Method for Measuring Microscopic Carrier Concentration Based on Non-Contact Atomic Force Microscopy

Abstract

The present invention discloses a method for measuring the carrier concentration in a micro-region based on a non-contact atomic force microscope. The method is as follows: The dielectric force modulation differences at different positions of a semiconductor sample to be measured and several standard semiconductor samples are obtained by using a two-step scanning method. The two-step scanning method is: The probe of the atomic force microscope is used to scan the semiconductor sample once to obtain the surface topography and surface potential; after the probe is lifted relative to the surface topography, a secondary scan is performed, a DC voltage and a modulation voltage are applied to cancel the surface potential, and the dielectric force modulation difference is obtained; A numerical simulation method is used to obtain the quantitative correspondence between the dielectric force modulation difference of the semiconductor sample to be measured and the carrier concentration. The quantitative correspondence is calibrated according to the dielectric force modulation differences and carrier concentrations of the standard semiconductor samples to obtain a simulated relationship curve, and finally the carrier concentration of the semiconductor sample to be measured is obtained. This method can avoid measurement errors caused by probe scratching and obtain the carrier concentration in a micro-region with spatial resolution.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor micro-region carrier concentration detection, and specifically relates to a method for measuring micro-region carrier concentration based on a non-contact atomic force microscope. Background Art

[0002] Semiconductor materials and devices are widely used in fields such as integrated circuits, communications, displays, and new energy. Their performance is significantly affected by the carrier concentration distribution. Commonly used carrier concentration measurement methods, such as field effect, Hall effect, and capacitance-voltage curves, have high accuracy but no spatial resolution. Carrier concentration distribution measurement methods based on contact atomic force microscopes, such as scanning microwave impedance microscopy and scanning capacitance microscopy, rely on special probe / sample designs, and the accuracy is easily changed with probe / sample wear. Summary of the Invention

[0003] (1) Technical problems to be solved by the present invention

[0004] The technical problem solved by the present invention is: how to provide a non-contact measurement method for micro-region carrier concentration that has both spatial resolution and can avoid damaging the probe and the sample.

[0005] (2) Technical solutions adopted by the present invention

[0006] A method for measuring micro-region carrier concentration based on a non-contact atomic force microscope, the micro-region carrier concentration measurement method includes:

[0007] Obtaining the dielectric force modulation difference at different positions of a semiconductor sample to be measured and several standard semiconductor samples by using a two-step scanning method. Among them, the carrier concentration of each standard semiconductor sample has been pre-calibrated. The two-step scanning method is: using the probe of the atomic force microscope to scan the semiconductor sample once to obtain the surface topography and surface potential; after lifting the probe to a preset height relative to the surface topography, perform a second scan. During the second scan, a DC voltage and a modulation voltage are applied. The DC voltage is used to cancel the surface potential to obtain the dielectric force modulation difference at different positions of the semiconductor sample;

[0008] Adopting a numerical simulation method to obtain the quantitative correspondence relationship between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be measured, calibrating the quantitative correspondence relationship according to the dielectric force modulation difference and the carrier concentration of each standard semiconductor sample to obtain a simulation relationship curve, and obtaining the carrier concentration of the semiconductor sample to be measured according to the measured dielectric force modulation difference of the semiconductor sample to be measured and the simulation relationship curve.

[0009] Preferably, in the two-step scanning method, the method of using the probe of an atomic force microscope to scan a semiconductor sample to obtain the surface topography of the semiconductor sample is as follows:

[0010] Apply a first AC voltage V to the piezoelectric ceramic ac0 sinω0t to drive the mechanical vibration of the probe, and perform line-by-line scanning in the tapping mode to obtain the surface topography of the semiconductor sample.

[0011] Preferably, the method of obtaining the surface potential of the semiconductor sample is as follows:

[0012] Apply a second AC voltage V between the probe and the semiconductor sample ac1 sinω1t, and use a Kelvin controller to apply a DC voltage V dc to cancel the amplitude signal of ω1, and use a data acquisition table to read the DC voltage V applied by the Kelvin controller during the scanning process dc at different spatial positions to obtain the surface potential of the semiconductor sample;

[0013] Alternatively, apply a second AC voltage V between the probe and the semiconductor sample ac1 sinω1t, use a phase-locked loop to track the phase of the mechanical vibration of the probe at ω0, and use a Kelvin controller to apply a DC voltage V dc to cancel the periodic phase change of ω0, the frequency of the periodic phase change of ω0 is ω1, and use a data acquisition table to read the DC voltage V applied by the Kelvin controller during the scanning process dc at different spatial positions to obtain the surface potential of the semiconductor sample;

[0014] Alternatively, apply a second AC voltage V between the probe and the semiconductor sample ac1 sinω1t, and use a Kelvin controller to apply a DC voltage V dc to cancel the amplitude signals of ω0±ω1, and use a data acquisition table to read the DC voltage V applied by the Kelvin controller during the scanning process dc at different spatial positions to obtain the surface potential of the semiconductor sample.

[0015] Preferably, the method of applying a DC voltage during the scanning process to cancel the surface potential is as follows: Use a data acquisition table to apply a cached DC voltage V between the probe and the semiconductor sample dc to cancel the surface potential;

[0016] The specific method of applying a modulation voltage between the probe and the semiconductor sample during the scanning process to obtain the dielectric force modulation difference at different positions of the semiconductor sample includes:

[0017] Apply a third AC voltage V between the probe and the semiconductor sample ac2 sinω2t and a DC modulation voltage V g ;

[0018] Measure the first amplitude signal of 2ω2 at -V g and the second amplitude signal of 2ω2 at +V g ; obtain the dielectric force modulation difference according to the difference between the first amplitude signal and the second amplitude signal.

[0019] Preferably, the method of applying a DC voltage during the scanning process to cancel the surface potential is as follows: Use a data acquisition table to apply a buffered DC voltage V dc between the probe and the semiconductor sample to cancel the surface potential;

[0020] The specific method of obtaining the dielectric force modulation difference at different positions of the semiconductor sample by applying a modulation voltage between the probe and the semiconductor sample during the scanning process includes:

[0021] Apply a third AC voltage V ac2 sinω2t and a fourth AC voltage V ac3 sinω3t between the probe and the semiconductor sample;

[0022] Measure the amplitude signal of 2ω2 + ω3 or 2ω2 - ω3 to obtain the dielectric force modulation difference.

[0023] Preferably, the method of applying a DC voltage during the scanning process to cancel the surface potential is as follows: Use a data acquisition table to apply a buffered DC voltage V dc between the probe and the semiconductor sample to cancel the surface potential;

[0024] The specific method of obtaining the dielectric force modulation difference at different positions of the semiconductor sample by applying a modulation voltage between the probe and the semiconductor sample during the scanning process includes:

[0025] Apply a first AC voltage V ac0 sinω0t and a third AC voltage V ac2 sinω2t on the piezoelectric ceramic to drive the mechanical vibration of the probe, and use a phase-locked loop to track the phase of the mechanical vibration of the probe at ω0;

[0026] Apply a DC modulation voltage V g between the probe and the semiconductor sample, measure the phase change of ω0 at -V g and the phase change of ω0 at +V g ; the frequency of the phase change of ω0 is 2ω2, according to the phase change of ω0 at -V g and the phase change of ω0 at +V gThe difference in phase change under ω0 gives the dielectric force modulation difference.

[0027] Preferably, the method of applying a DC voltage to offset the surface potential during the scanning process is: using a data acquisition table to apply a buffered DC voltage V between the probe and the semiconductor sample dc , to offset the surface potential;

[0028] A specific method of applying a modulation voltage between the probe and the semiconductor sample during scanning to obtain a dielectric force modulation difference at different positions of the semiconductor sample includes:

[0029] Apply a first AC voltage V to the piezoelectric ceramic. ac0 sinω0t drives the probe to vibrate mechanically, and applies a third AC voltage V between the probe and the semiconductor sample. ac2 sinω2t and the fourth AC voltage V ac3 sinω3t and, using a phase-locked loop to track the phase of the probe’s mechanical vibration at ω0;

[0030] The phase change of ω0 is measured to obtain the dielectric force modulation difference, and the frequency of the phase change of ω0 is 2ω2+ω3 or 2ω2-ω3.

[0031] Preferably, the specific method of using the numerical simulation method to obtain the quantitative correspondence between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be tested is:

[0032] Building a model based on the actual size and spatial position relationship between the probe and the semiconductor sample to be tested and the semiconductor physical parameters of related materials;

[0033] The model is divided into finite elements, and the Poisson equation and the continuity equation are combined to solve the dielectric force modulation difference caused by the carrier polarization difference of the semiconductor sample under different probe gate voltages under the preset semiconductor sample carrier concentration, so as to obtain the quantitative correspondence between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be tested.

[0034] Preferably, the range of the finite element block division is 0.01 nanometers to 10 nanometers, and the range of the carrier concentration of the semiconductor sample to be measured is 10 16 -10 19 The carrier concentration of each standard semiconductor sample ranges from 10 16 -10 19 Per cubic centimeter.

[0035] Preferably, the quantitative corresponding relationship is calibrated according to the dielectric force modulation difference and carrier concentration of each standard semiconductor sample, and the method for obtaining the simulated relationship curve is:

[0036] Multiply the dielectric force modulation difference corresponding to different carrier concentrations obtained by simulation by a preset proportionality coefficient to optimize the fitting of the simulated quantitative correspondence relationship with the measurement results of each standard semiconductor sample, and obtain a simulated relationship curve.

[0037] (III) Beneficial effects

[0038] The present invention discloses a method for measuring micro-region carrier concentration based on a non-contact atomic force microscope. Compared with the prior art, it has the following technical effects:

[0039] The non-contact measurement method of this solution measures the spatially resolved dielectric force modulation difference of the semiconductor sample to be measured and the standard semiconductor sample. By combining the numerical simulation method, the spatially resolved carrier concentration distribution value of the semiconductor sample to be measured can be further obtained, which can avoid the measurement error caused by the wear of the sample and the probe in the original contact measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flowchart of a method for measuring micro-region carrier concentration based on a non-contact atomic force microscope according to Embodiment 1 of the present invention;

[0041] Figure 2 It is a circuit schematic diagram of a method for measuring micro-region carrier concentration based on a non-contact atomic force microscope according to Embodiment 1 of the present invention;

[0042] Figure 3 It is a schematic diagram of the numerical simulation and standard sample calibration process according to Embodiment 1 of the present invention;

[0043] Figure 4 For A, it is a surface topography image of the cross-section of a III-V semiconductor heterojunction; for B, it is a surface potential image of the cross-section of a III-V semiconductor heterojunction; for C, it is a dielectric force modulation difference image of the cross-section of a III-V semiconductor heterojunction; for D, it is a calibrated carrier concentration distribution image. DETAILED DESCRIPTION OF THE INVENTION

[0044] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] Before describing various embodiments of the present application in detail, first briefly describe the technical concept of the present application: When measuring the carrier concentration of a micro-region semiconductor sample in the prior art, there are technical problems of no spatial resolution and easy damage to the sample. For this reason, this solution provides a method for measuring the carrier concentration of a micro-region based on a non-contact atomic force microscope. This measurement method mainly includes three parts: experimental measurement, numerical simulation, and calibration. First, the dielectric force modulation difference with spatial resolution of the semiconductor sample to be measured and a series of standard semiconductor samples is obtained through a non-contact measurement method; then, a numerical simulation method is used to construct a quantitative correspondence between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be measured; then, the quantitative correspondence between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be measured is calibrated by using the experimentally measured dielectric force modulation difference of the standard semiconductor sample and the pre-calibrated carrier concentration. Finally, the carrier concentration distribution value of the semiconductor sample to be measured is obtained according to the actually measured dielectric force modulation difference of the semiconductor sample to be measured and the calibrated quantitative correspondence. Since a non-contact measurement method is adopted, damage to the sample and the probe can be avoided.

[0046] Specifically, as Figure 1 and Figure 2 shown, Embodiment 1 of the present disclosure discloses a method for measuring the carrier concentration of a micro-region based on a non-contact atomic force microscope. This measurement method includes the following steps:

[0047] Step S10: Obtain the dielectric force modulation differences at different positions of the semiconductor sample to be measured and several standard semiconductor samples by using a two-step scanning method. Among them, the carrier concentrations of the standard semiconductor samples have been pre-calibrated. The two-step scanning method is as follows: Use the probe of the atomic force microscope to scan the semiconductor sample once to obtain the surface topography and surface potential; after lifting the probe to a preset height relative to the surface topography, perform a secondary scan. A DC voltage and a modulation voltage are applied during the secondary scan. The DC voltage is used to cancel the surface potential to obtain the dielectric force modulation differences at different positions of the semiconductor sample.

[0048] Step S20: Use a numerical simulation method to obtain the quantitative correspondence between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be measured. Calibrate the quantitative correspondence according to the dielectric force modulation differences and carrier concentrations of the standard semiconductor samples to obtain a simulated relationship curve. According to the measured dielectric force modulation difference of the semiconductor sample to be measured and the simulated relationship curve, obtain the carrier concentration of the semiconductor sample to be measured.

[0049] Next, taking the semiconductor sample to be measured as an example, illustrate the measurement process of the dielectric force modulation difference. The measurement process of the dielectric force modulation difference of the standard semiconductor sample is exactly the same as that of the former.

[0050] Among them, in step S10, the method for obtaining the surface topography of the semiconductor sample is as follows: Apply a first AC voltage V to the piezoelectric ceramic ac0 sinω0t to drive the mechanical vibration of the probe, and perform line-by-line scanning in the tapping mode to obtain the surface topography of the semiconductor sample. Among them, the range of the micro-region size selected on the semiconductor sample is 5 nm × 5 nm - 120 μm × 120 μm, the range of the scanning duration of each line is 0.1 - 10 s, and the amplitude V of the AC voltage ac0 is in the range of 0.01 - 1 V, and the range of the frequency ω0 is the 1st - 4th order eigenresonance frequency of the probe. While measuring the surface topography, apply a first AC voltage V between the probe and the sample ac1 sinω1t, and various modes can be selected to measure the surface potential of semiconductor materials and devices.

[0051] Furthermore, the first method for measuring the surface potential is the amplitude modulation mode: Apply a second AC voltage V between the probe and the semiconductor sample ac1 sinω1t, use a Kelvin controller to apply a DC voltage V dc to cancel the amplitude signal of ω1, and use a data acquisition table to read the DC voltage V applied by the Kelvin controller during the scanning process dc at different spatial positions to obtain the surface potential of the semiconductor sample distributed with space. Among them, the amplitude V of the second AC voltage ac1 is in the range of 0.1 - 5 V, the range of the frequency ω1 is the 1st - 4th order eigenresonance frequency of the probe, the range of the lock-in amplifier bandwidth is 1 - 10000 Hz, and the range of the proportional gain and integral gain of the Kelvin controller is generally 1 - 100 and 1 - 50. After obtaining the surface potential, it can be stored in the cache. The range of the reading rate of the data acquisition table is 100 - 1000000 samples per second, the range of the array length of the surface potential signal stored in the cache after being read by the data acquisition table is 20 - 20000, and the DC voltage V applied by the Kelvin controller dc is in the range of -100 V to +100 V.

[0052] The second method for measuring the surface potential is the frequency modulation mode: Apply a second AC voltage V between the probe and the semiconductor sample ac1 sinω1t, use a phase-locked loop to track the phase of the mechanical vibration of the probe at ω0, use a Kelvin controller to apply a DC voltage V dc to cancel the phase change of ω0, the frequency of the phase change of ω0 is ω1, and use a data acquisition table to read the DC voltage V applied by the Kelvin controller during the scanning process dc at different spatial positions to obtain the surface potential of the semiconductor sample. The amplitude V of the second AC voltage ac1ranges from 0.1 - 10 volts, the frequency ω1 ranges from 0.5 - 20 kHz, the PLL bandwidth ranges from 1 - 1000 Hz, the lock-in amplifier bandwidth generally ranges from 1 - 1000 Hz, and the proportional gain and integral gain of the Kelvin controller generally range from 1 - 100 and 100 - 10000.

[0053] The third method for measuring surface potential is the sideband detection mode: Apply a second AC voltage V ac1 sinω1t between the probe and the semiconductor sample, and use the Kelvin controller to apply a DC voltage V dc to cancel the amplitude signals of ω0 ± ω1, and use a data acquisition table to read the DC voltage V dc applied by the Kelvin controller during the scanning process at different spatial positions to obtain the surface potential of the semiconductor sample to be measured. The amplitude V ac1 of the second AC voltage ranges from 0.5 - 10 volts, the frequency ω1 ranges from 0.5 - 20 kHz, the lock-in amplifier bandwidth ranges from 1 - 1000 Hz, and the proportional gain and integral gain of the Kelvin controller range from 1 - 100 and 100 - 10000.

[0054] The fourth method for measuring surface potential is the heterodyne detection mode: Apply a second AC voltage V ac1 sinω1t between the probe and the semiconductor sample to be measured, and use the Kelvin controller to apply a DC voltage V dc to cancel the amplitude signal of ω0 + ω1 or ω0 - ω1, and use a data acquisition table to read the DC voltage V dc applied by the Kelvin controller during the scanning process at different spatial positions to obtain the surface potential of the semiconductor sample to be measured. The amplitude V ac1 of the second AC voltage ranges from 0.5 - 10 volts, the frequency ω1 ranges from 0.5 - 20 kHz, the lock-in amplifier bandwidth ranges from 1 - 10000 Hz, and the proportional gain and integral gain of the Kelvin controller range from 1 - 500 and 500 - 100000.

[0055] Further, lift the probe to a preset height relative to the surface topography and then scan the semiconductor sample, and apply a DC voltage between the probe and the semiconductor sample during the scanning process to cancel the surface potential; multiple modes can be used to measure the dielectric force modulation difference of the semiconductor sample. Among them, the preset height can be the lift height relative to the overall topography contour line or the lift height relative to the average height of the surface topography. The range of the preset height for lifting the probe is 0 - 100 nm. The method for applying a DC voltage during the scanning process to cancel the surface potential is: Use a data acquisition table to apply a buffered DC voltage V dc between the probe and the semiconductor sample to cancel the surface potential;

[0056] The first method for measuring the difference in dielectric force modulation is the DC gate voltage - amplitude modulation mode: A third AC voltage V ac2 sinω2t and a DC modulation voltage V g are applied; Measure the first amplitude signal of 2ω2 at -V g and the second amplitude signal of 2ω2 at +V g . The former and the latter are the dielectric forces at -V g and +V g respectively. Take the difference between the two to obtain the difference in dielectric force modulation. The range of the DC voltage V g is generally from -10 V to +10 V. The amplitude V ac2 of the third AC voltage ranges from 0.5 - 10 V, the frequency ω2 ranges from 5 kHz to 800 kHz, and the bandwidth of the lock - in amplifier ranges from 1 - 10000 Hz. It should be noted that the dielectric force reflects the conductivity of the sample micro - region, and the dielectric forces modulated by the positive and negative gate voltages can reflect the carrier conduction type, such as p / n, and can theoretically reflect the carrier concentration.

[0057] The second method for measuring the difference in dielectric force modulation is the AC gate voltage - amplitude modulation mode: A third AC voltage V ac2 sinω2t and a fourth AC voltage V ac3 sinω3t are applied; Measure the amplitude signal of 2ω2 + ω3. According to the side - band principle, the amplitude signal of 2ω2 + ω3 corresponds to the difference between the amplitude signals of 2ω2 at -V ac3 and +V ac3 . And the amplitude signal of 2ω2 is the dielectric force. Thus, the amplitude signal of 2ω2 + ω3 is obtained as the difference in dielectric force modulation. The amplitude V ac2 of the third AC voltage generally ranges from 0.5 - 10 V, the frequency ω2 ranges from 5 kHz - 800 kHz, the amplitude V ac3 of the third AC voltage ranges from 0.5 - 10 V, the frequency ω3 ranges from 1 Hz - 5 kHz, and the bandwidth of the lock - in amplifier ranges from 1 - 10000 Hz.

[0058] The third method for measuring the difference in dielectric force modulation is the DC gate voltage - frequency modulation mode: A first AC voltage V ac0 sinω0t and a third AC voltage V ac2 sinω2t are applied to drive the mechanical vibration of the probe on the piezoelectric ceramic, and a phase - locked loop is used to track the phase of the mechanical vibration of the probe at ω0; A DC modulation voltage V g is applied between the probe and the semiconductor sample. Measure the phase change of ω0 at -V g and at +V gPhase change of ω0, where the frequency of the phase change of ω0 is 2ω2, and the former and the latter are -V respectively g and +V g Under the dielectric force gradient, take the difference between the two to obtain the dielectric force modulation difference.

[0059] Among them, the amplitude V of the first AC voltage ac0 ranges from 0.01 to 1 V, the frequency ω0 ranges from the 1st to 4th order eigenresonance frequencies of the probe, the PLL bandwidth ranges from 1 to 1000 Hz, and the DC voltage V g ranges from -10 V to +10 V, the third AC voltage V ac2 ranges from 0.5 to 10 V, the frequency ω2 ranges from 5 kHz to 800 kHz, and the lock-in amplifier bandwidth ranges from 1 to 10000 Hz.

[0060] The fourth method for measuring the dielectric force modulation difference is the AC gate voltage - frequency modulation mode: Apply the first AC voltage V ac0 sinω0t to drive the mechanical vibration of the probe, and apply the third AC voltage V ac2 sinω2t and the fourth AC voltage V ac3 sinω3t between the probe and the semiconductor sample to be measured. Use a phase-locked loop to track the mechanical vibration phase of the probe at ω0; Measure the amplitude signal of the phase change of ω0 at the frequency of 2ω2 + ω3. According to the sideband principle, the amplitude signal of 2ω2 + ω3 corresponds to the difference between the amplitude signals of -V ac3 and +V ac3 at 2ω2. The amplitude signal of 2ω2 is the dielectric force gradient, and thus the amplitude signal of 2ω2 + ω3 is obtained as the dielectric force modulation difference. The amplitude V of the first AC voltage ac0 ranges from 0.01 to 1 V, the frequency ω0 ranges from the 1st to 4th order eigenresonance frequencies of the probe, the PLL bandwidth ranges from 1 to 1000 Hz, the third AC voltage V ac2 ranges from 0.5 to 10 V, the frequency ω2 ranges from 5 kHz to 800 kHz, and the lock-in amplifier bandwidth ranges from 1 to 10000 Hz. The amplitude V of the AC voltage ac3 ranges from 0.5 to 10 V, the frequency ω3 ranges from 1 Hz to 5 kHz, and the lock-in amplifier bandwidth ranges from 1 to 10000 Hz.

[0061] Therefore, according to the above four methods, after canceling the surface potential, the dielectric force modulation difference with spatial resolution can be measured.

[0062] In step S20, as Figure 3As shown, the specific method of using numerical simulation to obtain the quantitative correspondence between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be tested is: construct a model according to the actual size and spatial position relationship between the probe and the semiconductor sample to be tested and the semiconductor physical parameters of the related materials; divide the model by finite element, combine the Poisson equation and the continuity equation, solve the dielectric force modulation difference caused by the carrier polarization difference of the semiconductor sample under different probe gate voltages under the preset semiconductor sample carrier concentration, and obtain the quantitative correspondence between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be tested. Among them, the specific process of numerical simulation is well known to those skilled in the art and will not be repeated here. The quantitative correspondence is calibrated according to the dielectric force modulation difference and carrier concentration of each standard semiconductor sample, and the method for obtaining the simulation relationship curve is: multiply the dielectric force modulation difference corresponding to the different carrier concentrations obtained by simulation by a preset proportional coefficient, so that the simulated quantitative correspondence is optimally fitted with the results of the measurement of each standard semiconductor sample, and the simulation relationship curve is obtained.

[0063] Through experiments, it is found that the carrier concentration and dielectric force modulation difference of the same category of semiconductor samples have a similar trend of change relationship. Therefore, under the condition of ensuring that the experimental measurement conditions of the standard semiconductor sample and the semiconductor sample to be tested are the same, the simulation relationship curve calibrated according to the change relationship between the carrier concentration and dielectric force modulation difference of the standard semiconductor sample can be used as the quantitative correspondence between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be tested. Finally, the carrier concentration distribution value of the semiconductor sample to be tested can be obtained based on the dielectric force modulation difference distribution of the semiconductor sample to be tested obtained by actual measurement and the calibrated simulation relationship curve.

[0064] The above describes in detail various implementations of each step of the present embodiment. The following further describes the micro-area carrier concentration measurement method using III-V semiconductor heterojunction n-AlGaN / n-GaN / u-GaN / u-AlGaN as the semiconductor sample to be measured.

[0065] (1) Prepare a group III-V semiconductor heterojunction by metal-organic chemical vapor deposition and mechanically dissociate it to obtain a cross-section. Connect one end of the group III-V semiconductor heterojunction to the grounded end of the atomic force microscope using silver paste. (2) Turn on the atomic force microscope and first perform a topography scan in tapping mode to find a flat area of 4 μm × 4 μm. (3) Connect the ports of the atomic force microscope to the corresponding ports of the signal generator, lock-in amplifier, etc. (4) Set the parameters such as the DC voltage feedback of the Kelvin controller, AC bias amplitude, frequency, demodulation bandwidth, gain value, etc. used for measuring the surface potential, dielectric force, and differential dielectric force modulation in the lock-in amplifier control software. (5) Set the signal channels for applying the bias voltage and acquiring images in the atomic force microscope control software, set the scan duration for each line to 5 seconds, and click start scanning. (6) During the first scan in the measurement process, use the first-order resonance frequency of the probe, 120.6 kHz, as the frequency ω0 for surface topography measurement. (7) At the same time, apply an AC voltage with a frequency ω1 = 649.2 kHz and an amplitude = 3 V between the probe and the sample, and use the Kelvin controller to apply a DC voltage V dc to cancel the amplitude signal of the frequency ω0 + ω1 = 769.8 kHz collected and demodulated by the system. V dc The change with spatial position is the surface potential V sp of the semiconductor sample. (8) Input the measured surface potential V sp into the data acquisition table and cache it for backup. (9) During the second scan, lift the probe 10 nm relative to the surface topography contour line of the first scan. (10) Apply the DC voltage V dc cached between the probe and the sample to cancel the surface potential V sp of the sample. (11) Apply two AC biases with a frequency ω2 = 60 kHz and an amplitude = 3 V and a frequency ω3 = 2 kHz and an amplitude = 4 V to the probe. (12) Use the lock-in amplifier to demodulate the signal with a frequency 2ω2 = 120 kHz to obtain the dielectric force, and demodulate the signal with a frequency 2ω2 + ω3 = 122 kHz to obtain the differential dielectric force modulation, and output it to the atomic force microscope for imaging. (13) At the same time, based on the quantitative correlation between the differential dielectric force modulation and the carrier concentration obtained by numerical simulation and calibration with a standard sample, obtain the carrier concentration distribution of the sample to be measured and output it to the atomic force microscope for imaging.

[0066] Exemplarily, as Figure 4 shown, A is the surface topography image of the cross-section of the group III-V semiconductor heterojunction, B is the surface potential image of the cross-section of the group III-V semiconductor heterojunction, C is the differential dielectric force modulation image of the cross-section of the group III-V semiconductor heterojunction, D is the calibrated carrier concentration distribution image, and the average carrier concentrations in the n-AlGaN, n-GaN, u-GaN, and u-AlGaN thin films are 1.6×10 18, 2.3×10 18 , 8.7×10 16 and 3.4×10 16 per cubic centimeter, which is in the same order of magnitude as the doping concentrations of 1.5×10 18 , 2.0×10 18 , 5.3×10 16 and 1.9×10 16 per cubic centimeter for n-AlGaN, n-GaN, u-GaN and u-AlGaN when the material is grown, verifying the reliability of this solution.

[0067] The specific embodiments of the present invention have been described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that these embodiments can be modified and perfected without departing from the principles and spirit of the present invention defined by the claims and their equivalents, and such modifications and perfections should also be within the protection scope of the present invention.

Claims

1. A method for measuring the carrier concentration in a micro-region based on a non-contact atomic force microscope, characterized in that, The micro-area carrier concentration measurement method comprises: A two-step scanning method is used to obtain the dielectric force modulation difference at different positions of a semiconductor sample to be tested and several standard semiconductor samples, wherein the carrier concentration of each standard semiconductor sample has been pre-calibrated, and the two-step scanning method is: using an atomic force microscope probe to scan the semiconductor sample once to obtain the surface morphology and surface potential; lifting the probe to a preset height relative to the surface morphology and performing a second scan, applying a DC voltage and a modulation voltage during the second scanning process, wherein the DC voltage is used to offset the surface potential, and obtain the dielectric force modulation difference at different positions of the semiconductor sample; A quantitative corresponding relationship between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be tested is obtained by a numerical simulation method, the quantitative corresponding relationship is calibrated according to the dielectric force modulation difference and the carrier concentration of each standard semiconductor sample to obtain a simulation relationship curve, and the carrier concentration of the semiconductor sample to be tested is obtained according to the measured dielectric force modulation difference of the semiconductor sample to be tested and the simulation relationship curve; The specific method of using the numerical simulation method to obtain the quantitative corresponding relationship between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be tested is as follows: constructing a model according to the actual size and spatial position relationship between the probe and the semiconductor sample to be tested and the semiconductor physical parameters of related materials; performing finite element division on the model, combining the Poisson equation and the continuity equation, solving the dielectric force modulation difference caused by the carrier polarization difference of the semiconductor sample under different probe gate voltages under a preset semiconductor sample carrier concentration, and obtaining the quantitative corresponding relationship between the dielectric force modulation difference and the carrier concentration of the semiconductor sample to be tested.

2. The method for measuring the carrier concentration in a micro-region according to claim 1, wherein In the two-step scanning method, the method of scanning the semiconductor sample using the probe of the atomic force microscope to obtain the surface morphology of the semiconductor sample is as follows: Apply a first alternating voltage V to the piezoelectric ceramic ac0 to drive the probe to vibrate mechanically, and perform a line-by-line scan in the tapping mode to obtain the surface topography of the semiconductor sample.

3. The micro-region carrier concentration measurement method according to claim 2, characterized in that, The method for obtaining the surface potential of the semiconductor sample is: Apply a second alternating voltage V ac1 sinω1t between the probe and the semiconductor sample, and apply a DC voltage V dc using a Kelvin controller to cancel the amplitude signal of ω1, and read the DC voltage V applied by the Kelvin controller using a data acquisition table during the scanning process dc at different spatial positions to obtain and cache the surface potential of the semiconductor sample; Alternatively, apply a second AC voltage V ac1 sinω1t between the probe and the semiconductor sample, use a phase-locked loop to track the phase of the mechanical vibration of the probe at ω0, and apply a DC voltage V dc using a Kelvin controller to cancel the periodic change in the phase of ω0, the frequency of the periodic change in the phase of ω0 being ω1, and read the DC voltage V applied by the Kelvin controller using a data acquisition table during the scan dc at different spatial positions to obtain and cache the surface potential of the semiconductor sample; Alternatively, a second alternating voltage V ac1 sinω1t is applied between the probe and the semiconductor sample, and a direct current voltage V dc is applied using a Kelvin controller to cancel the amplitude signals of ω0±ω1, and the value of the direct current voltage V applied by the Kelvin controller is read using a data acquisition table during the scanning process dc at different spatial positions to obtain and cache the surface potential of the semiconductor sample.

4. The method for measuring the micro-region carrier concentration according to claim 1, wherein The method of applying a DC voltage during the scanning process to cancel the surface potential is as follows: Use a data acquisition table to apply a buffered DC voltage V dc to the probe and the semiconductor sample to cancel the surface potential; The specific method of applying a modulation voltage during scanning to obtain the dielectric force modulation difference at different positions of the semiconductor sample includes: Apply a third AC voltage V ac2 sinω2t and a DC modulation voltage V g ; Measurement - V g The first amplitude signal of 2ω2 under - V and +V g The second amplitude signal of 2ω2 under - V. The dielectric force modulation difference is obtained based on the difference between the first amplitude signal and the second amplitude signal.

5. The method for measuring the carrier concentration in a micro-region according to claim 1, wherein The method of applying a DC voltage during the scanning process to cancel the surface potential is as follows: Use a data acquisition table to apply a buffered DC voltage V dc to the probe and the semiconductor sample to cancel the surface potential; The specific method of applying a modulation voltage during scanning to obtain the dielectric force modulation difference at different positions of the semiconductor sample includes: Apply a third AC voltage V ac2 sinω2t and a fourth AC voltage V ac3 sinω3t between the probe and the semiconductor sample; ac2 sinω2t and a fourth AC voltage V ac3 sinω3t; The amplitude signal of 2ω2+ω3 or 2ω2-ω3 is measured to obtain the dielectric force modulation difference.

6. The method for measuring the carrier concentration in a micro-region according to claim 1, wherein The method of applying a DC voltage during the scanning process to cancel the surface potential is as follows: Use a data acquisition table to apply a buffered DC voltage V between the probe and the semiconductor sample dc to cancel the surface potential; The specific method of applying a modulation voltage during scanning to obtain the dielectric force modulation difference at different positions of the semiconductor sample includes: Apply a first AC voltage V to the piezoelectric ceramic ac0 sinω0t and a third AC voltage V ac2 sinω2t to drive the mechanical vibration of the probe, and use a phase-locked loop to track the phase of the mechanical vibration of the probe at ω0; Apply a DC modulation voltage V between the probe and the semiconductor sample g , measure the phase change of ω0 at -V g and the phase change of ω0 at +V g , where the frequency of the phase change of ω0 is 2ω2. Obtain the dielectric force modulation difference based on the difference between the phase change of ω0 at -V g and the phase change of ω0 at +V g .

7. The method for measuring the carrier concentration in a micro-region according to claim 1, wherein The method of applying a DC voltage during scanning to cancel the surface potential is as follows: Use a data acquisition table to apply a buffered DC voltage V between the probe and the semiconductor sample dc to cancel the surface potential; The specific method of applying a modulation voltage during scanning to obtain the dielectric force modulation difference at different positions of the semiconductor sample includes: Apply a first AC voltage V to the piezoelectric ceramic ac0 to drive the mechanical vibration of the probe by sinω0t, and apply a third AC voltage V ac2 sinω2t and a fourth AC voltage V ac3 sinω3t, and use a phase-locked loop to track the phase of the mechanical vibration of the probe at ω0; The phase change of ω0 is measured to obtain the dielectric force modulation difference, and the frequency of the phase change of ω0 is 2ω2+ω3 or 2ω2-ω3.

8. The method for measuring the carrier concentration in a micro-region according to claim 1, wherein The range of the finite element block division is from 0.01 nanometers to 10 nanometers, and the range of the carrier concentration of the semiconductor sample to be measured is 10 16 -10 19 per cubic centimeter, and the range of the carrier concentration of each standard semiconductor sample is 10 16 -10 19 per cubic centimeter.

9. The method for measuring the micro-region carrier concentration according to claim 1, characterized in that, The quantitative correspondence is calibrated according to the dielectric force modulation difference and carrier concentration of each standard semiconductor sample to obtain a simulated relationship curve as follows: The dielectric force modulation difference corresponding to different carrier concentrations obtained by simulation is multiplied by a preset proportionality coefficient so that the simulated quantitative correspondence is optimally fitted with the results of measurement of each standard semiconductor sample to obtain a simulated relationship curve.

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