edge portion. The thickness measuring unit 50 is arranged toward the periphery of the wafer 1. Each of the optical measurement systems 10 and 20 includes a light emitter 11 or 21 that emits measurement light 12 or 22, a collimator lens 14 or 24 that uses the measurement light 12 or 22 as a parallel beam, and a reference plane through which the parallel beam passes. Lenses 15 and 25, wafer 1
The measurement light reflected by the main surface 1a and the back surface 1b of the reference plane lenses 15 and 25 and the collimator lens 14,
The light receiving devices 16 and 26 which enter through the light receiving device 24 and the like, the computing device 17 into which interference fringes formed by the reference plane lenses 15 and 25 and the main surface 1a and the back surface 1b of the wafer 1 are taken in.
It has. Then, in the light receivers 16 and 26, reflected light from the reference plane lenses 15 and 25 and interference fringes formed by the main surface 1 a and the back surface 1 b of the wafer 1 are observed. The main surface 1 of the wafer 1 is determined based on the interference fringe images observed by the light receivers 16 and 26.
a and the plane shape of the back surface 1b are calculated, and the true shape of the wafer 1 is determined based on the actual thickness measured at a predetermined position of the wafer 1 measured by the thickness measuring unit 50.

[0004] In the proposed optical shape measuring apparatus for a wafer, the flatness of the main surface and the back surface are obtained by using interference fringes obtained from the main surface and the back surface of the wafer, respectively.
Since the true shape of the wafer is calculated based on the actual measured value of the thickness of the wafer obtained by the thickness measuring device, the flatness can be measured with high accuracy in a very short time as compared with the conventional method.
Further, the main surface shape, the back surface shape, the flatness, and the absolute thickness are obtained from the calculated true shape. Further, since the wafer to be measured is held vertically in a stationary state, it is used for measurement without being affected by gravity. In addition, there is little opportunity for dust and flaws to adhere, and deterioration of wafer characteristics is prevented. It is said that such an effect can be obtained.

[0005]

By the way, in the wafer optical shape measuring device proposed in the above-mentioned publication, although the above-mentioned effects are expected to be obtained, the surface shape of a thin-walled object such as a wafer is expected. In the case of measuring, since it is desired to measure the entire surface of the front surface and / or the back surface of the subject, a method of holding the object via the edge portion of the subject is used, and a method of supporting three points around the subject is generally used. Be taken. In the state where the periphery is supported in this manner, the subject is caused to vibrate by the influence of vibration (sound) propagating in the air, so that it is difficult to perform highly accurate measurement. In particular, when the subject is a wafer,
For a high-precision (20 nm or less) measurement required for wafer flatness measurement, a measurement error due to vibration is in a non-negligible order.

Incidentally, in the optical shape measuring device for wafers proposed in the above publication or the shape measuring device proposed by the present applicant (Japanese Patent Application No. 12-53591), the optical measuring system is a Fizeau interference type. The reference plane substrate incorporated in the optical system (referred to as the reference plane lens in the above description of the prior art, but since this part only transmits light in parallel, The shape of the wafer is measured by measuring the relative distance between the surface of the wafer (object) and the relative distance between the surface of the wafer (object), but as described above, when the wafer vibrates, the relative distance to the reference plane substrate is measured. Is changed, and high-precision shape measurement cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made based on the above-mentioned circumstances, and has as its object to accurately and precisely measure flatness, thickness, etc. of a thin plate-shaped test object, particularly a wafer. An object of the present invention is to provide an optical shape measuring device capable of measuring a shape.

[0008]

In order to achieve the above object, an optical shape measuring apparatus according to the present invention (claim 1) has a thin flat plate which is held substantially vertically via an edge portion. An optical shape measuring apparatus for a test object having a rectangular shape, wherein a rigid flat plate forming a parallel gap with the test object is arranged close to the test object. When a rigid flat plate that forms a parallel gap is disposed close to the subject in this manner, the air layer acts as a resistance component of vibration (sound) and causes an attenuation effect as the close interval becomes narrow. Thereby, the vibration of the subject is suppressed, and the shape such as flatness and thickness can be measured with high accuracy. In this case, the rigid flat plate may be the reference flat substrate itself incorporated in the optical shape measuring apparatus, or may be a steel plate, an aluminum plate, a flat glass plate made of optical glass or the like separately from the reference flat substrate. Certain flat plates can also be used. A material that does not transmit light, such as the above-mentioned steel plate or aluminum plate, is used for shape measurement of one surface of a subject, and in that case, it is disposed to face a surface other than the surface to be measured.

It is desirable that the distance between the rigid flat plate and the subject is less than 20 mm (claim 2). If the distance exceeds 20 mm, the thickness of the air layer becomes large. This is because the effect of the vibration (sound) as a resistance component cannot be sufficiently obtained, so that it is difficult to obtain an attenuation effect, and it is difficult to accurately measure the shape of the subject such as flatness and thickness. Further, it is more preferably 10 mm or less.

The optical shape measuring apparatus according to the present invention (Claim 3) is characterized in that two reference flat substrates are disposed on the main surface side and the rear surface side of a wafer held substantially vertically via an edge portion. And a transparent rigid flat plate which forms a parallel gap with the wafer between the reference plane substrate and the wafer and is arranged close to the wafer.

The above configuration shows a preferred example of the configuration of the optical shape measuring apparatus according to the first aspect of the present invention when the subject is specified as a wafer. That is, in the case of a wafer, since both the main surface and the back surface are to be measured, optical measuring means are provided on both sides thereof, and a parallel gap with respect to the wafer is provided between the wafer and the reference plane substrate of the optical measuring means. A transparent rigid plate to be formed is arranged close to,
Even when the transparent rigid flat plate that forms a parallel gap with respect to the wafer is arranged close to the wafer, the air layer acts as a resistance component of vibration (sound) as the close gap is narrowed, similarly to the above-described claim 1. Causes a damping effect. Thereby, the vibration of the wafer is suppressed, and the shape such as flatness and thickness can be measured with high accuracy. In this case, a reference plane substrate of the optical measuring means may be arranged close to the transparent rigid flat plate.

The transparent rigid flat plate is not particularly limited as long as it is transparent and can transmit light, but a generally used flat glass made of optical glass is desirable (claim 4).

Further, the interval at which the transparent rigid flat plate is arranged close to the wafer is set to 2 for the same reason as in claim 2.
It is desirable that the thickness be 0 mm or less (claim 5). That is, if the distance exceeds 20 mm, the thickness of the air layer becomes large, so that the effect as the resistance of vibration (sound) cannot be sufficiently obtained, and the damping effect is hardly obtained.
This is because it becomes difficult to measure the shape such as the thickness with high accuracy. Further, it is more preferably 10 mm or less.

In the present invention described above, the reason why the thin plate-shaped test object (wafer) is held substantially vertically is that the test sample is held vertically so that the deflection of the test object is not affected by gravity. There is an effect of reducing the amount, but the effect is substantially the same even if it is held at an angle of about 5 degrees from vertical, so that it is held substantially vertical. The parallel gap is not intended only to be parallel so that the plane parallel between the rigid flat plate and the object plane is completely coincident with each other. This includes that there may be some inclination to avoid.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. The same parts as those in the conventional technique are denoted by the same reference numerals. FIG. 1 is a schematic explanatory view of an optical shape measuring apparatus according to the present invention. In the figure, 1 is a wafer, 19,
29 is a flat glass (rigid flat plate), 10 and 20 are optical measuring means, and 17 is a calculator.

The outer peripheral edge portion of the wafer 1 is held vertically by appropriate holding means conventionally used.

The flat glass plates 19 and 29 are made of optical glass and are arranged on both sides of the wafer 1 close to each other at an interval h and in plane parallel. The interval h is desirably 20 mm or less, and more desirably 10 mm or less.

The optical measuring means 10 and 20 are arranged outside the flat glass 19 and 29, and the light emitting devices 11 and 21, the half mirrors 13 and 23, the collimator lenses 14 and 24,
Reference plane substrates 15 and 25 and light receivers 16 and 26 are provided.

The arithmetic unit 17 has a monitor 18 to which the light emitters 11 and 21 and the light receivers 16 and 26 are connected.

In the above-mentioned optical shape measuring apparatus, the light emitting device 1
The measurement lights 12, 22 emitted from the light sources 1, 21 are sent to the collimator lenses 14, 24 via the half mirrors 13, 23, and transmitted as parallel beams through the reference flat substrates 15, 25 and the flat glass plates 19, 29. Main surface 1a of wafer 1
And irradiate the back surface 1b. The measurement light beams 12 and 22 are reflected on the main surface 1a and the back surface 1b of the wafer 1, but a part of the light is also reflected on the reference flat substrates 15 and 25 facing the main surface 1a and the back surface 1b of the wafer 1.

The main surface 1a and the back surface 1 of the wafer 1
b and the measurement light 12 reflected by the reference plane substrates 15 and 25,
A half mirror 1 transmits through the reference plane substrates 15 and 25 and the collimator lenses 14 and 24 along the reverse path, and
The light is reflected by the light receiving devices 3 and 23 and is taken into the light receiving devices 16 and 26. The measurement light beams 12 and 22 reflected by the main surface 1a and the back surface 1b of the wafer 1 have different optical path differences from the measurement light beams 12 and 22 reflected by the reference plane substrates 15 and 25. Since the optical path difference reflects the surface shape of the wafer 1 as described above, the plane shapes of the main surface 1a and the back surface 1b of the wafer 1 can be determined from the observed interference fringes.

Two interference fringes captured by the light receivers 16 and 26 and formed by the reference flat substrates 15 and 25 and both surfaces (the main surface 1a and the back surface 1b) of the wafer 1 are simultaneously captured by the arithmetic unit 17. The arithmetic unit 17 calculates and records the shapes of the main surface 1a and the back surface 1b of the wafer 1 from the taken interference fringes. In addition, the flatness of the wafer 1 is calculated from the interference fringes on the basis of the shape of one main surface or the back surface and recorded.

In the shape measurement such as the flatness of the wafer 1 obtained as described above, the flat glasses 19 and 29 are arranged on both sides of the wafer 1 close to each other at an interval h and parallel to the plane. Does not vibrate under the influence of vibration (sound) propagating in the air, and can accurately measure shapes such as flatness and thickness.

The wafer 1 having a diameter of 300 mm was measured using the optical shape measuring apparatus constructed as described above, and the flat glass 19 and 29 were used as the shape dimensions 360 m.
Using quartz glass flat glass with m square and 15 mm thickness,
Further, in an actual measurement environment in which the wafer 1 vibrates at the natural frequency of the wafer 1 under the influence of vibration (sound) propagating in the air, the distance h between the wafer 1 and the flat glass 19, 29 is set to 10 mm to 50 mm. If you change between
The effect of vibration damping was confirmed between the case where the plate glasses 19 and 29 were not provided.

As a result, in the state where the plate glasses 19 and 29 are not provided (the distance between the wafer 1 and the reference flat substrates 15 and 25 is about 65 mm), the natural frequency: f = 39 Hz and the vibration amplitude: A = 45 nm (effective Value) was observed. On the other hand, in a state where the distance h between the wafer 1 and the flat glasses 19 and 29 is closely arranged to be 10 mm, it was confirmed that the vibration amplitude of the vibration of the wafer 1 was attenuated to A = 8 nm (effective value). . Further, when the distance h between the wafer 1 and the flat glasses 19 and 29 is set to about 50 mm, it is almost the same as the state where the flat glasses 19 and 29 are not provided. It was confirmed that there was.

From the above results, it is confirmed that the vibration damping effect tends to increase as the distance h decreases, and assuming that the vibration damping effect is linear, the vibration damping effect required by the flatness measurement of the wafer 1 is high. For accuracy (20 nm) measurement, the interval h needs to be 20 mm or less. And
More preferably, it is 10 mm or less.

FIG. 2 is a schematic explanatory view of another optical shape measuring apparatus according to the present invention. The optical shape measuring device shown in FIG. 2 is the same as the optical shape measuring device shown in FIG. 1 except that one of the flat glasses 19 and 29 disposed on both sides of the wafer 1 except the flat glass 29 is removed. This is the same as the optical shape measuring device shown.

Even when only the flat glass 19 is arranged close to the wafer 1 at the distance h as described above, the vibration (sound) of the wafer 1 propagating in the air is the same as in the optical shape measuring apparatus shown in FIG. Vibration does not occur due to the influence of, and the shape such as flatness and thickness can be measured with high accuracy. In addition, according to the same measurement as in the example of FIG. 1, the interval h is 2 for the high accuracy (20 nm) measurement required for the flatness measurement of the wafer 1.
0 mm or less, more preferably 10 mm
The following was confirmed to be good.

FIG. 3 is a schematic explanatory view of another optical shape measuring apparatus according to the present invention. The optical shape measuring apparatus shown in FIG. 3 is different from the optical shape measuring apparatus shown in FIG. 1 in that both the flat glasses 19 and 29 arranged on both sides of the wafer 1 are removed, and the reference plane substrate of the optical measuring means 10 and 20 is removed. The configuration except that the wafers 15 and 25 are arranged close to the wafer 1 with an interval h is the same as the optical shape measuring apparatus shown in FIG.

As described above, even when the reference flat substrates 15 and 25 are disposed close to the wafer 1 except for the flat glasses 19 and 29 at a distance h from the wafer 1, the wafer 1 is still in the same manner as the optical shape measuring apparatus shown in FIG. Vibration does not occur under the influence of vibration (sound) propagating in the air, and highly accurate shape measurement such as flatness and thickness can be performed. In addition, by the same measurement as in the example of FIG. 1, the high accuracy (20
nm), it has been confirmed that the interval h needs to be 20 mm or less, more preferably 10 mm or less. In the prior art shown in FIG. 5, the distance between the wafer 1 and the reference plane substrates 15 and 25 is also reduced, but even if the distance is reduced, the distance is 30 to 50 mm.
The reason for the narrowing is to prevent air fluctuations, and is not intended to provide the effect of damping the vibration of the subject (including the wafer) as in the present invention.

FIG. 4 is a schematic explanatory view of another optical shape measuring apparatus according to the present invention. The optical shape measuring apparatus shown in FIG. 4 is an apparatus applied when measuring the shape such as the flatness of one side surface of a thin flat plate-shaped subject 1 (or the wafer 1). Components that constitute the same parts as those of the optical shape measuring apparatus shown in FIG. 1 are denoted by the same reference numerals.
Although FIG. 4 illustrates the case where the flat glass 19 is disposed close to the back side of the measurement surface of the subject 1, in this example, it is not necessary to use the transparent flat glass 19, and the steel plate and the aluminum plate are used. It may be a rigid flat plate made of a material such as a resin plate.

Even in the optical shape measuring apparatus as described above, the flat glass 19 is arranged close to the wafer 1 at an interval h so that the wafer 1 can be air-flowed similarly to the optical shape measuring apparatus shown in FIG. Vibration does not occur under the influence of vibration (sound) propagating through the inside, and highly accurate shape measurement such as flatness and thickness can be performed. In addition, by the same measurement as in the example of FIG. 1, the high accuracy (20
nm), it has been confirmed that the interval h needs to be 20 mm or less, more preferably 10 mm or less.

The following points must be taken into consideration for the flat glasses 19 and 29 in the above example. That is, when the measurement light emitted from the light emitters 11 and 21 passes through the plate glasses 19 and 29 as a parallel beam, the plate glasses 19 and 29
When part of the measurement light is reflected on both surfaces of the wafer 9, interference light noise is generated with respect to the formation of interference fringes observed between the reference plane substrates 15 and 25 and both surfaces 1 a and 1 b of the wafer 1. For example, the reflectance of the surface of an optical glass such as quartz glass generally used as an optical material is about 4%. If the above phenomenon cannot be ignored due to the reflection, the flat glass 19,
It is preferable to apply anti-reflection surface coating processing to both surfaces of the photoreceptor 29 to remove disturbance light noise. Alternatively, the above phenomenon is achieved by setting the parallelism of the thickness of the flat glass 19, 29 to 0.1.
Since the problem can be solved by increasing the thickness by at least the degree, the parallelism of the thickness of the flat glass 19, 29 may be set to 0.1 degree or more.

[0034]

As described above, according to the optical shape measuring apparatus of the present invention, the vibration caused by the vibration (sound) propagating in the air can be applied to a thin plate-shaped subject. It is possible to measure the shape of the subject such as flatness and thickness with high accuracy while suppressing the occurrence of the problem.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an optical shape measuring apparatus according to the present invention.

FIG. 2 is a schematic explanatory view of an optical shape measuring apparatus according to another embodiment of the present invention.

FIG. 3 is a schematic explanatory view of an optical shape measuring apparatus according to another embodiment of the present invention.

FIG. 4 is a schematic explanatory view of an optical shape measuring apparatus according to another embodiment of the present invention.

FIG. 5 is a schematic explanatory view of a conventional optical shape measuring device.

[Explanation of symbols]

1: Wafer (subject) 10, 20: Optical measuring means 11, 21: Light emitter 12, 22: Measurement light 13, 23: Half mirror 14, 24: Collimator lens 15, 25: Reference plane substrate 16, 26 Light receiver 17: arithmetic unit 18: monitor 19, 29: flat glass

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsutomu Morimoto 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Inside Kobe Research Institute, Kobe Steel Ltd. (72) Eiji Takahashi Takatsuka, Nishi-ku, Kobe City, Hyogo Prefecture 1-5-5 Daiko Kobe Steel, Ltd. Kobe Research Institute (72) Inventor Hidetoshi Tsunagi 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Prefecture F-term (reference) 2F065 BB01 BB03 BB22 BB25 CC03 CC19 CC21 DD14 FF52 FF61 LL00 LL04 PP11 QQ23

Claims (5)

[Claims] 1. An optical shape measuring apparatus for a thin plate-shaped subject held substantially vertically via an edge portion, wherein a rigid flat plate forming a parallel gap with the subject is close to the subject. An optical shape measuring device, wherein the optical shape measuring device is arranged. 2. The optical shape measuring apparatus according to claim 1, wherein the rigid flat plates are arranged on the subject at intervals of 20 mm or less. 3. An optical measuring means comprising two reference plane substrates opposed to each other on a main surface side and a back surface side of a wafer held substantially vertically via an edge portion, and between the reference plane substrate and the wafer. An optical shape measuring apparatus, comprising: a transparent rigid flat plate that forms a parallel gap with a wafer and is disposed close to the wafer. 4. The optical shape measuring apparatus according to claim 3, wherein the transparent rigid flat plate is a flat glass made of optical glass. 5. The optical shape measuring apparatus according to claim 3, wherein transparent rigid flat plates are arranged on the wafer at intervals of 20 mm or less.