JPS60136324A - Method of measuring minute depth and apparatus therefor - Google Patents

Abstract

PURPOSE:To enable the depth of a groove formed by etching or the like on a substrate having minute concavo-convex patterns thereon, by radiating light with various wavelengths on the substrate and detecting the spectral intensity distribution of diffracted light other than the zeroth one from the direction inclined to the substrate. CONSTITUTION:A measurement apparatus comprises, for example, a light source 22, a spectroscope 24, an optical system 26 and a light detector 31. Light separated into spectra is made parallel beams having a diameter of 2-3mm. by the optical system 26 and slits 27 and 28, and radiated on an object to be measured 30. The light reflected and diffracted on the object to be measured 30 is reflected by a concave mirror 29 and reaches the light detector 31, where the light intensity is determined and transmitted to a signal processing system 35. The spectroscope 24 automatically changes the wavelength by rotating a diffraction grating 32 through a driving system 33. Thus, the depth of the object 30 can be calculated and determined by detecting the wavelengths lambda1 and lambda2 in which the light intensities become the extremes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a microgroove depth measuring method for measuring the depth of microscopic irregularities formed on a substrate by, for example, etching.

[Background of the invention]

As a conventional method for measuring the depth of a fine groove, a depth measuring method using light interference shown in FIGS. 1 to 6 is known. The apparatus for carrying out this measurement method includes a tungsten lamp light source 1, an entrance slit 7, a concave bell-shaped diffraction grating 9. It is composed of a spectrometer 2 composed of mirrors 8 and 11 degrees and an exit slit 10, a photodetector 3, and a signal processing section 4.

Next, a case will be described in which the depth of the uneven patterns shown in FIGS. 2 and 6 is measured using this apparatus. That is, the sample 5 placed on the sample stage 6 and having the uneven pattern shown in FIGS. 2 and 3 is placed on the tungsten lamp light source 1.
irradiated by. As shown in Figure 3, two sides 1 of sample 5
B.

The light reflected by 19 is separated into spectra by a spectrometer 2 and detected by a photodetector 3. The separated light detected by the photodetector 3 is obtained by interference of the light reflected from the surface 18 and the surface 19 shown in FIG.

Before considering the intensity of this interference light, diffraction will be explained.

In other words, if we consider parallel slits with a slit @d, a distance between slit centers @l, and a number of slits N, and when this slit is irradiated with coherent light with a wavelength λ, the intensity distribution I of the diffraction image in a 7-Lanhofer region with a distance @b is as follows. Follow the formula.

Here, x is the position on the screen based on the point where the light travels straight and reaches the screen installed in the 7 run ho 77 area.

Therefore, the light intensity in the direction where x=0, that is, the direction in which the light travels straight (0th order diffraction direction), is proportional to the square of the groove width d.

Therefore, when the groove 17 is formed in the shape shown in Fig. 3, the groove width d is d/l = 1/10 in both the vertical and horizontal directions relative to the groove pitch l. Therefore, the ratio of the reflected light intensity Ie of the groove surface 19 and the reflected light intensity Ia of the surface 18 is approximately the relationship le/Is = 1/10000 by applying the above relationship Ieocd2 twice in the vertical and horizontal directions. Become. Therefore, the light intensity factor 2 detected by the photodetector 5 has a relationship approximately expressed by the following equation (2), where λ is the wavelength of light.

■λoc I s -) Ie -25e JTic
os (4π number) h Ki Is --Ia cos (4π) ... Concave ... Curved ... (2) EIO, 7 However, h indicates the depth of the groove.

In this way, the area ratio of the surface 18 and the groove surface 19 is 1/10.
When it becomes about 0, the intensity change of the light when the light specularly reflected from the two surfaces (vertical direction from the sample surface) interferes is 11
It is impossible to detect changes in light intensity as small as 5o.

This is 8/N (signal m pressure/noise voltage) of the photodetector.
This is due to That is, generally the photodetector S
/N is about 20, and when s/N is about 20, 115
A light intensity change of about o cannot be distinguished from noise □
It is difficult to measure the etching depth.

As described above, the conventional depth measuring method has the disadvantage that it is difficult to measure the depth h because changes in light intensity cannot be detected.

[Purpose of the invention]

The object of the present invention is to eliminate one of the drawbacks of the above-mentioned conventional techniques and to provide a method and method for measuring the depth of fine grooves that can accurately and accurately measure the depth and width of fine grooves formed on a substrate by etching or the like. We are in the process of providing equipment.

[Summary of the invention]

That is, the present invention is a groove depth measuring method using optical interferometry, in which when light is irradiated onto a fine uneven pattern formed on a substrate, the light reflected from the surface and the bottom of the groove is reflected by the Babinet. According to the principle of (Babinet),
Focusing on the fact that each light is diffracted with exactly the same light intensity distribution, we irradiate a substrate with a fine uneven pattern with varying wavelengths of light, and detect non-zero-order diffracted light from a direction tilted to the substrate. This method is characterized by detecting the spectral intensity distribution and measuring the depth of the groove from the wavelength of light that indicates the extreme value of this spectral intensity distribution. According to this Babinet principle, a diffraction image due to a certain figure that causes diffraction and a diffraction image due to a figure created by replacing the transparent and opaque parts of that figure are the central part of the diffraction image surface (0-order They have exactly the same light intensity distribution except for the diffraction image (diffraction image).

Therefore, in a measurement object that is etched into the shape shown in FIGS. 2, 3, and 3, the non-etched part and the etched part have the same shape that causes two diffraction based on the above-mentioned Babinet principle. The light intensity distributions of the interference lights corresponding to each other and reflected and diffracted from each other will have exactly the same light intensity distribution except for the zero-order diffraction image. Therefore, if we detect the light intensity of the diffraction image in directions other than the zero-order direction and perform the same interference measurement as before, two light beams with the same light intensity will interfere, so the light intensity will be approximately as follows (5 ), and it becomes almost 0 at a position where the light intensity is weak, so that changes in light intensity can be easily detected.

I oc Is + Ie -25e Fcoa (flat) --- C5) [Embodiments of the Invention] The present invention will be specifically described below based on the embodiments shown in FIGS. 2 to 5.

The present invention does not measure in the 0-order direction like conventional measuring devices, but in the 1-order direction.
Detection of diffracted light of the following order or higher 1: Detecting changes in light intensity when scanning wavelengths.

An embodiment of the micro groove depth measuring device of the present invention mainly includes a light source 22, a spectrometer 24, an optical system 26, as shown in FIG.
, and a photodetector 31. The light source 22 is a xenon lamp, a halogen lamp, or a tungsten lamp with low brightness, and is cooled by a cooling blower 21. In order to effectively enter the entrance slit of the spectrometer 24, the concave mirror 34 of the light source 22
It is installed so as to focus on the slit of the spectrometer 24.

The separated light 25 is transmitted through an optical system 26 and a slit 27 .
28, the beam becomes a parallel beam with a diameter of 2 to 40 mm, and is irradiated onto the object to be measured 30.

The light reflected and diffracted on the object to be measured 50 is reflected by the concave mirror 29 and reaches the photodetector 31 installed at the focal point of the concave mirror, where the light intensity is measured and transmitted to the signal processing system 65. .

Furthermore, the spectrometer 24 can automatically change the wavelength by rotating the diffraction grating 32 using the drive system 56.
At the same time, information on the orientation of the diffraction grating 32, ie, spectrometer wavelength information, is transmitted to the signal processing system 35.

Furthermore, by inserting an infrared cut filter 23, failure of the spectrometer 24 etc. due to heat is prevented.

Next, a method for calculating the depth will be explained in detail using FIGS. 2, 3, and 5.

The planar and cross-sectional shapes of the object to be measured are shown in Figure 2 and
This is an uneven pattern as shown in FIG.

At this time, based on the Babinet principle, planes 18 and 19
The intensity of light reflected and diffracted by the surface is determined only by the amplitude reflectance of each surface. Assuming that the amplitude reflectances of the surfaces 18 and 19 are respectively rssre and the wavelength of the irradiated light is λ, the light intensity Iλ of the detected n-th order diffracted light follows the following equation.

%formula%)() Further, the direction θ of the diffracted light follows the following equation.

θ = 3,. - (ni=, ), (5) FIG. 5 illustrates equation (4). Here, the wavelength at which the light intensity Iλ takes an extreme value is λ1. Assuming that λ is λ, the depth h is expressed by the following equation.

Therefore, the wavelength λ1. at which the light intensity Iλ takes an extreme value. λ.

All you have to do is detect it.

In the signal processing system 65 shown in FIG. 4, the wavelength signal from the spectrometer 24 and the light intensity signal from the photodetector 31 are taken in, and the wavelengths λ1 and λ showing the extreme values in FIG. The depth h is calculated and measured using equation (6).

Furthermore, the direction of the diffracted light changes as the wavelength λ is scanned, as shown by equation (5). The concave mirror 29 is used for the photodetector 31 which is set at a fixed position even if the direction θ changes.
This is to allow the diffracted light to reach the top. Therefore, the concave mirror 29 is a spheroidal mirror, and the two focal points 57 and 58 are each set to be one detection surface of the measurement point photodetector 31. A diffuser plate 56 is provided to eliminate the influence of corners.

In the above embodiment, the wavelength of the irradiated light is scanned using the spectroscope 24, but other means for continuously changing the wavelength,
For example, the wavelength of the irradiation light may be determined by a laser whose oscillation wavelength can be changed continuously.

In addition, in this example, the white light source is spectrally separated and then irradiated onto the object to be measured, and the change in interference intensity of □ is detected when the wavelength is changed. The same thing can be achieved by detecting changes in interference intensity with respect to wavelength by spectrally dispersing the reflected and diffracted light.

Next, a case will be described in which the present invention is used in a semiconductor device manufacturing process.

Semiconductor devices are becoming increasingly highly integrated.

The deep groove technology described below is also an indispensable technology for achieving high integration of such semiconductor devices.

For one thing, a deep trench technique is used as an element isolation technique for separating semiconductor elements constituting a semiconductor device on one substrate. Conventionally, isolation between elements was achieved using an oxide layer, which is an insulator, but grooves are provided between the elements to reduce the area used for isolation and increase the degree of integration.

Further, a capacitor used in a memory using a field effect transistor is formed using a deep groove. By forming capacitors, which were conventionally formed in a plane, vertically, it is possible to form a capacitor with a sufficient capacity in a small area in a plane, thereby making it possible to improve the degree of integration.

When forming a capacitor, this deep groove is filled with an insulating material. Figures 6 and 7 show an overview of the device isolation deep groove described above, and Figures 8 and 9 show the deep groove for the capacitor, respectively. show.

Further, the above-mentioned deep grooves are formed on the silicon substrate by dry etching using a silicone chemical film formed on the substrate as a mask. Here, dry etching is a process in which a low-pressure reactive gas is flowed into a vacuum processing chamber, a plasma state is created by high-frequency discharge, microwave discharge, etc., and the generated radicals and ions in an active state react with the material to be etched. This is a method of etching the material to be etched.

Furthermore, a groove having the same shape as the deep groove described above is also formed in the optical disk recording bit groove.

At this time, it is necessary to inspect the depth of the groove formed.
Until now, there has been no suitable depth measurement method.

The non-destructive etching depth measurement of a semiconductor device as described above becomes possible only by using the apparatus according to the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, when measuring the depth of a groove formed on a substrate by interferometry, it is possible to measure the depth of a groove formed on a substrate not only when the area of the groove is large or when the area of the groove and the surface is about the same. In fact, even if the area of the groove is small and the area ratio to the surface is large, the intensity of the light emitted from the groove and the light emitted from the surface can be made to be about the same, so the area of the etched part is small. This has the effect of making it possible to measure the depth of trenches such as deep trenches for memory capacitors and deep trenches for element isolation using field effect transistors.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional groove depth measuring device, Figure 2 is a block diagram showing a conventional groove depth measuring device.
5 is a plan view showing an example of an etching pattern, FIG. 5 is a sectional view taken along line AA in FIG. 2, FIG. 6 is a diagram showing the relationship between the wavelength detected by the apparatus shown in FIG. 4 and the light intensity distribution, and FIG. 6 is a plan view showing another example of the object to be measured. 7 is a sectional view taken along line BB in FIG. 6, FIG. 8 is a plan view showing still another example of the object to be measured, and FIG. 9 is a sectional view taken along line cl-c in FIG. 22... Light source, 24... Spectrometer, 26... Lens system, 29... Concave mirror, 60... Measured object, 31
...Photodetector. 61 drawings 7 drawing blue ul many 7 drawings 1 0 mouth 0 mouth 0 mouth 0 mouth 0 mouth 0 mouth 0 mouth mouth mouth

Claims (1)

[Claims] 1. A parallel light beam of varying wavelength is irradiated perpendicularly to the substrate on a substrate in which fine grooves are formed, and the spectroscopy of non-zero-order diffracted light from the substrate is performed. A micro-groove depth measuring method characterized by detecting an intensity distribution and measuring the depth of the groove from a plurality of wavelengths of light showing extreme values of the spectral intensity distribution. 2. Light irradiation means that irradiates a substrate with fine grooves at right angles to the substrate with a parallel light beam of varying wavelength, and detects the spectral intensity distribution of non-zero-order diffracted light from the substrate. and a measuring means that calculates a plurality of wavelengths of light showing extreme values from the spectral intensity distribution detected by the detection means and measures the depth of the groove from the calculated wavelengths of the plurality of lights. A micro groove depth measuring device characterized by: 3. The light irradiation means includes a light source, a spectrometer that separates the light emitted from the light source and changes the wavelength of this light, and an optical device that converts the light obtained from the spectrometer into a parallel light beam. 3. A microgroove depth measuring device according to claim 2, characterized in that the microgroove depth measuring device comprises a system. 4. The detection means includes a spheroidal mirror installed so that the measurement point is positioned at one focal position, and a photodetector equipped with a diffuser plate installed at the other focal position of the spheroidal mirror. A microgroove depth measuring device according to claim 2, characterized in that it has the following.