JP2002323303A - Diafragm thickness measurement method, its device, and manufacturing method for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out non-contact measurement of thickness of a SOI base board having a buried oxide film inside in real time. SOLUTION: In an etching process for forming a diaphragm and the like, the film thickness D of the diaphragm 2 is detected by performing irradiation with a laser beam from a laser beam source 3 while varying its wavelength and performing frequency analysis of the intensity of its reflected light for measuring an etching quantity. In this process, a component of reflection of the laser beam L0 reflected on the front and back faces of the buried oxide film exerts bad influence, however, when irradiation is carried out with the laser beam within a wavelength range satisfying a condition that the reflected light components on the front and back faces of the buried oxide film interfere with each other, the film thickness D of the diaphragm 2 can be detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film thickness measuring method, a film thickness measuring apparatus, and a method for manufacturing a semiconductor device, in which a light beam is applied to a measurement site of a film to be measured to measure the film thickness.

[0002]

In recent years, a semiconductor device having a structure in which a mechanical structure is integrally formed on a surface portion of a semiconductor element has been developed. Such a semiconductor device has been proposed as a semiconductor device having a high degree of integration by diverting the semiconductor integration technology. However, since these semiconductor devices need to form a fine structure, There is a need to be able to further enhance and control the processing accuracy of the material.

[0003] For example, when a silicon diaphragm is formed by etching, the thickness of the diaphragm is usually controlled by controlling the etching time. This is because various parameters such as temperature and concentration governing the etching conditions are controlled. In some cases, the thickness of the diaphragm may vary due to variations and the like, and as a result, the thickness of the diaphragm may vary. Therefore, there remains a problem in establishing a process technology having good reproducibility in terms of processing accuracy. From such a point, it has been desired to be able to monitor the silicon thickness in real time during the etching and to improve the controllability of the etching amount.

In response to such a demand, recently, as disclosed in Japanese Patent Application Laid-Open No. 2-307003, for example, interference light such as reflected light or transmitted light obtained from a semiconductor layer by irradiating a semiconductor with a laser beam. A technique has been proposed in which the thickness of a semiconductor layer is detected in a non-contact state and in real time to monitor the etching thickness by observing a change in the intensity of the semiconductor layer.

As another method, there has been proposed a method of measuring silicon thickness by irradiating silicon with halogen light and spectrally analyzing the halogen light (MEMS / 94 Procee).
dings pp.217-pp.222). Further, JP-A-7-306
As disclosed in JP-A-018, a method of changing the wavelength of a laser beam and measuring the film thickness from the waveform of the reflected wave is being studied.

Incidentally, the above-mentioned Japanese Patent Application Laid-Open No. 7-306018
In the method disclosed in Japanese Patent Application Laid-Open Publication No. H11-163, it is an effective method when measuring the film thickness when only the silicon layer is to be measured. However, in the case of a laminated structure, for example, a so-called SOI (structure in which an insulating film is sandwiched between silicon) is used. Silicon On Insulato
r) When measuring the thickness of a silicon layer such as a silicon wafer having a structure, the measurement may not be possible by applying this method as it is because it is affected by the insulating film embedded inside. .

Therefore, for example, a silicon layer of an SOI substrate is etched to form a diaphragm such as a pressure sensor while leaving a desired film thickness, or a structure of an acceleration sensor as disclosed in JP-A-2000-31502. In the middle of the process of forming the body,
In some cases, it was not possible to measure an accurate film thickness, and this was to be solved as a technical problem. This is because, when the silicon film thickness is measured, the irradiated measurement light beam is buried in the SOI substrate in the insulating film (generally, S
When the interference intensity changes depending on the silicon film thickness (SOI thickness) on the insulating film and becomes higher due to the reflection at the interface of iO2), the detection sensitivity of the film thickness of the entire silicon diaphragm becomes higher. Because it becomes dull.

In this case, when the thickness of the diaphragm is sufficiently larger than the thickness of the SOI film, the peak of the film thickness near the SOI thickness is excluded from the plurality of measured film thickness peaks. A peak corresponding to the thickness of the diaphragm can be specified and its thickness dimension can be measured. However, when the etching progresses and the diaphragm thickness approaches the thickness of the SOI layer, the peaks overlap, so that it is not possible to judge by this method, and as a result, the etching end point cannot be detected accurately. It was to be.

The present invention has been made in view of the above circumstances, and an object of the present invention is to accurately measure the thickness of a target layer even when layers of different materials are laminated inside the target film. Film thickness measurement method that can be detected at
An object of the present invention is to provide a film thickness measuring device and a method for manufacturing a semiconductor device.

[0010]

According to the first aspect of the present invention, the measuring light emitted from the measuring light source to the film to be measured is
A film thickness measuring method in which the wavelength is changed in the transmitted light wavelength region of the film to be measured, the reflected light or the transmitted light is detected, and the film thickness of the film to be measured is detected from a change state of the intensity. In the case where the film to be measured has a structure in which a heterogeneous layer made of a material having a different refractive index is laminated inside, when measuring the film thickness of the film to be measured, the wavelength of the measurement light emitted from the measurement light source Since the wavelength is changed using a wavelength in a range that satisfies the condition of the interference generated due to the light component reflected by the heterogeneous layer among the wavelengths in the transmitted light wavelength region,
By suppressing the reflection component due to the heterogeneous layer, the interference component of the reflected light or transmitted light due to the thickness of each film in the portion divided by the heterogeneous layer of the film to be measured can be suppressed. As a result, the film thickness can be measured based on the components of the light reflected or transmitted by both the upper surface and the lower surface of the film to be measured, and the entire film thickness can be accurately measured in a non-contact manner and in real time. Will be able to Thus, for example, the amount of etching can be directly monitored while the etching process or the like is being performed, and the etching can be controlled with high accuracy.

According to the second aspect of the present invention, in the above invention, when measuring the reflected light when the measurement light is applied to the film to be measured and detecting its thickness, the refractive index of the heterogeneous layer is set to n.
Assuming that 0 and the film thickness are d, the wavelength changes in a wavelength region around a wavelength λ satisfying 2 · n0 · d = m · λ (where m is a natural number) as an interference condition of the measurement light. By irradiating the film, the components reflected on the upper surface and the lower surface of the heterogeneous layer in the film to be measured are in a condition where they interfere with each other, and the influence of the reflected light component can be reduced. This means that interference components depending on the film thickness of the divided partial layers of the film to be measured located on both the upper surface (one side) and the lower surface (the other side) of the heterogeneous layer can be suppressed. This means that the measurement can be performed in a state where the component of the reflected light relative to the entire thickness of the film to be measured is relatively large, and the accurate thickness of the film to be measured can be measured. become able to.

According to the third aspect of the present invention, in each of the above inventions, the wavelength range of the measurement light corresponds to the thickness of the film to be measured obtained with respect to the center wavelength when the measurement wavelength range is a fixed width. The value of the ratio of the peak intensity to the peak intensity corresponding to the thickness of the partial layer of the film to be measured divided by the heterogeneous film is 1
Since the wavelength range is set as described above, for the wavelength λ that satisfies the above-described equation of the interference condition, the wavelength range of the measurement light that can be sufficiently used for the measurement can be specifically set. In this case, since the intensity of the peak value of the film to be measured can appear at a ratio of 1 or more to the peak value of the other partial film, the intensity of the film to be measured can be surely determined without being buried in another peak value. The film thickness can be measured.

According to the invention of claim 4, in each of the above inventions, when the film to be measured is a silicon layer interposed inside as an extraneous layer, the measurement wavelength range is 2 · n0 · d / (m + 0.2) ≦ λ ≦ 2 · n0 · d / (m−0.2) (b) (where n0 is the refractive index of the insulating film, d is the thickness of the insulating film,
(m is a natural number), so that the conditional expression (b) is satisfied. Therefore, from the values of the refractive index n and the film thickness d of the insulating film as the heterogeneous layer interposed inside the silicon layer, this conditional expression (b) is obtained. Can be set.

In this case, the numerical value “0.2” set in the denominator of the fractions on the left and right sides for setting the upper and lower limits of the conditional expression is the center value when the measurement wavelength range is set to a constant width. The value of the ratio of the intensity of the peak value corresponding to the thickness of the film to be measured obtained with respect to the wavelength to the intensity of the peak value corresponding to the film thickness of the partial layer of the film to be measured divided by the heterogeneous film is 1 or more. Is a value that satisfies the condition of the wavelength range λ such that it substantially matches the range of the wavelength.

According to a fifth aspect of the present invention, in each of the above-mentioned inventions, a laser light source whose oscillation center wavelength can be changed continuously or at a specific interval is used as the measurement light of the measurement light source. By guiding by means, it is possible to irradiate only a limited area of the surface of the film to be measured, thereby performing accurate film thickness measurement even in applications where the local film thickness of the film to be measured is measured Can be. For example, this is an effective means when a partial etching process is performed to measure the film thickness.

According to a sixth aspect of the present invention, in each of the above-mentioned inventions, the measuring light of the measuring light source is applied to the reference measuring film having the same structure as the film to be measured and having a known film thickness, and the reflected light or transmitted light is reflected. Measures the intensity and detects the thickness of the film to be measured from the way of the change and the method of change of the intensity of the reflected light or transmitted light of the film to be measured, so that the wavelength of the measuring light of the measuring light source can be accurately measured. The thickness of the film to be measured can be accurately measured without comparison with a reference measurement film having a known film thickness.

According to the seventh aspect of the present invention, in the configuration in which the film to be measured is irradiated with the measuring light and the intensity of the reflected light or transmitted light is detected to detect the film thickness of the film to be measured, Irradiates the measurement light by changing the wavelength within the transmission light wavelength region of the film to be measured, and guides the measurement light to the measurement site of the film to be measured by the optical means, and the measurement light irradiated to the film to be measured by the measurement means. Measure the intensity of the reflected or transmitted light of the
It is assumed that the thickness of the film to be measured is calculated by calculation based on the result of the intensity of the reflected light or transmitted light measured by the measuring means by the calculating means. In this case, the film to be measured as the film to be measured is assumed. When a material having a different layer of a material having a different refractive index is interposed therein, the control means causes the light source to be reflected by the different layer with respect to the measurement light source. The measurement is performed by changing the wavelength of the measurement light within a wavelength range that satisfies the interference condition. As a result, components reflected by the front and back surfaces of the heterogeneous layer in which the measurement light applied to the measurement target film is interposed interfere with each other, and the thickness of the partial layer divided by the heterogeneous layer of the measurement target film is reduced. The intensity of the component caused can be suppressed, and as a result, the light component related to the thickness of the film to be measured is mainly used, and the thickness of the film to be measured can be accurately measured.

According to an eighth aspect of the present invention, in the above invention, the measuring means is provided so as to detect the reflected light of the measuring light, and the control means sets the refractive index of the foreign layer to n0 and the film thickness to d.
As the interference condition of the measuring light at the time of the following, the measuring light is changed by changing the wavelength in a wavelength region centering on the wavelength λ satisfying 2 · n0 · d = m · λ (where m is a natural number). Since the measurement light source is configured to be illuminated, components of light reflected by the front and back surfaces of the heterogeneous layer can be made to interfere with each other, thereby relatively increasing the light intensity related to the thickness of the film to be measured. Will be able to do it.

According to the ninth aspect of the present invention, the seventh and eighth aspects are provided.
In the invention of the above, by the control means, for the measurement light source,
The wavelength range of the measurement light, the intensity of the peak value corresponding to the thickness of the film to be measured obtained with respect to the center wavelength when the measurement wavelength range is a fixed width, and the partial layer of the film to be measured divided by the heterogeneous film Is controlled so that the value of the ratio of the intensity to the peak value corresponding to the thickness of the layer is set to be 1 or more. As a result, the peak value caused by the thickness of the other partial layer is suppressed, and the information of the light caused by the thickness of the film to be measured is in a range that can be distinguished from the other peak values. The condition can be satisfied, and the wavelength change range of the measurement light can be maximized to improve the measurement accuracy.

According to a tenth aspect of the present invention, in the invention of the seventh to ninth aspects, when the film to be measured is a silicon layer having an insulating film interposed as an extraneous layer, the control means controls the measurement light source. On the other hand, the measurement wavelength range is set within the range satisfying the conditional expression (b), and the control is performed so that the wavelength of the measurement light is changed to output the light. Therefore, as a heterogeneous layer interposed inside the silicon layer, Refractive index n of the insulating film
The wavelength range λ satisfying the conditional expression (b) can be set based on the value of the film thickness d.

According to the eleventh aspect of the present invention, in the seventh to tenth aspects, the measurement light source is constituted by using a laser light source capable of changing the oscillation center wavelength of the measurement light continuously or at specific intervals. By guiding the measurement light through the optical system, it is possible to irradiate only a limited area of the surface of the film to be measured, thereby making it possible to accurately measure the local thickness of the film to be measured even in applications where the film thickness is to be measured. Thickness measurements can be made. For example, this is an effective means when a partial etching process is performed to measure the film thickness.

According to a twelfth aspect of the present invention, in each of the seventh to eleventh aspects, a reference measurement film having the same structure as the film to be measured and having a known film thickness is provided, and the reference optical system is used to control the measurement light source. The measurement light is guided to the reference measurement film and irradiated, the intensity of the reflected light or transmitted light is measured by the reference measurement unit, and the calculation unit calculates the intensity of the reflected light or transmitted light measured by the measurement unit. The thickness of the film to be measured is calculated by referring to the result of the intensity of the reflected or transmitted light measured by the reference measuring means in addition to the result, so that the wavelength of the measuring light of the measuring light source can be accurately measured. The thickness of the film to be measured can be accurately measured without comparison with a reference measurement film having a known film thickness.

According to the thirteenth aspect of the present invention, a measurement light emitted from a measurement light source to a measurement target film of the semiconductor device is applied to a semiconductor device having a measurement target film such as a diaphragm formed by an etching process or the like. Manufacturing of a semiconductor device in which the wavelength is changed in the transmitted light wavelength region of the film to be measured, the reflected light or the transmitted light is detected, and the film thickness of the film to be measured is detected from the change in the intensity. In the method, when the film to be measured has a structure in which a heterogeneous layer made of a material having a different refractive index is laminated inside, when measuring the film thickness of the film to be measured, the measurement light emitted from the measurement light source is measured. Since the wavelength is changed using a wavelength within a range that satisfies the condition of the interference generated due to the light component reflected by the heterogeneous layer among the wavelengths of the transmitted light wavelength region, the reflection component by the heterogeneous layer is suppressed. thing Therefore, the interference component of the reflected light or the transmitted light caused by the thickness of each film in the portion divided by the heterogeneous layer of the film to be measured can be suppressed, and as a result, the upper surface and the lower surface of the film to be measured The film thickness can be measured based on the components of light reflected or transmitted by both, and the entire film thickness can be accurately measured in real time in a non-contact manner.

Accordingly, for example, when it is necessary to accurately form the thickness of a film to be measured such as a diaphragm formed in a semiconductor device, the non-contact and non-contact state may be maintained while the etching process for forming the diaphragm is being performed. The thickness of the film to be measured can be detected in real time and accurately. Therefore, it is possible to improve the quality in the case of manufacturing a semiconductor device as a sensor that detects pressure, acceleration, and the like using a diaphragm or the like, and also to shorten the time and cost in the manufacturing process. .

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. In this embodiment, an SOI (Silicon On Insulator) substrate 1 is used as an object to be measured.
For example, the present invention is applied to a case where an etching amount is measured in an etching process when a diaphragm portion of a semiconductor dynamic quantity sensor such as a pressure sensor or an acceleration sensor which is a semiconductor device formed using the SOI substrate 1 is processed. . FIG. 2 is a schematic view showing a state in which the diaphragm 2 is formed by etching the SOI substrate 1.

The SOI substrate 1 is made of single crystal silicon (Si)
A buried oxide film 1b made of silicon dioxide (SiO2), which is an insulating film as a heterogeneous film, is stacked on a substrate 1a, and an SOI layer 1c made of single crystal silicon (Si) is stacked thereon. / SiO2 / Si). In this case, the buried oxide film 1b has a thickness d (μm) of, for example, 2 μm, and the thickness D1 of the SOI layer 1c is formed to be about 15 μm. The refractive index n0 of the buried oxide film 1b is 1.45 (the refractive index of silicon dioxide), and the SOI layer 1c and the single crystal silicon substrate 1a
Has a refractive index n1 of 3.44.

In order to form the diaphragm 2 on the SOI substrate 1, a concave portion 2a is formed by performing a wet etching process on a portion opened by patterning from the single crystal silicon substrate 1a side, and a thickness dimension of the single crystal silicon substrate 1a is formed. D
Adjust 2. The diaphragm 2 having a desired thickness D (μm) is formed by stopping the etching process at an appropriate time. Here, the film to be measured in the present invention corresponds to the portion of the diaphragm 2, and the thickness D of the diaphragm 2 is the sum of the thicknesses of the respective films, that is, D = D1 + d + D2.

Next, a schematic configuration of the measurement system will be described with reference to FIG. Laser light source 3 as measurement light source
Is a laser beam L in a near-infrared wavelength region that passes through silicon.
0 is emitted as measurement light, and the oscillation center wavelength λ of the laser light L0 can be changed continuously or at regular intervals. Laser light L0 emitted from the laser light source 3 is guided to the SOI substrate 1 by a reflecting mirror 4, a half mirror 5, and a lens 6 provided as an optical system.

That is, the laser beam L 0 is bent in the right angle direction by the reflecting mirror 4, then passes through the half mirror 5, and is focused on the diaphragm 2 portion of the SOI substrate 1, which is a film to be measured, while being narrowed down by the lens 6. Irradiated. At this time, SOI
The substrate 1 is in a state where the etching process is being performed as described above, and is set so as to irradiate the laser beam L0 to the portion of the diaphragm 2 that is immersed in an etching tank of an etching apparatus (not shown). .

Laser light L0 applied to SOI substrate 1
Is reflected on the front and back surfaces of each film of the above-mentioned laminated structure, becomes interference light depending on the thickness of each layer and the entire film, and returns to the lens 6 side. The light component of the reflected light passes through the lens 6 as light to be detected, is deflected in a direction perpendicular to the light through the half mirror 5, and is incident on a photodetector 7 as a measuring means. The photodetector 7 converts the received reflected light into an electrical detection signal indicating the intensity of the reflected light and outputs the signal to the light receiving circuit 8. The light receiving circuit 8 performs various processing such as noise processing on the detection signal given from the photodetector 7, performs digital conversion processing, and outputs the result to the control circuit 9.

Control circuit 9 as arithmetic means and control means
Is mainly composed of a microcomputer or the like, and sets and controls the wavelength λ of the laser light L0 emitted from the laser light source 3 and also uses the information of the wavelength λ and the detection signal from the light receiving circuit 8 to be described later. In this way, a program is stored in advance so as to calculate the thickness of the diaphragm 2 of the SOI substrate 1 by performing arithmetic processing.

Next, the operation of the present embodiment will be described. First, the principle of measurement is explained briefly, and then,
A specific measurement operation will also be described. The control circuit 9
Drive control is performed on the laser light source 3 so as to emit the laser light L0. In this case, the laser light source 3 changes the wavelength λ of the laser light L0 as the measurement light in a wavelength range described later. The rate of change of the wavelength λ is sufficiently faster than the etching rate of the SOI substrate 1, and the film thickness D of the diaphragm 2 is assumed to be a very small etching amount during one sweep.

Next, a wavelength range which is a change range of the wavelength λ of the laser light L0 will be described. Since the buried oxide film 1b is laminated inside the SOI substrate 1, if the component of the light reflected on each of the upper and lower surfaces becomes large, an interference effect on other reflected light occurs, which affects the measurement. Become.
Then, when the intensity of the reflected light from the silicon dioxide film was obtained by simulation to suppress this effect, the result as shown in FIG. 5 was obtained. As described above, the refractive index n0 of the silicon dioxide film is set to 1.45, and the thickness d is set to 2 μm, which is the same thickness as the buried oxide film 1b. The interference condition of the light reflected on the front surface and the back surface is represented by the following equation (a). 2 · n0 · d = m · λ (a)

That is, when the wavelength λ is 1450 nm, the interference condition is satisfied and the reflectance becomes zero. As the wavelength deviates from this wavelength, the reflectance becomes larger. This means
When the laser light L0 having a wavelength out of the interference condition is irradiated, components of light reflected on the front and back surfaces of the buried oxide film 1b become relatively large, and the surface of the SOI layer 1c and the single crystal silicon substrate 1a Means a component that causes interference with the light reflected by the surface portion of.

For example, considering the SOI layer 1c,
In the composite film structure (SOI / SiO2) with the silicon dioxide film corresponding to the buried oxide film, as shown in the simulation result in FIG. 6, a value showing a peak value of 15 μm which is the thickness of the SOI layer is repeated. It can be seen that the reflectance greatly fluctuates due to the influence of the reflected light shown under the condition of the silicon dioxide film thickness of 2 μm. And this SO
The change in the reflected light intensity at the portion corresponding to the I layer greatly affects the peak value corresponding to the entire film thickness of the diaphragm 2 as the film to be measured.

FIG. 7 shows a simulation result assuming the same structure as the structure of the film to be measured. The SOI layer, the buried oxide film, and the silicon substrate were formed at 15 μm, 2 μm, and 20 μm.
The result when m was set is shown. The distribution of the peak corresponding to the entire film thickness D, ie, 37 μm, is a state in which the peak of the film thickness of the SOI layer and the peak of the film thickness of the silicon substrate are mixed, and a complicated peak value appears repeatedly.

In this case, in the wavelength region where the fluctuation of the peak value near the center of the wavelength of 1450 nm in FIG. 6 is small, the change in the peak value in FIG. 7 is the total film thickness of 37 μm.
The peak value is caused by the thickness of the film, and a complex waveform is observed in a wavelength range out of this range. As a result, the wavelength λ, which is the interference condition of the buried oxide film 1b, is 145.
By changing the wavelength of the laser light L0 in the vicinity of 0 nm, generation of a peak due to the thickness of the SOI film 1c can be suppressed. It can be seen that the detection of can be performed with high accuracy.

The above point is that, in the structure shown in FIG. 2, when the laser beam L0 is incident from the SOI layer 1c side of the diaphragm 2, the reflected light component L1 on the surface of the SOI layer 1c and the buried oxide film 1b The reflected light component L2 on the front surface (upper surface), the reflected light component L3 on the rear surface (lower surface), and the single crystal silicon substrate 1
The light is divided into a reflected light component L4 on the lower surface of a and a transmitted light component. In this measurement, since the reflected light component is detected, each of the reflected light components L1 to L4 is incident on the photodetector 7, but the laser light L0 in the wavelength range satisfying the above-mentioned conditional expression is used.
, The reflected light components L2 and L3 interfere with each other, and the reflected light components L1 and L4 mainly enter the photodetector 7.

When the film thickness D is actually detected in accordance with the above-described detection principle, the reflection obtained when the wavelength λ of the laser beam L0 is changed in the wavelength range satisfying the conditional expression (a) described above. A signal indicating light intensity is obtained by performing frequency analysis. When the wavelength λ of the laser light L0 is changed by a fixed amount Δλ (here, 50 nm) in the above-mentioned wavelength range, the reflected light components are reflected light components L1 and L4 depending on the film thickness D of the diaphragm 2, and It changes by interfering with the change.

Accordingly, when the wavelength λ is plotted on the horizontal axis, a waveform is obtained in which the center frequency f is slightly frequency-modulated. Relationship between the thickness D of the center frequency f and the measured film 2, as shown in ^{JP-A-7-306018, D = (λ0 2/} 2 · n1 · Δλ) · f ... (c (Where λ0 is the center wavelength of the laser beam L0, n1 is the refractive index of the film to be measured, ie, silicon, and f is Δλ is the fundamental period (f
= 1 period)).
In this equation (c), other values except the value of the center frequency f on the right side are known, so that the film thickness D of the film 2 to be measured can be obtained by detecting the center frequency f. .

Now, a specific detecting operation for detecting the film thickness D as described above will be described. The laser light source 3 emits the laser light L0 while changing the center wavelength λ0 to 1450 nm and changing the range of 25 nm (Δλ = 50 nm) before and after as the wavelength range (1425 nm to 1475 nm). This wavelength range is a range around the wavelength λ that satisfies the interference condition of the above-described equation (a) when the thickness d of the buried oxide film 1b is 2 μm.

A portion of the diaphragm 2 of the SOI substrate 1 where the etching process is in progress is irradiated with the laser light L 0, and the reflected light is received by the photodetector 7. The light receiving circuit 8 divides the detection signal indicating the intensity of the reflected light output from the photodetector 7 by the characteristic value of the wavelength characteristic of the detection sensitivity measured in advance to obtain the influence of the sensitivity change. And the frequency component outside the range of the interference signal frequency f obtained by substituting the upper and lower limits of the range in which the film thickness of the diaphragm 2 is to be detected into the equation (c) is band-passed. It is removed by a filter, whereby unnecessary information other than information on the film thickness of the diaphragm 2 can be removed.

Next, in the control circuit 9, the light receiving circuit 8
The frequency analysis is performed from the digitally processed signal input from the PC to obtain the spectrum of the interference signal. In this case, as described above, the film thickness D of the diaphragm 2 is 37 μm.
m is taken as an example, and the breakdown is SOI layer 1
c, the thickness D1 is 15 μm, and the thickness d of the buried oxide film 1b is 2 μm.
μm, and the thickness D2 of the single-crystal silicon substrate 1a is 20 μm.

FIG. 3 shows this result. The frequency component f at which the peak value corresponding to the film thickness D of the diaphragm 2 indicates the maximum power (the value of the frequency f is approximately 6 in the peak value in FIG. 3). ). Therefore, by substituting the value of the frequency f into the above equation (c), a value of the film thickness corresponding to the film thickness D of the diaphragm 2 can be obtained.

In FIG. 3, since the wavelength range of the laser beam L0 is changed from 1425 nm to 1475 nm, the reflected light components L2 and L3 on the front and back surfaces of the buried oxide film 1b slightly appear. , This reflected light component L2,
The SOI layer 1c and the single-crystal silicon layer 1a due to L3
Peaks depending on the film thicknesses D1 and D2. However, since the reflected light components L2 and L3 are at levels suppressed by interference, these peaks are also at levels suppressed as compared with the peaks for the film thickness D of the diaphragm 2.

If the inventors satisfy the condition that the peak with respect to the film thickness D of the diaphragm 2 becomes 1 or more with respect to the other peaks as described above, the inventors can make the film thickness D of the diaphragm 2 substantially without hindrance. Assuming that detection is possible, the wavelength range of the laser beam L0 satisfying this condition was determined.

FIG. 4 shows the result. In the measurement of the diaphragm 2 having the above-described structure, the width Δλ of the sweep range of the laser beam L0 is fixed at 50 nm, and the center wavelength λ
When 0 is changed in the range of 1375 nm to 1625 nm at intervals of 25 nm, the ratio of the peak intensity caused by the film thickness D of the diaphragm 2 to the peak intensity caused by the film thickness D1 of the SOI layer 1c is plotted. are doing.

In the above case, corresponding to FIG.
0 is 1475 nm (the sweep range is 1450 nm to 1500
nm), the result is as shown in FIG. Similarly, when the center wavelength λ0 is 1525 nm and when 1625n
In the case of m, the results are as shown in FIGS. 9 and 10, respectively. When the center wavelength λ0 is 1475 nm, S
Although a peak due to the film thickness D1 of the OI layer 1c appears, it does not significantly affect the measurement. Center wavelength λ0
Exceeds 1500 nm, the peak caused by the thickness D1 of the SOI layer 1c becomes larger than the peak caused by the thickness D of the diaphragm 2, as shown in FIGS.

From these results, as shown in FIG. 4, a range in which the peak intensity ratio is 1 or more, that is, a wavelength range suitable for performing measurement is obtained from 1400 nm to 1500 nm.
It turns out that it is the range of. Therefore, if the measurement is performed by selecting the center wavelength λ0 of this wavelength range, the diaphragm 2
, The peak of the film thickness D can be obtained as the maximum value.

From the results, if the measurement is performed in the wavelength range of 1375 nm to 1525 nm including the peak intensity ratio of 1 or more, the peak of the film thickness D caused by the diaphragm 2 can be reliably detected. Accurate film thickness measurement can be performed. The condition indicating the range of the wavelength λ is as follows: 2 · n0 · d / (m + 0.2) ≦ λ ≦ 2 · n0 · d / (m−0.2) (b) (where n0 is embedded The refractive index of the buried oxide film 1b, d is the film thickness of the buried oxide film 1b, and m is a natural number are substantially equivalent to satisfying the relational expression (b). Would be a good choice.

Since the wavelength range suitable for measurement depends on the thickness d of the buried oxide film 1b, if the thickness d changes, the range also changes. For example, in the case shown in FIG. 9, since the thickness d of the buried oxide film 1b is 2 μm, a large peak of the SOI layer 1c appears in the sweep range. Thickness d
Becomes 2.1 μm, as shown in FIG.
The peak caused by the film thickness D1 of b is considerably suppressed.

In other words, even when the wavelength range used for measurement cannot be largely changed, the buried oxide film 1b
The film thickness D of the diaphragm 2 is changed by slightly changing the film thickness of the diaphragm 2.
Can be adjusted so as to maximize the peak caused by. If the device characteristics are not affected even if the thickness d of the buried oxide film 1b is changed, the thickness d of the buried oxide film 1b under conditions suitable for measurement is selected by using this point. You can also.

According to such a first embodiment, the SO
When measuring the film thickness D of the diaphragm 2 having a structure in which the buried oxide film 1b is interposed like the I-substrate 1, the interference condition is determined from the refractive index n0 and the film thickness d of the buried oxide film 1b. By measuring the wavelength λ in the vicinity of the wavelength λ that satisfies 2 · n0 · d = m · λ (a) in the expression (a), the reflection on the front and back surfaces of the buried oxide film 1b is obtained. The light components L2 and L3 can be made to interfere with each other, and the peak value caused by the film thickness D of the diaphragm 2 can be accurately detected. Further, by selecting the range shown in the equation (b) as the wavelength range satisfying the above interference condition, the peak value caused by the film thickness D of the diaphragm 2 is made to have a ratio of 1 or more to other peak values. Measurement.

As a result, the diaphragm 2 is placed on the SOI substrate 1.
It is possible to accurately detect the film thickness D of the diaphragm 2, that is, the etching amount in real time and in a non-contact state during the etching process for forming the etching process, and to accurately detect the stop timing of the etching process. The processing accuracy of the etching process can be improved.

(Second Embodiment) FIG. 12 shows a second embodiment of the present invention.
The second embodiment is different from the first embodiment in that the thickness D of the diaphragm 2 is accurately detected by using a measurement signal of a reference sample. That is, in the first embodiment, since the measurement is performed while changing the wavelength λ of the laser light L0 emitted from the laser light source 3, a configuration that accurately measures the wavelength λ and the absolute value of the change amount is required. . On the other hand, in this embodiment, as a configuration for improving the measurement accuracy, a reference sample 10 having the same configuration as the diaphragm 2 as the film to be measured and having its thickness Dref accurately measured in advance is used. The configuration is adopted.

In FIG. 12, a reference sample 10 as a reference measurement film has the same material and structure as the diaphragm 2 of the SOI substrate 1 shown in FIG.
2, d and the total film thickness D were accurately measured in advance. The reference sample 10 is simultaneously irradiated with the laser light L0 emitted from the laser light source 3. As a reference optical unit, a half mirror 11 is provided instead of the reflecting mirror 4, and the laser light L 0 passing through the half mirror is deflected in the orthogonal direction by the reflecting mirror 12, and is deflected through the half mirror 13 and the lens 14. The reference sample 10 is configured to be irradiated.

The reflected light of the laser light L0 applied to the reference sample 10 is received by the photodetector 15 serving as reference measuring means via the lens 14 and the half mirror 13, and the light receiving circuit 16 performs signal processing. is there. The light detector 15 and the light receiving circuit 16 are configured by the same components as the light detector 7 and the light receiving circuit 8.

When measuring the film thickness D of the diaphragm 2 of the SOI substrate 1, the control circuit 9 simultaneously irradiates the reference sample 10 with the laser light L0 emitted from the laser light source 3 and reflects the reflected light at that time. Light is received by the photodetector 15 and signal processing is performed by the light receiving circuit 16. The signal processing in the light receiving circuit 16 is set to perform the same processing as the signal processing in the light receiving circuit 8. At this time, the wavelength range of the laser light L0 is the same as the wavelength range described in the first embodiment, and is a condition under which reflected light components on the front and back surfaces of the buried oxide film 1b interfere with each other.

Then, in the same manner as described above, the film thickness D of the diaphragm 2 is obtained by analyzing the frequency of the received light signal and comparing it with the detection result from the reference sample 10. Assuming that the frequency obtained from the output signal of the light receiving circuit 16 is fref and the frequency obtained from the output signal of the light receiving circuit 8 is f as described above, the film thickness D and Dref of the two are:
The following relationship holds:

D = (f / fref) · Dref (d) Therefore, the film thickness D of the diaphragm 2 can be accurately measured without accurately measuring the wavelength of the laser light L0 of the laser light source 3. Become.

(Other Embodiments) The present invention is not limited to the above embodiment, but can be modified or expanded as follows. In each of the above embodiments, the method and the configuration for detecting the thickness of the diaphragm 2 by measuring the reflected light are adopted. However, the present invention is not limited to this, and the transmitted light of the laser light L0 applied to the diaphragm 2 is measured. Alternatively, a method or a configuration for detecting the data may be adopted. In this case, since the interference condition of the buried oxide film 1b is different, the appropriate wavelength range of the laser beam L0 is also different. However, if the interference condition is satisfied, the film thickness of the diaphragm 2 is exactly the same in principle. Can be accurately detected.

In each of the above embodiments, the silicon dioxide film interposed in silicon has been described as an example of the heterogeneous film. However, the present invention is not limited to this, and a layer having a different material and a different refractive index may be used for the film to be measured. The present invention can be applied to an interposed structure. The film to be measured can also be applied to a structure in which a plurality of types of films are compositely laminated.

In other words, this means that the present invention can be applied to selectively measuring the thickness of a specific layer on a film to be measured having a structure in which a plurality of types of films are laminated in a complex manner. are doing. That is, in order to set the conditions of reflected light and transmitted light necessary for measuring the thickness of the corresponding film in the laminated film, the unnecessary interference condition of the reflected light is calculated from the film thickness and the refractive index using the formula ( The measurement can be performed by setting the condition of a) so as to obtain a wavelength region in a range where the condition is satisfied, and sweeping the wavelength in the range to perform the measurement.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a measurement system according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a film to be measured.

FIG. 3 is a diagram showing a frequency analysis result when a diaphragm portion is measured by sweeping a laser beam in an optimum wavelength range.

FIG. 4 is a characteristic diagram in which values of ratios of peak levels of a film thickness of a diaphragm and a film thickness of an SOI layer are plotted with respect to a center frequency.

FIG. 5 is a characteristic diagram in which the reflectance when the oxide film is irradiated while changing the wavelength of the laser beam is calculated by simulation.

FIG. 6 is a characteristic diagram in which the reflectance when a laser beam is irradiated while changing its wavelength is calculated by simulation using the structure of an oxide film and an SOI layer as a model;

FIG. 7 is a characteristic diagram in which the reflectance when a laser beam is irradiated while changing its wavelength is calculated by simulation using the structure of a film to be measured as a model;

FIG. 8 is a diagram showing a frequency analysis result when a diaphragm portion is measured by sweeping laser light in different wavelength ranges (part 1).

FIG. 9 is a diagram showing a frequency analysis result when a diaphragm portion is measured by sweeping laser beams in different wavelength ranges (part 2).

FIG. 10 is a diagram showing a frequency analysis result when a diaphragm portion is measured by sweeping laser light in different wavelength ranges (part 3).

FIG. 11 is a diagram corresponding to FIG. 9 when the thickness of the oxide film in the structure of the film to be measured is changed.

FIG. 12 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;

[Explanation of symbols]

1 is an SOI substrate, 1a is a single crystal silicon substrate, 1b is a buried oxide film (heterogeneous film), 1c is an SOI layer, 2 is a diaphragm (measurement film), 3 is a laser light source (measurement light source), 4 is a reflecting mirror 5 is a half mirror, 6 is a lens (optical means), 7
Is a photodetector (measuring means), 8 is a light receiving circuit, 9 is a control circuit (arithmetic means, control means), 10 is a reference sample (reference measuring film), 11 is a half mirror, 12 is a reflecting mirror, 13
Is a half mirror, 14 is a lens, 15 is a photodetector (reference measuring means), and 16 is a light receiving circuit.

Continued on the front page F term (reference) 2F065 AA30 BB13 BB17 CC17 DD04 FF51 GG04 GG12 GG25 HH04 HH13 JJ01 JJ09 JJ15 LL00 LL04 LL12 NN06 QQ03 QQ27 QQ29 RR08 UU01 5F043 AA02 BB02 DD25FF01

Claims (13)

[Claims] A wavelength of a measurement light emitted from a measurement light source to a film to be measured is changed in a transmission light wavelength region of the film to be measured. In the film thickness measuring method for detecting the film thickness of the film to be measured from a change state, wherein the film to be measured has a structure in which a heterogeneous layer made of a material having a different refractive index is laminated inside, The wavelength of the measurement light emitted from the measurement light source is changed by using a wavelength in a range that satisfies a condition of interference generated due to a light component reflected by the heterogeneous layer among the wavelengths in the transmission light wavelength region. A film thickness measuring method for detecting the film thickness of the film to be measured. 2. The method of measuring a film thickness according to claim 1, wherein when measuring the reflected light when the measurement light is applied to the film to be measured to detect the film thickness of the film to be measured, Assuming that the refractive index of the heterogeneous layer is n0 and the film thickness is d, the wavelength λ satisfying 2 · n0 · d = m · λ (a) (where m is a natural number) is used as the interference condition of the measurement light. A method for measuring the thickness of a film, wherein the irradiation is performed while changing the wavelength in the wavelength region described above. 3. The film thickness measuring method according to claim 1, wherein the wavelength range of the measurement light is a film thickness of a film to be measured obtained with respect to a center wavelength when the measurement wavelength range is a constant width. The ratio of the intensity of the peak value corresponding to the above to the intensity of the peak value corresponding to the thickness of the partial layer of the film to be measured divided by the heterogeneous film is set to a wavelength range where the value is 1 or more. Thickness measurement method. 4. The film thickness measuring method according to claim 1, wherein the film to be measured is a silicon layer having an insulating film interposed as the heterogeneous layer, and the measurement wavelength range is A film thickness measuring method characterized by satisfying the following conditional expression (b). 2 · n0 · d / (m + 0.2) ≦ λ ≦ 2 · n0 · d / (m−0.2) (b) (where n0 is the refractive index of the insulating film, d is the thickness of the insulating film,
m is a natural number) 5. The method according to claim 1, wherein the measurement light from the measurement light source is a laser light source capable of changing the oscillation center wavelength continuously or at specific intervals. Characteristic film thickness measurement method. 6. The film thickness measurement method according to claim 1, wherein the measurement light from the measurement light source is applied to a reference measurement film having the same structure as the film to be measured and having a known film thickness. Measuring the intensity of the reflected light or transmitted light and detecting the thickness of the film to be measured from the manner of change and the method of changing the intensity of the reflected light or transmitted light of the film to be measured. Film thickness measurement method. 7. A film thickness measuring apparatus which irradiates a film to be measured with measuring light and detects the intensity of reflected light or transmitted light to detect the film thickness of the film to be measured. A measurement light source that can irradiate the light by changing the wavelength within the transmitted light wavelength region of the film to be measured, and an optical unit that guides the measurement light from the measurement light source to a measurement site of the film to be measured; Measuring means for measuring the intensity of the reflected light or transmitted light of the measuring light applied to the film to be measured; and the thickness of the film to be measured based on the result of the intensity of the reflected light or transmitted light measured by the measuring means. Calculating means for detecting by calculation, the material of the film to be measured as the film to be measured is a material having a different refractive index and a heterogeneous layer made of a material having a different refractive index when the target is the measurement light source Reflect at the heterogeneous layer Thickness measuring apparatus characterized by comprising a control means for causing the measurement so as to change the wavelength of the measurement light in the wavelength region of satisfying the range of the interference caused by the components. 8. The film thickness measuring device according to claim 7, wherein the measuring means is provided to detect a reflected light of the measuring light, and the control means sets a refractive index of the foreign layer to n0, Film thickness d
Then, as the interference condition of the measurement light, the measurement light is changed by changing the wavelength in a wavelength region centered on a wavelength λ satisfying 2 · n0 · d = m · λ (where m is a natural number). A film thickness measuring device, wherein the measuring light source is controlled so as to irradiate. 9. The film thickness measuring apparatus according to claim 7, wherein the control means sets a center of the wavelength range of the measurement light with respect to the measurement light source when the measurement wavelength range is a constant width. The ratio of the intensity of the peak value corresponding to the film thickness of the film to be measured to the wavelength and the intensity of the peak value corresponding to the film thickness of the partial layer of the film to be measured divided by the heterogeneous film is 1 or more. A film thickness measuring apparatus characterized in that the thickness is controlled so as to be set within a range of wavelengths. 10. The film thickness measuring device according to claim 7, wherein when the film to be measured is a silicon layer having an insulating film interposed therein as the heterogeneous layer, the control means: A film thickness measuring apparatus, wherein the measurement light source is set to a measurement wavelength range that satisfies the following conditional expression (b), and control is performed so as to change and output the wavelength of the measurement light. 2 · n0 · d / (m + 0.2) ≦ λ ≦ 2 · n0 · d / (m−0.2) (b) (where n0 is the refractive index of the insulating film, d is the thickness of the insulating film,
m is a natural number) 11. The film thickness measuring apparatus according to claim 7, wherein the measurement light source is a laser light source capable of changing the oscillation center wavelength of the measurement light continuously or at a specific interval. A film thickness measuring device characterized in that: 12. The film thickness measuring device according to claim 7, wherein the reference measurement film has the same structure as the film to be measured and has a known film thickness, and the measurement light source is the reference measurement film. A reference optical system for guiding the film, and a reference measurement unit for measuring the intensity of reflected light or transmitted light of the measurement light applied to the reference measurement film, wherein the calculation unit is measured by the measurement unit. In addition to the result of the intensity of the reflected light or transmitted light, the film thickness of the film to be measured is calculated by referring to the result of the intensity of the reflected light or transmitted light measured by the reference measuring means. A film thickness measuring device characterized by comprising. 13. A measurement light emitted from a measurement light source to a film to be measured of a semiconductor device is changed in wavelength in a transmission light wavelength region of the film to be measured, and the reflected light or the transmitted light is detected. In the method for manufacturing a semiconductor device, wherein the thickness of the film to be measured is detected from a change in the intensity, the film to be measured has a structure in which a heterogeneous layer made of a material having a different refractive index is laminated inside. In the case, the wavelength of the measurement light emitted from the measurement light source, using the wavelength of the range of the wavelength of the transmitted light wavelength range that satisfies the condition of the interference generated due to the light component reflected by the heterogeneous layer. A method for manufacturing a semiconductor device, wherein a thickness of the film to be measured is detected by changing a wavelength.