JPH04346663A - Formation of crystalline film - Google Patents

Abstract

PURPOSE:To form an oxide high-temp. superconductor film having high-quality crystallinity and superconduction transition temp. by using the ions of atoms having the heavier mass than the mass of the atoms constituting a target as ions for sputtering at the time of forming the crystalline film by a sputtering method. CONSTITUTION:The particle mass of an incident ion beam 5 on the target 4 is made larger than the mass of the target 4. The energy which is reflected by the target 4 and collides against a substrate 6 is prevented from breaking the structure of the film crystals in this way and the high-quality oxide high- temp. superconductor film is formed with good reproducibility. The film is formed by determining the geometrical arrangement of the target 4 and the substrate 6, the incident angle of the incident ion beam 5 on the target 4, and the target irradiation energy of the ion beam 5 in such a manner that the energy attains the threshold value to break the crystallinity of the crystal film formed on the substrate 6 or below.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a crystalline film forming method for forming a high-quality thin film with excellent crystallinity and density on a substrate by sputtering when forming an oxide high-temperature superconductor film. It is something.

0002

[Prior Art] Oxide superconductors are expected to be used in various applications due to their high superconducting transition temperatures, and the formation of thin films with high quality transition temperatures and crystallinity is being considered for application to devices. has been done. A sputtering method is a thin film manufacturing method.

In this method, plasma is generated by low-pressure discharge, ions in the plasma collide with a target made of a film material, and the film material ejected from the target due to the collision is deposited on a substrate to form a film. It is.

One of the sputtering methods is the ion beam sputtering method. The ion beam sputtering method is a method of forming a film by irradiating (colliding) a target with an ion beam generated by an ion source. Pull out ions from the plasma generated in the ion source plasma chamber by holding the extraction electrode.
Since it is a method of irradiating a target, it is possible to form a film by independently controlling the quality and energy of the ions, and therefore it is a method with good reproducibility of film formation.

An apparatus for forming an oxide superconductor crystalline film using ion beam sputtering is shown in FIG. 3, and the conventional forming method, including its operation, will be explained. In Figure 3, 1
2 is a high-density, large-current ECR ion source, 2 is an ECR plasma source, and 3 is a vacuum chamber, which is connected to an exhaust system (not shown). 4 is a sputter target made of a film material, 5 is an ion beam extracted from the ECR ion source 1, 6 is a substrate fixed to a heating sample stage 7, and 8 is an EC
This is a plasma flow generated by the R plasma source 2 and irradiated onto the substrate 6.

[0006] This apparatus is configured to sputter a target using an ECR ion beam to supply a film-forming material onto a substrate, and to promote oxidation using a plasma flow from an ECR plasma source 2. Conventional ion beam sputtering is used to form oxide high-temperature superconductor films using sintered targets of yttrium, barium, and copper oxides as sputtering targets, and inexpensive argon as the sputtering gas. was.

Furthermore, in order to promote oxidation of the film that has reached the substrate 6, irradiation with active oxygen is performed during film formation. In this method, the oxygen plasma irradiation for promoting oxidation and the ion beam for film formation can be controlled independently and with high precision, making it possible to form films with good reproducibility.

[0008]

[Problems to be Solved by the Invention] However, in such a conventional formation method, the atomic weight of barium, which is a target material, is larger than that of argon, which is an ion for sputtering, so argon ions that collide with barium emit high energy. This poses a problem in that the light is reflected when held and incident on the substrate 6, destroying the crystals of the film or displacing atoms in the crystal structure from their normal positions.

[0009] Therefore, the formation of a film with an orientation other than a thermodynamically stable crystal axis orientation is promoted, and there is a problem that a film with high quality crystallinity and superconducting transition temperature cannot be obtained. In order to prevent this, it is necessary to reduce the energy of the argon ions, but this places a large limit on the ion extraction voltage from the ion source. Furthermore, when the energy of argon ions is lowered, there is a problem in that the film formation rate decreases.

The present invention has been made in view of the above circumstances, and provides a method for forming a crystalline film that can form an oxide high temperature superconductor film with high quality crystallinity and superconducting transition temperature. .

[0011]

[Means for Solving the Problems] In order to solve the above-mentioned problems, a first invention uses ions of atoms having a mass heavier than atoms constituting the target material as sputtering ions. The second invention provides a method for attaching a target to a target material so that the energy of sputtering ions that are reflected by collision with a target material and incident on a substrate is below a threshold value that destroys the crystallinity of a crystalline film formed on a substrate. The film is formed by determining the geometrical arrangement of the substrate, the incident angle of the ion beam on the target, and the target irradiation energy of the ion beam.

0012

[Operation] When the mass of the incident ion is larger than the mass of the target, reflection of the incident ion becomes difficult to occur, and the atomic positions in the crystal structure are not shifted.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to figures. When studied in a laboratory or the like, when an incident particle of mass M1 elastically collides with a stationary particle of mass M2, the direction of reflection and the reflected energy are expressed by equation (1).

[0014]

[Equation 1] Here, θ is the angle between the particle incident direction and the reflection direction, and E
0 is the energy of the incident particle, and E1 is the energy of the reflected particle of mass M1.

If the mass M1 of the incident particle is larger than the mass M2 of the target atom, it retains momentum in the direction of incidence even after the collision. That is, in FIG. 3 showing an example of a conventional device, M1≧
In the case of M2, ions that are incident on the target from above will not go above the collision point on the target surface.

However, for M1≦M2, incident ions are reflected from the target. For example, argon and xenon ions are reflected by barium targets. FIG. 1 shows calculation results of the reflection direction and the ratio of reflected energy to incident energy when argon and xenon ions collide with barium atoms of a sintering target and are reflected by elastic collision.

[0017] The reflective particles have the lowest energy.
This is the case when the angle θ is 0 in equation (1) when the light is reflected in the opposite direction to the incident direction. In the case of argon ions, the angle θ is 0
Even when ions are reflected, the energy is reflected with 30% or more of the energy of the incident ions, so the energy incident on the substrate on which the reflective particles form a film is 30% or more of the energy incident on the target of the ions.

This value is large and means that sputtering ions must be used at very low energies. For example, in the case of yttrium-barium-copper-oxygen oxide superconductors, the threshold energy at which oxygen atoms shift from their normal positions in the crystal is reported to be about 20 eV (Don M. Parkin, Metal-
lurgical transaction A,
Vol. 21A, May, 1990 pp1015)
.

In order to reduce the energy of the reflective particles to below this value, the incident argon ion energy must be below 70 eV. It is difficult to extract high-density ions with energy in this range, and therefore a high-current ion beam cannot be obtained. Furthermore, since such low-energy ions have a low sputtering rate, the film formation rate becomes extremely low.

On the other hand, with xenon, high energy of up to 20 keV can be used in a wide area where the reflection angle with respect to ion incidence on the substrate to the target is up to 50 degrees. This means that a high voltage of 20 kV can be used as the ion extraction voltage. Generally, the ion current density Ja extracted by the ion extraction electrode is expressed by the Child-Langmuir equation (2).

[0021]

##EQU00002## Here, V is the ion extraction voltage, M is the mass of the ions, and d is the distance between the electrodes.

[0022] Xenon, which has a large ion mass, requires a larger ion extraction voltage than argon to obtain the same ion current density. However, the maximum extraction voltage allowed for xenon due to the energy constraints of reflected ions is much larger than that for argon, which means that ion beams with much higher density and higher current can be used with xenon. Therefore, by using xenon ions, a high-quality oxide superconductor film can be formed at high speed.

Next, a case where the method is applied to the formation of a europium/barium/copper/oxygen oxide high temperature superconductor film will be described. Europium has a larger mass than barium. In Figure 2 (1
) shows the ratio of reflected ion energy to incident ion energy at each reflection angle when xenon ions collide with europium and barium atoms, calculated using the formula.

Assuming that the threshold energy for breaking the crystal is 20 eV, which is the same as for yttrium, barium, copper, and oxygen,
2.5k when the board is placed at a position with a reflection angle of up to 40 degrees
When the incident ion energy is up to about eV, the energy of reflected ions incident on the substrate is 20 eV or less. Thus, the heavier the atoms in the target material, the more restrictions there are on substrate placement and sputtering ion energy.

When ions reflected from the target are incident on the substrate, there is a small probability that the incident ions will impart most of their total energy to the colliding atoms in one collision with the atoms constituting the film. Therefore, it is not the case that a crystal film cannot be formed unless the reflected ion energy is lower than 20 eV, which is the threshold energy for breaking the crystal.

In fact, by forming a europium/barium/copper/oxygen film using an argon ion beam with an energy of 5 keV, a film with a certain degree of crystal structure and a superconducting transition temperature Tc of up to 80 degrees K was produced. It has gained. However, since an ideal film has a superconducting transition temperature Tc of 90 degrees K or higher, it is thought that the crystals of the film formed with argon ions are considerably damaged. In a film formed using xenon ions with the same energy of 5 keV, the superconducting transition temperature Tc increased to 87 degrees K.
The effect of reducing reflected ion energy has appeared.

[0027]

[Effects of the Invention] As explained above, in the present invention, the mass of the particles incident on the target is made larger than the mass of the target, so that the energy reflected from the target and colliding with the substrate destroys the structure of the film crystal. It has the effect of being able to reproducibly form a high-quality oxide high-temperature conductor film.

[Brief explanation of drawings]

[Figure 1] Graph showing reflected energy of argon and xenon

[Figure 2] Graph showing reflected energy of europium

[Figure 3] Diagram showing an example of a conventional device

[Explanation of symbols]

1 ECR ion source 2 ECR plasma source 3 Vacuum chamber 4 Sputter gate 5 Ion beam 6 Board 7 Heating sample stage 8 Plasma flow

Claims (2)

[Claims] 1. A method for forming a crystalline film in which a crystalline film is formed on a substrate by sputtering a target material by ion bombardment, in which ions of atoms having a mass heavier than atoms constituting the target material are used as sputtering ions. A crystalline film forming method characterized by: 2. In a method for forming a crystalline film using an ion beam sputtering film forming method, the energy of sputtering ions reflected by collision with a target material and incident on a substrate causes crystals to form on the substrate. A crystallinity film characterized by forming a film by determining the geometrical arrangement of the target and substrate, the incident angle of the ion beam to the target, and the target irradiation energy of the ion beam so that the value is below a threshold value that destroys the crystallinity of the film. Film formation method.