JPH1030915A - Surface-shape measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the improvement of measurement accuracy and a compact configuration by applying a double-mode channel waveguide having the incident light input end of the reflected light of the surface of a sample. SOLUTION: The emitted light of a laser diode 1 having wavelength of 670nm is reflected from a half mirror 2 and condensed on the surface of a sample 5 on a biaxial stage 4 driven by a stepping motor with an objective lens 3. The reflected light is made incident on a double-mode waveguide 7 formed in the silicon oxide thin film on an Si substrate 6 through a lens 3 and a mirror 2 in a slightly offset pattern. The light, which has excited the double-mode waveguide 7, is divided into channel waveguides 9 and 10 with a waveguide dividing part 8 and excites the respective waveguides. Two detectors 11 and 12 located at the emitting ends of the waveguides 9 and 10 detect the intensities of the propagating lights of the channel waveguides 9 and 10 and convert the light into the electric signals. The difference signal of the outputs of the photodetectors 11 and 12 is obtained by a subtracting circuit 14. The difference signal is inputted into a biaxial stage 15, and the biaxial stage 4 is scanned into the two-dimensional directions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface shape measuring apparatus for measuring a warp of a silicon wafer used in a semiconductor process or the like, a thickness of a formed metal thin film, and the like.

[0002]

2. Description of the Related Art An optical surface shape measuring device has a characteristic that the shape of a sample surface can be measured without damaging the sample due to non-contact. The optical displacement measuring device used in these surface shape measuring devices is a method of measuring the amount of deviation from the focal position on the sample surface based on the size of the spot of the condensed light represented by the knife edge method, Based on the shape of the spot represented by the aberration method, there are methods such as a method of measuring the amount of deviation from the focal position on the sample surface and a method of detecting the position of reflected return light due to oblique incidence represented by triangulation. Have been used. In either method, the light emitted from the optical displacement measuring device is scanned one-dimensionally or two-dimensionally on the surface of the sample, whereby the one-dimensional or two-dimensional shape on the surface of the sample is measured.

When the surface shape of a sample is measured using a condensed light spot, if the step that is considered to be present on the surface of the sample to be measured is relatively small, the above-described deviation from the focal position of the sample surface, and the like. Shape measurement is performed based on the object. If the step is relatively large, the optical displacement detector is moved up and down relative to the sample surface so that the amount of deviation from the focal position on the sample surface is constant, The shape of the sample surface is measured from the movement amount.

[0004]

With these conventional methods for determining the amount of deviation of the sample surface from the focal position based on the spot shape and spot size of the condensed light, high measurement accuracy cannot be expected. Further, in the case of using the trigonometry, there is a problem that the optical path becomes large in order to increase the accuracy, and the device itself becomes large.

[0005] It is an object of the present invention to provide a surface shape measuring apparatus which has high measurement accuracy and can be miniaturized.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a light source, a condensing optical system for condensing light emitted from the light source, a substrate, and formed on the substrate. A surface using an optical displacement detection device having a double mode channel waveguide having an incident end for receiving light reflected on the sample surface, and a light detection device for measuring an electric field distribution at an emission end of the double mode channel waveguide. Provided is a shape measuring device.

[0007] The change in the electric field distribution at the exit end of the double-mode waveguide is caused by the fact that the photodetector is connected to the exit end of the double-mode waveguide and the two waveguide branches connected to the waveguide branch. In the case where a channel waveguide and two light receiving elements for detecting the light intensity from the emission ends of the two channel waveguides are included, it is known as a change in the value of the difference signal between the outputs of these two light receiving elements. be able to. The surface shape measuring apparatus of the present invention is based on the principle of measuring the amount of displacement by detecting the inclination of the wavefront of light generated at a position other than the focal position of condensed light.

[0008]

FIG. 1 is a schematic configuration diagram showing a surface shape measuring apparatus according to an embodiment of the present invention. The principle of displacement detection of the optical displacement detection device used in the surface profile measuring device of the present invention is one that applies mode interference in a waveguide. Light incident on the end face of the double mode waveguide excites even mode and odd mode light in the double mode waveguide based on the asymmetry of the electric field distribution. Due to the interference of these even-mode and odd-mode light, the light intensity distribution in the double-mode waveguide becomes meandering. By appropriately selecting the length of the double mode waveguide, the asymmetry of the phase or amplitude distribution of the incident light can be known from the light intensity distribution resulting from this mode interference.

There has been proposed a laser scanning mode interference microscope for observing a step on a sample surface and a change in reflectance by utilizing such mode interference in a double mode optical waveguide.
(H.Ooki and J.Iwasaki, Optics comminications 85 (19
91) 177). A mode interference device formed on a substrate used at that time is proposed in Japanese Patent Application Laid-Open No. 4-208913.

Further, there is a method for detecting a change in the distance from the sample surface by detecting the inclination of the wavefront of light generated by the condensing optical system by making the light incident on the incident end face of the double mode optical fiber slightly shifted. Suggested (R. Juskait
is and T. Wilson, Applied Opics 31 (1992) 4569). In this case, the length L of the double mode waveguide is represented by L, which is the complete coupling length between the even mode and the odd mode guided in the double mode waveguide.
_{When c}

[0011]

L = L _c (2m + 1) / 2 (m = 0,
It is known that the displacement amount is efficiently detected when the length can be represented by (1, 2,...). FIG. 4 is a schematic diagram of an apparatus for detecting a tilt of a wavefront of light generated by a converging optical system using a double mode waveguide device proposed in Japanese Patent Application Laid-Open No. 4-208913.

The light emitted from the light source 23 is transmitted to a half mirror 24
And is converged on the sample surface 26 by the lens 25. Sample surface
The reflected return light from 26 is returned to the lens 25 and half mirror 24 again.
And a slight offset to the incident end face of the double mode channel waveguide 28 formed on the substrate 27 (the center of the double mode waveguide and the center of the light spot formed on the incident end face are slightly shifted in the horizontal direction of the paper surface). It is shifted) and incident. The light of the even mode and the odd mode generated by this incident light excites the double mode waveguide 28 while causing mode interference, and the two channel waveguides 30 and 31
And excites two channel waveguides 30, 31 respectively. The two photodetectors 32 and 33 disposed at the emission ends of the two channel waveguides 30 and 31 respectively detect the intensity of the light propagating through the two channel waveguides 30 and 31 and convert them into electric signals. . The two photodetectors 3 by the subtraction circuit 34
A difference signal of 2,33 outputs is obtained.

[0013] The complete coupling length between the length L of the double mode channel waveguide 28 of the even and odd modes for guiding the double-mode channel waveguide 28 when the L _c

[0014]

L = L _c (2m + 1) / 2 (m = 0,
When the length of the sample surface 26 in the vertical direction is plotted on the horizontal axis 35 and the difference signal of the subtraction circuit 34 is plotted on the vertical axis 36,
As shown in FIG. 5, when the sample surface 26 is at the focal position of the lens 25, a curve 37 passing through a point where the difference signal becomes zero is obtained. Therefore, the vertical displacement of the sample surface 26 can be known from the difference signal.

According to the study by the inventors, the amount of vertical displacement that can be measured in this way is extremely accurate, and is sufficient for use as a displacement detector used in a surface shape measuring device. It turned out to be.

[0016]

FIG. 1 shows a laser diode 1 having a wavelength of 670 nm.
Is reflected by the half mirror 2 and condensed by the objective lens 3 on the surface of the sample 5 arranged on the biaxial stage 4 driven by the stepping motor. The reflected return light from the sample 5 passes through the objective lens 3 and the half mirror 2, and enters the double mode waveguide 7 formed in the silicon oxide thin film deposited on the Si substrate 6 with a slight offset. The light excited in the double mode waveguide 7 is distributed to the two channel waveguides 9 and 10 by the waveguide branch portion 8, and excites the two channel waveguides 9 and 10, respectively. The two silicon photodiodes 11 and 12 disposed at the emission ends of the two channel waveguides 9 and 10 respectively detect the intensity of light propagating through the two channel waveguides 9 and 10 and convert them into electric signals. .

In this embodiment, the objective lens 3, the half mirror 2, the waveguide substrate 6 and the like are arranged and fixed on a metal chassis 13 to constitute one compact displacement amount detecting device in which an illumination light receiving system is integrated. ing. 2 by the subtraction circuit 14
The difference signal between the outputs of the two silicon photodiodes 11, 12 is obtained. This difference signal is input to the controller 15. The controller 15 scans the two-axis stage 4 driven by the stepping motor in the two-dimensional direction.

At this time, the signal of the subtraction circuit 14 is converted into displacement amount information, and the surface shape of the sample 5 is reconstructed and displayed on the monitor 16. In the case of the present example, it was possible to measure a step on the sample surface with a resolution of 1 nm. In addition, the range of the step that can be measured in this example was about 30 μm. Figure 2
FIG. 6 is a schematic configuration diagram of a second embodiment according to the present invention. In this embodiment, the same components as those in the embodiment shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The surface shape measuring apparatus in this embodiment further has a piezo drive Z-axis stage 17 capable of moving the metal chassis 13 up and down by a predetermined amount. The controller 15 drives the piezo drive Z-axis stage 17 up and down so that the signal of the subtraction circuit 14 becomes constant. Highest displacement S
Since a / N ratio can be obtained, it is desirable to use zero as the value of this signal.

The controller 15 reconstructs the shape of the surface of the sample 5 from the displacement of the piezo drive Z-axis stage 17 and displays it on the monitor 16. In the case of the present embodiment, the measurement range can be extended to the movable range of the piezo drive Z-axis stage 17. In the case of this example, it was possible to measure a step on the sample surface with a resolution of 5 nm. In addition, the range of the step that can be measured in this example was about 200 μm.

FIG. 3 is a perspective view of a third embodiment according to the present invention. In this embodiment, the same components as those in the embodiment shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. In the present embodiment, the lens 3 is a collimator lens. The light from the lens 3 is reflected downward by the dichroic mirror 18 that selectively reflects only the light of 670 nm. The light reflected by the dichroic mirror 18 is focused on the surface of the sample 5 by the objective lens 19. The return light reflected from the surface of the sample 5 passes through the objective lens 19 and the dichroic mirror 18 again.
It is incident on 3.

In this embodiment, a subtraction circuit for calculating the difference between the outputs of the two silicon photodiodes 11 and 12 is built in the controller 15. The controller 15 is an operation panel 20
Scans the two-axis stage 4 driven by the stepping motor in the two-dimensional direction. At this time, the objective lens 19 is connected to the piezo-driven objective lens Z-axis moving device 1 connected to the objective lens 19 such that the difference between the outputs of the two silicon photodiodes 11 and 12 is preferably a constant value of zero.
Drive up and down using 7. The controller 15 reconstructs the shape of the surface of the sample 5 from the displacement amount of the piezo-driven objective lens Z-axis moving device 17 and displays it on the monitor 16.

In the present embodiment, since the optical path of the optical displacement measuring device is bent by the dichroic mirror 18, the surface of the sample 5 is illuminated with the illumination light from the epi-illumination optical system 21. Visually sample through imaging optics 22
It is possible to measure the surface shape of the sample 5 while observing the surface of the sample 5.

[0024]

As described above, according to the present invention, by applying a double mode waveguide device, it is possible to provide a surface shape measuring apparatus which has high measurement accuracy and can be miniaturized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a surface profile measuring apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the surface shape measuring device of the present invention.

FIG. 3 is a perspective view showing a third embodiment of the surface shape measuring device of the present invention.

FIG. 4 is a schematic diagram of an apparatus for detecting a wavefront inclination of light generated by a focusing optical system using a double mode waveguide device.

5 is a graph showing a relationship between a position of a sample obtained by the apparatus of FIG. 4 and a difference signal of a photodetector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Beam splitter 3 ... Objective lens 4 ... Biaxial stage 5 ... Sample 6 ... Silicon substrate 7 ... Double mode channel waveguide 8 ... Waveguide Branch 9, 10, channel waveguide 11, 12, photodetector 13, metal chassis 14, subtraction circuit 15, controller 16, monitor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H01L 21/66 H01L 21/66 P

Claims (5)

[Claims] 1. A stage, an optical displacement detection device, and a stage and an optical displacement detection device which are relatively positioned so that light emitted from the optical displacement detection device scans on a surface of a sample arranged on the stage. A scanning device that moves automatically, a surface shape measurement device that measures the shape of the sample surface based on signals from the scanning device and the optical displacement detection device, wherein the optical displacement detection device includes a light source, A light condensing optical system for condensing light emitted from the light source on a sample surface disposed on the stage, a substrate, and an incident end formed on the substrate and receiving light reflected on the sample surface; A surface shape measuring device comprising: a double mode channel waveguide; and a photodetector for measuring an electric field distribution at an emission end of the double mode channel waveguide. 2. The surface shape measuring device according to claim 1, wherein said light detecting device includes at least two light receiving elements. 3. The light detecting device according to claim 1, wherein the light guide comprises a waveguide branch portion connected to an output end of the double mode waveguide, two channel waveguides connected to the waveguide branch portion, and the two channel waveguides. The surface shape measuring apparatus according to claim 1, further comprising two light receiving elements that respectively detect the light intensity from the emission end of the surface. 4. The surface shape measuring apparatus according to claim 1, wherein the return light reflected from the sample surface is incident with an offset from the center of the incident end of the double mode waveguide. 5. The length L of the double mode waveguide is, when a complete coupling length between the even and odd modes guided through the double mode waveguide and L _c, Equation 1] L = L _c (2m + 1) / 2 (m = 0,
The surface shape measuring apparatus according to claim 1, wherein the length is a length that can be represented by (1, 2, ...).