JP2688040B2 - Fluorescence characteristic inspection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an apparatus for inspecting a fluorescent property of a sample, and particularly to a light emitting diode (LED), a laser diode (LD), a field effect transistor (FET), a photo diode (PD), an optoelectronic integrated device ( OEIC), integrated device (I
It is possible to obtain the spatial intensity distribution image and lifetime distribution image of the photoluminescence generated from the sample, which is suitable for evaluating the quality of semiconductor wafers such as GaAs wafers used in C) etc. The present invention relates to a fluorescent property inspection device.

[Prior art]

Ga used for manufacturing LEDs, LDs, FETs, PDs, OEICs, ICs, etc.
As-wafer quality is the biggest issue for these manufacturers and is by no means reassuring at the moment. In general, when a semiconductor crystal is irradiated with a light beam having an energy larger than the band gap to excite electrons from the valence band, fluorescence is observed in the process of the excited electrons losing energy due to recombination, and this emission Is called Photoluminescence. The lifetime of fluorescence in this photoluminescence is also determined by the quality of the crystal, surface treatment, surface distortion, flaws, and the like. Therefore, the recombination centers on the surface may decrease and the fluorescence life may become longer as the polishing → etching and processing steps proceed. This corresponds to looking at the surface recombination rate. Generally, the change in fluorescence lifetime is due to the influence of crystal quality, crystal defects, surface condition, surface treatment, etc. As shown by the solid line A in the figure, the fluorescent life is long, whereas the wafer of low quality has a shorter fluorescent life as shown by the solid line B in FIG. Therefore,
When evaluating the quality of a GaAs wafer, it is important to measure its fluorescence lifetime. Further, not only the fluorescence lifetime but also the fluorescence efficiency (quantum efficiency, absolute value of fluorescence, that is, fluorescence intensity) is important for the quality of a GaAs wafer. Usually, as shown in FIG. 13, the fluorescence efficiency and the lifetime are correlated, but in some cases it may not be so, so it is important to measure the fluorescence intensity.

[Problems to be solved by the invention]

However, the conventional apparatus for investigating the crystal quality using photoluminescence senses the sample with continuous light (DC light) of wavelength λ1 and generates the wavelength λ2 (> λ1).
The sample was evaluated from the intensity distribution of the photoluminescence of the. In addition, as a mode-locked pulse laser, a technique of irradiating a sample with pulsed light of a semiconductor laser and using a sampling streak camera to measure the fluorescence lifetime of the generated photoluminescence has been proposed. However, since the measurement result can be obtained only for a single measurement point or for a single wavelength, there is a problem that it takes time to move the sample and measure each point. The present invention has been made to solve the above-mentioned conventional problems, and it is possible to obtain a fluorescence intensity and fluorescence lifetime of photoluminescence generated from a sample, or a spatial distribution image of the correlation at high speed. It is an object of the present invention to provide a fluorescent characteristic inspection device that can be used.

[Means for achieving the object]

The present invention relates to a fluorescence characteristic inspection apparatus, a pulse light source 12 for exciting a sample 10 with a slit-like light beam, and a light from the pulse light source 12 as shown in the basic configuration of FIG. Irradiation optical system 14 that irradiates the sample 10 in a slit shape.
A moving means (a stage 16 in the figure) for moving the measurement position of the sample 10, and a focusing optical system 18 for extracting photoluminescence generated from the sample 10 and guiding it to a detector (20).
The streak tube having a slit-shaped photocathode or accelerating electrode is provided, and in synchronization with the pulse light source 12, the information on the time intensity waveform of the photoluminescence is two-dimensionally read out to obtain the light beam. The streak camera 20 for detecting in parallel the information at one or more measurement points on the slit-shaped irradiated portion of the sample 10 irradiated by the sample, and the plurality of samples detected in parallel while moving the sample measurement position. The signal processing device 22 for analyzing and processing the information on the temporal intensity waveform at the measurement point to obtain a spatial intensity distribution of photoluminescence, a life distribution, or a correlation distribution thereof, and further, the condensing optical system. Between the system 18 and the streak camera 20, controlled by the signal processing device 22, the sample 10
Spectrometer 26 to disperse photoluminescence emitted from
Is provided. The photoluminescence is guided to the spectroscope 26 from the condensing optical system 18 through the spectroscope incidence slit 26A in a direction perpendicular to the spectroscopic direction of the spectroscope 26. For example, as shown in FIG. 2, the spectroscope 26 is capable of wavelength scanning from which the photoluminescence is directly guided from the condensing optical system 18 without passing through the input optical system (incident slit and relay lens of streak camera). Is a spectroscopic means,
The streak camera 20 sweeps in a direction perpendicular to the spectral direction (λ direction) to perform time-resolved spectroscopy of photoluminescence from one measurement point on the slit-shaped irradiated portion,
The multi-wavelength spatial intensity distribution, life distribution, or correlation distribution thereof are obtained in parallel. Also, as shown in FIG. 3, for example, the streak camera
In 20, the photoluminescence is swept in the spectral direction, the spatial intensity distribution for each predetermined wavelength of photoluminescence at a plurality of measurement points on the slit-shaped irradiated portion, the life distribution or its correlation distribution. Are obtained in parallel. Further, the streak tube of the streak camera has a structure having a photocathode or an acceleration electrode formed in a slit shape, so that an incident slit and a relay lens of the streak camera are unnecessary.

[Action and effect]

In the fluorescence characteristic inspection device according to the present invention, the pulse light source 12
Is used to excite the sample 10 with a slit-like light beam, and the streak camera 20 is two-dimensionally read out in synchronization with the pulse light source 12, so that the slit-like cover of photoluminescence generated from the sample is detected. Information about the time intensity waveform at one or more measurement points on the irradiation unit is detected in parallel, and the information about the time intensity waveform at the plurality of measurement points detected in parallel while moving the sample measurement position is analyzed. By processing, the spatial intensity distribution and life distribution of photoluminescence or its correlation distribution are obtained. Therefore, both the fluorescence intensity and the life of the sample can be simultaneously measured at high speed, and the quality of the GaAs wafer or the like can be accurately evaluated. Furthermore, since a spatial distribution image of the fluorescence intensity and the lifetime or its correlation can be obtained, local defects and the like can be easily inspected. Also, for example, as shown in FIG.
In the case of sweeping in the direction perpendicular to the spectral direction of the spectroscopic means (spectrometer 26) in 20, the time-resolved spectroscopic analysis of photoluminescence from one measurement point on the slit-shaped irradiated portion is performed. , It becomes possible to calculate spatially intensity distribution of multiple wavelengths, lifetime distribution or its correlation distribution in parallel.
In particular, it is suitable for inspecting a sample having a fluorescent life that varies depending on the wavelength. Further, as shown in FIG. 3, for example, in the case where the streak camera 20 is swept in the spectral direction of the spectroscopic means (26), photoluminescence at a plurality of measurement points on the slit-like irradiated portion is measured. It is possible to obtain the spatial intensity distribution, the life distribution or the correlation distribution thereof for each predetermined wavelength in parallel. Further, since the streak tube of the streak camera has a structure having a photocathode or an acceleration electrode formed in a slit shape, it is possible to eliminate the incident slit and the relay lens of the streak camera. That is, normally, in a streak camera, an input optical system including an incident slit and a relay lens is arranged immediately before the streak tube. The purpose of this input optical system is to cut out the incident light into slits and form the slit light of the incident light on the photocathode of the streak tube. On the other hand, USP4630925 is a device that performs time-resolved spectrophotometry using a streak camera.The input of the spectroscope is a pinhole slit, and the input optical system is not used. Techniques for measuring brightness changes are disclosed. In the case of this method, assuming a planar photocathode and using the input slit of the spectroscope as a pinhole, the imaging system of the spectroscope forms a slit image of incident light that has been wavelength-resolved on the photocathode of the streak tube. Imaging allows the above measurements without input optics. However, if the slit of the spectroscope is a pinhole, only one point of the sample can be measured. Therefore, as suggested in, for example, Japanese Patent Publication No. 58-58005, the photocathode of the streak tube or the acceleration electrode is formed in a slit shape, and in the present invention, the slit of the spectroscope is not a pinhole and the input optical system is omitted. did. In this case, the input optical system can be omitted and multiple points of the sample can be measured simultaneously.

【Example】

An embodiment of a fluorescent characteristic inspection device according to the present invention applied to a semiconductor wafer evaluation device will be described in detail below with reference to the drawings. In the first embodiment of the present invention, as shown in FIG. 1, a pulsed light source 12 for exciting a sample 10 such as a GaAs semiconductor wafer with a slit-shaped light, and the light from the pulsed light source 12 are used for the sample 10.
Irradiation optical system 14 to irradiate, and the position of the sample 10 with respect to the pulsed light source 12 in the direction perpendicular to the slit light longitudinal direction finely, by roughly moving in the slit light longitudinal direction, by the sample 10 of. A stage 16 for moving the measurement position (pulse light irradiation position), and a beam pretter 18A for extracting the photoluminescence generated from the sample 10 and guiding it to the detector, and wavelength components of the photoluminescence are extracted. Optical system including a filter 18B and a lens 18C for
18, a streak camera 20 for two-dimensionally reading out information about the time intensity waveform of the photoluminescence (hereinafter referred to as a fluorescent waveform) by using the output of the pulse light source 12 as a trigger signal, and the stage. By moving 16 the sample measurement position is moved and detected in parallel, the information about the fluorescent waveform at a plurality of slit-like measurement points (see FIG. 4) is analyzed and processed. , A signal processing device 22 for obtaining a spatial intensity distribution of photoluminescence, a life distribution or a correlation distribution thereof, and a spatial intensity distribution image, a life distribution image obtained by the signal processing device 22 or a correlation thereof. A display device 24 for displaying a distribution image, and a spectroscope arranged between the condensing optical system 18 and the streak camera 20 and controlled by a signal processing device 22 to disperse photoluminescence generated from the sample 10. It consists of 26.
As shown in FIG. 2, photoluminescence is guided to the spectroscope 26 from the condensing optical system 18 through the spectroscope incidence slit 26A in a direction perpendicular to the spectroscopic direction of the spectroscope 26. As the pulse light source 12, for example, a laser diode (LD) that can stably oscillate pulsed light having a wavelength of about 600 to 680 nm and a pulse width of about 50 psec can be used. As a method of obtaining a trigger signal from the pulse light source 12, for example, the pulsed light of the pulsed light source 12 is branched and one of the lights is converted into an electric signal by a high-speed photodiode such as an avalanche photodiode (APD), and a streak is generated. It can be used as a trigger signal for the camera 20. The streak camera 20
As shown in the basic configuration of FIG. 5, incident light is applied to the photocathode 36 of the streak tube 34 through an input optical system composed of an incident slit plate 30 and a lens 32 to convert the incident light into electrons, which are then deflected. By swiftly sweeping as the photoelectrons pass between the electrodes 38, the time-varying incident light intensity is changed to the fluorescent surface.
It is measured as a change in luminance at the position above 42. In the figure, 40 is a multi-channel plate (MCP) for multiplying photoelectrons just before the fluorescent surface 42.
The image appearing on the output fluorescent surface 42 in this way is called a streak image. For example, as shown in FIG. 1, this image is output by the television camera 50 using a vidicon or CCD. By quantifying the brightness distribution along the time axis direction of 1, the change over time in the intensity of the light under measurement can be known. Specifically, for example, the output of the television camera 50 is A / D converted by an analog / digital (A / D) converter 52, held in a temporary storage device 54, and then output to the signal processing device 22. With the streak camera 20, for example, fluorescence waveforms as shown in FIG. 6 are obtained in parallel at each measurement point arranged in a slit shape, and the fluorescence intensity and life at each measurement point obtained from this are measured. By spatially plotting two-dimensionally in correspondence with points, a spatial intensity distribution image and a life distribution image can be quickly obtained. In this embodiment, since the length of the slit light is made to coincide with the measurement range, it is usually unnecessary to move the sample in the longitudinal direction of the slit light. When measuring a wider range, the stage can be roughly moved in the longitudinal direction and the vertical direction of the slit light. The analysis and processing of the information regarding the fluorescent waveform in the signal processing device 22 is performed as follows. That is, based on the fluorescence waveform shown in FIG. 6, the fluorescence lifetime τ, which is the time until the fluorescence intensity I (t) reaches 1 / e (about 37%), is first obtained. Specifically, when the fluorescence lifetime τ is one, the waveform in which the vertical axis of the fluorescence waveform is expressed in logarithm is as shown in FIG. Then, the nearest coefficient term A and the life τ are found, for example, by the least square method. I (t) = A · exp (−t / τ) (1) When there are multiple fluorescence lifetimes (τ ₁ , τ ₂ , τ ₃ , ...), the fluorescence waveform is logarithmic. Since the waveform represented by is as shown in FIG. 8, the fluorescence lifetime τ ₁ , τ _1
2 , τ ₃ , ... Can be obtained. I (t) = A ₁ · exp (−t / τ ₁ ) + A ₂ · exp (−t / τ ₂ ) + A ₃ · exp (−t / τ ₃ ) + ・ ・ ・ …… (2) The (total) intensity of light is the total area of the waveform (7th
(Indicated by diagonal lines in FIGS. 8 and 9), the value I (t) of the waveform is integrated over the entire range, or is calculated when the fluorescence lifetime is calculated using the following equation. It can be calculated from the constant A _i and the fluorescence lifetime τ _i . ∫I (t) = A ₁ τ ₁ + A ₂ τ ₂ + A ₃ τ ₃ + ... (3) The fluorescence lifetime and fluorescence intensity obtained in this way are
It is displayed on the display device 24 as a spatial distribution image. FIG. 9 shows an example of the display image of the fluorescence lifetime. In FIG. 9, the distribution of the fluorescence lifetime τ is represented, for example, by shading. When the fluorescence intensity and the lifetime are imaged, it is possible to display not only the black and white density but also the color image with different colors or three-dimensional display. or,
When the fluorescence lifetime also includes the second-order component τ ₂ and the third-order component τ ₃ , for example, only the first-order component τ ₁ is mapped with green,
Map the _first and second order components τ ₁ , τ ₂ in red and
The second, third and third order components τ ₁ , τ ₂ , τ ₃ can be mapped in yellow. In addition, a primary component τ ₁ and red, the second order component τ ₂ and green, the third-order component τ ₃ and blue, Yotsute to be superimposed sequentially. As a result, the primary component τ ₁ red, secondary It is also possible to display the component τ ₂ in yellow and the third-order component τ ₃ in white. Furthermore, when displaying an image, smoothing processing may be appropriately performed to make the image easier to see. Further, the signal processing device 22 performs a calculation such as obtaining a correlation between different intensity distribution images and life distribution images, for example, a ratio,
It is also possible to display the calculation result (that is, the correlation distribution image). As shown in Fig. 2, time-resolved spectroscopy of photoluminescence from the measurement point was performed by sweeping with the streak camera 20 in the direction perpendicular to the spectral direction, and a spatial intensity distribution image and lifetime distribution of multiple wavelengths were obtained. Since the image is obtained, the number of measurement points per measurement is one, but the lifetimes of multiple wavelengths can be measured in parallel. In FIG. 2, 26A is a spectroscope 2 arranged on the image plane.
6 is an incident slit, 30 is an incident slit of the streak camera 20, 38 is also a deflection electrode, and 42 is also a fluorescent surface. According to the first embodiment, information of multiple wavelengths can be measured at the same time. For example, as shown in FIG. 10, even if the fluorescence lifetime varies depending on the wavelength, the fluorescence lifetime for each wavelength can be measured. It is possible to accurately obtain τ ₁ and τ ₂ . In the first embodiment, since the fluorescence waveform containing the wavelength information is immediately obtained, the wavelength scanning in the spectroscope 26 is unnecessary. Next, a second embodiment of the present invention will be described in detail. This second embodiment is the same semiconductor wafer evaluation apparatus as that of the first embodiment. As shown in FIG. 3, the streak camera 20 sweeps in the spectral direction to obtain a plurality of slit-shaped irradiated portions. The spatial intensity distribution image and the lifetime distribution image for each wavelength at the measurement point or the correlation distribution image thereof are obtained in parallel. Since the other points are similar to those of the first embodiment, detailed description thereof will be omitted. In each of the above-described embodiments, the stage 16 that moves in the one-dimensional direction or the two-dimensional direction is used as the moving means for moving the measurement position of the sample 10, but the sample measurement position is moved. The means for moving is not limited to this. For example, when the sample 10 is flowing on a belt conveyor or the like, one moving means can be omitted. Further, instead of using a mechanical scanning unit, pulsed light may be electro-optically deflected to perform scanning. Further, as in the third embodiment shown in FIG. 11, an epi-illumination light source 80 different from the pulse light source 12 is provided to illuminate the sample 10 through, for example, the lens 80A, and the reflected light is reflected by the mirror 82A and the lens 82C. To the TV camera 84, and the TV camera 84 captures a reflection image, A / D converter 86 A / D-converts it, inputs it to the signal processing device 22, and stores it in an image memory (not shown). Display device
It is also possible to display an image on the display 24 and confirm the position of the pulsed light on the sample 10 and monitor the state of the measurement region. or,
It is also possible to superimpose and display the reflection image, the lifetime distribution image of the photoluminescence, the intensity distribution image, and the like. Further, the epi-illumination light source 80 is provided with a wavelength filter 80B matched to the absorption wavelength of the sample 10, the entire surface of the sample 10 is irradiated, the photoluminescence image generated at that time, through a predetermined wavelength filter 82B, the Imaged by TV camera 84, 2
It is also possible to obtain a three-dimensional photoluminescence intensity distribution. Furthermore, a light source 90 for transparent illumination, lenses 90A and 90C, and a wavelength filter 90B are provided on the back side of the sample 10, and an image of the transmitted light of the sample is acquired by the TV camera 84 or the high-speed photodetector 20, and the photo is taken. It is also possible to compare the life of the luminescence, the intensity distribution image, etc. At this time, the second harmonic (SHG) component due to the non-linearity of the sample 10 is extracted by the spectroscopic means 60 provided in front of the high-speed photodetector 20, and the sample 10 is scanned to obtain a non-linear optical characteristic image. it can. Further, in each of the above-mentioned embodiments, the present invention is applied to the semiconductor wafer evaluation apparatus for inspecting the defects of the semiconductor wafer, but the scope of application of the present invention is not limited to this, and dielectrics, It is obvious that the invention can be similarly applied to devices for inspecting other fluorescent characteristics such as a light surface, medicine, paper, and biopsy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the constitution of the first embodiment of the fluorescence characteristic inspection device according to the present invention, and FIG. 2 is a perspective view showing the constitution of the essential parts of the first embodiment of the present invention. FIG. 4 is a perspective view showing an essential configuration of a second embodiment of the present invention, FIG. 4 is a plan view showing an example of measurement points on the sample surface in the first embodiment, and FIG. FIG. 6 is a sectional view showing the basic structure of a streak camera used, FIG. 6 is a diagram showing an example of excitation light and fluorescence waveforms, and FIGS. 7 and 8 explain a method for obtaining fluorescence lifetime. FIG. 9 is a plan view showing a display example of a spatial distribution of fluorescence lifetime, and FIG. 10 is a wavelength dependence of fluorescence lifetime measurable by the first and second embodiments. FIG. 11 is a block diagram showing the configuration of the third embodiment of the present invention, and FIG. 12 is an example of the relationship between the quality of the semiconductor wafer and the fluorescent waveform. It is to diagram. 10 ... Sample, 12 ... Pulse light source, 14 ... Irradiation optical system, 16 ... XY stage, 18 ... Condensing optical system, 18B ... Filter, 20 ... Streak camera, 22 ... Signal processing Device, 26 …… Spectroscope, 26A …… Spectroscope entrance slit, 30 …… Streak camera entrance slit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hirofumi Suga, Hirofumi Suga, 1126, Nomachi, Hamamatsu, Shizuoka, 1126, Hamamatsu Photonics Co., Ltd. (72) Yoshihiko Mizushima, 1126, 1126, Nomachi, Hamamatsu, Shizuoka, Hamamatsu Photonics, Inc. (56) References JP-A-63-53443 (JP, A) JP-A-59-58745 (JP, A) JP-A-58-41337 (JP, A) JP-A-58-205839 (JP, A) Japanese Patent Publication Sho 58-58005 (JP, B2) US Patent 4630925 (US, A)

Claims (3)

(57) [Claims] 1. A pulsed light source for exciting a sample with a slit-shaped light beam, an irradiation optical system for irradiating the sample with light from the pulsed light source in a slit-like manner, and a measuring position for moving the sample. Moving means, a focusing optics for extracting the photoluminescence generated from the sample and guiding it to the detection system, and a photo-guided from the focusing optics through a spectroscopic incidence slit in a direction perpendicular to the spectral direction. A spectroscope capable of wavelength scanning luminescence and a streak tube having a structure having a streak camera incident slit on a photocathode or an acceleration electrode are provided, and the extracted and spectroscopic incident slit is synchronized with the pulse light source. ,
Information about the time intensity waveform of photoluminescence incident through the spectroscope is read out two-dimensionally, and information at one or a plurality of measurement points on the slit-like irradiated portion of the sample irradiated by the light beam is read. Streak camera for detecting in parallel, and the parallel detection while moving the sample measurement position,
Or a signal processing device that analyzes and processes information about the temporal intensity waveform at a plurality of measurement points to obtain a spatial intensity distribution of photoluminescence, a life distribution, or a correlation distribution thereof. Fluorescence characteristic inspection device. 2. The streak camera entrance slit according to claim 1, wherein said streak camera incident slit is in a spectroscopic direction, and said streak camera sweeps said photoluminescence in a direction perpendicular to said spectroscopic direction, Time-resolved spectroscopy of photoluminescence from one measurement point on the slit-shaped irradiated portion is performed, and spatial intensity distribution of multiple wavelengths, lifetime distribution or correlation distribution thereof are obtained in parallel. Fluorescence characteristic inspection device. 3. The streak camera incident slit is set in a direction perpendicular to a spectroscopic direction of the spectroscope, and the photoluminescence is swept in the streak camera in the spectroscopic direction according to claim 1. A fluorescence characteristic inspection device characterized in that a spatial intensity distribution, a life distribution, or a correlation distribution thereof of photoluminescence for each predetermined wavelength at a plurality of measurement points on a slit-shaped irradiated portion are obtained in parallel.