JPH0868757A - Evaluation of surface of sample - Google Patents

Abstract

PURPOSE: To simply and rapidly detect the emission spectrum related only to the surface state of a sample. CONSTITUTION: An internally vacuum cryostat 8 is provided on a fine adjustment stand 14 and a heat sink 12 is provided in the cryostat 8 and a tank 13 storing liquid nitrogen is provided to the heat sink 12 while a semiconductor substrate sample 7 is attached to the upper surface of the heat sink 12 by mounting vacuum grease 11 and laser beam 1 is condensed by an objective lens 4 until the diameter thereof becomes about several μm to irradiate the end surface of the semiconductor substrate sample 7 and the photoluminescence beam 2 and reflected beam from the semiconductor substrate sample 7 are received through the objective lens 4 to be separated by a beam splitter 3 and the spectrum of the photoluminescence beam 2 is detected by a sepctroscope 5 and a photodetector 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample surface evaluation method for evaluating a sample surface state, and more particularly to a sample surface evaluation method for evaluating various levels near the surface of a semiconductor substrate generated during semiconductor crystal growth or process treatment. Is.

[0002]

2. Description of the Related Art Damage near the surface caused by crystal growth or process treatment is an important factor that determines the characteristics of semiconductor devices. Therefore, with the recent demand for high integration, a simple and accurate sample surface evaluation method is indispensable in order to produce a high quality microdevice.

Conventionally, a scanning electron microscope (SE
M), scanning tunneling microscope (STM), atomic force microscope (AFM) for direct observation of surface irregularities of the sample, and photoluminescence (PL) method and cathodoluminescence (CL) method for measuring optical properties near the surface of the crystal sample. Has been used to evaluate the sample surface condition.

[0004]

However, in the sample surface evaluation method using the scanning electron microscope, the scanning tunneling microscope, and the atomic force microscope, only the information about the unevenness of the sample surface can be obtained, and the optical property near the surface of the semiconductor substrate can be obtained. Insufficient in assessing properties.

On the other hand, in the photoluminescence method and the cathodoluminescence method, the optical characteristics of the surface of the semiconductor substrate can be evaluated. However, in the prior art, the excitation light was radiated perpendicularly to the surface of the crystal sample. Since it is difficult to separate and evaluate the luminescence related to the sample surface state and the luminescence related to the bulk state due to the excitation light penetrating inside the sample, there is a problem that the emission spectrum related to only the sample surface state cannot be detected. is there.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a sample surface evaluation method capable of simply and quickly detecting an emission spectrum relating to only the sample surface state.

[0007]

In order to achieve this object, in the present invention, in the sample surface evaluation method of irradiating the sample surface with beam-shaped excitation light and detecting photoluminescence light, the excitation light is Irradiate the sample surface almost in parallel.

In this case, the wavelength of the excitation light is changed.

Further, the irradiation position of the excitation light is changed.

Further, the photoluminescence light is detected through an optical fiber.

[0011]

In this sample surface evaluation method, only the vicinity of the sample surface can be selectively excited by the excitation light.

Further, when the wavelength of the excitation light is changed, the penetration depth of the excitation light into the sample surface can be changed.

Further, when the irradiation position of the excitation light is changed, the photoluminescence light from each irradiation position can be detected.

When the photoluminescence light is detected through the optical fiber, the photoluminescence light can be effectively received.

[0015]

Embodiments of the sample surface evaluation method according to the present invention will be described below with reference to the drawings.

(1) Sample end face upper excitation upper light receiving type system FIG. 1 is a schematic sectional view showing an apparatus for carrying out the sample surface evaluation method according to the present invention. As shown in the drawing, a cryostat 8 having a vacuum inside is provided on a fine movement table 14, a window 9 is provided in the cryostat 8, a heat sink 12 made of copper is provided in the cryostat 8, and a liquid for cooling is provided in the heat sink 12. Tank 1 for storing nitrogen
3 is provided, the semiconductor substrate sample 7 is mounted on the heat sink 12 by the mounting vacuum grease 11 having good thermal conductivity, the laser beam generator 17 is provided above the window 9, and the laser beam generator 17 generates the laser beam. The wavelength of the beam 1 can be changed, a beam splitter 3 and an objective lens 4 are provided between the laser beam generator 17 and the window 9, a spectroscope 5 is provided near the beam splitter 3, and a spectroscope 5 is provided. A photodetector 6 is provided for detecting the light dispersed by.

In order to evaluate the surface state of the semiconductor substrate sample 7 by the apparatus shown in FIG. 1, first, the laser beam 1 as the excitation light is focused by the objective lens 4 to a beam diameter of about several μm, and then the state shown in FIG. As shown, the end surface 15 of the semiconductor substrate sample 7 is irradiated. Then, the photoluminescence light and the reflected light from the semiconductor substrate sample 7 are received through the objective lens 4, and after the photoluminescence light 2 and the reflected light are separated by the beam splitter 3, the spectroscope 5 and the photodetector 6 photo The spectrum of the luminescence light 2 is detected.

FIG. 3 is a graph showing a photoluminescence spectrum in the vicinity of an end face (cleavage face) 15 of a semiconductor substrate sample 7 made of non-dope InP measured at a low temperature of 81 K using the apparatus shown in FIG. Is. As the laser beam 1, a He-Ne laser beam (wavelength 0.
633 μm), and the laser beam 1 is focused by the objective lens 4 to about 3 μm at the focal position. FIG.
In the spectra indicated by lines a, b, and c in FIG. 4, the irradiation position of the laser beam 1 on the semiconductor substrate sample 7 is shown in FIG.
It corresponds to cases A, B, and C shown in FIG.

Line a in FIG. 3 indicates the upper surface 16 of the semiconductor substrate sample 7.
FIG. 3 is a spectrum when the laser beam 1 is vertically radiated on the main beam (peak wavelength 904 nm) which is the light emission from the bulk state inside the semiconductor substrate sample 7 and the width on the long wave side corresponding to the light emission from the surface state. The spectrum is a combination of broad sub-peaks (peak wavelength near 920 nm). According to the conventional photoluminescence method in which the laser beam 1 is vertically incident on the semiconductor substrate sample 7, such a spectrum is obtained, and it is difficult to separate and evaluate only the surface state. However, when the irradiation position of the laser beam 1 is near the end surface 15 of the semiconductor substrate sample 7, the shape of the emission spectrum changes significantly.

Line b in FIG. 3 is a spectrum when the irradiation position is on the end face 15. In this case, the laser beam 1
Since only a part of the light enters the inside of the semiconductor substrate sample 7, the intensity of the main peak, which is the light emission from the bulk state, is reduced to nearly half the intensity of the line a. On the other hand, it can be seen that the intensity of the sub-peak on the long wave side has not decreased, and only the surface state is being selectively excited.

The line c in FIG. 3 indicates that the irradiation position is the semiconductor substrate sample 7
This is a spectrum when the laser beam 1 irradiates the end face 15 further approximately 15 μm away from the end face 15 and is substantially parallel to the end face 15 to excite only the surface state. As is clear from a comparison between the spectrum of the line a and the spectrum of the line c, in the case of the line c, the main peak, which is the light emission from the bulk state, disappears completely, and the main peak from the surface state disappears. Only the wide subpeak on the long-wave side, which is the emission, is observed. Therefore, if the laser beam 1 is irradiated substantially parallel to the end face 15, the light emission from the bulk state inside the semiconductor substrate sample 7 and the light emission from the surface state, which are difficult by the conventional photoluminescence method, are completely completed. It is possible to separate, and it is possible to measure the optical characteristics of only the surface state of the end face 15.

As described above, in the sample surface evaluation method using the apparatus shown in FIG. 1, it is possible to measure the optical characteristics of only the surface state, and among the optical characteristics of only the surface state, the surface Since it contains useful information about changes in chemical composition and damage in the vicinity, if the obtained results are reflected in crystal growth conditions or process conditions,
A dramatic development can be expected in the improvement of crystal quality, the progress of process technology, and the improvement of the characteristics of semiconductor devices.
Also, the wavelength of the laser beam 1 can be changed,
Since the penetration depth into the inside of the semiconductor substrate sample 7 can be changed according to the wavelength of the laser beam 1, it is also possible to obtain knowledge about the change in the surface state of the end face 15 in the depth direction. Further, the cryostat 8 is installed on the fine movement table 14, and the cryostat 8 is set to X, Y, Z.
Can move rapidly in the direction of μm,
Since the irradiation position of the laser beam 1 can be scanned with respect to each surface of the semiconductor substrate sample 7 in the order of μm, the laser beam 1 is incident substantially parallel to the end face 15, and only the surface condition of the end face 15 can be excited. Since the irradiation area 18 can be easily found and the irradiation area 18 can be scanned within the end surface 15, it is also possible to examine the distribution of the surface state within the end surface 15. In addition, the semiconductor substrate sample 7 was heated to the liquid nitrogen temperature (77
Since it can be cooled to the vicinity of K), more detailed information on the surface state that has been erased by the thermal disturbance can be obtained.

(2) Upper Surface of Sample Upper Excitation Side-Reception Type Method FIG. 5 is a schematic perspective view showing a part of an apparatus for carrying out another sample surface evaluation method according to the present invention. As shown in the figure, the sample mounting jig 3 is mounted on the heat sink 12 shown in FIG.
5 is installed, and a mechanism (not shown) for finely adjusting the tilt angle θ of the sample mounting jig 35 is provided.
5, a semiconductor substrate sample 30 is attached, and an optical fiber 33 for receiving light is provided near the upper surface 31 of the semiconductor substrate sample 30.

In the sample surface evaluation method using the apparatus shown in FIG. 5, the semiconductor substrate sample 30 is a horizontal plane (XY plane).
It will be placed almost vertically to. Therefore, the laser beam 1 from above is applied to the upper surface 3 of the semiconductor substrate sample 30.
The light is incident substantially parallel to 1 and only the surface vicinity of the upper surface 31 is selectively photoexcited. Here, the upper surface 31 is a crystal surface that has been subjected to a process such as a dry process or crystal growth, and is a surface that includes damage that determines device characteristics. Therefore, the photoluminescence light 34 from the irradiation area 32 is monitored. By doing so, direct knowledge regarding damage near the surface of the upper surface 31 can be obtained. However, since the semiconductor substrate sample 30 usually has an upper surface 31 with an area of several cm ² or so, the irradiation area 32 is considerably expanded. Therefore, the photoluminescence light 34 is received through the optical fiber 33. The spatial resolution can be increased and more accurate measurement can be performed. Further, using the fine movement table 14, the irradiation area 32 is moved to the sample surface 31.
If the scanning is performed inside, it is possible to measure the in-plane distribution such as damage. Further, since the mechanism for finely adjusting the tilt angle θ is provided, the incident angle of the laser beam 1 with respect to the upper surface 31 can be adjusted, so that the conditions for parallel excitation can be easily searched for.

Although the semiconductor substrate samples 7 and 30 are used as the samples in the above-mentioned embodiments, various light emitting materials may be used as the samples. Also, in the above embodiment,
Although the laser beam 1 is used as the beam-shaped excitation light, other beam-shaped excitation light such as a white light source condensed by a lens may be used. Further, in the above-described embodiment, the tank 1 for storing the liquid nitrogen for cooling in the heat sink 12
However, a tank for storing liquid helium may be provided in the heat sink.

[0026]

As described above, in the sample surface evaluation method according to the present invention, since only the vicinity of the sample surface can be selectively excited by the excitation light, the light emission related to only the sample surface state can be carried out easily and quickly. The spectrum can be detected.

Further, when the wavelength of the excitation light is changed, the penetration depth of the excitation light into the sample surface can be changed, so that the change in the depth method of the sample surface state can be evaluated.

Further, when the irradiation position of the excitation light is changed, the photoluminescence light from each irradiation position can be detected, so that the in-plane distribution of the surface state can be measured.

Further, when the photoluminescence light is detected through the optical fiber, the photoluminescence light can be effectively received, so that the measurement can be performed more accurately.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an apparatus for carrying out a sample surface evaluation method according to the present invention.

FIG. 2 is a perspective view showing a part of the device shown in FIG.

FIG. 3 is a graph showing a photoluminescence spectrum measured using the device shown in FIG.

FIG. 4 is a diagram showing a laser beam irradiation position on a semiconductor substrate sample.

FIG. 5 is a schematic perspective view showing a part of an apparatus for carrying out another sample surface evaluation method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser beam 2 ... Photoluminescence light 7 ... Semiconductor substrate sample 30 ... Semiconductor substrate sample 33 ... Optical fiber 34 ... Photoluminescence light

Claims (4)

[Claims] 1. A sample surface is irradiated with beam-shaped excitation light,
A sample surface evaluation method for detecting photoluminescence light, which comprises irradiating the sample surface with the excitation light substantially in parallel. 2. The sample surface evaluation method according to claim 1, wherein the wavelength of the excitation light is changed. 3. The sample surface evaluation method according to claim 1, wherein the irradiation position of the excitation light is changed. 4. The sample surface evaluation method according to claim 1, wherein the photoluminescence light is detected via an optical fiber.