Gallium-rich defect detection method for GaN devices based on second harmonic enhancement

Abstract

The present invention relates to a gallium-rich defect detection method for a gallium nitride device based on second harmonic enhancement, which belongs to the field of semiconductor detection technology, including: detecting the second harmonic intensity of the gallium-rich region and the non-gallium-rich region on the surface of a single crystal gallium nitride in the second harmonic mode of a confocal Raman imaging microscope, only the gallium-rich region produces the second harmonic enhancement phenomenon, which is used as the detection basis of the gallium-rich region; the gallium nitride device includes a silicon substrate and a gallium nitride film epitaxially grown on the silicon substrate, the silicon substrate is etched to expose a part of the gallium nitride film, and the second harmonic intensity of the entire area of ​​the exposed gallium nitride film is scanned, and if the second harmonic enhancement phenomenon occurs somewhere, it is judged that there is a gallium-rich region, that is, a defective region. The present invention can identify gallium-rich defects by only scanning the gallium nitride surface with the second harmonic intensity in the second harmonic mode of a confocal Raman imaging microscope, which is highly practical and easy to operate.

Description

Technical Field

[0001] The invention relates to a gallium-rich defect detection method for a gallium nitride device based on second harmonic enhancement, and belongs to the technical field of semiconductor detection. Background Art

[0002] Semiconductor inspection technology is an important part of the semiconductor manufacturing process and has developed along with the development of semiconductor integrated circuits. Since the advent of the Moore's Law era, microelectronic devices have gradually developed towards high precision, high sensitivity, small size, and easy integration. In particular, ultra-precision devices of micro-nano size have stricter and more demanding quality requirements for semiconductor materials. Controlling and detecting semiconductor defects is particularly important for the development of high-tech industries.

[0003] Semiconductor defect detection is an important part of the semiconductor manufacturing industry. Semiconductor defects have a significant impact on the performance, reliability and life of semiconductor devices. For example, the new generation of semiconductor material gallium nitride has piezoelectric, pyroelectric, photoelectric effect and other properties, which makes it widely used in microelectronics and optoelectronic devices, such as field effect transistors, MEMS resonators, photodetectors, LEDs, lasers, solar cells and other high-power devices. Its high electron mobility and other characteristics make it very valuable in communication, power converters and national defense. However, the defects generated by gallium nitride during the preparation and processing process have seriously affected its application and development in these fields. For example, Yu. Ya.Tomashpolsky et al. studied GaN prepared by metal organic chemical vapor deposition (MOCVD) technology. For GaN with different epitaxial thicknesses, the GaN with thinner thickness has a significant excess of Ga, and even forms single Ga nanoparticles; Chaoyue Zhang et al. used molecular dynamics simulation to study the subsurface damage during GaN nanogrinding. During the processing, a large number of defects such as interstitial atoms, vacancy defects and atomic clusters will be introduced; Yan Zhang et al. explained the influence of defects such as nitrogen vacancies (the sites where nitrogen atoms should have been in the GaN lattice structure become vacancies) and interstitial gallium (gallium atoms fill the interstitial positions of the GaN lattice) on the electron transport mechanism, which damages the efficiency and service life of the device. Therefore, it is very necessary to detect defects in semiconductor materials. Common detection methods are mainly the following:

[0004] 1. Optical inspection

[0005] Optical inspection generally uses an optical microscope to detect semiconductor surface morphology and macroscopic defects, or obtains a high-resolution three-dimensional image of the semiconductor surface through confocal technology. Chuen-Lin Tien et al. used optical automatic positioning and wafer defect detection systems to achieve automatic detection of spots and scratches. Although it is a non-destructive test, it is limited to surface physical defects such as surface roughness, scratches, cracks, particle contamination, etc. However, for problems such as imbalanced element content in compound semiconductors, optical inspection methods are insufficient.

[0006] 2. Electron beam testing

[0007] Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are both electron beam detection methods that use high-energy electrons to interact with semiconductor materials to detect their surface and internal properties. Kwame Owusu-Boahen and others used electron beam detection methods to detect defects and components inside semiconductor materials. Although it is possible to achieve nanometer or even atomic level precision, high-energy electron beams can cause irreversible damage to semiconductor materials and are destructive tests. In addition, scanning electron microscopy has certain requirements for the conductivity of semiconductor materials, and if conductive materials are required, additional contamination will be introduced.

[0008] 3. Spectral detection

[0009] Spectral detection is a technology that uses the absorption, emission and scattering characteristics of semiconductor materials to analyze their elemental composition, crystal structure and defects. Common spectral detection methods include UV-Vis spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Some of these methods require a high vacuum environment during the test process, such as X-ray photoelectron spectroscopy; some have high requirements for sample preparation and require single crystal or polycrystalline powder, such as X-ray diffraction; and UV-Vis spectroscopy is easily affected by light scattering and is insensitive to defects in certain special types of semiconductor materials.

[0010] Traditional GaN device defect detection methods, the most common of which are scanning electron microscopy (SEM) and transmission electron microscopy (TEM), can obtain information on GaN surface morphology or internal defects. However, these detection methods all use high-energy electron beams to bombard the GaN surface during testing. High energy is concentrated in the micron or even nanometer area, which will directly destroy the structure of GaN. High-energy electron beam bombardment can cause irreversible damage and even device failure.

[0011] For semiconductor material defect detection, it is very important to achieve large-area, high-precision non-destructive defect detection without damaging the sample or introducing contaminants. Summary of the invention

[0012] In view of the shortcomings of the prior art, the present invention provides a method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement. Gallium-rich defects can be identified by simply scanning the second harmonic intensity of the gallium nitride surface using the second harmonic mode of a confocal Raman imaging microscope. The method has strong practicality and is easy to operate.

[0013] The present invention adopts the following technical solution:

[0014] A method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement comprises the following steps:

[0015] S1: The second harmonic intensity of the gallium-enriched area and the non-gallium-enriched area on the surface of single-crystal gallium nitride is detected in the second harmonic mode of confocal Raman imaging microscope. Only the gallium-enriched area produces the second harmonic enhancement phenomenon, which is used as the basis for the detection of the gallium-enriched area.

[0016] S2: The gallium nitride device includes a silicon substrate and a gallium nitride film epitaxially grown on the silicon substrate. The silicon substrate is etched to expose a portion of the gallium nitride film. The second harmonic intensity of the entire exposed gallium nitride film is scanned. If the second harmonic enhancement phenomenon occurs at a certain location, it is determined that there is a gallium-enriched area, that is, a defective area.

[0017] Preferably, the process of step S1 is:

[0018] S11: placing a single crystal gallium nitride in a beaker, and ultrasonically treating the single crystal gallium nitride with acetone, alcohol, and deionized water in sequence, and drying the surface of the single crystal gallium nitride after the ultrasonic treatment with nitrogen;

[0019] S12: placing the dried single crystal gallium nitride on a vibration-damping table, firstly aligning the non-gallium-enriched area of ​​the single crystal gallium nitride after calibration with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal, so as to detect the second harmonic intensity and analyze whether the second harmonic enhancement phenomenon occurs;

[0020] S13: Then, the gallium-enriched region after calibration of the single crystal gallium nitride is aligned with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal, so as to detect the second harmonic intensity and analyze whether the second harmonic enhancement phenomenon occurs.

[0021] When collecting the second harmonic signal, the single crystal gallium nitride needs to be calibrated. The gallium-enriched area can be calibrated using existing technologies such as optical imaging and element content measurement to determine the non-gallium-enriched area and gallium-enriched area of ​​the single crystal gallium nitride.

[0022] Preferably, the process of collecting the second harmonic signal in steps S12 and S13 is as follows:

[0023] The computer controls the laser controller to make the laser emit a laser with a power of 100mW and a wavelength of 1064nm. After the laser beam quality is adjusted by a half-wave plate, the light with wavelengths other than 1064nm is filtered out by filter A, and then irradiated to the surface of the single crystal gallium nitride sample by reflector A. Due to the non-centrosymmetric structure of gallium nitride, the energy of the two photons of the same frequency of the incident laser is combined to produce a photon with a frequency twice that of the original, that is, a wavelength of 532nm (that is, the double frequency effect). The energy and momentum are conserved in the whole process. The combined photon is then reflected by reflector B to another filter B to filter out 1 The 532nm laser beam is used to transmit the light of 1064nm wavelength to the confocal Raman imaging microscope (to ensure that the 532nm laser is not interfered by the 1064nm incident light). The CCD camera in the confocal Raman imaging microscope is equipped with a sensor that can convert the light signal into an electrical signal based on the position of each measurement point. The strength of the electrical signal is proportional to the light intensity. The value of each measurement point represents the second harmonic intensity at the corresponding position. The computer is connected to the confocal Raman imaging microscope, and the computer can analyze the light intensity of each area, including the initial intensity and the second harmonic intensity, and display it in the form of a surface scanning (Mapping) image.

[0024] In the actual application test process, as long as the element ratio in single crystal gallium nitride is unbalanced and the gallium content is higher than nitrogen, it can be detected by second harmonic scanning. The second harmonic enhancement in gallium-enriched areas is determined based on the collective oscillation of free electrons in gallium under the excitation of the light field, which can significantly enhance the interaction between light and matter. The surface plasmon resonance effect of gallium can enhance the local electric field. The intensity of the second harmonic is proportional to the power exponent of the electric field intensity, thereby improving the efficiency of the second harmonic and enhancing it (that is, the enhancement effect is related to the gallium content). Therefore, in the second harmonic scanning image, the second harmonic intensity in the gallium-enriched area is much higher than that in the non-gallium-enriched area.

[0025] Preferably, in step S11, the capacity of the beaker is 80-120 mL, and acetone, alcohol and deionized water with a volume of 20 mL each are used for ultrasonic treatment in sequence, and the ultrasonic treatment time for each time is 15-25 min.

[0026] Preferably, the process of step S2 is:

[0027] S21: first, spin-coat an anti-etching adhesive on the silicon substrate to protect the area where the gallium nitride film does not need to be exposed, and etch the silicon substrate of the gallium nitride device by a wet etching method to expose part of the gallium nitride film, release part of the silicon-based gallium nitride, and suspend the gallium nitride film;

[0028] The present invention first etches the silicon substrate, suspends the gallium nitride film, and then tests the gallium nitride film. This is because the silicon substrate has a greater impact on the second harmonic and it is not easy to observe surface defects, so it is etched first and then tested. Silicon-based gallium nitride has important applications in light-emitting diodes, lasers, and two-dimensional devices. When the thickness of the gallium nitride film is relatively thin, higher requirements are placed on the growth process and detection method. Because the thickness of the gallium nitride film is generally several hundred nanometers, it is easy to produce defects such as hillocks during the growth process. Due to stress, imbalance of growth raw materials, and other problems, the imbalance of the ratio of nitrogen and gallium elements will also cause gallium enrichment defects. If conventional methods such as scanning electron microscopy (SEM) and transmission electron microscopy are used for detection, the high-energy electron beam will directly destroy the film, causing irreversible damage. For devices that require substrate transfer technology, destructive detection methods are even more undesirable. Therefore, the present invention is also suitable for defect detection of nanometer-thick gallium nitride films and related devices.

[0029] S22: placing the etched gallium nitride device on a vibration-damping table, aligning the exposed gallium nitride film with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal. The collection process of the second harmonic signal is the same as that of steps S12 and S13. By observing the intensity response image on the computer, the second harmonic signal in the gallium-enriched area is significantly stronger than that in the non-gallium-enriched area.

[0030] Preferably, in step S21, wet etching of the silicon substrate is achieved by a mixed solution of hydrofluoric acid, nitric acid and acetic acid, the volume ratio of hydrofluoric acid, nitric acid and acetic acid is 1:2:5, and the etching time is 20 minutes to 3 hours, which can be flexibly adjusted according to the quality of the silicon substrate.

[0031] Preferably, after step S22, the following steps are further included:

[0032] Step S23: a laser with a wavelength of 1064 nm is emitted to the surface of the silicon substrate that is not etched in the gallium nitride device by a laser, and the laser power is I, and the size of I is gradually increased from 10 mW to 100 mW. During the change of the laser power, the interaction at the heterogeneous interface of the silicon substrate and the gallium nitride film is observed to cause the second harmonic to generate splitting phenomenon, so as to study the influence of the heterogeneous interface between silicon and gallium nitride on the second harmonic.

[0033] Preferably, the laser power is I and gradually increases to 10mW, 20mW, 30mW, 40mW, 50mW, and 100mW respectively.

[0034] For GaN, it has heteroepitaxial and homoepitaxial growth modes. The GaN grown on sapphire substrates in homoepitaxial and heteroepitaxial growth is thicker and has higher light transmittance. In this case, the influence of the substrate on the second harmonic can be ignored. However, for GaN grown on silicon substrates, it is thinner and has poor light transmittance. The temperature at the interface is easily affected by the light intensity and produces interference, etc., which will cause more complex electron-phonon coupling and affect the waveform and generation efficiency of the second harmonic. Therefore, variable power testing to explore the changes in the second harmonic is more important for studying the influence of heterogeneous interfaces on the second harmonic.

[0035] Preferably, a defect detection device is used to implement the above-mentioned gallium-rich defect detection method of gallium nitride devices based on second harmonic enhancement, and the defect detection device includes a computer, a laser controller, a laser, a half-wave plate, a filter A, a reflector A, a vibration reduction table, a reflector B, a filter B and a confocal Raman imaging microscope;

[0036] The computer, the laser controller and the laser are connected in sequence, the computer is used to send a power signal to the laser controller, and the laser controller controls the laser to emit laser light; the computer is connected to the confocal Raman imaging microscope, and the computer is used to receive and process the signal of the confocal Raman imaging microscope; the vibration reduction table is used to place the single crystal gallium nitride sample or the etched gallium nitride device;

[0037] The laser emitted by the laser is incident on the single crystal gallium nitride sample or the etched gallium nitride device on the vibration-damping table through the half-wave plate, filter A, and reflector A in sequence. The light beam reflected by the sample is sequentially captured by the CCD camera of the confocal Raman imaging microscope through the reflector B and filter B and transmitted to the computer.

[0038] Preferably, the confocal Raman imaging microscope internally comprises a CCD camera and an ultra-high throughput spectrometer for capturing and analyzing second harmonic signals.

[0039] For any details not provided in the present invention, please refer to the prior art.

[0040] The beneficial effects of the present invention are:

[0041] 1. The method of enhancing second harmonic generation by using gallium surface plasmon resonance in the present invention can realize the detection of defects in gallium-enriched regions of gallium nitride and related semiconductor devices, which is highly practical and easy to operate.

[0042] 2. The present invention is easy to operate, can realize large-area and rapid defect detection, and has high sensitivity.

[0043] 3. The present invention is the first to use the method of enhancing the second harmonic by the plasmon resonance of gallium-enriched defects in gallium nitride to realize the detection of defects in gallium nitride devices, which is of great significance for practical applications such as improving device performance and extending device life.

[0044] 4. Although the present invention needs to perform substrate etching to expose the gallium nitride film during detection, this belongs to substrate transfer technology. Substrate transfer technology is widely used in silicon-based gallium nitride devices, such as bonding diamonds to dissipate device heat after etching the silicon substrate. The etching solution during substrate etching and the stress release process after substrate etching do not directly damage gallium nitride. The present invention adopts non-contact non-destructive detection, which will not damage gallium nitride or introduce additional pollution, which is beneficial to the subsequent device preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0046] Figure 1 It is a schematic diagram of a gallium-rich defect detection device for gallium nitride devices based on second harmonic enhancement of the present invention;

[0047] Figure 2 This is an optical photograph of defects in the gallium-enriched area of ​​single-crystal gallium nitride;

[0048] Figure 3 This is a second harmonic surface scanning image of defects in the gallium-enriched area of ​​single-crystal gallium nitride;

[0049] Figure 4 This is a Raman surface scanning image of defects in the gallium-enriched area of ​​single-crystal gallium nitride;

[0050] Figure 5 This is the EDS element spectrum of defects in the gallium-enriched area of ​​single-crystal gallium nitride;

[0051] Figure 6 This is an optical photograph of defects in the gallium-enriched area of ​​the GaN film that was partially released from GaN on silicon.

[0052] Figure 7 This is a second harmonic surface scanning image of defects in the gallium-enriched part of the gallium nitride film released from the substrate;

[0053] Figure 8 This is the second harmonic intensity diagram of silicon-based gallium nitride under laser power of 10mW, 20mW, 30mW, 40mW, 50mW, and 100mW;

[0054] In the figure, 1-sample, 2-vibration-absorbing table, 3-confocal Raman imaging microscope, 4-computer, 5-laser controller, 6-laser, 7-half-wave plate, 8-reflector B, 9-reflector A, 10-filter A, 11-filter B. DETAILED DESCRIPTION

[0055] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the implementation of this specification, but are not limited to this. Anything not fully described in the present invention shall be based on the conventional technology in the art.

[0056] Example 1

[0057] A method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement comprises the following steps:

[0058] S1: The second harmonic intensity of the gallium-enriched area and the non-gallium-enriched area on the surface of single-crystal gallium nitride is detected in the second harmonic mode of confocal Raman imaging microscope. Only the gallium-enriched area produces the second harmonic enhancement phenomenon, which is used as the basis for the detection of the gallium-enriched area.

[0059] S2: The gallium nitride device includes a silicon substrate and a gallium nitride film epitaxially grown on the silicon substrate. The silicon substrate is etched to expose a portion of the gallium nitride film. The second harmonic intensity of the entire exposed gallium nitride film is scanned. If the second harmonic enhancement phenomenon occurs at a certain location, it is determined that there is a gallium-enriched area, that is, a defective area.

[0060] Example 2

[0061] A method for detecting gallium-rich defects in a gallium nitride device based on second harmonic enhancement is as described in Example 1, except that the process of step S1 is as follows:

[0062] S11: placing a single crystal gallium nitride in a 100 mL beaker, and sequentially using 20 mL of acetone, alcohol, and deionized water to ultrasonically treat the single crystal gallium nitride, each ultrasonic treatment lasting 20 min, and blowing nitrogen to dry the surface of the single crystal gallium nitride after the ultrasonic treatment;

[0063] S12: placing the dried single crystal gallium nitride on a vibration-damping table, firstly aligning the non-gallium-enriched area of ​​the single crystal gallium nitride after calibration with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal, so as to detect the second harmonic intensity and analyze whether the second harmonic enhancement phenomenon occurs;

[0064] S13: Then, the gallium-enriched region after calibration of the single crystal gallium nitride is aligned with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal, so as to detect the second harmonic intensity and analyze whether the second harmonic enhancement phenomenon occurs.

[0065] When collecting the second harmonic signal, the single crystal GaN needs to be calibrated. The existing technologies such as optical imaging and element content measurement can be used to calibrate the GaN-enriched area to determine the non-GaN-enriched area and GaN-enriched area of ​​the single crystal GaN. Figure 2 As shown, it is a high-magnification image of the sample surface morphology in the optical mode of the confocal Raman imaging microscope, and the gallium-enriched area on the surface can be observed. In this embodiment, a relatively obvious gallium-enriched area is selected, which has a relatively obvious metallic luster in the optical image, and the ratio of gallium to nitrogen in the element content test is 7:3, and the gallium content is significantly higher than nitrogen, which is a gallium-enriched defect.

[0066] The process of collecting the second harmonic signal in steps S12 and S13 is as follows:

[0067] The computer controls the laser controller through software to make the laser emit a laser with a power of 100mW and a wavelength of 1064nm. After the laser beam quality is adjusted by a half-wave plate, the light with wavelengths other than 1064nm is filtered out by filter A, and then irradiated to the surface of the single crystal gallium nitride sample by reflector A. Due to the non-centrosymmetric structure of gallium nitride, the energy of the two photons of the same frequency of the incident laser is combined to produce a photon with a frequency twice that of the original, that is, a wavelength of 532nm (that is, the double frequency effect). The energy and momentum are conserved throughout the process. The combined photons are then reflected by reflector B to another filter B to filter out the 1064nm wavelength beam (to ensure that the 532nm laser is not interfered by the 1064nm incident light), and then by the CC in the confocal Raman imaging microscope. The CCD camera is equipped with a sensor that can convert the optical signal into an electrical signal based on the position of each measurement point. The strength of the electrical signal is proportional to the light intensity. The software that comes with the confocal Raman imaging microscope is selected and adjusted to the second harmonic detection mode. The grating and the center peak position are switched through the software of the confocal Raman imaging microscope. The grating is located in the ultra-high flux spectrometer. The grating is set to G1 mode and the center peak position is set to 500nm. Then the area is scanned for the second harmonic intensity. The value of each measurement point represents the second harmonic intensity at the corresponding position. The computer is connected to the confocal Raman imaging microscope. The computer can analyze the light intensity of each area, including the initial intensity and the second harmonic intensity, and present it in the form of a surface scanning (Mapping) image. The initial intensity (background intensity) refers to the intensity when the second harmonic signal is not generated during the second harmonic measurement.

[0068] In this embodiment, the single crystal GaN is a sample of n-type doped Si, and its size is: 10 mm in length, 10 mm in width, and the thickness of GaN is 440 μm. The second harmonic response curve can be analyzed by software and displayed in the form of a surface scan image, such as Figure 3The figure shows the surface scanning (mapping) image of the second harmonic generation (SHG). The initial intensity of single-crystal GaN is 487 a.u., and the second harmonic intensity of the GaN in the Ga-rich region is 619 a.u.; the second harmonic intensity of the non-GaN-rich region is 490 a.u., which is 44 times higher than that in the GaN region, that is, (619-487) / (490-487)=44.

[0069] like Figure 4 The figure shows a Raman surface scanning (Mapping) image of defects in the gallium-enriched area of ​​single-crystal gallium nitride. The Raman Mapping image is obtained by directly scanning the surface of the gallium nitride Raman peak using a confocal Raman imaging microscope (the input laser of the Raman Mapping here is 532nm, the grating mode is G1, the central peak is 2200nm, the filter is 532nm instead of 1064nm, the half-wave plate is in the off state, and the rest of the processing is the same as the second harmonic mapping image SHG Mapping), which is used to obtain relevant information about the gallium nitride crystal quality in this area, such as Figure 4 It can be seen that compared with the second harmonic surface scanning image, the Raman Mapping image has a smaller degree of change and cannot intuitively observe gallium-rich defects. Therefore, the gallium-enriched defects in single-crystal gallium nitride are not suitable for Raman surface scanning images, but are very suitable for second harmonic defect detection.

[0070] In the actual application test process, as long as the element ratio in the single crystal gallium nitride is unbalanced and the gallium content is higher than that of nitrogen, it can be detected by second harmonic scanning. In this embodiment, the ratio of gallium to nitrogen is 7:3, and the gallium content is significantly higher than that of nitrogen. The second harmonic enhancement in the gallium-enriched area is determined based on the collective oscillation of free electrons in gallium under the excitation of the light field, which can significantly enhance the interaction between light and matter. The surface plasmon resonance effect of gallium can enhance the local electric field, and the intensity of the second harmonic is proportional to the power exponent of the electric field intensity, thereby improving the efficiency of the second harmonic and enhancing it (that is, the enhancement effect is related to the gallium content). Therefore, in the second harmonic scanning image, the second harmonic intensity in the gallium-enriched area is much higher than that in the non-gallium-enriched area.

[0071] The EDS mode of scanning electron microscopy (SEM) is used to test the element content of defects in the gallium-enriched area of ​​single-crystal gallium nitride, such as Figure 5 As shown in the figure, in the EDS spectrum measurement, the full range of the measurement is 1983 counts, and the cursor is located at the starting position of the spectrum. Figure 5 The blue color in the upper right part represents the distribution of gallium (Ga) elements, and the blue color in the lower right part represents the distribution of nitrogen (N) elements. The gallium content is higher than that of nitrogen, which further confirms the practicality of this method for defect detection in gallium-rich areas.

[0072] The present invention can realize defect detection of single crystal gallium nitride and related devices through the second harmonic enhancement phenomenon of the gallium-enriched region of single crystal gallium nitride. In addition to the gallium-enriched defects generated during the growth and preparation process of gallium nitride, the material damage and gallium enrichment will also be caused in the processing and treatment process after growth. For example, Wang Hong et al. used three different bonding substrates and different laser energy densities for laser stripping in the influence of wafer bonding and laser stripping on the residual stress of GaN-based vertical structure light-emitting diode chips to prepare GaN-based LED devices with different stress states. However, when using laser to strip gallium nitride grown on sapphire substrates, the high-energy laser acting on gallium nitride will cause the nitrogen in gallium nitride to withstand ultra-high temperatures and pyrolyze to produce nitrogen, and gallium enrichment will be formed on the surface. In addition, high-temperature bonding will also produce similar effects. SO Kucheyev et al. studied the damage of ion implantation to GaN in Ion implantation into GaN, including the damage accumulation and amorphization of GaN during high-energy ion implantation, as well as the loss of nitrogen during ion bombardment, which also leads to gallium enrichment. Zhang Zhi-Rong et al. studied the effect of surface pretreatment on GaN homoepitaxial growth in Highmobility AlGaN / GaN highelectronic mobility transistors on GaN homo-substrates, and obtained AlGaN / GaN heterojunction materials with high electron mobility. The impurities on the surface of the GaN substrate were removed by alternately passing a mixture of ammonia and hydrogen into the reaction chamber with hydrogen. However, while removing impurities, the surface of the GaN can be etched in a high-temperature hydrogen environment. Due to the reducibility of hydrogen, the GaN is reduced to nitrogen and gallium, and gallium enrichment is also formed on the surface. The presence of gallium can accelerate device aging, and the leakage current generated by its own conductivity is not conducive to the manufacture of large-scale integrated circuits, etc. Therefore, the method of enhancing second harmonic generation by gallium surface plasmon resonance is not only applicable to grown gallium nitride, but also to gallium-enriched defects in processing and device preparation. It can cover the entire process from semiconductor growth to device preparation. It will not introduce pollution or damage to gallium nitride during the detection process. It has fast detection speed, strong practicality and easy operation.

[0073] Example 3

[0074] A method for detecting gallium-rich defects in a gallium nitride device based on second harmonic enhancement is as described in Example 2, except that the process of step S2 is as follows:

[0075] S21: First, an anti-etching glue is spin-coated on the silicon substrate to protect the area where the gallium nitride film does not need to be exposed, and the silicon substrate of the gallium nitride device is etched by a wet etching method to expose a part of the circular gallium nitride film, and the silicon-based gallium nitride is partially released to suspend the gallium nitride film, such as Figure 6 As shown;

[0076] In this embodiment, since the etching solution is isotropically etching the silicon substrate, the exposed area of ​​the gallium nitride film after etching is circular, so it is necessary to spin-coat the silicon of the silicon-based gallium nitride with an anti-etching glue before etching to expose the circular area to be etched.

[0077] In this embodiment, the wet etching of the silicon substrate is achieved by a mixed solution of hydrofluoric acid, nitric acid and acetic acid, the volume ratio of hydrofluoric acid, nitric acid and acetic acid is 1:2:5, and the etching time is 20 minutes;

[0078] The present invention first etches the silicon substrate, suspends the gallium nitride film, and then tests the gallium nitride film. This is because the silicon substrate has a greater impact on the second harmonic and it is not easy to observe surface defects, so it is etched first and then tested. Silicon-based gallium nitride has important applications in light-emitting diodes, lasers, and two-dimensional devices. When the thickness of the gallium nitride film is relatively thin, higher requirements are placed on the growth process and detection method. Because the thickness of the gallium nitride film is generally several hundred nanometers, it is easy to produce defects such as hillocks during the growth process. Due to stress, imbalance of growth raw materials, and other problems, the imbalance of the ratio of nitrogen and gallium elements will also cause gallium enrichment defects. If conventional methods such as scanning electron microscopy (SEM) and transmission electron microscopy are used for detection, the high-energy electron beam will directly destroy the film, causing irreversible damage. For devices that require substrate transfer technology, destructive detection methods are even more undesirable. Therefore, the present invention is also suitable for defect detection of nanometer-thick gallium nitride films and related devices.

[0079] S22: Place the etched gallium nitride device on a vibration-damping table, and align the exposed gallium nitride film with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal. The second harmonic signal collection process is the same as the second harmonic signal collection process of steps S12 and S13. In this embodiment, the gallium nitride film of the gallium nitride device is a circular gallium nitride film that partially releases the silicon substrate, and the substrate material is a (111) oriented silicon substrate; the size of the gallium nitride device used is: 5mm long, 5mm wide, the silicon substrate thickness is 850μm, the gallium nitride film thickness is 950nm, and the release area diameter is 100μm~2mm. In this embodiment, the initial intensity of the gallium nitride film is 487a.u., and the second harmonic intensity of the gallium-enriched area in the gallium nitride film is 562a.u., such as Figure 7As shown; the second harmonic intensity in the non-gallium-enriched region is 491 a.u., which is increased by about 19 times, that is, (562-487) / (491-487)≈19.

[0080] It is worth noting that, for unknown defect locations, the second harmonic mode of the confocal Raman imaging microscope can be directly used to perform regional scanning to obtain defect-related information. Larger defects can also be directly observed using the optical lens of the confocal Raman imaging microscope (if the particle size or thickness of the gallium-enriched area is too large, much larger than the wavelength of light, and exceeds the starting limit of coherent oscillation, because the diameter or thickness is already greater than 1 micron, it can be directly observed through the optical lens of the confocal Raman imaging microscope). For smaller and difficult-to-observe gallium-enriched defects, because the particle size of the gallium-enriched area is much smaller than the wavelength of light (such as the wavelength of light in this embodiment is 1064nm, that is, the gallium-enriched area with a thickness or diameter less than 1064nm), it is not necessary to meet the momentum matching condition to generate coherent oscillation, and the generated surface plasmon resonance effect can enhance the local electric field, thereby enhancing the second harmonic intensity. Directly scanning the second harmonic intensity can achieve the detection of gallium-enriched defects in gallium nitride.

[0081] Example 4

[0082] A method for detecting gallium-rich defects in a gallium nitride device based on second harmonic enhancement is as described in Example 3, except that after step S22, the method further includes:

[0083] Step S23: a laser with a wavelength of 1064 nm is emitted to the surface of the silicon substrate that is not etched in the gallium nitride device by a laser, and the laser power is I, and the size of I is gradually increased from 10 mW to 100 mW. During the change of the laser power, the interaction at the heterogeneous interface of the silicon substrate and the gallium nitride film is observed to cause the second harmonic to generate splitting phenomenon, so as to study the influence of the heterogeneous interface between silicon and gallium nitride on the second harmonic.

[0084] The laser power is I and gradually increases to 10mW, 20mW, 30mW, 40mW, 50mW, and 100mW. Figure 8 As shown in the figure, the interaction between the heterogeneous interface of silicon and gallium nitride was observed during the change of laser power, which resulted in the splitting phenomenon of second harmonic generation.

[0085] For GaN, it has heteroepitaxial and homoepitaxial growth modes. The GaN grown on sapphire substrates in homoepitaxial and heteroepitaxial growth is thicker and has higher light transmittance. In this case, the influence of the substrate on the second harmonic can be ignored. However, for GaN grown on silicon substrates, it is thinner and has poor light transmittance. The temperature at the interface is easily affected by the light intensity and produces interference, etc., which will cause more complex electron-phonon coupling and affect the waveform and generation efficiency of the second harmonic. Therefore, variable power testing to explore the changes in the second harmonic is more important for studying the influence of heterogeneous interfaces on the second harmonic.

[0086] At the interface between gallium nitride and silicon in step S23, as the laser power continues to increase, the temperature of the silicon substrate increases, resulting in an increase in the temperature at the interface. From the Bose-Einstein distribution relationship, it can be seen that the higher the temperature, the more phonons there are in gallium nitride. In addition, the energy is The photons can excite the electrons in the silicon substrate, the electrons generated by the GaN pyroelectricity, and the polarization charges generated at the heterogeneous interface due to the lattice constant mismatch between GaN and the silicon substrate, which further increase the number of phonons by coupling with phonons. Figure 8 The splitting phenomenon in .

[0087] The present invention can detect gallium-enriched defects in gallium nitride by scanning the second harmonic intensity. This is because the particle size of gallium at the gallium-enriched defect is much smaller than the wavelength of light, and the electric field of the incident light causes the free electrons in the metal to oscillate coherently, and the excitation of surface plasmons does not need to meet the momentum matching condition. The quasi-static theory is used for analysis, assuming that the electric field of the incident light is :

[0088] ;

[0089] in, is the electric field strength; For time; is the unit vector of the incident light direction; is the frequency of the incident light. When the particle size of the nano-gallium particles is much smaller than the wavelength of light When the dipole momentum of the electric dipole and The relationship is approximately:

[0090] ;

[0091] in, is the polarizability; is the dielectric constant of vacuum; is the dielectric constant of the dielectric, such as air, water or other non-metallic media. To simplify the calculation, it can be assumed to be the dielectric constant of air. By solving the classical Laplace equation, we can get:

[0092] ;

[0093] in, is the dielectric constant of the nano-gallium particles, Represents the particle size of nano-gallium particles.

[0094] The distance between the nano-gallium particle and the center of the sphere The electric field strength at is:

[0095] ;

[0096] in, , is the distance between the nano-gallium particle and the center of the sphere, is the unit direction vector; Represents the electric dipole moment. The electric field on the surface of the nano-gallium particle is composed of the electric field of the incident light and the dipole electric field caused by the nano-gallium particle. Therefore, the local electric field enhancement effect of the nano-gallium particle plasmon can enhance the nonlinear effect.

[0097] Gallium nitride is a polar crystal composed of Ga 3+ and N 3- The hexagonal structure formed by the lack of inversion symmetry allows GaN to exhibit nonlinear optical effects, including electric dipole optical second harmonic generation (SHG), which is a second-order nonlinear process. The incident photons are combined into a frequency The energy of the whole process is conserved, that is, Then the relationship between the second-order nonlinear polarization intensity and the incident optical electric field is expressed as:

[0098] ;

[0099] in, is the second-order nonlinear polarizability tensor of the material, is the electric field strength of the incident light; Indicates the frequency The polarization intensity of the photons generated by the nanogallium particles is increased due to the local surface plasmons, so the local electric field can be Approximate use To replace the incident light electric field, we can get the following formula:

[0100] ;

[0101] In addition, the SHG intensity of the second harmonic generation The electric field strength has the following relationship:

[0102] ;

[0103] The localized surface plasmon effect of nanogallium particles enhances the local electric field, thereby enhancing the second harmonic intensity, and both theoretical and test results have been verified.

[0104] Example 5

[0105] A method for detecting gallium-rich defects in a gallium nitride device based on second harmonic enhancement is as described in Example 3, except that a defect detection device is used to implement the method. Figure 1 As shown, the defect detection device includes a computer 4, a laser controller 5, a laser 6, a half-wave plate 7, a filter A 10, a reflector A 9, a vibration reduction table 2, a reflector B 8, a filter B 11 and a confocal Raman imaging microscope 3;

[0106] The computer 4, the laser controller 5 and the laser 6 are connected in sequence. The computer 4 is used to send a power signal to the laser controller 5, and the laser controller 5 controls the laser 6 to emit a laser. The computer 4 is connected to the confocal Raman imaging microscope 3, and the computer 4 is used to receive and process the signal of the confocal Raman imaging microscope 3. The vibration-damping table 2 is used to place single-crystal gallium nitride samples or etched gallium nitride devices, which can offset the vibration generated during the test and improve the measurement accuracy. The vibration-damping table selects the Swiss HERZ TS-150 series.

[0107] The laser light emitted by the laser 6 is incident on the single crystal gallium nitride sample or the etched gallium nitride device (i.e., sample 1) on the vibration-damping table 2 through the half-wave plate 7, the filter A 10, and the reflector A 9 in sequence. The light beam reflected by the sample is captured by the CCD camera of the confocal Raman imaging microscope 3 through the reflector B8 and the filter B 11 in sequence, and is transmitted to the computer 4.

[0108] Laser 6 is a Rainbow 1064 OEM ultrafast fiber laser produced by NPI Lasers, with a repetition frequency of 50 MHz and a pulse width of <15 ps. The output power can be adjusted by a computer and is used to output a second harmonic excitation signal. Confocal Raman imaging microscope 3 contains a CCD camera and an ultra-high throughput spectrometer for capturing and analyzing second harmonic signals. The confocal Raman imaging microscope can use an existing model, such as WITecalpha300 RS from Germany.

[0109] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A gallium-rich defect detection method for gallium nitride devices based on second harmonic enhancement, characterized in that: The steps include: S1: The second harmonic intensity of the gallium-enriched area and the non-gallium-enriched area on the surface of single-crystal gallium nitride is detected in the second harmonic mode of confocal Raman imaging microscope. Only the gallium-enriched area produces the second harmonic enhancement phenomenon, which is used as the basis for the detection of the gallium-enriched area. S2: The GaN device includes a silicon substrate and a GaN film epitaxially grown on the silicon substrate. The silicon substrate is etched to expose a portion of the GaN film. The second harmonic intensity of the entire exposed GaN film is scanned. If the second harmonic enhancement phenomenon occurs at a certain location, it is determined that there is a GaN-rich region, i.e., a defective region. The process of step S1 is: S11: placing a single crystal gallium nitride in a beaker, and ultrasonically treating the single crystal gallium nitride with acetone, alcohol, and deionized water in sequence, and drying the surface of the single crystal gallium nitride after the ultrasonic treatment with nitrogen; S12: placing the dried single crystal gallium nitride on a vibration-damping table, firstly aligning the non-gallium-enriched area of ​​the single crystal gallium nitride after calibration with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal, so as to detect the second harmonic intensity and analyze whether the second harmonic enhancement phenomenon occurs; S13: Then aligning the calibrated gallium-enriched region of the single crystal gallium nitride with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal, so as to detect the second harmonic intensity and analyze whether the second harmonic enhancement phenomenon occurs; The process of collecting the second harmonic signal in steps S12 and S13 is as follows: The computer controls the laser controller to make the laser emit a laser with a power of 100mW and a wavelength of 1064nm. After the laser beam quality is adjusted by a half-wave plate, the light with wavelengths other than 1064nm is filtered out by filter A, and then irradiated to the surface of the single crystal gallium nitride sample by reflector A. Due to the non-centrosymmetric structure of gallium nitride, the energy of two photons of the same frequency of the incident laser is combined to produce a photon with a frequency twice that of the original. The combined photon is then reflected by reflector B to another filter B to filter out the 1064nm wavelength beam, and then captured by the CCD camera in the confocal Raman imaging microscope. The CCD camera is equipped with a sensor that can convert the optical signal into an electrical signal based on the position of each measuring point. The strength of the electrical signal is proportional to the light intensity, and the value of each measuring point represents the second harmonic intensity at the corresponding position. The computer is connected to the confocal Raman imaging microscope, and the computer can analyze the light intensity of each area, including the initial intensity and the second harmonic intensity, and display it in the form of a surface scanning image.

2. The method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement according to claim 1, characterized in that: In step S11, the capacity of the beaker is 80-120 mL, and acetone, alcohol and deionized water with a volume of 20 mL each are used for ultrasonic treatment in sequence, and the ultrasonic treatment time for each time is 15-25 minutes.

3. The method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement according to claim 2, characterized in that: The process of step S2 is: S21: first, spin-coating an anti-etching adhesive on the silicon substrate to protect the area where the gallium nitride film does not need to be exposed, and etching the silicon substrate of the gallium nitride device by a wet etching method to expose part of the gallium nitride film; S22: placing the etched GaN device on a vibration-damping table, aligning the exposed GaN film with the optical path of the confocal Raman imaging microscope to collect the second harmonic signal. The second harmonic signal collection process is the same as the second harmonic signal collection process of steps S12 and S13.

4. The method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement according to claim 3, characterized in that: After step S22, the following steps are also included: Step S23: a laser with a wavelength of 1064 nm is emitted to the surface of the silicon substrate that is not etched in the gallium nitride device by a laser, and the laser power is I, and the size of I is gradually increased from 10 mW to 100 mW. During the change of the laser power, the interaction at the heterogeneous interface of the silicon substrate and the gallium nitride film is observed to cause the second harmonic to generate splitting phenomenon, so as to study the influence of the heterogeneous interface between silicon and gallium nitride on the second harmonic.

5. The method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement according to claim 4, characterized in that: The laser power is I and gradually increases to 10mW, 20mW, 30mW, 40mW, 50mW and 100mW respectively.

6. The method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement according to claim 5, characterized in that: The defect detection device is used for realization. The defect detection device includes a computer, a laser controller, a laser, a half-wave plate, a filter A, a reflector A, a vibration reduction table, a reflector B, a filter B and a confocal Raman imaging microscope; The computer, the laser controller and the laser are connected in sequence, the computer is used to send a power signal to the laser controller, and the laser controller controls the laser to emit laser light; the computer is connected to the confocal Raman imaging microscope, and the computer is used to receive and process the signal of the confocal Raman imaging microscope; the vibration reduction table is used to place the single crystal gallium nitride sample or the etched gallium nitride device; The laser emitted by the laser is incident on the single crystal gallium nitride sample or the etched gallium nitride device on the vibration-damping table through the half-wave plate, filter A, and reflector A in sequence. The light beam reflected by the sample is sequentially captured by the CCD camera of the confocal Raman imaging microscope through the reflector B and filter B and transmitted to the computer.

7. The method for detecting gallium-rich defects in gallium nitride devices based on second harmonic enhancement according to claim 6, characterized in that: The confocal Raman imaging microscope contains a CCD camera and an ultra-high throughput spectrometer for capturing and analyzing second harmonic signals.

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