CN1363820A - Short-pulse laser and ultrasonic method and equipment for presisely measuring thickness - Google Patents
Short-pulse laser and ultrasonic method and equipment for presisely measuring thickness Download PDFInfo
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- CN1363820A CN1363820A CN 02100479 CN02100479A CN1363820A CN 1363820 A CN1363820 A CN 1363820A CN 02100479 CN02100479 CN 02100479 CN 02100479 A CN02100479 A CN 02100479A CN 1363820 A CN1363820 A CN 1363820A
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Abstract
The invention discloses a method and device for accurately measuring thickness by using short pulse laser and supersonic wave. Sound wave is excited on the front surface of the specimen to be measured by ultra fast beam of short pulse laser. When transmitting to the back surface of the specimen, the sound wave causes distortion of the back surface. First deflection of another detecting light reflected from the back surface occurs caused by said distortion. The sonic pulse reaches to the back surface then reflected to the front surface and back to the back surface again so as to complete a reflecting cycle. At the time, the detecting light detects second deflection with a delay between the two deflections. The sickness of the specimen is equal to that the time deference between the two deflections multiplies sound transmitting speed and divides two. The device is composed of light source, beam splitter, focusing system and receiving system. Thickness of very thin single specimen and difference of thickness can be measured by the method and the device.
Description
Technical field: the invention belongs to the Technology of Precision Measurement field, especially a kind of method and apparatus that the less device of size is carried out precision measurement.
Background technology: various size of devices are more and more littler in the current high-tech area, thus the monitoring that needs to have more and more higher degree of accuracy technically.In these monitoring, the precision measurement of thickness of sample has occupied important status.Widely used PULSE method in microelectronics industry is a kind of psec ultrasound wave laser sonar technology in recent years, and it is used to measure the thickness of the metal film of single or multiple lift, and measurement range micron does not wait from 20 nanometers to 5.But the shortcoming of this technology is, the surface of testing sample has one deck coating at least, thereby can make light activated sound pulse to return from the surface reflections of two kinds of different mediums, and reflected sound wave is got off by instrument record, obtains the data of thickness.Therefore, this method can not be carried out thickness measuring to the sample of individual layer especially material such as semiconductor.
Summary of the invention: the purpose of this invention is to provide a kind of the need, can carry out the technology of accurate thickness measuring to the individual layer testing sample at sample surfaces coating.
The ultrasonic accurate thickness measuring method of short-pulse laser of the present invention is to utilize ultrafast short pulse laser beam in sample front surface excite sound waves, when sound wave passes to the rear surface, cause that deformation takes place in the sample rear surface, deflection for the first time can take place owing to current deformation from sample rear surface detection light reflected in another bundle; Sound pulse arrives behind the rear surface again from the rear surface to front surface reflection, and a periods of reflections is finished in return reflection surface rear surface in the past again, at this moment surveys light and will detect the deflection second time of certain delay was arranged on the time; The mistiming of twice deflection be multiply by the velocity of propagation of sound wave in sample, is exactly sample thickness divided by two again.
In the electric light of described laser pulse process high frequency or the frequency range that acousto-optic modulator is modulated at MHz.
Realize that the measuring thickness device of above-mentioned thickness measuring method is made up of following components:
(1) light source: adopt pulsed laser;
(2) beam splitting system: the light beam that light source is provided is divided into pumping and surveys the two-way light beam;
(3) focusing system: with pump light with survey light two-way light beam and gather front and rear surfaces respectively at sample, pump light excites ultrafast sound wave at front surface, sound wave is delivered to the rear surface of sample, can cause the miniature deformation of rear surface, do the appearance of the detection light meeting of mirror reflection simultaneously from the rear surface, and small angular deflection takes place owing to this deformation;
(4) receiving system: form by a photoelectricity position sensitive detector and signal processing system, the photoelectricity position sensitive detector is a small photoelectric device that moves forward into line item to light beam, when surveying the rear surface reflex time of light from sample, when the rear surface does not have deformation, we aim at beam reflected at the center of position sensitive detector, at this moment the signal from position sensitive detector output is zero, when deformation produces, surveying light can be because small angular deflection takes place in the inclination of reflecting surface, and this small deflection angle is directly proportional owing to sound pulse arrives the deformation that causes with the rear surface; Simultaneously, beam deflection is exactly a hot spot in small the moving in its surface for position sensitive detector, and this moves and can make position sensitive detector produce certain photocurrent, and photocurrent outputs to signal processing system, just can obtain the information about the surface deformation size.Postpone by the relative time of regulating pump light and detection light, we can note the rear surface owing to sound pulse arrives the whole process of deformation that produces, just the waveform of the sound wave that record is next complete.Acoustic waveform can be used for that first sound is arrived the sample rear surface and carry out point-device processing with the mistiming of the sample of sound wave arrival for the second time rear surface, thereby obtains the parameter of thickness of sample.
Described device also comprises the electric light or the acousto-optic modulator of a high frequency, and the beam modulation that is used for light source is provided is in the frequency range of MHz.
Can be with method and apparatus of the present invention to extremely thin individual layer sample thickness, and the difference of thickness is measured, there is different fluctuatings on surface such as a slice sample, means that the time that sound pulse is passed through can be variant, and this difference can be noted very accurately.
Be to test on 100 microns the monocrystalline germanium with method and apparatus of the present invention at thickness, when the thickness of laboratory sample is respectively 114 microns and 114.5 microns, obtain two curves, the mistiming of its peak value, be exactly the time delay of sound pulse by different-thickness, it is very good that experimental result and Theoretical Calculation meet.
This method is very simple, implement easily, and measurement is touchless to sample thickness, need not again to sample process (as in the PULSE method at the overlay coating of sample), applicable scope is very extensive, can measure the thickness of various solid materials.Can use the electric light or the acousto-optic modulator of high frequency in addition, laser beam is modulated in the frequency range of MHz, the noise that this frequency range inner laser band comes can reduce greatly, be reduced to the level of shot noise, the mechanical noise that cause this moment because experiment porch etc., the noise that the shake of laser beam in the space causes etc. can be eliminated effectively.So this high frequency modulated can improve the signal to noise ratio (S/N ratio) of experiment measuring significantly, this just means that we can measure more small thickness of sample difference, can reach higher degree of accuracy during measuring samples thickness.
Description of drawings:
Fig. 1 is the structural representation of measuring thickness device of the present invention
1-titanium sapphire femto-second laser; The 2-laser beam; The 3-spectroscope; The 4-pump light; 5-surveys light; 6, the 7-level crossing; 8, the 11-prism; The 9-digital delay line; 10-copped wave dish; 12,14, the 15-convex lens; The 13-laboratory sample; The 16-position sensitive detector; The 17-lock-in amplifier.
Fig. 2 obtains the acoustic waveform synoptic diagram of a periods of reflections for lock-in amplifier.
Among the figure, T1 is the time of the crest of sound wave that laser pulse excites at the sample front surface first sound wave that lock-in amplifier extracts when passing to the rear surface; T2 is the time of the crest of first sound wave second sound wave that in the past lock-in amplifier extracts during the return reflection surface rear surface again after front surface reflection from the rear surface.
Embodiment:
As shown in Figure 1, light source adopts titanium sapphire femto-second laser 1, its output wavelength is 830nm (nanometer), pulsewidth is the laser beam 2 of 120fs (femtosecond), the average power of laser is 1W, be divided into pump light 4 and survey light 5 two-way through spectroscope 3, pump light 4 is through a digital delay line, then by of the frequency copped wave of a mechanical copped wave dish 10 with 1200Hz, focus on the front surface of laboratory sample 13 by the focal length convex lens 12 that are 10cm, the convex lens 14 that detection light 5 is 6cm by a focal length focus on the rear surface, because pump light 4 acts on laboratory sample 13 front surfaces and excites ultrafast sound wave, when this sound wave passes to the rear surface, cause the immediate set on surface, survey light 5 and have small angular deflection, this deflection is noted by position sensitive detector (PSD) 16, position sensitive detector 16 produces certain photocurrent, photocurrent outputs to lock-in amplifier 17, lock-in amplifier 17 has the characteristic of surveying feeble signal, can from very complicated waveform, extract the required signal that is modulated at certain frequency (in our experiment, being 1200Hz), obtain surface deformation size time dependent process, the i.e. waveform of a sound wave.When sound wave reflexes to front surface when going back to the rear surface by front surface reflection again from the rear surface, lock obtains the waveform of a sound wave once more to amplifier 17, thereby obtains the acoustic waveform (as shown in Figure 2) of a periods of reflections.Then the mistiming (T2 subtracts T1) of the waveform of gained is analyzed, can be learnt sample thickness, or the difference of thickness, be i.e. the ÷ 2 of the velocity of propagation of sound wave in laboratory sample 13 * (T2-T1).
Be to test on the monocrystalline germanium of 100 μ m with this cover system at thickness, be respectively 114 μ m when the thickness of laboratory sample with 114.5 μ m the time, obtain two curves, the mistiming of its peak value, be exactly the time delay of sound pulse by different-thickness, it is very good that experimental result and Theoretical Calculation meet.
Claims (4)
1. the ultrasonic accurate thickness measuring method of short-pulse laser, it is characterized in that utilizing ultrafast short pulse laser beam in testing sample front surface excite sound waves, when sound wave passes to the rear surface, cause that deformation takes place in the sample rear surface, deflection for the first time can take place owing to current deformation from sample rear surface detection light reflected in another bundle; Sound pulse arrives behind the rear surface again from the rear surface to front surface reflection, and a periods of reflections is finished in return reflection surface rear surface in the past again, at this moment surveys light and will detect the deflection second time of certain delay was arranged on the time; The mistiming of twice deflection be multiply by the velocity of propagation of sound wave in sample, is exactly sample thickness divided by two again.
2. the ultrasonic accurate thickness measuring method of short-pulse laser as claimed in claim 1 is characterized in that described laser pulse is through in the electric light of high frequency or the frequency range that acousto-optic modulator is modulated at MHz.
3. device of realizing the ultrasonic accurate thickness measuring method of short-pulse laser as claimed in claim 1, form by following components:
(1) light source: adopt pulsed laser;
(2) beam splitting system: the light beam that light source is provided is divided into pumping and surveys the two-way light beam;
(3) focusing system: with pump light with survey light two-way light beam and gather front and rear surfaces respectively at testing sample, pump light excites ultrafast sound wave at front surface, sound wave is delivered to the rear surface of sample, can cause the miniature deformation on surface, do the appearance of the detection light meeting of mirror reflection simultaneously from the rear surface, and small angular deflection takes place owing to this deformation;
(4) receiving system: form by a photoelectricity position sensitive detector and signal processing system, the photoelectricity position sensitive detector writes down and produces certain photocurrent to the minute angle deflection of surveying light, photocurrent outputs to signal processing system, obtain information about sample surfaces deformation size, postpone by the relative time of regulating pump light and detection light, signal processing system is noted the rear surface owing to sound pulse arrives the whole process of deformation that produces, just write down the waveform of next complete sound wave, acoustic waveform can be used for the mistiming of the double arrival sample of sound wave rear surface is carried out point-device processing, thereby calculates thickness of sample.
4. device as claimed in claim 3 is characterized in that described device also comprises high frequency electric light or the acousto-optic modulator of beam modulation in the frequency range of MHz that light source is provided.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CNB02100479XA CN1137371C (en) | 2002-02-05 | 2002-02-05 | Short-pulse laser and ultrasonic method and equipment for presisely measuring thickness |
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| CNB02100479XA CN1137371C (en) | 2002-02-05 | 2002-02-05 | Short-pulse laser and ultrasonic method and equipment for presisely measuring thickness |
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| CN1363820A true CN1363820A (en) | 2002-08-14 |
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Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100416222C (en) * | 2003-06-23 | 2008-09-03 | 仁宝电脑工业股份有限公司 | Film thickness measuring method and microwave measuring apparatus |
| CN102322939A (en) * | 2011-08-29 | 2012-01-18 | 华东师范大学 | Transient detection method for solid surface acoustic waves and device thereof |
| CN101632002B (en) * | 2007-02-19 | 2012-07-18 | 荷兰应用科学研究会(Tno) | Ultrasonic surface monitoring |
| CN102967281A (en) * | 2012-11-29 | 2013-03-13 | 中国航空综合技术研究所 | System for measuring longitudinal wave thickness of pulse laser |
| CN103792191A (en) * | 2012-10-30 | 2014-05-14 | 波音公司 | System and method for testing a composite structure by using a laser ultrasound testing system |
| CN104567735A (en) * | 2013-10-16 | 2015-04-29 | 北京航天计量测试技术研究所 | Dynamic small-angle resolution testing method |
| CN104990521A (en) * | 2015-06-23 | 2015-10-21 | 烟台富润实业有限公司 | Non-contact type composite material thickness measurement device and method |
| CN106537088A (en) * | 2014-07-30 | 2017-03-22 | 新日铁住金株式会社 | Method for measuring thickness of slag floating on surface of molten metal |
| CN112556585A (en) * | 2020-11-19 | 2021-03-26 | 深圳中科飞测科技股份有限公司 | Measuring system and measuring method |
| CN113311074A (en) * | 2021-04-26 | 2021-08-27 | 长江存储科技有限责任公司 | Method, device and system for determining Young modulus of thin film |
| CN114216857A (en) * | 2021-11-25 | 2022-03-22 | 长江存储科技有限责任公司 | Detection method of thin film |
| CN114216858A (en) * | 2021-11-25 | 2022-03-22 | 长江存储科技有限责任公司 | Detection method of thin film |
| CN114812457A (en) * | 2022-06-28 | 2022-07-29 | 太原理工大学 | Light path alignment self-adjusting laser ultrasonic metal composite plate thickness measuring device and method |
-
2002
- 2002-02-05 CN CNB02100479XA patent/CN1137371C/en not_active Expired - Fee Related
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100416222C (en) * | 2003-06-23 | 2008-09-03 | 仁宝电脑工业股份有限公司 | Film thickness measuring method and microwave measuring apparatus |
| CN101632002B (en) * | 2007-02-19 | 2012-07-18 | 荷兰应用科学研究会(Tno) | Ultrasonic surface monitoring |
| CN102322939A (en) * | 2011-08-29 | 2012-01-18 | 华东师范大学 | Transient detection method for solid surface acoustic waves and device thereof |
| CN103792191B (en) * | 2012-10-30 | 2021-01-08 | 波音公司 | System and method for inspecting composite structures using a laser ultrasonic inspection system |
| CN103792191A (en) * | 2012-10-30 | 2014-05-14 | 波音公司 | System and method for testing a composite structure by using a laser ultrasound testing system |
| CN102967281A (en) * | 2012-11-29 | 2013-03-13 | 中国航空综合技术研究所 | System for measuring longitudinal wave thickness of pulse laser |
| CN104567735A (en) * | 2013-10-16 | 2015-04-29 | 北京航天计量测试技术研究所 | Dynamic small-angle resolution testing method |
| CN106537088A (en) * | 2014-07-30 | 2017-03-22 | 新日铁住金株式会社 | Method for measuring thickness of slag floating on surface of molten metal |
| CN104990521A (en) * | 2015-06-23 | 2015-10-21 | 烟台富润实业有限公司 | Non-contact type composite material thickness measurement device and method |
| CN112556585A (en) * | 2020-11-19 | 2021-03-26 | 深圳中科飞测科技股份有限公司 | Measuring system and measuring method |
| CN113311074A (en) * | 2021-04-26 | 2021-08-27 | 长江存储科技有限责任公司 | Method, device and system for determining Young modulus of thin film |
| CN114216857A (en) * | 2021-11-25 | 2022-03-22 | 长江存储科技有限责任公司 | Detection method of thin film |
| CN114216858A (en) * | 2021-11-25 | 2022-03-22 | 长江存储科技有限责任公司 | Detection method of thin film |
| CN114216858B (en) * | 2021-11-25 | 2023-11-17 | 长江存储科技有限责任公司 | Method for detecting film |
| CN114216857B (en) * | 2021-11-25 | 2023-12-22 | 长江存储科技有限责任公司 | Method for detecting film |
| CN114812457A (en) * | 2022-06-28 | 2022-07-29 | 太原理工大学 | Light path alignment self-adjusting laser ultrasonic metal composite plate thickness measuring device and method |
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| CN1137371C (en) | 2004-02-04 |
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