JP2005084019A - Temperature measuring method of substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure accurately the temperature of a substrate having a plurality of layers even if a thin film layer causing multiple interference exists, concerning a temperature measuring method of the substrate. <P>SOLUTION: A measuring object 31 and a reference light mirror 32 are irradiated with low coherence light from two or more different low-coherence light sources 51, 52, 53 having different center wavelengths, and interference intensities are measured in each wavelength from interference waveforms of reflected light. Then, a mutual ratio in each wavelength is determined and compared with a film thickness-interference ratio characteristic acquired beforehand, to thereby estimate the film thickness of the thin film layer of the measuring object 31. Then, the temperature of the measuring object 31 is determined from the change of an optical path length after subtracting an influence portion of the thin film layer from the interference waveform. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a substrate temperature measuring method.

  It has been proposed to measure an interference waveform from the back side of a multilayer structure using a low coherence interferometer, and to measure the temperature of each layer from the phase change (see Non-Patent Document 1). In this method, the temperature of the sample is measured by measuring the interference waveform between the reflected light and the reference light obtained when the sample is irradiated with low-coherent light and comparing it with that before the temperature change.

"Temperature Measurement Method for Multi-layered Samples Using Optical Fiber Type Low Coherence Interferometer" (Proceedings of the 2001 Kansai Branch Federation of Electrical Engineering Society)

  However, in the prior art, if there is a very thin thin film layer shorter than the wavelength of the low coherent light in the structure having a multilayer structure, the interference waveforms overlap each other and can be recognized as only one interference waveform. As a result, the substrate temperature cannot be measured.

In order to improve this, if the wavelength of the low coherent light is shortened, some materials may be absorbed and not reflected, and an interference waveform may not be obtained. Moreover, as the currently available low-coherence length light source, the one with the center wavelength of 1.3 μm and the lowest coherence has a coherence length of about 2 μm. Can be separated, but the equipment is very expensive and has practical problems.
Furthermore, when the peaks of the interference waveform overlap, there arises a problem that it is impossible to correctly measure a thickness that can be measured correctly.

  The present invention has been made in view of such a point, and an object of the present invention is to measure the temperature of the substrate in a non-contact manner even if an extremely thin film is formed on the substrate to be measured.

  Therefore, the substrate temperature measurement method of the present invention is a method for measuring the temperature of a multi-layer substrate having a thin film layer having a thickness shorter than the coherence length of the low coherence light using low coherence light, Low coherence light is irradiated on the front or back surface of the substrate, the interference between the reflected light from the substrate and the reference light is measured, the interference waveform at that time is regarded as the entire multi-layer substrate, Measuring a deviation (for example, length between peaks, phase deviation, etc.) from a similar interference waveform of a layer substrate, and determining the temperature of the substrate based on a change in optical path length obtained thereby. It is.

  The measurement of the film thickness by measuring the interference waveform is known, for example, in a Michelson interferometer or the like. The principle when an SLD (Super Luminescent Diode) is used as the low coherence light will be described here. For example, FIG. As described above, the light emitted from the low coherence light source 1 is demultiplexed into two by the beam splitter 2. One is reflected by the reference light mirror as reference light, and the other is reflected by the sample A as signal light and returns to the beam splitter 2. Both are combined again by the beam splitter 2 to cause interference, and the interference light signal is received by the light receiver 5.

  At this time, since the coherence length of the low-coherence light source is as short as several tens of μm, the interference range is narrow, and interference occurs only when the optical path lengths of the reference light and the signal light match within the coherent length range. When the sample A is a layer structure such as a semiconductor substrate, light is reflected by each layer. Therefore, the reference light mirror 3 is driven at a constant speed by the drive mechanism 6 and the reference light path length is continuously changed. , An interference waveform having a Gaussian peak is obtained at a position where the optical distances are approximately equal. From this, it becomes possible to measure each film by separating various films, for example, various films, in the depth direction of the sample A which is a layer structure using a low coherence interferometer.

Here, the interference waveform of the low coherence interferometer will be described first. The distances from the beam splitter to the sample and the reference light mirror in the initial state where the reference light mirror 3 is not driven are defined as l ₁ and l ₂ respectively. Let the movement distance of the mirror be Δl.
In the interferometer of FIG. 1, the electric fields of the light waves reflected from the reference light mirror 3 and the sample A are respectively

  The combined electric field E incident on the light receiver 5 is based on the principle of superposition.

The photocurrent i from the light receiver 5 is expressed as follows.

In the low coherence interferometer, the reference light optical path length is changed by driving the reference light mirror 3. When the reference light mirror 3 is moved at a constant speed V, the reference optical path length l ′ ₁ changes as l ′ ₁ = l ′ ₁ + Vt. Here, l ′ ₁ is the optical path to the center of the movable range of the mirror, and t is the time taken to move from the center to a certain point. The frequency of the reference light slightly changes because of the Doppler effect as the reference light mirror 3 moves. The frequency f ₁ received by the reference light mirror 3 is

Then, the light wave having the shifted frequency is reflected from the moving reference light mirror and travels to the beam splitter, which becomes the reference light. Therefore, the frequency f _{2 of the} reference light is

And the Doppler shift frequency fd is

It becomes. Since the optical interference in the optical interferometer using the light source having a wide spectrum width from the expression (1-3) moves the reference light mirror 3 at a constant speed, a large number of reference light frequencies slightly different from each other. It is considered to be the sum of sine functions. The power spectral density at that time

Then the interference light intensity is

And by solving this,

Is required. Here, f ₀ is the center frequency of the light source, and Δf is the full width at half maximum.

  Further, as can be seen from the equation (1-6), the Doppler shift frequency increases in proportion to the scanning speed of the reference light mirror 3. At this time, the interference light intensity is expressed by rewriting equation (1-5) with the amplitude intensity as A (t) and the phase of the interference signal as θ (t).

  From the expressions (1-5) and (1-10), the amplitude intensity A (t) is

  The interference light intensity depends on the speed of the reference light mirror 3 and changes on the beat frequency shifted by the Doppler shift, and an interference waveform having a Gaussian peak is detected.

  By using the low-coherence interferometer that can be explained as described above and obtaining the peak of the Gaussian peak in the interference waveform, the distance between the layer boundaries in the depth direction, for example, the film thickness on the substrate can be known.

  Next, the principle of measuring the temperature of the substrate by measuring such a film thickness will be described. As described above, by using a low-coherence interferometer, it is possible to measure in the depth direction of a measurement object that is a layer structure. Therefore, the temperature change can be measured by detecting the change in the film thickness due to the linear expansion at a certain temperature and the change in the optical path length of each layer due to the change in the refractive index.

The case where the sample A shown in FIG. 1 has the layer structure of the samples A1 and A2 will be described as an example. In FIG. 1, (1) is the surface of the sample 1, and (2) is the sample A1 and the sample. The boundary surface of A2, (3) represents the back surface of the sample A2. Further, the distance from the beam splitter 2 to the reference light mirror 3 in the initial state where the reference light mirror 3 is not moved is defined as l ₁ , and the distance from the sample A as the measurement object is defined as l _2. Let the distance be Δfl. When the film thicknesses of the samples A1 and A2 are d ₁ and d ₂ and the refractive indexes are n ₁ and n ₂ , the optical path length L ₁ of the sample A1 is

It becomes.

Here, when the temperature change is given to each sample, if the temperature at which the optical path length changes due to the change in the film thickness due to the linear expansion and the change in the refractive index changes by ΔT,
Change in film thickness due to linear expansion d ₁ → d ₁ (1 + α ₁ ΔT) (2-2)
Refractive index change n ₁ → n ₁ (1 + β ₁ ΔT) (2-3)
(Α ₁ : linear expansion coefficient of sample A1
β ₁ : Temperature coefficient of change in refractive index of sample A1)
As described above, both the film thickness and the refractive index change. Here, α has no wavelength dependence, but β has wavelength dependence. In other words, if the optical path length when the temperature is changed by ΔT is L ₁ ′,
L ₁ ′ = n ₁ (1 + β ₁ ΔT) × (1 + α ₁ ΔT)
= N ₁ · d ₁ {1+ (α ₁ + β ₁ ) ΔT} (2-4)
The amount of change in the optical path length is
L ₁ ′ − L ₁ = n ₂ {1+ (α ₁ + β ₁ ) ΔT} d ₁ −n ₁ · d ₁
= N ₁ · d ₁ (α ₁ + β ₁ ) ΔT (2-5)
It can be expressed as From these equations, if α ₁ and β ₁ are known, the temperature change ΔT can be obtained.

In addition, the optical path length L _{1 + 2 obtained} by superimposing the sample A1 and the sample A2 is

  Furthermore, when the temperature of the sample changes by ΔT ′, from equations (2-6) and (2-7)

As is clear from the equation (2-7), L ₁ ′ −L ₁ is obtained from the change in the optical path length of the sample A1, so that if α ₂ and β ₂ are known, the film thickness and temperature of each layer can be determined from the change in the optical path length. It can be measured. Therefore, it is possible to measure the temperature of the data by comparing the data before the temperature change and measuring the change in the optical path length.

  From the above, the width of the peak position of the interference waveform changes before and after the temperature change. More specifically, referring to the sample A1 and the sample A2 shown in FIG. 1, when the sample A is heated by, for example, the heater 7 as shown in FIG. 2, the interference waveform is changed before and after the temperature change. The phase is shifted. By reading the phase shift due to this temperature change, it becomes possible to know the temperature change of each sample.

  However, as described above, in the structure having a multilayer structure, when an extremely thin thin film layer shorter than the wavelength of the low coherent light is present, the interference waveforms are overlapped with each other so that only one interference waveform can be recognized. The waveform cannot be separated.

  The inventors have noted that the effect of such a thin film layer on temperature is extremely small compared to other layers. In other words, it is difficult to measure the temperature of an extremely thin film layer shorter than the wavelength of the low coherent light, but after all it is an extremely thin film layer, so the substrate without the thin film layer and other layers are combined. If the temperature of the entire substrate is regarded as the temperature of the entire multilayer substrate having the thin film layer, there is no practical problem. Therefore, the front or back surface of the substrate is irradiated with low-coherence light, the interference between the reflected light from the substrate and the reference light is measured, and the interference waveform at that time is regarded as the entire multi-layer substrate and superimposed (multiplexed) The optical path length obtained by the interfering waveform is treated as being practically acceptable even if it is assumed to be the whole of the target substrate, and the temperature obtained by the change from the optical path length before the change is determined as the substrate (that is, plural It becomes possible to obtain the temperature of the entire layer substrate).

  In addition, the low coherence light referred to in this specification means that having a coherence length of 1 to 100 μm.

When the interference between the reflected light and the reference light causes multiple interference due to the presence of the thin film layer, the overlapped portion has a variation in the phase width corresponding to the overlap as compared with the case where multiple interference does not occur. Usually, the waveform of the interference wave (the waveform of the envelope obtained along the peak value of each interference waveform) curve is slow.
By utilizing this, it is possible to estimate the thickness of the thin film layer that causes multiple interference by taking a pattern of the film thickness-waveform characteristics of the substrate in advance and comparing the measured interference waveform with the pattern.
After that, it is possible to subtract the multiple interference due to the film thickness of the thin film from the measured interference waveform and calculate the optical path length change from the result to determine the temperature of the substrate.

  That is, the envelope of the interference waveform affected by the multiple interference collapses from the normal Gaussian shape. From this waveform analysis, the film thickness of the thin film layer is obtained, and the influence of multiple interference calculated based on the film thickness is removed from the original interference waveform, whereby the temperature of the substrate can be obtained by correcting the Gaussian shape.

  This will be explained with reference to FIG. 3. The multiple interference signal in the thin film layer of the low coherence light source when the back surface incidence of the thin film substrate is performed is

It is represented by here,

  It is. The first term of this equation represents the interference signal at the interface between the substrate and the thin film layer, and the second term is the interference signal at the interface between the thin film layer and the atmospheric layer. The following terms are terms due to multiple interference in the thin film layer.

When the thin film thickness d ₃ is varied, the intensity of the second term following the interference signal changes by the above formula. When the optical path length of the thin film layer is shorter than the coherence length of the low-coherence light source, signals due to multiple interference are superimposed, and the intensity of the obtained interference signal changes. Therefore, by subtracting the second and subsequent terms from the multiple interference signal, the interference signal at the interface between the substrate and the thin film layer can be corrected, and the optical path length of the substrate can be accurately measured even under conditions where the thin film thickness changes. . The temperature can be measured from the change in the optical path length.

  If the multiple interference of the upper thin film layer includes not only the film thickness but also the refractive index change, the difference in the interference waveform affected by the multiple interference is also affected by the temperature using a low-coherence light source with a different wavelength. Using the smallness, the film thickness of the upper thin film layer is obtained from the fringe shape of the difference (envelope obtained along the peak value of each interference waveform). Similarly, the temperature of the substrate is obtained by correcting the influence of multiple interference calculated from this film thickness.

  The specific calculation in this case is the same as the calculation formula described with reference to FIG. 3, and the substrate thickness d2 may be obtained and then calculated by the calculation formula.

  Further, two or more different low coherence lights having different center wavelengths are irradiated on the front surface or the back surface of the substrate, and the thickness of the thin film is estimated by taking the mutual ratio of the maximum amplitude values of each interference waveform, that is, the intensity ratio. Then, multiple interference components may be calculated, subtracted from the interference waveform, and the temperature of the substrate may be determined based on the optical path length change obtained thereby.

  According to the inventor's knowledge, when two or more different low-coherence lights having different center wavelengths are irradiated on the front or back surface of the substrate, the intensity of the interference waveform differs for each low-coherence light having a different wavelength. discovered. Therefore, if the intensity ratio-film thickness characteristic is taken in advance, the film thickness of the thin film layer that causes multiple interference can be calculated by back calculation.

  According to the present invention, even if an extremely thin film that causes multiple interference is formed on a measurement target substrate, the temperature of the substrate can be measured in a non-contact manner.

  Hereinafter, a preferred embodiment of the present invention will be described. FIG. 4 shows an outline of an example of a temperature measurement system, and an SLD is used as the low coherence light source 11. The center wavelength was 1.5 μm and the coherence length was 48 μm. Further, a laser diode having a wavelength of 0.85 μm is used as the displacement measuring light source 12 for measuring the peak deviation width of the interference waveform. That is, the phase shift of the interference waveform can be read by examining the wave number (fringe number) of the interference waveform of the laser beam with respect to the peak of the interference waveform. In this system shown in FIG. 4, a single mode fiber for the 0.85 μm band is used for the optical fiber cable 13 that becomes the optical path and connects the members to form the optical path.

The low-coherence light emitted from the low-coherence light source 11 and the laser light emitted from the displacement measurement light source 12 and passed through the optical isolator 14 are combined by the optical fiber coupler 21 and sent to the optical fiber coupler 22. In the optical fiber coupler 22, the low-coherence light is branched and one is irradiated from the collimating fiber 23 to the measurement object 31 and the other is irradiated from the collimating fiber 24 to the reference light mirror 32. In the present embodiment, the measurement object 31 is prepared by forming a SiO ₂ film on a Si substrate. The reference light mirror 32 can be moved with high accuracy and high speed in the front-rear direction by a voice coil motor 33 that applies the principle of driving a speaker.

  The reflected light from the measurement object 31 and the reflected light from the reference light mirror 32 are irradiated from the collimated fiber 41 to the multilayer mirror 43 in the box 42 via the optical fiber coupler 22. In this multilayer mirror 43, the laser beam for measurement and the low coherence light having an interference waveform are separated, and the laser light is detected by the photodetector 44. The low coherence light having the interference waveform is detected by the photo detector 45. Is detected. The optical signals detected by the photodetectors 44 and 45 are taken into the personal computer 47 for processing via the DAQ card 46, and the interference wave and the like are calculated as data by a necessary calculation program and displayed on the screen. It has become so.

An example of a temperature measurement method using such a temperature measurement system will be described.
(Measurement Example 1)
For example, in the measurement sample 31, when the SiO ₂ film is sufficiently thin relative to the Si substrate and the film thickness is less than 48 μm, the interference waveform due to reflection from the boundary surface between the SiO ₂ film and the Si substrate and the SiO ₂ The peak of the interference waveform cannot be separated. In other words, when the film thickness is large, three interference waveforms should be measurable, but the interference waveforms are superimposed to form multiple interference, so that only two interference wave peaks can be measured. ing. The interference waveform shown in FIG. 5 is shown by an envelope connecting fringe peaks, and only the upper half is shown. In this case, for example, the influence of the SiO ₂ film on the temperature is considered to be sufficiently smaller than that of the Si substrate, and the deviations of the peaks of the two interference waves before and after the temperature change are measured, and the change in the optical path length is determined from this. indexing, the result the temperature calculated on the basis of, by treating the temperature of the SiO ₂ film + Si entire substrate becomes possible to measure the SiO ₂ film + Si substrate overall temperature. Note that the measurement of the inter-peak position can be done by, for example, measuring the number of interference waves of the measurement laser beam, or measuring the interference wave of the measurement laser beam including even the phase shift for more accurate measurement. Good.

(Measurement example 2)
Cause multiple interference due to SiO ₂ thin film layer, when the interference wave due to reflection from the interface between the therefore the SiO ₂ film and the Si substrate is superimposed, the interference waveform is causing multiple interference, its peak When the waveform pattern changes, the interference wave is superimposed when it cannot be separated, but the waveform itself should have a unique shape corresponding to the thickness of the thin film.
Therefore, the film thickness-waveform pattern data is taken in advance and compared with the measured waveform pattern, so that the film thickness of the thin film can be estimated from the measured interference waveform.
If the thickness of the thin film is estimated, the change in the optical path length due to the temperature change of the substrate itself can be seen. Accordingly, the multiple interference due to the film thickness is subtracted from the measured multiple interference waveform, and from the result, the temperature of the substrate itself excluding the influence of the film thickness is calculated from the change in the optical path length of only the substrate. Since the film thickness is so thin that the peaks cannot be separated from each other, the influence is extremely small compared to the substrate. Therefore, there is no practical problem even if this is handled as the film thickness + the temperature of the entire substrate.

  Next, an example of a temperature measurement system using two or more low-coherence light sources having different center wavelengths will be described. In addition, the same code | symbol is attached | subjected to the same member as the temperature measurement system of FIG. 4 shown previously.

  FIG. 6 shows an outline of an example of the temperature measurement system at that time. The low-coherence light source includes three low-coherence light sources 51 to 53 having different center wavelengths of 1.55 μm, 1.40 μm, and 1.31 μm. Using. Both are SLDs and the coherence length is 48 μm. Further, a laser diode having a wavelength of 0.85 μm is used as the displacement measuring light source 54 for measuring the peak deviation width of the interference waveform.

  The low coherence light emitted from the three low coherence light sources 51 to 53 and the laser light emitted from the displacement measurement light source 54 are combined by the optical fiber coupler 21 and further sent to the optical fiber coupler 22 to be collimated. The object 23 is irradiated with low-coherence light having three different center wavelengths from the fiber 23, and at the same time, the reference light mirror 32 is irradiated from the collimating fiber 24.

  The reflected light from the measurement object 31 and the reflected light from the reference light mirror 32 are irradiated to the spectroscope 61 having the diffraction grating in the box 42 from the collimating fiber 41 via the optical fiber coupler 22. Is done. In this spectroscope 61, the laser beam for measurement and the low-coherence light of three wavelengths having the interference waveform are separated, and the laser light is detected by the photodetector 62, and the low-coherence light having the interference waveform is , Detected by the photodetectors 63 to 65 for each wavelength. The optical signals detected by the photodetectors 62 to 65 are taken into the personal computer 47 for processing via the DAQ card 46, and interference waves and the like are calculated as data by a necessary calculation program.

(Measurement Example 3)
The interference between the reflected light from the substrate and the reference light is measured for each low-coherence light, the differential waveform of each interference waveform is calculated, the film thickness of the thin film is estimated, and the multiple interference component is calculated. Is subtracted from the interference waveform, and the temperature of the substrate is obtained based on the change in the optical path length obtained thereby.

More specifically, for example, when an SLD having a center wavelength of 1.55 μm and 1.31 μm is used to form Si of 2 μm and 5 μm on a 1 mm thick SiO ₂ substrate, 1.55 μm SLD output (interference waveform) FIG. 7 (when Si is formed to 2 μm) and FIG. 8 (when Si is formed to 5 μm) are shown as waveforms obtained by subtracting 1.31 μm SLD output (output of interference waveform) from (output). As is apparent from these figures, the waveform pattern varies greatly depending on the film thickness. On the other hand, since the difference waveform does not change depending on the temperature, the film thickness on the substrate can be estimated from this. Based on the film thickness obtained here, as described in the description of the multiple interference signal described above in accordance with FIG. 3, multiple interference components are calculated, and multiple interference is calculated from the observed waveform (for example, a waveform of only 1.55 μm SLD). By subtracting, the interference waveform from only the boundary between the substrate and the thin film can be calculated, and the influence of multiple interference calculated based on the film thickness described above is obtained from the peak position and the interval between the peak positions on the back of the substrate. It is possible to obtain the temperature of the substrate by removing it from the interference waveform and correcting it to a Gaussian shape, that is, a method using the equations (2-1) to (2-7).

(Measurement Example 4)
The mutual ratio of the maximum amplitude value of each interference waveform is taken to estimate the film thickness of the SiO ₂ thin film of the measurement sample 31 to calculate the multiple interference component, which is subtracted from the interference waveform, and the optical path length obtained thereby The temperature of the substrate is obtained based on the change.

(1) When two wavelengths are used Si film (film thickness 1 nm to 500 nm) -Si-SiO when a low coherence of 1.55 μm and 1.31 μm is irradiated to a SiO ₂ substrate having a thickness of 500 nm _The film thickness-interference intensity ratio obtained by calculating the interference intensity at the boundary surface ₂ was as shown in FIG. Here, the interference intensity (au) is obtained by the equation (1-11) described above. That is, the peak value in the interference waveform (envelope) of each wavelength. The interference intensity ratio is a ratio of peak values in the interference waveform (envelope) of each wavelength.

  As shown in FIG. 9, the interference intensity has a result that it is almost periodically changed between about 0.13 and about 0.8 for each wavelength. It can be seen that the interference intensity varies even with the thickness.

  Therefore, when the ratio (1.31 μm wavelength / 1.55 μm wavelength) is taken for each film thickness, the result is as shown in FIG.

Next, the materials of the film and the substrate are exchanged, and Si 2 when the low coherence of the central wavelengths 1.55 μm and 1.31 μm is irradiated to the Si ₂ substrate (film thickness 1 nm to 500 nm) -500 nm thick. The film thickness-interference intensity ratio obtained by calculating the interference intensity at the boundary surface of SiO ₂ is as shown in FIG. Further, when the ratio (1.31 μm wavelength / 1.55 μm wavelength) was taken for each film thickness, the result was as shown in FIG.

According to this, it is not possible to determine at what film thickness the value is simply the ratio value, but the film thickness can be specified even at the same value by following the process of increasing film thickness. Therefore, if it is measured and calculated constantly, the film thickness can be estimated from the values and history before and after that. That is, the thickness of the thin film layer of the Si ₂ SiO ₂ film can be estimated. When the film thickness is sufficiently thin and the film thickness is uniquely determined from the interference intensity ratio, it is not necessary to always measure.
After that, by subtracting the multiple interference amount corresponding to this film thickness from the interference waveform at the Si-SiO ₂ interface, the change in optical path length of only the SiO ₂ substrate and the Si substrate can be read out. The temperatures of the _two substrates and the Si substrate can be measured. By subtracting the multiple interferences for this film thickness from the interference waveform, the optical path length change and temperature change of the substrate alone can be eliminated by removing the influence of the multiple interference calculated based on the film thickness from the original interference waveform. It can be obtained by a method of obtaining the temperature of the substrate by correcting to a Gaussian shape.

(2) When 3 wavelengths are used Si film (film thickness 1 nm to 500 nm)-Three low coherence lights with center wavelengths of 1.55 μm, 1.40 μm, and 1.31 μm are applied to a SiO ₂ substrate having a thickness of 500 nm. The film thickness-interference intensity ratio obtained by calculating the interference intensity at the Si—SiO ₂ boundary surface when irradiated was as shown in FIG.

  Further, when the ratio (1.31 μm wavelength / 1.55 μm wavelength, 1.40 μm wavelength / 1.55 μm wavelength, 1.40 μm wavelength / 1.55 μm wavelength) is taken for each film thickness, as shown in FIG. Became.

Next, the materials of the film and the substrate are switched, and three low coherences with the center wavelengths of 1.55 μm, 1.40 μm, and 1.31 μm are applied to the SiO ₂ film (film thickness 1 nm to 500 nm) -500 nm thick Si substrate. FIG. 15 shows the film thickness-interference intensity ratio obtained by calculating the interference intensity at the Si—SiO ₂ boundary surface when. Further, when the ratio (1.31 μm wavelength / 1.55 μm wavelength, 1.40 μm wavelength / 1.55 μm wavelength, 1.40 μm wavelength / 1.55 μm wavelength) is taken for each film thickness, as shown in FIG. Became.

  According to this, in any case, it is possible to estimate the film thickness simply by using the ratio values by using the three ratio values. Therefore, the film thickness of the thin film layer that causes multiple interference can be obtained by measuring only at a specific time without monitoring and measuring the progress and history of the film thickness change. Thereafter, the multiple interference due to the thin film layer is subtracted from the interference waveform, the optical path length obtained thereby is compared with the optical path length before the temperature change, and the temperature is obtained from the change. The LD interference waveform is used when obtaining the last optical path length change.

  When the temperature change is 100 ° C or higher, the change in the refractive index difference due to the difference in wavelength due to the temperature can be neglected by about three orders of magnitude compared to the simple temperature change in the refractive index. Is possible.

  The present invention is not limited to the case where a thin film layer causing multiple interference is formed on the uppermost surface of the substrate, but also to a multi-layer substrate in which the thin film layer exists in an intermediate layer of a substrate having a multilayer film structure of three or more layers. It can also be applied to.

  In the present invention, since the film thickness of an extremely thin film layer can be estimated, the present invention can be used for film thickness measurement and can be measured even during the process. It can be used for end point detection in the etching process.

  Since the present invention can measure the temperature of a substrate having an extremely thin film in a non-contact manner, for example, in the manufacturing process of a semiconductor device or FPD, the temperature of the substrate in etching or CVD processing is measured, and a suitable process is performed. Suitable for realization.

It is the schematic of the interferometer for showing the principle of a low coherence optical interferometer. It is explanatory drawing which shows the mode of the interference wave for showing the principle of a low coherence optical interferometer. It is explanatory drawing which shows the mode of multiple interference. It is explanatory drawing which shows the outline of the temperature measurement system using the low-coherence light source of 1 wavelength. It is explanatory drawing which shows the interference waveform which has caused the multiple interference in the two-layer structure which has a thin film layer. It is explanatory drawing which shows the outline of the temperature measurement system using the low-coherence light source of 2 wavelengths or more. It is a graph of a waveform obtained by subtracting an interference waveform output by a 1.31 μm SLD from an interference waveform output by a 1.55 μm SLD when 2 mm of Si is formed on a 1 mm thick SiO ₂ substrate. It is a graph of a waveform obtained by subtracting an interference waveform output by a 1.31 μm SLD from an interference waveform output by a 1.55 μm SLD when 5 mm of Si is formed on a 1 mm thick SiO ₂ substrate. It is a graph of the film thickness-interference intensity characteristic in two wavelengths by Si film thickness change. 10 is a graph of film thickness-interference intensity ratio characteristics based on the results of FIG. Film thickness at two wavelengths by SiO ₂ film thickness changes - is a graph of the interference strength properties. It is a graph of the film thickness-interference intensity ratio characteristic based on the result of FIG. It is a graph of the film thickness-interference intensity characteristic in 3 wavelengths by Si film thickness change. It is a graph of the film thickness-interference intensity ratio characteristic based on the result of FIG. Film thickness at three wavelengths by SiO ₂ film thickness changes - is a graph of the interference strength properties. It is a graph of the film thickness-interference intensity ratio characteristic based on the result of FIG.

Explanation of symbols

11, 51, 52, 53 Low coherence light source 12, 54 Light source for displacement measurement 21, 22 Optical fiber coupler 31 Object to be measured 32 Reference light mirror 43 Multilayer mirror 44, 45, 62, 63, 64, 65 Photo detector 61 Spectroscopy vessel

Claims (6)

A method for measuring the temperature of a multi-layer substrate having a thin film layer having a thickness shorter than the coherence length of the low coherence light by using low coherence light,
Irradiating the front or back surface of the substrate with the low-coherence light, measuring the interference between the reflected light from the substrate and the reference light, and considering the interference waveform at that time as the entire multilayer substrate;
A method for measuring a temperature of a substrate, comprising: measuring a deviation from an interference waveform of the multi-layer substrate before a temperature change, and obtaining a temperature of the substrate based on a change in an optical path length obtained thereby. A method for measuring the temperature of a multi-layer substrate having a thin film layer having a thickness shorter than the coherence length of the low coherence light by using low coherence light,
Irradiating the front or back surface of the substrate with the low-coherence light, measuring the interference between the reflected light from the substrate and the reference light, and considering the interference waveform at that time as the entire multilayer substrate,
The film thickness of the thin film layer is estimated by comparing with the waveform pattern of the film thickness characteristic of the interference waveform of the multilayer substrate obtained in advance,
Subtract multiple interference due to the film thickness from the interference waveform,
From the result, the optical path length change is calculated to obtain the temperature of the substrate,
Substrate temperature measurement method. A method for measuring the temperature of a multi-layer substrate having a thin film layer having a thickness shorter than the coherence length of the low coherence light by using low coherence light,
Irradiating the front or back surface of the substrate with two or more different low coherence lights having different center wavelengths;
Measure the interference between the reflected light from the substrate and the reference light for each low coherence light,
The film thickness of the thin film layer is estimated from the difference waveform of each interference waveform, and the multiple interference due to the thin film layer is calculated.
Subtracting this from the interference waveform and determining the temperature of the substrate based on the change in the optical path length obtained thereby, the substrate temperature measuring method. A method for measuring the temperature of a multi-layer substrate having a thin film layer having a thickness shorter than the coherence length of the low coherence light by using low coherence light,
Irradiating the front or back surface of the substrate with two or more different low coherence lights having different center wavelengths;
Estimating the film thickness of the thin film layer by taking the mutual ratio of the maximum amplitude value of each interference waveform, and calculating the multiple interference due to the thin film layer,
Subtracting this from the interference waveform and determining the temperature of the substrate based on the change in the optical path length obtained thereby, the substrate temperature measuring method. The substrate temperature measuring method according to claim 1, wherein the film is formed on an uppermost surface of the substrate. 6. The substrate temperature measuring method according to claim 1, wherein the multi-layer substrate is a multilayer substrate having three or more layers.

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