CN106840000B - A kind of method of the white light reflection measurement film thickness of fraction Fourier conversion - Google Patents
A kind of method of the white light reflection measurement film thickness of fraction Fourier conversion Download PDFInfo
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- CN106840000B CN106840000B CN201710011662.2A CN201710011662A CN106840000B CN 106840000 B CN106840000 B CN 106840000B CN 201710011662 A CN201710011662 A CN 201710011662A CN 106840000 B CN106840000 B CN 106840000B
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- white light
- film thickness
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- light reflectance
- fourier conversion
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
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Abstract
The invention discloses a kind of methods of the white light reflection of fraction Fourier conversion measurement film thickness.White light reflectance spectrum signal has been carried out fraction Fourier conversion by the present invention, filters out noise signal on the Fourier domain of signal, is quickly judged finally by the characteristic value for seeking filtered signal film thickness to be measured.Good wave filtering effect of the present invention, fast speed can preferably distinguish the difference between useful signal and noise, improve the accuracy rate that characteristic value judges film thickness.
Description
Technical field
The invention belongs to optical precision measurements and field of signal processing, specifically design a kind of using fraction Fourier conversion
Processing is carried out to judge the method for film thickness to white light reflectance spectrum signal.
Background technique
The measurement of film thickness film photovoltaic power generation, semiconductor chip production, optical coating etc. nanoscale or
Secondary nanophase application has vital effect.More specifically, either film power generation photoelectric characteristic, semiconductor chip
Performance or optical anti-reflection coating directly affected by film thickness.Therefore, Dynamic High-accuracy measures in process
Thin film layer thickness just seems very necessary.
White light reflectance spectrum (white light reflectance spectroscopy, WLRS) is a kind of high-precision
Measure film thickness method.The specific measurement model of white light reflectance spectrometry film thickness is as shown in Fig. 1.Its principle is benefit
It is right in the case where non-contact object surface with there is one-to-one relationships between white light reflectance spectrum and film thickness to be measured
Film to be measured is into measurement.Its full accuracy even can achieve nanoscale, Subnano-class, but dynamic measures in process
White light reflectance spectrum often introduces a large amount of noise, and the frequency band of these noises often has part with useful signal frequency band again
Overlapping causes measurement error.Therefore, being analyzed and processed using correct quickly algorithm to white light reflectance spectrum signal is just seemed
It is most important.
Traditional Fourier transform is that signal is rotated pi/2 from time shaft, so that signal be made to rotate from time shaft to frequency
On axis, and fraction Fourier conversion (fractional Fourier transform, FrFT) and traditional Fourier transform
Difference, it can do signal on time shaft and frequency axis rotates at any angle, divides under any angle signal
Analysis.Therefore, the Time-Frequency Information of signal can more be utilized.
In the time domain, the rotational invariance according to Wigner-Ville distribution for fraction Fourier conversion, fractional order
Fourier can be regarded as signal on the fractional order Fourier domain u that Time Domain Planar is constituted after origin any rotation α
Expression, Wigner-Ville transformation, the existing only rotationally-varying relationship of coordinate between short time discrete Fourier transform, not
Influence the time domain distribution character of signal.This property can in the case where non-stationary process, using fractional Fourier come
Time-frequency Filter is realized, thus also available better filter effect under the premise of reducing computational expense.
Summary of the invention
In view of the above-mentioned deficiencies in the prior art, it is an object of the present invention to provide it is a kind of using fraction Fourier conversion to white light
Reflectivity spectral signal carries out quickly processing to the method for accurate judgement film thickness.
Technical solution used by this method, comprising the following steps:
1) white light source vertical irradiation film to be measured is utilized, white light reflectance is obtained by optical monitoring system and composes original letter
Number；
2) the resulting white light reflectance spectrum original signal of step 1 is subjected to the Fourier transform of initial score rank, obtained original
The initial Time-Frequency Information of signal；
3) the initial Time-Frequency Information of the obtained original signal of analytical procedure 2, obtains fraction Fourier conversion and most preferably revolves
Gyration α and order p, and p rank fraction Fourier conversion is carried out to white light reflectance spectrum original signal, it obtains postrotational
White light reflectance composes Time-Frequency Information；
4) the resulting postrotational white light reflection spectrum Time-Frequency Information of step 3 is subjected to the filtering of time window function, is filtered
White light reflectance afterwards composes Time-Frequency Information；
5) the filtered white light reflectance spectrum Time-Frequency Information obtained step 4 carries out p rank fractional Fourier inverse transformation,
Obtain filtered white light reflectance spectrum signal；
6) characteristic value is extracted to the filtered white light reflectance spectrum signal that step 5 obtains, is acquired by characteristic value to be measured
The film thickness of film.
The beneficial effects of the present invention are: good wave filtering effect, fast speed can preferably distinguish useful signal and noise
Between difference, improve the accuracy rate that characteristic value judges film thickness.
Detailed description of the invention
Fig. 1 measurement model；
Fig. 2 present invention is whole to realize procedural block diagram；
The white light reflectance of different-thickness composes dynamic measurement results figure (500-550nm) before Fig. 3 is filtered；
Characteristic parameter distribution map (500-550nm) before Fig. 4 is filtered；
Fig. 5 film white light reflectance composes fast Flourier result figure (film thickness: 500nm)；
White light reflectance time-frequency figure (film thickness: 500nm, p=0.82) after Fig. 6 fraction Fourier conversion；
The filtered white light reflectance time-frequency figure of Fig. 7 (film thickness: 500nm)；
The white light reflectance spectrogram (500-550nm) of different-thickness after Fig. 8 filtering；
Characteristic parameter distribution map (500-550nm) after Fig. 9 filtering；
Specific embodiment
Below in conjunction with attached drawing, 2 couples of present invention are further illustrated.
1) white light source vertical irradiation film to be measured is utilized, white light reflectance is obtained by optical monitoring system and composes original letter
Number；
Specifically: dynamic measurement is consistent in principle with static measurement, and detailed measurements model is as shown in Fig. 1.It will
Beam of white light A is to inject film to be measured close to 0 ° of incidence angle.Wherein, incidence angle maximum angle is no more than ± 5 °.
Since incident light is in interface S1、S2On repeatedly carry out optical path difference caused by refraction reflection so that each wavelength light is in difference
Different reflectivity is shown in the case where film thickness.It is acquired by the sampling fibre-optical probe of optical monitoring system in signal acquisition region
Project light B1、B2、…、Bn, the reflectivity of each wavelength light is calculated, obtains last white light reflectance spectrum original signal.
2) the resulting white light reflectance spectrum original signal of step 1 is subjected to the Fourier transform of initial score rank, obtained original
The initial Time-Frequency Information of signal；
Specifically: the Fourier transform of initial score rank is only merely to obtain optimal rotation angle and best score rank to be subsequent
Order is prepared, theoretically can be with Any Order.For ease of calculation, initial order p will be set0It is 0.
3) the initial Time-Frequency Information of the obtained original signal of analytical procedure 2, obtains fraction Fourier conversion and most preferably revolves
Gyration α and order p, and p rank fraction Fourier conversion is carried out to white light reflectance spectrum original signal, it obtains postrotational
White light reflectance composes Time-Frequency Information；
Specifically: since the energy in effective white light signal time-frequency figure is more concentrated and energy is larger in narrow line style,
And noise signal is then relatively dispersed.
It sets the point in Time-Frequency Information greater than ceiling capacity one third and most energy area blocks occurs as useful signal
Region.
Linear fitting is carried out to useful signal region, finds out slope k.It then can be according to α=tan-1(- k), p=2 α/π are found out
The order p of optimal rotation angle α and fraction Fourier conversion.
4) the resulting postrotational white light reflection spectrum Time-Frequency Information of step 3 is subjected to the filtering of time window function, is filtered
White light reflectance afterwards composes Time-Frequency Information；
Specifically: time window function is provided mainly to just depending on useful signal area size in concrete signal time-frequency figure
Effective energy region is covered well.
5) the filtered white light reflectance spectrum Time-Frequency Information obtained step 4 carries out p rank fractional Fourier inverse transformation,
Obtain filtered white light reflectance spectrum signal；
6) characteristic value is extracted to the filtered white light reflectance spectrum signal that step 5 obtains, is acquired by characteristic value to be measured
The film thickness of film.
Specifically: ask optical wavelength corresponding to the last one wave crest of filtered white light reflectance spectrum signal to be characterized
Value, there is certain linear relationships with film thickness to be measured for characteristic value, and the thickness of film to be measured can be found out by this feature value
Degree.
The content of present invention is further expalined below by way of example, with this method to the white light reflectance of practical film thickness
Spectrum signal is analyzed.50 white light reflectances spectrum of 1nm is divided between 500-550nm with the film thickness of practical dynamic measurement
For, as shown in Fig. 3, wherein 5 curves are only shown here.It can be introduced unavoidably during dynamic measures white light reflectance
Certain noise, so that calculating film thickness with characteristic value produces certain error, it is difficult to accurate discrimination actual film depth information,
It is specifically shown in shown in attached drawing 4, can not find out apparent linear relationship.White light reflectance spectrum is complex, does not also fix relatively
Frequency range, and noise band is often with the frequency band of useful signal in the presence of partly overlapping in the measurements, so being used for traditional
Fourier transform can not then find out the useful component in signal, and signal all concentrates on nearly direct current region, as shown in Fig. 5.Therefore,
It is fixed frequency range tradition filtering algorithm useful signal is then difficult to separate with noise signal.Therefore to white light reflectance
Spectrum signal carries out 0 rank fraction Fourier conversion, slope k ≈ -3.442 is found out, so 1.2881 (arc of optimal rotation angle α ≈
Degree system).Best score rank order can be found out in 500nm by α, best score rank Fourier transform order p is equal to 0.82,
Time-frequency figure is shown in attached drawing 6.There are more noise, letter in intermediate narrow range in white light reflectance spectrum signal two sides as can be seen from Figure
It number is in filament type, energy more concentrates, and can be determined as useful signal part.To the Time-Frequency Information after fraction Fourier conversion
Window function filtering is carried out, filters out the useless noise signal in two sides, filter result is as shown in Fig. 7.To filter out after noise signal when
Frequency information carries out 0.82 rank fractional Fourier inverse transformation, obtains filtered white light reflectance spectrogram, so analogizes, by 500-
The signal of 550nm all does following processing, and as a result as shown in Fig. 8, treated, and waveform is relatively smooth, and filter effect is good.It is right
Filtered white light reflectance spectrum seeks optical wavelength corresponding to its last one wave crest, draws the curve of characteristic value and film thickness,
Obtained result is as shown in Fig. 9, and characteristic value and film thickness are in line style distribution substantially, preferable can must distinguish corresponding to each characteristic value
Film thickness situation.
Claims (6)
1. a kind of method of the white light reflection measurement film thickness of fraction Fourier conversion, which comprises the steps of:
1) white light reflectance is obtained by optical monitoring system to irradiate film to be measured close to 0 ° of incidence angle using white light source
Compose original signal；
2) the resulting white light reflectance spectrum original signal of step 1) is subjected to the Fourier transform of initial score rank, obtains original signal
Initial Time-Frequency Information；
3) analytical procedure 2) obtained original signal initial Time-Frequency Information, obtain the best rotation angle of fraction Fourier conversion
α and order p is spent, and p rank fraction Fourier conversion is carried out to white light reflectance spectrum original signal, obtains postrotational white light
Reflectivity spectral Time-Frequency Information；
4) the resulting postrotational white light reflection spectrum Time-Frequency Information of step 3) is subjected to the filtering of time window function, obtained filtered
White light reflectance composes Time-Frequency Information；
5) the filtered white light reflectance spectrum Time-Frequency Information obtained step 4) carries out p rank fractional Fourier inverse transformation, obtains
To filtered white light reflectance spectrum signal；
6) characteristic value is extracted to the filtered white light reflectance spectrum signal that step 5) obtains, film to be measured is acquired by characteristic value
Film thickness.
2. a kind of method of the white light reflection measurement film thickness of fraction Fourier conversion according to claim 1, feature
It is being the step 1) specifically: by beam of white light to inject film to be measured close to 0 ° of incidence angle；Wherein, incidence angle is maximum
Angle is no more than ± 5 °；
Incident light repeatedly carries out optical path difference caused by refraction reflection in film interface to be measured and base interface, so that each wavelength light
Different reflectivity is shown in the case where different film thickness；By the sampling fibre-optical probe of optical monitoring system in signal acquisition area
Light is projected in domain acquisition, calculates the reflectivity of each wavelength light, obtains last white light reflectance spectrum original signal.
3. a kind of method of the white light reflection measurement film thickness of fraction Fourier conversion according to claim 1, feature
It is, sets initial order as 0 in the initial score rank Fourier transform of the step 2).
4. a kind of method of the white light reflection measurement film thickness of fraction Fourier conversion according to claim 1, feature
It is, the step 3) is specifically:
It sets the point in Time-Frequency Information greater than ceiling capacity one third and most energy area blocks occurs as useful signal region；
Linear fitting is carried out to useful signal region, finds out slope k；Then according to a=tan-1(- k), p=2 α/π find out best rotation
The order p of gyration α and fraction Fourier conversion.
5. a kind of method of the white light reflection measurement film thickness of fraction Fourier conversion according to claim 1, feature
It is, the time window function in the step 4) is main to be arranged depending on useful signal area size in concrete signal time-frequency figure
To be just covered with effect energy area.
6. a kind of method of the white light reflection measurement film thickness of fraction Fourier conversion according to claim 1, feature
It is, the step 6) is specifically: seeking light wave wave corresponding to the last one wave crest of filtered white light reflectance spectrum signal
A length of characteristic value, there is certain linear relationships with film thickness to be measured for characteristic value, find out film to be measured by this feature value
Thickness.
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| CN107462176A (en) * | 2017-08-17 | 2017-12-12 | 中国计量大学 | White light reflection dynamic measurement film thickness method based on Mallat algorithms |
| CN107887289B (en) * | 2017-11-13 | 2021-03-09 | 北京半导体专用设备研究所（中国电子科技集团公司第四十五研究所） | Method and device for obtaining parameter value of film to be measured |
Citations (4)
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| JPS56115905A (en) * | 1980-02-19 | 1981-09-11 | Unitika Ltd | Measuring method for thickness of transparent film and device therefor |
| EP1467177A1 (en) * | 2003-04-09 | 2004-10-13 | Mitsubishi Chemical Engineering Corporation | Method and apparatus for measuring thicknesses of layers of multilayer thin film |
| CN101514888A (en) * | 2008-02-22 | 2009-08-26 | 横河电机株式会社 | Apparatus and method of measuring film thickness |
| CN106123805A (en) * | 2016-08-15 | 2016-11-16 | 华南师范大学 | The plated film device three-dimensional topography measurement method interfered based on white light scanning |
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- 2017-01-07 CN CN201710011662.2A patent/CN106840000B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56115905A (en) * | 1980-02-19 | 1981-09-11 | Unitika Ltd | Measuring method for thickness of transparent film and device therefor |
| EP1467177A1 (en) * | 2003-04-09 | 2004-10-13 | Mitsubishi Chemical Engineering Corporation | Method and apparatus for measuring thicknesses of layers of multilayer thin film |
| CN101514888A (en) * | 2008-02-22 | 2009-08-26 | 横河电机株式会社 | Apparatus and method of measuring film thickness |
| CN106123805A (en) * | 2016-08-15 | 2016-11-16 | 华南师范大学 | The plated film device three-dimensional topography measurement method interfered based on white light scanning |
Non-Patent Citations (1)
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| 白光反射谱测薄膜厚度实验;刘滢滢等;《仪器仪表标准化与计量》;20080226(第01期);第45-46页 * |
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Application publication date: 20170613 Assignee: Xinchang China Metrology University Enterprise Innovation Research Institute Co.,Ltd. Assignor: China Jiliang University Contract record no.: X2021330000071 Denomination of invention: A method of measuring film thickness by white light reflection based on fractional Fourier transform Granted publication date: 20190101 License type: Common License Record date: 20210816 |
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Assignee: Xinchang China Metrology University Enterprise Innovation Research Institute Co.,Ltd. Assignor: China Jiliang University Contract record no.: X2021330000071 Date of cancellation: 20211231 |