Raman spectroscopy method and device for non-contact detection of semiconductor substrate temperature

Abstract

The present invention discloses a Raman spectroscopy method and device for non-contact detection of semiconductor substrate temperature. The device includes a Fourier transform infrared spectroscopy system, an infrared laser, an external coupling optical path system connecting infrared laser excitation and Raman scattering signal detection, a multi-dimensional adjustment frame for installing samples and adjusting positions, and a computer data processing program. Based on the above equipment, the present invention combines the advantages of low heating effect and large penetration depth of infrared laser and high throughput, multi-channel and fast measurement of Fourier transform infrared spectrometer, significantly improves the signal-to-noise ratio of infrared Raman spectroscopy, effectively extracts the Raman spectroscopy characteristics of semiconductor substrates, and quickly obtains temperature values ​​by calculating the corresponding relationship between Raman scattering intensity and temperature, thereby realizing non-contact testing of semiconductor structure substrate temperature. Tests on indium phosphide substrates show that the method of the present invention is a convenient and reliable semiconductor temperature testing method, which is very suitable for substrate temperature detection of semiconductor device materials.

Description

Technical Field

[0001] The present invention relates to a spectral method and device for detecting the temperature of a semiconductor substrate, belonging to the field of semiconductor testing and spectral technology. Specifically, the present invention mainly relates to a Fourier transform Raman spectroscopy method and an implementation device for non-contact testing of the temperature of a semiconductor substrate. Background Art

[0002] The optical and electrical performance testing of semiconductor epitaxial materials usually requires low temperature and strict control of the material temperature. The common temperature control method is to install the semiconductor on the cold finger of the thermostat and control the temperature of the epitaxial material through the thermal conduction effect of thermal grease and substrate. Since the thickness of the substrate is generally large, usually measured in millimeters, its thermal conductivity will affect the actual temperature of the semiconductor epitaxial material. Optical testing requires light irradiation to the material to be tested, and the absorption of light energy will cause the heating of the material to be tested and thus the temperature rise effect; electrical testing requires voltage and current bias to the material to be tested, and the resistance of the material to be tested itself causes power loss and electrical heating effect. Both effects will inevitably lead to the deviation of the apparent temperature of the material to be tested from the cold finger, resulting in experimental deviations in the photoelectric performance test of the material. Therefore, the experimental process needs to monitor the actual temperature of the substrate, and the interference-prone characteristics of semiconductor materials and photoelectric test experiments determine that it is difficult to directly use contact temperature sensors on semiconductor substrates.

[0003] Raman spectroscopy is a non-destructive, non-contact semiconductor testing spectroscopy method that has received widespread attention and application. For example, the invention patent CN106018377A discloses a systematic Raman spectroscopy method for comprehensive measurement of thermal conductivity and optical properties of supported and suspended nanomaterials. By extracting the Stokes and anti-Stokes Raman scattering intensity analysis of the material, the temperature of the material can be quickly and directly obtained, thus becoming an important choice for semiconductor temperature detection. Previously, industry insiders have demonstrated the use of ultraviolet and visible light excitation Raman spectroscopy based on grating monochromators for temperature measurement above room temperature of materials [Appl. Phys. Lett. 79, 937 (2001); Opt. Lett. 40, 2041 (2015) etc.]. However, for the photoelectric performance test experiment of semiconductor epitaxial materials, on the one hand, ultraviolet and visible light will be absorbed by most of the epitaxial layer semiconductors, which is not only difficult to penetrate to the substrate, but also will cause serious errors in the photoelectric test results of the epitaxial materials; on the other hand, for semiconductors below room temperature, the intensity of Raman spectroscopy, especially anti-Stokes scattering, is seriously reduced, resulting in a decrease in the signal-to-noise ratio of the Raman spectroscopy, thereby limiting the application of this method.

[0004] The use of infrared excitation light with a longer wavelength not only helps to reduce the side effects caused by surface absorption, but also significantly increases the penetration depth of the excitation light. Therefore, the infrared Raman spectroscopy method based on Fourier transform infrared spectrometer was developed in the 1980s [Appl. Spectrosc. 40, 133 (1986)]. Unfortunately, due to mechanism limitations, the Raman scattering intensity is inversely proportional to the fourth power of the excitation wavelength. For example, the Raman scattering intensity excited by a laser with a wavelength of 1064 nanometers is only 1 / 16 of the Raman intensity excited by a laser with a wavelength of 514 nanometers. This results in Fourier transform infrared Raman spectroscopy being applicable only to the occasion of strongly scattering samples, and its application in semiconductors is often limited, not to mention the detection of low-temperature temperatures of semiconductor substrates based on Fourier transform infrared Raman spectroscopy. Summary of the invention

[0005] In summary, how to obtain high signal-to-noise ratio infrared Raman spectra for semiconductor materials and reliably identify and extract the intensity of Stokes and anti-Stokes features of semiconductor substrates is the key to accurately obtain substrate temperature, and is also the key technical problem to be solved by the present invention. The present invention provides a Raman spectrum test method and implementation device for fast and convenient testing of semiconductor substrate temperature, which can reliably measure the temperature of semiconductor device material substrates without contact, and provide a new non-destructive testing method for reliable temperature control of semiconductor epitaxial material photoelectric testing experiments.

[0006] The core of the technical concept of the present invention is to use infrared laser source, external coupling optical path system connecting infrared laser excitation and spectrometer Raman signal detection, and Fourier transform infrared spectroscopy system and other components. By making full use of the large penetration depth of infrared laser and the high throughput, multi-channel and fast measurement advantages of Fourier transform infrared spectrometer, the excitation, collection and measurement of weak Raman signals of semiconductor material substrate can be realized through the optimization design of optical path. The Stokes and anti-Stokes scattering intensities of corresponding Raman features are extracted, and the substrate temperature of the semiconductor is obtained through computer program.

[0007] The specific technical solutions are as follows:

[0008] A Raman spectroscopy method and implementation device for non-contact testing of semiconductor substrate temperature, the device comprising:

[0009] -Infrared laser source, which can output laser with photon energy lower than the bandgap width of the epitaxial material of the sample to be tested, the power controller is used to stabilize the laser power and emission direction for a long time, and the narrow-band filter is used to suppress the stray wavelength signal of the laser output;

[0010] - An external coupling optical path system connecting laser excitation and spectrometer detection, wherein the first reflector, the second reflector, the third reflector, and the micro reflector are all used to guide the laser, and the laser is focused on the sample to be tested through the aspheric lens. The sample Raman signal is collected again by the aspheric lens and fed into the spectral system through the parabolic mirror;

[0011] -The Fourier transform infrared spectroscopy system includes a Fourier transform infrared spectrometer and a notch filter, wherein the spectrometer covers the working range of Stokes and anti-Stokes Raman signals and is equipped with a broadband flat light source, and the notch filter has a narrow-band cutoff laser wavelength;

[0012] -Multi-dimensional adjustment frame, which can be freely and finely adjusted in three dimensions perpendicular and parallel to the laser incident direction;

[0013] - A data processing computer, which is equipped with a calculation program for the relationship between the Raman scattering Stokes and anti-Stokes intensities and temperature.

[0014] The laser can be, but is not limited to, an infrared laser with a wavelength of 1064 nanometers. It should be understood that the specific laser wavelength parameters involved here are only for the needs of subsequent description, and do not limit the scope of protection of this patent. In fact, as long as it can provide an infrared laser output with a photon energy less than the bandgap width of the epitaxial layer of the sample to be tested, and the power is stable and not less than 10 milliwatts, it can be used to implement the patent of this invention.

[0015] The Fourier transform infrared spectrometer can be, but is not limited to, a Bruker Vertex 80 Fourier transform infrared spectrometer. It must be understood that the specific spectrometer manufacturer and model mentioned here are only for the convenience of subsequent description, and do not limit the scope of protection of this patent. In fact, as long as the Fourier transform infrared spectrometer whose working band covers the Stokes and anti-Stokes Raman scattering bands of the sample to be tested can be used to implement the patent of this invention.

[0016] According to the same inventive concept, the Raman spectroscopy method for non-contact testing of semiconductor substrate temperature of the present invention comprises the following steps:

[0017] S1. Select a suitable laser output wavelength according to the bandgap width of the epitaxial layer of the sample to be tested, and ensure that the output photon energy is less than the bandgap width of the epitaxial layer of the sample;

[0018] S2. Select and install matching laser narrowband filters and notch filters according to the laser wavelength to ensure the monochromaticity of the excitation light source, high cutoff efficiency in the Rayleigh scattering band, and high optical transmittance in the Raman scattering band;

[0019] S3, respectively fine-tuning the first reflector, the second reflector, the third reflector, the micro reflector and the aspheric condensing lens to ensure that the infrared laser is incident along the optical axis of the aspheric condensing lens and forms a focused light spot at the rear focus of the condensing lens;

[0020] S4. Install the sample to be tested on the adjustment seat, and adjust the adjustment seat in multiple dimensions to place the sample exactly at the rear focus of the condenser lens. The scattered light of the sample is converted into parallel light by the aspheric condenser lens again, and fed into the Fourier transform infrared spectroscopy system through the parabolic mirror;

[0021] S5, switching the channel to be measured of the Fourier transform infrared spectrometer to a state optically connected to the parabolic mirror, monitoring the intensity of the Raman scattering signal in real time and maximizing the intensity of the Raman scattering signal;

[0022] S6, start the Raman spectrum test of the Fourier transform infrared spectrometer to obtain Raman spectrum data; after the spectrum test is completed, switch the spectrometer test channel to the built-in broadband light source, test the spectrum again, and obtain the spectrometer system transfer function spectrum;

[0023] S7. Use the system transfer function spectrum to normalize and preprocess the Raman spectrum data, extract the Stokes and anti-Stokes scattering intensities of the corresponding Raman characteristics of the semiconductor substrate, and obtain the substrate temperature of the semiconductor through a computer program.

[0024] The advantages of the present invention are:

[0025] 1. There is no contact with the sample to be measured. The infrared laser with photon energy lower than the bandgap width of the material has a very weak heating effect on the sample. The measurement is fast and convenient, and it is a non-destructive measurement;

[0026] 2. The spectrum detection depth is large and the sensitivity is high, which is particularly suitable for substrate temperature detection and thermal performance evaluation in the process of photoelectric performance test of semiconductor epitaxial materials;

[0027] 3. The detection temperature range is large. Compared with the Raman method based on grating monochromator, the present invention can test the temperature of semiconductor materials below room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1This is a schematic diagram of an implementation device for a non-contact test method for semiconductor substrate temperature based on Fourier transform Raman spectroscopy. 1 is an infrared laser source, 1-1 is an infrared laser, 1-2 is a laser power controller, 1-3 is a laser narrowband filter that matches the output laser wavelength; 2 is an external coupling optical path system connecting infrared laser excitation and spectrometer Raman signal detection, 2-1 is a first reflector, 2-2 is a second reflector, 2-3 is a third reflector, 2-4 is a micro reflector, 2-5 is an aspheric focusing lens, and 2-6 is a parabolic mirror; 3 is a Fourier transform infrared spectroscopy system, 3-1 is a Fourier transform infrared spectrometer, 3-2 is a notch filter; 4 is a mounting and adjusting frame for the sample to be tested, 4-1 is a multi-dimensional adjustment seat, and 4-2 is the sample to be tested; 5 is a data processing computer.

[0029] Figure 2 These are the Raman spectra, Stokes and anti-Stokes scattering characteristics of indium phosphide substrates at different temperatures tested by the above experimental device.

[0030] Figure 3 It is a comparison diagram of the temperature of the indium phosphide substrate placed in the thermostat and the temperature of the cold finger of the thermostat measured by the present invention. DETAILED DESCRIPTION

[0031] According to the following Figure 1-Figure 3 Preferred examples of the present invention are given and described in detail to better illustrate the technical features and functional characteristics of the present invention, rather than to limit the scope of the present invention.

[0032] The implementation device of the present invention is as follows Figure 1 As shown, it includes: an infrared laser source 1, including an infrared laser 1-1, a laser power controller 1-2 for long-term laser stabilization, and a narrowband filter 1-3 for matching the laser wavelength; an external coupling optical path system 2, including a first reflector 2-1 for guiding the laser, a second reflector 2-2, a third reflector 2-3, a micro reflector 2-4, an aspheric lens 2-5 for converging the laser, and a parabolic mirror 2-6 for guiding the Raman signal; a Fourier transform infrared spectroscopy system 3 includes a Fourier transform infrared spectrometer 3-1, and a notch filter 3-2 placed in front of the detector; a multi-dimensional adjustment frame 4, which includes a multi-dimensional adjustment seat 4-1 and a sample to be measured 4-2, and the multi-dimensional adjustment seat 4-1 can be freely fine-tuned in three dimensions perpendicular and parallel to the laser incident direction; a data processing computer 5, which is installed with a calculation program for the correspondence between the Raman scattering Stokes and anti-Stokes intensities and temperature.

[0033] It is necessary to ensure that the output photon energy of the laser 1-1 is less than the bandgap width of the epitaxial layer of the sample 4-2. Ensure that the narrowband filter 1-3 can cut off the stray wavelength of the infrared laser 1-1, ensure the monochromaticity of the excitation light source, and ensure that the notch filter 3-2 has a high cutoff efficiency in the Rayleigh scattering band and a high optical transmittance in the Raman scattering band.

[0034] The implementation process of the present invention is described below using an indium phosphide substrate as an example:

[0035] The bandgap of indium phosphide is about 1.34 eV, corresponding to a wavelength of 925 nm. The photon energy output by the infrared laser 1-1 with an output wavelength of 1064 nm is less than the bandgap of the sample. According to the laser wavelength, a 1064 nm narrowband filter 1-3 and a 1064 nm notch filter 3-2 are selected and installed to ensure the monochromaticity of the excitation light source, high cutoff efficiency in the Rayleigh scattering band, and high optical transmittance in the Raman scattering band.

[0036] Turn on the laser 1-1, and fine-tune the first reflector 2-1, the second reflector 2-2, the third reflector 2-3, the micro reflector 2-4, and the aspheric condenser lens 2-5 respectively to ensure that the infrared laser is incident along the optical axis of the aspheric condenser lens 2-5 and forms a focused spot at the rear focus of the condenser lens 2-5. During the adjustment process, an infrared imager is used, which has a good response to the near-infrared band that is invisible to the human eye.

[0037] The indium phosphide sample 4-2 to be tested is mounted on the adjustment seat 4-1, and the adjustment seat 4-1 is finely adjusted in multiple dimensions so that the sample 4-2 is placed exactly at the rear focus of the focusing lens 2-5. The scattered light of the sample 4-2 is again converted into parallel light by the aspheric focusing lens 2-5 and fed into the Fourier transform infrared spectroscopy system 3 through the parabolic mirror 2-6.

[0038] The channel to be measured of the Fourier transform infrared spectrometer 3-1 is switched to a state of being optically connected to the parabolic mirror 2-6, so as to monitor the intensity of the Raman scattering signal in real time and maximize the intensity of the Raman scattering signal.

[0039] Start the Raman spectrum test of Fourier transform infrared spectrometer 3-1 and obtain Raman spectrum data I RM (δ); After the spectrum test is completed, switch the spectrometer 3-1 test channel to the built-in broadband light source, test the spectrum again, and obtain the spectrometer system transfer function spectrum I BS (δ);

[0040] Computer 5 uses the system transfer function spectrum to normalize the Raman spectrum data to obtain I(δ)=I RM (δ) / I BS (δ), the obtained indium phosphide Raman spectrum is as follows Figure 2As shown. The positive Raman shift is Stokes scattering and the negative Raman shift is anti-Stokes scattering. The Stokes scattering intensity I is extracted respectively. S and the anti-Stokes scattering intensity I AS Based on the Boltzmann approximation of phonon distribution, the temperature value T can be obtained by solving the following formula using computer 5:

[0041]

[0042] Where δ0 is the laser wave number, Δδ is the Raman wave number, h, c and k are Planck constant, vacuum light speed and Boltzmann constant respectively.

[0043] Figure 2 The Raman spectra of the InP substrate obtained at three different temperatures are given, which have a high signal-to-noise ratio and can reliably identify and extract the Stokes and anti-Stokes scattering intensities, thereby obtaining the temperature of the InP sample. Figure 3 The comparison between the temperature result of the indium phosphide substrate placed in the thermostat measured by the present invention and the test result of the thermostat cold finger temperature contact sensor shows that the present invention is effective and feasible.

Claims

1. A Raman spectroscopic device for non-contact detection of semiconductor substrate temperature, comprising: An infrared laser source (1), an external coupling optical path system (2) connecting infrared laser excitation and spectrometer Raman signal detection, a Fourier transform infrared spectroscopy system (3), a multi-dimensional adjustment frame (4) for mounting a sample to be tested, and a data processing computer (5), characterized in that: The infrared laser source (1) comprises an infrared laser (1-1) whose output photon energy is lower than the effective bandgap width of the sample to be tested, a laser power controller (1-2) for long-term stabilization of the laser power and emission direction, and a laser narrowband filter (1-3) matching the output laser wavelength; The external coupling optical path system (2) can transmit the laser light of the infrared laser source (1) to the sample (4-2) and collect the Raman scattering signal to the Fourier transform infrared spectroscopy system (3), and comprises a first reflector (2-1) for guiding the laser light, a second reflector (2-2), a third reflector (2-3), a micro reflector (2-4), an aspheric condensing lens (2-5) for converging the laser light, and a parabolic mirror (2-6) for introducing the Raman signal into the spectroscopy system; the aspheric condensing lens (2-5) has the ability to focus the laser spot to a size of less than 200 microns, and the micro reflector (2-4) is located on the optical axis of the aspheric condensing lens (2-5) to guide the laser light to enter the aspheric condensing lens (2-5) in parallel along the optical axis; The Fourier transform infrared spectroscopy system (3) comprises a Fourier transform infrared spectrometer (3-1), and a notch filter (3-2) placed in front of a detector inside the spectrometer (3-1); wherein the spectrometer (3-1) is equipped with a detector and a beam splitter covering the Stokes and anti-Stokes Raman ranges of the sample to be tested (4-2), and a built-in broadband flat light source of the corresponding wavelength band; the notch filter (3-2) has a cutoff band wavelength covering the output wavelength of the infrared laser (1-1), and a transmission band covering the Stokes and anti-Stokes Raman signals of the sample to be tested (4-2); The test sample mounting adjustment frame (4) comprises a multi-dimensional adjustment seat (4-1) and a test sample (4-2); wherein the multi-dimensional adjustment seat (4-1) can be freely finely adjusted in three dimensions perpendicular and parallel to the laser incident direction, and the test sample (4-2) is rigidly mounted on the adjustment seat (4-1); The data processing computer (5) is installed with a calculation program for the corresponding relationship between Raman scattering Stokes and anti-Stokes intensities and temperature.

2. A non-contact test method for semiconductor substrate temperature based on the Raman spectroscopic device for non-contact detection of semiconductor substrate temperature according to claim 1, mainly comprising the following steps: 1) Select a suitable laser output wavelength according to the bandgap width of the epitaxial layer of the sample to be tested (4-2), and ensure that the output photon energy is less than the bandgap width of the epitaxial layer of the sample; 2) Selecting and installing matching laser narrowband filters (1-3) and notch filters (3-2) according to the laser wavelength to ensure the monochromaticity of the excitation light source, high cutoff efficiency in the Rayleigh scattering band, and high optical transmittance in the Raman scattering band; 3) respectively fine-tuning the first reflector (2-1), the second reflector (2-2), the third reflector (2-3), the micro reflector (2-4) and the aspheric condensing lens (2-5) to ensure that the infrared laser is incident along the optical axis of the aspheric condensing lens (2-5) and forms a focused light spot at the rear focus of the condensing lens (2-5); 4) The sample (4-2) to be tested is mounted on the adjustment seat (4-1), and the adjustment seat (4-1) is finely adjusted in multiple dimensions so that the sample (4-2) is exactly placed at the rear focus of the condensing lens (2-5). The scattered light of the sample (4-2) is again converted into parallel light by the aspheric condensing lens (2-5), and is fed into the Fourier transform infrared spectroscopy system (3) through the parabolic mirror (2-6); 5) switching the channel to be measured of the Fourier transform infrared spectrometer (3-1) to a state of being optically connected to the parabolic mirror (2-6), monitoring the intensity of the Raman scattering signal in real time and maximizing the intensity of the Raman scattering signal; 6) Starting the Raman spectrum test of the Fourier transform infrared spectrometer (3-1) to obtain Raman spectrum data; After the spectrum test is completed, the test channel of the spectrometer (3-1) is switched to the built-in broadband light source, and the spectrum is tested again to obtain the transfer function spectrum of the spectrometer system; 7) Using the system transfer function spectrum to normalize and preprocess the Raman spectrum data, extract the Stokes and anti-Stokes scattering intensities of the corresponding Raman characteristics of the semiconductor substrate, and obtain the substrate temperature of the semiconductor through a computer (5) program.

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