JPS62255810A - Method and device for measuring depth of very small groove - Google Patents

Abstract

PURPOSE:To exactly measure depth by an intense interference light intensity, by irradiating a very small groove by a narrow band wavelength light beam, and using a 0th-order diffracted light beams (regularly reflected light beams). CONSTITUTION:White light beams from a white light source 5 are fetched from a slit 6, condensed 8 and made to pass through an acousto-optical filter 8, wavelength of a light beam of a narrow band, which has been fetched is scanned, for instance, from short to long, and a scan frequency is set by a scan oscillator 12, and determined to, for instance, 1kHz, from a relation of an amplification band of an amplifier 10. Modulation light beams are converted 13 to parallel rays, and projected vertically to a substrate 1 having a very small groove through a semi-mirror 9. Incident light beams 20 are diffracted by a surface 1a and a groove surface 1b, a 0th-order diffracted light beams 21 are reflected along the incident light beams and a high order diffracted light beams 22 expand to both sides. Since the groove area is extremely small, when the wavelength is scanned by 1kHz extending from short to long, only an interference component of a 0th-order diffracted intensity I0 can be fetched. By using a difference DELTAlambdaof its wavelength lambda0 and the next maximum value lambda1, depth d=lambda0 (lambda0+DELTAlambda)/2DELTAlambda is derived.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for easily controlling the depth of minute grooves arranged at equal intervals on a plane, such as grooves and holes formed for VLSI capacitors. The present invention relates to a method and apparatus for measuring with high accuracy.

[Conventional technology]

The micro groove for the VLS I capacitor has a depth of 3 to 5 μm1.
It is formed with a width of 0.5 to 1 μm and a width of several thousand μm to several tens of μm, and one method for measuring its depth is to cut the Si substrate and observe its cross section with a scanning electron microscope. However, since this method involves destructive measurement, it has the disadvantage that the measured element itself can no longer be used as an element after the measurement.

On the other hand, a measurement method using optical interference is being researched as a non-destructive method of measuring the depth of a groove. FIG. 7 is a schematic diagram showing this measuring method.

Irradiation light 2 having a narrow band wavelength is perpendicularly incident on a Si substrate 1 in which a capacitor groove is formed. The wavelength of this irradiation light 2 is scanned from the short wavelength side to the long wavelength side, and one scan is performed in about 1 to 10 minutes.

The vertically incident light 2 is reflected vertically and is also diffracted because the dimensions of the cells formed on the substrate 1 are on the wavelength order. Reference numeral 3 indicates the diffracted light, and reference numeral 4 indicates a detector for detecting the intensity of the diffracted light. Using diffraction theory, the intensity ■ of higher-order diffracted light is given by... (1). Here, Sc is the area of the cell surface (portion other than the groove), St is the surface area of the groove portion, σ is the amount of attenuation of light in the groove, d is the groove depth, and λ is the wavelength of the incident light.

As can be seen from this equation, by changing λ, the intensity I changes, and the change depends on the groove depth d. Moreover, since the attenuation amount σ takes a value close to 1, such as 0.7 or 0.8, the interference component'), Fcos (4rc
The value of d/λ) can take a sufficiently large value in comparison with the DC component (1+σ), and has a large influence on the overall intensity ■. Therefore, when the wavelength λ is changed, the diffracted light intensity I changes with a large contrast, making it possible to detect the groove depth d. 13
).

[Problem that the invention seeks to solve]

However, the reflection intensity of high-order diffracted light is extremely low, and the detector 4 has to be positioned at the position where the n-th order diffracted light is present, which requires alignment for each measurement.

[Means for solving problems]

The present invention has been made in view of the above-mentioned problems, and involves measuring the intensity of the 0th-order diffracted light by making the wavelength-scanned narrow band wavelength light incident on the surface of a sample provided with microgrooves. However, the depth of the micro groove is calculated from the change in intensity according to the change in wavelength. Further, light having a narrow band wavelength whose wavelength is scanned is incident on the surface of the first sample provided with the microgrooves, and the intensity of the 0th order diffracted light is measured, and the previous epoch is determined from the first sample surface. The intensity of the 0th order diffracted light is measured by entering a second sample made of the same material with a flat surface, and the intensity of the 0th order diffracted light from the first sample is equal to the 0th order diffraction light from the second sample. The depth of the micro groove is calculated by dividing by the intensity of the next diffracted light and by changing the division result according to the change in wavelength.

[Effect]

Since the 0th-order diffracted light is measured, a much stronger interference light intensity can be obtained than when measuring higher-order diffracted light. Furthermore, the 0th order diffracted light is nothing but specularly reflected light, and its direction is uniquely determined by the angle of incidence of the incident light, so it is very easy to align the detector for detecting the diffracted light.
Almost no adjustment is necessary for this purpose.

〔Example〕

Hereinafter, the present invention will be described in detail along with examples.

FIG. 1 is a block diagram for explaining one embodiment of the present invention, and the same or corresponding parts as in FIG. 7 are given the same reference numerals. In the figure, 5 is a white light source, 6 is a slit, 7 and 13 are lenses, 8 is an acousto-optic filter as an optical variable filter, 9 is a half mirror, 210 is an amplifier, 11 is a waveform observation device, and 12 is a sweep oscillator. be.

White light from a white light source 5 is extracted using a slit 6, focused by a lens 7, and introduced into an acousto-optic filter 8.

The acousto-optic filter 8 utilizes anisotropic diffraction generated by transverse ultrasonic waves propagating in a tellurium dioxide single crystal, and can extract a narrow band color close to monochromatic light from the incident white light. Moreover, the wavelength of the narrow band of light that can be extracted can be scanned at high speed from the short wavelength side to the long wavelength side or from the long wavelength side to the short wavelength side, and the scanning frequency at this time is determined by the sweep oscillator 12. Can be set. In this embodiment, the scanning frequency is set to IKHz in relation to the amplification band of the amplifier 10.

The light thus modulated is converted into a parallel beam by the lens 13, and is further incident perpendicularly through the half mirror 9 onto the Si substrate 1 in which a microgroove for a capacitor is formed.

FIG. 2 is a schematic cross-sectional view showing the state of light diffraction in the Si substrate 1, and the incident light 20 is transmitted to the cell surface 1a and the groove surface 1b.
diffracts at From the figure, it can be seen that the 0th-order diffracted light 21 is reflected perpendicularly to the substrate 1, that is, along the incident light 20, and the higher-order diffracted light 22 spreads on both sides thereof.

The vertically reflected zero-order diffracted light reaches the half mirror 9 again, is reflected there, and is guided to the detector 4, where its intensity is converted into an electrical signal. The output signal of the detector 4 is amplified by an amplifier 10 and supplied to a waveform observation device 11 .

Here, the light intensity of the 0th order diffracted light will be explained.

The electric fields Ec and Et of the zero-order diffracted light from the cell surface 1a and the groove surface 1b are given by the following, respectively. Here, Sc is the area of the cell surface (portion other than the groove), St is the surface area of the groove portion, σ is the amount of attenuation of light in the groove, d is the groove depth, and λ is the wavelength of the incident light. The phase term exp[-4πid] of Et represents a phase delay due to reciprocation within the groove.

From the above equations (2) and (3), the intensity I of the 0th order diffracted light
(0) becomes 1 "' = IEc+Et 1".

Since the capacitor groove area St is generally much smaller than the cell area Sc, the intensity of the 0th order diffracted light ■(0) is the (4th)
The first term in the curly brackets of the equation has a large contribution, and the second term, which represents interference,
Term [2! cos (4rc d / λ) is difficult to observe. However, in the present invention, since the wavelength λ is scanned from the short wavelength side to the long wavelength side or from the long wavelength side to the short wavelength side at a high frequency (in this embodiment, IKHz as described above),
Noise can be removed and the intensity of the 0th order diffracted light I(0)
Only the alternating current component (interference component) can be extracted.

Now, let the wavelength at which the alternating current component (interference component) of 1 (01 is maximum be λ.), then the wavelength at which it is maximum be λ1, and Δλ=s, −λ. −(5), then the following equation holds true.

4πd/λ. =4πd/ (λ.+Δλ)+2π...
(6) Transforming this, d=λ. (λ. 1Δλ) / 2Δλ ... (7)
Therefore, the groove depth d can be measured.

Figure 3 is a waveform diagram showing a specific measurement waveform, approximately 5μ
The results of measuring a capacitor groove with a depth of m are shown. In the same figure, λ. = 510 nm, λ+ = 536 nm, and from equation (7) it was determined that d = 5.2 μm.

FIG. 4 is a schematic configuration diagram showing a second embodiment of the present invention.
Mechanical shutters 41, 42 and calculation means 43 are added. Note that the distance between the half mirror 9 and the Si substrate 40 is approximately equal to the distance between the half mirror 9 and the Si substrate 1.

This embodiment is the same as the first embodiment described above until light is introduced into the half mirror 9. When the mechanical shutter 41 is opened and the mechanical shutter 42 is closed, the light introduced into the half mirror 9 is reflected by the half mirror 9, passes through the mechanical shutter 41, is reflected by the surface-polished Si substrate 40, and is again mechanically transmitted. The light passes through the shutter 41 and further passes through the half mirror 9 to enter the detector 4 (first path). The light guided to the detector 4 is converted into an electrical signal and sent to the amplifier 10.
Only the alternating current component is amplified and input to the calculation means 43.

The calculation means 43 synchronizes the optical signal from the amplifier 10 with the output signal of the sweep oscillator 12 to create a stationary waveform of interference intensity according to a change in wavelength λ, and stores this.

Next, the states of the mechanical shutters 41 and 42 are switched to close the shutter 41 and open the shutter 42. In this case, the light passes through the half mirror 9, passes through the mechanical shutter 42, is reflected by the Si substrate 1 on which the capacitor groove is formed, passes through the mechanical shutter 42 again, and exits the half mirror.
9 and guided to the detector 4 (second path). Here too, the light guided to the detector 4 is converted into an electrical signal,
Only the alternating current component is amplified by the amplifier 10 and inputted to the calculation means 43, and in synchronization with the output signal of the sweep oscillator 12, a stationary waveform of the interference intensity corresponding to the change in the wavelength λ is created and stored.

Next, in the calculation means 43, the intensity of the light passing through the second path, that is, the intensity of the reflected light from the Si substrate 1 in which the capacitor groove is formed, is changed from the intensity of the light passing through the first path, that is, the intensity of the reflected light from the Si substrate 1 formed with the capacitor groove. The wavelength of the incident light is divided by the intensity of the reflected light from the Si substrate 40. The result is then synchronized with the output of the sweep oscillator 12 and output to the waveform observation device 11.

In this example, the distribution of the intensity according to the wavelength of the white light source and the distribution of the reflection intensity of the Sil plate according to the wavelength are corrected by the above-mentioned division, so that the interference light with almost equal intensity distribution is The signal can be observed, and the result is
)2, the groove depth d is calculated. In this embodiment, since the signal of the interference light becomes clearer than in the first embodiment, the depth of the microgroove for the capacitor can be measured with higher accuracy.

FIG. 6 is a schematic configuration diagram showing a third embodiment, in which a high-speed scanning spectrometer 60 is used instead of the acousto-optic filter 8 of the first embodiment.
It uses High-speed scanning spectrometer 60 is 400 nm
It functions as an optical variable filter that can scan light with a wavelength of ~600 nm once in 0.5 seconds.

In this embodiment, first, the light from the white light S:S is transferred to the lens 7.
and enters the slit 62 of the high-speed scanning spectrometer 60 through the slit 62 of the high speed scanning spectrometer 60. The diffraction grating 61 in the high-speed scanning spectrometer 60 rotates once every 0.5 seconds in synchronization with the sweep oscillator 12, and a constant wavelength for each angle of the diffraction grating 61 is connected to the slit of the high-speed scanning spectrometer 60. 63, light that sweeps the wavelength range of 400 nm to 600 nm in 0.5 seconds can be obtained. As a result, the depth of the VLSI groove can be measured using the same principle as in the first embodiment.

Note that in the first and second embodiments, the wavelength scanning frequency is IKHz, and in the third embodiment it is 2Hz, but interference components can be sufficiently extracted at a reasonably high frequency of IHz or higher. .

[Effects of the Invention] As explained above, according to the micro-groove depth measuring method and apparatus of the present invention, since the 0th-order diffracted light is measured, the temperature is lower than when measuring higher-order diffracted light. A strong interference light intensity can be obtained. Therefore, it becomes possible to measure the depth of the groove more accurately. In addition, the 0th order diffracted light is nothing but specularly reflected light, and its direction is uniquely determined by the angle of incidence of the incident light, so it is very easy to align the detector for detecting the diffracted light. is almost unnecessary. Therefore, there is an advantage that the reproducibility of measurement is extremely good.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing the first embodiment of the present invention;
3 is a waveform diagram showing the measurement results of the first embodiment. FIG. 4 is a schematic configuration diagram showing the second embodiment of the present invention. FIG. 5 is a waveform diagram showing measurement results according to the second embodiment, FIG. 6 is a schematic block diagram showing the third embodiment, and FIG. 7 is a schematic block diagram showing the conventional groove depth measuring method. DESCRIPTION OF SYMBOLS 1... Si substrate provided with minute grooves, 4... Detector, 5... White light source, 8... Acousto-optic filter, 9...
...Half mirror 110...Amplifier, 11...Waveform observation device, 12...Sweep oscillator, 40...
Si substrate with polished surface, 41.42... Mechanical shutter, 43... Calculation means, 60... High speed scanning spectrometer.

Claims (4)

[Claims] (1) The intensity of the 0th-order diffracted light is measured by inputting narrow band wavelength light whose wavelength is scanned onto the sample surface provided with microgrooves, and measuring the intensity of the 0th-order diffracted light according to the wavelength change. A micro groove depth measuring method characterized by calculating the depth of a groove. (2) a white light source generating means; an optically variable filter that extracts light with a narrow band wavelength from the white light emitted by the white light source generating means while scanning the wavelength; and a variable optical filter that transmits a part of the light from the optically variable filter. The transmitted light is incident on the sample surface where microgrooves are provided, and the reflected light from the sample is
a half mirror that reflects a part of the order diffracted light and takes it out in a desired direction; a detector that receives the 0th order diffracted light taken out by the half mirror and outputs an electric signal according to its intensity; A micro groove depth measuring device comprising: a waveform observation device that observes in synchronization with the scanning period of the narrow band wavelength. (3) The wavelength of light with a narrow band wavelength being scanned is incident on the first sample surface provided with microgrooves, and the 0
The intensity of the 0th-order diffracted light is measured, and the light is incident on a second sample that is made of the same material as the first sample and has a flat surface, and the intensity of the 0th-order diffracted light is measured. The intensity of the 0th-order diffracted light from the sample is divided by the intensity of the 0th-order diffracted light from the second sample in correspondence with the wavelength, and the depth of the microgroove is calculated from the division result according to the wavelength. Micro groove depth measurement method. (4) white light source generating means; an optical variable filter that extracts light with a narrow band wavelength from the white light emitted by the white light source generating means while scanning the wavelength; and a variable optical filter that receives the light from the optical variable filter and extracts a part of the light. A first sample that is provided with a half mirror that reflects and partially transmits light, a microgroove that allows the transmitted light (or reflected light) from the half mirror to enter perpendicularly on its surface, and the reflection from the half mirror. A second sample whose surface is made of the same material as the first sample and whose surface is flat, on which light (or transmitted light) is incident perpendicularly, and an optical path between the half mirror and the first sample. a first shutter disposed in the optical path between the half mirror and the second sample to selectively block the optical path; and a shutter disposed in the optical path between the half mirror and the second sample to block the optical path by an operation opposite to that of the first shutter. , the 0th-order diffracted light reflected by the first sample, which is reflected by the half mirror (or transmitted by the half mirror) after passing through the first shutter, is received and its intensity is determined. A first electric signal corresponding to the second sample is output, and the second electrical signal is transmitted through the half mirror (or reflected by the half mirror) after passing through the second shutter, which is the 0th order diffracted light reflected by the second sample. a detector that receives the 0th-order diffracted light and outputs a second electrical signal according to the intensity of the 0th-order diffracted light; and a detector that converts the light intensity indicated by the first electrical signal into the second electrical signal. A micro-groove depth measuring device comprising: arithmetic means for dividing according to the wavelength by the indicated light intensity; and a waveform observation device for observing the division result of the arithmetic means in synchronization with the scanning period of the narrow band wavelength. .