JPH04152546A - Radioactivation inspection method of lattice defect material - Google Patents

Abstract

PURPOSE:To obtain an inspection method which can evaluate, over a wide range, the lattice defect concentration of a material under test in a high-temperature state without causing irradiation damage to the material under test by a method wherein only a layer, to be radioactivated, which has been formed on the surface of the material under test is radioactivated to a short-life positron radiation source. CONSTITUTION:A layer 22 to be radioactivated is formed on the surface of a material 25 under test; a high-energy beam 21 is remote-irradiated; one part of the layer 22 to be radioactivated is radioactivated to a short-life positron radiation source RI by a nuclear reaction. Said layer 22 to be radioactivated and the material 25 under test are set to arbitrary surroundings; the energy spectrum of radiated extinction gammarays 28 when positrons 27 radiated from said positron radiation source are extinguished at reduced speed in the material 25 under test is measured; the defect concentration of the material 25 under test is remote-measured by means of the spread of the width of the energy spectrum. For example, polysilicon, as a layer to be radio- activated, which has been doped with <10>B is deposited on silicon as a material 25 under test; it is irradiated with <2>He<+2> as a high-energy beam 21: <13>N is generated as a radioactivated part 23.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a lattice defect material activation inspection method for remotely measuring the lattice defect concentration of a functional material such as a semiconductor.

[Conventional technology]

FIG. 3 is an explanatory diagram showing the first conventional lattice defect inspection method using positrons. In the figure, il+ is a positron beam source,
21 is a positron, (3) is a material to be inspected, (4a) is an interstitial position, (4b) is a defect position, (5m), (5b) is a σγ ray, and is a 161H semiconductor detector.

When using, for example, 53p as the positron IiI source il+,
Positrons 121 having a maximum energy of 2.5 M@V are emitted and are irradiated onto the material to be inspected (3) such as silicon.

Positrons (2:) lose energy and decelerate due to inelastic collisions with surrounding electrons in the material to be inspected (31), and finally become thermalized positrons that move to interstitial positions (4s) and defect positions (
4b) etc. causes pair annihilation with electrons, resulting in annihilation r-rays (5m)
=(5b) Two pieces of each are released. This inspection method utilizes the fact that the energy spectrum of annihilation gamma rays (5s) changes depending on the difference in defect concentration. The principle will be explained below.

Generally, when a positron and an electron annihilate, they emit rest mass and kinetic energy as photons according to Einstein's relation. At this time, γ released from the law of conservation of energy
The total energy of the line is ET-2fflc +E-+E
+...Indicated by 11+.

Here, m is the mass of the electron and positron, C is the speed of light, and 2-
is the kinetic energy of the electron.E+ is the kinetic energy of the positron, which is sufficiently smaller than that of the E+ double electron, so it can be ignored. Now, if we consider the case where two gamma rays are emitted, in a laboratory system, the energy of the gamma rays is spread by the kinetic energy of the electrons due to the Hadopppler effect. That is, Eγ=mc2(1±v−CO5θ/2c)
=42 where V is the velocity of the annihilated electron and θ is γ
It is the angle between the direction of motion of the line and the electron. Assuming that the energy of the electron is 4 eV, the second term in equation 121 above is 2 KeV. In other words, the kinetic energy of the electron is amplified approximately 500 times by the positron. The resolution half width (FWHM) of recent semiconductor detectors is approximately 1 keV.
Therefore, the motion distribution corresponding to the electron energy of &eV can be sufficiently detected.

Based on the above positron annihilation mechanism, FIGS. 4 and 5 show the energy spectra of each annihilation gamma ray when the positron annihilates in a perfect crystal and when it annihilates within a lattice defect. Figure 4 shows the energy spectrum of annihilation gamma rays caused by positrons annihilated in a perfect crystal. Since the positron has a positive charge, it receives a repulsive force from the ion shell due to Coulomb interaction. Therefore, in a perfect crystal, there is a high probability of annihilation at interstitial positions. Conduction electrons have a relatively small kinetic energy, so the energy range of their annihilation gamma rays is small, but core electrons have a relatively large kinetic energy, so the energy range of their annihilation rM is wide ((according to equation 21) .Now, all counts & A, Eγ-51
From the count number C near 1 keV, S = C/A (3) is defined and is called the S parameter. The S parameter is the central part of the Doppler spread divided by the total count, which normalizes the contribution of conduction electrons by the total count. Assuming that the above-mentioned dimension meter is a perfect crystal, it will have a specific value depending on the material.

FIG. 5 shows the energy spectrum of annihilation ra in a sample with a relatively high concentration of vacancy-type lattice defects.

If a vacancy-type lattice defect exists, it will be captured by a positron,
The probability of annihilation with core electrons decreases, and the probability of annihilation with conduction electrons increases. Therefore, the Doppler spread becomes sharper than in the case of positron annihilation in a perfect crystal, and the S parameter @ increases. This change can be used to evaluate the concentration of vacancy-type lattice defects, and it has been put into practical use as a highly sensitive inspection method.

Next, as the second conventional lattice defect concentration inspection method,
An example shown in Publication No. 0-1577 will be explained.

This inspection method remotely irradiates the material to be inspected with high-energy X-rays or high-energy electron beams, and the material to be inspected is almost uniformly activated by a positron emission source, thereby generating positrons almost uniformly in the material to be inspected. Unlike the conventional method using external positron irradiation, the average defect concentration of the entire material to be inspected can be measured at any temperature, without being affected by the condition of the surface layer. The purpose is to make it possible to do so depending on the situation.

Figures 6 and WC7 are related to the above method, with Figure 6 showing the side view of the situation in which the material to be inspected is irradiated with high-energy X-rays or high-energy electron beams, and Figure 7 showing the annihilation gamma-ray measurement chamber. It is a schematic cross-sectional view. In the figure, (10) shows high-energy X-rays or high-energy electron beams, and the material to be inspected (
IIs) is activated by irradiation for several minutes. Immediately after this, it is transferred to the extinction rm measurement chamber 1121 by a conveyor or the like, and is stored in the electric furnace αa and set at an arbitrary temperature state. (141 is a lead shield for radiation III! shielding, a water jacket or aluminum foil for OaH heat shielding, etc. Also, a semiconductor detector is installed outside the opening of the electric furnace (13 and lead shield θ4). annihilation gamma rays (1 lb) emitted from the activated inspected material (llb).
Measure the energy of '6. The gist of the interpretation of the energy spectrum is the same as that described in the conventional example shown in FIG.

[Problem to be solved by the invention]

Since the first conventional lattice defect concentration inspection method is configured as described above, an external irradiation positron beam source must be used. Conventionally, H22Nm +
``Cu There was a problem in that the available gas was limited to 19N, an inert gas element, in order to avoid chemical reactions between the positron beam source and the material to be inspected and evaporation of the positron beam source.

In addition, when the material to be inspected is a functional material such as p-IJ, the conventional second lattice defect concentration inspection method uses a lattice generated by high-energy X-rays or high-energy electron beams irradiated for activation. There was a problem in that it was difficult to evaluate low-concentration defects because the defects had a concentration that could not be ignored.

This invention was made to solve the above-mentioned problems, and its purpose is to provide a lattice defect material activation inspection method that can evaluate the lattice defect concentration of a material to be inspected in a high temperature state over a wide range. .

[Means to solve section @]

The activation inspection method for a lattice defect material according to the present invention involves forming an activation layer on the surface of the material to be inspected in advance, and remotely irradiating a high-energy ion beam to partially destroy the activation layer through a nuclear reaction. A first step of activating the positron emission source (RE), setting the material to be inspected integrated with the layer to be energized in an arbitrary environment, and emitting positrons from the positron emission source into the material to be inspected. The energy spectrum e1llJ of the annihilation r-rays emitted by deceleration and annihilation is determined, and the defect concentration of the material to be inspected can be remotely measured from the spread of the energy spectrum width.

[Effect]

In the lattice defect concentration inspection method of the present invention, only the layer to be activated which is formed on the surface of the material to be inspected is activated by a short-lived positron emission source, so that the positron beam can be used without causing radiation damage to the material to be inspected. It can be integrated with the source and also enable measurements at high temperatures.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is an explanatory diagram showing a lattice defect material activation inspection method which is an embodiment of the present invention. In the figure, H is the high-energy ion beam, solid 2 is the activated layer, and (b) is the activated part.
(2'7) is a positron, (81) is an annihilation r-ray, and (2) is a semiconductor detector.

When measuring the lattice defect concentration of silicon as the material to be inspected (c), for example, if polysilicon doped with IOH is deposited as the layer to be activated and irradiated with 2 He2'' as a high-energy ion beam Qυ, 10B ( α,
n) 13N is produced as the activated moiety by the 13N reaction. This has the characteristics of a half-life of 9.96 minutes and a maximum positron energy of 1-19 May. Note that the threshold energy of the nuclear reaction is 4.7 MeV, but if high-energy ion beams are irradiated at 6 MeV, Rp-ao, gm. Accordingly, by making the thickness of the layer to be activated larger than the thickness nRp, it is possible to avoid radiation damage directly caused to the material to be inspected by high-energy ion mixing. Also, acceleration energy 1.
Since the range of a positron having 19 MeV f in silicon is about 2000 m, there is no problem of hindering the positron even if the irradiated layer is made somewhat thicker. Next, it is placed in an electric furnace Q31 as shown in the conventional example in Fig. 7 and set to an arbitrary temperature state. After that, the annihilation rM(ha) released? Captured by four semiconductor detectors,
It is possible to evaluate the defect concentration by evaluating the energy spectrum.

In the above example, the nuclear reaction of 10B(αon)13N was used to demonstrate the case, but since there are many reactions that can be a suitable positron beam source, it is possible to dope it into polysilicon and chemically If an element with good stability is selected, it becomes possible to measure the defect concentration under a wider range of environmental conditions.

In addition to the above-mentioned method of determining the defect concentration from the spread of the energy spectrum width of annihilation r@(c), a second inspection method is to measure the lifetime of positrons (goods) to determine the type and concentration of defects. You may.

The principle is shown in Figure 2. When β0 decay occurs in the positron 111cIυ, a decay r-ray is emitted at the same time as the positron □□□. Based on the time when this was detected by the semiconductor detector, the time it takes for one positron (capital) to be captured by a lattice defect and for the later emitted annihilation gamma ray (c) to be detected by the semiconductor detector Defining it as the lifetime of an electron, the type of defect can be identified based on the lifetime distribution of positrons since the amount of time a positron stays in the trapped MK differs depending on the type of defect.

〔Effect of the invention〕

As described above, according to the present invention, a short-lived positron beam source is generated by activating only the nine activation layers that are preformed on the surface of the material to be inspected, thereby preventing the material to be inspected from being damaged. It can be integrated with the activated layer containing positron #,
This method has the advantage that the defect concentration under high temperature conditions can be measured from a lower degree range than before.

[Brief Description of the Drawings] Fig. 1 is an explanatory diagram showing a method for testing the activation of lattice-defect materials according to an embodiment of the present invention, and Fig. 2 is an explanatory diagram showing a method for testing the activation of lattice-defect materials according to another embodiment of the present invention. An explanatory diagram showing
Fig. 3 is an explanatory diagram showing the conventional first lattice defect concentration inspection method, and Fig. 4 annihilation γ due to positrons annihilated in μ perfect crystal.
Figure 5 is a characteristic diagram showing the energy spectrum of the annihilation γ゛ ray applied to a sample with a relatively high concentration of vacancy-type defects. This shows the lattice defect concentration inspection method. Figure 6 is a side view showing the situation in which the material to be inspected is irradiated with high-energy X-rays or high-energy electron beams, and Figure 7 is a schematic cross-sectional view of the annihilation rM measurement chamber. .

Claims (1)

[Claims] A layer to be activated is formed on the surface of the material to be inspected, a high-energy ion beam is irradiated remotely, and a part of the layer to be activated is activated by a nuclear reaction into a short-lived positron emission source (RI). A first step, in which the material to be inspected integrated with the layer to be radiated is set in an arbitrary environment, and positrons emitted from the positron emission source decelerate and annihilate in the material to be inspected and are emitted. A lattice defect material activation inspection method characterized by measuring the energy spectrum of γ-rays and remotely measuring the defect concentration of the inspected material from the spread of the energy spectrum width.