JP2018081975A - Membrane structure and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film structure capable of increasing the piezoelectric constant of a piezoelectric film in a film structure having a conductive film formed on a silicon substrate and a piezoelectric film formed on the conductive film. A method for manufacturing a film structure includes a step (b) of forming a film containing zirconium on a substrate 11 as a silicon substrate, and a step (b) containing zirconium oxide epitaxially grown on the substrate 11 after the step (b). It has the step (c) of forming the alignment film 12b. Further, the method for producing the film structure includes a step (d) of forming a conductive film 13 containing platinum epitaxially grown on the alignment film 12b and a step (e) of forming an epitaxially grown piezoelectric film 15 on the conductive film 13. And have. [Selection diagram] Fig. 1

Description

  The present invention relates to a membrane structure and a manufacturing method thereof.

As a film structure having a substrate, a conductive film formed on the substrate, and a piezoelectric film formed on the conductive film, the substrate, a conductive film containing platinum formed on the substrate, and the conductive film And a piezoelectric film containing lead zirconate titanate (PZT), that is, Pb (Zr _1-x Ti _x ) O ₃ (0 <x <1), is known. A piezoelectric element is formed by processing such a film structure. A silicon substrate can be used as a substrate included in the film structure.

In JP-A-2015-154015 (Patent Document 1), in a ferroelectric ceramic, a ZrO ₂ film oriented in (200), a Pt film formed on the ZrO ₂ film and oriented in (200), A technology including a piezoelectric film formed on a Pt film is disclosed.

Japanese Patent Laid-Open No. 2015-154015

When a zirconium oxide (ZrO ₂ ) film is directly formed on a silicon substrate, the crystallinity of the formed ZrO ₂ film is lowered, and the ZrO ₂ film may not be epitaxially grown satisfactorily. In such a case, the conductive film cannot be favorably epitaxially grown on the ZrO ₂ film, and the piezoelectric film cannot be favorably epitaxially grown on the conductive film. In a piezoelectric film including PZT, for example, when an electric field is applied along a direction parallel to the polarization direction or a direction having a certain angle with the polarization direction, the piezoelectric constant is large. Therefore, if the piezoelectric film is not epitaxially grown well, the polarization direction is not uniform throughout the piezoelectric film, so that the piezoelectric constant of the piezoelectric film cannot be increased, and the characteristics of the piezoelectric element deteriorate.

  The present invention has been made to solve the above-described problems of the prior art, and has a film structure including a conductive film formed on a silicon substrate and a piezoelectric film formed on the conductive film. An object of the present invention is to provide a film structure that can increase the piezoelectric constant of the piezoelectric film.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  The manufacturing method of the film structure as one aspect of the present invention includes a step (a) of preparing a silicon substrate, a step (b) of forming a first film containing zirconium on the silicon substrate, and a step (b). And (c) forming a second film containing zirconium oxide epitaxially grown on the silicon substrate. The method for manufacturing a film structure includes a step (d) of forming a first conductive film containing platinum epitaxially grown on the second film, and a step (e) of forming a piezoelectric film epitaxially grown on the first conductive film. And having.

  As another aspect, the silicon substrate may have a main surface made of a (100) plane. In the step (c), a second film is formed by epitaxial growth on the main surface and having a cubic crystal structure and containing (100) oriented zirconium oxide. In the step (d), a cubic crystal is formed. A first conductive film having platinum and containing (100) -oriented platinum may be formed.

  As another embodiment, in the step (b), the first film may be formed by a vapor deposition method, and in the step (c), the second film may be formed by a vapor deposition method.

  As another aspect, in the step (b), a first film having a thickness of 5 to 10 nm may be formed at a temperature of 650 to 700 ° C.

  As another aspect, in the step (c), the second film may be formed at a temperature of 500 to 600 ° C.

  As another aspect, in the step (c), a second film having a thickness of 8 to 12 nm may be formed.

  As another embodiment, in the step (e), a piezoelectric film having a tetragonal crystal structure and containing (001) -oriented lead zirconate titanate may be formed.

  As another embodiment, in the step (e), a piezoelectric film having a rhombohedral crystal structure and containing (100) -oriented lead zirconate titanate may be formed.

  As another aspect, the method for manufacturing a film structure may include a step (f) of forming a second conductive film on the piezoelectric film.

  A film structure as one embodiment of the present invention includes a silicon substrate, a first film containing zirconium formed on the silicon substrate, a second film containing zirconium oxide epitaxially grown on the first film, and a second film A first conductive film containing platinum epitaxially grown thereon; and a piezoelectric film epitaxially grown on the first conductive film.

  As another aspect, the silicon substrate has a main surface made of a (100) plane, the second film has a cubic crystal structure and includes (100) -oriented zirconium oxide, The first conductive film may include platinum having a cubic crystal structure and (100) orientation.

  As another aspect, the first film may have a thickness of 5 to 10 nm, and the second film may have a thickness of 8 to 12 nm.

  As another embodiment, the piezoelectric film may have a tetragonal crystal structure and may contain (001) -oriented lead zirconate titanate.

  As another embodiment, the piezoelectric film may include rhombohedral crystal structure and (100) -oriented lead zirconate titanate.

  As another aspect, the film structure may include a second conductive film formed on the piezoelectric film.

  By applying one embodiment of the present invention, the piezoelectric constant of a piezoelectric film can be increased in a film structure including a conductive film formed over a silicon substrate and a piezoelectric film formed over the conductive film. it can.

It is sectional drawing of the film | membrane structure of embodiment. It is sectional drawing of a film structure in case the film structure of embodiment has the electrically conductive film as an upper electrode. It is a figure explaining the state which the orientation film contained in the film structure of an embodiment epitaxially grew. It is a figure explaining the state where the orientation film contained in a film structure has not grown epitaxially. It is sectional drawing of a film | membrane structure in case the orientation film of the film | membrane structure of embodiment has a two-layer structure. It is sectional drawing in the manufacturing process of the film | membrane structure of embodiment. It is sectional drawing in the manufacturing process of the film | membrane structure of embodiment. It is sectional drawing in the manufacturing process of the film | membrane structure of embodiment. It is sectional drawing in the manufacturing process of the film | membrane structure of embodiment. It is sectional drawing in the manufacturing process of the film | membrane structure of embodiment. It is sectional drawing in the manufacturing process of the film | membrane structure of embodiment. It is sectional drawing of the film | membrane structure of the modification of embodiment. Is a graph showing an example of a theta-2 [Theta] spectrum by XRD Method membrane structure to the ZrO ₂ film is formed. Is a graph showing an example of a theta-2 [Theta] spectrum by XRD Method membrane structure to the ZrO ₂ film is formed. The table | surface which classified and arranged the peak observed by the (theta) -2 (theta) spectrum of Examples 1-20 according to the thickness of the Zr film | membrane and the substrate temperature at the time of forming a Zr film | membrane is shown. The table | surface which classified and arranged the peak observed by the (theta) -2 (theta) spectrum of Examples 21-40 according to the thickness of Zr film | membrane and the substrate temperature at the time of forming Zr film | membrane is shown. The table | surface which classified and arranged the peak observed by the (theta) -2 (theta) spectrum of Examples 41-60 according to the thickness of the Zr film | membrane and the substrate temperature at the time of forming a Zr film | membrane is shown. It is a graph which shows the example of theta-2theta spectrum by the XRD method of the film | membrane structure in which even the SRO film | membrane was formed. It is a graph which shows the example of (theta) -2 (theta) spectrum by the XRD method of the film | membrane structure in which even the PZT film | membrane was formed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  It should be noted that the disclosure is merely an example, and those skilled in the art can easily conceive of appropriate modifications while maintaining the gist of the invention are naturally included in the scope of the present invention. In addition, the drawings may be schematically represented with respect to the width, thickness, shape, and the like of each part as compared with the embodiments for the sake of clarity of explanation, but are merely examples, and the interpretation of the present invention is not limited thereto. It is not limited.

  In addition, in the present specification and each drawing, elements similar to those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description may be omitted as appropriate.

  Furthermore, in the drawings used in the embodiments, hatching (shading) added to distinguish structures may be omitted depending on the drawings.

(Embodiment)
<Membrane structure>
First, a film structure according to an embodiment which is an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view of the film structure according to the embodiment. FIG. 2 is a cross-sectional view of the film structure when the film structure of the embodiment has a conductive film as an upper electrode.

  As shown in FIG. 1, the film structure 10 of the present embodiment includes a substrate 11, an alignment film 12, a conductive film 13, a conductive film 14, and a piezoelectric film 15. The alignment film 12 is formed on the substrate 11. The conductive film 13 is formed on the alignment film 12. The conductive film 14 is formed on the conductive film 13. The piezoelectric film 15 is formed on the conductive film 14.

  As shown in FIG. 2, the film structure 10 of the present embodiment may include a conductive film 16. The conductive film 16 is formed on the piezoelectric film 15. At this time, the conductive films 13 and 14 are conductive films as lower electrodes, and the conductive film 16 is a conductive film as upper electrodes. Thereby, an electric field can be applied to the piezoelectric film 15 in the thickness direction.

  The substrate 11 is a silicon substrate made of, for example, silicon (Si) single crystal. The substrate 11 has an upper surface 11a as a main surface.

The alignment film 12 includes, for example, zirconium oxide (ZrO ₂ ) epitaxially grown on the upper surface 11 a of the substrate 11. The conductive film 13 contains a metal, for example, platinum (Pt) epitaxially grown on the alignment film 12. The conductive film 14 is epitaxially grown on the conductive film 13. The piezoelectric film 15 is epitaxially grown on the conductive film 14.

  Here, when two directions orthogonal to each other in the upper surface 11a as the main surface of the substrate 11 are an X-axis direction and a Y-axis direction, and a direction perpendicular to the upper surface 11a is a Z-axis direction, a film is epitaxially grown. The term “has” means that the film is oriented in any of the X-axis direction, the Y-axis direction, and the Z-axis direction.

  When the alignment film 12 is not epitaxially grown on the substrate 11 and the conductive film 13 is not epitaxially grown on the alignment film 12, the conductive film 14 cannot be epitaxially grown on the conductive film 13, and the piezoelectric film is formed on the conductive film 14. 15 cannot be epitaxially grown. In the piezoelectric film 15, for example, when an electric field is applied along a direction parallel to the polarization direction or a direction having a certain angle with the polarization direction, the piezoelectric constants d33 and d31 are large. Therefore, when the piezoelectric film 15 is not epitaxially grown, the polarization directions are not uniform throughout the piezoelectric film 15, so that the piezoelectric constants d33 and d31 of the piezoelectric film 15 cannot be increased, and the characteristics of the piezoelectric element deteriorate.

  On the other hand, in this embodiment, since the alignment film 12 is epitaxially grown on the substrate 11 and the conductive film 13 is epitaxially grown on the alignment film 12, the conductive film 14 can be epitaxially grown on the conductive film 13. The piezoelectric film 15 can be epitaxially grown on the film 14. Therefore, the polarization direction can be made uniform throughout the piezoelectric film 15, the piezoelectric constants d33 and d31 of the piezoelectric film 15 can be increased, and the characteristics of the piezoelectric element can be improved.

Preferably, the conductive film 14 includes a metal oxide and includes strontium ruthenate (SrRuO ₃ , also referred to as SRO hereinafter) epitaxially grown on the alignment film 12. In addition, the piezoelectric film 15 is composed of lead zirconate titanate (Pb (Zr _1-x Ti _x ) O ₃ (0 <x <1), hereinafter referred to as PZT) epitaxially grown on the conductive film 13 via the conductive film 14. Say).

  When the piezoelectric film 15 includes PZT, the piezoelectric constant of the piezoelectric film 15 can be increased as compared with the case where the piezoelectric film 15 does not include PZT.

  Further, the SRO included in the conductive film 14 has a crystal structure similar to the perovskite structure that is the crystal structure of PZT included in the piezoelectric film 15. Therefore, PZT contained in the piezoelectric film 15 is easily oriented in a certain direction. In addition, since PZT included in the piezoelectric film 15 has a tetragonal crystal structure or a rhombohedral crystal structure, the PZT included in the piezoelectric film 15 is easily oriented in a certain direction, and the polarization direction is constant. It becomes easy to align in the direction, and the piezoelectric characteristics are improved.

  As will be described later with reference to FIG. 12, the film structure 10 may not have the conductive film 14, and the piezoelectric film 15 may be directly formed on the conductive film 13. In this case, the piezoelectric film 15 is not easily oriented as compared with the case where it is formed on the conductive film 14 containing SRO, but can be oriented in a certain direction even on the conductive film 13 containing platinum.

Preferably, the silicon single crystal included in the substrate 11 has an upper surface 11a as a main surface made of a (100) plane in a cubic crystal structure. Zirconium oxide (ZrO ₂ ) contained in the alignment film 12 has a cubic crystal structure and is (100) -oriented. Platinum (Pt) contained in the conductive film 13 has a cubic crystal structure and is (100) -oriented.

  Thereby, when the SRO contained in the conductive film 14 has a pseudo-cubic crystal structure, the conductive film 14 can be (100) -oriented on the substrate 11. In addition, when the PZT included in the piezoelectric film 15 has a tetragonal crystal structure, the piezoelectric film 15 can be (001) -oriented on the substrate 11, and the PZT included in the piezoelectric film 15 is rhombohedral. The piezoelectric film 15 can be (100) oriented on the substrate 11 when having the crystal structure of

  Here, the alignment film 12 is (100) -oriented. The (100) plane of the alignment film 12 having a cubic crystal structure is the (100) plane of the substrate 11 made of silicon single crystal. It means that it is along the upper surface 11a as a main surface. In addition, the alignment film 12 is preferably (100) -oriented. Preferably, the (100) plane of the alignment film 12 is parallel to the upper surface 11a of the (100) plane of the substrate 11 made of silicon single crystal. It means that. In addition, the (100) plane of the alignment film 12 is parallel to the upper surface 11 a made of the (100) plane of the substrate 11 only when the (100) plane of the alignment film 12 is completely parallel to the upper surface 11 a of the substrate 11. In addition, the case where the angle formed by the plane completely parallel to the upper surface 11a of the substrate 11 and the (100) plane of the alignment film 12 is 20 ° or less is included.

  Zirconium oxide as a bulk material has a monoclinic crystal structure at room temperature, and when the temperature is increased from room temperature, the phase transition occurs at about 1170 ° C. to have a tetragonal crystal structure. When the temperature is raised, a phase transition occurs at about 2370 ° C. and a cubic crystal structure is obtained. However, since the stress is applied to the zirconium oxide contained in the alignment film 12 from the upper and lower films or the substrate, the behavior of the phase transition of zirconium oxide contained in the alignment film 12 is the phase transition of zirconium oxide as a bulk material. The behavior is different. Further, since the alignment film 12 is as thin as several tens of nm or less, it is possible to accurately distinguish whether the crystal structure of zirconium oxide contained in the alignment film 12 is a tetragonal crystal structure or a cubic crystal structure. Have difficulty.

  Therefore, hereinafter, the case where the zirconium oxide included in the alignment film 12 has a tetragonal crystal structure may be regarded as the case where the zirconium oxide has a cubic crystal structure. In other words, in the present specification, when the zirconium oxide contained in the alignment film 12 has a cubic crystal structure, the zirconium oxide actually has a cubic crystal structure, and actually has a square rather than a cubic crystal structure. And a crystal structure of a crystal.

  Similarly, in the following, the case where the SRO included in the conductive film 14 has an orthorhombic crystal structure is regarded as the case where the SRO has a pseudo-cubic crystal structure. It may be considered that it has a crystal structure of That is, in the present specification, when the SRO included in the conductive film 14 has a cubic crystal structure, the SRO actually has a cubic crystal structure, and the actual SRO is not a cubic crystal structure. And a case of having a pseudo-cubic crystal structure.

Preferably, the piezoelectric film 15 has a tetragonal crystal structure and is (001) -oriented. When P in Pb (Zr _1-x Ti _x ) O ₃ (0 <x <1) satisfies 0.48 <x <1, the PZT included in the piezoelectric film 15 has a tetragonal crystal structure. Epitaxial growth becomes easier and (001) orientation becomes easier. When PZT having a tetragonal crystal structure is (001) oriented, the polarization direction parallel to the [001] direction and the electric field direction parallel to the thickness direction of the piezoelectric film 15 are parallel to each other. The piezoelectric characteristics are improved. That is, in PZT having a tetragonal crystal structure, large piezoelectric constants d33 and d31 are obtained when an electric field along the [001] direction is applied. Therefore, the piezoelectric constant of the piezoelectric film 15 can be further increased.

Alternatively, the piezoelectric film 15 preferably has a rhombohedral crystal structure and is (100) -oriented. When P in Pb (Zr _1-x Ti _x ) O ₃ (0 <x <1) satisfies 0.20 <x ≦ 0.48, the PZT contained in the piezoelectric film 15 has a rhombohedral crystal structure. It becomes easy to grow epitaxially and (100) orientation becomes easy. When PZT having a rhombohedral crystal structure is (100) oriented, the PZT has a so-called engineered domain structure, and a polarization direction parallel to each direction equivalent to the [111] direction, Since the angle with the electric field direction parallel to the thickness direction of the piezoelectric film 15 becomes equal in any polarization domain, the piezoelectric characteristics are improved. That is, in PZT having a rhombohedral crystal structure, large piezoelectric constants d33 and d31 are obtained when an electric field along the [100] direction is applied. Therefore, the piezoelectric characteristics of the piezoelectric film 15 can be further increased.

  FIG. 3 is a diagram illustrating a state in which the alignment film included in the film structure according to the embodiment is epitaxially grown. On the other hand, FIG. 4 is a diagram illustrating a state in which the alignment film included in the film structure is not epitaxially grown. In FIG. 3, each layer of the substrate 11, the alignment film 12, the conductive films 13 and 14, and the piezoelectric film 15 is schematically shown. In FIG. 4, the substrate 11 and the alignment film 12 are schematically shown. Yes.

The lattice constant of Si included in the substrate 11, the lattice constant of ZrO ₂ included in the alignment film 12, the lattice constant of Pt included in the conductive film 13, the lattice constant of SRO included in the conductive film 14, and included in the piezoelectric film 15. Table 1 shows the lattice constant of PZT.

As shown in Table 1, the lattice constant of Si is 0.543 nm, the lattice constant of ZrO ₂ is 0.514 nm, and the mismatch of the lattice constant of ZrO ₂ with respect to the lattice constant of Si is 5.3%. Therefore, the consistency of the lattice constant of ZrO ₂ with respect to the lattice constant of Si is good. Therefore, as shown in FIG. 3, the alignment film 12 containing ZrO ₂ can be epitaxially grown on the main surface made of the (100) plane of the substrate 11 containing a silicon single crystal. Therefore, the alignment film 12 containing ZrO ₂ can be (100) oriented in a cubic crystal structure on the (100) plane of the substrate 11 containing a silicon single crystal, thereby improving the crystallinity of the orientation film 12. be able to.

As shown in Table 1, the lattice constant of ZrO ₂ is 0.514 nm and the lattice constant of Pt is 0.392 nm, but when Pt rotates 45 ° in the plane, the length of the diagonal line is 0.554 nm, and the mismatch of the length of the diagonal line with respect to the lattice constant of ZrO ₂ is as small as 7.8%. Therefore, the lattice constant of Pt with respect to the lattice constant of ZrO ₂ is good. Therefore, as shown in FIG. 3, the conductive film 13 containing Pt can be (100) oriented with a cubic crystal structure on the (100) plane of the orientation film 12 containing ZrO _2. The crystallinity of can be improved.

  Further, as shown in Table 1, the lattice constant of Pt is 0.392 nm, the lattice constant of SRO is 0.390 to 0.393 nm, and the mismatch of the lattice constant of SRO with respect to the lattice constant of Pt is Since it is as small as 0.51% or less, the consistency of the lattice constant of SRO with the lattice constant of Pt is good. Therefore, the conductive film 14 containing SRO can be (100) oriented with a cubic crystal structure on the (100) plane of the conductive film 13 containing Pt, and the crystallinity of the conductive film 14 can be improved. it can.

  Further, as shown in Table 1, the lattice constant of SRO is 0.390 to 0.393 nm, the lattice constant of PZT is 0.401 nm, and the mismatch of the lattice constant of PZT with respect to the lattice constant of SRO is Since it is as small as 2.0 to 2.8%, the consistency of the lattice constant of PZT with that of SRO is good. Therefore, the piezoelectric film 15 containing PZT is oriented on the (100) plane of the conductive film 14 containing SRO with a (001) orientation with a tetragonal crystal structure or a (100) orientation with a rhombohedral crystal structure. The crystallinity of the piezoelectric film 15 can be improved.

On the other hand, as shown in FIG. 4, in the state where the alignment film 12 containing ZrO ₂ is not epitaxially grown on the main surface made of the (100) plane of the substrate 11 containing a silicon single crystal, for example, the alignment film containing ZrO ₂ 12 is (111) -oriented in the crystal structure of, for example, a cubic crystal on the (100) plane of the substrate 11 containing a silicon single crystal. Therefore, the crystallinity of the alignment film 12 cannot be improved.

Further, as shown in FIG. 4, in the state where the alignment film 12 containing ZrO ₂ is not epitaxially grown on the main surface made of the (100) plane of the substrate 11 containing silicon single crystal, the illustration is omitted in FIG. However, the conductive film 13 containing Pt has, for example, a cubic crystal structure and (111) orientation. Therefore, the crystallinity of the conductive film 13 cannot be improved. When the conductive film 13 containing Pt is in a (111) orientation with a cubic crystal structure, for example, the conductive film 14 containing SRO cannot be (100) oriented in a cubic crystal structure. The piezoelectric film 15 containing PZT cannot be (001) oriented with a tetragonal crystal structure or (100) oriented with a rhombohedral crystal structure.

  Preferably, the alignment film 12 has a thickness of 13 to 22 nm. When the thickness of the alignment film 12 is less than 13 nm, since the thickness of the alignment film 12 is too thin, the effect of facilitating the epitaxial growth of the alignment film 12 on the substrate 11 is reduced. Therefore, when the thickness of the alignment film 12 is less than 13 nm, a part of the alignment film 12 is not (100) oriented but (111) oriented.

  Even when the thickness of the alignment film 12 exceeds 22 nm, since the alignment film 12 is too thick, the effect of facilitating the epitaxial growth of the alignment film 12 on the substrate 11 is reduced. Therefore, even when the thickness of the alignment film 12 exceeds 22 nm, a part of the alignment film 12 is not (100) aligned but (111) aligned.

  FIG. 5 is a cross-sectional view of the film structure when the alignment film of the film structure of the embodiment has a two-layer structure.

  The alignment film 12 may include a film 12a and an alignment film 12b. The film 12a contains zirconium formed on the substrate 11, but the zirconium contained in the film 12a is not oxidized and is metallic zirconium. That is, the film 12a is a metal film containing zirconium. On the other hand, the alignment film 12b contains zirconium oxide epitaxially grown on the film 12a. Therefore, the alignment film 12 shown in FIGS. 1 and 2 corresponds to the alignment film 12b shown in FIG.

When the alignment film 12b is formed on the substrate 11 via the film 12a, the epitaxial growth is easier than when the alignment film 12b is formed on the substrate 11 without the film 12a. Therefore, the alignment film 12b containing ZrO ₂ can be more stably epitaxially grown on the upper surface 11a as the main surface made of the (100) surface of the substrate 11 containing silicon single crystal. Therefore, the alignment film 12 containing ZrO ₂ can be more stably (100) oriented on the (100) plane of the substrate 11 containing a silicon single crystal, and the crystallinity of the alignment film 12 is further improved. Can do.

However, when the alignment film 12b containing ZrO ₂ is formed, the film 12a may disappear and become the alignment film 12b due to oxidation of Zr contained in the film 12a. In such a case, as shown in FIG. 1, the alignment film 12b is formed directly on the substrate 11, and the alignment film 12 including only the alignment film 12b formed directly on the substrate 11 is formed. .

  Preferably, the film 12a has a thickness of 5 to 10 nm. When the thickness of the film 12a is less than 5 nm, since the thickness of the film 12a is too thin, the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced. Therefore, when the thickness of the film 12a is less than 5 nm, a part of the alignment film 12b is not (100) oriented but (111) oriented.

  Even when the thickness of the film 12a exceeds 10 nm, the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced because the film 12a is too thick. Therefore, even when the thickness of the film 12a exceeds 10 nm, a part of the alignment film 12b is not (100) oriented but (111) oriented.

  Preferably, the alignment film 12b has a thickness of 8 to 12 nm. When the thickness of the alignment film 12b is less than 8 nm, the thickness of the alignment film 12b is too thin, so that the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced. Therefore, when the thickness of the alignment film 12b is less than 8 nm, a part of the alignment film 12b is not (100) aligned but (111) aligned.

  Also, when the thickness of the alignment film 12b exceeds 12 nm, the alignment film 12b is too thick, so that the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced. Therefore, even when the thickness of the alignment film 12b exceeds 12 nm, a part of the alignment film 12b is not (100) aligned but (111) aligned.

  Note that the film structure 10 of the present embodiment does not include the conductive film 14 and the piezoelectric film 15 but may include only the substrate 11, the alignment film 12, and the conductive film 13. Even in such a case, the piezoelectric film 15 sandwiched between the conductive film 13 and the conductive film 16 from above and below is formed by forming the piezoelectric film 15 and the conductive film 16 as the upper electrode on the film structure 10. The piezoelectric element which has can be formed easily.

<Method for producing membrane structure>
Next, a method for manufacturing the film structure of the present embodiment will be described. 6-11 is sectional drawing in the manufacturing process of the film | membrane structure of embodiment.

  First, as shown in FIG. 6, a substrate 11 as a silicon substrate is prepared (step S1).

Preferably, the substrate 11 has a cubic crystal structure and has an upper surface 11a as a main surface made of a (100) plane. An oxide film such as a SiO ₂ film as a natural oxide film may be formed on the upper surface 11 a of the substrate 11.

  Note that various substrates other than a silicon substrate can be used as the substrate 11, and for example, a substrate made of various semiconductor single crystals other than silicon can be used.

  As shown in FIG. 6, two directions orthogonal to each other in the upper surface 11a of the (100) plane of the substrate 11 made of silicon single crystal are defined as an X-axis direction and a Y-axis direction, and a direction perpendicular to the upper surface 11a is defined as Z Axial direction.

  Next, as shown in FIG. 7, a film 12a is formed (step S2). In step S <b> 2, a film 12 a containing zirconium is formed on the substrate 11.

  In step S2, the case where the alignment film 12 is formed by using an electron beam evaporation method will be described as an example. However, the alignment film 12 can be formed by using various methods such as a sputtering method.

In step S2, first, the substrate 11 is placed in a vacuum chamber of an electron beam evaporation apparatus, and the pressure in the vacuum chamber is adjusted in a constant vacuum atmosphere such as 2.1 × 10 ⁻⁵ Pa. The substrate 11 is heated to 600 to 750 ° C., for example.

  Next, in step S2, Zr is evaporated by an electron beam vapor deposition method using a zirconium (Zr) single crystal vapor deposition material. At this time, the evaporated Zr is formed as a zirconium (Zr) film. Then, a film 12 a containing zirconium having a thickness of, for example, 20 nm or less is formed on the substrate 11. Note that zirconium contained in the film 12a is not oxidized and is metallic zirconium. That is, the film 12a is a metal film containing zirconium.

  Preferably, in step S2, a film 12a having a thickness of 5 to 10 nm is formed. When the thickness of the film 12a is less than 5 nm, the thickness of the film 12a is reduced, and the effect of facilitating epitaxial growth of the alignment film 12b (see FIG. 8 described later) on the substrate 11 is reduced. Therefore, when the thickness of the film 12a is less than 5 nm, a part of the alignment film 12b is not (100) oriented but (111) oriented.

  Even when the thickness of the film 12a exceeds 10 nm, the thickness of the film 12a is increased, and the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced. Therefore, even when the thickness of the film 12a exceeds 10 nm, a part of the alignment film 12b is not (100) oriented but (111) oriented.

  Preferably, in step S2, the film 12a is formed at a temperature of 650 to 700 ° C. When the temperature of the substrate 11 is lower than 650 ° C., the temperature of the substrate 11 is lowered, and the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced. Therefore, when the temperature of the substrate 11 is lower than 650 ° C., a part of the alignment film 12b is not (100) oriented but (111) oriented.

  Further, when the temperature of the substrate 11 exceeds 700 ° C., the temperature of the substrate 11 is increased, and the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced. Accordingly, even when the temperature of the substrate 11 exceeds 700 ° C., a part of the alignment film 12b is not (100) oriented but (111) oriented.

  Next, as shown in FIG. 8, an alignment film 12b is formed (step S3). In this step S3, an alignment film 12b containing zirconium oxide epitaxially grown on the film 12a is formed.

  In step S3, as in step S2, the case where the alignment film 12 is formed using an electron beam evaporation method will be described as an example. However, the alignment film 12 can be formed using various methods such as a sputtering method.

In step S3, first, the substrate 11 is placed in a vacuum chamber of an electron beam vapor deposition apparatus, oxygen (O ₂ ) gas is allowed to flow into the vacuum chamber at a flow rate of 10 sccm, for example, and the pressure in the vacuum chamber is set to 7. The substrate 11 is heated to, for example, 500 to 600 ° C. in a state adjusted to 0 × 10 ⁻³ Pa.

Next, in step S3, Zr is evaporated by an electron beam vapor deposition method using a zirconium (Zr) single crystal vapor deposition material. At this time, evaporated Zr reacts with oxygen on the film 12a to form a zirconium oxide (ZrO ₂ ) film. Then, an alignment film 12b made of a ZrO ₂ film as a single layer film is formed. Then, an alignment film 12b containing zirconium oxide is formed by epitaxial growth on the film 12a containing zirconium.

The alignment film 12b is epitaxially grown through the film 12a on the upper surface 11a as the main surface made of the (100) plane of the substrate 11 made of silicon single crystal. The alignment film 12 has a cubic crystal structure and includes (100) -oriented zirconium oxide (ZrO ₂ ). In other words, the alignment film 12 containing (100) -oriented zirconium oxide (ZrO ₂ ) is formed on the upper surface 11a of the (100) plane of the substrate 11 made of silicon single crystal through the film 12a.

  As described with reference to FIG. 6 described above, the two directions orthogonal to each other in the upper surface 11a of the (100) plane of the substrate 11 made of silicon single crystal are the X-axis direction and the Y-axis direction, and the upper surface 11a The vertical direction is taken as the Z-axis direction. At this time, that a certain film is epitaxially grown means that the film is oriented in any of the X-axis direction, the Y-axis direction, and the Z-axis direction.

  Preferably, in step S3, an alignment film 12b having a thickness of 8 to 12 nm is formed. When the thickness of the alignment film 12b is less than 8 nm, the thickness of the alignment film 12b is reduced, and the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced. Therefore, when the thickness of the alignment film 12b is less than 8 nm, a part of the alignment film 12b is not (100) aligned but (111) aligned.

  Also, when the thickness of the alignment film 12b exceeds 12 nm, the thickness of the alignment film 12b is increased, and the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 is reduced. Therefore, even when the thickness of the alignment film 12b exceeds 12 nm, a part of the alignment film 12b is not (100) aligned but (111) aligned.

  As described above, preferably, in step S3, the alignment film 12b is formed at a temperature of 500 to 600 ° C. When the temperature of the substrate 11 is less than 500 ° C., the temperature of the substrate 11 is lowered, and for example, it becomes difficult to rearrange zirconium atoms and oxygen atoms on the film 12 a, so that the alignment film 12 b easily grows epitaxially on the substrate 11. The effect becomes smaller. Accordingly, when the temperature of the substrate 11 is less than 500 ° C., a part of the alignment film 12b is not (100) oriented but (111) oriented.

  Further, when the temperature of the substrate 11 exceeds 600 ° C., the temperature of the substrate 11 becomes high, and the effect of facilitating the epitaxial growth of the alignment film 12b on the substrate 11 becomes small. Therefore, even when the temperature of the substrate 11 exceeds 600 ° C., a part of the alignment film 12b is not (100) oriented but (111) oriented.

When the alignment film 12b containing ZrO ₂ is formed, the film 12a may disappear and become the alignment film 12b due to oxidation of Zr contained in the film 12a. In such a case, as shown in FIG. 9, the alignment film 12b is formed directly on the substrate 11, and the alignment film 12 including only the alignment film 12b formed directly on the substrate 11 is formed. . Preferably, a new alignment film 12b having a total thickness of 13 to 22 nm is included by the film 12a having a thickness of 5 to 10 nm and the original alignment film 12b having a thickness of 8 to 12 nm. An alignment film 12 is formed. In the following description, as shown in FIG. 9, the case where the alignment film 12b is directly formed on the substrate 11 in step S3 will be described as an example.

  Next, as shown in FIG. 10, a conductive film 13 is formed (step S4). In step S4, a conductive film 13 is formed as a part of the lower electrode, which is epitaxially grown on the alignment film 12b. The conductive film 13 is made of metal. For example, a conductive film containing platinum (Pt) is used as the conductive film 13 made of metal.

  When a conductive film containing Pt is formed as the conductive film 13, the conductive film 13 epitaxially grown on the alignment film 12 by sputtering at a temperature of 550 ° C. or lower, preferably 400 ° C. Form as part. The conductive film 13 containing Pt is epitaxially grown on the alignment film 12b. Further, platinum contained in the conductive film 13 has a cubic crystal structure and is (100) -oriented.

  For example, a conductive film containing iridium (Ir) can be used as the conductive film 13 made of metal instead of the conductive film containing platinum (Pt).

Next, as shown in FIG. 11, the conductive film 14 is formed (step S5). In this step S5, a conductive film 14 is formed as a part of the lower electrode, which is epitaxially grown on the conductive film 13. The conductive film 14 is made of a metal oxide. As the conductive film 14 made of a metal oxide, for example, a conductive film containing strontium ruthenate (SrRuO ₃ : SRO) is used.

  In the case where a conductive film containing SRO is formed as the conductive film 14, the conductive film 14 epitaxially grown on the conductive film 13 at a temperature of about 600 ° C. is formed as a part of the lower electrode. The conductive film 14 containing SRO is epitaxially grown on the conductive film 13. The SRO contained in the conductive film 14 has a cubic crystal structure and is (100) -oriented.

As the conductive film 14 made of metal oxide, for example, strontium titanate (Sr (Ti _y Ru _1-y ) O ₃ (0 ≦ y ≦ 0.4)) is used instead of the conductive film containing SRO. A conductive film including the conductive film can also be used.

Next, as shown in FIG. 1, the piezoelectric film 15 is formed (step S6). In step S6, for example, by a coating method or a sputtering method such as a sol-gel method, on the conductive film 14, epitaxially grown lead zirconate titanate _{(Pb (Zr 1-x Ti} x) O 3 (0 <x <1): A piezoelectric film 15 containing PZT) is formed.

  When the piezoelectric film 15 is formed by the sol-gel method, in step S6, first, a film containing PZT precursor is formed on the conductive film 14 by applying a solution containing lead, zirconium, and titanium. The process is repeated multiple times. Thus, a film including a plurality of films stacked on each other is formed.

  When the piezoelectric film 15 is formed by the sol-gel method, in step S6, the film is then heat-treated to oxidize and crystallize the precursor, thereby forming the piezoelectric film 15 containing PZT.

Preferably, the piezoelectric film 15 has a tetragonal crystal structure and is (001) -oriented. When P in Pb (Zr _1-x Ti _x ) O ₃ (0 <x <1) satisfies 0.48 <x <1, the PZT included in the piezoelectric film 15 has a tetragonal crystal structure. Epitaxial growth becomes easier and (001) orientation becomes easier. When PZT having a tetragonal crystal structure is (001) oriented, the polarization direction parallel to the [001] direction and the electric field direction parallel to the thickness direction of the piezoelectric film 15 are parallel to each other. The piezoelectric characteristics are improved. That is, in PZT having a tetragonal crystal structure, large piezoelectric constants d33 and d31 are obtained when an electric field along the [001] direction is applied. Therefore, the piezoelectric constant of the piezoelectric film 15 can be further increased.

Alternatively, the piezoelectric film 15 preferably has a rhombohedral crystal structure and is (100) -oriented. When P in Pb (Zr _1-x Ti _x ) O ₃ (0 <x <1) satisfies 0.20 <x ≦ 0.48, the PZT contained in the piezoelectric film 15 has a rhombohedral crystal structure. It becomes easy to grow epitaxially and (100) orientation becomes easy. When PZT having a rhombohedral crystal structure is (100) oriented, the PZT has a so-called engineered domain structure, and a polarization direction parallel to each direction equivalent to the [111] direction, Since the angle with the electric field direction parallel to the thickness direction of the piezoelectric film 15 becomes equal in any polarization domain, the piezoelectric characteristics are improved. That is, in PZT having a rhombohedral crystal structure, large piezoelectric constants d33 and d31 are obtained when an electric field along the [100] direction is applied. Therefore, the piezoelectric characteristics of the piezoelectric film 15 can be further increased.

  In this way, the film structure 10 shown in FIG. 1 is formed. When forming the alignment film 12b, if the film 12a remains without disappearing, the film structure 10 shown in FIG. 5 is formed.

When the alignment film 12b containing zirconium oxide (ZrO ₂ ) is directly formed on the substrate 11 as a silicon substrate, the formed ZrO ₂ film may have low crystallinity, and the alignment film 12b may not be satisfactorily epitaxially grown. In such a case, the conductive film 13 cannot be favorably epitaxially grown on the alignment film 12b, and the piezoelectric film 15 cannot be favorably epitaxially grown on the conductive film 13. In the piezoelectric film 15, for example, when an electric field is applied along a direction parallel to the polarization direction or a direction having a certain angle with the polarization direction, the piezoelectric constants d33 and d31 are large. Therefore, when the piezoelectric film 15 is not epitaxially grown well, the polarization direction is not uniform in the entire piezoelectric film 15, so that the piezoelectric constants d33 and d31 of the piezoelectric film 15 cannot be increased, and the characteristics of the piezoelectric element are deteriorated. .

On the other hand, in this embodiment, after the film 12a containing zirconium (Zr) is formed on the substrate 11, the alignment film 12b containing ZrO ₂ is epitaxially grown on the substrate 11. Zirconium contained in the film 12a is not oxidized and is metallic zirconium. In such a case, the alignment film 12 can be epitaxially grown better than when the alignment film 12b containing ZrO ₂ is directly formed on the substrate 11. Therefore, the conductive film 13 can be favorably epitaxially grown on the alignment film 12b, and the piezoelectric film 15 can be favorably epitaxially grown on the conductive film 13. Therefore, the polarization direction can be made uniform throughout the piezoelectric film 15, the piezoelectric constants d33 and d31 of the piezoelectric film 15 can be increased, and the characteristics of the piezoelectric element can be improved.

  In addition, after forming the piezoelectric film 15, you may form the electrically conductive film 16 (refer FIG. 2) as an upper electrode on the piezoelectric film 15 as step S7. Thereby, an electric field can be applied on the piezoelectric film 15 in the thickness direction.

<Modification of Embodiment>
In the embodiment, as shown in FIG. 1, the piezoelectric film 15 is formed on the conductive film 13 via the conductive film 14. However, the piezoelectric film 15 may be directly formed on the conductive film 13 without using the conductive film 14. Such an example will be described as a modification of the embodiment.

  FIG. 12 is a cross-sectional view of a film structure according to a modification of the embodiment.

  As shown in FIG. 12, the film structure 10 of the present modification includes a substrate 11, an alignment film 12, a conductive film 13, and a piezoelectric film 15. The alignment film 12 is formed on the substrate 11. The conductive film 13 is formed on the alignment film 12. The piezoelectric film 15 is formed on the conductive film 13.

  That is, the film structure 10 of the present modification is the same as that of the embodiment except that the piezoelectric film 15 is directly formed on the conductive film 13 without the conductive film 14 (see FIG. 1). It is the same as the body 10.

  When the piezoelectric film 15 containing PZT is formed on the conductive film 13 containing Pt without the conductive film 14 containing SRO (see FIG. 1), the conductive material containing SRO is formed on the conductive film 13 containing Pt. Compared with the case where the piezoelectric film 15 containing PZT is formed through the film 14 (see FIG. 1), the crystallinity of the piezoelectric film 15 is lowered. However, even when the piezoelectric film 15 containing PZT is formed on the conductive film 13 containing Pt without the conductive film 14 containing SRO (see FIG. 1), the conductive film 13 is oriented on the orientation film 12. Or it is easy to grow epitaxially. Therefore, the piezoelectric film 15 formed on the conductive film 13 is also easily oriented or epitaxially grown to some extent, and the crystallinity of the piezoelectric film 15 can be improved to some extent.

  Note that the film structure 10 of the present modification may also include the conductive film 16 (see FIG. 2), similar to the film structure 10 of the embodiment.

  Hereinafter, the present embodiment will be described in more detail based on examples. The present invention is not limited to the following examples.

(Examples 1 to 60)
Below, the film | membrane structure 10 demonstrated using Embodiment in FIG. 1 was formed as a film | membrane structure of Examples 1-60. The film structures of Examples 1 to 60 are the thickness of the film 12a (see FIG. 7), the substrate temperature when forming the film 12a, and the substrate when forming the alignment film 12b (see FIG. 8). It is formed while changing each of the temperatures.

  First, as shown in FIG. 6, a wafer having a top surface 11 a as a main surface made of a (100) surface and made of a 6-inch silicon substrate was prepared as the substrate 11.

Next, as shown in FIG. 7, a zirconium (Zr) film was formed as a film 12a on the substrate 11 by an electron beam evaporation method. The conditions at this time are shown below.
Apparatus: Electron beam deposition apparatus Pressure: 2.10 × 10 ⁻⁵ Pa
Deposition source: Zr
Acceleration voltage / emission current: 7.5kV / 1.50mA
Thickness: 20 nm or less Deposition rate: 0.005 nm / s
Oxygen flow rate: 0 sccm
Substrate temperature: 600-750 ° C

Next, as shown in FIG. 8, a zirconium oxide (ZrO ₂ ) film was formed as the alignment film 12 by an electron beam evaporation method. The conditions at this time are shown below.
Apparatus: Electron beam vapor deposition apparatus Pressure: 7.00 × 10 ⁻³ Pa
Vapor deposition source: Zr + O ₂
Acceleration voltage / emission current: 7.5kV / 1.80mA
Thickness: 10nm
Deposition rate: 0.005 nm / s
Oxygen flow rate: 10 sccm
Substrate temperature: 500-600 ° C

Here, the thickness of the Zr film, the substrate temperature when forming the Zr film, and the substrate temperature when forming the ZrO ₂ film in each of Examples 1 to 60 are shown in Tables 2 to 4. . Examples 1 to 20 shown in Table 2 are cases in which the substrate temperature when forming the ZrO ₂ film is 500 ° C. Examples 21 to 40 shown in Table 3 are cases in which the substrate temperature when forming the ZrO ₂ film is 550 ° C. The examples 41-60 in Table 4, the substrate temperature in forming the ZrO ₂ film has a case 600 ° C.. As described above, the thickness of the ZrO ₂ film in each of Examples 1 to 60 is 10 nm. In Tables 2 to 4, the evaluation results of the crystallinity of the ZrO ₂ film are shown by single circles and double circles. The double circle indicates higher crystallinity than the single circle.

For example 1 to 60, X-ray diffraction of the film structure to the ZrO ₂ film was formed was measured with theta-2 [Theta] spectrum by (X-ray Diffraction XRD) method. FIG. 13 and FIG. 14 are graphs showing examples of the θ-2θ spectrum by the XRD method of the film structure formed up to the ZrO ₂ film. The horizontal axis of each graph in FIGS. 13 and 14 represents the angle 2θ, and the vertical axis of each graph in FIGS. 13 and 14 represents the intensity of X-rays.

FIG. 13 illustrates the case where the thickness of the Zr film is 7 nm, the substrate temperature when forming the Zr film is 700 ° C., and the substrate temperature when forming the ZrO ₂ film is 550 ° C. . FIG. 14 illustrates the case where the thickness of the Zr film is 7 nm, the substrate temperature when forming the Zr film is 750 ° C., and the substrate temperature when forming the ZrO ₂ film is 550 ° C. . 13 and 14, T-ZrO ₂ means tetragonal ZrO ₂ , and M-ZrO ₂ means monoclinic ZrO ₂ . As described above, it is assumed that the ZrO ₂ in tetragonal contained in ZrO ₂ cubic.

In the example shown in FIG. 13, a peak corresponding to (200) of ZrO ₂ having a tetragonal crystal structure was observed in the θ-2θ spectrum. Therefore, it was found that the alignment film 12b includes a tetragonal crystal structure and includes (100) -oriented ZrO ₂ .

In the example shown in FIG. 13, no peaks other than the peak corresponding to (200) of ZrO ₂ having a tetragonal crystal structure were observed in the θ-2θ spectrum. Therefore, the alignment film 12b has a tetragonal crystal structure and ZrO ₂ oriented in a plane other than the (100) plane, or ZrO ₂ having a monoclinic crystal structure is at least above the detection limit. It was found that the content ratio was not included.

On the other hand, in the example shown in FIG. 14, a peak corresponding to (200) of ZrO ₂ having a tetragonal crystal structure was observed in the θ-2θ spectrum. Therefore, it was found that the alignment film 12b includes a tetragonal crystal structure and includes (100) -oriented ZrO ₂ .

However, in the example shown in FIG. 14, in the θ-2θ spectrum, as a peak other than the peak corresponding to (200) of ZrO ₂ having a tetragonal crystal structure, (111) of ZrO ₂ having a tetragonal crystal structure is used. And a peak corresponding to (111) of ZrO ₂ having a monoclinic crystal structure were observed. Therefore, the alignment film 12b has a tetragonal crystal structure and has a tetragonal crystal structure and a (111) orientation, although the content ratio is small as compared with (100) -oriented ZrO _2. ZrO ₂ and a monoclinic crystal structure and (111) -oriented ZrO ₂ were included to some extent.

As described above, in the film structures of Examples 1 to 60, the thickness of the Zr film, the substrate temperature when forming the Zr film, and the substrate temperature when forming the ZrO ₂ film were changed. Formed. Such a membrane structure peaks observed in the measured theta-2 [Theta] spectra for examples 1 to 60, the thickness of the Zr layer, the substrate temperature during the formation of the Zr layer, and to form a ZrO ₂ film Sorted according to the substrate temperature at the time. 15 to 17 show tables in which the peaks observed in the θ-2θ spectra of Examples 1 to 60 are classified and arranged according to the thickness of the Zr film and the substrate temperature when forming the Zr film. . Each of FIGS. 15 to 17 shows a case where the substrate temperature when forming the ZrO ₂ film is any one of 500 ° C., 550 ° C., and 600 ° C. Further, each column in FIGS. 15 to 17 corresponds to a different Zr film thickness, and each row in FIGS. 15 to 17 corresponds to a substrate temperature at the time of forming different Zr films. ing.

First, as shown in FIG. 15, when the substrate temperature when forming the ZrO ₂ film is 500 ° C., the thickness of the Zr film is 20 nm or less and the substrate temperature when forming the Zr film is 600. for to 750 ° C., (100) oriented ZrO ₂ peaks (described as _ZrO 2 (200) in FIG. 15) was observed. On the other hand, although not shown in FIG. 15, when the substrate temperature when forming the ZrO ₂ film is 500 ° C., when the thickness of the Zr film exceeds 20 nm, the substrate temperature when forming the Zr film is When the temperature was lower than 600 ° C. or when the substrate temperature at the time of forming the Zr film exceeded 750 ° C., the peak of (100) -oriented ZrO ₂ was not observed.

As shown in FIG. 16, when the substrate temperature when forming the ZrO ₂ film is 550 ° C., the thickness of the Zr film is 20 nm or less, and the substrate temperature when forming the Zr film is 600. In the case of ˜750 ° C., a (100) -oriented ZrO ₂ peak (denoted as ZrO ₂ (200) in FIG. 16) was observed. On the other hand, although not shown in FIG. 16, when the substrate temperature when forming the ZrO ₂ film is 550 ° C., the thickness of the Zr film exceeds 20 nm, the substrate temperature when forming the Zr film is When the temperature was lower than 600 ° C. or when the substrate temperature at the time of forming the Zr film exceeded 750 ° C., the peak of (100) -oriented ZrO ₂ was not observed.

As shown in FIG. 17, when the substrate temperature when forming the ZrO ₂ film is 600 ° C., the thickness of the Zr film is 20 nm or less, and the substrate temperature when forming the Zr film is 600. for to 750 ° C., (100) oriented ZrO ₂ peaks (described as _ZrO 2 (200) in FIG. 17) was observed. On the other hand, although not shown in FIG. 17, when the substrate temperature when forming the ZrO ₂ film is 600 ° C., when the thickness of the Zr film exceeds 20 nm, the substrate temperature when forming the Zr film is When the temperature was lower than 600 ° C. or when the substrate temperature at the time of forming the Zr film exceeded 750 ° C., the peak of (100) -oriented ZrO ₂ was not observed.

Although not shown in FIGS. 15 to 17, as examples other than Examples 1 to 60 shown in FIGS. 15 to 17, all other conditions are the same, and ZrO ₂ having a thickness of 5 nm or 20 nm. When the film was formed, the same result as that obtained when the ZrO ₂ film having a thickness of 10 nm was formed was obtained.

From the above results, a film 12a containing zirconium having a thickness of 20 nm or less is formed at a temperature of 600 to 750 ° C., and an alignment film 12b containing zirconium oxide having a thickness of 5 to 20 nm is formed. When forming at a temperature of 500 to 600 ° C., it was found that a (100) -oriented ZrO ₂ peak was observed. In such a case, the alignment film 12b has a tetragonal crystal structure and contains more (100) -oriented zirconium oxide.

Further, as shown by hatching in FIG. 15, when the substrate temperature when forming the ZrO ₂ film is 500 ° C., the thickness of the Zr film is 5 to 10 nm and the Zr film is formed. When the substrate temperature was 650 to 700 ° C., no peaks other than the (100) -oriented ZrO ₂ peak were observed. On the other hand, when the substrate temperature when forming the ZrO ₂ film is 500 ° C., when the thickness of the Zr film is less than 5 nm, when the thickness of the Zr film exceeds 10 nm, the substrate when forming the Zr film When the temperature was less than 650 ° C., or when the substrate temperature when forming the Zr film exceeded 700 ° C., peaks other than ZrO ₂ (100) were observed. The observed peaks are, for example, the (111) -oriented ZrO ₂ peak (described as ZrO ₂ (111) in FIG. 15), the (111) -oriented Zr ₃ O peak (Zr ₃ O (111) in FIG. 15), and the like. Description) and (101) oriented Zr ₃ O peak (denoted as Zr ₃ O (101) in FIG. 15).

The above results when the substrate temperature at the time of forming the ZrO ₂ film is 500 ° C. are shown in the column “ZrO ₂ film crystallinity” in Table 2 as follows. That is, when the thickness of the Zr film is 5 to 10 nm and the substrate temperature when forming the Zr film is 650 to 700 ° C. (Examples 7 to 9 and 12 to 14), the evaluation result of the crystallinity is single. It is shown as a double circle, which is better than a circle. On the other hand, in other cases (Examples 1 to 6, 10, 11, 15 to 20), the crystallinity evaluation results are indicated by single circles.

In addition, as shown by hatching in FIG. 16, when the substrate temperature when forming the ZrO ₂ film is 550 ° C., the thickness of the Zr film is 5 to 10 nm and the Zr film is formed. When the substrate temperature was 650 to 700 ° C., no peaks other than the (100) -oriented ZrO ₂ peak were observed. On the other hand, when the substrate temperature when forming the ZrO ₂ film is 550 ° C., when the thickness of the Zr film is less than 5 nm, when the thickness of the Zr film exceeds 10 nm, the substrate when forming the Zr film When the temperature was less than 650 ° C., or when the substrate temperature when forming the Zr film exceeded 700 ° C., peaks other than ZrO ₂ (100) were observed. The observed peaks are, for example, the (111) -oriented ZrO ₂ peak (described as ZrO ₂ (111) in FIG. 16), the (111) -oriented Zr ₃ O peak (Zr ₃ O (111) in FIG. 16) Description) and (101) oriented Zr ₃ O peak (denoted as Zr ₃ O (101) in FIG. 16).

The above results when the substrate temperature at the time of forming the ZrO ₂ film is 550 ° C. are shown in the “Crystallinity of ZrO ₂ film” column of Table 3 as follows. That is, when the thickness of the Zr film is 5 to 10 nm and the substrate temperature at the time of forming the Zr film is 650 to 700 ° C. (Examples 27 to 29, 32 to 34), the evaluation result of crystallinity is single. It is shown as a double circle, which is better than a circle. On the other hand, in other cases (Examples 21 to 26, 30, 31, 35 to 40), the crystallinity evaluation results are shown by single circles.

Further, as shown in FIG. 17 with hatching, when the substrate temperature when forming the ZrO ₂ film is 600 ° C., the thickness of the Zr film is 5 to 10 nm and the Zr film is formed. When the substrate temperature was 650 to 700 ° C., no peaks other than the (100) -oriented ZrO ₂ peak were observed. On the other hand, when the substrate temperature when forming the ZrO ₂ film is 600 ° C., when the thickness of the Zr film is less than 5 nm, when the thickness of the Zr film exceeds 10 nm, the substrate when forming the Zr film When the temperature was less than 650 ° C., or when the substrate temperature when forming the Zr film exceeded 700 ° C., peaks other than ZrO ₂ (100) were observed. The observed peaks are, for example, the (111) -oriented ZrO ₂ peak (described as ZrO ₂ (111) in FIG. 17), the (111) -oriented Zr ₃ O peak (Zr ₃ O (111) in FIG. 17), and the like. Description) and (101) oriented Zr ₃ O peak (denoted as Zr ₃ O (101) in FIG. 17).

The above results when the substrate temperature when forming the ZrO ₂ film is 600 ° C. are shown in the column of “Crystallinity of ZrO ₂ film” in Table 4 as follows. That is, when the thickness of the Zr film is 5 to 10 nm and the substrate temperature at the time of forming the Zr film is 650 to 700 ° C. (Examples 47 to 49, 52 to 54), the evaluation result of the crystallinity is single. It is shown as a double circle, which is better than a circle. On the other hand, in other cases (Examples 41 to 46, 50, 51, 55 to 60), the crystallinity evaluation results are indicated by single circles.

In FIGS. 15 to 17, the peak intensity described as “ZrO ₂ (200) weak” is less than 5.0 × 10 ³ cps, and other “ZrO ₂ (200)” is described. It means less than half of the peak intensity.

Although not shown in FIGS. 15 to 17, ZrO ₂ having a thickness of 10 nm is formed even when a ZrO ₂ film having a thickness of 8 nm or 12 nm is formed as an example other than Examples 1 to 60. The same results as those obtained when _two films were formed were obtained.

  From the above results, a film 12a containing zirconium having a thickness of 5 to 10 nm is formed at a temperature of 650 to 700 ° C., and an alignment film 12b containing zirconium oxide having a thickness of 8 to 12 nm is obtained. It has been found that it is preferable to form at a temperature of 500 to 600 ° C. Under such conditions, the alignment film 12b has a tetragonal crystal structure and can contain more (100) -oriented zirconium oxide.

Zirconium (Zr) is easier to oxidize and ionize than silicon (Si). Therefore, a film 12a containing zirconium having a thickness of 5 to 10 nm is formed at a temperature of 650 to 700 ° C., and an alignment film 12b containing zirconium oxide having a thickness of 8 to 12 nm is formed to 500 to 600. By forming at a temperature of ° C., the natural oxide film (SiO ₂ ) present on the upper surface 11a of the substrate 11 which is a silicon substrate can be more completely removed. Therefore, the alignment film 12 b containing zirconium oxide (Zr) can be directly epitaxially grown on the upper surface 11 a of the substrate 11.

In Examples 1 to 60, when the alignment film 12b containing ZrO ₂ was formed, Zr contained in the film 12a was oxidized, whereby the film 12a disappeared and became the alignment film 12b. Therefore, the alignment film 12b is formed directly on the substrate 11, and the alignment film 12 including only the alignment film 12b formed directly on the substrate 11 is formed.

Next, as shown in FIG. 10, a platinum (Pt) film was formed as the conductive film 13 on the alignment film 12 by a sputtering method. The conditions at this time are shown below.
Apparatus: DC sputtering apparatus Pressure: 3.20 × 10 ⁻² Pa
Deposition source: Pt
Power: 100W
Thickness: 100nm
Deposition rate: 0.14 nm / s
Ar flow rate: 16sccm
Substrate temperature: 400 ° C

In the θ-2θ spectrum of the ZrO ₂ film, when peaks of ZrO ₂ (111), Zr ₃ O (111), and Zr ₃ O (101) are observed in addition to the peak of ZrO ₂ (200), In the θ-2θ spectrum, a peak of Pt (111) was observed in addition to the peak of Pt (200). On the other hand, in theta-2 [Theta] spectrum of the ZrO _{2 film,} if in addition to the peak of _{ZrO 2 (200), ZrO 2} (111), Zr 3 peak of O (111) and _Zr 3 O (101) is not observed, Pt film In the θ-2θ spectrum, no Pt (111) peak is observed other than the Pt (200) peak, and the crystallinity of the conductive film 13 can be improved.

Next, as illustrated in FIG. 11, an SRO film was formed as the conductive film 14 on the conductive film 13 by a sputtering method. The conditions at this time are shown below.
Equipment: RF magnetron sputtering equipment Power: 300W
Gas: Ar
Pressure: 1.8Pa
Substrate temperature: 600 ° C
Deposition rate: 0.11 nm / s
Thickness: 20nm

  About Examples 1-60, (theta) -2 (theta) spectrum by the XRD method of the film | membrane structure in which even the SRO film | membrane was formed was measured. FIG. 18 is a graph showing an example of the θ-2θ spectrum by the XRD method of the film structure in which up to the SRO film is formed. The horizontal axis of the graph of FIG. 18 indicates the angle 2θ, and the vertical axis of the graph of FIG. 18 indicates the intensity of X-rays.

FIG. 18 illustrates a case where the thickness of the Zr film is 7 nm, the substrate temperature when forming the Zr film is 700 ° C., and the substrate temperature when forming the ZrO ₂ film is 550 ° C. .

  In the example shown in FIG. 18, a peak corresponding to (200) of Pt having a cubic crystal structure was observed in the θ-2θ spectrum. Therefore, it was found that the conductive film 13 includes Pt having a cubic crystal structure and (100) orientation.

  In the example shown in FIG. 18, a peak corresponding to (100) of SRO having a cubic crystal structure was observed in the θ-2θ spectrum. Therefore, it was found that the conductive film 13 includes SRO having a cubic crystal structure and (100) orientation.

Next, as shown in FIG. 1, a laminated film in which a Pb (Zr _0.52 Ti _0.48 ) O ₃ film (PZT film) is laminated as the piezoelectric film 15 on the conductive film 14 by a coating method. Formed. The conditions at this time are shown below.

An organometallic compound of Pb, Zr, and Ti is mixed so as to have a composition ratio of Pb: Zr: Ti = 100 + δ: 52: 48, and Pb (Zr _0. 2 is added to a mixed solvent of ethanol and 2-n-butoxyethanol _. A raw material solution was prepared so that the concentration of ₅₂ Ti _0.48 ) O ₃ was _0.35 mol / l. Here, δ is a surplus Pb amount in consideration of volatilization of the Pb oxide in the subsequent heat treatment process, and in this example, δ = 20. Further, 20 g of polypyrrolidone having a K value of 27 to 33 was dissolved in the raw material solution.

Next, 3 ml of the prepared raw material solution is dropped onto the substrate 11 made of a 6-inch wafer, rotated at 3000 rpm for 10 seconds, and the precursor solution is applied onto the substrate 11 to thereby apply the precursor. A containing film was formed. Then, the substrate 11 is placed on a hot plate at a temperature of 200 ° C. for 30 seconds, and further, the substrate 11 is placed on a hot plate at a temperature of 450 ° C. for 30 seconds to evaporate the solvent and form a film. Dried. Thereafter, the precursor was oxidized and crystallized by heat treatment at 600 to 700 ° C. for 60 seconds in a 0.2 MPa oxygen (O ₂ ) atmosphere to form a piezoelectric film having a thickness of 100 nm. By repeating the steps from application of the raw material solution to crystallization, for example, five times, a PZT film having a thickness of, for example, 500 nm was formed.

  About Examples 1-60, (theta) -2 (theta) spectrum by the XRD method of the film | membrane structure in which even the PZT film | membrane was formed was measured. FIG. 19 is a graph showing an example of the θ-2θ spectrum by the XRD method of the film structure in which up to the PZT film is formed. The horizontal axis of the graph of FIG. 19 indicates the angle 2θ, and the vertical axis of the graph of FIG. 19 indicates the intensity of the X-ray.

FIG. 19 illustrates a case where the thickness of the Zr film is 7 nm, the substrate temperature when forming the Zr film is 700 ° C., and the substrate temperature when forming the ZrO ₂ film is 550 ° C. .

  In the example shown in FIG. 19, peaks corresponding to (001) and (002) of PZT having a tetragonal crystal structure were observed in the θ-2θ spectrum. Therefore, it was found that the piezoelectric film 15 includes P001T having a tetragonal crystal structure and (001) orientation.

  Further, when the PZT film is formed by a coating method, when the substrate temperature is formed in a temperature range of 600 to 700 ° C. wider than that of the conventional substrate, the piezoelectric film 15 is square as in the example shown in FIG. It has been found that it has a crystal structure of crystals and contains (001) -oriented PZT.

Apart from Examples 1 to 60, when the PZT film was formed by the sputtering method instead of the coating method as the piezoelectric film 15, the same result was obtained. Conditions for forming a PZT film as the piezoelectric film 15 by sputtering are shown below.
Equipment: RF magnetron sputtering equipment Power: 2500W
Gas: Ar / O ₂
Pressure: 0.14 Pa
Substrate temperature: 425-525 ° C
Deposition rate: 0.63 nm / s

  In the case of forming the PZT film by a sputtering method instead of the coating method, when the substrate temperature is formed in a wide temperature range of 425 to 525 ° C. as compared with the conventional case, as in the example shown in FIG. It was found that the piezoelectric film 15 has a tetragonal crystal structure and contains (001) -oriented PZT.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  In the scope of the idea of the present invention, those skilled in the art can conceive various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention.

  For example, those in which the person skilled in the art appropriately added, deleted, or changed the design of the above-described embodiments, or those in which the process was added, omitted, or changed the conditions are also included in the present invention. As long as the gist is provided, it is included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Film structure 11 Substrate 11a Upper surface 12, 12b Alignment film 12a Film 13, 14, 16 Conductive film 15 Piezoelectric film

Claims (15)

(A) preparing a silicon substrate;
(B) forming a first film containing zirconium on the silicon substrate;
(C) after the step (b), forming a second film containing zirconium oxide epitaxially grown on the silicon substrate;
(D) forming a first conductive film containing platinum epitaxially grown on the second film;
(E) forming a epitaxially grown piezoelectric film on the first conductive film;
A method for producing a membrane structure, comprising: In the manufacturing method of the membrane structure according to claim 1,
The silicon substrate has a main surface composed of (100) planes,
In the step (c), the second film containing zirconium oxide epitaxially grown on the main surface, having a cubic crystal structure, and containing (100) -oriented zirconium oxide is formed.
In the step (d), a method for manufacturing a film structure, wherein the first conductive film having a cubic crystal structure and containing (100) -oriented platinum is formed. In the manufacturing method of the membrane structure according to claim 1 or 2,
In the step (b), the first film is formed by vapor deposition,
In the step (c), the second structure is formed by a vapor deposition method. In the manufacturing method of the membrane structure according to claim 3,
In the step (b), the first structure having a thickness of 5 to 10 nm is formed at a temperature of 650 to 700 ° C. In the manufacturing method of the membrane structure according to claim 4,
In the step (c), the film structure is formed by forming the second film at a temperature of 500 to 600 ° C. In the manufacturing method of the membrane structure according to claim 5,
In the step (c), the film structure manufacturing method, wherein the second film having a thickness of 8 to 12 nm is formed. In the manufacturing method of the film | membrane structure as described in any one of Claims 1 thru | or 6,
In the step (e), the piezoelectric film having the tetragonal crystal structure and containing the (001) -oriented lead zirconate titanate is formed. In the manufacturing method of the film | membrane structure as described in any one of Claims 1 thru | or 6,
In the step (e), a method for manufacturing a film structure, wherein the piezoelectric film having a rhombohedral crystal structure and containing (100) -oriented lead zirconate titanate is formed. In the manufacturing method of the membrane structure according to any one of claims 1 to 8,
(F) forming a second conductive film on the piezoelectric film;
A method for producing a membrane structure, comprising: A silicon substrate;
A first film containing zirconium formed on the silicon substrate;
A second film comprising zirconium oxide epitaxially grown on the first film;
A first conductive film containing platinum epitaxially grown on the second film;
A piezoelectric film epitaxially grown on the first conductive film;
A membrane structure. The membrane structure according to claim 10,
The silicon substrate has a main surface composed of (100) planes,
The second film has a cubic crystal structure and includes (100) -oriented zirconium oxide,
The first conductive film has a cubic crystal structure and includes (100) -oriented platinum. The membrane structure according to claim 10 or 11,
The first film has a thickness of 5 to 10 nm;
The second film is a film structure having a thickness of 8 to 12 nm. The film structure according to any one of claims 10 to 12,
The piezoelectric film has a tetragonal crystal structure and includes (001) -oriented lead zirconate titanate. The film structure according to any one of claims 10 to 12,
The piezoelectric film has a rhombohedral crystal structure and includes (100) -oriented lead zirconate titanate. The film structure according to any one of claims 10 to 14,
A film structure having a second conductive film formed on the piezoelectric film.

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