JPH02268255A - Apparatus for inspecting fluorescence characteristic - Google Patents

Abstract

PURPOSE:To make it possible to measure both of the fluorescence intensity and the life of a sample at the same time at a high speed by moving the measuring position of a sample, and analyzing and processing the data of the time intensity waveforms which are detected with a streak camera at a plurality of measuring points. CONSTITUTION:A pulse light source 12 is used, and a sample 10 is excited with a slit shaped light beam or a plurality of light beams. The image is read out through a streak camera 10 in two dimensions in synchronization with the pulse light source 12. The data of the time intensity waveforms of photoluminescence generated from the sample 10 at a plurality of measuring points are detected in parallel. Then the measuring position of the sample is moved with a stage 16. The data measured at each measuring point are analyzed and processed in a signal processing device 22. The space distribution and the life distribution of the photoluminescence or the correlations of both are obtained. Therefore, both the luminescence intensity and the life of the sample can be measured at the same time at a high speed. The quality of a GaAs wafer and the like can be accurately evaluated. Furthermore, local defects and the like can be readily inspected.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an apparatus for inspecting the fluorescent properties of a sample, and in particular to a light emitting diode (LED), a laser diode (LD), a field effect transistor (FET), a photodiode (PD), an opto-electrical integrated device ( OEI
C) Spatial intensity distribution image and lifetime distribution image of photoluminescence generated from a sample suitable for use in evaluating the quality of semiconductor wafers such as Ga AS wafers used in integrated devices (ICs) etc. This invention relates to a fluorescent property testing device that can obtain the following characteristics.

[Conventional technology]

The quality of Qa AS wafers used to manufacture LEDs, LDIFETs, PDs, OE ICs, ICs, etc. is the biggest issue for these manufacturers, and the current situation is far from reliable. In general, when a semiconductor crystal is irradiated with a light beam with energy greater than the forbidden band width to excite electrons from the valence band, fluorescence occurs as the excited electrons lose energy through recombination. This luminescence is called 7 otoluminescence. The lifetime of the fluorescence in this photoluminescence is also determined by the quality of the crystal, surface treatment, surface distortion, flaws, etc. Therefore, as the processing process progresses from polishing to etching, the number of recombination centers on the surface decreases and the lifetime of the fluorescence may become longer. This corresponds to looking at the surface recombination rate. - Inside the shell, the fluorescence lifetime changes due to the effects of crystal quality, crystal defects, surface condition, surface treatment, etc., and wafers with good conditions, that is, good quality, As shown by the solid line A in Figure 13, the fluorescent life becomes longer, but the wafers of lower quality also
As shown by the solid line B in the figure, the lifetime of the fluorescent light is shortened. Therefore, when evaluating the quality of Ga AS wafers, it is important to measure their fluorescence lifetime. Furthermore, for the quality of a GaAS wafer, not only the fluorescence lifetime but also the fluorescence efficiency (quantum efficiency, absolute value of fluorescence, that is, fluorescence intensity) is important. Usually, as shown in FIG. 13, there is a correlation between fluorescence efficiency and lifetime, but this may not always be the case, so it is also important to measure the fluorescence intensity.

[Problem to be achieved by the invention]

However, conventional equipment for examining the quality of crystals using photoluminescence irradiates a sample with continuous light (DC light) of wavelength λ1, and generates a wavelength of λ2 (>λ1).
The sample was evaluated based on the intensity distribution of photoluminescence. Furthermore, a technique has been proposed in which a sample is irradiated with pulsed light from a mode-locked pulsed laser or a semiconductor laser, and the fluorescence lifetime of the generated photoluminescence is measured using a sampling streak camera. However, since measurement results can only be obtained for a single measurement point or for a single wavelength, there are problems such as it takes time to move the sample and measure each point. The present invention was made to solve the above-mentioned conventional problems, and it is possible to quickly obtain a spatial distribution image of the fluorescence intensity and fluorescence lifetime of photoluminescence generated from a sample, or the correlation thereof. An object of the present invention is to provide a fluorescent property testing device.

[Means to achieve the task]

The present invention provides a fluorescence characteristic testing apparatus, the basic configuration of which is illustrated in FIG. An irradiation optical system 14 that irradiates the sample 10 with light, a moving means (stage 16 in the figure) for moving the measurement position of the sample 1o, and a detector (20) that extracts photoluminescence generated from the sample 10. A condensing optical system 18 for guiding and synchronizing with the pulsed light source 12 collects information regarding the time-intensity waveform of the photoluminescence.
A streak camera 20 for reading out dimensionally and detecting information at a plurality of measurement points in parallel, and information about the time-intensity waveform at a plurality of measurement points detected in parallel while moving the sample measurement position. Analyze, process,
The above object has been achieved by including a signal processing device 22 for determining the spatial intensity distribution, lifetime distribution, or correlation distribution thereof of photoluminescence. Further, for example, as shown in FIG. 2, the streak camera 2
A spectroscopic means (26) is provided in front of 0, and the spectroscopic direction (λ direction)
This method performs time-resolved spectroscopy of photoluminescence from a measurement point by sweeping in a direction perpendicular to the wavelength, and the spatial intensity distribution of multiple wavelengths, lifetime distribution, or their correlation distribution can be obtained in parallel. In this case, the pulsed light that excites the sample may be in the form of a spot. Further, as shown in FIG. 3, for example, the streak camera 2
A scanning spectroscopic means (26) is provided in front of the 0, and is swept in the spectral direction to measure the spatial intensity distribution, lifetime distribution, or correlation distribution thereof for each predetermined wavelength of photoluminescence at a plurality of measurement points in parallel. It was made so that people could ask for it. Further, the streak tube of the streak camera has a structure having a photocathode or an accelerating electrode formed in a slit shape,
This eliminates the need for the entrance slit and relay lens of the streak camera. [Operations and Effects] In the fluorescent property testing device according to the present invention, the pulsed light source 12
sample 10 with a slit shape or multiple light beams using
By exciting the pulsed light source 12 and reading the streak camera 20 two-dimensionally in synchronization with the pulsed light source 12, information regarding the time-intensity waveform of photoluminescence generated in the sample at a plurality of measurement points is detected in parallel. and analyzes and processes information regarding the time-intensity waveforms at multiple measurement points, which are detected in parallel while moving the sample measurement position,
The spatial intensity distribution and lifetime distribution of photoluminescence or their correlation distribution are determined. Therefore,
Both the fluorescence intensity and lifetime of a sample can be measured simultaneously at high speed, making it possible to accurately evaluate the quality of GaAs wafers and the like. Furthermore, since a spatial distribution image of the fluorescence intensity and lifetime or their correlation can be obtained, local defects etc. can be easily inspected. Further, for example, as shown in FIG. 2, the streak camera 2
If a spectroscopic means (spectrometer 26) is installed in front of 0 and sweeps in a direction perpendicular to the direction of spectroscopy, time-resolved spectroscopy of photoluminescence from the measurement point is performed to obtain spatial multi-wavelength spectroscopy. It becomes possible to obtain the intensity distribution, lifetime distribution, or their correlation distribution in parallel, which is particularly suitable when inspecting samples whose fluorescence lifetimes differ depending on the wavelength. Furthermore, as shown in FIG. 3, for example, if a scanning spectroscopic means (26) is provided in front of the streak camera 2o to sweep in the spectroscopic direction, the predetermined wavelength of photoluminescence at a plurality of measurement points can be It becomes possible to obtain spatial intensity distributions, lifetime distributions, or their correlation distributions in parallel. Further, when the streak tube of the streak camera has a structure having a photocathode or an accelerating electrode formed in the shape of a slit, the entrance slit and relay lens of the streak camera can be made unnecessary. That is, in a streak camera, an input optical system consisting of an entrance slit and a relay lens is usually arranged immediately in front of the streak tube. The purpose of this input optical system is to cut out the incident light into a slit shape and form an image of the slit light of the incident light on the photocathode of the streak tube. on the other hand,
USP 4,630,925 describes a device that performs time-resolved spectrophotometry using a streak camera, and uses a pinhole slit as the input of the spectrometer to measure the time-wavelength luminance change of fluorescence from a certain point on the sample without an input optical system. Techniques for measuring are disclosed. This method assumes a planar photocathode, uses the input slit of the spectrometer as a pinhole, and uses the imaging system of the spectrometer to form a slit image of the wavelength-resolved incident light on the photocathode of the streak tube. By imaging, the above-mentioned measurement is possible without an input optical system. however,
If the slit of the spectrometer is a pinhole, only one point on the sample can be measured. Therefore, for example,
5, the input optical system can be omitted by forming the photocathode or accelerating electrode of the streak tube in the shape of a slit instead of using the slit of the spectrometer as a pinhole. In this case, it is possible to omit the input optical system and measure multiple points on the sample simultaneously. [Example] Hereinafter, an example of a fluorescent property inspection apparatus according to the present invention applied to a semiconductor wafer evaluation apparatus will be described in detail with reference to the drawings. As shown in FIG. 1, the first embodiment of the present invention includes a pulsed light source 12 for exciting a sample 10 such as a QaAs semiconductor wafer with slit-shaped light, and a pulsed light source 12 for exciting a sample 10 such as a QaAs semiconductor wafer with light from the pulsed light source 12. The measurement position of the sample 10 ( a stage 16 for moving the pulsed light irradiation position), a beam splitter 18A for extracting photoluminescence generated from the sample 10 and guiding it to the detector, and a filter 18 for extracting the wavelength component of the photoluminescence.
B and a condensing optical system 18 including a lens 18G and the output of the pulsed light a112 as a trigger signal to two-dimensionally read out information regarding the time-intensity waveform of the photoluminescence (hereinafter referred to as a fluorescence waveform). Information regarding the fluorescence waveform at a plurality of measurement points arranged in a slit shape (see FIG. 4) detected in parallel while moving the sample measurement position by moving the streak camera 20 and the stage 16. a signal processing device 22 that analyzes and processes the photoluminescence to determine the spatial intensity distribution, lifetime distribution, or correlation distribution thereof; and the signal processing device 22
The display device 24 displays a spatial intensity distribution image, a lifetime distribution image, or a correlation distribution image thereof obtained by the above. The pulsed light 8!12 has a wavelength of 600 to 6, for example.
A laser diode (LD) that can stably emit pulsed light of about 80 nIn and a pulse width of about 50 psec can be used. A method for obtaining a trigger signal from the pulsed light source 12 is, for example, by branching the pulsed light from the pulsed light source 12 and converting one of the lights into an electrical signal using a high-speed photodiode such as an avalanche photodiode (APD). There may be 20 trigger signals. The streak camera 20, as shown in its basic configuration in FIG.
By applying the photoelectrons to the photocathode 36 and converting them into electrons, and sweeping the photoelectrons at high speed as they pass between the deflection electrodes 38, the time-varying incident light intensity is converted into a brightness change at a position on the fluorescent surface 42. It is something to be measured. In the figure, 4
0 is a multi-channel plate (MCP) for multiplying photoelectrons immediately in front of the fluorescent surface 42. The image that appears on the output fluorescent surface 42 in this way is called a streak image, and as shown in FIG. By quantifying the brightness distribution along the time axis direction, it is possible to know the change in the intensity of the measured light over time. Specifically, for example, the output of the television camera 50 is converted into an analog/
The signal is A/D converted by a digital<A/D) converter 52, stored in a -time storage device 54, and then output to the signal processing device 22. Using the streak camera 20, 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 lifespan obtained for each measurement point are measured. By plotting two-dimensionally in correspondence with points, spatial intensity distribution images and lifetime distribution images can be quickly obtained. In this embodiment, since the length of the slit light is made to match the measurement range, it is usually not necessary to move the sample in the longitudinal direction of the slit light. In addition, when measuring an even wider range, the stage can be roughly moved in the longitudinal direction and perpendicular direction of the slit light. Analysis and processing of information regarding the fluorescence waveform in the signal processing device 22 is performed as follows. That is, based on the fluorescence waveform as shown in FIG. 6 above,
First, the fluorescence lifetime τ, which is the time until the fluorescence intensity 1 (t) becomes 1/e (approximately 37%), is determined. Specifically, if there is only one type of fluorescence life, the waveform expressed logarithmically on the vertical axis of the fluorescence waveform will be as shown in Figure 7, so for this waveform, the following equation can be used. By applying the equation shown in , the nearest coefficient term A and the life τ are determined by, for example, the method of least squares. 1 (t) −A −exp(−t/τ) ・
(1) Also, there are multiple fluorescent lifetimes (τ1, τ2, τ3,...
) In some cases, the logarithmic waveform of the fluorescence waveform is
As shown in the figure, by correspondingly applying the following equation, each fluorescent life τ1
, τ2, τ3, . . . can be obtained. I(t)-Aj exp(-t/r1)+A2 ・e
xp(-t/τ2) +A3 ・eXI)(-t/τ3) +... ・・・・・・・・・(2) On the other hand, the (total) intensity of the fluorescence is the total area of the waveform ( Figures 7 and 8
(shown with diagonal lines in the figure), the value of the waveform I (
t) over the entire range, or can be calculated from the constant Ai and the fluorescence lifetime τi obtained when determining the fluorescence lifetime using the following equation. fI(t)=, A+τ1+A2τ2+A3τ3+...
(3) The fluorescence life and fluorescence intensity thus determined are displayed on the display device 24.
is displayed as a spatial distribution image. An example of a display image of the fluorescent life is shown in FIG. In FIG. 9, the distribution of the fluorescence lifetime τ is represented by, for example, shading. When visualizing the fluorescence intensity and lifespan, in addition to displaying in black and white density, it is also possible to display a color image with different colors, or to perform three-dimensional display. In addition, if there are also a second blowing component τ2 and a third blowing component τ3 in the fluorescent life, for example, only the first component 1 is mapped in green, and 1
Mapping the next and second order components τ1 and τ2 in red, the first order,
The secondary and tertiary components τ1, τ2, and τ3 can be mapped in yellow. Also, by making the first-order component τ1 red, the second-order component τ2 green, and the third-order component τ3 blue, and sequentially overlapping them, as a result, the first-order component 1 is red, and the second-order component τ2 is
It is also possible to display the third-order component τ3 in yellow and the third-order component τ3 in white. Furthermore, when displaying an image, it is possible to perform appropriate smoothing processing to make it easier to see. Further, the signal processing device 22 performs calculations such as calculating a correlation between different intensity distribution images and lifetime distribution images, for example, calculating a ratio.
It is also possible to display the calculation results (ie, the correlation distribution image). Next, a second embodiment of the present invention will be described in detail with reference to FIG. This second embodiment uses a pulsed light ai 12 or a spot light source and an irradiation optical system 14 similar to the first embodiment.
, a stage 16, a condensing optical system 18, a streak camera 20, a signal processing device 22, a display device 24, a television camera 50, an A/D converter 52, and a -time storage device 52. In the semiconductor wafer evaluation device, further,
A spectroscope 26 that is controlled by a signal processing device 22 and separates photoluminescence generated from the sample 1o is provided between the streak cameras 20, and as shown in FIG. The time-resolved spectroscopy of the photoluminescence from the measurement point is performed by sweeping the light to obtain a multi-wavelength spatial intensity distribution image and lifetime distribution image. In this case, the number of measurement points is one, but the lifetime of each of multiple wavelengths can be measured in parallel. In FIG. 2, 26A is an entrance slit of the spectrometer 26 disposed on the imaging plane, 3o is an entrance slit of the streak camera 20, 38 is a deflection electrode, and 42 is a fluorescent surface. According to this second embodiment, information on multiple wavelengths can be measured simultaneously. For example, even if the fluorescence lifetime differs depending on the wavelength, as shown in FIG. 11, the fluorescence lifetime τ1 for each wavelength, τ2 can be determined accurately. In this second embodiment, since a fluorescence waveform containing wavelength information is immediately obtained, wavelength scanning in the spectrometer 26 is not necessary. Next, a third embodiment of the present invention will be described in detail. In the third embodiment, in a semiconductor wafer evaluation apparatus similar to the second embodiment, as shown in FIG. 3, the streak camera 20 sweeps in the spectral direction, and the A spatial intensity distribution image, a lifetime distribution image, or a correlation distribution image thereof can be obtained in parallel. Since other points are the same as those in the second embodiment, detailed explanation will be omitted. In each of the above embodiments, the stage 16 that moves in a one-dimensional direction or two-dimensional direction was used as a moving means for moving the measurement position of the sample 10. The means of transportation for this purpose is not limited to this. For example, if the sample 10 is flowing on a belt conveyor or the like, one moving means can be omitted. Alternatively, instead of using mechanical scanning means, a configuration may be adopted in which the pulsed light is electro-optically deflected and scanned. Further, as in the fourth example shown in FIG. 12, the pulsed light source 12
An epi-illumination light source 80 separate from the lens 80 is provided, for example.
The sample 10 is irradiated through the mirror 82, and this reflected light is sent to the mirror 82.
A and a lens 82C lead to a TV camera 84, the TV camera 84 converts the reflected image into a silver image, and an A/D converter 86 converts the reflected image into an A/D converter.
After conversion, it is input to the signal processing device 22, stored in an image memory (not shown), and displayed on the display device 24 to confirm the position of the pulsed light on the sample 10 and the state of the measurement area. can also be monitored. Further, it is also possible to display this reflection image and a photoluminescence lifetime distribution image, an intensity distribution image, etc. in an overlapping manner. Moreover, the epi-illumination light if! A wavelength filter 80B matching the absorption layer of the sample 10 is provided at 80, and the entire surface of the sample 10 is irradiated, and the photoluminescence image generated at that time is transmitted to the TV camera 84 through a predetermined wavelength filter 82B.
It is also possible to create a lid image and obtain a two-dimensional photoluminescence intensity distribution. Furthermore, a light source 90 for transparent illumination is provided on the back side of the sample 10.
Lenses 90A, 90C and wavelength filter 90B are provided,
It is also possible to obtain an image of the transmitted light of the sample using the TV camera 84 or the high-speed photodetector 20 and compare it with the photoluminescence lifetime, intensity distribution image, etc. At this time, the spectroscopic means 60 provided in front of the high-speed photodetector 20
The second harmonic (SHG) due to the nonlinearity of sample 10 is
It is also possible to extract the components and scan the sample 10 to obtain a nonlinear optical characteristic image. Furthermore, in each of the above embodiments, the present invention was applied to a semiconductor wafer evaluation device for inspecting semiconductor wafers for defects, but the scope of application of the present invention is not limited to this, and is applicable to dielectrics, fluorescent materials, etc. It is clear that the present invention is equally applicable to devices for testing other fluorescent properties such as light surfaces, drugs, paper, biological tests, etc.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of a fluorescent property testing device according to the present invention; FIG. 2 is a perspective view showing the configuration of main parts of a second embodiment of the present invention; The figure is a perspective view showing the configuration of main parts of the third 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. A cross-sectional view showing the basic configuration of the streak camera used; Fig. 6 is a diagram showing an example of excitation light and fluorescence waveforms; Figs. 7 and 8 explain a method for determining the fluorescence lifetime. FIG. 9 is a plan view showing an example of displaying the spatial distribution of fluorescence lifetime; FIG. 10 is a block diagram showing the configuration of the second embodiment of the present invention; FIG. , a diagram showing an example of the wavelength dependence of fluorescence lifetime that can be measured by the second and third embodiments, FIG. 12 is a block diagram showing the configuration of the fourth embodiment of the present invention, and FIG. FIG. 2 is a diagram showing an example of the relationship between semiconductor wafer quality and fluorescence waveform. 10...Sample, 12...Pulse light source, 14...Irradiation optical system, 16...X-Y stage, 18...Condensing optical system, 18B...Filter, 20...Streak Camera, 22... Signal processing device, 26... Spectrometer.

Claims (4)

[Claims] (1) A pulsed light source for exciting a sample with a slit-shaped or multiple light beams, an irradiation optical system for irradiating the sample with light from the pulsed light source, and a moving means for moving the measurement position of the sample. , a condensing optical system that extracts photoluminescence generated from a sample and guides it to a detector; and a condensing optical system that two-dimensionally reads out information regarding the time-intensity waveform of the photoluminescence in synchronization with the pulsed light source, and detects the photoluminescence at a plurality of measurement points. a streak camera for detecting information in parallel at multiple measurement points;
Processing the spatial intensity distribution of photoluminescence,
A signal processing device for determining a lifetime distribution or a correlation distribution thereof; A fluorescence characteristic testing device comprising: (2) In claim 1, a spectroscopic means is provided in front of the streak camera, and performs time-resolved spectroscopy of photoluminescence from a measurement point by sweeping in a direction perpendicular to the spectroscopic direction, and spatially intensifies multiple wavelengths. A fluorescence characteristic testing device characterized by determining distribution, lifetime distribution, or their correlation distribution in parallel. (3) In claim 1, a scanning spectroscopic means is provided in front of the streak camera, and the spectroscopic means sweeps in the spectroscopic direction to determine the spatial intensity distribution, lifetime distribution, or lifetime distribution of photoluminescence at a plurality of measurement points for each predetermined wavelength. A fluorescence characteristic testing device characterized by obtaining the correlation distribution in parallel. (4) A fluorescence characteristic testing device according to any one of claims 1 to 3, wherein the streak tube of the streak camera has a photocathode or an accelerating electrode formed in a slit shape.