JPH04232251A - Formation of lanthanum aluminate thin film - Google Patents

Abstract

PURPOSE: To form a lanthanum aluminate thin film which is free from cracking and has a smooth surface as a buffer layer for depositing a superconductor on a silicon substrate.

CONSTITUTION: Amorphous lanthanum aluminate 3 is deposited by RF magnetron sputtering on the silicon substrate 1. The thin film is crystallized by slow cooling after heating of the thin film. The crystallized lanthanum aluminate thin film 4 is free from cracking and its surface is smooth.

COPYRIGHT: (C)1992,JPO

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a process for producing a high-temperature superconductor thin film, and in particular, to a process for producing a high-temperature superconductor thin film, in particular, YBa2 Cu3 O7-x
The present invention relates to a method for forming crack-free and smooth lanthanum aluminate (LaAlO3) thin films on silicon substrates for forming high-temperature superconductor thin films.

0002

[Prior art] Lanthanum aluminate (LaAlO3
) became more likely to be applied to optoelectronic materials in the 1950s, and a single crystal of this material was developed. However, single crystals of lanthanum aluminate are lithium niobate (L
Due to its inferior properties compared to the single crystal of iNbO3), its application has become difficult, and until recently there has been no further research and development.

However, recently developed YBa2 Cu3
O7-x Single crystal lanthanum aluminate has been evaluated as the most excellent substrate for high-temperature superconductor thin films, and demand for it has rapidly increased.

Lanthanum taluminate single crystal substrates have a small dielectric constant, and their crystal structure, lattice constant, and coefficient of thermal expansion are approximately equal to those of high temperature superconductor thin films. However, single crystal substrates have the problem of being too expensive for practical use.

One solution to this problem is to use a low cost silicon substrate. However, it is not possible to form a superconductor thin film on a silicon substrate using conventional techniques.

Silicon (Si) and gallium arsenide (GaA)
In order to deposit a high temperature superconductor thin film on the substrate of s),
A buffer layer must be deposited on the substrate. This buffer layer has properties that prevent chemical reactions from occurring at the interface between the substrate and the high-temperature superconductor thin film, and enable epitaxial growth of the high-temperature superconductor thin film. It must have certain characteristics.

[0007]

[Problems to be Solved by the Invention] It is known that a lanthanum aluminate thin film is the most excellent buffer layer between a silicon substrate and a high-temperature superconductor thin film. Due to the large difference in thermal expansion coefficient, many cracks occur on the surface of the thin film,
The high temperature superconductor thin film deposited on its upper surface deteriorates in quality, causing deterioration in the characteristics of the device.

Accordingly, it is an object of the present invention to provide a method for forming a crack-free and smooth lanthanum aluminate thin film as a buffer layer for depositing a high temperature superconductor thin film on a silicon substrate.

[0009]

[Means for Solving the Problems] The present invention includes: mounting a silicon substrate (1) in a sputtering vacuum chamber;
cleaning under vacuum; supplying a gas mixture into the chamber; forming an amorphous lanthanum aluminate thin film (3) on the silicon substrate (1); 3) is characterized by crystallization.

0010

[Operation] In the present invention, high frequency (Radio Fr.
After depositing an amorphous lanthanum aluminate thin film on a silicon substrate by magnetron sputtering method and heat-treating the lanthanum aluminate thin film,
By slow cooling in an oxygen atmosphere, the lanthanum aluminate thin film is crystallized due to the large difference in thermal expansion coefficient between the silicon substrate and the lanthanum aluminate thin film, and is heat-treated so that it can function as a buffer layer. As a result, the occurrence of many cracks on the surface of the thin film can be prevented, and a crystalline lanthanum aluminate thin film without cracks and having a smooth surface can be formed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail with reference to the accompanying drawings.

FIG. 1 shows the process of depositing and growing a lanthanum aluminate thin film, including the process of depositing the thin film on a silicon substrate by high frequency magnetron sputtering using a lanthanum aluminate ceramic sputtering target.

After mounting the silicon substrate (1) in a sputtering vacuum chamber (not shown),
After cleaning the inside of the chamber and the silicon substrate (1) under a vacuum of 10-5 Torr, argon (Ar
) and oxygen (O) at a ratio of 3:1 is supplied to the inside of the chamber, and the pressure inside the chamber is 10 mTo.
Make it rr. In this case, plasma is formed between a lanthanum aluminate ceramic sputtering target (not shown) and the silicon substrate (1), and atoms (2) of the sputtering target are transferred to the silicon substrate (1).
) for 2 hours.

[0014] At this time, the high frequency applied voltage is 50 to 150W.
The distance between the sputtering target and the silicon substrate (1) was 20 to 50 mm.

FIG. 1(a) shows the state of transfer of target atoms (2) onto a silicon substrate.

As shown in FIG. 1(b), after the atoms (2) of the sputtering target are deposited to a certain thickness on the upper surface of the silicon substrate (1), an amorphous lanthanum aluminate thin film (3) is formed. It is formed on the upper surface of a silicon substrate (1).

Next, in order to crystallize the amorphous lanthanum aluminate thin film (3), the silicon substrate (1) on which the amorphous lanthanum aluminate thin film (3) has been deposited is placed in a furnace (not shown). It is installed horizontally and performs heating and cooling processes while supplying oxygen gas to the inside of the furnace. Heat treatment is 90
The temperature is increased at a rate of 4°C/min from 0 to 1200°C and maintained at that temperature for 30 minutes to 2 hours. Cooling treatment is 0.5
Cool to room temperature at a rate of ~1°C/min. By this treatment, a crack-free and smooth crystalline lanthanum aluminate thin film (4) is formed on the silicon substrate. Figure 1(c)
shows a cross section of a crystallized lanthanum aluminate thin film.

FIG. 2 shows a cross section of a high temperature superconductor thin film deposited on a lanthanum aluminate thin film. Silicon substrate (
1) Crystalline lanthanum aluminate crystal thin film on top (4)
YBa2 Cu3 O7-x is formed on it by a general high frequency magnetron sputtering method.
By depositing the high temperature superconductor thin film (5) it is possible to fabricate semiconductor devices with high temperature superconductors.

Y formed on the upper surface of the crystalline lanthanum aluminate thin film (4) formed on the silicon substrate (1)
The Ba2 Cu3 O7-x high temperature superconductor thin film (5) can be patterned by an etching process in a general semiconductor manufacturing process. The desired fine line pattern formed by the etching described above can be used for Josephson elements, semiconductor wiring, etc.

[0020]

Effects of the Invention The semiconductor including the high-temperature superconductor manufactured in this manner has the advantage of being faster in operating speed and requiring extremely less operating power than other semiconductors.

Therefore, the method for producing a lanthanum aluminate thin film of the present invention has a low dielectric constant, low dielectric loss,
A lanthanum aluminate single crystal substrate, which has almost the same crystal structure, lattice constant, thermal expansion coefficient, etc. as a high-temperature superconductor thin film, is the most suitable substrate for manufacturing a high-temperature superconductor thin film, but its price is too high. This method solves the problems that are difficult to put into practical use, and uses a silicon substrate (1), which is inexpensive and has a universal process, and is coated with a crystalline lanthanum aluminate thin film (4). A fine pattern is formed by forming a YBa2Cu3O7-x high-temperature superconductor thin film (5) on it using a general high-frequency magnetron sputtering method to fabricate a semiconductor device equipped with a high-temperature superconductor. Not only can it be used for Josephson devices and semiconductor wiring, but also it is possible to produce semiconductor devices with high operating speed and extremely low operating power.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the manufacturing process of the present invention.

FIG. 2 is a cross-sectional view showing a YBa2 Cu3 O7-x high temperature superconductor thin film manufactured using a lanthanum aluminate thin film according to the present invention.

[Explanation of symbols]

1 Silicon substrate 2 Atom

Claims (9)

[Claims] 1. Mounting a silicon substrate (1) in a sputtering vacuum chamber; cleaning the inside of the chamber and the silicon substrate (1) under vacuum; supplying a mixed gas into the chamber; (1
1.) A method for forming a lanthanum aluminate thin film, comprising: forming an amorphous lanthanum aluminate thin film (3) on the lanthanum aluminate thin film (3); and crystallizing the amorphous lanthanum aluminate thin film (3). 2. The cleaning step cleans the chamber once.
The method of forming a lanthanum aluminate thin film according to claim 1, further comprising evacuation to a vacuum state of 0-5 Torr. 3. Formation of a lanthanum aluminate thin film according to claim 1 or 2, wherein the step of supplying the mixed gas includes maintaining the temperature of the silicon substrate (1) at 100 to 400°C. Method. 4. In the step of supplying the mixed gas, a gas containing argon and oxygen mixed at a ratio of 3:1 is supplied at 10 mT.
Claim 1 characterized in that the inflow is made under a pressure of orr.
4. The method for forming a lanthanum aluminate thin film according to any one of items 3 to 3. [Claim 5] The lanthanum aluminate thin film (3)
The process of forming sputtering target atoms (
5. The method for forming a lanthanum aluminate thin film according to claim 1, wherein the lanthanum aluminate thin film is transferred onto the silicon substrate (1) for 2 hours. [Claim 6] The lanthanum aluminate thin film (3)
6. The step of forming is carried out at a high frequency applied voltage of 50 to 150 W and a distance between the lanthanum aluminate ceramic sputtering target and the silicon substrate (1) of 20 to 50 mm. The method for forming the described lanthanum aluminate thin film. 7. The crystallizing step is a step of mounting the silicon substrate (1) on which the lanthanum aluminate thin film is deposited in a furnace; heating the substrate (1) and cooling the substrate (1). The method for forming a lanthanum aluminate thin film according to any one of claims 1 to 6, comprising: 8. The heating step is characterized by raising the temperature to 900 to 1200°C at a rate of 4°C/min while supplying oxygen gas, and then maintaining the temperature for 30 minutes to 2 hours. The method for forming a lanthanum aluminate thin film according to claim 7. 9. Formation of a lanthanum aluminate thin film according to claim 8, wherein the cooling step includes gradually cooling the lanthanum aluminate thin film to room temperature at a rate of 0.5 to 1° C./min while supplying oxygen gas. Method.