JPH07330487A - Production of oxide thin film - Google Patents

Abstract

PURPOSE:To provide a process for producing oxide thin films capable of easily forming an epitaxial or orientable oxide buffer layer on a single crystal semiconductor substrate. CONSTITUTION:The surface of the single crystal semiconductor substrate is subjected to a passivation treatment, by which a passivation layer consisting of an extremely thin film contg. the elements different from the elements constituting the semiconductor is formed and thereafter or further, after the passivation layer is partially sublimated, the epitaxial or orientable oxide buffer layer is grown in vapor phase on the surface of the single crystal semiconductor substrate. The epitaxial or oxide ferroelectric thin film is grown in vapor phase or solid phase on the formed oxide buffer layer. Production of elements, such as high-performance non-volatile memories, capacitors or optical modulation elements on the semiconductor substrate is possible according to this invention.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an epitaxial or oriented oxide buffer layer on a semiconductor single crystal substrate, and further to an epitaxial or oriented ferroelectric substance on the semiconductor single crystal substrate. The present invention relates to a method for forming a thin film.

[0002]

2. Description of the Related Art Conventionally, an oxide ferroelectric thin film has a surface acoustic wave such as a non-volatile memory due to many properties of a ferroelectric material such as ferroelectricity, piezoelectricity, pyroelectricity and electro-optical effect. Many applications such as elements, infrared pyroelectric elements, acousto-optical elements, and electro-optical elements are expected. Among these applications, the production of single-crystal thin films is indispensable in order to achieve low optical loss in thin-film optical waveguide structures and polarization characteristics and electro-optical effects comparable to single crystals. Therefore, BaTiO ₃ , PbTiO _3
3 , Pb _1-x La _x (Zr _1-y Ti _y ) _{1-x / 4} O ₃ (P
LZT), LiNbO ₃ , KNbO ₃ , Bi ₄ Ti ₃ O
Epitaxial ferroelectric thin films such as ₁₂ are subjected to Rf-magnetron sputtering, ion beam sputtering, laser ablation, metalorganic chemical vapor deposition (M
The oxide single crystal substrate is often formed by a method such as OCVD.

However, it is necessary to form a ferroelectric thin film on a semiconductor substrate for integration with a semiconductor element. Epitaxial growth of a ferroelectric thin film on a semiconductor substrate is difficult due to high growth temperature, mutual diffusion between the semiconductor and the ferroelectric, oxidation of the semiconductor, and the like. Also, G
Regarding the case of forming a ferroelectric thin film on an aAs substrate, there are very few reports on this, but PLZT
It is known that the diffusion of Pb into GaAs is detected when GaAs grows.
At 0 ℃ or higher, the surface As decreases, and at 690 ℃ or higher, A
It is known that sublimation of As and Ga starts one by one without s ₄ atmosphere. For these reasons, GaAs
Epitaxial growth of a ferroelectric thin film on a substrate is difficult. For these reasons, there is a need for a capping layer for semiconductors that grows epitaxially on semiconductors at low temperatures, assists in epitaxial growth of ferroelectric thin films, and also acts as a diffusion barrier. Further, in an FET element in which an insulator is formed between a ferroelectric substance and a semiconductor, it is possible to prevent injection of charges from the semiconductor during polarization of the ferroelectric substance, and to maintain a polarization state of the ferroelectric substance. Layers are needed. Further, the refractive index of the ferroelectric substance is generally smaller than that of GaAs or Si, but if a buffer layer having a smaller refractive index than the ferroelectric substance is obtained, the semiconductor laser light can be confined in the ferroelectric thin film optical waveguide. This makes it possible to fabricate an optical modulator on a semiconductor laser and an optical integrated circuit on a Si semiconductor integrated circuit.

On the other hand, M on Si (100) single crystal
It is possible to epitaxially grow a ferroelectric compound on a substrate that has been epitaxially grown using gAl ₂ O ₄ (100) or MgO (100) as a buffer layer.
As disclosed in Japanese Patent No. 185808, Si (100)
The crystallographic relationship between MgO (100) and MgO (100) has not been clarified. In fact, in a subsequent study, when MgO with (100) orientation was produced on a Si (100) single crystal, MgO only showed that the (100) plane was parallel to the Si (100) plane. Is a randomly oriented polycrystalline MgO
(P. Tiwari
J. J. et al. Appl. Phys. 69, 8358 (199
1)). In fact, since the (100) plane of MgO is electrically neutral and has low energy, even in a polycrystalline thin film (10
It is known that the orientation of (0) is easily obtained. Therefore, it is considered that a special treatment on the surface of the semiconductor substrate is required to epitaxially grow MgO.

The present inventors have already proposed to epitaxially grow MgO on a single crystal semiconductor substrate (Japanese Patent Laid-Open No. 327034/1993), and further use the MgO buffer layer to epitaxially or orient it on the semiconductor substrate. It has already been proposed to prepare the ferroelectric thin film of Japanese Patent Application Laid-Open No. 5-327034 and Japanese Patent Application No. 5-1638.
91). The crystallographic relationship at this time is, for example, GaAs.
For BaTiO ₃ on (100), BaTiO ₃
(001) // MgO (100) // GaAs (100),
In-plane orientation BaTiO ₃ [010] // MgO [001] //
The present inventors have clarified that it is GaAs [001].

[0006]

However, in the case of a single crystal semiconductor substrate, especially GaAs, the orientation of grown MgO is greatly affected by the difference in the pretreatment method. Subsequent research has revealed. The formed MgO thin film often becomes polycrystalline and may not be epitaxial or oriented, and its improvement is demanded. Therefore, when the GaAs surface immediately before the growth of MgO was examined, it was found that the GaAs substrate surface should not be simply removed by natural oxide film etching, but that an oxide film or the like should be provided as a passivation layer in an appropriate state. , The surface of GaAs is roughly divided into a passivated state, a state of GaAs only, and an intermediate state thereof, and it was found that it is important to control these states. Therefore, an object of the present invention is to easily form an epitaxial or oriented oxide buffer layer on a single crystal semiconductor substrate,
Another object of the present invention is to provide a method for producing an oxide thin film that can be formed with good reproducibility. Another object of the present invention is to provide a method for forming an epitaxial or oriented oxide ferroelectric thin film on a semiconductor single crystal by using an epitaxial or oriented oxide thin film as a buffer layer.

[0007]

The present inventors have completed the present invention as a result of extensive studies on the surface treatment method for a single crystal semiconductor substrate. The method for producing an oxide thin film of the present invention comprises the step of passivating the surface of a single crystal semiconductor substrate to form a passivation layer made of an ultrathin film containing an element different from the element constituting the semiconductor, It is characterized in that an epitaxial or oriented oxide buffer layer is vapor-phase grown on the surface of the crystalline semiconductor substrate. In another method for producing an oxide thin film of the present invention, the surface of a single crystal semiconductor substrate is passivated to form a passivation layer made of an ultrathin film containing an element different from an element constituting the semiconductor, After partially sublimating the passivation layer, an epitaxial or oriented oxide buffer layer is vapor-phase grown on the surface of the single crystal semiconductor substrate. Yet another method for producing an oxide thin film of the present invention is characterized in that an epitaxial or oriented oxide thin film is vapor-phase grown or solid-phase grown on the oxide buffer layer formed as described above. To do.

In the present invention, the single crystal semiconductor substrate may be a single semiconductor such as Si, Ge, diamond or III-.
VAs compound semiconductors such as AlAs, AlSb, Al
P, GaAs, GaSb, InP, InAs, InS
b, AlGaP, AlInP, AlGaAs, AlIn
As, AlAsSb, GaInAs, GaInSb, G
aAsSb, InAsSb, II-VI based compound semiconductors ZnS, ZnSe, ZnTe, CdSe, CdT
e, HgSe, HgTe, CdS (10
Those with a 0) or (111) orientation are used.

The above-mentioned semiconductor single crystal substrate is subjected to passivation treatment before the oxide buffer layer is provided. The passivation treatment can be performed by cleaning the semiconductor single crystal substrate with a solvent, etching with a solution such as sulfuric acid, and then cleaning with deionized water. Alternatively, the semiconductor single crystal substrate can be exposed to an oxygen atmosphere. As a result, an ultrathin oxide film is formed as a passivation layer on the surface of the semiconductor single crystal substrate.
The passivation can also be performed as follows.
For example, although a Sb (antimony) layer is formed on a GaAs single crystal substrate by molecular beam epitaxy (MBE), or is treated with ammonium sulfide or the like, the surface structure is currently under study, but a passivation layer is formed. Can be formed. Also, for example, a Si single crystal substrate is
It is effective to form a passivation layer by H of Si surface dangling bond by treating with an F-based solution. By forming the passivation layer by these passivation treatments, the surface of the semiconductor single crystal substrate is chemically stabilized, and it becomes possible to prevent chemical changes on the surface and changes in the surface structure.

The passivation layer formed by the passivation treatment as described above can be partially sublimated if desired. For example, for a GaAs single crystal substrate, partial sublimation of the passivation layer is RHEED (surface electron diffraction)
Thus, the pattern from the substrate surface can be confirmed by the change from the halo pattern due to the passivation layer to the broad streak pattern (different from the pattern due to the GaAs surface). The degree of partial sublimation is preferably in a state of showing this streak pattern, and the details of the structure of the GaAs surface in this state are different from those of the passivation layer and the GaAs surface, although it is not clear yet.

Next, an epitaxial or oriented oxide buffer layer having a (100) or (111) orientation is formed on the semiconductor single crystal substrate treated as described above. The oxide buffer layer is preferably made of MgAl ₂ O ₄ (spinel) or MgO, and MgO is particularly preferable. These oxide buffer layers are formed by electron beam evaporation, flash evaporation, ion plating, Rf-
Magnetron sputtering, ion beam sputtering, laser ablation, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), plasma CVD, metalorganic chemical vapor deposition (MO)
It can be formed by a vapor phase growth method selected from CVD, etc.

On the epitaxial or oriented MgO buffer layer formed as described above, an oxide ferroelectric thin film can be epitaxially or oriented grown to produce the oxide thin film of the present invention. That is, MgO
On the buffer layer, (100), (001) or (11
1) Epitaxial or orientationally grown ABO ₃ type oxide ferroelectric thin film having orientation. The material forming the oxide ferroelectric thin film is ABO ₃ in which A is Li, K,
It is selected from one or more of Mg, Sr, Ba, La, Pb and Bi, and B is Ti, Zr, Nb and Ta.
A compound selected from any one or more of the above, and specifically, for example, BaTiO ₃ , PbTiO ₃ , Pb
_1-x La _x (Zr _1-y Ti _y ) _{1-x / 4} O ₃ (PZT, P
LT, PLZT), Pb (Mg _1/3 Nb _2/3 ) O ₃ , K
It is selected from ferroelectrics typified by NbO ₃ , LiNbO ₃ , LiTaO _{3 and the} like and substituted derivatives thereof. These oxide ferroelectric thin films include electron beam evaporation, flash evaporation, ion plating, Rf-magnetron
By a vapor deposition method selected from sputtering, ion beam sputtering, laser ablation, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), plasma CVD, metal organic chemical vapor deposition (MOCVD), etc. Alternatively, it can be formed by a solid phase growth method by crystallization of an amorphous thin film obtained at a low temperature using these vapor phase growth methods or an amorphous thin film obtained by a sol-gel method or the like.

In the oxide thin film of the present invention produced as described above, the relationship between the crystal orientations of the oxide ferroelectric thin film, the oxide buffer layer, and the single crystal semiconductor substrate is as follows. 001) // oxide buffer layer (10
0) // single crystal semiconductor substrate (100), oxide ferroelectric thin film (100) // oxide buffer layer (100) // single crystal semiconductor substrate (100), oxide ferroelectric thin film (111) / /
Oxide buffer layer (111) // single crystal semiconductor substrate (10
0) or a ferroelectric thin film (111) // oxide buffer layer (111) // single crystal semiconductor substrate (111).

[0014]

【Example】

Example 1 An epitaxial layer was formed on a GaAs substrate by an electron beam evaporation method using a MgO target. G
aAs substrate (cubic crystal, zinc blend structure, a = 5.
653 angstroms), n-type, (100) ±
A 0.2 °, 15 × 15 mm wafer was used. The surfaces of these substrates were washed with a solvent and then the surfaces were etched with a H ₂ SO ₄ based solution. Next, this substrate was rinsed with deionized water to form an ultrathin film of GaAs oxide on the substrate surface and passivated the surface. Then, spin drying with ethanol was performed under a nitrogen stream. After spin-drying, the substrate was immediately introduced into the deposition chamber and heated to 250 to 450 ° C. to deposit 100 to 1000 Å of MgO film. When analyzed by X-ray diffraction, the formed MgO
It was confirmed that (cubic crystal, NaCl structure, a = 4.213 angstrom) was an epitaxial film having a (100) plane unidirectional orientation under a wide range of conditions. MgO
In order to identify the relationship between the in-plane crystallographic orientation of GaAs and GaAs, X
Line diffraction phi scan was performed. In the cubic system (1
It has an angle of 45 ° to the (00) plane (202)
In the phi scan of the surface, MgO (100)
/ GaAs (100) shows a sharp peak with a rotation period of 90 ° with respect to MgO, and its position is GaAs.
It coincided with the peak position of. From these things, Mg
The crystallographic relationship between O and GaAs has a lattice mismatch of 25.5%.
However, it was found that the relationship between the crystal orientations of MgO and GaAs is MgO (100) // GaAs (100) and the in-plane orientation MgO [001] // GaAs [001]. When observing the interface between the epitaxial MgO and the semiconductor with a high resolution transmission electron microscope, MgO (10
At the 0) -GaAs (100) interface, MgO: GaA =
A two-dimensional superlattice was formed by 4: 3 lattice matching, and no secondary layer or the like was formed at the interface, resulting in a steep interface. Considering 4: 3 lattice matching, MgO: GaA
When s = 4: 3, it becomes 0.7%, and the stress in the film is relaxed despite having a large lattice mismatch, and MgO [00
It is considered that the epitaxial growth of 1] // GaAs [001] was realized.

Example 2 In the same manner as in Example 1, the GaAs surface was passivated and spin-dried on the substrate surface, then the substrate was immediately introduced into the deposition chamber, and the background pressure was set at 580.
The surface passivation layer was partially sublimated by heating at 0 ° C for a short time, and subsequently heated at 450 ° C to form a MgO film of 100 to 1000 angstrom. When analyzed by X-ray diffraction, it was found that the formed MgO was a (111) -plane single orientation film even though the substrate was a (100) -plane.

Comparative Example 1 As a comparative example, a GaAs substrate having a passivated surface was introduced into a deposition chamber and then heated at 600 ° C. at a background pressure to release the passivation layer on the GaAs surface ( Sublimation), and subsequently, MgO film was formed at 350 ° C. In this case, only a polycrystalline thin film of MgO was obtained. Remove the GaAs oxide surface layer,
The reason why only polycrystalline MgO can be obtained with the aAs surface is considered to be that the change in the reconstructed structure of the GaAs surface has a large influence.

Example 3 A 6 × 6 mm n-type GaAs (100) ± 0.2 ° substrate was washed with a solvent and then surface-etched with a H ₂ SO ₄ type solution. Next, this substrate was rinsed with deionized water to form an ultrathin oxide film on the substrate surface, and passivation of the surface was performed. Then, spin drying was performed with ethanol under a nitrogen flow. After spin-drying, the substrate was immediately introduced into the deposition chamber and heated at 600 ° C. at the background pressure to achieve total desorption (sublimation) of the passivation layer on the GaAs surface. Subsequently, 5 × 10 ⁻⁶ to 1 × 10 ⁻⁴ To
By introducing O ₂ of rr and exposing the surface of the GaAs substrate from which the passivation layer has been desorbed to this O ₂ atmosphere, G
The effect of passivation treatment by vapor phase oxidation was examined by covering with an ultra-thin film of aAs oxide. Then immediately 250-450
A MgO film having a thickness of 40 to 400 angstrom was formed at a temperature of ℃. The film formation was performed by an excimer laser deposition method in which the target surface was instantaneously heated by a UV laser pulse for vapor deposition. Laser is XeCl
An excimer laser (wavelength 308 nm) was used. As the target, metallic Mg was used because MgO has no absorption at a wavelength of 308 nm. Since MgO has a high binding energy of 10 eV or more, the film was formed by introducing O ₂ during the film formation, whereby Mg was easily oxidized. When analyzed by X-ray diffraction, the formed MgO becomes a high-quality epitaxial film with a single orientation of the (100) plane, and the crystallographic relationship between MgO and GaAs is MgO (100) // GaAs (100) It was found to be MgO [001] // GaAs [001]. Following the growth of an epitaxial MgO thin film, B
A film of aTiO ₃ was formed. The film formation was performed by an excimer laser deposition method in which the target surface was instantaneously heated by a UV laser pulse for vapor deposition.
The laser is a XeCl excimer laser (wavelength 308n
m) was used. BaTiO ₃ was used as a target. 600-800 ° C, 1 × 10 ^{-4 -1} × 10 ^-2 Tor
BaTiO 3 having a film thickness of 500 to 2000 angstroms grown in situ on the MgO buffer layer under the condition of rO _2.
All ₃ were epitaxially grown. BaTiO identified by X-ray diffraction pattern and Phi scan
The relationship between the crystal orientation of ₃ and MgO / GaAs is BaTiO 3.
₃ (001) // MgO (100) // GaAs (10
0), BaTiO ₃ [010] // MgO [001] // G
It was aAs [001]. The surface of BaTiO ₃ observed by a scanning electron microscope was extremely smooth.
Furthermore, the surface of BaTiO ₃ is examined by atomic force microscopy.
Observing in the range of × 1 μm ² , it was found that it had a smoothness like that of optically polished glass. The BaTiO ₃ film thus formed is expected to lead to good low optical attenuation characteristics as an optical waveguide in terms of surface smoothness. In addition, Cr / 2000 angstrom -BaTiO _3/400 angstrom -M
In the capacitor structure of gO / GaAs, BaTi
When the polarization characteristics of O ₃ are measured, the PE characteristics due to this structure show a hysteresis loop, and BaTiO ₃ has a polarization axis of single crystal GaA as estimated by structural analysis.
It was found to be a ferroelectric phase (tetragonal crystal) oriented perpendicular to the s substrate.

Although the electron beam evaporation and the excimer laser deposition method are used in the above embodiments, the film forming process is not limited to this, and Rf-magnetron sputtering, ion beam sputtering, Flash evaporation, ion plating, molecular beam epitaxy (MBE), ionization cluster-beam epitaxy, chemical vapor deposition (C
VD), metal organic chemical vapor deposition (MOCVD), plasma CVD, and other vapor phase growth methods are similarly effective. Also,
In the above examples, the passivation of GaAs was performed by a thin oxide layer.
Passivation with (antimony) or ammonium sulfide was also effective. The relationship between the crystal orientations of the oxide ferroelectric thin film, the oxide buffer layer, and the single crystal semiconductor substrate obtained in Example 3 is as follows.
Oxide buffer layer (100) // Single crystal semiconductor substrate (10
0), but other crystal orientation relationships include oxide ferroelectric thin film (100) // oxide buffer layer (10).
0) // single crystal semiconductor substrate (100), oxide ferroelectric thin film (111) // oxide buffer layer (111) // single crystal semiconductor substrate (100), or oxide ferroelectric thin film (11)
1) // Oxide buffer layer (111) // single crystal semiconductor substrate (111) can be similarly prepared.

[0019]

According to the method for producing an oxide thin film of the present invention,
Since an oxide buffer layer that assists the epitaxial growth of an oxide ferroelectric thin film and that also functions as an expansion barrier can be easily formed on any single crystal semiconductor, the present invention enables the formation of an oxide buffer layer on a semiconductor single crystal substrate. An epitaxial or oriented oxide ferroelectric thin film can be formed, and a high-performance nonvolatile memory, a capacitor, or a device such as a light modulation device can be manufactured on a semiconductor substrate. Furthermore, according to the present invention, since the orientation of the oxide ferroelectric thin film can be controlled, it is possible to obtain a large remanent polarization value and good optical characteristics. In addition, the refractive index of oxide ferroelectrics is generally smaller than that of semiconductors, but the semiconductor laser light is confined in the ferroelectric thin film optical waveguide by an oxide buffer layer having a smaller refractive index than oxide ferroelectrics. It becomes possible to manufacture the optical modulator on the GaAs semiconductor laser and the optical integrated circuit on the Si semiconductor integrated circuit.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C30B 33/08 9261-4G H01L 21/314 A 21/316 X

Claims (5)

[Claims] 1. A passivation treatment is performed on the surface of a single crystal semiconductor substrate to form a passivation layer made of an ultrathin film containing an element different from an element constituting the semiconductor, and then the surface is epitaxially grown on the surface of the single crystal semiconductor substrate. Alternatively, a method for manufacturing an oxide thin film, which comprises vapor-phase growing an oriented oxide buffer layer. 2. A single crystal semiconductor substrate surface is passivated to form a passivation layer composed of an ultrathin film containing an element different from an element constituting the semiconductor, and then epitaxially formed on the single crystal semiconductor substrate surface. Or an oxide characterized by vapor-depositing an oriented oxide buffer layer and vapor-phase or solid-phase growing an epitaxial or oriented oxide ferroelectric thin film on the formed oxide buffer layer. Method for manufacturing thin film. 3. A passivation treatment is performed on the surface of a single crystal semiconductor substrate to form a passivation layer made of an ultrathin film containing an element different from an element constituting the semiconductor, and the passivation layer is partially formed. After the sublimation, an epitaxial or oriented oxide buffer layer is vapor-phase-grown on the surface of the single crystal semiconductor substrate to prepare an oxide thin film. 4. The method for producing an oxide thin film according to claim 1, wherein the single crystal semiconductor substrate is a GaAs substrate. 5. The method for producing an oxide thin film according to claim 1, wherein the oxide buffer layer is made of MgO.