JPH01134239A - Electron spin resonance device - Google Patents

Abstract

PURPOSE:To classify and assign overlapping plural peaks of an electron spin resonance spectrum by detecting the modulated frequency component of a microwave absorption signal and the delay of the phase of a 2nd higher harmonic component. CONSTITUTION:A sample 4 in a cavity resonator 2 is supplied with a microwave from a microwave source 5 and the composite magnetic field produced by an electromagnet 1 and a modulating coil 3, and the reflected microwave is detected by a detector 6 and inputted to an amplifier 7. A current amplifier 8 which feeds a cosine current of frequency (f) to the modulating coil 3 is connected to an oscillator 9. Further, the oscillator 9 supplies the signal of frequency (f) and the 2nd higher harmonic signal 2f to phase detectors 10 and 11 as reference signals. The phase detectors 10 and 11 detects the phase delay quantities theta and phi of the components of frequencies (f) and 2f behind a reference signal supplied from an oscillator 9. The phase delay quantities theta and phi are selected by a switch 19, processed by tan(theta or phi)/(2pif) through a computing element 12, and inputted to a two-dimensional recording device 14, thereby recording a spectrum to electrostatic magnetic field intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an atomic spin resonance apparatus, particularly when there are multiple types of defects in a sample that is a signal source.

The present invention relates to an electron spin resonance apparatus that can easily analyze electron spin resonance spectra.

[Prior art] Conventional electron spin resonance (hereinafter referred to as ESR) devices are explained, for example, on page 1387 of the Physics Dictionary Editorial Committee's "Physics Dictionary" (Baifukan, Tokyo, 1984). Based on this principle, the amount of microwave absorption in a sample was measured as a function of the magnetic field.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, multiple peaks appearing in the ESR spectrum are determined by the number of different types of defects present in the sample.
Unable to find out which cause is the cause,
In particular, in the ESR spectrum of a sample in which many types of defects coexist, the peaks (usually multiple) caused by each defect are
Since they all appear superimposed, there is a problem in that spectrum analysis becomes extremely difficult.

An object of the present invention is to provide a means for classifying and attributing a plurality of overlapping peaks to each defect.

[Means for solving problems]

The above object is achieved by modulating the magnetic field at each peak of the ESR spectrum and detecting the phase delay between the modulation frequency component of the microwave absorption signal and the second harmonic component, which vary accordingly.

[Effect]

In the present invention, a magnetic field is modulated, and a phase delay between a modulation frequency component of a microwave absorption signal and a second harmonic component that fluctuates accordingly is detected. moreover.

From the calculation that combines this phase delay and modulation frequency,
The spin-lattice relaxation time can be obtained.

The phase delay or spin-lattice relaxation time described above depends on the type of defect, but is always constant for peaks caused by the same defect. Therefore, it is easy to classify and attribute multiple peaks in the ESR spectrum to one type of different defect.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure is a basic configuration diagram of an embodiment of the device according to the present invention.

In FIG. 1, a cavity resonator 2. and a magnetic field modulation coil 3 are installed. Cavity resonator 2
A sample 4 can be fixed inside the sample 4, and the sample 4 receives microwaves generated by a microwave source 5, a combination of a static magnetic field generated by an electromagnet 1, and an oscillating magnetic field generated by a modulation coil 3. A magnetic field is supplied. The microwave reflected from the cavity resonator 2 is detected by a microwave detector 6 and amplified by an amplifier 7 into an electrical signal suitable for subsequent signal processing. The current amplifier 8 that supplies current to the modulation coil 3 is driven by a cosine signal from the first oscillator 9, and the first oscillator 9 that supplies the cosine current to the modulation coil 3 is
The same frequency as the cosine signal supplied to the current amplifier l18 (hereinafter referred to as f; in FIG. 1, ω = 2πf,
) and its second harmonic signal as reference signals to the phase detector A 10 and the phase detector port 11, respectively. The amplitude of the component with f (A in FIG. 1) or the phase delay (θ in FIG. 1) with respect to the reference signal supplied from the oscillator 9 is detected. On the other hand, the phase detector port 11 extracts a component having a frequency of 2f from the signal from the amplifier 7, and extracts a component having a frequency of 2f from the signal from the amplifier 7.
φ) in the figure is output. The phase delays θ and φ are selected by the switch 19, and one of them and the oscillation frequency f of the oscillator 9 are set to tan by the arithmetic unit 12.
It undergoes the processing of (θ or φ)/(2mf). The result of this processing output from the arithmetic unit 12 (τ in FIG.
1) and the output of the phase detector A 10 are selected by a switch 13 and become one-dimensional information for a two-dimensional recording device 14 such as a recorder. As information on the other dimension of the two-dimensional recording device 14, a signal corresponding to the strength of the static magnetic field is input from the excitation power source 15 of the electromagnet 1. This static magnetic field can be swept, and the two-dimensional recording device 14 obtains a spectrum of τl or A in FIG. 1 with respect to the static magnetic field strength.

Next, the knowledge obtained from this example will be explained. Defects with unpaired electrons (electrons not involved in chemical bonds) in sample 4 absorb electromagnetic waves (electron spin resonance, hereinafter referred to as ESR) when a magnetic field is applied to sample 4. When the frequency of electromagnetic waves is constant, the strength of the magnetic field (resonant magnetic field) that must be applied to cause absorption depends on the type of defect and its direction with respect to the magnetic field. Therefore, by examining the value of this resonant magnetic field and the amount of absorption, it is possible to know the type and amount of defects in the sample 4. The above electromagnetic waves are 9 to 10
In the case of microwaves in the GHz (X band) region, the resonant magnetic field is usually around 3300 GHz.

Next, with reference to FIG. 2, the amount of electromagnetic wave absorption when ESR is established will be explained. By applying a magnetic field to sample 4, the defect changes to a low energy state (a in Figure 2).
It is divided into a high energy state (b in Figure 2).

Let Na and Nb be the number of low-energy states and high-energy states in a thermal equilibrium state, respectively, let E be the energy difference between the high-energy state and the low-energy state, let T be the temperature of sample 4, and let k be the Boltzmann constant.

Nb/Na=exp (-E/kT),
Let the actual numbers of low energy states and high energy states be na and n-, respectively, then the difference between the numbers of both states is na-nb
tries to approach the value N a - N b in thermal equilibrium at a constant speed (1/τ k in Figure 2) (this is called spin-lattice relaxation 16), where τl is the spin-lattice relaxation time The amount depends on the temperature of the sample 4 and the type of defect. Sample 4 has a frequency ν, ν=E/h
When irradiated with electromagnetic waves that satisfy the relationship (h Nyblank constant), ESR occurs, and the low energy state absorbs the electromagnetic waves17 and transitions to a high energy state, while the high energy state emits electromagnetic waves with a frequency ν (stimulated emission). 18)
and transitions to a low energy state.

Since the probabilities of absorption 17 and stimulated emission 18 are the same, if the rate at which the above transition occurs in one defect per unit time is P, the energy absorbed per unit time by a defect in sample 4 is hνP (na-nJ It is.

And, how much energy is lost as heat per unit time due to the spin-lattice relaxation mentioned above?

-h9 [(na-nb)-(Na-NJ] /cx
=-hy[(na-Na)/τi+hv(nb-Nb
)/li. In other words, in order to approach thermal equilibrium,
The low energy state of na is per unit time.

Sample 4 absorbs thermal energy of h9(na Na)/τ1 and transitions to a high energy state, and the high energy state of nb is .

Per unit time, h v (nIll-Nb) / ? It is thought that the energy of 1 is released as heat to the sample 4, and the sample 4 transitions to a low energy state. After all, as mentioned above, the spin lattice relaxation 16
．． Absorption 17. Due to stimulated emission 18, the time change of na@nb is.

becomes. Therefore, the time change of nan- is...(
3) It can be expressed as The transition ratio P described above is determined by the product of the electromagnetic wave intensity and the transition efficiency. In this embodiment, the intensity of the microwave electromagnetic field is constant, and the transition efficiency is determined by using the magnetic field modulation by the modulation coil 3 in FIG. It is made to fluctuate in one cycle. Therefore, the transition ratio P in this example is: P = Ps+ PIICO! l ((1) t)
It can be expressed as = (4). Here Ps, P-
is a constant, ω is the modulation angular frequency, and t is time. Substituting equation (4) into equation (3) yields τ... (5) In equation (5), assuming that the second term on the right-hand side is smaller than the other terms on the right-hand side, n@- The solution of nb is found in the range up to the -th order of p under the initial condition (t; condition at 0), na-nb=Na-Nb.

So, here.

L+2Psτ , when sufficient time has passed since t=0.

x cos (ω is one φ)] (8), and it can be seen that the phase is delayed by φ with respect to the magnetic field fluctuation. As mentioned above, the absorption amount of microwave electromagnetic waves is p (n
Since it is proportional to a-nb), equation (4).

And from equation (8).

Koe [Ps+Pacos (c+>t)]
(na-nb)Na-Nb 1+2Piτl is obtained. here.

2 Ps t zsinφ (10). When the modulation frequency f is 0, use the condition that ω=0 in equation (9) and that p is small.

1+2Pgτ1 If ω=0 on the right side of equation (4) mentioned above, the transition probability P is a constant value that does not depend on time.

Since P s + P *, N in equation (11)
a −N b 1 + 2 (Ps+ P,) t x is the difference in the distribution between the low energy state and the high energy state in the steady state when the transition probability P is constant (Pa + P−) n Jl −
It turns out that n b. This result was obtained by assuming that P=constant in equation (3). From equation (9), if the spin-lattice relaxation time τ1 is very short.

KOI: (Na-Nb) [Ps+Pmcos (
(11t)], and the time variation of the amount of absorption of microwave electromagnetic waves follows the magnetic field variation, but as τ1 becomes longer, the phase gradually begins to lag, and moreover, the second harmonic component appears. I understand that. here.

The phase delay φ of the second harmonic is connected to the spin-lattice relaxation time τ1 by the simple relationship of equation (7). When the strength of microwave electromagnetic waves is not very strong.

2 Ps τt< 1 − (1
2) holds, and the spin-lattice relaxation time τ1 is obtained as ω. φ.

Alternatively, if the value of tanφ/ω does not depend on the intensity of the microwave electromagnetic wave, it can be determined that condition (12) is satisfied, and in this case, the zero condition (12 ) holds true, and the modulation frequency j is sufficiently small.

τ lω (1-・-(14) If both hold true, then from equation (7).

φNumaτ1ω Also, from equation (10), θNumaτω
) (t −τ engineering)]−P+a”τxcos[2ω(t
−)] −Pm”τt) (15) 1 normal if condition (13) is satisfied.

Since p, τ(1...(16)) also holds true, in this case, equation (15) can be further transformed into K
cc (Na-Nb)(Pg+Pacog [(1
1(t −τx) (17), that is, conditions (12), (14), (1
If both of 6) hold true, then by equation (17), from the phase delay θ of the O tan θ component that oscillates at one frequency f in the absorption amount of microwave electromagnetic waves, - or □ calculation ω
ω gives the spin-lattice relaxation time τl, and the amplitude of the same component gives p. Here, θ tan
θ − or □, or the above amplitude is microω
If it is not dependent on the intensity of the ω-wave type magnetic wave and the modulation frequency f, it can be determined that conditions (12), (14), and (16) are satisfied. P corresponds to the differential coefficient (absorption differential) of the absorption amount of microwave electromagnetic waves in the central magnetic field of the oscillating magnetic field with respect to the magnetic field.

To summarize the above, 2Psτt<1...(
12) When both τlω(1...(14) P and τ1(1...(16)) hold, the amount of absorption of microwave electromagnetic waves that fluctuates periodically due to magnetic field modulation is It oscillates at a modulation frequency f of If only condition (12) holds, then from the phase delay φ of the component with a frequency of 2f (second harmonic),
The spin-lattice relaxation time τl is determined.

The above is an explanation of the operating principle of this embodiment and the findings obtained therefrom.6 Next, an example of measurement by this embodiment is shown in Fig. 3. These are the results of measuring the absorption differential and the spectrum for a magnetic field with a spin-lattice relaxation time of 1 for a semiconductor substrate processed by the process. There are 6 peaks in the absorption differential,
Pl.

Pg, PM, Pl, and Pst Pe appear at the positions of the resonant magnetic field, Hz, Hz, Ha, H4, Hs, and He, respectively. Comparing this with the spectrum of the spin lattice relaxation time τ, it is found that these peaks are caused by three types of defects, and the peak P4゜P6 is due to τ1 = t
The defect a, peaks Pt, Pz, and Pg can be attributed to the defect τ1=τb, and the peak P8 can be attributed to the defect τ1=τC. Of course, the types of defects are different, but if there are defects with the same spin-lattice relaxation time, the above method cannot distinguish between them. In such a case, the same measurement can be performed by changing the temperature of sample 4. It is effective to do so. This is because the temperature dependence of the spin-lattice relaxation time is sensitive to the type of defect, so even if the spin-lattice relaxation times τ1 of two types of defects coincidentally match at a certain temperature, there is no possibility that they will match again at another temperature. , because there are very few.

In addition, if the purpose is only to classify each peak in the ESR spectrum and the value of the spin-lattice relaxation time τ1 itself is not necessary, simply measuring the spectrum with respect to the magnetic field with respect to phase delays θ and φ can be performed using the method described above. It goes without saying that peak classification can be performed using the same procedure as .

Furthermore, the spin-lattice relaxation time τ1 does not depend on the orientation of the magnetic field with respect to the sample 4. Therefore, as in the case of anisotropy analysis in a solid sample, the movement of each peak position is determined by rotating the sample 4 with respect to the magnetic field. In the case of tracking as well, by focusing on peaks with a specific spin-lattice relaxation time τl, it is possible to easily and without error examine the angular change of each peak.

[Effects of the Invention] As described above, according to the present invention, for a material in which many types of defects coexist, multiple peaks that appear when the ESR vector is measured as absorption or absorption derivative,
Complex ESR can be easily attributed to individual defects by phase lag, θ, r or spin-lattice relaxation time τ1.
This has the effect of significantly simplifying spectrum analysis. Furthermore, the spin-lattice relaxation time τ1 can also be easily measured as a spectrum with respect to the magnetic field.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of an embodiment of the present invention, and Fig. 2 is a basic configuration diagram of an embodiment of the present invention.
FIG. 3 is a diagram for explaining the operating principle of the embodiment shown in the figure, and is a diagram showing the result of using the embodiment of FIG. 1. DESCRIPTION OF SYMBOLS 1... Electromagnet, 2... Cavity resonator, 3... Modulation coil, 4... Sample, 5... Microwave source, 6...
Microwave detector, 7... Amplifier, 8... Current amplification, 9... Oscillator, 10.11... Phase detector, 12
... Arithmetic unit, 13°19... Switch, 14... Two-dimensional recording device, 15... Excitation power source, 16... Energy lost due to spin lattice relaxation, 17... Absorption,
18...Stimulated emission.謬 l concave 2nd mouth 3I! ] Chamber 17 Ro/i Shrine 5ζ. I8 Dare to hold

Claims (1)

[Claims] 1. A static magnetic field source that sweeps a magnetic field applied to a sample, a cavity resonator containing the sample, a microwave supply means for supplying microwaves to the cavity resonator, and a cavity resonator. It consists of a microwave detection means for detecting the microwaves reflected from the cavity, and a means for obtaining the microwave absorption spectrum of the sample from the microwaves supplied to the cavity resonator and the microwaves reflected from the cavity resonator. In the electron spin resonance apparatus, a modulated magnetic field generating means modulates the magnetic field, and a specific frequency component of a microwave signal detected by the microwave detecting means periodically fluctuating in accordance with the magnetic field modulation is phase-detected. An electron spin resonance apparatus comprising: a detection means; and a means for detecting a phase delay of a specific frequency component of the microwave signal with respect to the magnetic field modulation. 2. The electron spin resonance apparatus according to claim 1, wherein the detection means phase-detects a frequency component of the microwave signal that is the same as the magnetic field modulation frequency. 3. Claim 2, characterized by comprising means for outputting the spin-lattice relaxation time by calculating the phase delay of the detected microwave signal with respect to the magnetic field modulation and the magnetic field modulation frequency. The described electron spin resonance apparatus. 4. The electron spin resonance apparatus according to claim 1, wherein the detection means phase-detects a component of the microwave signal having a frequency twice the magnetic field modulation frequency. 5. Claim 4, characterized by comprising means for outputting the spin-lattice relaxation time by calculating the phase delay of the detected microwave signal with respect to the magnetic field modulation and the magnetic field modulation frequency. The described electron spin resonance apparatus. 6. An electron spin resonance apparatus according to any one of claims 1 to 5, characterized by having means for controlling the temperature of the sample.