JP3068901B2 - Thin film preparation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin film having piezoelectricity and dielectric properties for use in devices such as surface acoustic wave devices, piezoelectric actuators, electro-optic devices, and dielectric memories.

[0002]

2. Description of the Related Art Surface acoustic wave devices, piezoelectric actuators,
Pressure used for elements such as electro-optical elements and dielectric memories
As a thin film material having electrical and dielectric properties, ZnO, Al
N, Ta _TwoO_Five, PbTiO_Three, Bi_FourTi_ThreeO₁₂, BaTi
O_Three, SrTiO_Three, PZT [Pb (Ti, Zr) O_Three], Li
NbO_ThreeEtc. are known. These thin film materials are CV
D method, sputtering method, vacuum evaporation method, ion beam evaporation method
Which method is used to form a thin film
Processed. These elements have piezoelectric and dielectric properties
When the orientation direction of the polarization axis in the thin film is
It is important that the axes are aligned,
In some cases, thin films with a high degree of polarization axis orientation have been fabricated.
You.

Here, the orientation direction of the polarization axis is a direction in which the polarization axis of each domain is oriented as a whole, and the degree of orientation is such that the direction of the polarization axis of each domain is in the orientation direction. It is a scale that indicates how much they are complete.
Generally, the orientation direction of the polarization axis is determined by the material of the thin film and the material of the substrate.

As a method of controlling the alignment of the polarization axes in the orientation direction in these thin films and improving the electromechanical coupling coefficient, a method of applying an electric field in the in-plane direction of the substrate during the production of the thin film (Japanese Patent Laid-Open No. 62-81076) ) Has been done. Further, as a method of reversing the orientation direction of the polarization axis, a method of thermally diffusing Ti and a method of performing a heat treatment at a temperature close to the Curie point on a LiNbO ₃ plate are performed (Technical Research of IEICE) Report US86-18).

[0005]

The reversal of the orientation direction of the polarization axis by the method of thermally diffusing Ti and the method of performing heat treatment at a temperature close to the Curie point is limited to LiNbO _{3 because the} material capable of realizing this is limited to LiNbO _3. However, it has been difficult to apply the method to the above-mentioned materials, and no study has been made on the case of forming a thin film. In the conventional method described above, it is generally difficult to control the arrangement of atoms and the orientation direction of the polarization axis, or to reverse the orientation direction.

An object of the present invention is to provide a method for producing a thin film capable of controlling the orientation direction of the polarization axis and realizing reversal of the orientation direction of the polarization axis.

[0007]

According to the present invention, there is provided a thin film forming method for forming a thin film having a polarization axis on a substrate, the method comprising the steps of: using ion beam evaporation; The orientation direction and degree of orientation of the polarization axis in the thin film are controlled by changing the acceleration voltage.

[0008]

According to the present invention, when a thin film having a polarization axis is formed using ion beam evaporation, the orientation direction of the polarization axis is controlled and inverted by changing the ionization current and / or acceleration voltage at this time. It is based on a new finding that it can be done. In the present invention, piezoelectric,
The material is not particularly limited as long as it has dielectric properties and has spontaneous polarization, and the orientation direction of the polarization axis can be inverted. Therefore, in a thin film such as a piezoelectric material, the direction of displacement with respect to the same applied electric field can be arbitrarily changed. Here, ion beam deposition means that some of the evaporated molecules or atoms from the evaporation source are ionized,
This is a method of performing evaporation by applying an acceleration voltage. Generally, ionization is performed by irradiating charged particles to evaporated molecules or atoms, and the current of the charged particles is referred to as ionization current. When ionization is performed by plasma discharge, the current of this plasma discharge can be regarded as ionization current.

Here, in order to explain the function of the present invention, a description will be given of a research process leading to the present invention. First, an experiment in which the orientation direction of the polarization axis is reversed to form a piezoelectric material thin film will be described.

FIG. 1 is a schematic sectional view showing the structure of an example of the ion beam evaporation apparatus used in this experiment. An evaporation source 5 including a crucible and a heating means is provided at the bottom of the vacuum vessel 1 capable of evacuating, and a substrate 4 on which a thin film is formed is placed inside the vacuum vessel 1 so as to face the evaporation source 5. A substrate holder 3 for holding the substrate downward is provided. The substrate holder 3 is conductive, so that the substrate 4 is kept at the same potential as the substrate holder 3. An electron emission source 6 that emits an electron beam for ionizing a part of evaporated molecules or atoms from the evaporation source 5 and an acceleration electrode 7 are provided near the evaporation source 5. The accelerating electrode 7 is generally kept at the same potential as the substrate holder 3. Further, a gas introduction pipe 2 having an open end for introducing gas into the vacuum vessel 1 is provided. The other end of the gas introduction pipe 2 is connected to a gas supply source (not shown). Further, the evaporation source 5 and the substrate holder 3 are respectively connected to both poles of a power supply 8 for applying an acceleration voltage in ion beam evaporation. In FIG. 1, the power source 8 is positive on the evaporation source 5 side and negative on the substrate holder 3 side, but can change the polarity and voltage of positive and negative. In the following description, a positive acceleration voltage means that the evaporation source 5 side is positive with respect to the substrate holder 3, and a negative acceleration voltage is defined as that the evaporation source 5 side is negative. .

The vacuum vessel 1 can be evacuated by an exhaust device (not shown), and the temperature of the substrate 4, the temperature of the evaporation source 5,
The current of the electron beam emitted from the electron emission source 6, that is, the ionization current, and the flow rate of the gas introduced into the vacuum vessel 1 from the gas introduction pipe 2 can be independently controlled by a controller (not shown). Has become.

(Experiment 1) A bimorph-type thin-film cantilever-type displacement element 10 having a five-layer structure as shown in FIG. 2 was manufactured using AlN which is one of the typical piezoelectric materials. This thin-film cantilever-type displacement element 10 is composed of a lower electrode 11 of 0.1 μm in thickness made of a laminated film of Cr / Au, a lower piezoelectric thin film 12 of 0.3 μm in thickness of AlN, and Au on a substrate 4. Middle electrode 1 with a thickness of 0.1 μm
3. Upper piezoelectric thin film 1 made of AlN and having a thickness of 0.3 μm
4. An upper electrode 15 made of Au and having a thickness of 0.1 μm is sequentially laminated, and the substrate 4 under the lower electrode 11 is largely cut away, and the lower electrode 11 is located near one end thereof. Only in contact with the substrate 4. The dimensions of the thin film cantilever type displacement element 10 are 200 μm in length (lateral direction in the drawing) and 50 μm in width (depth direction in the drawing).
μm. Lower electrode 11, middle electrode 13, upper electrode 15
Are formed by ordinary resistance heating evaporation. The lower dielectric thin film 12 and the upper dielectric thin film 14 are formed under the same film forming conditions by ion beam evaporation using the above-described ion beam evaporation apparatus.

Here, the conditions for forming the lower dielectric thin film 12 and the upper dielectric thin film 14 will be described in detail. First, the evaporation source 5 was filled with Al, which is a raw material of a thin film, and the inside of the vacuum vessel 1 was evacuated. After that, the Al in the evaporation source 5 is heated and evaporated, and NH ₃ gas is further supplied from the gas introduction pipe 2 at a flow rate of 1.
While introducing at 0 ml / min and spraying on the surface of the substrate 4, the ionization current is set to 50 mA and the acceleration voltage is set to +0.5 k.
As V, ion beam evaporation was performed. At this time, the temperature of the substrate 4 was 200 ° C. At this time, the substrate holder 3 and the acceleration electrode 7 were grounded.

With respect to the thin-film cantilever type displacement element 10 thus manufactured, the lower electrode 15 and the upper electrode 17
Were short-circuited to ground and a voltage of +2 V was applied to the middle electrode 16, and the tip 20 of the element was displaced upward by 1 μm. Similarly, when a voltage of −2 V was applied, the displacement was 1 μm downward.

(Experiment 2) The ionization current was set to 100 under the conditions for forming the lower dielectric thin film 12 and the upper dielectric thin film 14.
A thin-film cantilever-type displacement element 10 was produced in the same manner as described above except that the acceleration voltage was set to -0.5 kV by reversing the polarity. This thin film cantilever type displacement element 1
When the same +2 V voltage as in Experiment 1 was applied to 0, a downward displacement of 1 μm was obtained.

From the results of Experiments 1 and 2, it was found that by changing the ionization current and the accelerating voltage, a thin film having the same piezoelectricity was formed in which the polarization axes were oriented in opposite directions.

That is, according to the present invention, when the above-described apparatus shown in FIG. 1 is used, the source material of the thin film is evaporated from the evaporation source 5 and the electron emission source 6 emits the electron beam from the source material vapor. To irradiate a part of it,
In addition, the above-mentioned ions are accelerated by a potential difference (acceleration voltage) between the substrate holder 3 and the evaporation source 5 to perform vapor deposition on the substrate surface to produce a thin film. By changing the orientation, the alignment of the polarization axes, that is, the degree of orientation is controlled, the orientation direction of the polarization axis is controlled, and the orientation direction of the polarization axis is reversed to produce a thin film.

If the thin film material to be manufactured contains a plurality of constituent elements, the ion beam
A plurality of ion gun units including an evaporation source, an electron emission source, an acceleration electrode, and a power supply for acceleration may be provided and used.

As the thin film material to which the present invention can be applied,
In addition to the aforementioned AlN, ZnO, Ta_TwoO_Five, PbTiO_Three, B
i_FourTi_ThreeO₁₂, BaTiO_Three, SrTiO_Three, PZT, LiN
bO _ThreeIt has spontaneous polarization, such as piezoelectric and dielectric properties
It is not particularly limited as long as it is a material. Thin film material
The material to be evaporated from the evaporation source as
Simple substance of the metal element constituting the film material or its metal element
Melting point, vapor pressure, evaporation source crucible, etc.
An appropriate one may be selected in consideration of the reactivity with the like.

When a thin film material containing a plurality of metal elements, such as PbTiO ₃ , is used, it is preferable to use a plurality of ion gun sections provided by the number of the metal elements. Alternatively, a metal element alone or a compound of the metal element constituting the thin film material may be mixed at an appropriate ratio and deposited from a single ion gun portion. As a heating method in the evaporation source, resistance heating, electron beam heating, heating by a laser beam, or the like can be used.

The ionization method in the present invention includes:
In addition to the electron beam irradiation as described above, there is a method using plasma discharge, and the method is not particularly limited. FIG.
The method of applying a voltage to the substrate holder, the substrate, the evaporation source, and the acceleration electrode when performing ion beam evaporation using the apparatus as shown in (1) is generally performed by grounding the substrate holder, the substrate, and the acceleration electrode. Is applied, but the method is not particularly limited to this.

The ionization current and the accelerating voltage in the present invention vary depending on various conditions such as the kind of the raw material to be evaporated from the evaporation source, its evaporation rate, and the substrate temperature, but are preferably selected from the following ranges.

Ionization current: 0 to 500 mA Acceleration voltage: -10 kV to +10 kV If both the ionization current and the acceleration voltage are too large, the energy and density of ions become too large, and so-called ion etching is performed. It will be the same. As a result, the crystallinity of the thin film is reduced, and deposition of the thin film does not occur. For this reason, the ionization current and the acceleration voltage are set to such a value that a necessary crystalline thin film is obtained within a range where such an undesirable phenomenon does not occur.

The orientation of the polarization axis is controlled mainly by changing the value of the acceleration voltage. Further, it can be performed by reversing the polarity of the acceleration voltage. At this time, since the crystallinity of the thin film may change, the change in the crystallinity is compensated by changing the ionization current.

The gas to be introduced into the vacuum vessel of the ion beam evaporation apparatus is appropriately selected depending on the thin film material to be produced. That is, when an oxide-based thin film such as ZnO or PbTiO ₃ is formed, O _{2 or} O ₃ , N ₂ O, NO ₂ ,
Oxygen radicals and the like are used, and N ₂ or NH ₃ is used for a nitride-based thin film such as AlN. Further, plasma or ions obtained by ionizing these gases may be introduced.

[0026]

EXAMPLES Next, examples of the method for producing a thin film of the present invention will be described with specific numerical values.

Example 1 A thin-film cantilever-type displacement element using ZnO, which is one of the typical piezoelectric materials, was manufactured using the ion beam evaporation apparatus described above with reference to FIG. The vacuum vessel 1 can be evacuated to about 2 × 10 ⁻⁷ Torr by an exhaust device (not shown).

This thin film cantilever type displacement element 10
It is a bimorph type having a five-layer structure, which is almost the same as that produced in Experiments 1 and 2 described above, and the configuration is shown in FIG. The thin-film cantilever-type displacement element 10 has a Cr / Si
A lower electrode 11 made of a multilayer film of Au and having a thickness of 0.1 μm;
A 0.3 μm-thick lower piezoelectric thin film 12 made of ZnO;
A middle electrode 13 made of Au having a thickness of 0.1 μm, an upper piezoelectric thin film 14 made of ZnO having a thickness of 0.3 μm, and an upper electrode 15 made of Au having a thickness of 0.1 μm are sequentially laminated. The lower electrode 11, the middle electrode 13, and the upper electrode 15
Each is formed by normal resistance heating evaporation. The lower dielectric thin film 12 and the upper dielectric thin film 14 are formed under the same film forming conditions by ion beam evaporation using the ion beam evaporation apparatus shown in FIG. The thin-film cantilever-type displacement element 10 was formed by forming each of these layers on the substrate 4 and then patterning it into a cantilever type. For patterning, a photoresist was used, dry etching was performed using a CF ₄ gas by a reactive ion etching apparatus, then the resist was peeled off, and the anisotropic etching of the substrate 4 was performed using an aqueous potassium hydroxide solution. It was completed as The dimensions of the thin film cantilever type displacement element 10 were 200 μm in length (horizontal direction in the drawing) and 50 μm in width (depth direction in the drawing).

Next, the relationship between the film forming conditions of the lower dielectric thin film 12 and the upper dielectric thin film 14 and the displacement characteristics of the thin film cantilever type displacement element 10 will be described in detail. Each of these dielectric thin films 12 and 14 is first filled with Zn, which is a raw material of the thin film, in the evaporation source 5 and the inside of the vacuum vessel 1 is evacuated. Then, the Zn in the evaporation source 5 is heated to evaporate. Introductory pipe 2
The O ₂ gas was introduced into the vacuum vessel 1 at a flow rate of 12 ml / min, and was sprayed onto the surface of the substrate 4 while changing the ionization current and the acceleration voltage to form a film. The substrate temperature at this time was 200 ° C.

First, an element was manufactured under the above film forming conditions, with an ionization current of 50 mA, an acceleration voltage of +0.5 kV, and a thickness of each of the dielectric thin films 12 and 14 of 0.3 μm. When the lower electrode 11 and the upper electrode 15 of the fabricated cantilever-type displacement element 10 were short-circuited and grounded, and a voltage of +2 V was applied to the middle electrode 13, the tip 20 of the element was displaced upward by 2 μm. Similarly, when a voltage of −2 V was applied, the displacement was 2 μm downward.

On the other hand, an ionization current of 5
0 mA, the acceleration voltage is -0.5 kV by reversing the polarity,
When a device was manufactured with a thickness of 0.3 μm, the lower electrode 11 and the upper electrode 15 of the manufactured cantilever type displacement device 10 were short-circuited and grounded, and a voltage of +2 V was applied to the middle electrode 13. The tip 20 is 1.5 μm downward.
Displaced. Similarly, when a voltage of -2 V is applied,
It was displaced 1.5 μm upward. Since the direction of displacement was reversed in this way, it was confirmed that the orientation direction of the polarization axis of each dielectric thin film was reversed. However, the application of the accelerating voltage during the film formation in the opposite direction reduced the crystal orientation inside the dielectric thin film, disordered the alignment of the polarization axes, reduced the electromechanical coupling coefficient, and reduced the displacement. For this reason, when the ionization current was increased to 100 mA to form each of the dielectric thin films 12 and 14, a displacement of 2 μm was also obtained downward with respect to the same +2 V applied voltage, the polarization direction was reversed, and the same piezoelectric property was obtained. It was confirmed that a thin film having the following was formed.

As described above, by controlling the ionization current and the accelerating voltage, it is possible to control the alignment of the polarization axes of the thin film, control the orientation direction of the polarization axes, and further invert the orientation direction to produce the thin film. did it.

(Embodiment 2) In Embodiment 1, ZnO was used for the lower dielectric thin film 12 and the upper dielectric thin film 14. Here, a thin film having the structure shown in FIG. 2 was formed using PbTiO ₃ which is a ferroelectric. A cantilever displacement element 10 was manufactured. Note that a Ti / Pt laminated film was used for the lower electrode 11, and a Pt film was used for the middle electrode 13 and the upper electrode 15. Since PbTiO ₃ contains two kinds of metal elements, each of the dielectric thin films 1 is formed by using an ion beam deposition apparatus having two ion gun sections each including an evaporation source, an electron emission source, an acceleration electrode, and a power supply for acceleration.
2,14 were formed.

First, the configuration of the ion beam evaporation apparatus will be described with reference to FIG. At the bottom of the evacuable vacuum vessel 1 ', two evaporation sources 5 including a crucible and a heating means are provided, and a conductive material is provided inside the vacuum vessel 1' so as to face both the evaporation sources 5. Substrate holder 3 is provided. The substrate holder 3 includes a substrate 4 on which a thin film is formed.
Is held downward, and the substrate 4 is kept at the same potential as the substrate holder 3. An electron emission source 6 for emitting an electron beam for ionizing a part of the evaporated molecules or atoms from the evaporation source 5 and an acceleration electrode 7 are provided near each evaporation source 5. The accelerating electrode 7 is generally kept at the same potential as the substrate holder 3. Further, a gas introduction pipe 2 having an open end for introducing gas into the vacuum vessel 1 'is provided, and the other end of the gas introduction pipe 2 is connected to a gas supply source (not shown). Further, each evaporation source 5 is connected to one end of each power supply 8 for applying an acceleration voltage in ion beam evaporation, and the other end of each power supply 8 is connected to the substrate holder 3. The polarity and voltage of each power supply 8 can be set arbitrarily. Further, the vacuum vessel 1 'can be evacuated to about 2 × 10 ^-7 Torr by an exhaust device (not shown).
, The ionization current in each electron emission source 6, and the gas flow rate from the gas introduction tube 2 can be independently controlled by a control device (not shown).

Next, a method of manufacturing the thin-film cantilever type displacement element 10 of this embodiment will be described. First, a lower electrode 11 having a thickness of 0.1 μm is formed on a substrate 4 made of Si by ordinary RF sputtering, and then the lower dielectric thin film 1 is formed by ion beam evaporation using the apparatus shown in FIG.
2, a middle electrode 13 having a thickness of 0.1 μm is formed by ordinary RF sputtering, and an upper dielectric thin film 14 is formed by ion beam evaporation using the apparatus shown in FIG.
Finally, the film thickness is 0.1 μm by ordinary RF sputtering.
The upper electrode 15 having a thickness of m was formed to form a five-layer structure, and then processed into a cantilever type element in the same manner as in Example 1 described above. The film forming conditions for the dielectric thin films 12 and 14 are the same. The dimensions of the thin film cantilever type displacement element 10 are 200 μm in length (lateral direction in the drawing) and 50 μm in width (depth direction in the drawing).
μm.

Next, the relationship between the film forming conditions of the lower dielectric thin film 12 and the upper dielectric thin film 14 and the displacement characteristics of the thin film cantilever type displacement element 10 will be described in detail. Each of these dielectric thin films 12 and 14 is first supplied to one evaporation source 5 of the apparatus shown in FIG.
And the other evaporation source 5 is filled with Ti, which is another raw material, and the inside of the vacuum vessel 1 'is evacuated. Subsequently, each evaporation source 5 is heated to evaporate each raw material. Further, an O ₂ gas was introduced into the vacuum vessel 1 ′ at a flow rate of 12 ml / min from the gas introduction pipe 2 and sprayed onto the surface of the substrate 4 while changing the ionization current and the acceleration voltage to form a film. At this time, the substrate temperature was set to 400 ° C.

First, under the above film forming conditions, the ionization currents for PbO and Ti were both set to 50 mA.
The acceleration voltage was set to +0.5 kV, and each dielectric thin film 1
The thin film cantilever type displacement element 10 was manufactured by setting the film thicknesses of 2, 14 to 0.3 μm. Lower electrode 11 of fabricated device
And the upper electrode 15 are short-circuited to ground, and +5 is applied to the middle electrode 13.
When a voltage of V was applied, the tip 20 of the element was displaced upward by 7 μm. Similarly, when a voltage of −5 V was applied, the displacement was 7 μm downward.

On the other hand, under the above film forming conditions, the ionization currents for PbO and Ti were both 50 mA,
The acceleration voltage is reversed in polarity to −0.5 kV, the film thickness is set to 0.3 μm to produce a thin-film cantilever-type displacement element 10, the lower electrode 11 and the upper electrode 15 of the produced element are short-circuited and grounded, When a voltage of +5 V was applied to the middle electrode 13, the tip 20 of the element was displaced downward by 4 μm. Similarly, when a voltage of -5 V is applied, 4 μm
Displaced.

As described above, the direction of displacement was reversed in the same manner as in Example 1, and it was confirmed that the orientation direction of the polarization axis of each dielectric thin film was reversed. As a result, the orientation of the crystals in each of the dielectric thin films 12 and 14 was reduced, the arrangement of the polarization axes was disturbed, the electromechanical coupling coefficient was reduced, and the displacement was reduced. Therefore, when the ionization current was increased and the dielectric thin films 12 and 14 were formed with PbO and Ti both set to 100 mA, a displacement of 7 μm was also obtained for the same applied voltage of +5 V, and the polarization direction was reversed. As a result, it was confirmed that a thin film having the same piezoelectricity was produced. In addition, these dielectric thin films are made of PbT
heated to 490 ° C. or higher, the Curie temperature of iO ₃ ,
When the current generated by the disappearance of the polarization was measured, it was confirmed that a current was generated in the reverse direction and the reversal of the polarization occurred as in the measurement of the piezoelectricity.

As described above, even when PbTiO ₃ , which is a ferroelectric, is used as the thin film material, the alignment of the polarization axes of the thin film to be formed is controlled by controlling the ionization current and the acceleration voltage, and the orientation of the polarization axes is controlled. The direction was controlled, and the orientation direction was further reversed, whereby a thin film could be produced.

[0041]

As described above, according to the present invention, the orientation direction of the polarization axis can be controlled and reversed by using ion beam evaporation and changing the ionization current and / or acceleration voltage at this time. There is an effect that an element having various functions using a thin film having piezoelectricity and dielectric properties can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of an example of an ion beam evaporation apparatus.

FIG. 2 is a schematic sectional view showing a configuration of a thin-film cantilever displacement element.

FIG. 3 is a schematic sectional view showing the configuration of another example of the ion beam evaporation apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1 'Vacuum container 2 Gas introduction tube 3 Substrate holder 4 Substrate 5 Evaporation source 6 Electron emission source 7 Acceleration electrode 8 Power supply 10 Thin film cantilever type displacement element 11 Lower electrode 12 Lower piezoelectric thin film 13 Middle electrode 14 Upper piezoelectric thin film 15 Upper electrode

────────────────────────────────────────────────── (5) References JP-A-53-114786 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 41/24 C23C 14/00 H01L 21 / 203

Claims (2)

(57) [Claims] 1. A method for forming a thin film having a polarization axis on a substrate, comprising the steps of: using ion beam deposition, changing an ionization current and / or an acceleration voltage during the ion beam deposition to form a thin film on the substrate. A method for producing a thin film, comprising controlling an orientation direction and a degree of orientation of the polarization axis. 2. A method for producing a thin film having a polarization axis on a substrate, comprising the steps of: using ion beam deposition, changing an ionization current and / or an acceleration voltage during the ion beam deposition to form a thin film on the substrate. A method for producing a thin film, comprising: inverting the orientation direction of the polarization axis.