JPS6318250A - Method and apparatus for evaluating impurities in semiconductor crystal - Google Patents

Abstract

PURPOSE:To enable accurate observation and evaluation of the type or the like on impurities, by observing a photoluminescence light and Raman scattered light simultaneously. CONSTITUTION:After the position and intensity thereof is corrected, Raman scattered light and photoluminescence light as signal light released from a sample 1 enters a spectroscope 8. A computer 9 is connected to a cooler 2 to control the temperature of a sample 1 inside while being connected to an exciting light source control system 4 to control the length of a laser light source 5. It is also connected to a spectroscope 8 through a wavelength driving system 11 to control wavelength data on the Raman scattered light and the photoluminescence light and further, connected direct to the spectroscope 8 to control a intensity signal of signal light. Moreover, the computer is connected to a Y-Z driving system 3 to control the position of spot irradiation with the light source 5 for a sample 1 in a device 2 while being connected to a display 10, an analysis software 12, a data bank 13, a printer 14 and the like. Thus, the results of the observation and evaluation can be made clear immediately.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method and apparatus for evaluating impurities in a semiconductor crystal, and more specifically, to a method for evaluating impurities in a semiconductor crystal. This invention makes it possible to evaluate the type, amount, distribution state, energy position in the band structure, arrangement within the crystal lattice, etc. of a wide range of impurities, ranging from small to shallow impurity levels.

"Prior Art" As is well known, high purity is required of semiconductor crystals to obtain high-performance integrated circuits, and many means for evaluating impurities in semiconductor crystals have been developed accordingly.

Examples of conventionally widely used methods for this purpose include: (a) photoconductivity method, Japanese Patent Application Laid-Open No. 59-96743, and (b) thermal stimulation capacitance method.

C1 photocapacitance method, JP-A No. 59-143339, d, thermally stimulated current method, e, deep level transient spectroscopy (DLTS method), f, activation analysis method (\AA method), g, frameless Atomic absorption spectrometry (FAAS method).

JP-A No. 60-230041, Infrared absorption method using h1 localized lattice vibration mode (LVh method)
, JP-A No. 60-25444, i. Spark ion mass spectrometry (SSMS method).

, j, secondary ion mass spectrometry (SIMS method), k, ion microanalyzer method (IMA method), 1, X-ray microanalyzer method (XMA method), m, Rutherford backscattering method (RBS method), n1 particle Line-excited X-ray detection method (P
IXE method), 0, photoluminescence method (PL method),
etc.

"Problems to be Solved by the Invention" However, each of these means has its advantages and disadvantages, and there is no method that is superior overall, and there are problems as described below.

For example, each of the means a, b, c, d, and e described above requires contact with the sample via an electrode, a probe, etc., and therefore there is a risk that the state of the sample may be changed.

The means f, g, i, j, m, and n described above are destructive methods that perform cutting, etching, etc., and cannot maintain the sample as it is.

Above a, b, c, d, e, g, h, i, j, k, 1
, m, and n each means that the impurity is approximately 101s in a unit volume.
The sensitivity of the analysis is low in that it cannot be analyzed unless it is loaded more than !l-'', and it cannot be applied to all samples.

Each of the above-mentioned means a, b, c, d, e, f, g, h, i, j, and l requires the same size as when attaching an electrode, for example. The purpose cannot be effectively achieved for samples whose size makes manipulation impossible.

Each of the above-mentioned means e, f, g, m, and o has a limited number of impurities to be analyzed, and cannot be applied to all samples.

Although each of the methods a, b, c, d, e, f, g, h, n, and 0 described above can determine the total amount of impurities contained, there remains a problem in that the spatial resolution is low.

Although it is possible to determine the relative amount of impurities contained in each of the above-mentioned means i, j, and k, the absolute amount is unknown and quantitative analysis has not been established.

And the above, d, f, g, h, i, j, k, ■
, m, and n reveal the type, amount, etc. of impurities contained, but do not actually reveal the distribution state within the crystal or the energy position in the band structure.

Detecting impurities in crystals with high sensitivity and at a lower cost without external processing is essential for the development and production of high-performance devices such as opto-electronic integrated circuits and ultra-ultra large-scale integrated circuits. However, none of the conventional means for evaluating impurities in semiconductor crystals described above can sufficiently meet the above requirements.

The present invention is a method and apparatus for evaluating impurities in a semiconductor crystal developed to solve the above-mentioned conventional problems, drawbacks, and inconveniences. The purpose is to comprehensively evaluate the type, amount, distribution state, energy position in the band structure, arrangement within the crystal lattice, etc. of a wide range of impurities up to the level. do.

Means and Effects for Solving the r Problem" Hereinafter, the structure of the present invention will be explained based on drawings showing embodiments of the present invention.

In the method of evaluating impurities in a semiconductor crystal according to the present invention, first, the band gap energy of sample 1, which is a semiconductor crystal, is measured in a temperature range from liquid helium temperature to room temperature. It also irradiates a laser with sufficiently high energy.

It is known that an electronic system that has absorbed energy often passes through an intermediate step and emits light by transitioning from an excited state to a state with lower energy (Stokes' law). 20 meV
Raman scattered light unique to impurities due to local vibration modes is emitted on the low energy side, and photoluminescence light is emitted on the energy side about 20 to 40 meV lower than the band gap energy.

By simultaneously measuring the emitted Raman scattered light and photoluminescence light, we can determine the type, amount, distribution state, energy position of the band structure, and arrangement of impurities in the crystal lattice of sample 1. etc. are evaluated.

That is, the emitted Raman scattered light and photoluminescence light reflect the electronic state of the impurity in the sample 1 crystal, and are unique to the impurity.
By analyzing the waveforms of the Raman scattered light and photoluminescence light described above, the type of impurity, etc. can be analyzed.

In other words, the Raman scattered light and photoluminescence light emitted from an impurity can be analyzed as waveforms unique to this impurity, so the type, amount, energy position in the band structure, and arrangement within the crystal lattice of this impurity can be analyzed. However, it is possible to analyze a wide range from deep impurity levels to shallow impurity levels, and furthermore, by observing the entire sample 1 as described below, it is possible to analyze the distribution state of impurities.

In photoluminescence light, the analysis focuses on the acceptor impurity, but if the ionization energy of the acceptor is E^, then E = EGr - E^ + 1/24aT 〼a; Boltzmann's constant T; corresponds to the energy expressed in absolute temperature Light can be observed.

However, since multiple lights are emitted for one impurity, it is necessary to observe the temperature dependence of multiple spectra and systematically evaluate them.

On the other hand, for Raman scattered light observed with one local vibration mode, observation at low temperatures is advantageous in order to evaluate the fine structure using the energy difference due to impurities.
Therefore, a temperature range from liquid helium temperature to room temperature is required.

The observation achieved in this way is spot-like in a small part of the sample 1, so in order to observe the entire sample 1, a laser By changing the wavelength of the light, the depth direction (X direction), which is the reach distance of the laser light into the inside of the sample 1, is controlled,
In addition, by moving the laser beam spot in the Y and Z directions, observation data obtained through these controlled movements will be integrated to perform a comprehensive evaluation of the spatial distribution of impurities. .

Also, an apparatus for realizing the above method.

A cooling device 2 that houses the semiconductor crystal that will become the sample 1 and is capable of controlling the temperature from liquid helium temperature to room temperature, and a laser beam that is connected to the excitation light source control system 4 and irradiates the sample 1 crystal in the cooling device 2. g5, a spectroscope 8 that receives the photoluminescence light and Raman scattered light emitted from the crystal 1, and the cooling device described above to two-dimensionally move the incident spot on the sample 1 from the laser light source 5. 2, exchanges temperature information with the cooling device 2, exchanges excitation light source information with the above-described excitation light source control system 4, and exchanges excitation light source information with the above-mentioned excitation light source control system 4, and via the above-mentioned spectrometer 8 and wavelength drive system 11. The computer 9 exchanges wavelength information with the Y-2 drive system and also exchanges position information with the Y-2 drive system.

The excitation light source control system 4 controls the intensity and wavelength of the laser light source 5, and uses the difference in the absorption coefficient of the sample 1 due to the difference in wavelength to determine the depth profile of impurities in the sample 1. You will get it.

Similarly, by moving the cooling device 2 via the y-z drive system 3, the incident spot position of the laser beam on the sample 1 is moved two-dimensionally, and information on the entire area of the sample 1 can be obtained. . A predetermined optical system 6.7 is arranged between the laser light source 5 and the sample 1 and between the sample 1 and the spectrometer 8.

Since shifting these rm r is optically complicated and time-consuming, the sample 1 itself must be moved two-dimensionally.

Furthermore, as described above, by controlling the temperature within the cooling device 2 within the above temperature range, a wide range of data may be obtained from the emitted Raman scattered light or photoluminescence light.

By means and configuration of the present invention, impurities in sample 1, which is a semiconductor crystal, can be removed non-destructively and with high sensitivity (1014
an-'), it becomes possible to obtain three-dimensional profiles for each impurity using the height with high spatial resolution (1-3 μm).

``Example'' An example of the present invention will be described below with respect to a + GaAs half body.

The band gap energy of GaAs is 1.51
Since the energy is 89 eV, by irradiating the laser light source 5 with a sufficiently higher energy than this, for example, an argon ion laser with an energy of 2.410 eV or a heliamne laser with an energy of 1,960 eV, the Raman scattering as described above can be achieved. Light, photoluminescent light, will be emitted.

In the cooling device 2, which is arbitrarily controlled in the temperature range mentioned above, the sample 1 is fully temperature controlled with an accuracy of ±0.05°.

At this time, the entire cooling device 2 is operated by the computer 9 as described above.
The movement is controlled two-dimensionally via a Y-Z drive system 3 that operates by exchanging position information with the robot.

The Raman scattered light and the photoluminescence light, which are signal lights emitted from the sample 1, are subjected to positional correction and intensity correction by the optical system 6, and then enter the spectroscope 8.

Since the signal light here is divided into a Raman wavelength block and a photoluminescence wavelength block, a no-signal region EL-0, 1 eV-EleV (EL; energy of the excitation light source laser) exists between the two.

The signal region of Raman scattered light is approximately EL-EL-0,1eV and EL - EL + 0.1eV The signal area of photoluminescence light is approximately El ~E!　　　1. OeV That's about it.

It is preferable that the wavelength driving of Raman scattered light is about 1710 times faster than the wavelength driving of photoluminescence light. Therefore, in the above-mentioned no-signal region, it is better to make this speed as fast as possible. Therefore, the wavelength drive system 11 located between the spectrometer 8 and the computer 9 functions in order to scan excluding this no-signal area.

Now, when implementing the present invention and observing data on specific impurities, for example, for Zn impurities and C impurities, due to basic (e, A') emission, E (Zn)
= 1.4888eV E (C) = 1.4935eV corresponds to the photoluminescence light. In this case, wavelength accuracy of about 0.1 A' is sufficient.

In addition, the Raman scattered light accompanying the local vibration mode is 8E (Zn) = 21, 7 mgVΔE (C) from Rayleigh light.
observed as a shift of = 18.4 meV.

Note that the computer 9 is connected to the cooling device 2 and the sample 1 inside is connected to the cooling device 2.
It is connected to the excitation light source control system 4 to control the wavelength of the laser beam @ 5, and is connected via the spectrometer 8 and the wavelength drive system 11 to transmit wavelength information of Raman scattered light and photoluminescence light. It is directly connected to the spectrometer 8 to control the intensity signal of the signal light, and is connected to the yz drive system to control the spot irradiation position of the laser beam g5 on the sample 1 in the cooling device 2. Furthermore, display 1o,
Analysis software 12, data bank 13, printer 14
etc., so that observation and evaluation can be immediately determined.

"Effects" The present invention is constructed and operates as described above.

Therefore, by simultaneously observing photoluminescence light and Raman scattered light emitted from impurities in semiconductor crystal samples, we can detect a wide range of impurity levels from deep to shallow impurity levels in semiconductor crystals. ,
The type, amount, distribution state, energy position in the band structure, arrangement within the crystal lattice, etc. can be observed and evaluated accurately, reliably, and quickly.

In other words, there is no need to contact the sample through electrodes, probes, etc., so there is no risk of changing the state of the sample, and since there is no destructive process such as cutting or etching, the sample can be left in its original state. It has high analytical sensitivity in that it can be analyzed even if only about 10"(!11-') of impurities are contained in the unit volume, and can be used for all samples. , the sample size is just the spot size of the laser beam narrowed down by an optical system, and all kinds of impurities can be analyzed, and the total amount of impurities contained can be clarified, and the spatial resolution is excellent, and the relative amount of contained impurities can be analyzed. It is possible to determine the absolute amount of the impurities contained therein, and furthermore, it is possible to clarify the actual distribution state of the contained impurities within the crystal and the energy position in the band structure.

Furthermore, the device of the present invention for realizing the above-mentioned means has an extremely simple configuration, and therefore can detect impurities in a crystal with high sensitivity and at a lower cost without external processing of the crystal. This is an epoch-making invention that has many excellent functions and effects, and is expected to make a significant contribution to the development and production of high-performance devices such as optoelectronic integrated circuits and ultra-large scale integrated circuits. be.

[Brief explanation of the drawing]

The drawings are explanatory diagrams showing the configuration of the present invention. Explanation of symbols 1: sample, 2; cooling device, 3; Y-Z drive system, 4; excitation light source control system, 5; laser light source, 6.7; optical system, 8;
Spectrometer, 9; calculator.

Claims (2)

[Claims] (1), in the temperature range from liquid helium temperature to room temperature,
By irradiating a semiconductor crystal with a laser whose energy is sufficiently higher than the band gap energy of the crystal and simultaneously measuring photoluminescence light and Raman scattered light emitted from the crystal, A method for evaluating impurities in a semiconductor crystal, characterized by evaluating the type, amount, distribution state, energy position in a band structure, arrangement in a crystal lattice, etc. of impurities therein. (2) a cooling device in which a semiconductor crystal to be a sample is housed and whose temperature can be controlled from liquid helium temperature to room temperature; and a laser light source connected to an excitation light source control system and irradiating the crystal in the cooling device. , a spectrometer that receives photoluminescence light and Raman scattered light emitted from the crystal, and a Y-Z drive that controls the movement of the cooling device to two-dimensionally move the incident spot on the sample from the laser light source. a computer that exchanges temperature information with the cooling device, excitation light source information with the excitation light source control system, wavelength information with the spectrometer, and position information with the YZ drive system; An apparatus for evaluating impurities in semiconductor crystals, consisting of: