JPS618649A - Optical measuring device - Google Patents

Abstract

PURPOSE:To make a light analysis of photoluminescence emitted from a sample over a wide wavelength range by observing the sample with high magnification and irradiating an extremely small area with laser light for excitation. CONSTITUTION:The laser light 3 for excitation is incident from beside a microscope 2 provided over the sample 1 and guided to the lower part in the optical path of the microscope 2 through a half-mirror 4, and the light is converged through an objective lens 5 to illuminate the surface of the sample 1. At the same time, the surface of the sample 1 is observed with high magnification. At this time, the angle-directional intensity distribution of photoluminescence light emitted from the extremely small irradiated area part of the sample 1 is isotropic in the vertical direction of the sample 1. Its light energy is smaller than the forbidden band width of the sample. Therefore, half of the photoluminescence light is emitted from the surface of the sample at the same side with the laser light irradiation side, and the remainder propagates downward in the sample 1 and is emitted from its reverse surface.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a microscopy method for evaluating impurities, defects, etc. in minute regions in a semiconductor crystal by observing photoluminescence excited by irradiating light onto a minute dominant region of the semiconductor crystal. This invention relates to an optical measurement device using photoluminescence method.

[Prior art]

Si, GaA widely used in various electronic devices
Impurities and defects present in semiconductor crystals such as S, GaP, etc. have a large effect on device characteristics.

Recently, as devices have become more highly integrated and of higher quality, the distribution of impurities and defects in minute regions in material crystals has become a problem. In particular, oxygen precipitates in CZ-9i (rotation-pulled Si) crystals for VLSI and semi-insulating G for high-speed ICs
The non-uniform distribution within the wafer surface of minute defects that form deep levels, such as anti-site defects in aAs crystals, has become important. To investigate the uneven distribution of micro defects that form such deep levels, the photoluminescence method is extremely effective because it is in principle possible to measure microscopic areas with high sensitivity. Although there have been several reports so far, sufficient evaluation has not been conducted due to the following drawbacks.

FIGS. 1 and 2 show schematic configuration examples of a microscopic measurement optical system conventionally used when performing photoluminescence observation of a minute area by the above-mentioned photoluminescence method.

The optical system shown in FIG. 1 uses an ordinary optical microscope to irradiate excitation light and collect photoluminescence light. As this excitation light, high brightness light with energy larger than the forbidden band width of the semiconductor sample is required, so for example, Ar laser light or He-
Ne laser light or the like is used. That is, the laser beam 3 is emitted from the side of the microscope 2 installed above the sample 1.
is made incident, and this laser beam 3 is focused by a semi-transparent mirror 4 and cooled to the temperature of liquid nitrogen or liquid helium.

Now, since the photoluminescence emitted from the surface of the sample 1 irradiated with the laser beam 3 precedes the photoluminescence, a filter 8 is required to separate this reflected light from the photoluminescence light.

In such a conventional method, there is no problem with laser light irradiation and sample observation, but there is a problem with photoluminescence focusing in that a standard objective lens is used. In other words, ordinary objective lenses are designed to correct aberrations such as chromatic aberration in the wavelength range of 400 to 800 nm, keeping in mind that they will be used in the visible light region.
In a wavelength region of 800 nm or more, aberrations increase rapidly and transmission characteristics also deteriorate significantly depending on the lens material and coating material. Therefore, deep levels in GaAs and GaP and S
It becomes impossible to measure the photoluminescence of l. In addition, even in the short wavelength region, it is extremely effective against weak photoluminescence light and strong light energy near the forbidden band width in GaP of several orders of magnitude. It was completely ineffective to achieve very high spatial resolution by raying onto the sample surface.

On the other hand, the method using the optical system shown in FIG. 2 eliminates the above-mentioned drawback by separating the excitation laser optical system and the photoluminescence focusing system6. A regular objective lens 5 is used for irradiating the laser beam 3, and a quartz lens optical system 10 (or a spherical reflection lens) is used to collect the photoluminescence light, which also enables measurement in a long wavelength range. mirror optical system). However, since photoluminescence light is generally weak, it is necessary to give priority to the light collection system 10 over the laser irradiation system 5. Therefore, the laser irradiation system 5 has a photoluminescence light collection path as shown in FIG. Therefore, the distance from the objective lens 5 to the sample 1 (operating distance) becomes long. Therefore, an objective lens with high magnification cannot be used as the objective lens 5, and the narrowing down of the laser beam becomes difficult. In previous reports using this method,
When the sample is placed in a cooling container, the minimum beam diameter is only about 5071 m at most. In addition, observation of the sample surface also had the disadvantage of resulting in a blurred image due to oblique incidence.

In this way, the microscopic photoluminescence method is theoretically capable of highly sensitive evaluation of impurities and defects in extremely small areas, but in reality, as long as conventional methods are used, deep This was considered a major problem as it could not be applied to evaluations such as rank.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the conventional optical measurement device using the microscopic photoluminescence method described above, and to make it possible to observe a sample with a microscope at high magnification. An object of the present invention is to provide an optical measuring device that can perform spectroscopic analysis of emitted photoluminescence over a wide wavelength range.

[Key points of the invention]

That is, in the optical measuring device of the present invention.

It is characterized by the fact that among the photoluminescence generated by irradiating an extremely small area on the sample surface with an excitation laser beam, the component that has passed through the sample is efficiently focused from the back surface of the sample.

〔Example〕

The present invention will be described in detail below with reference to the drawings. FIG. 3 shows an embodiment of the present invention, and the part for irradiating the sample 1 with excitation laser light uses an optical system with the same configuration as the conventional example shown in FIG. 1 above. . That is, an excitation laser beam 3 is incident from the side of a microscope 2 placed on a sample 1, and this laser beam 3 is transmitted through a semi-transparent mirror 4.
The light is guided downward into the microscope optical path 2 by the lens 5, and further narrowed down by the objective lens 5, and irradiated onto the surface of the sample 1. At the same time, the surface of the sample 1 is observed at high magnification through the eyepiece 6. At this time, half of the irradiated light of the sample 1 is emitted from the surface of the sample 1 on the same side as the laser beam irradiation, and the remainder propagates downward within the sample 1 and is emitted from the back surface thereof.

In addition, ■ The sample l to be measured is mainly a wafer used for manufacturing electronic devices, and its thickness is several hundreds of lumens.
■ The photoluminescence that we particularly want to focus on in the measurement comes from a deep level and has an energy much smaller than the forbidden band energy.For the above reasons, Sample 1 Absorption of photoluminescent light during propagation within the rays is small and can be ignored in practice. Therefore, as shown in this figure, by installing a condensing lens system 10 such as a quartz lens (or a reflecting mirror type condensing system) capable of handling a wide wavelength range on the back side of the sample 1°, the laser beam 3 can be Photoluminescence light emitted from the irradiation point can be collected with high efficiency and guided to the spectrometer 8 through the filter 8.

Generally, energy greater than the forbidden band energy is absorbed to a large extent, and the transmitted light intensity is 1/1000 to 1/1/1000.
It decreases to 10,000. Therefore, the photoluminescence of the excitation laser beam, which was a problem in the conventional method shown in FIGS.
When an As wafer is used as sample 1 in FIG.
m). This sample 1 was cooled to liquid helium temperature, and the sample 1 was moved in the direction perpendicular to the plane of the paper in the arrangement shown in FIG. 3, and changes in the one-dimensional distribution of photoluminescence intensity were measured using a spectrometer 8. In addition, a lens with a long working distance of 5 times is used as the objective lens 5, and the At laser beam 3 with a wavelength of 514.5 nm is transmitted with a diameter of 20p and m.
I was able to narrow it down to. The photoluminescence spectrum of the GaAs crystal described above is due to residual carbon impurities of 1,413. eV (832 nm) emission band and E
0, 6, which is thought to be caused by a deep level called L2.
5 eV (1.8 lumen) emission band.

The intensity distribution of the 1.4!3 eV emission band is shown in waveform a in Figure 4.
This is consistent with the results reported previously.

On the other hand, there have been no reports of measurement with high spatial resolution for the 0.85 eV emission band;
According to the illustrated apparatus of the present invention, as described above, the excitation laser beam 3 can be narrowed down to a diameter of 20 g, m for measurement, and as a result, as shown in the waveform of FIG. 0.85e as far as the sample is concerned
It has been found that the intensity of the V emission band is not affected by dislocations.

The above measurement results are based on preliminary experiments.
It is expected that photoluminescence analysis will become possible in a very small region over a wide wavelength range up to about 1.5 gm.

〔effect〕

As is clear from the above, by using the optical measuring device of the present invention, Si, which is used for manufacturing various devices,
It has become possible to measure the photoluminescence of GaAs and GaP wafers over a wide wavelength range with a high spatial resolution of several ILffl.

Ru. This is something that could not be done using conventional methods.

Furthermore, the apparatus of the present invention has the special effect of being able to extremely reduce the amount of excitation laser light that is harmful to photoluminescence measurements.

In addition, the microscopic photoluminescence method using the optical measurement device of the present invention is not only extremely useful for investigating the relationship between dislocations, minute precipitates, etc. in semiconductor crystals and deep levels, but also This research is expected to greatly contribute to the study of the effects of microscopic defects and microscopic non-uniform distribution of impurities on device characteristics, as well as to the elucidation of defective microelements in highly integrated devices.

[Brief explanation of the drawing]

FIGS. 1 and 2 are internal configuration diagrams showing the principle of the microphotoluminescence method using a conventional optical measurement device, respectively. FIG. 3 is an internal configuration diagram showing the principle of the microphotoluminescence method using the optical device of the present invention, and FIG. The figure shows the 1.49eV emission bands B and O, E15eV near the dislocation line of the GaAs crystal.
FIG. 3 is an owner curve diagram showing a 15 eV intensity distribution. DESCRIPTION OF SYMBOLS 1... Sample, 2... Optical microscope, 3... Laser for excitation, 4... Semi-transparent mirror, 5... Objective lens, 6... Eyepiece, -7... Reflecting mirror, 8...Filter, 9...Spectroscope, 10...Condensing lens. Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] When performing photoluminescence analysis of semiconductor wafers used in various electronic devices, while observing the surface of the wafer using an ordinary microscope optical system, aiming at the location of the wafer where the photoluminescence analysis is to be performed. An excitation laser beam is focused and irradiated to a very small area at the location, and photoluminescence light emitted from the irradiated point, propagated within the wafer, and emitted to the back surface of the wafer is placed on the back surface of the wafer. The excitation laser beam and the photoluminescence light are completely separated by condensing the light using a condensing optical system and guiding it to a spectrometer, thereby performing photoluminescence analysis in an extremely small area over a wide range of wavelength regions. An optical measurement device featuring: