JPH04278453A - Method for monitoring oxidation degree of oxide superconductor membrane - Google Patents

Abstract

PURPOSE:To monitor the oxidation degree of an oxide superconductor membrane during formation in a non-contact state within a real time. CONSTITUTION:When an oxide superconductor membrane is formed within a vacuum container 1, the oxide superconductor membrane during formation is irradiated with the primary ion seed of energy of 2kV or less from an ion gun 11 and the secondary ion seed from the membrane at this time is subjected to mass analysis by a mass analyzer 12. Since the oxide superconductor membrane having good superconductive characteristics is formed when the secondary ion seed is detected but not formed when no secondary ion seed is detected, by monitoring the presence of the secondary ion seed, the quality of a film forming condition can be judged. The oxidation degree of the oxide superconductor membrane can be monitored in a non-contact state within a real time.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for monitoring the degree of oxidation of oxide superconductor thin films, and more specifically, the present invention relates to a method for monitoring the degree of oxidation of oxide superconductor thin films. A method for monitoring the degree of oxidation of an oxide superconductor thin film, in which the degree of oxidation of a certain thin film is monitored non-contactly and in real time, and the obtained monitoring data is used as feedback to the device operating conditions in order to optimize the properties of the thin film. Regarding.

0002

[Prior Art] Conventionally, as a method for evaluating the characteristics of an oxide superconductor thin film being formed on a substrate in a film forming apparatus, high-speed electron diffraction (RHEED) has been used to analyze the crystal structure of the thin film. A method of evaluating based on orientation is known. However, this method cannot evaluate the degree of oxidation of the thin film.

[0003] Furthermore, the degree of oxidation, critical temperature, critical current density, and composition of an oxide superconductor thin film have a correlation with the electrical resistance of the thin film. , the characteristics of the thin film have been evaluated. in this case,
Characteristics are evaluated using the following two methods. The first method is to form a thin film of a predetermined thickness in a film forming apparatus, then perform a predetermined heat treatment if the film requires further heat treatment, and then form an electrode for electrical resistance on the obtained thin film. This method measures desired electrical characteristics.

[0004] The second method is to separately set current and voltage terminals for measuring electrical resistance in the film forming apparatus, and to monitor one of the substrates on which the oxide superconductor thin film is to be formed. Evaluate the characteristics of the oxide superconductor thin film that is being formed on the monitor substrate by arranging an electrode on the substrate and connecting the electrode to the current/voltage terminal with a lead wire. This is a method for evaluating the characteristics of oxide superconductor thin films on other substrates in real time.

[0005]

[Problems to be Solved by the Invention] However, the first method is a method that can only be applied to oxide superconductor thin films that have already been formed on a substrate or to heat-treated products thereof. However, there is a problem in that the evaluation results cannot be fed back to the operating conditions of the film forming apparatus in real time, resulting in poor efficiency.

In addition, in the case of the second method, the above-mentioned current/voltage terminals must be set separately in the film-forming apparatus, so these terminals not only hinder the smooth progress of the film-forming operation, but also interfere with the monitoring. There is a problem in that electrodes must be formed on the substrate in advance. Moreover, if the substrate is rotated or the substrate temperature is increased during film formation, the lead wires connecting the electrodes and terminals may be damaged due to the rotation of the monitoring substrate, and the electrodes and terminals may be deteriorated due to the high temperature.
Alternatively, the surface temperature of the monitor board is thermally conducted to the lead wires, and a different element is interposed between the monitor board and other boards, making it impossible to compare them.

The present invention solves the above-mentioned problems in characterizing oxide superconductor thin films, and evaluates the degree of oxidation of oxide superconductor thin films being formed in a non-contact manner and in real time, among the thin film characteristic items. The purpose of the present invention is to provide a method for monitoring the degree of oxidation of oxide superconductor thin films, which is useful for producing oxide superconductor thin films with appropriate characteristics by feeding back the evaluation results to the operating conditions of the film-forming equipment. do.

[0008]

[Means and effects for solving the problem] By the way, among the yttrium-based oxide superconductors, YBa2 Cu3 O
The compound represented by 7-X (x is a number of 7 or less) has two types of crystal structures: CuO4 type as shown in Figure 1 and CuO5 type as shown in Figure 2.
As the degree of oxidation increases (x decreases), the critical temperature increases and the critical current density increases.

[0009] The present inventor has discovered that YBa2 Cu3 O7-X
When forming a thin film, when ion species with a predetermined energy are irradiated onto the thin film, CuO4 − , Cu
It has been discovered that molecular ions such as O5 - are detected by a mass spectrometer, and that these molecular ions are not detected from thin films that do not have good superconducting properties.

Based on the above knowledge, the present inventors irradiated ion species to an oxide superconductor thin film in the process of film formation, and at that time, CuO4 - and CuO5 were irradiated as secondary ion species.
The idea was that by measuring whether or not - is detected, it would be possible to evaluate the characteristics of the oxide superconductor thin film that is being formed non-contact and in real time, and the oxide superconductor of the present invention We have developed a method for monitoring the oxidation degree of thin films.

That is, the method for monitoring the oxidation degree of an oxide superconductor thin film of the present invention is to monitor the oxidation degree of the oxide superconductor thin film by monitoring at least one of a plurality of substrates arranged in an oxide superconductor thin film deposition apparatus. As a monitoring sample, during the process of film formation, the surface of the sample is irradiated with primary ion species having an energy of 2 KV or less, and the presence or absence of secondary ion species generated from the sample surface is detected with a mass spectrometer. It is characterized by

The method of the present invention is carried out using a film forming apparatus as shown in the schematic diagram of FIG. First, vacuum exhaust mechanism 2
In the inner bottom of the vacuum container 1 equipped with
For example, an electron beam heating source 3 is disposed, and an evaporation material 4, which is a raw material for the oxide superconductor thin film to be formed, is housed therein. A substrate rotation mechanism 5 is disposed at the upper part of the vacuum container 1, and a substrate holder 6 is set on the lower surface 5a thereof. A plurality of substrates 7 are attached to the lower surface of the substrate holder 6, and these substrates 7 are heated to a predetermined temperature by a heater 8 connected to a temperature control mechanism (not shown). The material for the substrate 7 is not particularly limited, and for example, an MgO plate or the like may be used.

A monitor 9 for monitoring and controlling the deposition rate of the deposition material 4, such as a quartz crystal film thickness monitor, is interposed between the heat source 3 and the substrate 7, and a A shutter 10 is disposed at this position so that vapor deposition onto the substrate 7 can be controlled. On the side of the vacuum container 1, one of the plurality of substrates 7 has an irradiation port 11a.
An ion gun 11 is disposed so as to irradiate the substrate (the oxide superconductor thin film in the film forming process) with primary ion species of a predetermined energy from the ion gun 11 .

[0014] As the primary ion species to be irradiated, for example,
Ar+ , O2 + , Cs+ , N2 + , He+
, Ne+, Kr+, Xe+, etc. At this time, if the energy of these primary ion species is too high, even if the oxide superconductor thin film being formed has excellent superconducting properties, the secondary ion species generated by ion bombardment will be CuO4 -, Instead of becoming CuO5 -, it becomes atomic ions such as Cu- and O- or low coordination ions such as CuO- and CuO2 -, so the ion gun is set so that the energy of the primary ion species is 2KV or less 11 is activated.

A mass spectrometer 12 is disposed on the other side of the vacuum chamber 1, with its reception port 12a facing the substrate to which the primary ion species are irradiated. Secondary ion species generated from the oxide superconductor thin film on the substrate 7 by ion bombardment are received at the receiving port 12a, and subjected to mass spectrometry. Such a mass spectrometer 12
For example, a quadrupole mass spectrometer can be used.

The method of the present invention is carried out as follows. First, the vacuum evacuation mechanism 2 is operated to bring the inside of the vacuum container 1 to a predetermined oxygen partial pressure, the substrate 7 is heated by the heater 6, the evaporation material 4 is evaporated by the operation of the electron beam heating source 3, and the evaporation rate is monitored by the monitor 9. An oxide superconductor thin film having a predetermined composition is formed on the substrate 7 by controlling the following steps.

In this process, the oxide superconductor thin film is irradiated with primary ion species having a predetermined energy from the ion gun 11. Secondary ion species are generated from the thin film, which are subjected to mass spectrometry using the mass spectrometer 12 to identify CuO4 − , CuO5 −
Measure the presence or absence of When the above molecular ions are detected, the superconducting properties of the oxide superconductor thin film being formed are good. If molecular ions are not detected, the superconducting properties of the oxide superconductor thin film cannot be said to be good, so the operating conditions of the device should be examined.

[0018]

[Example] In the apparatus shown in FIG. 3, the substrate 7 is MgO (
100) Single crystal plate, quartz crystal film thickness monitor as monitor 9, O2 + ion gun as ion gun 11, quadrupole mass spectrometer (QMASS) as mass spectrometer 12
The operation was carried out using Y, Ba, and Cu as vapor deposition materials. The number of substrates set in the substrate holder 6 was five.

[0019] The oxygen partial pressure inside the container is set to 3.0×10-4To.
rr, the substrate temperature was set to 700°C, the evaporation material 4 was evaporated from the electron beam heating source 3, and the molar ratio of Y:Ba:Cu was 1.
The rate of film formation on the substrate 7 was controlled by the monitor 9 so that the ratio was 2:3. In this state, the ion gun 11 is operated to provide O2 with an energy of 0.5 KV and an ion current of 30 nA.
+ 1 of an oxide superconductor thin film that is being formed
．． An area of 7 mm2 was irradiated, and the generated secondary ion species were subjected to mass spectrometry using QMASS.

[0020] The mass monitored at this time was 127,1
29, 143, and 145 atm, but these are 63CuO4 −, 65CuO4 −, and 63C, respectively.
This corresponds to the molecular ions of uO5 − and 65CuO5 − . For the remaining four oxide superconductor thin films obtained, the critical temperature (Tc) and critical current density (Jc) at the liquid nitrogen temperature were measured using the usual four-terminal method. On average,
Tc: 89K, Jc: 1×106/cm2.

[0021] Next, CuO4 − and C
When film formation was performed under operating conditions where uO5 - molecular ions were detected, Tc: 88-90K, Jc: 0
．． An oxide superconductor thin film having a characteristic range of 5 to 2.0 x 10-6 A/cm2 could be formed with good reproducibility. For comparison, a film forming operation was carried out under the same conditions as in the example except that the oxygen partial pressure was set to 3.0 x 10-5 Torr. At this time, CuO4 − and CuO5 − could not be detected by QMASS.

The Tc of the obtained oxide superconductor thin film is 35
K, and did not exhibit superconducting properties even at the temperature of liquid nitrogen.

[0023]

[Effects of the Invention] As is clear from the above explanation, according to the method of the present invention, the degree of oxidation of the formed oxide superconductor thin film can be measured using a mass spectrometer to determine whether or not secondary ion species are generated. This enables contactless and real-time monitoring. That is, by using the above monitoring data, an oxide superconductor thin film having desired electrical properties can be formed with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a CuO4 type crystal structure.

FIG. 2 is a schematic diagram showing a CuO5 type crystal structure.

FIG. 3 is a schematic diagram showing an example of a film forming apparatus for forming an oxide superconductor thin film used in the method of the present invention.

[Explanation of symbols]

1 Vacuum container 2 Evacuation mechanism 3 Electron beam heating source 4 Vapor deposition material 5 Substrate rotation mechanism 5a Lower surface of substrate rotation mechanism 6 Substrate holder 7 Substrate 8 Heater 9 Vapor deposition rate monitor 10 Shutter 11 Ion gun 12 for primary ion species Mass spectrometer 12a Inlet for secondary ion species

Claims (1)

[Claims] 1. At least one of a plurality of substrates placed in an oxide superconductor thin film deposition apparatus is used as a sample for monitoring the oxidation degree of the oxide superconductor thin film, and in the process of the film deposition operation, the sample is Oxidation degree monitoring of an oxide superconductor thin film, characterized in that the surface of the sample is irradiated with primary ion species having an energy of 2 KV or less, and the presence or absence of secondary ion species generated from the sample surface is detected by a mass spectrometer. Method.