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CN-122016660-A - Method and system for nondestructively detecting polarity of AlN crystal

CN122016660ACN 122016660 ACN122016660 ACN 122016660ACN-122016660-A

Abstract

The invention discloses a method and a system for nondestructively detecting the polarity of an aluminum nitride (AlN) crystal, wherein the method realizes detection based on the phase matching relation between the polarity of the AlN crystal and a Second Harmonic (SHG). The AlN crystal is of an asymmetric wurtzite structure, the phase of an SHG signal generated by exciting an Al polar surface and an N polar surface along a c-axis has an inherent phase difference with a period of pi, the precise judgment of the polarity of the AlN crystal is realized by depending on the phase matching characteristic of the SHG signal, and no physical damage is caused in the detection process. When the method is implemented, pulse laser is normally incident to the AlN monocrystal surface to be detected, SHG signals are collected and measured, phases of the signals to be detected are compared with phases of known Al polar surface standard samples, the phases of the signals to be detected are Al polar surfaces if the phases of the signals to be detected are identical, and the phases of the signals to be detected are N polar surfaces if the phases of the signals to be detected are different by 180 degrees (pi). The method is completely lossless, is simple and convenient to operate, has high detection speed, can be used for distinguishing the polarity of the AlN body monocrystal and the substrate slice, and is suitable for industrial production and detection of the aluminum nitride-based semiconductor material.

Inventors

  • GONG JIANCHAO
  • CHEN QINGQING

Assignees

  • 晶曜盛巳(宁波)半导体有限公司

Dates

Publication Date
20260512
Application Date
20260316

Claims (7)

  1. 1. A method for non-destructive testing of AlN crystal polarity, comprising the steps of: An AlN crystal with known polarity is used as a standard sample, and the phase information of a Second Harmonic (SHG) signal of an Al polar surface of the AlN crystal is calibrated under the condition of normal incidence of pulse laser; obtaining an AlN crystal to be detected; under the same conditions as the calibration step and the detection parameters, vertically irradiating pulse laser to the surface to be detected of the AlN crystal to be detected; acquiring and measuring a second harmonic signal generated by the surface to be measured, and acquiring phase information of the second harmonic signal; comparing the measured phase of the SHG signal with a reference value of the phase of the SHG signal of the Al polar surface of the standard sample; if the phase of the SHG signal of the surface to be detected is consistent with that of the SHG signal of the standard sample Al polar surface, judging that the surface is the Al polar surface; if the phase of the SHG signal of the surface to be detected is 180 degrees (pi) different from the phase of the SHG signal of the polar surface of the standard sample Al, the surface is judged to be the N polar surface.
  2. 2. The method of claim 1, wherein the AlN crystal is an AlN bulk single crystal or an AlN substrate sheet.
  3. 3. The method of claim 1, wherein the pulsed laser has a wavelength in the near infrared band.
  4. 4. A method according to claim 1 or 3, wherein the pulsed laser is a femtosecond laser pulse or a picosecond laser pulse.
  5. 5. The method according to claim 1, characterized in that the second harmonic signal is collected and measured, in particular using a spectrometer or a photodetector in combination with a lock-in amplifier.
  6. 6. A system for non-destructive testing of AlN crystal polarity for implementing the method of any one of claims 1-5, comprising: A laser source for generating pulsed laser light; An optical focusing and guiding component for guiding the pulse laser and vertically irradiating the pulse laser to a surface to be detected of the AlN crystal to be detected; a signal collection means for collecting a second harmonic signal generated by the surface to be detected; And the signal detection and processing unit is used for acquiring and measuring the second harmonic signal, comparing the SHG signal phase of the AlN crystal detection surface to be detected with the SHG signal phase of the standard sample Al polar surface, and outputting a polarity judgment result according to the comparison result.
  7. 7. The system of claim 6, wherein the signal detection and processing unit comprises a spectrometer or a combination of a photomultiplier tube and a phase-locked amplifier.

Description

Method and system for nondestructively detecting polarity of AlN crystal Technical Field The invention belongs to the technical field of semiconductor material characterization and nondestructive testing, and particularly relates to a method and a system for nondestructive testing of AlN crystal polarity. Background Aluminum nitride (AlN) is used as an important third-generation wide-bandgap semiconductor material, has a direct bandgap of up to 6.2eV, high thermal conductivity and good piezoelectric and thermoelectric properties, and has a huge application prospect in the fields of deep ultraviolet photoelectric devices, high-frequency Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) filters, high-power electronic devices, micro-electromechanical systems (MEMS) and the like. AlN crystals belong to a hexagonal wurtzite structure (space group) Has remarkable spontaneous polarization and piezoelectric polarization effects along the [0001] direction. The structure does not have center inversion symmetry, thus forming two distinct polar surfaces, namely an aluminum (Al) polar surfaceDirection) and nitrogen (N) polar plane (direction)). The crystal polarity directly influences the chemical stability, the surface adsorption energy and the etching characteristic of the material, and more fundamentally determines the energy band offset, the two-dimensional electron gas transport characteristic and the direction and the efficiency of piezoelectric response of the AlN-based heterojunction, which are core parameters for device design and performance optimization. For example, in GaN/AlN high electron mobility transistors, the correct polarity direction is the precondition for the formation of a high concentration of two-dimensional electron gas, and in acoustic wave devices, the polarity direction determines the effectiveness of the piezoelectric excitation. Therefore, accurately and reliably identifying the polarity of an AlN wafer is an indispensable key in material research and device manufacturing. Patent CN202110515624.7 discloses a method and a device for distinguishing polar surfaces based on AlN piezoelectric effect, by applying controllable deformation to a wafer, the polarity of induced charges generated thereby is detected, thereby realizing judgment of the polarity of the crystal. But AlN crystals are high in hardness and brittleness, chip breakage and scrapping are easily caused in the deformation applying process, and if the deformation amount is too small, the strength of the induced electrical signals is weak and the induced electrical signals are difficult to collect. In addition, in the detection process, the stylus is in direct contact with the surface of the wafer, scratches or pits are easily formed on the surface of the wafer, the surface flatness is damaged, and a secondary polishing process is additionally required to repair the damage. Patent CN2021102660873.5 proposes a corrosion distinguishing method based on the difference of chemical stability of AlN different polar surfaces, wherein after a wafer surface is treated by adopting a corrosion liquid with a specific proportion, the wafer surface appearance is kept flat and smooth to be an Al polar surface, and the surface is obviously roughened to be an N polar surface. The method is required to realize the visualization of polarity difference through corrosion reaction, and the method inevitably causes chemical damage to the surface of the wafer, and secondary surface treatment is required to be carried out to eliminate corrosion traces. In summary, the two AlN polarity detection methods have obvious limitations, cannot achieve both nondestructive detection and high efficiency, and are difficult to adapt to the actual requirements of nondestructive and rapid detection in industrial production. AlN crystals belong to a cluster of points that does not possess center inversion symmetry, which is the basis of the crystallographic structure of AlN crystals that is capable of producing nonlinear optical effects such as second harmonics. The basic parameters of the AlN lattice include a lattice constant a of about 3.110-3.113A, c of about 4.978-4.982A and a rimThe ratio of the length of the cationic to anionic bonds u (c/a) of the (c-axis) is about 1.6. The structural features described above result in the crystal forming a permanent dipole moment in the c-axis direction. The dipole moments of a large number of unit cells are aligned in a uniform manner along the polar axis and macroscopically represent spontaneous polarization vectors along the c-axis. The spontaneous polarization direction is known to be always alongThe direction is as shown in fig. 1. Since the second order nonlinear optical coefficient tensor is directly related to the crystal polarity structure, when nonlinear light is inconsistent with the spontaneous polarization direction, a phase change occurs in a second order harmonic (SHG) signal generated by the nonlinear light.