CN111610177A - Raman enhancement detection method and device for micro LED chip - Google Patents

Raman enhancement detection method and device for micro LED chip Download PDF

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CN111610177A
CN111610177A CN202010528322.9A CN202010528322A CN111610177A CN 111610177 A CN111610177 A CN 111610177A CN 202010528322 A CN202010528322 A CN 202010528322A CN 111610177 A CN111610177 A CN 111610177A
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陈志忠
潘祚坚
焦飞
张树霖
康香宁
陈怡帆
詹景麟
陈毅勇
聂靖昕
沈波
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Peking University
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Abstract

The invention discloses a Raman enhanced detection method and a Raman enhanced detection device for a micro LED chip. In the detection method provided by the invention, photoluminescence detection and Raman detection are combined, the photoluminescence detection provides luminescence wavelength and brightness information, and the Raman detection provides electrical properties, so that the problem of insufficient accuracy of the photoluminescence detection is solved; the Raman scattering intensity is 10 by adopting electron level resonance and surface plasmon resonance enhanced Raman technology3～108The enhancement of the optical sensor partially achieves the photoluminescence intensity, thereby laying a foundation for quick measurement; the metal nano structure not only improves the luminous efficiency of the micro LED chip, but also can enhance a Raman scattering signal by utilizing surface plasmons, thereby improving the detection speed; the micro-Raman detection is a non-destructive testing means, the detection process is simple,the method has the advantages of short required time, high detection speed, no need of special treatment on the micro LED chips, and suitability for mass detection of the micro LED chips.

Description

Raman enhancement detection method and device for micro LED chip
Technical Field
The invention relates to the field of semiconductor devices, in particular to a Raman enhanced detection method and a Raman enhanced detection device for a micro LED chip.
Background
The Micro LED display technology is a display technology in which self-luminous LEDs with a micron level (less than 50 microns) are used as light-emitting pixel units and are assembled on a driving panel to form a high-density LED array. When the Micro LED is used for displaying, the number of chips reaches millions or even tens of millions, and in the production process, the defective points in the display chips need to be detected in time for removal or repair. For example, for a display screen of a 4K television, 4K × 2K × 3 ═ 24M Micro LED chips are required, the conventional detection and sorting speed is in the order of 10K/hour, and the detection and sorting time of the Micro LED on a common 4-inch sheet will reach over 1000 hours, so that the rapid and accurate detection of the Micro LED display chip is an urgent problem to be solved.
The micro LED display chip detection technologies commonly used at present are Photoluminescence (PL) scanning and mapping (mapping) technology and Electroluminescence (EL) technology. PL mapping can carry out rapid scanning test on the light-emitting wavelength and the brightness of an LED chip under the condition of not contacting and not damaging the LED chip, but can not detect the problem on the electrical property of the chip and influence the detection accuracy. The EL test is performed by applying current to the LED chip, and has higher accuracy than PL mapping, but the test process is complicated, and requires multiple transfers, a special test apparatus is required, and some probes may cause chip damage. PL mapping is convenient, high in speed, but not high in accuracy, EL testing accuracy is high, but low in speed, high in process cost and easy to damage a detection chip, so that a new method capable of meeting the requirement of huge detection of micro LEDs is urgently needed.
Raman scattering refers to the phenomenon that when laser with a certain frequency irradiates the surface of a sample, molecules in a substance absorb or release part of energy, vibrate in different modes and degrees, and then scatter light with different frequencies. The frequency variation is determined by the characteristics of the scattering material, and the mode of vibration of different atomic groups is unique, so that scattered light with specific frequency can be generated, and the scattered light carries information of the vibration of partial molecules in the sample. The composition, structure, vibration symmetry and size of the substance to be measured determine the change of frequency, so that the Raman spectrum can be used as an effective means for researching the structure of the substance. However, because the Raman scattering signal is very weak, the scattering intensity is generally 10 times the incident light intensity-10Therefore, a specific method needs to be adopted to enhance the raman signal to ensure the detection speed.
To enhance the raman signal, it is common practice to increase the integration time of the raman test. The time required for the current commercial confocal micro-raman spectrometer to acquire the raman signal of all points of one frame image is often between several seconds and hundreds of seconds (CN201580032136.3), and the increase of the test time will limit the application of raman detection in micro LED. The enhanced raman scattering intensity and parallel testing method are expected to solve the problem of raman testing time, and the enhanced raman signal intensity can be generally realized by increasing the power density of exciting light, improving the collection efficiency of scattered light, enhancing the polarizability of a sample and the like. Based on a good focusing system of commercial microscopic confocal Raman, the energy of laser is focused on a micron-sized light spot, the influence on the temperature and the structural damage of a sample is considered, and the adjustment range of the laser power density is limited. Since the light spot of the confocal microscope is small and the collection angle of the scattered light is large, the collection efficiency of the scattered light is relatively high. The sample polarizability may be enhanced by means of electron level resonance, surface plasmon resonance, or the like.
The Raman signal can be effectively enhanced by adopting an electronic level resonance method, the conventional Raman spectrum adopts laser excitation with any wavelength to measure the Raman scattering, and the excitation wavelength of the electronic level resonance Raman needs to be carefully selected, so that the photon energy of the laser is equal to or similar to the energy of certain electronic transition, the resonance can greatly enhance the Raman scattering intensity, therefore, the detection precision is higher, and the measurement time is also obviously reduced. The resonant raman signal can be enhanced 10 compared to non-resonant raman light2-106Can play an important role in enhancing the Raman scattering signal of GaN, InGaN and other materials (Applied Physics Letters,1996,68(17):2404, Applied Physics Letters,1998,73(2): 241.). And resonance raman can be used in any raman instrument system, the measurement is also performed in a standard way, the only requirement is that there must be laser of appropriate excitation wavelength to meet the resonance condition. The surface plasmon resonance method can also enhance the Raman signal, when the sample molecules are adsorbed on the surface of some rough metals (such as silver, copper, gold and the like), the Raman scattering intensity corresponding to the sample molecules can be greatly enhanced, and the GaN surface is treated and covered with particles of silver, gold and the like, so that the Raman scattering signal of GaN can be increased to 106～1014Even monolayer Raman tests (Spectrochimica acta Part A,60 (2004)) 321-201327) can be carried out (J.Phys.chem.B 2005,109,20186-20191, appl.Phys.Lett.96,033109 (2010)). In general, the resonance Raman signal intensity of silver is 10 of that of gold2About twice as much as silver is widely used due to its good optical electric field enhancement effect, and silver can be well excited in the ultraviolet and visible light region bands (Optics Express,2006,14(21): 9971-. The surface plasmon resonance can be applied to any Raman instrument system, and the actual measurement is the same as the standard Raman measurement.
At present, the Raman test cannot directly give information such as forward bias, reverse leakage, short circuit, open circuit and the like of the LED, but the Raman spectrum already gives a plurality of information related to electrical propertiesFrom this information, the electrical properties of the LED can be judged. Kokubo et al, university of japan famous ancient houses, measures dislocation density (jpn.j.appl.phys.,58(c), sccB06(2019), appl.phys.exp.,11(6),061002(2018)) using micro Raman (μ -Raman), the dislocations have a small relationship with the electrical and optical properties of LEDs under normal operating conditions, but significantly affect the electrical and optical properties of LEDs under vertical structure LEDs or large injection operating conditions. μ -Raman can also measure the stress distribution of LED epitaxial layers (semi. sci. tech.32(10),105009(2017), rev. sci. instr.,88(11),1131111(2017)), which are related to the leakage, internal electric field of the LED. Activation of Mg acceptors can be measured by raman (phys. sol. stat. a,214(10),1700225 (2017)). By using a longitudinal optical phonon (LO) and a coupled (LOPC) raman signal (jpn.j.appl.phys.,56(8), 08LB07(2017)), the carrier concentration in the epitaxial layer can be measured, and the carrier concentration and the voltage have a clear correspondence. μ -Raman can also measure anomalies in stress and carrier distribution around defects such as V-pits (V-pit), voids (void), hillocks (hillock) (appl. phys. lett.92(21)212104(2008), phys. sol. stat. c,3(6), 2321) (2006), which can lead to electrical leakage and even shorting. The damage of the inductive coupling plasma etching (ICP) to the subsurface also seriously affects the electrical properties, and the mu-Raman has certain characterization capability to the etching damage (J.Phys.D., 34(18), 2748 (2001)). In the preparation process of the LED chip, a plurality of intermediate compounds are generated, and the intermediate compounds have obvious influence on the electrical properties of devices, such as AZO thin films and SiO2，SiNxFilm, GaCO3Layers, some of these products are contact layers, some are passivation layers, current blocking layers, and some are process by-products, which have a significant effect on p, n ohmic contact performance (Thin solid film, 676,125(2019), j.new mat. electrochem. sys.,19(1)11(2016)), and the structure of these materials can also be characterized by μ -Raman.
In conclusion, the stress condition, the device structure and the electrical property of the micro LED are expected to be rapidly obtained through the Raman signal enhancement technology and the micro Raman technology.
Disclosure of Invention
The invention provides a Raman enhancement detection method and a Raman enhancement detection device for a micro LED chip, and provides a high-speed Raman detection method.
One objective of the present invention is to provide a micro-raman combined photoluminescence detection device for micro LED chips.
The Micro LED chip array is a two-dimensional array with periodically arranged LED chip units, the size of each Micro LED chip unit is below 50 mu m, the size of the Micro LED chip array is in inch order, the size of a light spot for exciting Raman and photoluminescence signals is in micron order, the scanning range of the scanning galvanometer is in hundred micron order, and the Micro LED chip array is divided into a plurality of two-dimensionally arranged frames by the scanning range of the scanning galvanometer.
The invention adopts micro-Raman combined with photoluminescence detection, and the Raman enhanced detection device of the micro LED chip comprises: the device comprises a laser, a first spatial filter, a multi-face prism, a first beam splitter, a scanning galvanometer, an objective lens, an XYZ three-dimensional high-speed sample stage, a control system, an optical path switching device, an eyepiece, a CCD camera, a second spatial filter, a longitudinal cylindrical lens, a transverse cylindrical lens, a second beam splitter and a multi-channel spectrometer; the control system is respectively connected to the laser, the light path switching device, the scanning galvanometer, the CCD camera, the XYZ three-dimensional high-speed sample stage and the multi-channel spectrometer; the multi-channel spectrometer comprises a first channel and a second channel; the first channel comprises a first prism spectrometer and a first CCD area array detector, and the second channel comprises a second prism spectrometer and a second CCD area array detector; the laser emits parallel exciting light, the wavelength of the exciting light is 325-345nm, the wavelength of the exciting light is equal to the energy of partial electron transition, and the wavelength of the exciting light is 20-40 nm smaller than the wavelength of fluorescence generated by exciting a sample; or the wavelength of the exciting light is less than 350nm, the wavelength of the exciting light is within 20nm of the fluorescence wavelength generated by exciting the sample, and the wavelength of the exciting light is equal to the energy of partial electron transition; the exciting light is removed from stray light through a first spatial filter, is changed into a plurality of parallel lights with different angles through a multi-surface prism, passes through a first beam splitting sheet and then a scanning galvanometer, and is focused by an objective lens to form a plurality of one-dimensional arranged light spots; placing a micro LED chip array as a sample on an XYZ three-dimensional high-speed sample table; exciting light of the one-dimensional array of light spots is incident on a sample at a Brewster angle, all the exciting light parallel to a polarization plane is transmitted to the inside of the sample instead of being reflected by the surface, so that Raman light is excited, resonance is generated due to the fact that the wavelength of the exciting light is equal to the energy of partial electron transition, and a metal nano structure embedded into a micro LED unit and a quantum well form surface plasmon resonance, so that the Raman light is enhanced to a fluorescence magnitude, meanwhile, photoluminescence generates fluorescence, the one-dimensional array of light spots is simultaneously irradiated on a plurality of micro LED chip units, and the generated Raman light and the fluorescence are also the one-dimensional array of light spots; the fluorescence and Raman light enter an objective lens, pass through a scanning galvanometer and a first beam splitting sheet, are controlled by a light path switching device, are collected by an ocular lens and enter a CCD camera, and the surface morphology of a sample is observed; or the fluorescence and the Raman light are controlled by the light path switching device, stray light is filtered by the second spatial filter, then the light spots are shaped by the longitudinal cylindrical lens and the transverse cylindrical lens in sequence to become rectangular light spots, the rectangular light spots are divided into two beams of light with different directions by the second beam splitter, and then the two beams of light respectively enter a first channel and a second channel of the multi-channel spectrometer; the first beam of light is split by the first prism spectrometer, only fluorescence is reserved, and the first beam of light is received by the first CCD area array detector; the fluorescence is a one-dimensionally arranged light spot array, the first CCD area array detector is a two-dimensionally arranged pixel, each light spot of the fluorescence respectively corresponds to a row of pixels of the CCD area array detector, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, each wavelength of the fluorescence and corresponding brightness information are obtained, and therefore the fluorescence spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the fluorescence spectrum of the scanning positions of a plurality of corresponding micro LED chip units is obtained by the first CCD area array detector at the same time; if the wavelength of the exciting light is less than 20-40 nm of the fluorescence wavelength generated by exciting the sample, the Stokes Raman is adopted for combining fluorescence measurement, the second beam of light is split by the second prism spectrometer, only Stokes Raman light is reserved, and as the wavelength of the exciting light is less than 20-40 nm of the fluorescence wavelength generated by exciting the sample, and the wavelength of the Stokes Raman light is within 30nm of the wavelength of the exciting light, the spectrums of the fluorescence and the Stokes Raman light can be separated and received by the second CCD area array detector; or if the wavelength of the exciting light is less than the wavelength of the fluorescence generated by exciting the sample by 20nm, combining anti-stokes raman with fluorescence measurement, splitting the second beam of light by a second prism spectrometer, and only reserving anti-stokes raman light; the Raman light is a one-dimensional array of light spots, the second CCD area array detector is a two-dimensional array of pixels, each light spot of the Raman light corresponds to a row of pixels of the CCD area array detector respectively, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, the intensity and the brightness of each wavelength of the Raman light are obtained, and therefore a Raman light spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the second CCD area array detector simultaneously obtains the Raman light spectra of the scanning positions of the plurality of corresponding micro LED chip units; the scanning of the plurality of micro LED chip units corresponding to the exciting light of the one-dimensional arranged light spot array is completed by controlling the scanning galvanometer, the scanning galvanometer is further controlled, the exciting light of the one-dimensional arranged light spot array completes the scanning of one frame of the micro LED chip array, then the XYZ three-dimensional high-speed sample stage is controlled, the scanning of the next frame of the micro LED chip array is realized, the scanning of the micro LED chip array is completed, the fluorescence spectrum and the Raman spectrum of the micro LED chip array are obtained, the optical property is obtained through the fluorescence spectrum, the corresponding electrical property is obtained through the Raman spectrum of a plurality of measuring points on the micro LED chip unit, and the micro LED chip array is classified according to the optical property and the electrical property.
The laser adopts a semiconductor laser to ensure that the wavelength of exciting light is continuously adjustable in a near ultraviolet to visible light region. The laser can simultaneously excite and distinguish a fluorescence spectrum and a Raman spectrum, the spectrum of the Raman light is within 30nm of the spectrum of the excitation light, and the wavelength of the excitation light is selected to be less than 20-40 nm of the wavelength of the fluorescence, so that the spectrum of the Raman light can be separated from the spectrum of the fluorescence. In consideration of the resonance Raman spectrum, the photon energy of the laser is near the electron energy level, for example, for the Stokes resonance Raman excitation of GaN, the wavelength of the excitation light is in the range of 325-345nm, and if the InGaN resonance Raman with the luminescence of 460nm is to be measured, the wavelength of the excitation light is in the range of 405-425 nm. If the anti-stokes resonance raman peak is measured, the wavelength of the required laser can be closer to the wavelength of the fluorescence of the material, because the energy of anti-stokes raman scattering photons is higher than that of the fluorescence and is not interfered by the fluorescence.
The first spatial filter comprises a first lens, a first filtering slit and a second lens; the parallel exciting light is converged to the first filtering slit by the first lens, the stray light is removed by the first filtering slit, and the parallel exciting light is converged into parallel light by the second lens to be emitted. The second spatial filter comprises a third lens, a second filtering slit and a fourth lens; the parallel exciting light is converged to the second filtering slit by the third lens, the stray light is removed by the second filtering slit, and the parallel exciting light is converged into parallel light by the fourth lens to be emitted.
The scanning galvanometer comprises an X-axis galvanometer, a Y-axis galvanometer and a flat field lens, and the Z exciting light beam sequentially passes through the X-axis galvanometer, the Y-axis galvanometer and the flat field lens and then is emitted out, so that scanning is respectively carried out along the X axis and the Y axis. The scanning speed of the commercial confocal micro-Raman instrument is improved by using a galvanometer technology, but because of the problem of the sensitivity of the Raman spectrometer, the speed is typically several minutes per frame, and at the speed, if 20 frames are scanned in one hour, and the range of 10 times of the laser scanning light field is typically 400 microns multiplied by 400 microns, the number of detected micro LED units is about 15 multiplied by 15 to 225 per frame, and the number of detected micro LED units which can be measured in each hour is 4.5K, so that the requirement of the macro test of the micro LED array is far not met.
The scanning galvanometer and the three-dimensional high-speed displacement platform can rapidly and automatically adjust the positions of light spots and samples point by point, and point-by-point light excitation and collection are realized. In general, confocal microscopes provide a conjugate of the light source and collection point, reducing out-of-focus stray light. The galvanometer scanner scans points in a field of view rapidly, and the scanning speed is generally required to be more than 10 frames per second (500 pixels by 500 pixels), so that the number of micro LEDs detectable in one hour can reach 810 thousands. And moving the position of the sample in the XY displacement direction, wherein the general step length is the distance corresponding to the movement of one frame of sample, and the position of the focus can be adjusted in the Z direction or the sample is scanned in a layering manner. The focusing of the sample topography can be used for automatic fine tuning in the z-direction by adding an illumination source.
The invention adopts the polyhedral prism combined with the CCD area array detector array, the frame scanning speed can reach 10 frames/second, and the scanning speed is greatly improved. Although electro-optic deflectors can reach speeds of 1000 frames/second, the raman signal-to-noise ratio will deteriorate due to the weaker raman signal and the difficulty of enhancement techniques, with the larger scan rate implying smaller test integration times.
The multi-face prism adopts a multi-face cylinder prism and is provided with a bottom face and a plurality of edge faces; the incident surface is the bottom surface, and the emergent surface has the different planes of N inclination to become the different parallel light of N bundle angle, thereby improve N times scanning speed, N is 10 ~ 20 natural number, evenly distributed in laser scanning field (DuoScan) (notice not the objective light field). Therefore, the number of the LED units detected per hour can be increased by 10-20 times to 1 hundred million on the basis of the original 810 thousands, namely all the LED units on 4-5 micro LED chip arrays with 6 inches can be measured. One consideration for using a one-dimensional array is to use a faceted prism, which is very easy to machine accurately; the other element is that the spectrum of the one-dimensionally arranged light spot array can be obtained by a two-dimensional CCD area array detector array. The number of the light spots is 10-20, so that the distance between the light spots is large enough, and mutual interference does not exist on the CCD area array detector. Compared with the document CN201810712095.8, the invention combines the polygon prism with the CCD area array detector, so that the one-dimensionally arranged light spot array is received by the two-dimensional area array CCD area array detector to obtain the spectral distribution of each light spot, and the optical property and the electrical property can be obtained without complex laser frequency modulation and signal demodulation technology. And the first CCD area array detector and the second CCD area array detector are adopted to receive the fluorescence and the Raman light respectively, so that the saturation of the CCD area array detector when the fluorescence and the Raman light are measured simultaneously is prevented.
The light path switching device adopts a movable reflector, and when the reflector moves out of the light path, the fluorescence and the Raman light are collected by the ocular lens and enter the CCD camera; when the mirror is placed at 45 ° in the optical path, the fluorescence and raman light enters the multi-channel spectrometer.
The longitudinal cylindrical lens and the transverse cylindrical lens are cylindrical lenses, optical axes of the longitudinal cylindrical lens and the transverse cylindrical lens are perpendicular to each other and perpendicular to a light path, so that light spots are shaped, and the shaped light spots are rectangular. The shaped light spot is just completely placed on the CCD area array detector after passing through the prism spectrometer.
The multi-channel spectrometer uses a prism spectrometer and abandons a grating, thereby eliminating a sub-peak stray spectrum caused by the grating in the grating spectrometer.
Commercial confocal micro-Raman spectrometer has already done a lot of work in the directions of notch filter, focus tracking, inclined laser beam, multistage monochromator, etc., imaging quality has been improved remarkably, stray light suppression level reaches 50cm-1Left and right. Different from the existing commercial instrument, the excitation light adopts a multi-focus parallel measurement scheme, and the incident light beam angle has certain deflection of 1-3 degrees, so that the range of a laser scanning field (DuoScan) is increased, and the test speed is improved. The excitation light parallel to the polarization plane enters the sample completely by incidence at the Brewster angle, and the scattered light is collected to the detection light path by the objective lens, so that the influence of the excitation light on the whole light path is reduced. Furthermore, the invention shapes the round scattered light spots into a rectangle through the double-cylindrical lens, thereby improving the efficiency of the light collecting path and reducing the stray light. In addition, the prism spectrometer with long focal length is adopted to replace the existing grating light splitting system, so that the stray spectrum from the grating secondary peak is thoroughly eliminated, and the signal-to-noise ratio of the Raman scattering is greatly improved.
One objective of the present invention is to provide a method for detecting raman signal enhancement of a micro LED chip.
The invention adopts a high-speed Raman detection method of the micro LED chip, is used for accurately giving the electrical property of the micro LED chip and makes up the defect of photoluminescence detection.
The method for detecting the Raman signal enhancement of the micro LED chip is used for detecting the micro LED chips with two structures, namely the micro LED with an inverted structure and the micro LED with a vertical structure, and the chips are prepared on the basis of GaN and InGaN materials. The micro LED with the flip-chip structure comprises an unintentionally doped GaN layer, an n-GaN layer, a quantum well light-emitting layer, a p-GaN layer, a p electrode, an n electrode and a passivation layer, wherein the n-GaN layer is formed on the unintentionally doped GaN layer, the quantum well light-emitting layer is formed on the upper part surface of the n-GaN layer and consists of InGaN and GaN, the p-GaN layer is formed on the quantum well light-emitting layer, part of the p-GaN surface is etched, the p-GaN layer is etched to the n-GaN layer, the n electrode is formed on the surface of the n-GaN layer exposed by etching, the p electrode is formed on the surface of the p-GaN layer which is not etched, and the passivation layer is formed on the lower surface of the flip chip which does not emit light; the vertical structure micro LED comprises an unintentionally doped GaN layer, an n-GaN layer, a quantum well light emitting layer, a p-GaN layer, a p electrode, an n electrode and a passivation layer, wherein the n-GaN layer, the quantum well light emitting layer, the p-GaN layer and the p electrode are sequentially formed on the unintentionally doped GaN layer, the quantum well light emitting layer is composed of InGaN and GaN, the n electrode is formed on the back of the unintentionally doped GaN layer, and the passivation layers are formed on the upper surface and the lower surface of the vertical structure micro LED. Aiming at the surface plasmon enhanced Raman test, the invention requires that a periodic metal nano structure is embedded in the p-GaN layer.
Photoluminescence detection can carry out rapid scanning test on the luminous wavelength and brightness of a micro LED chip, but cannot detect the problem of the electrical property of the chip, and influences the detection accuracy. The Raman detection can provide information such as dislocation density, stress distribution, carrier concentration, etching damage, activation of an Mg acceptor, intermediate compounds generated in the process and the like of the chip, and can accurately judge the electrical properties of the micro LED chip. When the Raman detection is particularly applied to the huge quantity detection of micro LED chips, certain special points of the micro LED chips are selected as test points, measuring points are selected in a p electrode area to detect defects such as dislocation and the like, the activation concentration of p-type GaN and a p-type contact layer structure, measuring points are selected in a passivation layer area to detect the structure and the etching damage of a passivation layer, and measuring points are selected in an n electrode area to detect the etching damage of an n-type contact layer structure and an n-GaN layer and the like. At the test point, the spectrum of the laser excitation includes a PL spectrum and a Raman spectrum. The PL spectrum and the Raman spectrum are respectively analyzed after being separated, the PL spectrum provides the luminous wavelength and brightness information of the micro LED chip, the Raman spectrum provides the electrical property of the micro LED chip, and the dead spots in the micro LED chip are distinguished by integrating the information such as the luminous wavelength, the brightness and the electrical property and the like to be removed or repaired, so that the production yield is effectively guaranteed.
The Raman signal enhancement method of the micro LED chip comprises an electron energy level resonance method and a surface plasmon resonance method.
One method of enhancing raman signals of the present invention is a resonance enhancement method using electron energy levels. Due to the huge difference of energy, the interaction between the excited photon and the phonon needs to take electrons as media, and the non-resonance Raman scattering is that electrons are excited and then transited from a real state to a virtual state, and then absorb or release a phonon and transit from the virtual state to another real state, so as to emit Raman scattering light with different incident light frequencies. Resonant raman scattering is the raman scattering of electrons excited by incident light to transition from one solid state to another, and then absorb or emit a phonon to transition from the solid state back to a third solid state, emitting a different incident light frequency. The resonant raman signal can be enhanced 10 compared to non-resonant raman light2～106And (4) doubling. For resonant raman, the excitation wavelength needs to be chosen such that the laser photon energy is equal to or close to the energy of a certain electronic transition, generally in the ultraviolet and visible range. The main detection object of the Micro LED chip is a GaN material, the scattering peaks of GaN are mainly E2, A1(LO) and LOPC Stokes peaks, and E2 and A1 are irreducible representation symbols of phonon vibration. According to the GaN forbidden band width Eg of 3.42eV, the laser wavelength of 325-. Therefore, the transition of electrons between real states is ensured, and the positions of Raman peaks of E2, A1(LO) and LOPC are effectively avoided from band-edge photoluminescence peaks (the peak value is about 364nm, and the peak width is 10 nm). If an anti-Stokes Raman peak is tested, the exciting light is positioned at the band edge lightThe short wavelength limit of the photoluminescence peak is less than 350nm, and the generated anti-Stokes Raman scattered light is less interfered by photoluminescence, so that the signal to noise ratio is higher. Another material of the Micro LED chip requiring the emphasis detection is: an InGaN material. The present invention also considers the E2 and a1(LO) peaks of InGaN materials, and unlike GaN materials, InGaN materials exist only in the quantum well active region of an LED, the well layer is only a few nanometers thick, and the GaN layer is a few microns thick, so testing of InGaN materials must use resonance raman measurement. For the quantum well luminescence of 460nm blue light, the excitation wavelength is in the range of 405-425nm, so as to ensure that no strong photoluminescence interference exists, and meanwhile, energy level transition in GaN can not be excited. For SiO2、SiNxAnd ITO and associated passivation layers and surface process residues, should be matched using an appropriate excitation wavelength to obtain a resonance enhanced raman signal. The laser used in the invention is a semiconductor laser subjected to beam shaping, the current semiconductor laser can achieve watt-level power output, the wavelength of the laser is convenient to select, and the other laser can conveniently carry out frequency modulation, thereby further improving the signal-to-noise ratio.
Another method of the present invention for enhancing raman signal is an enhancement method using Surface Plasmon Resonance (SPR). Surface plasmons enhance the intensity of the raman signal in three ways. The method is characterized in that firstly, the intensity of exciting light is greatly enhanced through a lightning rod effect and a surface mirror image force effect, secondly, the sample polarization rate is greatly changed through a surface plasmon evanescent field, and thirdly, a scattering electric field of a near field is emitted to a far field through an antenna effect. The raman enhancement of surface plasmon resonance by resonance with excitation level can be up to 108～1014And (4) doubling. The invention prepares metal nano-structures near quantum wells of a sample to obtain enhancement of Raman signals, wherein the metals mainly comprise silver (Ag), gold (Au), platinum (Pt), copper (Cu) and aluminum (Al). Ag metal is widely applied to enhancing the luminous efficiency of InGaN/GaN LEDs because of the excellent characteristics of easy preparation, easy regulation and control of morphology, easy formation of surface plasmon resonance and the like, and is commonly used electrode metal and electrode metal for LEDsThe light reflection metal can be used for preparing light reflection layers of vertical structure and flip-chip structure LEDs. The size of the Ag particles is from dozens of nanometers to hundreds of nanometers, the corresponding SPR energy is from purple light to red light, the wavelength of a sample tested by people is covered, and for a quantum well with the light emitting wavelength of 460nm of blue light, the size of the Ag particles is 30 nm-50 nm, and larger SPR resonance can be obtained. And meanwhile, the lightning rod enhancement and antenna emission effects are enhanced by adopting a plurality of needle points or antenna-shaped Ag structures.
The invention discloses a Raman signal enhancement detection method of a micro LED chip, which adopts a method of electron level resonance and surface plasmon resonance to enhance Raman signals, and comprises the following steps:
1) embedding periodic metal nano structures in a p-GaN layer of a micro LED chip;
2) the laser emits parallel exciting light, the wavelength of the exciting light is 325-345nm, the wavelength of the exciting light is equal to the energy of partial electron transition, and the wavelength of the exciting light is 20-40 nm smaller than the wavelength of fluorescence generated by exciting a sample; or the wavelength of the exciting light is less than 350nm, the wavelength of the exciting light is within 20nm of the fluorescence wavelength generated by exciting the sample, and the wavelength of the exciting light is equal to the energy of partial electron transition;
3) the exciting light is removed of stray light through the first spatial filter, changed into a plurality of beams of parallel light with different angles through the multi-surface prism, and then passes through the first beam splitting sheet;
4) a plurality of parallel lights with different angles pass through a scanning galvanometer and are focused by an objective lens to form a plurality of one-dimensional arranged light spots;
5) the micro LED chip array is used as a sample and is positioned on a focal plane of an objective lens and is placed on an XYZ three-dimensional high-speed sample table; exciting light of the one-dimensional array of light spots is incident on a sample at a Brewster angle, all the exciting light parallel to a polarization plane is transmitted to the inside of the sample instead of being reflected by the surface, so that Raman light is excited, resonance is generated due to the fact that the wavelength of the exciting light is equal to the energy of partial electron transition, and a metal nano structure embedded into a micro LED unit and a quantum well form surface plasmon resonance, so that the Raman light is enhanced to a fluorescence magnitude, meanwhile, photoluminescence generates fluorescence, the one-dimensional array of light spots is simultaneously irradiated on a plurality of micro LED chip units, and the generated Raman light and the fluorescence are also the one-dimensional array of light spots;
6) the fluorescence and the Raman light return to the objective lens, then sequentially pass through the scanning galvanometer and the first beam splitter, are controlled by the light path switching device, are collected by the ocular lens and enter the CCD camera, and the surface morphology of the sample is observed;
7) or the fluorescence and the Raman light are controlled by the light path switching device, stray light is filtered by the second spatial filter, and then the light spots are shaped by the longitudinal cylindrical lens and the transverse cylindrical lens in sequence to become rectangular light spots;
8) the first beam splitter is used for splitting the light into two beams of light in different directions, and the two beams of light respectively enter a first channel and a second channel of the multi-channel spectrometer;
9) the first beam of light is split by the first prism spectrometer, only fluorescence is reserved, and the reserved fluorescence is received by the first CCD area array detector; the fluorescence is a one-dimensionally arranged light spot array, the first CCD area array detector is a two-dimensionally arranged pixel, each light spot of the fluorescence respectively corresponds to a row of pixels of the CCD area array detector, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, the intensity and the brightness of each wavelength of the fluorescence are obtained, and therefore the fluorescence spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the fluorescence spectrum of the scanning position of a plurality of corresponding micro LED chip units is obtained by the first CCD area array detector at the same time;
10) if the wavelength of the exciting light is less than 20-40 nm of the fluorescence wavelength generated by the sample excited by the exciting light, the Stokes Raman is combined with fluorescence measurement, the second beam of light is split by the second prism spectrometer, only Stokes Raman light is reserved, as the wavelength of the exciting light is less than 20-40 nm of the fluorescence wavelength generated by the sample excited by the exciting light and the wavelength of the Stokes Raman light is within 30nm of the wavelength of the exciting light, the fluorescence and the Stokes Raman light can be separated,
receiving by a second CCD area array detector;
or if the wavelength of the exciting light is less than the wavelength of the fluorescence generated by exciting the sample by 20nm, combining anti-stokes raman with fluorescence measurement, splitting the second beam of light by a second prism spectrometer, and only reserving anti-stokes raman light;
11) the Raman light is a one-dimensional array of light spots, the second CCD area array detector is a two-dimensional array of pixels, each light spot of the Raman light corresponds to a row of pixels of the CCD area array detector respectively, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, the intensity and the brightness of each wavelength of the Raman light are obtained, and therefore a Raman light spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the second CCD area array detector simultaneously obtains the Raman light spectra of the scanning positions of the plurality of corresponding micro LED chip units;
12) repeating the steps 2) to 11) by controlling the scanning galvanometer, and finishing scanning of the corresponding micro LED chip units by the exciting light of the one-dimensional array of the light spots;
13) further controlling a scanning galvanometer, and repeating the steps 2) -12), wherein the exciting light of the one-dimensional light spot array finishes scanning one frame of the micro LED chip array;
14) moving the sample to the next frame by controlling an XYZ three-dimensional high-speed sample stage, and repeating the steps 2) -13), thereby completing the scanning of the micro LED chip array and obtaining the fluorescence spectrum and the Raman spectrum of the micro LED chip array;
15) obtaining optical properties by fluorescence spectroscopy;
16) detecting dislocation defects, the activation concentration of p-type GaN and a p-type contact layer structure through a Raman spectrum of a measuring point in a p electrode region, detecting the structure and the etching damage of a passivation layer through the Raman spectrum of the measuring point in a passivation layer region, and detecting the etching damage of an n-type contact layer structure and an n-GaN layer through the Raman spectrum of the measuring point in an n electrode region, so that the integral electrical property of the micro LED chip is obtained according to the Raman spectrum of each measuring point;
17) the micro LED chip arrays are classified according to optical and electrical properties.
The invention has the advantages that:
in the detection device provided by the invention, the polygon prism is combined with the CCD area array detector, so that the one-dimensionally arranged light spot array is received by the two-dimensional area array CCD area array detector to obtain the spectral distribution of each light spot, the optical property and the electrical property can be obtained without complex laser frequency modulation and signal demodulation technologies, and the scanning speed is greatly improved; the Brewster angle incidence and the beam shaping of the bi-cylindrical lens are adopted, and the prism spectrometer is adopted to reduce the sub-peak stray spectrum caused by the grating, so that the suppression level of the stray spectrum is obviously improved;
in the detection method provided by the invention, photoluminescence detection and Raman detection are combined, the photoluminescence detection provides luminescence wavelength and brightness information, and the Raman detection provides electrical properties, so that the problem of insufficient accuracy of the photoluminescence detection is solved; the Raman scattering intensity is 10 by adopting electron level resonance and surface plasmon resonance enhanced Raman technology3～108The enhancement of the optical sensor partially achieves the photoluminescence intensity, thereby laying a foundation for quick measurement; the metal nano structure not only improves the luminous efficiency of the micro LED chip, but also can enhance a Raman scattering signal by utilizing surface plasmons, thereby improving the detection speed; the micro-Raman detection is a nondestructive testing means, has simple detection process, short required time and high detection speed, does not need to specially process the micro LED chips, and is suitable for the massive detection of the micro LED chips.
Drawings
FIG. 1 is a block diagram of a micro-Raman integrated photoluminescence detection device of a micro LED chip according to an embodiment of the invention; FIG. 2 is a schematic diagram of a multi-channel spectrometer of the micro LED chip with a micro Raman integrated photoluminescence detection device of the invention;
FIG. 3 is a flow chart of a detection method of one embodiment of micro-Raman combined photoluminescence detection of a micro LED chip of the invention;
fig. 4 is a schematic structural view of a micro LED with a flip-chip structure according to a first embodiment of the micro LED chip micro raman combined photoluminescence detection method of the present invention, wherein (a) is a cross-sectional view and (b) is a back perspective view;
FIG. 5 is a schematic diagram of a micro LED test point with an inverted structure according to a first embodiment of the micro LED chip micro Raman combined photoluminescence detection method of the invention;
fig. 6 is a schematic structural view of a micro LED with a vertical structure according to a second embodiment of the micro LED chip micro raman combined photoluminescence detection method of the invention, wherein (a) is a cross-sectional view and (b) is a back perspective view;
fig. 7 is a schematic diagram of a micro LED test point with a vertical structure according to a second embodiment of the micro LED chip micro raman combined photoluminescence detection method of the invention.
Detailed Description
The invention will be further elucidated by means of specific embodiments in the following with reference to the drawing.
The micro-raman integrated photoluminescence detection device of the micro LED chip in this embodiment is shown in fig. 1, and the micro-raman integrated photoluminescence detection device of the micro LED chip in this embodiment includes: the device comprises a laser, a first spatial filter, a multi-face prism, a first beam splitter, a scanning galvanometer, an objective lens, an XYZ three-dimensional high-speed sample stage, a control system, an optical path switching device, an eyepiece, a CCD camera, a second spatial filter, a longitudinal cylindrical lens, a transverse cylindrical lens, a second beam splitter and a multi-channel spectrometer; the multi-channel spectrometer comprises a first prism spectrometer, a first CCD area array detector, a second prism spectrometer and a second CCD area array detector, and is shown in FIG. 2; the control system is respectively connected to the laser, the light path switching device, the scanning galvanometer, the CCD camera, the XYZ three-dimensional high-speed sample stage and the first and second CCD area array detectors of the multi-channel spectrometer.
The laser emits parallel exciting light, the exciting light removes stray light through the first spatial filter, the stray light is changed into a plurality of parallel light beams with different angles through the multi-surface prism, and then the parallel light beams pass through the first beam splitting sheet; a plurality of parallel lights with different angles pass through a scanning galvanometer and are focused by an objective lens to form a plurality of one-dimensional arranged light spots; the micro LED chip array is used as a sample and is positioned on a focal plane of an objective lens and is placed on an XYZ three-dimensional high-speed sample table; exciting light of the one-dimensional arranged light spot arrays is incident on the sample at a Brewster angle, all the exciting light parallel to the polarization plane is transmitted to the inside of the sample instead of being reflected by the surface, so that Raman light is excited, photoluminescence generates fluorescence, the one-dimensional arranged light spot arrays simultaneously irradiate a plurality of micro LED chip units, and the generated Raman light and the fluorescence are also the one-dimensional arranged light spot arrays; the fluorescence and Raman light enter an objective lens, sequentially pass through a scanning galvanometer and a first beam splitting sheet, and are controlled by a light path switching device, the light path switching device adopts a movable reflector, and the fluorescence and Raman light are collected by an ocular lens and enter a CCD camera to observe the surface morphology of a sample; or the fluorescence and the Raman light are controlled by the light path switching device, stray light is filtered by the second spatial filter, then the light spots are shaped by the longitudinal cylindrical lens and the transverse cylindrical lens in sequence to become rectangular light spots, the rectangular light spots are divided into two beams of light with different directions by the second beam splitter, and then the two beams of light respectively enter a first channel and a second channel of the multi-channel spectrometer; the first channel comprises a first prism spectrometer and a first CCD area array detector, and the second channel comprises a second prism spectrometer and a second CCD area array detector; the first beam of light is split by the first prism spectrometer, fluorescence is reserved, other light such as Raman light and the like is removed, and the reserved fluorescence is received by the first CCD area array detector; the fluorescence is a one-dimensionally arranged light spot array, the first CCD area array detector is a two-dimensionally arranged pixel, each light spot of the fluorescence respectively corresponds to a row of pixels of the CCD area array detector, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, the intensity and the brightness of each wavelength of the fluorescence are obtained, and therefore the fluorescence spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the first CCD area array detector simultaneously obtains the fluorescence spectra of the scanning positions of a plurality of corresponding micro LED chip units; the second beam of light is split by the second prism spectrometer, the Raman light is reserved, other light such as fluorescence and the like is removed, and the reserved Raman light is received by the second CCD area array detector; the Raman light is a one-dimensional array of light spots, the second CCD area array detector is a two-dimensional array of pixels, each light spot of the Raman light corresponds to a row of pixels of the CCD area array detector, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, the intensity and the brightness of each wavelength of the Raman light are obtained, and therefore the Raman light spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the second CCD area array detector simultaneously obtains the Raman light spectra of the scanning positions of a plurality of corresponding micro LED chip units; the scanning of the plurality of corresponding LED chip units is completed by controlling the scanning galvanometer, the scanning of one-dimensional arranged exciting light of the light spot array is further controlled, the scanning of one frame of the micro LED chip array is completed by the exciting light of the one-dimensional arranged light spot array, then the scanning of the next frame of the micro LED chip array is realized by controlling the XYZ three-dimensional high-speed sample stage, so that the scanning of the micro LED chip array is completed, the fluorescence spectrum and the Raman spectrum of the micro LED chip array are obtained, the optical property is obtained through the fluorescence spectrum, the electrical property is obtained through the Raman spectrum, and the micro LED chip array is classified according to the optical property and the electrical property.
In general, the fluorescence intensity is 100 ten thousand times that of raman light, and the detection sensitivity and the stray light suppression requirement are greatly different. As shown in fig. 2, the fluorescence and raman light excited by the excitation light enter the fluorescence test channel and the raman light test channel, respectively, through the second beam splitter. The second beam splitting slice distributes light according to the light intensity ratio of the fluorescence light and the Raman light, and the control system sets different integration time according to the light intensity ratio of the fluorescence light and the Raman light. If only the resonance of the electron energy level exists, the intensity of the Raman light is 10 times weaker than that of the fluorescence light3～104The product of the scattered luminous flux and the integration time of the Raman test also reaches 10 of the fluorescence measurement3～104And (4) doubling. In the case of surface plasmon resonance, the intensity of raman light is enhanced to the same order of magnitude as or higher than the fluorescence intensity without consideration of increasing the flux or integration time of raman light.
In this embodiment, a flow chart of a detection method for detecting a micro LED chip based on micro raman combined with a photoluminescence detection device is shown in fig. 3.
In this embodiment, the test sample includes two micro LED chips, i.e., a flip chip and a vertical chip.
Example one
In this embodiment, the test sample is a micro LED chip with a flip-chip structure.
In the embodiment of the invention, the laser emission wavelength of the laser is adjusted, and the laser with the proper excitation wavelength is selected, so that the photon energy of the laser is equal to or similar to the energy of partial electron transition, and resonance is generated, thereby enhancing the Raman signal of the micro LED chip. The main detection objects of the Micro LED chip are GaN and InGaN materials, for E2, A1(LO) and LOPC Stokes peaks of the GaN material, E2 and A1 are irreducible representation symbols of phonon vibration, laser wavelength of 325-345nm is adopted, and for an anti-Stokes Raman peak of the GaN material, excitation light wavelength is less than 350nm, so that collected Raman signals can be subjected to resonance enhancement, and meanwhile interference of photoluminescence is small. The excitation wavelength used for the E2, a1(LO) peaks of InGaN material is in the range of about 405-425nm to ensure no strong photoluminescence interference and no energy level transitions in GaN are excited. For SiO2、SiNxITO and associated passivation layers and surface process residues, with appropriate choice of excitation wavelength to obtain a resonance enhanced raman signal.
In the embodiment, the periodic Ag metal nano structure and the InGaN/GaN quantum well are embedded in the p-GaN to form surface plasmon resonance, so that the Raman signal intensity of the micro LED chip is enhanced. Meanwhile, the high reflectivity of the metal Ag is utilized to prepare the light reflecting layers of the LEDs with the vertical structures and the inverted structures, so that the luminous efficiency of the micro LEDs can be improved. The size of the Ag metal nano structure embedded into the p-GaN is within the range of 30-50 nm, and a needle point-shaped or antenna-shaped array structure is formed. The coupling effect caused by the periodic Ag nano structures can generate a strong electric field and has high scattering efficiency, so that the Raman enhancement of the InGaN layer can reach 106More than twice. The enhanced Raman signal intensity can be close to photoluminescence intensity, the enhancement of the Raman signal can greatly improve the detection speed of micro Raman, and the requirement of micro LED detection is met.
FIG. 4(a) is a schematic view of a reverseThe micro LED chip 10 is installed with a structural cross section schematic diagram, wherein 101 is an unintentionally doped GaN layer, the thickness is 2-10 micrometers, the square size is 20 micrometers × micrometers, 102 is an n-GaN layer, the unetched thickness is 1-2 micrometers, the partially etched thickness is 0.3-1 micrometer, 103 is a quantum well light emitting layer, the thickness is 20 nm-100 nm, 104 is a p-GaN layer, the thickness is 200nm, 105 is a p electrode, the contact layer 1051 is made of ITO or AZO, the thickness is about 200nm, the reflecting layer 1052 containing Ag is about 200nm, the bonding layer 1053 is about 0.2-1 micrometer, the reflecting layer 1052 containing Ag is embedded into the p-GaN layer 105, the structure of the reflecting layer is a nano structure capable of forming surface plasmon with a quantum well, the size of embedded Ag particles is 30-50 nm, the surface plasmon resonance is formed with a quantum well light emitting layer of InGaN/GaN, 106 is an n electrode, the height of the contact layer is 200nm, the height of the bonding layer is equal to the 105, the size is about 356 micrometers, and the passivation layer 107 is made of SiO 842Or SiNxAnd the thickness is 200-1000 nm. FIG. 4(b) is a schematic diagram of the back surface of the structure of the flip micro LED chip 10, 105 is the reflection surface of the p-electrode, and all the structures 101-105 and the surface plasmon structures 1052 and 105, 104 can be observed through the back surface light transmission. 106 is an n-electrode contact layer, and the etched surfaces of 101, 102 and n-GaN can be observed through light transmission of the back surface. Structures 101, 102 and 107 and structures of the etched surface of portion 102 and the mesa sidewalls are observed at 107.
And placing the micro LED chip array to be detected on an XYZ three-dimensional high-speed sample table, and determining by using the position and the measurement space range. The position of the chip in the z direction is determined by the function of self-focusing. For a micro led chip array with a size of 6 inches, the test range was set to 15.5cm × 15.5 cm.
The position of the starting point is set, and the top right corner of the test range of 15.5cm multiplied by 15.5cm is determined as the vertex. According to the micro LED period of 20 micrometers, the testing range of each frame is determined to be 400 micrometers multiplied by 400 micrometers, the number of chip samples is 20 multiplied by 20 to 400, and the scanning resolution of the scanning galvanometer reaches 25 pixels multiplied by 25 pixels of each micro LED chip. The measurement instrument has limited response time and has low measurement value for partial point positions, where each chip test point has 10 test points, the positions are shown as:' in fig. 5, and the test points are located at 7 points on different positions of the p-electrode 105, and the measurement 101-105 structures include dislocation and defect measurement, and measurement of the active concentration of p-type GaN on the p-GaN layer 104 and the p-type contact layer structure of the p-GaN layer 104 and the p-electrode 105. And the etching damage of the side wall and the bottom is measured at two points of the passivation layer 107, the structure of the passivation layer 107 is measured, 1 point of the n electrode 106 is measured, the etching damage of the n-type contact layer structure and the n-GaN layer is measured, and the like.
Setting a measurement range and a classification standard of a PL spectrum; the PL spectrum was measured at 3 points set at different positions in the p-electrode 105, and the PL peak wavelength and peak intensity were obtained and classified according to the average value. If a certain measuring point has a larger difference with other measuring points, the test is unqualified.
Setting a measuring range and a classification standard of a Raman spectrum; and performing Raman tests of all 10 points, classifying the tested micro LED chip samples according to the corresponding relation between each Raman data and the electrical property in principle, and judging the electrical grade. And meanwhile, structural components are also marked and classified so as to obtain more indexes of micro LED performance.
And performing PL and Raman tests on all the flip chip test points in the visual field line by line point by point until all the micro LEDs on the whole sample substrate are measured. And carrying out statistics and classification on sample tests, generating files classified according to various parameter indexes, and drawing mapping graphs.
Example two
In this embodiment, the test sample is a micro LED chip with a vertical structure.
In the embodiment of the invention, the laser emission wavelength of the laser is adjusted, and the laser with the proper excitation wavelength is selected, so that the photon energy of the laser is equal to or similar to the energy of partial electron transition, and resonance is generated, thereby enhancing the Raman signal of the micro LED chip. The main detection objects of the Micro LED chip are GaN and InGaN materials, for E2, A1(LO) and LOPC Stokes peaks of the GaN material, laser wavelength of 325-345nm is adopted, and for anti-Stokes Raman peaks of the GaN material, excitation light wavelength is smaller than 350nm, so that the collected Raman signal can be subjected to resonance enhancement and is simultaneously interfered by photoluminescenceIs smaller. The excitation wavelength used for the E2, a1(LO) peaks of InGaN material is in the range of about 405-425nm to ensure no strong photoluminescence interference and no energy level transitions in GaN are excited. For SiO2、SiNxITO and associated passivation layers and surface process residues, with appropriate choice of excitation wavelength to obtain a resonance enhanced raman signal.
In the embodiment, the periodic Ag metal nano structure and the InGaN/GaN quantum well are embedded in the p-GaN to form surface plasmon resonance, so that the Raman signal intensity of the micro LED chip is enhanced. Meanwhile, the high reflectivity of the metal Ag is utilized to prepare the light reflecting layers of the LEDs with the vertical structures and the inverted structures, so that the luminous efficiency of the micro LEDs can be improved. The size of the Ag metal nano structure embedded into the p-GaN is within the range of 30-50 nm, and a needle point-shaped or antenna-shaped array structure is formed. The coupling effect caused by the periodic Ag nano-structure can generate a strong electric field and has high scattering efficiency, so that the Raman enhancement of the InGaN layer can reach 106More than twice. The enhanced Raman signal intensity can be close to photoluminescence intensity, the enhancement of the Raman signal can greatly improve the detection speed of micro Raman, and the requirement of micro LED detection is met.
FIG. 6(a) is a schematic cross-sectional view of a vertical micro LED chip 20, wherein 201 is an unintentionally doped GaN layer, 2-10 μm in thickness, 20 μm in square size × 20 μm, 202 is an n-GaN layer, 1-2 μm in thickness, 203 is a quantum well light-emitting layer, 20 nm-100 nm in thickness, 204 is a p-GaN layer, 200 nm-205 is a p-electrode, including a contact layer ITO or AZO layer 2051, 200nm in thickness, a reflective layer 2052 containing Ag is about 200nm, a bonding layer 2053 is about 0.2-1 μm in thickness, 206 is an n-electrode, including a contact layer 200nm, a bonding layer is about 0.2-1 μm in thickness, and a circular shape with a diameter of about 8 μm, the reflective layer 2052 containing Ag is embedded in a p-type layer 204 or the light-emitting layer 203, the reflective layer is a nanostructure capable of forming a surface plasmon with a quantum well light-emitting layer, the embedded Ag particles are 30-50 nm in size and resonate with an InGaN/quantum well structure, and a passivation layer 207 is a SiO passivation layer shown in FIG. 6(a2Or SiNx200 to 1000nm in thicknessThe vertical structure micro LED chip is arranged on the upper surface and the lower surface of the vertical structure micro LED chip. Fig. 6(b) is a schematic diagram of the structure back of the vertical micro LED chip 20, where all structures 201 to 205 and 207 can be observed through back light transmission, and surface plasmon structures associated with the reflective layer 2052 containing Ag, the p-electrode 205 and the p-GaN layer 204. The edge area is a passivation layer 207, and all structures of 201-204 can be observed through back light transmission.
And placing the micro LED chip array to be detected on an XYZ three-dimensional high-speed sample table, and determining by using the position and the measurement space range. The position of the chip in the z direction is determined by the function of self-focusing. For a micro led chip array with a size of 6 inches, the test range was set to 15.5cm × 15.5 cm.
The position of the starting point is set, and the top right corner of the test range of 15.5cm multiplied by 15.5cm is determined as the vertex. According to the micro LED period of 20 micrometers, the testing range of each frame is determined to be 400 micrometers multiplied by 400 micrometers, the number of chip samples is 20 multiplied by 20 to 400, and the scanning resolution of the galvanometer reaches 25 pixels multiplied by 25 pixels of each chip. Like the flip chip described above, each of the test points of the chip has a number of 10, and the positions are shown as ≧ in fig. 7, which are 6 points at different positions on the top of the test point 205, respectively, and the structures of the test points 201 and 204, including the measurement of dislocations and defects, the measurement of the active concentration of p-type GaN at 204, the p-type contact layer structure of the p-GaN layer 204 and the p-electrode 205, are measured. And 4 points are positioned in the edge area of the passivation layer 207, the etching damage of the side wall is measured, the structure of the passivation layer 207 is measured, and the stress, defect structure and the like of the division of the unintentionally doped GaN layer 201 and the n-GaN layer 202 are measured.
Setting a measurement range and a classification standard of a PL spectrum; the PL spectrum was measured at 3 points set at different positions in the p-electrode 205, and the PL peak wavelength, peak intensity, was classified according to the average. If a certain measuring point has a larger difference with other measuring points, the test is unqualified.
Setting a measuring range and a classification standard of a Raman spectrum; and performing Raman tests of all 10 points, classifying Raman peak frequency, peak intensity and the like according to the corresponding relation between each Raman data and the electrical property in the principle, and judging the electrical grade. And meanwhile, structural components are also marked and classified so as to obtain more indexes of micro LED performance.
And performing PL and Raman tests on all vertical structure chip test points in the visual field line by line point by point until all the micro LEDs on the whole sample substrate are measured. And carrying out statistics and classification on sample tests, generating files classified according to various parameter indexes, and drawing mapping graphs.
Finally, it is noted that the disclosed embodiments are intended to aid in further understanding of the invention, but those skilled in the art will appreciate that: various substitutions and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the embodiments disclosed, but the scope of the invention is defined by the appended claims.

Claims (10)

1. A Raman signal enhancement detection method of a micro LED chip is characterized in that a method of electron level resonance and surface plasmon resonance is adopted to enhance a Raman signal, and the detection method comprises the following steps:
1) embedding periodic metal nano structures in a p-GaN layer of a micro LED chip;
2) the laser emits parallel exciting light, the wavelength of the exciting light is 325-345nm, the wavelength of the exciting light is equal to the energy of partial electron transition, and the wavelength of the exciting light is 20-40 nm smaller than the wavelength of fluorescence generated by exciting a sample; or the wavelength of the exciting light is less than 350nm, the wavelength of the exciting light is within 20nm of the fluorescence wavelength generated by exciting the sample, and the wavelength of the exciting light is equal to the energy of partial electron transition;
3) the exciting light is removed of stray light through the first spatial filter, changed into a plurality of beams of parallel light with different angles through the multi-surface prism, and then passes through the first beam splitting sheet;
4) a plurality of parallel lights with different angles pass through a scanning galvanometer and are focused by an objective lens to form a plurality of one-dimensional arranged light spots;
5) the micro LED chip array is used as a sample and is positioned on a focal plane of an objective lens and is placed on an XYZ three-dimensional high-speed sample table; exciting light of the one-dimensional array of light spots is incident on a sample at a Brewster angle, all the exciting light parallel to a polarization plane is transmitted to the inside of the sample instead of being reflected by the surface, so that Raman light is excited, resonance is generated due to the fact that the wavelength of the exciting light is equal to the energy of partial electron transition, and a metal nano structure embedded into a micro LED unit and a quantum well form surface plasmon resonance, so that the Raman light is enhanced to a fluorescence magnitude, meanwhile, photoluminescence generates fluorescence, the one-dimensional array of light spots is simultaneously irradiated on a plurality of micro LED chip units, and the generated Raman light and the fluorescence are also the one-dimensional array of light spots;
6) the fluorescence and the Raman light return to the objective lens, then sequentially pass through the scanning galvanometer and the first beam splitter, are controlled by the light path switching device, are collected by the ocular lens and enter the CCD camera, and the surface morphology of the sample is observed;
7) or the fluorescence and the Raman light are controlled by the light path switching device, stray light is filtered by the second spatial filter, and then the light spots are shaped by the longitudinal cylindrical lens and the transverse cylindrical lens in sequence to become rectangular light spots;
8) the first beam splitter is used for splitting the light into two beams of light in different directions, and the two beams of light respectively enter a first channel and a second channel of the multi-channel spectrometer;
9) the first beam of light is split by the first prism spectrometer, only fluorescence is reserved, and the reserved fluorescence is received by the first CCD area array detector; the fluorescence is a one-dimensionally arranged light spot array, the first CCD area array detector is a two-dimensionally arranged pixel, each light spot of the fluorescence respectively corresponds to a row of pixels of the CCD area array detector, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, the intensity and the brightness of each wavelength of the fluorescence are obtained, and therefore the fluorescence spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the first CCD area array detector simultaneously obtains the fluorescence spectra of the scanning positions of a plurality of corresponding micro LED chip units;
10) if the wavelength of the exciting light is less than 20-40 nm of the fluorescence wavelength generated by exciting the sample, the Stokes Raman is adopted for combining fluorescence measurement, the second beam of light is split by the second prism spectrometer, only Stokes Raman light is reserved, and as the wavelength of the exciting light is less than 20-40 nm of the fluorescence wavelength generated by exciting the sample, and the wavelength of the Stokes Raman light is within 30nm of the wavelength of the exciting light, the spectrums of the fluorescence and the Stokes Raman light can be separated and received by the second CCD area array detector;
or if the wavelength of the exciting light is less than the wavelength of the fluorescence generated by exciting the sample by 20nm, combining anti-stokes raman with fluorescence measurement, splitting the second beam of light by a second prism spectrometer, and only reserving anti-stokes raman light;
11) the Raman light is a one-dimensionally arranged light spot array, the second CCD area array detector is a two-dimensionally arranged pixel, each light spot of the Raman light corresponds to a row of pixels of the CCD area array detector respectively, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, the intensity and the brightness of each wavelength of the Raman light are obtained, and therefore the Raman light spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the second CCD area array detector simultaneously obtains the Raman light spectra of the scanning positions of a plurality of corresponding micro LED chip units;
12) repeating the steps 2) to 11) by controlling the scanning galvanometer, and finishing scanning of the corresponding micro LED chip units by the exciting light of the one-dimensional array of the light spots;
13) further controlling a scanning galvanometer, and repeating the steps 2) -12), wherein the exciting light of the one-dimensional light spot array finishes scanning one frame of the micro LED chip array;
14) moving the sample to the next frame by controlling an XYZ three-dimensional high-speed sample stage, and repeating the steps 2) -13), thereby completing the scanning of the micro LED chip array and obtaining the fluorescence spectrum and the Raman spectrum of the micro LED chip array;
15) obtaining optical properties by fluorescence spectroscopy;
16) obtaining corresponding electrical properties through Raman spectra of a plurality of measuring points;
17) the micro LED chip arrays are classified according to optical and electrical properties.
2. The detection method of claim 1, wherein the sample polarizability is altered by the metal nanostructures; the metal nano structure adopts a plurality of needle points or antenna shapes, so that the lightning rod enhancement and the antenna emission effect are enhanced; and the surface plasmon resonance effect enhances the Raman signal and fluorescence signal intensity of the quantum well region, or enhances the Raman signal intensity of the GaN layer and the passivation layer.
3. The inspection method according to claim 1, wherein in step 16), dislocation defects, an activation concentration of p-type GaN, and a p-type contact layer structure are inspected by raman spectroscopy of a measurement point in a p-electrode region; and detecting the structure and the etching damage of the passivation layer through the Raman spectrum of the measuring point in the passivation layer region, and detecting the etching damage of the n-type contact layer structure and the n-GaN layer through the Raman spectrum of the measuring point in the n electrode region, so that the overall electrical property of the micro LED chip is obtained according to the Raman spectrum of each measuring point.
4. The utility model provides a detection apparatus for raman signal reinforcing of micro LED chip which characterized in that, detection apparatus for raman reinforcing of micro LED chip includes: the device comprises a laser, a first spatial filter, a multi-face prism, a first beam splitter, a scanning galvanometer, an objective lens, an XYZ three-dimensional high-speed sample stage, a control system, an optical path switching device, an eyepiece, a CCD camera, a second spatial filter, a longitudinal cylindrical lens, a transverse cylindrical lens, a second beam splitter and a multi-channel spectrometer; the control system is respectively connected to the laser, the light path switching device, the scanning galvanometer, the CCD camera, the XYZ three-dimensional high-speed sample stage and the multi-channel spectrometer; the multi-channel spectrometer comprises a first channel and a second channel; the first channel comprises a first prism spectrometer and a first CCD area array detector, and the second channel comprises a second prism spectrometer and a second CCD area array detector; the laser emits parallel exciting light, the wavelength of the exciting light is 325-345nm, the wavelength of the exciting light is equal to the energy of partial electron transition, and the wavelength of the exciting light is 20-40 nm smaller than the wavelength of fluorescence generated by exciting a sample; or the wavelength of the exciting light is less than 350nm, the wavelength of the exciting light is within 20nm of the fluorescence wavelength generated by exciting the sample, and the wavelength of the exciting light is equal to the energy of partial electron transition; the exciting light is removed from stray light through a first spatial filter, is changed into a plurality of parallel lights with different angles through a multi-surface prism, passes through a first beam splitting sheet and then a scanning galvanometer, and is focused by an objective lens to form a plurality of one-dimensional arranged light spots; placing a micro LED chip array as a sample on an XYZ three-dimensional high-speed sample table; exciting light of the one-dimensional array of light spots is incident on a sample at a Brewster angle, all the exciting light parallel to a polarization plane is transmitted to the inside of the sample instead of being reflected by the surface, so that Raman light is excited, resonance is generated due to the fact that the wavelength of the exciting light is equal to the energy of partial electron transition, and a metal nano structure embedded into a micro LED unit and a quantum well form surface plasmon resonance, so that the Raman light is enhanced to a fluorescence magnitude, meanwhile, photoluminescence generates fluorescence, the one-dimensional array of light spots is simultaneously irradiated on a plurality of micro LED chip units, and the generated Raman light and the fluorescence are also the one-dimensional array of light spots; the fluorescence and Raman light enter an objective lens, pass through a scanning galvanometer and a first beam splitting sheet, are controlled by a light path switching device, are collected by an ocular lens and enter a CCD camera, and the surface morphology of a sample is observed; or the fluorescence and the Raman light are controlled by the light path switching device, stray light is filtered by the second spatial filter, then the light spots are shaped by the longitudinal cylindrical lens and the transverse cylindrical lens in sequence to become rectangular light spots, the rectangular light spots are divided into two beams of light with different directions by the second beam splitter, and then the two beams of light respectively enter a first channel and a second channel of the multi-channel spectrometer; the first beam of light is split by the first prism spectrometer, only fluorescence is reserved, and the first beam of light is received by the first CCD area array detector; the fluorescence is a one-dimensionally arranged light spot array, the first CCD area array detector is a two-dimensionally arranged pixel, each light spot of the fluorescence respectively corresponds to a row of pixels of the CCD area array detector, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, each wavelength of the fluorescence and corresponding brightness information are obtained, and therefore the fluorescence spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the fluorescence spectrum of the scanning positions of a plurality of corresponding micro LED chip units is obtained by the first CCD area array detector at the same time; if the wavelength of the exciting light is less than 20-40 nm of the fluorescence wavelength generated by exciting the sample, the Stokes Raman is adopted for combining fluorescence measurement, the second beam of light is split by the second prism spectrometer, only Stokes Raman light is reserved, and as the wavelength of the exciting light is less than 20-40 nm of the fluorescence wavelength generated by exciting the sample, and the wavelength of the Stokes Raman light is within 30nm of the wavelength of the exciting light, the spectrums of the fluorescence and the Stokes Raman light can be separated and received by the second CCD area array detector; or if the wavelength of the exciting light is less than the wavelength of the fluorescence generated by exciting the sample by 20nm, combining anti-stokes raman with fluorescence measurement, splitting the second beam of light by a second prism spectrometer, and only reserving anti-stokes raman light; the Raman light is a one-dimensional array of light spots, the second CCD area array detector is a two-dimensional array of pixels, each light spot of the Raman light corresponds to a row of pixels of the CCD area array detector respectively, the light spots are separated according to the wavelength, different wavelengths correspond to different positions of the row of pixels, the intensity and the brightness of each wavelength of the Raman light are obtained, and therefore a Raman light spectrum of the scanning position of the corresponding micro LED chip unit is obtained, and the second CCD area array detector simultaneously obtains the Raman light spectra of the scanning positions of the plurality of corresponding micro LED chip units; the scanning of the plurality of micro LED chip units corresponding to the exciting light of the one-dimensional arranged light spot array is completed by controlling the scanning galvanometer, the scanning galvanometer is further controlled, the exciting light of the one-dimensional arranged light spot array completes the scanning of one frame of the micro LED chip array, then the XYZ three-dimensional high-speed sample stage is controlled, the scanning of the next frame of the micro LED chip array is realized, the scanning of the micro LED chip array is completed, the fluorescence spectrum and the Raman spectrum of the micro LED chip array are obtained, the optical property is obtained through the fluorescence spectrum, the corresponding electrical property is obtained through the Raman spectrum of a plurality of measuring points on the micro LED chip unit, and the micro LED chip array is classified according to the optical property and the electrical property.
5. The micro LED chip Raman signal enhanced detection device according to claim 4, wherein the laser is a semiconductor laser to ensure that the wavelength of the excitation light is continuously adjustable from near ultraviolet to visible light.
6. The micro LED chip Raman signal enhanced detection apparatus of claim 4, wherein the first spatial filter comprises a first lens, a first filter slit and a second lens; the parallel exciting light is converged to the first filtering slit by the first lens, the stray light is removed by the first filtering slit, and the parallel exciting light is converged into parallel light by the second lens to be emitted.
7. The micro LED chip Raman signal enhanced detection apparatus of claim 4, wherein the second spatial filter comprises a third lens, a second filter slit and a fourth lens; the parallel exciting light is converged to the second filtering slit by the third lens, the stray light is removed by the second filtering slit, and the parallel exciting light is converged into parallel light by the fourth lens to be emitted.
8. The micro LED chip Raman signal enhanced detection device of claim 4, wherein the multi-faceted prism adopts a multi-faceted cylindrical prism, having a bottom surface and a plurality of prism faces; the incident surface is the bottom surface, and the emergent surface has the different planes of N inclination to become the different parallel light of N bundle of angles, thereby improve scanning speed N times, N is 10 ~ 20 natural number, evenly distributed in the laser scanning field.
9. The micro LED chip Raman signal enhanced detection device of claim 4, wherein the optical path switching device employs a movable reflector, when the reflector moves out of the optical path, the fluorescence and Raman light are collected by the ocular lens and enter the CCD camera; when the mirror is placed at 45 ° in the optical path, the fluorescence and raman light enters the multi-channel spectrometer.
10. The micro LED chip Raman signal enhanced detection device according to claim 4, wherein the longitudinal cylindrical lens and the transverse cylindrical lens are cylindrical lenses, and the optical axes of the longitudinal cylindrical lens and the transverse cylindrical lens are perpendicular to each other and perpendicular to the optical path, so as to shape the light spot, and the shaped light spot is rectangular.
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