JPH04279069A - Ferroelectric thin film member - Google Patents

Abstract

PURPOSE:To provide a high-performance dielectric thin film device which can conjugate with Si or GeIC by forming a highly crystallized dielectric film in the form of a substrate. CONSTITUTION:In this ferroelectric thin film member having a ferroelectric oxide layer containing Pb atoms on a single crystal substrate containing at least one of Si atoms and Ge atoms, an intermediate layer which is composed of a cubic crystal and the deviation of the lattice constant of which is <=15% of the lattice constant of the single crystal substrate is provided by one or more layers between the substrate and ferroelectric oxide layer.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to optical switches, optical modulators, highly integrated memories, infrared sensors, ultrasonic sensors, microactuators, electroluminescent devices, and the like.

0002

[Prior Art] Pb and Ti in PbTiO3 and PbTiO3 are partially replaced with La and Zr, respectively (Pb, L
a) TiO3, Pb(Zr, Ti)O3, (Pb, La
) (Zr, Ti)O3 and other perovskite structure oxide dielectric materials containing Pb have the following excellent properties. (1) Depending on the composition ratio, it can be a paraelectric or antiferroelectric material in addition to ferroelectric. (2) Large dielectric constant. (3) Excellent piezoelectric and pyroelectric properties. (4) It has high first- and second-order electro-optical effects and memory effects corresponding to its dielectric properties. Besides these characteristics,
Translucency is also good. Various devices using thin films of this material have been proposed. Waveguide optical switches and optical modulators that utilize electro-optic effects, ultrasonic sensors that utilize piezoelectricity, infrared sensors that utilize pyroelectricity, and nonvolatile memories that utilize ferroelectricity have been reported. Furthermore, by utilizing the high dielectric constant of this material, it can be used as an insulating film for electroluminescent devices to lower the driving voltage of the device, and it can be used as a capacitor insulating film for dynamic RAM to reduce the area of cells. Attempts are being made to measure. By growing this perovskite structure dielectric material on a single-crystal substrate, the film becomes single-crystalline or highly oriented, resulting in improved crystallinity. Each of the above-mentioned properties of this dielectric material has crystallographic anisotropy, and as the crystallinity of the film is increased, the anisotropy of each of the above-mentioned properties appears more prominently, and if the plane orientation is selected, the properties become larger. can be extracted. In addition, increasing crystallinity reduces light scattering by grain boundaries and improves translucency. With this aim, films of this high dielectric constant material with good crystallinity have been formed on various single crystals. However, S
There is no example of directly growing this dielectric film with good crystallinity on an i or Ge single crystal substrate. The reason for this is that during the growth process of this oxide dielectric film, oxygen, which is a constituent element of the film, is
eThe surface is oxidized to form amorphous SiO2, GeO2 on the surface.
This is thought to be because the formation of a layer blocks the influence from the Si and Ge single crystal substrates during dielectric film growth.

[0003] Therefore, it is necessary to provide an epitaxially grown intermediate layer on the Si or Ge single crystal substrate. Examples using an intermediate layer include an example using a MgAl2O4 layer on a Si substrate (Japanese Patent Application Laid-Open No. 62-39825, Japanese Patent Application Laid-open No. 63-551).
98) and an example using SrF2 and CaF2 layers on a Si substrate. However, the growth temperature of the MgAl2O4 intermediate layer is 9
There are many limitations in the device manufacturing process due to harsh process conditions such as the high temperature of 50° C. and the use of HCl gas as the main reaction gas. CaF2, Sr
In the case of F2, considering the lattice matching with these ferroelectric materials, the single crystal substrate is preferably a (100) oriented plane for both Si and Ge. However, CaF2 does not grow epitaxially in the Si (100) orientation. SrF2 is Si(100)
Although it grows in the same direction, it has a large difference in lattice constant compared to Si,
This distortion is unfavorable in the production of ferroelectric materials. For these reasons, conventional growth methods have not been able to produce good single-crystal ferroelectric films that can be applied to devices.

0004

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a highly crystalline structure on a Si, Ge single crystal substrate that is inexpensive and allows the use of mature semiconductor integrated circuit technology in device manufacturing. An object of the present invention is to provide a high-performance dielectric thin film device that can be combined with Si, Ge, or Si1-XGeXIC by making it possible to form a dielectric film of.

[0005]

[Means for Solving the Problems] The structure of the present invention for solving the above problems is a thin film ferroelectric member as described in the claims. The details of this thin film ferroelectric member will be explained below. The substrate for the ferroelectric member is preferably a material containing at least one type of Si atoms or Ge atoms, ie, Si, SiGe, Ge, or the like. When attempting to grow a single crystal of Pb-based oxide directly on this material, Si, SiGe, Ge, etc. are very easily oxidized, and the crystal system between these layers is cubic and the lattice constant is close to that of these substrate materials. It is necessary to provide an intermediate layer whose surface is unlikely to become amorphous. If the difference between the lattice constant of the intermediate layer and the lattice constant of the single crystal substrate is larger than 15% of the lattice constant of the single crystal substrate, the intermediate layer becomes a polycrystalline substance, and the Pb-based oxide layer deposited on it becomes polycrystalline. It cannot be epitaxially grown.

[0006] This intermediate layer is made of a material containing Zn atoms, such as ZnS, ZnSe, Zn(S, Se), ZnM
nSe, materials containing Ga atoms, GaP, AlGaAs, and other materials such as InP, AlAs, AlP, CaS, C
Examples include aSe, SrS, etc. Further, when other devices are manufactured on the substrate material, if this intermediate layer is required to be an insulator, it is preferable that the intermediate layer contains F atoms. For example, CaF2, SrF2, BaF2, (Ca, Sr)F2
, (Ca,Ba)F2, (SrBa)F2, etc. However, since these layers are difficult to align on Si or Ge (100), it is necessary to have a multilayer structure. When creating a multilayer structure, consider matching with the substrate material and adjust the lattice constant,
It becomes possible to separate functions such as ease of orientation and coefficient of thermal expansion. The thickness of these intermediate layers is 10 Å to 2 Å in the case of a single layer.
000 Å, preferably 30 Å to 1000 Å. In the case of a multilayer structure, when using quantum effects, the thickness is 10 Å to 20 Å.
The thickness is preferably 0 Å, preferably 20 Å to 100 Å. In addition, when used as a functional separation layer, each layer has a thickness of 10 Å to 200 Å.
The thickness is preferably 0 Å, preferably 20 Å to 1000 Å. The manufacturing method of this intermediate layer is MBE method, ALE method, EB evaporation method, MO
CVD method, sputtering method, thermal CVD method, plasma C
Examples include the VD method and the MOCVD method.

Next, an oxide containing Pb atoms that satisfies the main functions of this structure is estimated. This oxide is PbT
iO3, (Pb, La)TiO3, Pb(Zn, Ti)
O3, (Pb, La) (Zn, Ti) O3, and these layers are produced in a single layer or multilayer structure depending on the purpose of use. The thickness of this layer is 0.1 μm to 20 μm in the case of a single layer.
The thickness is preferably 0.2 μm to 15 μm. When forming multiple layers of these layers, the thickness is preferably 10 Å to 200 Å, preferably 20 Å to 1
00 Å is good. If 100 to 5000 layers of this type are formed, it can be applied as a quantum effect device. It is also possible to separate these layers functionally by utilizing piezoelectricity, ferroelectricity, etc., and to make them multilayered. In this case, the thickness of one layer is 10
The thickness is preferably 0 Å to 2 μm. The fabrication method for these layers is MBE
method, ALE method, EB evaporation method, MO-CVD method, sputtering method, thermal CVD method, laser evaporation method, plasma CV
Examples include method D. FIG. 1 shows the basic configuration of the present invention, in which an intermediate layer 2 and a ferroelectric film 3 are sequentially formed on a single crystal substrate 1. In the previous examples, Si,
An intermediate layer is provided on the SiGe, Ge substrate, and Pb is placed on top of the intermediate layer.
Although it has been explained that an oxide layer containing Pb is provided, the intermediate layer and Pb
An oxide buffer layer made of a single crystal oxide is provided between the oxide layers containing single crystal oxide for the purpose of improving the bonding properties of these layers or for the purpose of further enhancing the function of the oxide ferroelectric film. These oxide buffer layers are not limited by the name of the material, but the arrangement of four atoms of at least one element among the constituent metal elements within at least one crystal plane of the crystal unit cell is
It forms a rectangle with a side length of 5.1 to 6.1 Å (
Matching condition A) or square shape in the range of 3.5 to 4.8 Å (matching condition B), and 4 Å in at least one crystal plane
The arrangement of oxygen atoms forms a rectangle with a side length of 3.5 to 4.8 Å (matching condition C), and a side length of 2.5 Å.
It is an oxide having a rectangular shape in the range of 5 to 3.4 Å (matching condition D). Matching conditions A and B are conditions for epitaxial growth of an oxide buffer layer on the underlying cubic intermediate layer, and matching conditions C and D are for growing an oxide ferroelectric layer containing Pb on the oxide buffer layer. This is a condition for epitaxial growth. In other words, the oxide buffer layers are AC, AD, B
It is made of a material having a crystal structure that satisfies either the combination of C and BD. Examples include C-ZrO2, ThO2 (matching condition ABD), γ-Al2O3, SrO (matching condition ABC
), MgO (matching condition BCD), MgAl2O4 (matching condition AD), SrTiO3, BaTiO3 (matching condition B
D) etc.

When producing these intermediate layers on a single crystal substrate containing Si and Ge, if oxides are formed as described in the section of the problem to be solved by the invention, SiO2 and GeO2 are formed on the Si and Ge surfaces. is formed. Therefore, Z
nS, ZnSe, Zn(S, Se), ZnMnSe, G
It is necessary to form aP, AlGaAs, InP, AlAs, AlP, etc. When Si and Ge substrates are left in the atmosphere, oxides are formed on their surfaces, so it is necessary to remove these oxides when forming these intermediate layers. There are roughly four types of methods for removing these oxides. First, a method of evaporating SiO2 with heat of 1000°C or higher, using an etching gas such as HCl, H2, etc.
A method of etching by heating to about 000℃,
After removing the oxide on the surface by wet etching etc., the surface is passivated with elements such as F, H, S, etc. and heated to about 700°C in vacuum to remove it. Silicon is evaporated in vacuum and SiO layer is removed. After forming on the surface, 70
Possible methods include evaporating SiO at about 0°C. Among these methods, preferred is the method of heating to about 700°C. When heated to high temperatures, Si or G
If the e-substrate is deformed or devices have been previously fabricated, it is expected that these devices will be destroyed. After performing these oxide removal methods, it is necessary to form an intermediate layer.

[0009]

[Examples] The present invention will be specifically explained below with reference to Examples. Example 1 Oxide is removed from a Si substrate by a wet etching method (RCA cleaning method), and the surface is passivated with H atoms and F atoms by immersing it in 99.99% HF. Several of these substrates are prepared, and one intermediate layer with different lattice constants is formed by vacuum evaporation.
000 Å was formed. The pressure of the vacuum evaporation equipment is 10-9To
rr to form an intermediate layer. Table 1 below shows the middle class.
The materials shown in were used. The lattice constant of the Si substrate is 5.43 Å
The intermediate layers used were BN, GaAs, ZnSe, and Z
nS and InSb were used. After forming these various intermediate layers, a 1 μm thick PbTiO3 thin film was formed by sputtering. Table 1 shows whether or not epitaxial growth can be performed after this thin film is formed and the surface properties. The lattice constant difference was defined by the following equation.

[Equation 1] The definition of surface property is ×: Rmax>5 μm, ○: 0.5 μm
m<Rmax<5 μm, ◎: 0.5 μm>Rmax. As can be seen from Table 1, when the difference between the lattice constant of Si and the lattice constant of the intermediate layer is 19% or more, the Pb-based oxide does not grow epitaxially and the surface properties are poor.

Example 2 When a Pb-based oxide is directly formed on the intermediate layer, the bonding strength of the film may be insufficient. In this case, the oxide buffer layer is formed between the Pb-based oxide and the intermediate layer. It's good to do that. In Example 2, the formation and effects of this oxide will be described. ZnS (100) is formed as an intermediate layer on a single crystal Ge (100) substrate, and γ-Al is deposited on top of this by MBE method.
A 2O3 layer is formed to a thickness of 100 Å. A 1 μm thick Pb(ZrTi)O3 thin film was formed on this γ-Al2O3 layer by sputtering. Due to the formation of the γ-Al2O3 layer, the adhesion of the film is improved by 2 compared to that of directly growing ZnS on the Ge substrate.
It improved by about 0%.

[Table 1]

The Pb-based single crystal thin film described above has sufficient crystallinity or surface properties to be used as a ferroelectric member. Device applications using this member will be described below. Optical devices using this member include optical switches, optical modulators, electroluminescent elements, and the like. Further examples include capacitors for optical integrated memory, infrared sensors, ultrasonic sensors, microactuators, and nonlinear optical elements. The Pb single crystal thin film is formed on a single crystal substrate containing at least one of S and Ge atoms, and a transistor drive circuit using this single crystal substrate directly drives the device applying the ferroelectric material. You can also do that. Furthermore, it is possible to fabricate O-O, O-E, and E-O devices by forming sensors and light-emitting elements on a substrate containing at least one of Si and Ge atoms, and combining them with devices applying the above-mentioned ferroelectric materials. Not even.

[0012] Optical switch elements and electronescence (
The configuration of an applied example will be described using an EL) element as an example. First, we will introduce TIR (Total), which is a type of waveguide switch.
This will be explained using an internal reflection) type switch. ZnS, ZnSe, which is a material with a cubic crystal system and a lattice constant of 5.2 to 5.9 Å, is deposited on a single crystal substrate containing at least one of Si atoms or Ge atoms.
, Zn(S, Se), CaS, CaSe, SrS, Ga
P, AlGaAs, GaAs, InP, SrF2, Ca
One or more intermediate layers of F2 etc. are 10~
Epitaxial growth is performed to a film thickness of 300,000 Å. The film formation method is MBE (Molecular Bezm Ep).
itaxy) method, ALE method (Atomic Layer
Epitaxy) method, electron beam evaporation method, M
OCVD (Metal Organic Chemical
This is carried out by a vapor deposition method, a sputtering method, a thermal CVD method, a plasma CVD method, or the like. Next, some of the Pb atoms and Ti atoms of PbTiO3 and PbTiO3 were replaced with La and Zr, respectively (Pb
, La)TiO3, Pb(Z,Ti)O3, (Pb,L
a) One or more layers of a dielectric film made of a perovskite structure oxide dielectric material containing Pb atoms such as (Zr, Ti)O3 are grown with good crystallinity to a film thickness of 100 to 300,000 Å. The method for forming this dielectric film is MBE method,
ALE method, electron beam evaporation method, MOCVD method,
By sputtering method, thermal CVD method, plasma CVD method, etc. Next, as an electrode layer, Al, Au, Pt, ITO, I
n2O3, SnO2, ZnO, etc. are formed using a MOCVD method, a sputtering method, a plasma CVD method, a thermal CVD method, an electron beam evaporation method, or the like. Note that as the oxide buffer layer, Si/G is used between the intermediate layer and the dielectric film.
e In order to prevent optical loss due to absorption of light in the single crystal substrate or intermediate layer, Z
rO2, Y2O3, La2O3, Al2O3, TiO2
, MgO, SrTiO3, BaTiO3, LiNbO3
, LiTaO3, MgAl2O4, etc. with a thickness of 100 to 300,000 Å, MBE method, AL
It may be provided by the E method, electron beam evaporation method, MOCVD method, sputtering method, thermal CVD method, or plasma CVD method. For the same purpose, SiO2, Ta2O5, Y2O3,
La2O3, Al2O3, TiO2, MgO, SrTi
O3, BaTiO3, LiNbO3, LiTaO3, M
gAl2O4, CaF2, SrF2, BaF2, ZnS
In some cases, an amorphous, polycrystalline, or epitaxially grown film such as the above may be provided with a thickness of 100 to 300,000 Å.

This will be explained using a double insulation structure electroluminescent (EL) element as an example. ZnS, ZnSe, Zn(S, Se), C on Si/Ge single crystal substrate
aS, CaSe, SrS, GaP, AlGaAs, Ga
An intermediate layer made of one or more layers of As or InP is epitaxially grown to a thickness of 10 to 300,000 Å. As a means for epitaxial growth, methods such as MBE method, ALE method, electron beam evaporation method, MOCVD method, sputtering method, thermal CVD method, plasma CVD method, etc. are used alone or in combination. Next, one or more layers of the dielectric film are grown on this intermediate layer to a thickness of 100 to 300,000 Å with good crystallinity. The method for forming this dielectric film is MBE method, ALE method, electron beam evaporation method, sputtering method, MOCVD method, thermal CVD method, plasma CVD method, or the like. A highly crystalline light emitting layer is grown on the dielectric layer. This light emitting layer is made of ZnS, ZnSe, Zn
(S, Se) etc. as a base material and Mn is added as a luminescent center, or a ZnS:Cu system material where Cu is added to the base material, or a rare earth fluoride (TbF3, A material system doped with ErF3, NdF3, SmF3, etc. is used. Further, materials that have SrS as a base material and have Ce, Sm, Tb, Er, Mn, etc. added to the luminescent center, or materials that have CaS as the base material and have Er, etc. added as the luminescent center can also be used as the light emitting layer. This light-emitting layer is not limited to a single layer, and may have a multilayer structure. Furthermore, an upper insulating layer made of the dielectric material, SiO2, S
iON, Si3N4, ZnO, Al2O3, MgO, S
rTiO3, Y2O3, Ta2O5, MgAl2O4,
Amorphous, polycrystalline, or epitaxially grown film of CaF2, SrF2, BaF2, etc. with a thickness of 100 to 300,000 Å
Provided by Film preparation methods include MBE method, ALE method,
Sputtering method, electron beam evaporation method, MOC
By VD method, thermal CVD method, plasma CVD method, etc.

Example 3 As shown in FIG. 2, a TIR type optical switch was fabricated on a Si single crystal substrate 1 using ZnS as an intermediate layer 2. A ZnS intermediate layer 2 was formed to a thickness of 1500 Å on a Si single crystal (100) substrate 1 at a substrate temperature of 500° C. by MBE. Intermediate layer 2 had a zinc blend structure and exhibited good orientation with a plane orientation of (100). Next, (Pb0.84La0.16)(Zr0.5Ti
0.5) A dielectric layer having a composition of 0.96O3 was formed to a thickness of 4000 Å at a substrate temperature of 600° C. by MOCVD. The dielectric layer had a perovskite structure and exhibited good compatibility with the (100) plane orientation. This was processed by ion beam etching to form a ridge-type waveguide having a width of 20 μm, a film thickness difference crossing angle of 2°, and a thickness of 600 Å. Further, a Ta2O5 thin film having a thickness of 2000 Å was formed at the intersection by reactive sputtering as a buffer layer 7 in order to prevent loss of guided light. On top of that, an Al planar electrode 6 for driving is formed by sputtering to create an electrode gap of 1.7 mm in length and 5 μm in width.
It was formed with a thickness of 2000 Å. In the switching operation experiment, a He-Ne laser beam with a wavelength of 0.633 μm was
A P prism was used to enter the waveguide. Switching operation was possible with a drive voltage of 15 V, and the extinction ratio was 1 ldB.

Comparative Example 1 For comparison, in the case of an element having a structure in which the ZnS intermediate layer was omitted from the structure of Example 1, a PLZT film formed directly on a Si single crystal was used.
The dielectric film has a perovskite structure with a plane orientation of (110) (
101) (100) (001) is a mixed polycrystalline substance,
Switching operation was not possible unless a high driving voltage of 25 V was applied, and the extinction ratio was 7 dB, which was insufficient.

Example 4 As shown in FIG. 3, G was deposited on a Si single crystal (100) substrate 1.
An aAs intermediate layer 2 is formed to a thickness of 300 Å at a substrate temperature of 500° C. using the MBE method. The membrane has a sink blend structure (1
00). Next, PbTiO3 dielectric layer 3
Using the sputtering method, the film thickness was 3000°C at a substrate temperature of 530°C.
A was formed. The dielectric layer 3 has a perovskite structure and has a (001) plane orientation. Next, by MOCVD method, Zn
S:Mn (Mn0.5 at%) light emitting layer 4 at substrate temperature 45
A film with a thickness of 3000 Å is formed at 0°C. The light emitting layer 4 has a zinc blend structure and a (100) plane orientation. Furthermore, Si3N
4 The upper insulating layer 5 is heated to the substrate temperature by plasma CVD method.
A film thickness of 3000 Å was formed at 50°C. This upper insulating layer 5 is an amorphous film. Finally, an ITO transparent conductive film 6 was formed to a thickness of 2000 Å by sputtering at a substrate temperature of 250°C. ITO, which is a transparent electrode, in the EL device produced by the above method
An alternating current voltage with a frequency of 3 KHz was applied between the substrate and the Si single crystal substrate, and the state of light emission was observed from the ITO side. This E
The light emission starting voltage of the L element was 130V, and a light emission brightness of 5000 cd/m2 was obtained under the condition of applying 150V.

For comparison, as shown in FIG. 4, an element was fabricated from the element fabrication process of Example 2, except that the GaAs intermediate layer was omitted. PbTiO deposited directly on Si single crystal 1
3 Film 3 exhibited (110) (101) (100) (001) orientation and was polycrystalline. The next ZnS:Mn light-emitting layer 4 also had a zinc blend structure and was a polycrystalline material with (220) and (331) orientations. In a light emission experiment under the same conditions as Example 3, the light emission starting voltage of this comparative example was 150V, and even around the breakdown voltage of 300V, it was 3500V.
cd/m2. Comparing the results of Example 4 and Comparative Example 1, Example 4 has a higher maximum efficiency and a lower luminescence starting voltage. The first reason for the high luminance is that
This is thought to be because the crystallinity of the light-emitting layer of Example 4 was better than that of Comparative Example 1. And due to the effect of the intermediate layer of the present invention,
This is thought to be because a PbTiO3 film with good crystallinity was obtained, so a ZnS:M light-emitting layer with good crystallinity was grown. In the case of Example 4, the first reason for the low emission starting voltage is P
This is thought to be because the driving voltage was efficiently applied to the light emitting layer because the bTiO3 film was oriented in the (001) plane, which provided a high dielectric constant.

[0018]

[Effects of the Invention] As explained above, since the dielectric film is grown with good crystallinity on a single crystal substrate via an intermediate layer, the characteristics of this dielectric film can be utilized to the maximum. It is possible to fabricate a device with Furthermore, even when films of other materials are laminated on this dielectric, they can be laminated with good crystallinity, and a multilayer high-performance element can be produced. Furthermore, the above-mentioned elements are inexpensive, high quality, and integrated circuit process technology is highly advanced.
By using i, Ge, or Si1-XGe single crystal as a substrate, it becomes possible to combine a thin film functional device using the dielectric film with an electronic device or a photodetector using the single crystal substrate.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the basic configuration of the ferroelectric member of the present invention,

FIG. 2 is an explanatory diagram showing the configuration of the optical switch of Example 3,

[Fig. 3] An explanatory diagram showing the configuration of the EL element of Example 4,

FIG. 4 is an explanatory diagram showing the configuration of an EL element of Comparative Example 1.

[Explanation of symbols]

1 Single crystal substrate 2 Middle class 3 Ferroelectric film 4 Luminescent layer 5 Upper insulating layer 6 Transparent electrode layer 7 Buffer layer

Claims (2)

[Claims] Claim 1: A thin film ferroelectric member having an oxide ferroelectric layer containing Pb atoms on a single crystal substrate containing at least one of Si atoms or Ge atoms, wherein the substrate and the oxide ferroelectric layer are bonded together. A thin film ferroelectric member characterized in that it has one or more intermediate layers having a cubic crystal system and a lattice constant deviation of 15% or less of the lattice constant of a single crystal substrate. 2. The thin film ferroelectric member according to claim 1, further comprising an oxide buffer layer between the intermediate layer and the oxide ferroelectric layer containing Pb atoms.