JPH0438246Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a recess depth measuring device for measuring the depth of recesses such as trenches or holes regularly formed on the surface of an object.

[Prior art and its problems] In DRAM, which has a storage capacity of several megabits,
Due to the need to increase integration density without reducing the capacitance of unit memory cells on a chip, various types of vertical capacitive cells have been devised. An example is shown in FIG. 5, in which the depth of the trench 10 is about 1 to 10 μm, and the unit cells 12 divided by the trench 10 are
The length of one side is approximately several μm.

A scanning electron microscope (SEM) is used as a trench depth measuring device. SEM not only provides highly accurate measurements, but also provides information about the local shape inside the trench.

However, SEM is expensive and difficult to handle. Furthermore, since measurements cannot be made without cutting the silicon wafer, sampling inspections are the main method, and real-time measurements on the production line are impossible.

Therefore, a trench depth measuring device using a scanning Fourier spectrometer as shown in FIG. 6 has been devised.

In this measuring device, a halogen lamp 14 or the like that emits light in a continuous wavelength range is used as a light source, and a part of the light beam collimated by the collimator lens 16 passes through the beam splitter 18, forming a trench on the surface. The formed silicon wafer 20 is vertically irradiated, and a part of the reflected light is reflected by the beam splitter 18, and then reflected by the plane mirror 22 and sent to the Michelson interferometer 24.
is incident on the And Michelson interferometer 24
The intensity of the emitted light is detected by the optical sensor 26 and supplied to the storage oscilloscope 32 via the amplifier 28 and filter 30, and the storage oscilloscope 32 operates in synchronization with the scanning of the movable mirror 34. On the tube surface of the storage oscilloscope 32,
Due to regular reflection from the surface of the unit cell 12 and the bottom of the trench 10, a main peak M and a sub-peak S
An interferogram having .

According to this device, the silicon wafer 20 can be measured non-destructively.

However, when a commercially available Fourier spectrometer is applied to such measurements, the number of sampling points m between the main peak M and the sub-peak S is extremely small, resulting in low measurement accuracy. That is, the maximum movement amount of the movable mirror 34 relative to the fixed mirror 36 is
2. If the total number of data points is N, the trench depth d
For, d=Xm/N holds true, and when X=1cm and N=8192, d=1μ
m = 0.8 for m, m = 8 for d = 10 μm, and the measurement accuracy is low.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a recess depth measuring device capable of highly accurate measurement.

[Means for solving the problem] The recess depth device according to the present invention includes a light source that emits light in a continuous wavelength range, a monochromator, and a cover that reflects light and has recesses regularly formed on its surface. A concave surface is disposed obliquely on the surface of the measurement object, a hole is bored in the concave surface through which light from the light source passes and specularly reflected light from the surface passes, and a hole is formed in the concave surface through which light from the light source passes and specularly reflected light from the surface passes. a concave mirror that reflects diffracted light other than the following on the concave surface and enters the monochromator; an optical sensor that detects the light intensity of the light emitted from the monochromator; and a light intensity included in the wave number or wavelength curve. The present invention is characterized by comprising: calculation means for calculating and outputting the depth of the recess from the inter-peak distances of a plurality of peaks.

[Example] Embodiments of the present invention will be described based on the drawings.

FIG. 1 shows the configuration of a first embodiment.

A spherical mirror 42 is disposed above a silicon wafer 40 as an object to be measured, with its concave surface facing diagonally downward. This silicon wafer 40
This is for DRAM, and trenches 10 as shown in FIG. 6 are regularly formed on this surface.
A circular hole 44 is bored in the center of the spherical mirror 42, and a white light source 48 is disposed above the circular hole 44 via a condensing lens 46. The white light from the white light source 48 is refracted by the condensing lens 46 and enters the circular hole 4.
4 , is condensed and projected substantially perpendicularly onto the surface of the silicon wafer 40 , and the non-zero-order diffracted light is reflected laterally by the concave surface of the spherical mirror 42 , condensed and incident on the monochromator 50 . .

This diffracted light is transmitted to the unit cell 1 as shown in FIG.
2 and the diffracted light from a surface (complementary surface) above the bottom surface of the trench 10 and at the same height as the surface of the unit cell 12 after being reflected at the bottom surface of the trench 10.
Further, the outer peripheral shape of the spherical mirror 42 is preferably circular, but may be elliptical, rectangular, or the like.

The light angularly dispersed according to the wave number by the monochromator 50 is projected onto a photodiode array 52 . The monochromator 50 is composed of, for example, a concave diffraction grating, and in this case, a photodiode array 52 is arranged along its imaging plane.

The photodiode array 52 is scanned by a microcomputer 54 via a driver 56 , and the received light intensity for each wave number is sequentially read out and supplied to an amplifier 58 , where it is digitally converted by an A/D converter 60 and sent to the microcomputer 54 .
supplied to The microcomputer 54 reads this and sequentially writes it into the built-in RAM.

If this written data is plotted and connected with a line, a curve as shown in FIG. 3A will be obtained. The horizontal axis of this figure is the number wave, and the vertical axis is the diffracted light intensity I ₁
It is. This curve has multiple peaks, and the distance between the peaks is theoretically 1/d (however,
Let the refractive index of the medium be 1. ). Here, d is the depth of the recess shown in FIG.

However, the distance between the peaks is not constant due to measurement errors. Therefore, the distance between adjacent peaks is sequentially determined, and the average value is used to determine the recess depth d=
Find 1/. Alternatively, find the distance L between the peaks P ₁ and P _o at both ends, and recess depth d = (n-
1) Find /L. Here n is the total number of peaks. Alternatively, the Fourier transform,
An analysis method in the frequency domain, such as the maximum entropy method, may be employed.

The measurement accuracy of trench depth d is the peak at both ends.
Photodiode array 5 between P ₁ and P _o
It is proportional to the number of elements. The number of elements of the generally used photodiode array 52 is about 1024, and the trench depth d can be accurately measured.

The microcomputer 54 displays this trench depth d on the display 62.

In the first embodiment, there is no need to provide a mechanism for performing wave number scanning in the monochromator 50, and there is no part to be moved during measurement unlike in the conventional system, so the configuration and adjustment are simple.

Next, a second embodiment of the present invention will be described based on FIG.

In this second embodiment, a beam splitter 64 is disposed between the spherical mirror 42 and the four condensing lenses, and a part of the light specularly reflected by the silicon wafer 40 is reflected by the beam splitter 64. , the light is focused by the optical coupling lens 66 and sent to the optical fiber 6.
8 and is guided by an optical fiber 68 and exits from the other end, and is connected to an optical coupling lens 70.
The light is focused and incident on the monochromator 72. The monochromator 72 has the same configuration as the monochromator 50, and the light angularly dispersed according to the wave number by the monochromator 72 is projected onto a photodiode array 74. The photodiode array 74 has the same configuration as the photodiode array 52, and is scanned by the driver 56 in correspondence with the photodiode array 52, and the optical intensity signal for each wave number is sequentially sent to the amplifier 76 and the A/D converter 7.
8 to the microcomputer 54. The microcomputer 54 is an A/D converter 6
The data from 0 and 78 are read and sequentially written to the built-in RAM.

If this written data is plotted and connected with a line, curves as shown in FIGS. 3A and 3B will be obtained. A shows the diffracted light intensity I ₁ with respect to the wave number, and B shows the specularly reflected light intensity I ₂ with respect to the wave number.

The microcomputer 54 calculates I ₁ −αI ₂ for each wavenumber and writes it into the built-in RAM. Here α is a constant. This I ₁ − with the horizontal axis as the wave number
If αI ₂ is plotted and connected with a line, a curve as shown in Figure 3C is obtained.

In this way, if I ₁ - αI ₂ is used, the peak position can be determined more accurately than in the first embodiment, so the trench depth d can be calculated by performing the same calculation as in the first embodiment. Measurements can be made with higher precision.

In addition, in the above embodiment, the case where the photodiode array 52 was used as the optical sensor was explained.
The present invention is not limited to this, and wavenumber scanning may be performed with the monochromator 50 using a photomultiplier tube or the like. The same applies to the photodiode array 74.

Alternatively, a sector mirror may be used to sequentially switch the reflected light from the spherical mirror 42 and the reflected light from the beam splitter 64 and supply them to a single monochromator 50. In this case, the components 72-78 shown in FIG. 2 become unnecessary.

[Effects of the invention] The recess depth measuring device according to the invention irradiates the surface of an object to be measured in which recesses are regularly formed with light in a continuous range, and only the diffracted light is reflected by a concave mirror. The intensity of the light emitted from the monochromator is detected by an optical sensor, and the depth of the recess is calculated from the distance between peaks included in the curve of this light intensity with respect to wave number or wavelength. Since the distance between the peaks can be measured with high precision, there is an excellent effect that the depth of the recess can be measured with high precision.

[Brief explanation of the drawing]

1 to 5 relate to an embodiment of the present invention, and FIG. 1 is a configuration diagram of a recess depth measuring device according to the first embodiment;
Fig. 2 is a configuration diagram of the recess depth measuring device of the second embodiment, Fig. 3 is a diagram showing the relationship between light intensity and wave number, and Fig. 4 is a diagram showing the surface area of a silicon wafer with trenches formed on its surface. FIG. 5 is a partial sectional view, FIG. 5 is a partial perspective view of the surface portion, and FIG. 6 is a configuration diagram of a conventional trench depth measuring device. 10...Trench, 40...Silicon wafer, 42...Spherical mirror, 44...Circular hole, 48...White light source, 52...Photodiode array, 64
...beam splitter, 66...optical coupling lens, 68...optical fiber, 70...optical coupling lens, 74...photodiode array.

Claims (1)

[Scope of Claim for Utility Model Registration] A light source that emits light in a continuous wavelength range, a monochromator, and a concave surface directed diagonally toward the surface of an object to be measured that reflects light and has concavities regularly formed on its surface. A hole is formed in the concave surface, through which light from the light source passes and specularly reflected light from the surface passes, and non-zero-order diffracted light from the surface is reflected by the concave surface. a concave mirror that causes the light to enter the monochromator; an optical sensor that detects the light intensity of the light emitted from the monochromator; A recess depth measuring device comprising: a calculation means for calculating and outputting a depth; and a recess depth measuring device.