JPH05139892A - Production of oxide ferroelectric thin film - Google Patents

Abstract

PURPOSE:To form a good epitaxial ferroelectric thin film on a silicon single crystal substrate, and to utilize a lower electrode layer. CONSTITUTION:A nickel silicide NiSi2 (100) as a buffer layer is epitaxially grown on the surface of a silicon single crystal (100). Further, a magnesium oxide MgO (100) layer is epitaxially grown on the surface, and an oxide ferroelectric thin film is epitaxially grown on the surface of the buffer layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide ferroelectric thin film. More specifically, the present invention relates to a method for manufacturing an oxide ferroelectric thin film used for an optical waveguide element, a piezoelectric element, an electro-optical element, an infrared detection element, a non-volatile memory and the like.

[0002]

2. Description of the Related Art With the rapid development of electronics and optoelectronics, there is an increasing demand for functional enhancement of electronic materials as the basis of these technologies. Under such circumstances, studies on fine crystal structures of various materials, precise structure control, etc. are being actively pursued.
The oxide ferroelectric materials are also being devised for higher functionality.

For such studies, thinning the oxide ferroelectric material is an important subject for application to the electronics field. In particular, it is important to epitaxially grow this oxide ferroelectric thin film on a silicon single crystal substrate. However, until now, when an oxide ferroelectric material was directly formed on the surface of a silicon substrate, silicon was diffused into the oxide ferroelectric material, or constituent atoms of the oxide ferroelectric material were diffused into the silicon. However, a high quality oxide ferroelectric thin film could not be obtained. Therefore, it has been attempted to form a metal material such as platinum or a silicon dioxide film that can be generated by heat treatment on the silicon surface as a barrier for atomic diffusion. In either case, the barrier function is not sufficient. Moreover, it is not possible to obtain a good quality oxide ferroelectric thin film. Further, it is difficult to say that these buffer layers are optimal materials in terms of epitaxial growth.

In order to solve this problem, the inventors of the present invention have found that magnesium oxide (Mg) is formed on a silicon substrate.
It is proposed that a buffer layer of O) is formed and an oxide ferroelectric thin film is formed on the buffer layer. This method is remarkable in producing a good oxide ferroelectric thin film. However, this method has a drawback that the lower electrode cannot be attached to the oxide ferroelectric thin film. This is because the lower electrode is indispensable depending on the type of device used, and the application range is remarkably narrowed without the lower electrode.

[0005]

As described above, according to the conventional technique, it is extremely difficult to form a high-quality oxide ferroelectric thin film on a silicon single crystal substrate, and the magnesium oxide which has already been proposed has been proposed. In the method of forming the buffer layer, it is necessary to use a magnesium oxide thin film as the buffer layer in order to raise the atomic diffusion suppressing ability of the epitaxial growth buffer layer to a practical level. There is a problem that the lower electrode cannot be attached to the dielectric thin film. Therefore, the present invention has an excellent ability to suppress atomic diffusion when forming an oxide ferroelectric thin film on a silicon single crystal substrate, and has a lattice constant suitable for epitaxially growing an oxide ferroelectric material, and further, a lower electrode. The purpose of the present invention is to provide a new method that enables the production of a high-quality oxide ferroelectric thin film by interposing a buffer layer having an electrical conductivity suitable for use as.

[0006]

The present invention is provided to solve the above-mentioned problems by (10) of a silicon single crystal substrate.
A nickel silicide (100) surface is epitaxially grown on the (0) surface as a buffer layer, magnesium oxide (100) is epitaxially grown on the surface, and then an oxide ferroelectric thin film is epitaxially grown on the surface of the buffer layer. A method of manufacturing an oxide ferroelectric thin film is provided.

That is, according to the present invention, nickel silicide NiSi ₂ which is electrically conductive (specific resistance: 0.02 ohm-cm 2) is epitaxially grown in the [100] direction on a Si (100) substrate, and the NiSi ₂ ( Paying attention to the small lattice mismatch between 100) and magnesium oxide MgO (100), the NiSi ₂ (100) film was used as the first buffer layer for forming the oxide ferroelectric thin film, and the oxide ferroelectric material composition was used. A MgO (100) film having extremely low reactivity with atoms and having a lattice constant close to that of an oxide ferroelectric material is epitaxially formed on NiSi ₂ (100) to form a second buffer layer.

[0008]

The first buffer layer NiSi ₂ is a good electrode. However, when the oxide ferroelectric material is directly formed on the silicon substrate, the silicon substrate whose surface is oxidized, or the silicon single crystal substrate on which the metal thin film such as platinum is formed, the constituent atoms of the oxide ferroelectric material are contained in the buffer layer. The problem that it often diffuses to reach the silicon substrate cannot be solved when only the NiSi ₂ (100) film is used as the buffer layer. This is because in this case, the composition of the oxide ferroelectric material is changed and a crystal phase such as pyrochlore having no ferroelectric property is generated. On the other hand, MgO (1
When a (00) film is formed on NiSi ₂ (100) as a second buffer layer and an oxide ferroelectric thin film is further formed on this MgO (100) film, the MgO (100) film is a strong oxide film. Since the diffusion of constituent atoms of the dielectric material is suppressed, the composition of the oxide ferroelectric material does not change, and a perovskite crystal phase having ferroelectricity is generated at an appropriate processing temperature. Since the formed oxide thin film has a perovskite crystal structure of almost 100%, the characteristics as a ferroelectric material can be sufficiently obtained.

NiSi ₂ (100) is Si (1
00) substrate can be epitaxially grown with 0.45% lattice mismatch, and MgO (100) can be epitaxially grown with 9% lattice mismatch on the epitaxially grown NiSi ₂ (100) surface. Furthermore, since many oxide ferroelectric materials have a lattice constant of about 4Å, Si (10
0) NiSi ₂ (100) / MgO (10) formed on
0) Many oxide ferroelectric materials can be epitaxially grown on the surface of the buffer layer with a lattice mismatch of about 5%.

Further, the NiSi ₂ (100) film is MgO.
Si (10) which hinders the epitaxial growth of (100)
0) It also has the effect of removing dangling bonds on the surface. Of course, in the present invention, various methods can be used as a method for forming the NiSi ₂ (100) film of the first buffer layer. For example, after depositing metallic nickel on the surface of the silicon single crystal Si (100) by sputtering, vacuum deposition, molecular beam epitaxy, etc., 1
It can be manufactured by annealing at a substrate temperature of 700 ° C. or higher in a high vacuum of about 0 ⁻⁶ Pa. Second buffer layer M
The same applies to the gO (100) film, and the vacuum deposition method,
Metallic magnesium is converted into NiSi by molecular beam epitaxy or the like.
₂ It can be prepared by depositing on the (100) surface and then oxidizing it at a substrate temperature of 800 ° C. or higher in oxygen gas 10 ⁻³ Pa excluding residual gas. Further, the oxide ferroelectric thin film formed on the Si (100) substrate on which the above buffer layer is formed is also formed by sputtering, vacuum deposition, molecular beam epitaxy,
The film can be formed by any method such as MO-CVD method and sol-gel method.

The thickness of the buffer layer composed of nickel silicide NiSi ₂ (100) and MgO (100) is PZT, P.
It can be appropriately set similarly to the oxide ferroelectric thin film such as LZT or barium titanate. Hereinafter, the present invention will be specifically described with reference to examples.

[0012]

Example 1 After cleaning a Si (100) substrate in hydrofluoric acid to remove a surface oxide film, an argon gas pressure was 1 Pa, a substrate temperature was room temperature, and a sputtering targeting nickel was performed in a vacuum chamber. A nickel thin film having a thickness of 50 nm was formed by the method. Then, at a vacuum degree of 10 ⁻⁶ Pa and a substrate temperature of 80
The nickel and silicon of the substrate were reacted at 0 ° C. for 10 minutes to epitaxially grow a NiSi ₂ (100) film. In this way the to form the NiSi ₂ (100) film on the surface, the vacuum degree 10 ^-6 Pa, the magnesium at room temperature for 10
After the vapor deposition of nm, oxygen gas was introduced up to 10 ⁻³ Pa, the substrate temperature was raised to 800 ° C., and magnesium and oxygen were reacted and reacted to form a MgO (100) film. Then, lead zirconate titanate (PZT) was produced by a molecular beam epitaxy method using an organometallic complex. In an ultrahigh vacuum chamber with a back pressure of 10 ⁻⁷ Pa, NiSi ₂ (10
0) / MgO (100) buffer layer deposited Si (10
0) Metallic lead, zirconium tetrapropoxide, and titanium tetraisopropoxide were vapor-deposited on the substrate at appropriate vapor pressures. At this time, since the substrate temperature is 500 ° C. and the oxygen gas pressure is 10 ⁻³ Pa, the zirconium tetrapropoxide and titanium tetraisopropoxide become zirconium and titanium on the substrate surface, respectively, and are oxidized and crystallized with lead. Become PZT. As a result, 50
A PZT epitaxial film having a thickness of 0 nm was obtained. By the x-ray diffraction method, it was confirmed that the obtained thin film was a rhombohedral PZT c-axis oriented film.

Example 2 A PZT layer was epitaxially grown on the MgO (100) surface formed in the same manner as in Example 1 by a sputtering method targeting a PZT sintered body under an oxygen gas pressure of 10 ⁻⁴ Torr. It was The thickness was 1000 nm. It was confirmed by x-ray diffraction method that the obtained thin film had c-axis orientation.

[0014]

As described in detail above, according to the present invention, NiSi ₂ (100) as a first buffer layer on the substrate,
By depositing MgO as the second buffer layer, the interaction between silicon and the oxide ferroelectric material can be suppressed, and the oxide ferroelectric thin film can be epitaxially grown. In addition, since NiSo ₂ (100) which is a buffer layer can be used as the lower electrode, application to an electronic device becomes easy.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 41/24 // C30B 25/06 9040-4G

Claims (2)

[Claims] 1. A nickel silicide (100) plane is epitaxially grown as a buffer layer on a (100) plane of a silicon single crystal substrate, and magnesium oxide (1) is further formed on the surface thereof.
00) surface is epitaxially grown, and then an oxide ferroelectric thin film is epitaxially grown on the surface of the buffer layer. 2. An oxide ferroelectric thin film produced by the method of claim 1.