Semiconductor thermal conductivity testing method and device based on pump-probe Raman spectroscopy

Abstract

The present invention discloses a method and apparatus for testing semiconductor thermal conductivity based on pump-probe Raman spectroscopy. The apparatus comprises a pump source excitation and detection subsystem, a pump laser spot adjustment subsystem, a sample and reference plane temperature control subsystem, a Raman excitation and collection subsystem, a spectrum measurement subsystem, an optical element switching control unit, and a computer control unit. This method uses the aforementioned apparatus to measure excitation light reflectivity and pump-probe Raman spectroscopy, accurately capturing semiconductor temperature changes caused by pump heating and thereby measuring thermal conductivity. The present invention offers the advantages of convenience, non-destructiveness, and non-contact, making it ideally suited for testing the thermal properties of micro-sized optoelectronic materials.

Description

Technical Field

[0001] The present invention relates to a testing technology and experimental device for semiconductor thermal conductivity, in particular to a method and device for measuring semiconductor thermal conductivity based on pump-probe Raman spectroscopy. Background Art

[0002] The thermal conductivity of semiconductors is a critical thermal performance parameter, directly related to the heat dissipation and power handling capabilities of the resulting semiconductor devices. With the rapid development of high-speed and highly integrated microelectronic and optoelectronic devices, the drastic reduction in unit size has placed high demands on the thermal conductivity of semiconductor materials. Therefore, measuring the thermal conductivity of microscale semiconductors has become a significant technical challenge.

[0003] At present, thermal conductivity can be mainly divided into indirect measurement and direct measurement. The former obtains the thermal conductivity by measuring other physical quantities related to the thermal conductivity. For example, the laser method obtains the diffusion coefficient of the material and then calculates the thermal conductivity in combination with the material density and specific heat value. Therefore, the accuracy of the thermal conductivity is directly related to the measurement accuracy of these three physical quantities. The latter calculates the thermal conductivity by measuring the heat and temperature gradient of the material according to the definition of thermal conductivity. A typical example is the steady-state method, but it faces limitations such as complex experimental conditions and the need for thermal contact with the sample. This makes it difficult to use for reliable measurement of the thermal conductivity of microscale semiconductors.

[0004] Semiconductors absorb photons with energies greater than their bandgap. Semiconductor photoluminescence efficiency is typically extremely low, especially near room temperature, where the radiated energy is negligible. Consequently, absorbed photons are converted into heat, resulting in a heating effect on the sample. The intensity ratio of the anti-Stokes peak to the Stokes peak in the Raman spectrum is a key parameter reflecting the sample temperature. Utilizing this property, temperature measurement is self-referencing, minimizing the effects of laser intensity fluctuations, the collection system, and optical path alignment.

[0005] Based on these characteristics, the present invention discloses a method and apparatus for measuring semiconductor thermal conductivity using pump-probe Raman spectroscopy. Specifically, by switching the modes of a series of optical components, the semiconductor's pump laser reflectivity and Raman spectral changes at different pump powers are measured. The tiny temperature changes caused by laser heating are then detected, and the semiconductor's thermal conductivity is calculated from these changes. Summary of the Invention

[0006] The present invention has the advantages of being convenient, non-destructive, and non-contact, and is very suitable for detecting the thermal properties of micro-sized optoelectronic materials. The device of the present invention includes a pump source excitation and detection subsystem, a pump laser spot adjustment subsystem, a sample and reference plane temperature control subsystem, a Raman excitation and collection subsystem, a spectrum measurement subsystem, an optical element switching control component, and a computer control. The method of the present invention uses the above-mentioned device to measure the excitation light reflectivity and pump-probe Raman spectrum, which can accurately obtain the semiconductor temperature change caused by pump heating, thereby measuring the thermal conductivity. The device subsystems are specifically described as follows:

[0007] The pump source excitation and detection subsystem 1 includes a first continuous laser 101, a narrow bandpass filter 102, an optical beam expander 103, a right-angle plane mirror 104, an optical attenuation plate 105 and a first photodetector 106;

[0008] The pump laser spot adjustment subsystem 2 includes a laser reflector 201, a guiding light path 202, and a laser focusing lens group 203 with adjustable focal length;

[0009] The temperature control subsystem 3 for the sample and reference plane includes an optical thermostat 301, a sample to be measured 302, a reference plane mirror 303, a high thermal conductivity metal sample holder 304, a temperature sensor 305, and a temperature display 306;

[0010] Raman excitation and collection subsystem 4, including a second continuous laser 401, a focusing lens 402, a parabolic reflector 403 with a small hole along the focusing direction, a parabolic reflector 404 and a scattered light guiding optical path 405;

[0011] Spectral measurement subsystem 5, including a large-area plane reflector 501, a spectrometer 502, a long-wave pass filter 503, a narrow-band notch filter 504, and a second photodetector 505;

[0012] The optical element switching control component 6 controls the laser reflective mirror 201, the metal sample holder 304 and the large-area plane reflective mirror 501;

[0013] The computer central control 7 reads the signals of the first photodetector 106 , the second photodetector 505 and the spectrometer 502 .

[0014] The energy of the photons emitted by the first continuous laser 101 is greater than the band gap width of the sample to be measured, and serves as pump light; the detection band of the first photodetector 106 covers the laser wavelength range; the laser focusing lens group 203 has an adjustable focal length function; the sample to be measured 302 has a smooth and flat surface and has zero transmittance to the pump light; the reference plane mirror 303 is of the same thickness as the sample to be measured 302 and has a reflectivity of nearly 100% at the pump laser wavelength; the energy of the photons generated by the second continuous laser 401 is less than the energy of the photons emitted by the first laser (101); the spectrometer (502) covers the Raman scattering signal band, and can be but is not limited to a Fourier transform infrared spectrometer and a grating spectrometer; the cutoff wavelength of the long-wave pass filter (503) is between the emission wavelength of the first laser (101) and the wavelength of the anti-Stokes scattered light; the narrow-band notch filter (504) corresponds to the emission wavelength of the second laser (401); and the second photodetector (505) covers the Raman scattering signal band.

[0015] According to the device, the present invention provides a method for measuring the thermal conductivity of a semiconductor, the specific steps are as follows:

[0016] S1. Install the sample to be tested (302) and the reference plane mirror (303) on the sample holder (304) and set the temperature of the thermostat (301);

[0017] S2. The laser reflector (201) and the large-area plane reflector (501) are set to the "off" state by switching the control component (6);

[0018] S3. Start the first laser (101), and adjust the position of the sample holder (304) by switching the control component (6) so that the pump laser spot falls completely on the reference plane mirror (303);

[0019] S4. The output signal of the first detector (106) is recorded by the computer control (7);

[0020] S5. Adjust the position of the sample holder (304) so ​​that the pump laser spot falls completely on the sample to be tested (302), record the output signal of the first detector (106) again, and obtain the reflectivity of the sample to be tested (302) to the pump laser based on the ratio of the two signal intensities;

[0021] S6. The laser reflector (201) and the large-area plane reflector (501) are set to the "on" state by switching the control component (6), and the laser focusing lens group (203) is adjusted to change the focus focal length so that the pump light spot size just covers the surface of the sample to be measured (302), and the pump light power at this time is recorded;

[0022] S7. Start the second laser (401) so that the emitted laser irradiates the surface of the sample to be tested (302);

[0023] S8. The computer control (7) starts the spectrometer (502) to scan, obtains the Raman spectrum in combination with the output signal of the second detector (505), and calculates the current actual temperature of the sample to be tested (302) according to the ratio of Stokes and anti-Stokes scattering intensities;

[0024] S9. Changing the output power of the pump laser (101), scanning the spectrum again to obtain the Raman spectrum and calculating the current actual temperature of the sample to be tested (302);

[0025] S10. Calculate two actual pump power changes based on the pump laser reflectivity, and then calculate the thermal conductivity of the sample to be tested (302) based on the thermal conductivity definition formula in combination with the actual temperature change.

[0026] The main advantages of the present invention are:

[0027] 1. The sample does not require pretreatment, the measurement is non-destructive and non-contact;

[0028] 2. The laser spot can be focused to the micron scale, which is very beneficial for measuring the thermal properties of microscale semiconductors;

[0029] 3. The ratio of the anti-Stokes and Stokes scattering intensities in Raman spectroscopy is highly sensitive to temperature changes and is very helpful in detecting small temperature changes.

[0030] 4. The thermal conductivity of the sample under test at different temperatures can be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of a semiconductor thermal conductivity testing device based on pump-probe Raman spectroscopy.

[0032] Among them, 101 is a continuous laser whose output photon energy is greater than the band gap width of the sample to be tested, 102 is a narrow bandpass filter corresponding to the laser wavelength, 103 is a laser wavelength optical beam expander, 104 is a right-angle plane reflector, 105 is a laser wavelength optical attenuation plate, and 106 is a photodetector whose detection range covers the laser wavelength; 201 is an electrically movable laser reflector with two states of "on" and "off", 202 is a guiding light path composed of laser reflectors, and 203 is a laser focusing lens group with adjustable focal length; 301 is an optical thermostat, 302 is the sample to be tested, 303 is a reference plane mirror of the same thickness as the sample to be tested, and 304 is an electrically movable high thermal conductivity metal The sample holder, 305 is a temperature sensor, 306 is a temperature display connected to the sensor; 401 is a second continuous laser, 402 is a focusing lens, 403 is a parabolic reflector with a small hole along the focusing direction, 404 is a parabolic reflector, 405 is a scattered light guiding optical path composed of several plane reflectors; 501 is a large-area plane reflector that can be moved electrically and has two states of "on" and "off", 502 is a spectrometer covering the Raman scattering signal band, 503 is a long-wave pass filter, 504 is a narrow-band notch filter, 505 is a second photodetector covering the Raman scattering signal band; 6 is an optical element switching control component; 7 is a computer central control.

[0033] Figure 2 It is a brief flow chart of the measurement. DETAILED DESCRIPTION

[0034] The specific implementation plan is as follows Figure 1 and attached Figure 2 The present invention will be described in detail below with reference to the accompanying drawings, which can better illustrate the technical features and functional characteristics of the present invention, but is not intended to limit the scope of the present invention.

[0035] First, according to the attached Figure 1 The optoelectronic logic sets up the optical and electrical components. Plane mirrors 201 and 501 are defined as "on" when placed in the optical path and "off" when removed from the path. Optical element switching control unit 6 controls the position of plane mirrors 201 and 501 and sample holder 304, respectively. Computer control unit 7 reads information from photodetectors 106 and 505 and spectrum 502.

[0036] During measurement, the sample to be measured 302 and the reference plane mirror 303 are first mounted on the sample holder 304 of the optical thermostat 301, keeping their surfaces parallel. The thermostat 301 is vacuum-cooled. The desired measurement temperature, T0, is set and the sample holder 304 is kept at a stable temperature. The temperature of the sample holder 304 is monitored by a temperature sensor 305 and displayed on a temperature display 306.

[0037] Set both mirrors 201 and 501 to the "off" position and activate the first laser 101. Adjust the beam expander 103 so that the output spot diameter fills the equivalent pupil of the optical path as closely as possible. The laser beam is now focused by the rectangular plane reflector 104, the guiding optical path 405, and the parabolic mirror 403 and enters the thermostat 301.

[0038] Move the sample holder 304 so that the laser spot completely falls on the reference plane mirror 303. The reflected laser light is then fed into the first photodetector 106 via the parabolic mirror 404, the guiding light path 405, the right-angle plane reflector 104, and the optical attenuation plate 105. The computer 7 reads the output signal Sg1 from the detector 106.

[0039] The sample holder 304 is moved again so that the laser spot falls on the surface of the sample 302. The computer 7 reads the output signal Sg2 of the detector 106 at this moment and calculates the reflectivity of the sample to the pump laser by Sg2 / Sg1.

[0040] Set both reflectors 201 and 501 to the "on" position. The pump laser now irradiates the surface of the sample 302 under test through the guiding optical path 202 and the focusing lens assembly 203. Adjust the equivalent focal length of the focusing lens assembly 203 and the position of the sample holder 304 so that the pump light spot size just covers the surface of the sample 302 under test. After stabilization, record the pump light power P1 before entering the thermostat 301.

[0041] The second laser 401 is turned on so that its emitted laser light passes through the lens 402 and the aperture of the parabolic mirror 403 and irradiates the surface of the sample 302 to be tested. The output power of the laser 401 is as much smaller as possible than the output power of the laser 101.

[0042] Spectrometer 502 is activated to perform a spectral scan on the optical signal collected by parabolic mirrors 403 and 404. The signal is then passed through longwavepass filter 503 and narrowband notch filter 504 and fed into second detector 505. Computer 7 synchronously captures the signals from spectrometer 502 and detector 505 to obtain a Raman spectrum from sample 302 containing both Stokes and anti-Stokes scattering peaks.

[0043] The Raman spectrum is extracted by Raman wave number Δδ, Stokes peak intensity I S and the anti-Stokes scattering intensity I AS The current temperature T1 is calculated by the following formula:

[0044]

[0045] Wherein δ0 is the wave number of the laser light emitted by the second laser 401, h is the Planck constant, c is the speed of light in vacuum, and k is the Boltzmann constant.

[0046] The output power of the first laser 101 is changed, and after stabilization, the pump light power P2 is recorded before entering the thermostat 301. The Raman spectrum is measured again and the temperature T2 of the sample to be measured is calculated based on the spectrum.

[0047] Since the thickness of the sample 302 to be tested is much greater than the wavelength of the pump laser, there is no pump light transmission. According to the definition, the thermal conductivity at temperature T0 can be obtained as follows:

[0048]

[0049] Where d is the sample thickness and A is the sample area. For precise measurements, the accuracy of thermal conductivity measurements can be improved by measuring multiple sets of pump power and temperature and establishing a slope relationship between the power and temperature coordinates.

Claims

1. A semiconductor thermal conductivity test device based on pump-probe Raman spectroscopy, comprising a pump source excitation and detection subsystem (1), a pump laser spot adjustment subsystem (2), a sample and reference plane temperature control subsystem (3), a Raman excitation and collection subsystem (4), a spectrum measurement subsystem (5), an optical element switching control component (6), and a computer control (7); characterized in that: The pump source excitation and detection subsystem (1) comprises a first continuous laser (101) whose output photon energy is greater than the bandgap width of the sample to be measured, a narrow bandpass filter (102) placed in front of the first continuous laser (101) and having a transmission band corresponding to the laser wavelength, an optical beam expander (103) that sequentially passes through the corresponding wavelength of the laser, a right-angle plane reflector (104), an optical attenuation plate (105) of the corresponding wavelength of the laser, and a first photodetector (106) covering the laser wavelength range; The pump laser spot adjustment subsystem (2) comprises a laser reflector (201) with an electric movement function, a guiding light path (202) composed of the laser reflector, and a laser focusing lens group (203) with an adjustable focal length; The sample and reference plane temperature control subsystem (3) comprises an optical thermostat (301), a sample to be measured (302) with a flat and smooth surface placed in the optical thermostat (301), a reference plane mirror (303) with the same thickness as the sample to be measured, a high thermal conductivity metal sample holder (304) with an electrically movable function, a temperature sensor (305) placed on the sample holder, and a temperature display (306) connected to the sensor; The Raman excitation and collection subsystem (4) includes a second continuous laser (401) that generates photon energy less than the energy of photons emitted by the first continuous laser (101), a focusing lens (402) corresponding to the wavelength of the laser, a parabolic reflector (403) having a small hole along the focusing direction, a parabolic reflector (404), and a scattered light guiding optical path (405) composed of a plurality of plane reflectors; The spectrum measurement subsystem (5) comprises a large-area plane reflector (501) with an electric movement function, a spectrometer (502) covering the Raman scattering signal band, a long-wave pass filter (503) with a cutoff wavelength between the output wavelength of the first continuous laser (101) and the wavelength of anti-Stokes scattered light, a narrow-band notch filter (504) corresponding to the output wavelength of the second continuous laser (401), and a second photodetector (505) covering the Raman scattering signal band; The pump source excitation and detection subsystem (1) is optically connected to the pump laser spot adjustment subsystem (2), the sample and reference plane temperature control subsystem (3), the Raman excitation and collection subsystem (4), and the spectrum measurement subsystem (5); The optical element switching control component (6) is electrically connected to the electrically movable laser reflector (201), the metal sample holder (304) and the large-area plane reflector (501); The computer central control (7) is connected to the first photoelectric detector (106), the second photoelectric detector (505) and the spectrometer (502) to read the detector and spectrometer signals.

2. A method for measuring semiconductor thermal conductivity based on pump-probe Raman spectroscopy, characterized by: The method is implemented by using the semiconductor thermal conductivity testing device based on pump-probe Raman spectroscopy as claimed in claim 1, and comprises the following steps: S1. Install the sample to be tested (302) and the reference plane mirror (303) on the sample holder (304) and set the temperature of the thermostat (301); S2. The laser reflector (201) and the large-area plane reflector (501) are set to the "off" state by switching the control component (6); S3. Start the first continuous laser (101), and adjust the position of the sample holder (304) by switching the control component (6) so that the pump laser spot falls completely on the reference plane mirror (303); S4. The output signal of the first photodetector (106) is recorded by the computer control (7); S5. Adjust the position of the sample holder (304) so ​​that the pump laser spot completely falls on the sample to be tested (302), record the output signal of the first photodetector (106) again, and obtain the reflectivity of the sample to be tested (302) to the pump laser based on the ratio of the two signal intensities; S6. The laser reflector (201) and the large-area plane reflector (501) are set to the "on" state by switching the control component (6), and the laser focusing lens group (203) is adjusted to change the focus focal length so that the pump light spot size just covers the surface of the sample to be measured (302), and the pump light power at this time is recorded; S7. Start the second continuous laser (401) so that the emitted laser irradiates the surface of the sample to be tested (302); S8. The computer control (7) starts the spectrometer (502) to scan, obtains the Raman spectrum in combination with the output signal of the second photodetector (505), and calculates the current actual temperature of the sample to be tested (302) according to the ratio of Stokes and anti-Stokes scattering intensities; S9. changing the output power of the first continuous laser (101), scanning the spectrum again to obtain a Raman spectrum and calculating the current actual temperature of the sample to be tested (302); S10. Calculate two actual pump power changes based on the pump laser reflectivity, and then calculate the thermal conductivity of the sample to be tested (302) based on the thermal conductivity definition formula in combination with the actual temperature change.

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