Semiconductor measurement system and semiconductor measurement method

Abstract

To provide a system and method for measuring a semiconductor using stimulated Raman scattering microscopy.SOLUTION: The semiconductor measurement system 100 includes an irradiation unit 102 that condenses pump light and Stokes light having different wavelengths in a wavelength band of a transparent region of a semiconductor on a sample S made of a semiconductor, and a measurement unit 104 having a photodetector that detects an intensity of stimulated Raman scattered light generated at a condensing point of the sample S. The irradiation unit 102 includes a laser light source 106 that generates an optical pulse in a communication wavelength band and an optical coupler 114 that branches the optical pulse into a first optical pulse and a second optical pulse, outputs the first optical pulse to a free space and uses the first optical pulse as pump light, includes a modulator that performs intensity modulation on the second optical pulse, propagates the intensity-modulated second optical pulse in an optical fiber 140, shifts the second optical pulse to a long wavelength by a soliton self-frequency shift effect, and outputs the wavelength-shifted second optical pulse to the free space and uses the second optical pulse as Stokes light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semiconductor measurement system and a semiconductor measurement method using Raman scattering. [Background technology]

[0002] Raman scattering is widely used as a method for evaluating defects and distortion in semiconductor crystals. In particular, spontaneous Raman microscopy has been used to measure residual stress in semiconductor packages such as through-silicon vias (TSVs) and flip chips (see, for example, Non-Patent Documents 1, 2, and 3). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] E. Anastassakis, A. Pinczuk, E. Burstein, FH Pollak, and M. Cardona, “Effect of static uniaxial stress on the Raman spectrum of silicon,” Solid State Communications, Volume 8, pp.133-138 (1970). [Non-patent document 2] Atsushi Ogura, Kosuke Yamasaki, Daisuke Kosemura, Satoshi Tanaka, Ichiro Chiba, and Ryosuke Shimidzu, “UV-Raman Spectroscopy System for Local and Global Strain Measurements in Si,” Japanese Journal of Applied Physics, Volume 45, pp.3007-3011 (2006). [Non-patent document 3] Alastair David Trigg, Li Hong Yu, Cheng Kuo Cheng, Rakesh Kumar, Dim Lee Kwong, Takeshi Ueda, Toshikazu Ishigaki, Kitaek Kang, and Woo Sik Yoo, “Three Dimensional Stress Mapping of Silicon Surrounded by Copper Filled through Silicon Vias Using Polychromator-Based Multi-Wavelength Micro Raman Spectroscopy,” Applied Physics Express, Volume 3, 086601 (2010). Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional Raman scattering measurements were limited to rough mapping due to their slow measurement speed. Furthermore, because they used excitation light equivalent to the semiconductor's optical absorption wavelength range (0.5 μm to 1.0 μm for Si), they were limited to measuring the semiconductor's surface. While it might be possible to measure the interior of a semiconductor using longer-wavelength excitation light, the intensity of the Raman scattered light attenuates inversely proportional to the fourth power of the wavelength, and the sensitivity of spectrometers is low in the infrared range. In recent years, advances in power semiconductor devices with three-dimensional structures and three-dimensional semiconductor stacking technology have created a demand for nondestructive, three-dimensional evaluation of internal strain and defects in semiconductor materials, including Si, with spatial resolution on the order of microns. However, no such evaluation method currently exists.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a system and method for measuring semiconductors using stimulated Raman scattering microscopy. [Means for solving the problem]

[0006] The semiconductor measurement system according to the present invention is a semiconductor measurement system using stimulated Raman scattering microscopy, and includes an irradiation unit that focuses and irradiates a sample made of a semiconductor with pump light and Stokes light of different wavelengths within the wavelength band of the transparent region of the semiconductor, and a measurement unit that has a photodetector that detects the intensity of stimulated Raman scattering light generated at the focusing point on the sample.

[0007] The semiconductor measurement method according to the present invention is a semiconductor measurement method using stimulated Raman scattering microscopy, in which an irradiation unit focuses pump light and Stokes light of different wavelengths within the wavelength band of the transparent region of the semiconductor onto a sample made of the semiconductor, and a photodetector detects the intensity of stimulated Raman scattering light generated at the focusing point on the sample. [Effects of the Invention]

[0008] According to the present invention, stimulated Raman scattering is generated using pump light and Stokes light of different wavelengths in the wavelength band of the transparent region of the semiconductor, thereby enabling high-speed measurement of the inside of the semiconductor. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a configuration diagram of a semiconductor measurement system according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram for explaining wavelength sweeping by a spectral focusing method. [Figure 3] 1 is a graph showing a Raman spectrum of silicon obtained by the semiconductor measurement system of the present embodiment. [Figure 4] 10 shows images of the peak wavenumber shift, peak intensity, and peak width of the Raman spectrum at various depths inside silicon obtained with the semiconductor measurement system of this embodiment. [Figure 5] 1 is a graph showing the temperature dependence of the Raman spectrum of silicon obtained by the semiconductor measurement system of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, which illustrate systems and methods for measuring semiconductors using stimulated Raman scattering (SRS) microscopy, known as a fast Raman imaging technique.

[0011] 1 shows a configuration diagram of a semiconductor measurement system 100 according to this embodiment. The semiconductor measurement system 100 includes an irradiation unit 102 that irradiates a sample S made of a semiconductor with pump light and Stokes light, each having a different wavelength within the wavelength band of the transparent region of the semiconductor, and a measurement unit 104 that has a photodetector that detects the intensity of the pump light modulated by the SRS effect that occurs at the focal point of the sample S.

[0012] The irradiation unit 102 includes a laser light source 106, an Er-doped fiber amplifier (EDFA) 112, an optical coupler 114, a first dispersion element 120, a delay stage 126, a servo motor 128, an optical coupler 130, an electro-optic modulator (EOM) 136, an EDFA 138, a long-pass filter (LPF) 142, a second dispersion element 144, a band-pass filter (BPF) 150, a galvanometer scanner 152, a scanner controller 154, lenses 156 and 158, and an objective lens 160.

[0013] The laser light source 106 generates optical pulses in the communication wavelength band with a predetermined repetition rate. For example, the laser light source 106 may be a mode-locked Er-doped fiber oscillator with a repetition rate of 44.5 MHz and a center wavelength of 1.56 μm.

[0014] EDFA 112 amplifies the optical pulse output from laser light source 106. Optical coupler 114 is connected to EDFA 112 via optical fiber 110 and is an optical branching element that branches the optical pulse amplified by EDFA 112 into two (a first optical pulse and a second optical pulse). For example, optical coupler 114 branches the optical pulse output from EDFA 112 at a branching ratio of 50:50. The first optical pulse is output into free space via a fiber collimator and is used as pump light.

[0015] Optical coupler 130 splits the second optical pulse output from optical coupler 114 into two optical pulses. For example, optical coupler 130 splits the second optical pulse at a splitting ratio of 90:10. One optical pulse is output to EOM 136, and the other optical pulse is output to photodiode (PD) 132.

[0016] The PD 132 converts the other optical pulse output from the optical coupler 130 into an electrical signal and outputs it to the frequency divider circuit 134. The frequency divider circuit 134 halves the frequency of the electrical signal output from the PD 132 and outputs the frequency-converted electrical signal to the EOM 136. The EOM 136 intensity-modulates one of the optical pulses output from the optical coupler 130 in accordance with the electrical signal output from the frequency divider circuit 134, thereby halving the repetition frequency.

[0017] The EDFA 138 amplifies the intensity-modulated second optical pulse. The second optical pulse amplified by the EDFA 138 is input to an optical fiber 140 (e.g., a polarization-maintaining (PM) fiber). The second optical pulse propagates through the optical fiber 140 and is shifted to a longer wavelength due to the soliton self-frequency shift effect within the optical fiber 140. For example, the wavelength of the second optical pulse is shifted from the 1.5 μm band to the 1.7 μm band due to the soliton self-frequency shift.

[0018] The wavelength-shifted second optical pulse is output into free space via a fiber collimator and used as the Stokes beam. The LPF 142 blocks the short wavelength components contained in the Stokes beam and passes only the desired long wavelength components.

[0019] In this embodiment, to acquire the SRS spectrum, a spectral focusing method is used, in which a negative chirp is applied to the pump light and the Stokes light in free space, and the timing difference between the chirped pump light and the Stokes light is changed.

[0020] The SRS effect occurs when the difference frequency between the pump light and the Stokes light is equal to the resonant frequency of the lattice vibration at the focal point of the sample S. As shown in graph A in Figure 2, the unchirped pump light and the Stokes light have a wide frequency range and a narrow time width (pulse width), which is Fourier transform limited. In this case, various difference frequency components are generated, making it impossible to induce only specific lattice vibrations.

[0021] Therefore, as shown in graph B of FIG. 2 , negative group delay dispersion is imparted to the pump light and the Stokes light to generate negatively chirped pulses whose frequencies decrease over time. Specifically, a first dispersive element 120 consisting of a transmissive diffraction grating pair 122 and a prism 124 is used to impart a negative chirp to the pump light, and a second dispersive element 144 consisting of a transmissive diffraction grating pair 146 and a prism 148 is used to impart a negative chirp to the Stokes light that has passed through the LPF 142. For example, a diffraction grating pair with 966.18 lines / mm is used for the diffraction grating pair 122 and the diffraction grating pair 146. In this way, the pulse widths of the pump light and the Stokes light are stretched to a predetermined value (e.g., 3 ps or more). If the pump light and the Stokes light have the same chirp, the difference frequency Ω1 remains constant over a long period of time.

[0022] As shown in graph C of Figure 2, when the timing of the chirped pump beam and the Stokes beam is shifted, the difference frequency changes to Ω2. Specifically, when the delay stage 126 having mirrors 127a and 127b is moved by the servo motor 128 to change the optical path length of the pump beam, the optical path difference between the pump beam and the Stokes beam changes, and the lattice vibration frequency (difference frequency) to be detected can be changed. In this way, when the delay stage 126 is moved, the wavelength is swept and an SRS spectrum can be obtained.

[0023] 1 shows the delay stage 126 having the mirrors 127a and 127b as the optical path length varying mechanism, but the mechanism is not limited to this. Any optical path length varying mechanism using various optical components such as a lens, a polygon mirror, or a resonant scanner can be used.

[0024] The BPF 150 functions as a combining element that combines the chirped pump light and the Stokes light. The galvanometer scanner 152 has a galvanometer mirror for the X axis and a galvanometer mirror for the Y axis, and by rotating these galvanometer mirrors in appropriate directions under the control of the scanner controller 154, the laser beam from the BPF 150 can scan the XY plane perpendicular to the optical axis.

[0025] The laser beam from the galvano scanner 152 is imaged on the pupil plane of the objective lens 160 by lenses 156 and 158, and is then focused on the sample S by the objective lens 160. For example, the objective lens 160 is a 50x objective lens. The sample S is placed on a stage that is movable in the optical axis direction (Z direction).

[0026] When the sample S is irradiated with pump light and Stokes light, and the difference frequency between the pump light and the Stokes light matches the lattice vibration frequency of the sample S, the SRS effect occurs, and the pump light is attenuated and the Stokes light is amplified. Since the Stokes light is periodically turned on and off by intensity modulation, when the Stokes light is on, the SRS effect appears and the pump light is attenuated, and when the Stokes light is off, the SRS effect does not appear. Therefore, periodic intensity modulation appears in the pump light. The change in the intensity of the pump light is measured by the measurement unit 104.

[0027] The measurement unit 104 includes an objective lens 162 , a short-pass filter (SPF) 164 , lenses 166 and 168 , a PD 170 , a lock-in amplifier (LIA) 172 , a data acquisition (DAQ) unit 174 , and a personal computer (PC) 176 .

[0028] The objective lens 162 collimates the transmitted light from the focal point of the sample S. The SPF 164 removes the Stokes light from the collimated transmitted light and extracts the pump light. The direction of the extracted pump light is adjusted by lenses 166 and 168, and the extracted pump light is input to the PD 170, which serves as a photodetector. The PD 170 detects the intensity of the pump light and outputs an electrical signal (photocurrent) corresponding to the intensity of the pump light. For example, an InGaAs photodiode can be used as the PD 170. The LIA 172 obtains an SRS signal by locking in the electrical signal output from the PD 170.

[0029] The DAQ unit 174 converts the analog signal, which is the SRS signal output from the LIA 172, into a digital signal and outputs the digital signal to the PC 176. The DAQ unit 174 also outputs a drive signal to the scanner controller 154 to control the galvanometer scanner 152. The PC 176 performs spectrum analysis and imaging analysis based on the input data and displays the results of these analyses on a monitor. The PC 176 also controls the delay stage 126 by outputting a drive signal to the servo motor 128.

[0030] In the semiconductor measurement system 100, an SRS image can be acquired by obtaining an SRS signal while scanning a laser beam using a scanning mechanism, and an SRS spectrum can be acquired by obtaining an SRS signal while changing the difference frequency by changing the optical path difference between the pump light and the Stokes light using an optical path length variable mechanism.

[0031] In addition, in Figure 1, a scanning mechanism is shown in which a laser beam scans the surface of the sample S, but it is also possible to fix the irradiation position of the laser beam and move the stage on which the sample S is placed in the X and Y directions perpendicular to the optical axis.

[0032] Next, the results of measuring Si using the semiconductor measurement system 100 will be described with reference to Figures 3 to 5. Figure 3 shows the SRS spectrum of Si. Here, the pump light and Stokes light irradiated onto the Si sample are in the wavelength bands in the transparent region of Si, the 1.5 μm band and the 1.7 μm band, respectively. From Figure 3, it can be seen that the wave number is 521 cm -1 It can be seen that a Raman peak appears.

[0033] Figure 4 shows the peak wavenumber shift (521 cm) of the SRS spectrum at various depths inside the Si substrate damaged by stealth dicing. -1 The images show two-dimensional distribution images of the peak intensity, peak width, and peak shift from the original position (Z). Measurements were taken while moving the Si substrate position Z in the optical axis direction (thickness direction) by 20 μm increments. The optical power of the pump beam was 8.1 mW, the optical power of the Stokes beam was 4.3 mW, the field of view was 20 μm × 20 μm, the pixel count was 100 × 100 pixels, and the pixel dwell time was 0.1 ms. To improve the signal-to-noise ratio, a 5 × 5 pixel averaging filter was applied, and each image was accumulated 10 times. Images were acquired at five wavenumber points around the peak, and the peak wavenumber was calculated using Gaussian fitting. Figure 4 shows that the peak wavenumber shift occurs at Z = +20 μm and +40 μm, indicating distortion. In this way, the peak wavenumber shift can visualize the internal distortion of the Si substrate.

[0034] Furthermore, when the Si substrate was heated with a heater and the SRS spectrum was measured at different temperatures (30°C, 40°C, 50°C), different peak wavenumber shifts and peak widths were obtained depending on the temperature. Figure 5 shows the results of calculating the average of all pixels in the two-dimensional distribution image of the SRS spectrum for each temperature. As shown in Figure 5, at 30°C, the shift in the central wavenumber was 0.0075 cm -1 , peak width 1.647cm -1 At 40°C, the shift in the central wave number is -0.142 cm -1 , peak width 1.906cm -1 At 50°C, the shift in the central wave number is -0.376 cm -1 , peak width 2.489 cm -1As can be seen, the peak wavenumber and peak width of the SRS spectrum change depending on the temperature.

[0035] According to this embodiment, SRS imaging using optical pulses in the wavelength band of the semiconductor's transparency makes it possible to measure the inside of a semiconductor. Furthermore, SRS enables faster measurement than conventional Raman scattering and also enables three-dimensional imaging.

[0036] In the above-described embodiment, Si is used as an example of a semiconductor to be measured, but it goes without saying that the semiconductor measurement system 100 and measurement method of this embodiment can also be applied to the measurement of other semiconductors such as GaAs and InP.

[0037] In addition, although the wavelengths of the pump light and the Stokes light are in the 1.5 μm band and the 1.7 μm band, respectively, which are wavelength bands in the transparent region of many semiconductors, the present invention is not limited to these. It is preferable that the pump light and the Stokes light have wavelengths at least longer than 1.3 μm.

[0038] Furthermore, in the semiconductor measurement system 100, optical pulses in the communication wavelength band generated by the laser light source 106 are used as pump light without wavelength conversion. Wavelength conversion increases noise, but an optical pulse that has been intensity-modulated and shifted to a longer wavelength is used as the Stokes light, and the intensity of the pump light that has not undergone wavelength conversion is detected, thereby maintaining a good signal-to-noise ratio.

[0039] Furthermore, the semiconductor measurement system 100 is designed so that the optical pulse generated by the laser light source 106 is not immediately output into free space but is propagated in an optical fiber, and the Stokes light is output into free space after intensity modulation and wavelength shift, thereby improving the stability of the system.

[0040] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the spirit of the present invention. Other embodiments and modifications made by those skilled in the art are also included in the present invention. [Explanation of symbols]

[0041] 100 Semiconductor Measurement System 102 Irradiation unit 104 Measurement section 106 Laser light source 110, 140 optical fiber 112, 138 EDFA 114, 130 Optical coupler 120 First dispersion element 126 Delay Stage 136 EOM 142 LPF 144 Second dispersion element 150 BPF 152 Galvanometer Scanner 154 Scanner Controller 160, 162 objective lenses 164 SPF 170PD 172 LIA 174 DAQ section 176 PC

Claims

1. A semiconductor measurement system using stimulated Raman scattering microscopy, an irradiation unit that irradiates a sample made of the semiconductor with pump light and Stokes light having different wavelengths in a wavelength band of a transparent region of the semiconductor, the pump light and the Stokes light being focused on the sample; a measuring unit having a photodetector for detecting the intensity of stimulated Raman scattered light generated at the focal point of the sample; A semiconductor measurement system comprising:

2. The irradiation unit is a laser light source that generates optical pulses in a communication wavelength band; an optical branching element connected to the laser light source via an optical fiber, which branches an optical pulse generated by the laser light source into a first optical pulse and a second optical pulse; 2. The semiconductor measurement system according to claim 1, wherein the first optical pulse is output into free space and used as the pump light.

3. The irradiation unit is a modulator that performs intensity modulation on the second optical pulse; the second optical pulse intensity-modulated by the modulator is propagated through an optical fiber, and shifted to a longer wavelength by the effect of soliton self-frequency shift; the wavelength-shifted second optical pulse is output into free space and used as the Stokes light; The measurement unit The semiconductor measurement system according to claim 2 , wherein the intensity of the pump light in the stimulated Raman scattered light is detected.

4. 4. The semiconductor measurement system according to claim 1, wherein the pump light and the Stokes light have wavelengths longer than 1.3 μm.

5. A semiconductor measurement method using stimulated Raman scattering microscopy, comprising: an irradiation unit irradiating a sample made of the semiconductor with pump light and Stokes light having different wavelengths in a wavelength band of a transparent region of the semiconductor; A semiconductor measurement method, comprising detecting the intensity of stimulated Raman scattered light generated at a focal point of the sample by a photodetector.

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