JP2000161930A - Method and apparatus for measuring forms - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain relative relations in heights or depths between protrusions and recesses by mounting on a face to be measured, a form measurement assisting member which is continuous over a plurality of protrusions discontinuously, which is flexible, and which has a conductive coating applied on a rear face for making measurement through interference. SOLUTION: A form measurement assist member comprises a glass wafer G, which has a conductive coating applied on a rear surface. A wafer holder WH vacuum-chucks the glass wafer G. A light flux from a laser source LS passes through a lens L1 and a half-wave plate WP1 and is incident to a beam splitter BS. The reflected flux transmits through a quarter-wave plate WP and is incident to a Fizeau optical element FP having a reference face R, and the becomes a reference light and is incident on the glass wafer G. An arithmetic processor GP calculates the surface form of the wafer holder WH, based on parallelism information between interference fringes formed by the reference light from the reference face R and measurement light from the glass wafer G, which passes through the beam splitter BS and the glass wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring a surface shape of a surface to be measured, in particular, a surface shape having uneven portions such that interference fringes become discontinuous in ordinary interference measurement. More specifically, the present invention relates to a method and an apparatus for measuring a surface shape of a wafer holder for a semiconductor manufacturing apparatus.

[0002]

2. Description of the Related Art Conventionally, when measuring the surface shape of, for example, a lens or a mirror with high accuracy, the shape is measured by an interferometer. The surface shape measurement by an interferometer divides a light beam from a light source into two, irradiates one light beam to a reference surface, and irradiates the other light beam to a surface to be measured. Next, interference fringes are obtained by causing the measurement light having a phase changed according to the surface shape of the surface to be measured to interfere with the reference light. Then, the surface shape of the surface to be measured is measured by analyzing the interference fringes. Here, in order to perform good interference measurement, it is desirable that the surface to be measured is a surface that changes smoothly and continuously.

[0003]

However, when the surface to be measured has a plurality of convex portions or concave portions as in a wafer holder for a semiconductor manufacturing apparatus, as shown in FIG. Although the partial shape in the portion or the concave portion T1 to T3 can be measured (FR1 to FR3), the relative relationship of the height or the depth between the convex portions or the concave portions cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and when a surface to be measured has a plurality of convex portions or concave portions, the relative height or depth between the convex portions or concave portions is determined. It is an object of the present invention to provide a shape measuring method and a measuring apparatus which can obtain a dynamic relationship or can perform good interference measurement even when the surface to be measured is a rough surface.

[0005]

According to the present invention, there is provided a method or apparatus for measuring the shape of a surface to be measured by interferometric measurement, wherein the surface to be measured is discontinuously at least two or more times. Having a convex portion, continuous over the at least two or more convex portions, having flexibility,
A shape measuring method or apparatus, wherein a shape measuring auxiliary member on which a conductive coating is applied on a side in contact with the measured surface is placed on the measured surface, and interference measurement is performed. provide.

At this time, it is preferable that the coating is substantially transparent with respect to the wavelength at which the interference measurement is performed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a shape measuring auxiliary member having the above-described features is used. The shape-measuring auxiliary member is a planar object (for example, a glass wafer) which deforms according to the shape of the surface to be mounted, and interferes with reflected light from the surface of the planar object and light reflected from the reference surface. By performing the measurement, the relative relationship of the height or the depth between the respective convex portions or concave portions can be obtained.

Further, in the present invention, as described above, a conductive coating is applied to the back surface of the shape measuring auxiliary member placed on the surface of the surface to be measured. Thus, even if the shape measurement auxiliary member is slightly charged, such as a glass wafer, it is possible to prevent adhesion of minute dust. As a result, fine dust is not caught between the wafer holder and the glass wafer, so that the glass wafer does not partially deform. In this manner, partial deformation of the glass wafer is eliminated, so that interference fringes following the shape of the measurement surface can be obtained, and accurate shape measurement of the measurement surface can be realized.

At this time, the conductive coating is
It is preferable to have a transmittance of 70% or more. this is,
This is because the light intensity of the light beam transmitted through the glass wafer is made as similar as possible to the light intensity of the light beam reflected on the reference surface. This suppresses the decrease in contrast of interference fringes,
It is possible to minimize the decrease in the S / N ratio, and finally, it is possible to perform highly accurate measurement.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a wafer holder will be described. The wafer holder has a surface to be measured discontinuously having at least two convex portions, and specifically has a plurality of concentric convex portions having a small width. The vacuum chuck is performed by drawing a vacuum from below to secure the wafer support. The wafer holder is incorporated in an exposure apparatus for semiconductor manufacturing, and holds a wafer to be projected and exposed to a mask pattern.

In the present embodiment, a planar object having good parallelism is set on the surface of the wafer holder, and the surface shape of the wafer holder is measured by measuring interference of light reflected from the surface. As the planar object, an object having good transparency that deforms along the shape of the bottom surface, for example, a glass wafer is used. If the parallelism of the planar object placed on the wafer holder is perfect, the planar object placed on the wafer holder follows the shape of the wafer holder, and the measurement result of the surface shape of the planar object will represent the shape of the wafer holder. . However, when the parallelism of the planar object is not perfect, the surface shape of the planar object does not represent the shape of the wafer holder itself. Therefore, it may be necessary to measure the parallelism in advance and correct the shape error later. When a transparent glass wafer is used as the planar object and the parallelism is measured in advance, the parallelism can be measured with an interferometer. Hereinafter, measurement of the parallelism (thickness d) of the glass wafer G will be described.

FIG. 1 is a diagram for explaining such parallelism interference measurement. The laser light source and the like are the same as those having the configuration described below, and will not be described. The reflected light from the reference surface R of the Fizeau optical element FP and the measurement light transmitted through the glass wafer G, reflected by the reference reflecting mirror M, and transmitted again through the glass wafer G are interfered with each other to obtain interference fringes. At this time, the measured phase W (x, y) is expressed by the following equation (1), W (x, y) = 2 (n−1) × d (x, y) (1) Here, n is the refractive index of the glass wafer G with respect to the light source wavelength, d (x, y) is the thickness of the glass wafer G,
That is, they represent the degree of parallelism. Therefore, the parallelism of the glass wafer G can be calculated by using the following formula (2), d (x, y) = W (x, y) / 2 (n-1) (2) if a material having a known refractive index n is used. As is clear from the above, it can be easily obtained from the observed wavefront W. The wavelength of the light source desirably transmits through the glass wafer G. The interferometer for measuring the thickness d of the glass wafer G may be a conventional interferometer. More preferably,
It is desirable to use a Fizeau interferometer used in the shape measuring apparatus according to the present embodiment, since the shape can be measured in the same coordinate system as the shape measurement of the wafer holder WH.

The glass wafer G is set on the wafer holder WH at the time of measurement, and is charged by friction or the like at that time. Due to this charging, it is inevitable that minute dust near the apparatus and minute dust remaining in the concave portion of the wafer holder WH are attracted. In this state, if the glass wafer G is placed on the wafer holder WH and held by suction, the surface of the glass wafer may be measured while dust is held between the glass wafer G and the wafer holder WH. As a result, the wafer holder WH is partially deformed. Therefore, in the present invention, as shown in FIGS. 1 and 3, a glass wafer G having a back surface coated with a coating C having good conductivity is used. By doing so, the suction of dust is reduced, and furthermore, as shown in FIG. 3, the glass wafer G is grounded and the potential is set to 0, thereby preventing the charging of the glass wafer G. Does not occur.

Incidentally, it is also possible to constitute a system for automatically transferring glass wafers using a robot arm. In such a system, the potential of the glass wafer can be reduced to zero by using a robot arm to ground.
When the conductive film C coated on the back surface of the glass wafer G is a film material having a high transmittance at the measurement wavelength of the interferometer, for example, a film such as an ITO film, the parallelism of the glass wafer G is as described above. The measurement can be performed by placing the glass wafer G in the optical path of the interferometer including the folding mirror and the reference plane.

Further, as shown in FIG.
When the conductive film coated on the back surface is a film material having a low transmittance at the wavelength measured by the interferometer, for example, a film such as a Si film or Al, the parallelism of the glass wafer G is determined by the luminous flux from the reference plane R. It can be measured by interference between the light beam from the back surface of the glass wafer G and the light beam. Here, when the thickness unevenness of the conductive film C cannot be ignored, the thickness of the glass wafer G is obtained in advance by equation (2), and then the back surface of the glass wafer G is coated with the conductive film C. The interference fringes between the wavefront from the reference reference plane R and the wavefront transmitted through the glass wafer G may be obtained by setting the wavefront again at the original position. At this time,
The measured phase W ₂ is W ₂ (x, y) = 2 (n ₁ −1) × d ₁ (x, y) +2 (n ₂ −1) × d ₂ (x, y) (3) Indicated by Here, n ₁ is the refractive index of the glass wafer G with respect to the light source wavelength, d ₁ (x, y) is the thickness of the glass wafer G, n ₂ is the refractive index of the conductive film C with respect to the light source wavelength, and d ₂ (x, y). y) is the thickness of the conductive film C. Accordingly, the thickness distribution of the conductive film C coated on the back surface of the glass wafer G is obtained from the expressions (1) and (3). As a result, the thickness of the glass wafer G coated with the conductive film C is obtained. The distribution can be measured.

It should be noted that reflected light at the interface between the glass wafer G and the conductive film C may cause multiple interference noise. After measuring the parallelism of the glass wafer G, a coating having a low transmittance with respect to the interferometer wavelength is applied to the surface of the glass wafer G to reduce the light reaching the wafer holder, and at the same time, the light reflected by the wafer holder returns to the interferometer. Can also prevent it. The distribution (unevenness) of the coating thickness is sufficiently smaller than the value required for measuring the surface shape of the wafer holder.

Next, an embodiment of a shape measuring apparatus according to the present invention will be described with reference to the accompanying drawings. The glass wafer G described below has a conductive coating C on the surface in contact with the wafer holder WH. FIG. 4 is a diagram illustrating a schematic configuration of the shape measuring apparatus according to the present embodiment. This apparatus measures the shape of a wafer holder WH of a semiconductor exposure apparatus as a surface to be measured. As described above, the wafer holder WH has a plurality of concentric concentric thin wafer supporting projections T, and performs vacuum chucking by pulling the glass wafer G from below in a vacuum by a vacuum device (not shown).

Next, the procedure of the interference measurement will be described.
A light beam from a laser light source LS such as a He-Ne laser having a wavelength of 632.8 nm transmits through the lens L1, the λ / 2 plate WP1, and enters the beam splitter BS. The light beam reflected by the beam splitter BS passes through the λ / 4 plate WP2 and then enters the Fizeau optical element FP having the reference surface R. Then, the light beam reflected by the reference surface R becomes reference light, and the light beam transmitted through the reference surface R enters the glass wafer G. As will be described later, the glass wafer G is mounted on a wafer holder WH, which is a surface to be measured, and the light beam reflected on the surface of the glass wafer G becomes measurement light.

Next, the reference light from the reference surface (Fizeau surface) R and the measurement light from the glass wafer G pass through the beam splitter BS, and form interference fringes on the image sensor D via the imaging lens L2. I do. The arithmetic processing unit CP calculates the surface shape of the wafer holder WH based on the interference fringes and the parallelism (thickness) information of the glass wafer G described later. Here, the glass wafer G deforms along the surface shape of the wafer holder WH such as a glass wafer having a thickness of about 1 mm, for example.

If the glass wafer G is a parallel flat plate, the surface shape of the deformed glass wafer G corresponds to the shape of the wafer holder WH. The shape of WH can be determined. When the glass wafer G is a substantially parallel flat plate, that is, a flat plate whose thickness changes in a wedge shape, if the parallelism is measured in advance, the glass wafer G
The shape of the wafer holder WH can be obtained by correcting the measured parallelism with respect to the measurement result of the surface shape.

FIG. 5A is a diagram showing the relationship between the glass wafer G and the wafer holder WH. When viewed from the Z direction,
As shown in FIG. 5B, the entire surface of the glass wafer G covers the wafer holder WH. FIG. 5C is a diagram showing interference fringes observed at this time. Since the interference fringes that are discontinuous in the conventional measurement are continuous, the relationship between the irregularities can be identified.

From the interference fringes, the shape Z of the wafer holder WH
A procedure for obtaining (x, y) will be described. The measured phase W ′ (x, y) is W ′ (x, y) = 2Z (x, y) + 2d (x, y) (4) Here, Z (x, y) indicates the shape of the wafer holder WH, and d (x, y) indicates the thickness of the glass wafer G. Therefore, the shape of the wafer holder WH is given by the following equation (5), Z (x, y) = W ′ (x, y) / 2−d (x, y) (5) By substituting equation (2) into equation (5), Z (x, y) = W '(x, y) / 2-W (x, y) / 2 (n-1) (6) Therefore, the shape Z of the wafer holder WH is determined based on the measured phase W ′ and the thickness d of the glass wafer G.
Can be requested.

In general, the surface of the wafer supporting portion T of the wafer holder WH is mirror-finished, so that the reflectance is extremely high. For this reason, when a glass wafer is used as the glass wafer G, since the glass wafer is transparent, the light transmitted through the glass wafer and reflected from the wafer holder WH with respect to the measurement light that is the reflected light from the surface of the glass wafer. It becomes noise light. Particularly, as described above, the intensity of the reflected light from the surface of the wafer supporting portion T is large, which is a problem.

In order to reduce such noise light, an interferometer using a light source at a wavelength at which the glass wafer becomes opaque, for example, ultraviolet light may be used. If a coating having an appropriate transmittance is applied to the surface of the glass wafer, a general interferometer using visible light can be used. In this case, it is desirable to apply a coating having a low transmittance to the wavelength of the light source, preferably a coating having a transmittance of 20% or less. Materials constituting the coating layer include Cr and TiO ₂ . When the glass wafer G is made of Ti, Ni, Ge, Si or the like, it is desirable to use ZnS, Cr ₂ O ₃ , SiO, ZrO ₂ or the like as a coating material. Such coating can reduce the amount of light reaching the wafer holder WH, and at the same time, prevent light reflected by the wafer holder, particularly the wafer support T having a high reflectance, from returning to the interferometer.

The condition that the distribution of the coating thickness (uneven coating) is sufficiently smaller than the value required for measuring the surface shape of the wafer holder is required. This condition can be easily satisfied. Here, a coating with low transmittance on the one hand may have a high reflectance on the other hand,
If the reflectivity is too high, the contrast of the measured interference fringes will be low, or noise due to multiple reflections may occur, which is not desirable. In a general Fizeau interferometer,
Since the reflectance of the reference surface (Fizeau surface) R is about 4%,
If the reflectivity of the surface coating of the glass wafer G is set to about 4%, the intensity of the reference light and the measurement light becomes almost the same, and the contrast of interference fringes can be maximized.

Further, the glass wafer G is placed on the wafer holder WH.
A more stable and accurate interference measurement can be performed by vacuum suction. When measuring an object having a structure that does not allow such suction, it is necessary to stably mount the glass wafer G on the surface to be measured so that the glass wafer G and the surface to be measured do not shift from each other. It is. For this purpose, it is desirable to make the surface to be measured horizontal.

Further, the present invention is not limited to a surface having a convex portion such as a wafer holder, and the shape measuring auxiliary member can be applied to a surface such as a rough surface where interference fringes cannot be obtained in a normal state. By using this, the surface shape (undulation component and the like) can be measured. As described above, according to this embodiment, the back surface of a substantially parallel object placed on the surface of a rough surface or a discontinuous measurement surface is coated with a conductive coating to prevent dust from adhering to the surface. By obtaining continuous interference fringes by using the reflected light from the object, it was possible to accurately measure the shape of the measurement surface.

[0028]

As described above, according to the present invention, when the surface to be measured has a plurality of convex portions or concave portions, the relative relationship of the height or depth between each convex portion or concave portion is obtained. It has become possible to provide a shape measuring method and a measuring apparatus capable of obtaining the following formula or performing good interference measurement even when the surface to be measured is a rough surface.

[Brief description of the drawings]

FIG. 1 is a view showing a method for correcting a thickness of a glass wafer according to the present invention.

FIG. 2 is a diagram showing another method of correcting the thickness of a glass wafer according to the present invention.

FIG. 3 is a diagram showing a part of a shape measuring apparatus according to the present invention.

FIG. 4 is a view showing a shape measuring apparatus according to the present invention.

FIG. 5 is a diagram showing a shape measuring method according to the present invention.

FIG. 6 is a diagram showing a conventional shape measuring method.

[Explanation of symbols]

 FP Fizeau plate G Glass wafer C Coating WH Wafer holder T Convex part

Continued on the front page (72) Inventor Masahiko Yomoto 3-2-3 Marunouchi, Chiyoda-ku, Tokyo F-term in Nikon Corporation (reference) 2F064 AA09 EE05 FF02 GG22 GG38 GG39 HH03 HH08 HH09 JJ01 2F065 AA24 AA25 AA47 BB05 CC17 FF01 FF04 FF52 GG05 GG21 HH04 JJ03 JJ19 JJ26 LL00 LL35 LL36 QQ31

Claims (3)

[Claims] 1. A method for measuring the shape of a surface to be measured by interference measurement, wherein the surface to be measured has at least two or more projections discontinuously, and is continuous over the at least two or more projections. A flexible, shape-measuring auxiliary member having a conductive coating on the side in contact with the surface to be measured is placed on the surface to be measured, and interference measurement is performed. A shape measuring method characterized by the above-mentioned. 2. An apparatus for measuring the shape of a surface to be measured by interference measurement, wherein the surface to be measured has at least two or more projections discontinuously, and is continuous over the at least two or more projections. A flexible, shape-measuring auxiliary member having a conductive coating on the side in contact with the surface to be measured is placed on the surface to be measured, and interference measurement is performed. A shape measuring device characterized by the above-mentioned. 3. The shape measuring method according to claim 1, wherein the coating is substantially transparent with respect to a wavelength at which the interference measurement is performed.