JP2017199719A - Ferroelectric film formation method, ferroelectric film, liquid discharge head, and liquid discharge device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a ferroelectric film formation method which enables the reduction in preparation cost by decreasing the number of kinds of precursor liquids to be prepared to a necessary minimum, and which enables the increase in the yield of ferroelectric elements to be fabricated from one substrate by reducing the variations in in-plane characteristics of a ferroelectric film obtained on one substrate; a ferroelectric film formed by the ferroelectric film formation method; a liquid discharge head arranged by use of the ferroelectric film; and a liquid discharge device.SOLUTION: A ferroelectric film formation method is arranged to form an amorphous film on a substrate 8 having a lower electrode film formed thereon by repeating the steps of coating the substrate with a precursor liquid, drying the precursor liquid coating, and causing a thermal decomposition in the dried coating more than once and then, performing a high-temperature treatment on the amorphous film to crystallize the amorphous film. The method comprises: a first step where a plurality of kinds of precursor liquid different in composition are mixed in different predetermined proportions according to the round of coating on the substrate 8 with the precursor liquid; a second step where the resultant precursor liquid is heated to a synthetic reaction temperature of the precursor liquid; a third step where the heated precursor liquid is cooled to a predetermined coating temperature; and a fourth step where the substrate 8 is coated with the precursor liquid thus cooled.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ferroelectric film forming method, a ferroelectric film, a liquid discharge head, and a liquid discharge apparatus.

  An ink jet in which a part of a pressure generating chamber communicating with a nozzle opening for discharging ink is constituted by a vibration plate, and the vibration plate is deformed by a piezoelectric element to pressurize the ink in the pressure generating chamber and discharge the ink from the nozzle opening. Recording devices are known. In this ink jet recording apparatus, two types of piezoelectric actuators are known, one that expands and contracts in the axial direction of the piezoelectric element and one that uses a bending force, and among these piezoelectric films that use the bending force, zircon titanate. A ferroelectric film made of a complex oxide crystal film such as lead acid (PZT) is used.

  In order to obtain a ferroelectric film having good characteristics, it is only necessary to prepare many kinds of precursor liquids with finely changed compositions and to form a laminated film while properly using them. Preparation of the precursor liquid takes a long synthesis process time and cost. Furthermore, regarding an apparatus that performs film formation using different types of prepared precursor liquids, for example, a plurality of coating lines corresponding to the types of precursor liquids to be used in a coating process part in which the precursor liquids are dropped and spin coated on a silicon wafer. (It is necessary to provide a pressurized tank, a liquid feed line, a discharge nozzle, and a control system for these, which individually set each precursor liquid), and it is extremely difficult to achieve without significant cost increase of the film forming apparatus.

  Therefore, the present inventor mixes and applies the precursor liquids having different compositions with different ratios according to the number of times of application of the precursor liquid (the number of times the amorphous film or thin crystal film is laminated), and apply the composition in the thickness direction. Disclose a method for reducing the change, and by mixing and applying the minimum kinds of precursor liquids at different ratios as appropriate, while suppressing the synthesis and preparation costs of the precursor liquids, various types of prepared precursor liquids with finely changed compositions A method has been proposed in which stacked film formation is used to obtain an effect of reducing the composition change in the thickness direction (see, for example, “Patent Document 1”).

  However, as a result of forming the PZT film, which is a ferroelectric film, by the above-described method, the composition variation in the thickness direction is eliminated, and improvement in characteristics as a ferroelectric or piezoelectric body is confirmed. There is a problem that the variation in the ferroelectric or piezoelectric characteristics in the inside becomes larger than the in-plane characteristic variation in the ferroelectric film formed by the conventional method.

  The present invention solves the above-mentioned problems, and provides a method for forming a ferroelectric film by a CSD method represented by a sol-gel method, in particular, characteristics of a ferroelectric film obtained by using a plurality of types of precursor liquids. In the improved method of forming a ferroelectric film, the kind of precursor liquid to be prepared is reduced to the minimum necessary and the preparation cost is reduced, and variation in in-plane characteristics of the ferroelectric film obtained on one substrate is reduced. Ferroelectric film formation method capable of improving the yield of ferroelectric elements fabricated from a single substrate by reducing the size, ferroelectric film formed by this film formation method, and this ferroelectric It is an object of the present invention to provide a liquid discharge head and a liquid discharge apparatus that use a body film.

  In the present invention, after applying the precursor liquid on the substrate on which the lower electrode is formed, drying, and thermal decomposition are repeated a plurality of times to form an amorphous film on the substrate, the amorphous film is subjected to high temperature treatment. In the method of forming a ferroelectric film to be crystallized, mixing is performed with a first step of mixing a plurality of types of the precursor liquids having different compositions at different predetermined ratios depending on the number of times of application onto the substrate. A second step of heating the precursor liquid to a synthesis reaction temperature of the precursor liquid; a third step of cooling the heated precursor liquid to a predetermined coating temperature; and applying the cooled precursor liquid on the substrate. And a fourth step.

  According to the present invention, the mixing state of each precursor liquid in the preparation precursor liquid becomes more uniform due to the heat treatment, and the polymerization reaction is promoted between the precursor liquids in the preparation precursor liquid, so that a strong bonding relationship is established between the two. Arise. As a result, the uniformity of the crystal film in the coating film coated on the substrate is further increased, and the in-plane uniformity of the obtained crystal film characteristics can be improved.

It is a flowchart explaining the film-forming process of the ferroelectric film by the CSD method applicable to one Embodiment of this invention. (A) A diagram showing a cross-sectional SEM image of a PZT film formed by the CSD method. (B) In-film by the GD-OES method from the surface of the PZT crystal film formed by the CSD method toward the inside in the film thickness direction. It is a figure which shows the result of having analyzed the element ratio of lead, zirconium, and titanium. It is the schematic of the automatic film-forming apparatus used for one Embodiment of this invention. It is the schematic explaining the spinner coating device and dripping mechanism used for one Embodiment of this invention. It is the schematic which shows the cross-sectional SEM image of the PZT film | membrane obtained through the process used for one Embodiment of this invention. (A) A PZT film obtained according to an embodiment of the present invention is measured with an X-ray diffractometer. (200) A diagram showing an in-plane distribution of crystal peak intensity. (B) A composite oxide component composition that differs depending on the number of laminations. In the conventional method, a ferroelectric film is formed by a method in which the precursor liquid is appropriately prepared by applying the minimum kind of precursor liquid prepared in advance for each coating process and applied, and heat treatment of the prepared precursor liquid is not performed. It is a figure which shows the in-plane distribution of the (200) crystal peak intensity which measured the formed PZT film | membrane with the X-ray-diffraction apparatus. It is a schematic sectional drawing of the liquid discharge head which can apply one Embodiment of this invention. 1 is a schematic perspective view of an ink cartridge to which an embodiment of the present invention can be applied. 1 is a schematic perspective view of a liquid ejection apparatus to which an embodiment of the present invention can be applied. 1 is a schematic front view of a liquid ejection apparatus to which an embodiment of the present invention can be applied.

  The ferroelectric film shown in an embodiment of the present invention is formed on a silicon wafer substrate on which a lower electrode is formed by a sputtering method or a CSD method such as a sol-gel method or a MOD method. Among these, a ferroelectric film forming method by a CSD method typified by a sol-gel method will be described below.

First, a precursor solution synthesized in accordance with the composite oxide composition of the ferroelectric film to be formed is applied onto a silicon wafer substrate on which the lower electrode is formed by spin coating or the like, and a coating film of the precursor solution is applied to the substrate. Formed on top (application process).
Next, the precursor liquid coating film is heated to the drying temperature which is the first heating temperature to evaporate the solvent remaining in the coating film, and a dried film obtained by drying the precursor liquid coating film is formed on the substrate. (Drying process).

Next, the dry film is heated to a thermal decomposition temperature that is a second heating temperature higher than the first heating temperature to decompose organic components in the dry film, thereby forming an amorphous film of a composite oxide on the substrate. (Pyrolysis process or degreasing process).
After repeating the steps of applying, drying, and pyrolyzing the precursor liquid coating film a predetermined number of times, the amorphous film formed on the substrate is heated to a crystallization temperature that is a third heating temperature higher than the second heating temperature. Crystallization is performed to form a complex oxide crystal film having ferroelectric characteristics (crystallization process).
Further, by repeating the above steps from application of the precursor liquid to crystallization a predetermined number of times, a ferroelectric film made of a complex oxide crystal film having a desired thickness is formed.

  FIG. 1 is a process flowchart of the CSD method described above. In the step shown in FIG. 1, the crystallization process is repeated Y times after repeating the coating or pyrolysis step X times, that is, the precursor liquid is applied X × Y times to form a ferroelectric film having a desired thickness. ing. The CSD method represented by the sol-gel method composed of such steps can easily change and control the metal component composition in the precursor liquid applied on the substrate, and the composite oxide obtained thereby It has a feature that the composition of the crystal film and the characteristics as a ferroelectric film can be controlled.

  By the way, when a ferroelectric film, which is a complex oxide crystal film formed on a silicon wafer substrate, is applied to a piezoelectric element used in an ink jet recording head, which is a liquid discharge head, a certain amount of force is required to generate a required bending force. It is necessary to form a ferroelectric film having the above thickness, preferably 1 to several μm. When a ferroelectric film having such a thickness is formed by the CSD method, the CSD method consisting of the coating of the precursor liquid, thermal decomposition, and crystallization steps is performed each time the precursor liquid supplied to the process passes through each step. The state of the film is changed while contracting the volume of the film, the amorphous film, and the crystal film. For this reason, when trying to obtain a ferroelectric film having a thickness on the order of μm in a single process, there is a problem that innumerable cracks are generated in the completed ferroelectric film.

  In order to overcome the above-mentioned problems and obtain a ferroelectric film having a thickness of μm without cracks, a thin crystal film is repeatedly formed and laminated on a silicon wafer substrate (the coating or crystallization process in FIG. 1). Is repeated Y times). For example, in order to obtain a ferroelectric film having a thickness of about 1 μm, a CSD process is performed in which the precursor liquid is applied several times, and a thin crystal film having a thickness of about 100 nm is laminated per one application of the precursor liquid. Thus, a ferroelectric film having a desired thickness can be obtained.

  However, there is often a problem that the characteristics of the ferroelectric film obtained by laminating the thin crystal films as described above do not reach sufficient values as compared with the calculated predicted values. In order to clarify this cause, a detailed analysis was performed on the ferroelectric film constituting the piezoelectric element. As a result, the composition of the complex oxide constituting the ferroelectric film was not enough to form the precursor liquid. While it is consistent with the composition of the precursor liquid used, many problems have been confirmed that the composition is not uniform in the thickness direction of the film.

The mechanism by which the composition in the film thickness direction of the ferroelectric film described above becomes non-uniform will be described below. In the CSD method, after the coating or thermal decomposition process of the precursor liquid synthesized according to the desired ferroelectric film composition is repeated X times, the obtained laminated amorphous composite oxide is heated and crystallized. In the crystallization process, a phenomenon occurs in which the composition in the film thickness direction of the ferroelectric film becomes non-uniform.
The reason is that each metal atom constituting the amorphous composite oxide first moves in the film by the thermal energy supplied during the heating process of the crystallization step, and coordinates to a predetermined position of the composite oxide crystal structure. This is because the ease of movement (hereinafter referred to as the movement speed) differs depending on the type and element of the metal atom.

  For example, in the case of a PZT film (lead oxide, zirconium, titanium composite oxide film) which is a typical ferroelectric film, titanium atoms move faster during the reaction than zirconium atoms, and during the crystallization process. A crystal structure is formed at a timing faster than that of a zirconium atom. For this reason, a phenomenon in which zirconium atoms having a relatively low moving speed cannot be coordinated to a predetermined position of the complex oxide crystal structure due to the movement of the titanium atoms is often caused. Furthermore, the vapor pressure of the lead element is low, and the lead atom easily volatilizes in the atmosphere by heat applied in the crystallization process.

  Due to the difference in the crystallization speed or separation from the reaction system, the thin film of the complex oxide crystal formed by one crystallization process may be partially exposed to an atmosphere outside the film particularly during the crystallization process. In the vicinity of the surface layer of the crystal film where components that are directly exposed and easily volatilize are easily released to the atmosphere outside the film, an excess or deficiency of metal elements to be coordinated in the crystal structure occurs. In addition, the degree of excess and deficiency of the metal element generated in the crystal structure is greatly influenced by the heating process conditions including the atmosphere control conditions.

As described above, the ferroelectric film obtained by repeating the crystallization process Y times and laminating the thin crystal film on the Y layer is located at the stack interface of the stacked thin crystal films, in other words, near the surface of the thin crystal film. In the corresponding region, the region where the excess or deficiency of the metal element occurs in the crystal structure appears in a layered manner with respect to the film thickness direction of the ferroelectric film.
As a result, since the crystal structure of the complex oxide that exhibits ferroelectricity is not perfect in the above-described region, the characteristics of the obtained ferroelectric film do not reach the theoretically expected value.

  FIG. 2A shows a cross-sectional SEM image of a PZT film formed by a conventional CSD method, and the stacked interface 1 when the above-described thin crystal film is stacked can be confirmed. When the composition of this interface region is analyzed in detail, the composition ratio of each element of lead, zirconium, and titanium is different from the upper and lower portions. Specifically, the ratio of lead element is low due to disappearance due to volatilization during the crystallization process, and the ratio of zirconium element is high due to the relatively slow crystallization rate and accumulation of atoms left behind in crystallization. At the same time, the ratio of titanium element is low.

FIG. 2B shows the result of analyzing the element ratio of lead, zirconium and titanium in the film by the GD-OES method from the surface of the PZT crystal film formed by the CSD method toward the inside in the film thickness direction. ing. In the figure, it can be confirmed that the composition ratio variation as described above occurs in the film thickness direction, centering on the crystal thin film stack interface.
On the other hand, the phenomenon in which excess or deficiency of metal elements appears in the crystal structure is also observed between the layers of the amorphous composite oxide laminated film formed before the crystallization step. The reason why the excess or deficiency of the metal element in the crystal structure changes between the layers of the amorphous composite oxide multilayer film will be described below.

  In the process of forming a ferroelectric film by the CSD method, first, a precursor solution is applied onto a lower electrode film that is a conductive layer, and this coating film is heated, dried, and degreased to form an amorphous composite oxide film. Crystallization is performed after the amorphous composite oxide film is laminated by repeating X times. For this reason, the amorphous composite oxide multilayer film to be crystallized is a conductive layer, an amorphous layer, or a complex oxide film that has already been crystallized, depending on the number and timing of lamination. These are in contact with layers having different properties. The upper surface is also in contact with an amorphous film or an air layer and a layer having completely different properties.

When an amorphous composite oxide multilayer film having different interface layers as described above is put into the crystallization process, the crystallization reaction proceeds while being influenced by the properties of the layers in contact, particularly in the vicinity of the interface. Therefore, the crystallization of the amorphous composite oxide multilayer film proceeds differently depending on the number of times and timing of the lamination.
As a result, in the prepared complex oxide thin crystal film, there is a difference in mobility and volatility of the metal elements forming the complex oxide, especially in the vicinity of the interface of the amorphous complex oxide multilayer film before the crystallization process. Due to this, there occurs a phenomenon that the state of excess or deficiency of the metal element to be coordinated in the crystal structure differs between the laminated films.

The phenomenon that the composition in the film thickness direction of the ferroelectric film becomes non-uniform due to the phenomenon that occurs during the crystallization process of such an amorphous composite oxide multilayer film is not only due to the thin crystal film stack interface but also inside the thin crystal film. It also occurs near the interface of the amorphous composite oxide multilayer film. As a result, since the crystal structure of the complex oxide that exhibits ferroelectricity is not perfect, the characteristics of the obtained ferroelectric film do not reach theoretically expected values.
In order to solve the above problems, the inventor of the present application is a method in which the surface layer portion of a thin crystal film in which excess or deficiency of metal elements is frequently generated in each repeated crystallization process is removed by CMP polishing to reduce composition variation in the thickness direction. Has been proposed by.

However, the above-described method is a method of alternately performing a polishing process that is completely different from the film forming process using the CSD method, and it becomes a complicated system in which a silicon wafer substrate is alternately exchanged between the two processes, and the throughput is reduced. And the problem that the polishing liquid that cannot be completely removed on the surface of the silicon wafer substrate after the polishing process causes defects in the subsequent film formation process.
Furthermore, by preparing multiple types of precursor liquids with different compositions by the CSD method and laminating films while finely changing the composition according to the number of laminations, the composition uniformity in the thickness direction of the obtained ferroelectric film is improved. The effect of enhancing and improving the ferroelectric characteristics and the piezoelectric characteristics can be obtained. On the other hand, however, there is a problem that the preparation cost of various precursor liquids whose compositions are finely changed in accordance with the number of laminations and the cost of an apparatus for forming a film by selectively using various precursor liquids are very high.

  In addition, a method of preparing a minimum number of types of precursor liquids, appropriately mixing them according to the number of laminations, and laminating a film while finely changing the composition can be obtained while suppressing the cost of preparing various types of precursor liquids. It is possible to increase the composition uniformity in the thickness direction of the ferroelectric film and to improve the ferroelectric characteristics and piezoelectric characteristics. However, on the other hand, the ferroelectric film formed on one silicon wafer substrate, and the characteristic variation between the elements of the ferroelectric element or the piezoelectric element obtained therefrom are increased in the substrate surface, and the yield is lowered. There was a problem.

  Therefore, in the method of the present invention, the prepared precursor liquid is appropriately prepared according to the optimum composition according to the number of laminations, and then the prepared precursor liquid is heated to the synthesis reaction temperature of the precursor liquid, After cooling to a predetermined coating temperature, a method of dropping it onto a silicon wafer substrate and applying it is adopted, and the coating film obtained by this method is further subjected to a predetermined drying, pyrolysis, and crystallization process. By performing the above steps to form a ferroelectric thin film, it is possible to obtain a ferroelectric film excellent in uniformity not only in the film thickness direction of the ferroelectric film but also in the substrate surface.

In the sol-gel method, which is representative of the CSD method, an organic or inorganic compound of a metal (M) is hydrolyzed in a solution, and then a polycondensation reaction proceeds to bond a metal-oxygen-metal (MOM) bond. This is a method for producing ceramics by forming a polymer having the polymer and heating the polymer. When the degree of polymerization of MOM is low, it is a liquid called “sol”, but when polycondensation proceeds, it becomes a solid called “gel”.
When producing a complex oxide crystal film that becomes a ferroelectric film by this sol-gel method, for example, a PZT crystal film, the metal forming the PZT crystal, that is, each compound of lead, zirconium, and titanium is hydrolyzed in one solution. What is necessary is just to prepare sol which is the solution which advanced the polycondensation reaction, apply | coat it on the silicon wafer board | substrate which formed the lower electrode into a film, and heat it. Incidentally, this sol becomes a precursor liquid for obtaining a PZT crystal film.

  The above-mentioned problems, particularly in the technique of preparing a minimum number of types of precursor liquids and appropriately mixing them according to the number of laminations and performing multilayer film formation while finely changing the composition, in the substrate surface of the ferroelectric characteristics Regarding the problem of the uniformity being lost, for example, in order to form a PZT crystal film, a PT (lead titanate) precursor solution and a PZ (lead zirconate) precursor solution are prepared, and both are appropriately set according to the number of times of lamination. Consider the case where a laminated film is formed while mixing and finely changing the composition.

The PZ precursor liquid contains a polymer of a compound having lead, a polymer of a compound having titanium, and a polymer in which both are bonded (double alkoxide). On the other hand, the PZ precursor liquid contains a polymer of a compound having lead, a polymer of a compound having zirconium, and a polymer in which both are bonded (double alkoxide).
When a PT precursor liquid and a PZ precursor liquid are prepared to prepare a PZT precursor liquid (prepared precursor liquid), each component ratio of PZT in the coating film obtained by uniformly mixing both precursor liquids and applying them onto the substrate Should be basically the same in any part of the coating on the substrate, but there is a strong bonding relationship such as a double alkoxide between the titanium polymer and the zirconium polymer in the preparation precursor liquid. Therefore, when the prepared precursor liquid is spread on the substrate by a spin coating method or the like to form a coating film, a difference occurs in how the titanium polymer and the zirconium polymer are spread. As a result, the composition uniformity of both cannot be made perfect as a whole coating film surface, and the in-plane uniformity of the obtained PZT crystal film characteristic will be impaired.

  In order to cope with this problem, the present invention adds a process of heating the precursor liquid prepared in accordance with the number of times of lamination to the synthesis reaction temperature of the precursor liquid before coating. By this heat treatment, the mixed state in the preparation precursor liquid becomes more uniform, and the polymerization reaction is promoted between the titanium polymer and the zirconium polymer in the preparation precursor liquid, and there is a strong bonding relationship between the two. Arise. As a result, the uniformity as the PZT crystal film in the coating film coated on the substrate is further increased, and the in-plane uniformity of the obtained PZT crystal film characteristics can be improved.

In other words, a deposition method in which a ferroelectric oxide film is formed by laminating a complex oxide crystal film having ferroelectricity by the CSD method, particularly in a precursor liquid application step by a spin coating method, which is put into a single crystallization step. Regarding the application of the precursor liquid by the spin coating method performed X times until the first time, the first, the second, ..., each composite oxide component composition dispersed in the liquid of the precursor liquid applied for the Xth time is laminated It is characteristic that it is defined while appropriately changing according to the number of times.
Further, it is characterized in that a precursor liquid having a different composite oxide component composition for each number of laminations is appropriately prepared and prepared by preparing in advance a minimum kind of precursor liquid prepared for each coating process.
The prepared precursor liquid is heated to the synthesis reaction temperature of the precursor liquid, then cooled to a predetermined application temperature, and then dropped and applied onto the substrate.
Hereinafter, the features of the present invention will be described in detail.

  FIG. 3 shows an automatic film forming apparatus 10 for forming a ferroelectric film by the method according to the present invention. This automatic film forming apparatus 10 is a sheet type apparatus for flowing a silicon wafer substrate (not shown) on which a lower electrode has been formed one by one. The automatic film forming apparatus 10 conveys a storage member 9 for storing a substrate and the substrate to each part in the apparatus. The transfer device 2, the substrate delivery in the device, the aligner 3 for positioning and centering the substrate in each part constituting the device, the spinner coating device 4 for applying the precursor liquid of the ferroelectric film on the substrate, It has a hot plate 5 for drying the precursor liquid, an RTA (Rapid Thermal Annealing) apparatus 6 for performing heat treatment in the thermal decomposition process and crystallization process of the dried film, and a cooling stage 7 for cooling the wafer after the heat treatment in the RTA apparatus. ing. In this embodiment, the thermal decomposition process and the crystallization process are performed by one common RTA apparatus 6, but the thermal decomposition process and the crystallization process are performed by two different RTA apparatuses, respectively, The decomposition process may be performed by the hot plate 5 and the crystallization process may be performed by the RTA apparatus 6.

  The substrate stored in the storage member 9 is first positioned and centered by the aligner 3, and then flows between the parts in charge of each process in the chart by the transport device 2 according to the flowchart shown in FIG. The substrate positioned and centered by the aligner 3 is put into the spinner coating device 4 to apply the precursor liquid, and the substrate on which the coating film of the precursor liquid is subsequently formed is put into the hot plate 5 by the transport device 2. The applied precursor coating is heated and dried. The substrate after the drying process is put into the RTA apparatus 6 by the transport apparatus 2, and the precursor dried film is heated and thermally decomposed.

  Subsequently, after repeating the coating process or the thermal decomposition process described above a predetermined number of times (X times), the laminated amorphous film formed on the silicon wafer substrate up to the crystallization temperature higher than the thermal decomposition temperature by the RTA apparatus 6. Is heated and crystallized to form a complex oxide crystal thin film having ferroelectricity. Then, the above-described coating process or crystallization process is repeated a predetermined number of times (Y times) to form a complex oxide crystal thin film to form a ferroelectric film having a desired thickness, and this is further processed Thus, a target device such as a piezoelectric element is obtained.

The feature of the present invention lies particularly in the coating step of coating the ferroelectric film precursor liquid on the wafer substrate in the above-described ferroelectric film forming process.
FIG. 4 shows a spinner coating apparatus 4 for coating the precursor liquid on the wafer substrate used in the present embodiment. The spinner coating device 4 is connected to a spinner chuck 11 that holds the silicon wafer substrate 8 by suction and a spindle motor 12 and rotates the silicon wafer substrate 8 that is sucked and held by the spinner chuck 11 according to a program input to the control device 13. And a dropping mechanism 15 for dropping the precursor liquid onto the silicon wafer substrate 8. The characteristic feature of the present invention resides in the dropping mechanism 15.

The dropping mechanism 15 has precursor liquid containers 16 a, 16 b, 16 c that store a precursor liquid (not shown), and a liquid feed line 17 that connects each precursor liquid container 16 and the preparation tank 19. A constant volume pump 18 for feeding a precursor liquid of a volume determined by the control device 13 from the precursor liquid container 16 to the preparation tank 19 is incorporated in the liquid feed line 17 in the middle.
The blending tank 19 is provided with a heating mechanism 20 and a stirring mechanism 21 controlled by the control device 13, and a pressurizing line 23 for feeding the blending precursor liquid in the blending tank 19 to the cooling tank 22. A purge line 24 for cleaning the inside of the tank is connected.
Further, the cooling tank 22 is provided with a cooling mechanism 25 and a stirring mechanism 26 controlled by the control device 13, and the prepared precursor liquid in the cooling tank 22 is discharged from the nozzle 28 via the arm 27. A pressure line 29 for dropping on the silicon wafer substrate 8 and a purge line 30 for cleaning the inside of the tank and the inside of the dropping line from the cooling tank 22 to the nozzle 28 via the arm 27 are connected.

Moreover, in this embodiment, as the liquid feeding line 17 for feeding the precursor liquid from the precursor liquid container 16 to the preparation tank 19 via the constant volume pump 18, a coating film that is dropped and formed according to the number of times of coating (number of times of lamination). In order to adjust the composition to an appropriate composition, the number corresponding to the number of precursor liquids necessary and minimum is provided.
And, for the precursor liquid applied for the first time, the second time, ..., the Xth time, the minimum number of precursor liquids prepared in advance so as to have a complex oxide component composition that is finely determined according to each number of times. Each of them is metered by a constant capacity pump 18 and sent to a blending tank 19 for blending. Next, the precursor liquid prepared in the preparation tank 19 is heated to the synthesis reaction temperature of the precursor liquid before preparation. Then, the prepared precursor liquid is fed to the cooling tank 22, cooled to a predetermined coating temperature, and then dropped and coated on the silicon wafer substrate 8, and this is put into the processes after the coating process shown in FIG. Then, a ferroelectric film having a desired film thickness is formed.

The ferroelectric film obtained by such a process is finely changed in composition according to the number of laminations so as to compensate for the composition fluctuation in the complex oxide crystal generated in the heating process in the crystallization process or the thermal decomposition process. Since the film is formed using the precursor liquid, it is possible to obtain excellent ferroelectric characteristics and piezoelectric characteristics with high composition uniformity in the thickness direction.
In addition, the precursor liquid whose composition is finely changed according to the number of times of lamination is prepared by preparing the minimum kind of precursor liquid and appropriately mixing it according to the number of times of lamination, so that the composition is finely changed. The cost of preparing body fluid can be suppressed.

Furthermore, in the present invention, the precursor liquid prepared in an appropriate composition for each coating process is heated to the synthesis reaction temperature of the precursor liquid before preparation before coating, and polymerization between the respective precursor liquid components mixed and adjusted is performed. Since the prompting operation is performed, the uniformity of the prepared precursor liquid is improved, and the uniformity of the ferroelectric film on which the liquid is formed in the silicon wafer substrate is increased. As a result, the yield of elements taken out from one silicon wafer substrate is improved.
And, since the preparation precursor liquid heated to the synthesis reaction temperature of the precursor liquid before preparation is dropped and applied on the silicon wafer substrate, an operation of cooling to a predetermined application temperature is performed, so that the obtained ferroelectric film Even between substrates having different film thicknesses, the quality of the obtained ferroelectric element can be stabilized.
A specific example is shown below.

  A ferroelectric film with a thickness of 1.2 μm of lead zirconate titanate (lead: zirconium: titanium = 100: 53: 47) having an MPB composition known to have good ferroelectric and piezoelectric properties is shown in FIG. In the process shown in FIG. 4, the film is manufactured under conditions of X = 4 and Y = 4. Under these conditions, the ratio of lead, zirconium, and titanium in the precursor liquid at X = 1 (application of the precursor liquid for the first process) is 115: 52: 48, hereinafter X = 2 and 110: 54: 46, X = 3, a precursor solution having a composition of 110: 56: 44 and X = 4 of 120: 50: 50 is applied at the timing of each lamination.

In order to prepare the precursor liquid having the above-mentioned PZT composition, lead acetate trihydrate, zirconium propoxide, titanium isopropoxide as a starting material, 2-methoxyethanol as a common solvent, and the following three types of precursors Body fluid (stock solution) was synthesized.
PZ precursor liquid (PZ concentration 0.5 mol / L, lead zirconium composition ratio = 110: 100)
PT precursor liquid (PT concentration 0.5 mol / L, lead titanium composition ratio = 110: 100)
Lead precursor liquid (PB concentration 0.5 mol / L)

First, the synthesis of the PZ precursor liquid will be described. After weighing a predetermined amount of lead acetate trihydrate in 2-methoxyethanol, the solution temperature exceeds the boiling point (125 ° C) of 2-methoxyethanol in a dry atmosphere, preferably 130-135 ° C. For 12 hours. During this time, crystal water is fractionated and dehydrated with 2-methoxyethanol, and a reaction in which the acetate group of lead acetate and the methoxyethoxy group of 2-methoxyethanol are substituted proceeds.
Next, after the lead acetate trihydrate dehydration step is completed, a predetermined amount of zirconium propoxide is added in a state where the solution temperature is lowered to 80 ° C. or lower, and the solution temperature exceeding the boiling point of 2-methoxyethanol again, Preferably it heated at the solution temperature of 128-130 degreeC for 12 hours. During this time, an alcohol exchange reaction in which the propyl group of zirconium propoxide and the methoxyethoxy group of 2-methoxyethanol are substituted, and an esterification reaction between the acetate group and the alcohol group of lead acetate occurs. While these side reaction products are fractionated together with 2-methoxyethanol, the polymerization reaction also proceeds between the lead compound and the zirconium compound in the solution.
Then, 2-methoxyethanol is added to the synthesis solution, which is completed after the above-described reaction, is stopped to heat, and cooled to room temperature, so as to obtain a predetermined concentration, thereby completing the PZ precursor solution.
The synthesis of the PT precursor liquid is performed in the same manner as the synthesis of the PZ precursor liquid. Moreover, the lead precursor liquid is completed by adding 2-methoxyethanol so that the lead precursor liquid has a predetermined lead precursor concentration at the end of the first half of the PT precursor liquid synthesis process. This is the first step of the present invention.

Next, the formation of a PZT ferroelectric film will be described.
The synthesized PZ precursor liquid, PT precursor liquid, and lead precursor liquid are respectively injected into the precursor liquid containers 16a, 16b, and 16c shown in FIG. Next, the silicon wafer substrate 8 housed in the housing member 9 of the automatic film forming apparatus 10 shown in FIG. 3 is positioned and centered by the aligner 3 and then loaded into the spinner coating device 4 by the transport device 2. First, the precursor liquid is applied (X = 1, Y = 1 in FIG. 1).
At this time, the PZ precursor liquid PT precursor liquid and the lead precursor liquid are respectively charged into the preparation tank 19 at a ratio of 52: 48: 6 from the precursor liquid containers 16a, 16b and 16c by the constant volume pump 18 and stirred, and the solution temperature is increased. It is heated until it reaches 132 ° C., which exceeds the synthesis reaction temperature of the precursor liquid before blending (it becomes a blended precursor liquid with PZT ratio = 115: 52: 48). This is the second step of the present invention.

Subsequently, the preparation precursor liquid is transferred to the cooling tank 22 by operating the pressurizing line 23, and is cooled so that the solution temperature becomes 25 ° C. therein. At this time, the inside of the preparation tank 19 is cleaned by the cleaning liquid (2-methoxyethanol) introduced by operating the purge line 24, and the waste liquid used for cleaning is discharged from the purge line 24 to the waste liquid tank 31. This is the third step of the present invention.
Then, the prepared precursor liquid cooled to the predetermined solution temperature is discharged from the nozzle 28 via the arm 27 by the pressurized gas introduced by operating the pressure line 29 and dropped onto the silicon wafer substrate 8. . After the dropping of the blended precursor liquid, in the cooling tank 22 and the dripping line from the cooling tank 22 to the nozzle 28, the purge line 30 is operated in the same manner as the blending tank 19 to clean the inside of the tank and the dropping line. The used cleaning waste liquid is discharged to a waste liquid tank 31. This is the fourth step of the present invention.

Subsequently, with respect to the prepared precursor liquid dropped on the silicon wafer substrate 8, the spindle 14 is rotated up to 2500 rpm in accordance with a program input to the control device 13, and the excess prepared precursor liquid is shaken off. A coating film of the precursor liquid is formed thereon (application process).
The silicon wafer substrate 8 on which the coating film of the precursor liquid is formed is put into the hot plate 5 heated to the set temperature of 120 ° C. by the transfer device 2 for 1 minute, and the precursor coating film is heated and dried (drying process). ).

The silicon wafer substrate 8 that has finished the drying process is put into the RTA apparatus 6 by the transfer apparatus 2 and performs heating and pyrolysis treatment of the precursor dry film under the conditions of a set temperature of 480 ° C. and a heating time of 5 minutes (thermal decomposition).・ Degreasing process).
The silicon wafer substrate 8 that has been subjected to the thermal decomposition process is put into the cooling stage for 5 minutes or more by the transfer device 2 and cooled to room temperature (cooling step).

The above-described coating process or thermal decomposition process (cooling process) is repeated three more times. The ratio of the PZ precursor liquid, PT precursor liquid, and lead precursor liquid prepared in the second coating process is 54: 46: 0 ( PZT ratio = 110: 54: 46 preparation precursor liquid) The ratio of the PZ precursor liquid, PT precursor liquid, and lead precursor liquid prepared in the third coating step is 56: 44: 0 (PZT ratio = 110: 56: 44 preparation precursor liquid) The ratio of the PZ precursor liquid, PT precursor liquid, and lead precursor liquid prepared in the fourth coating step is 50:50:12 (PZT ratio = 120: 50: 50 preparation precursor liquid). Change formulation conditions.
After repeating the process a predetermined number of times (X = 4 times), the laminated amorphous film formed on the silicon wafer substrate 8 is heated up to 780 ° C., which is a crystallization temperature higher than the thermal decomposition temperature, in the RTA apparatus 6, This is held for 7 minutes for crystallization to form a complex oxide crystal thin film having ferroelectricity. By repeating this coating step or crystallization step a predetermined number of times (Y = 4 times), a composite oxide crystal thin film is laminated to form a ferroelectric film having a desired thickness of 1.2 μm.

  FIG. 5 shows a cross-sectional SEM image of the PZT film obtained through the above-described process. Unlike the PZT film (see FIG. 2A) formed by the conventional CSD method, the interface between the stacked crystal films is not recognized and has a uniform composition in the thickness direction. As a result, the characteristics of the ferroelectric element or the piezoelectric element obtained by further processing the PZT film, which is the ferroelectric film obtained in the present invention, are better than those of the conventional one. .

  In order to evaluate the crystallinity of the PZT film obtained by the method of the present invention, the in-plane distribution of (200) crystal peak intensity measured with an X-ray diffractometer is shown in FIG. Further, as in the present invention, a ferroelectric film is formed by a method in which a precursor liquid having a composite oxide component composition that is different for each number of laminations is appropriately prepared by applying a minimum number of precursor liquids prepared in advance for each coating process. FIG. 6B shows the in-plane distribution of the (200) crystal peak intensity of the PZT film formed by the conventional method in which the film is formed but the prepared precursor liquid is not heated.

From the comparison of the in-plane distribution of the (200) crystal peak intensity of the PZT film, the present invention in which the heat treatment is performed before applying the prepared precursor liquid is obtained in comparison with the conventional method in which the heat treatment is not performed. It can be seen that the in-plane variation in crystallinity in the ferroelectric crystal film is small (in-plane uniformity is improved).
As a result, the ferroelectric crystal film obtained by the film forming method of the present invention exhibits uniform ferroelectric characteristics or piezoelectric characteristics within the silicon wafer substrate surface on which the film is formed. The variation between the elements of the ferroelectric element or the piezoelectric element obtained by processing can be suppressed small, and the yield can be improved.

  In addition, as another factor of the effect of improving the uniformity of the ferroelectric film described above, a predetermined coating temperature is applied before dropping and coating the prepared precursor liquid heated to the precursor liquid synthesis reaction temperature on the silicon wafer substrate. Cooling to a low temperature. As a result, the uniformity of the film thickness of the obtained ferroelectric film is increased within a single silicon wafer substrate and between different substrates, resulting in variations in ferroelectric characteristics or piezoelectric characteristics due to film thickness variations. Is suppressed, and the quality of the obtained ferroelectric element is stabilized in the substrate and between different substrates.

FIG. 7 is a cross-sectional view in the longitudinal direction of the liquid chamber of a liquid discharge head using a ferroelectric element obtained by processing a ferroelectric film created by the film forming method of the present invention. In the figure, a liquid discharge head 31 is of a side shooter type that discharges droplets from nozzle holes provided on one surface of a substrate. The liquid discharge head 31 includes a plurality of pressurizing liquid chambers partitioned by a pressurizing liquid chamber partition including a piezoelectric element 33 made of a ferroelectric element that generates droplet discharge energy and a vibration plate 34 on a flow path plate 32. 35, a fluid resistance portion 36, and a common liquid chamber 37 are formed.
The flow path plate 32 is provided with a vibration plate 34 that constitutes a partial wall surface of the pressurized liquid chamber 35 and vibrates by driving the piezoelectric element 33, and the pressurized liquid chamber is interposed via the vibration plate 34. A piezoelectric element 33 is provided at a portion facing 35. A common liquid channel 37 is formed in the common liquid chamber 37, through which ink that is liquid droplets can be supplied from the outside. The piezoelectric element 33 includes a common electrode 39 as a lower electrode, an individual electrode 40 as an upper electrode, and a piezoelectric body 41 made of a ferroelectric film. The piezoelectric body 41 is sandwiched between the common electrode 39 and the individual electrode 40. Has been.

The frame 42 disposed above the flow path plate 32 allows the liquid droplet supply port 43 for supplying liquid droplets from the outside, the common liquid flow path 38 as the liquid flow path section, and the bending of the vibration plate 34. A recess 44 is formed. In addition, nozzle holes 46 are formed at positions corresponding to the individual pressurized liquid chambers 35 in the nozzle plate 45 disposed below the flow path plate 32. An interlayer insulating film 47 is formed above the common electrode 39, a wiring 48 is formed above the common electrode 39, and a passivation film 49 is formed above the common electrode 39 for the purpose of protecting the wiring 48.
In the above configuration, the actuator substrate 50 is configured by the flow path plate 32, the piezoelectric element 33, the vibration plate 34, the common electrode 39, the interlayer insulating film 47, and the wiring 48. Then, the liquid ejection head 31 is configured by joining the actuator substrate 50, the frame 42, and the nozzle plate 45. Further, the wiring 48 and the individual electrode 40 are connected to each other through a connection hole 51 formed in the interlayer insulating film 47.

In the liquid droplet ejection head 31 configured as described above, image data is sent from a control unit (not shown) in a state where each pressurized liquid chamber 35 is filled with a liquid, for example, a recording liquid such as ink. Then, based on the sent image data, the individual electrodes 40 corresponding to the nozzle holes 46 to which the recording liquid is to be discharged are connected via the connection holes 51 formed in the wiring 48 and the interlayer insulating film 47 by the oscillation circuit. For example, a pulse voltage of 20V is applied. By applying the pulse voltage, the piezoelectric body 41 itself contracts in a direction parallel to the diaphragm 34 due to electrostriction, and the diaphragm 34 bends in the direction of the pressurized liquid chamber 35. As a result, the pressure in the pressurized liquid chamber 35 rises rapidly, and the recording liquid is discharged from the nozzle hole 46 communicating with the pressurized liquid chamber 35.
After applying the pulse voltage, since the contracted piezoelectric body 12 is restored, the deflected diaphragm 3 returns to its original position, so that the pressurized liquid chamber 5 has a negative pressure compared to the common liquid chamber 8. . As a result, the ink supplied from the outside through the droplet supply port 66 is supplied from the common droplet channel 9 and the common liquid chamber 8 to the pressurized liquid chamber 5 through the fluid resistance portion 7. By repeating this, the droplets can be ejected continuously, and an image can be formed on a recording medium (for example, paper) disposed facing the droplet ejection head 1.

Next, a liquid cartridge in which the above-described liquid discharge head 31 is integrated will be described.
An ink cartridge 52 as a liquid cartridge shown in FIG. 8 is obtained by integrating a droplet discharge head 31 having a nozzle hole 46 and the like and an ink tank 53 that supplies ink to the droplet discharge head 31. In the ink cartridge 52 integrally including the ink tank 53 and the droplet discharge head 31, a ferroelectric element manufactured from a single substrate by reducing variations in in-plane characteristics of the ferroelectric film. The yield can be improved, and the cost can be reduced.

Next, an ink jet recording apparatus as a liquid discharge apparatus equipped with the above-described liquid discharge head 31 will be described with reference to FIGS.
An ink jet recording apparatus 54 as a liquid ejecting apparatus has a carriage 55 that is movable in the main scanning direction and in which the liquid ejecting head 31 is mounted. Further, inside the apparatus main body, a printing mechanism unit 57 and the like including a liquid discharge head 31 and an ink cartridge 56 that supplies ink to the liquid discharge head 31 are stored. A paper feed cassette (or a paper feed tray) 59 capable of stacking a large number of sheets 58 from the front side is detachably attached to the lower part of the apparatus main body. Further, the apparatus main body is provided with a manual feed tray 60 that is opened when the paper 58 is manually fed. The ink jet recording apparatus 54 takes in the paper 58 fed from the paper feed cassette 59 or the manual feed tray 60, records a desired image by the printing mechanism unit 57, and then arranges the paper 58 after image formation on the rear side. The paper is discharged to the paper discharge tray 61.

The printing mechanism 57 holds a main guide rod 62, a sub guide rod 63, and a carriage 55, which are guide members stretched between left and right side plates (not shown), so as to be slidable in the main scanning direction. The carriage 55 is provided with a liquid ejection head 31 that ejects ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). The liquid ejection head 31 is mounted with the plurality of nozzles arranged in a direction intersecting the main scanning direction with the ink droplet ejection direction facing downward.
In addition, each ink cartridge 56 that supplies each color ink to the liquid discharge head 31 is replaceably mounted on the carriage 55. The ink cartridge 56 has an air outlet that communicates with the atmosphere above, and a supply port that supplies ink to the liquid ejection head 31 below. A porous body filled with ink is provided inside the ink cartridge 56, and the ink supplied to the liquid ejection head 31 is maintained at a slight negative pressure by the capillary force of the porous body. In addition, although the individual liquid ejection heads 31 are used for the respective colors, a single liquid ejection head having nozzles for ejecting ink droplets of the respective colors may be used.

The carriage 55 is slidably fitted to the main guide rod 62 on the downstream side in the paper conveyance direction, and is slidably mounted on the secondary guide rod 63 on the upstream side in the paper conveyance direction, which is the front side. Yes. In order to move and scan the carriage 55 in the main scanning direction, a timing belt 67 is stretched between a driving pulley 65 and a driven pulley 66 that are rotationally driven by a main scanning motor 64, and the timing belt 67 is fixed to the carriage 55. . With this configuration, the carriage 55 is reciprocated by forward and reverse rotation of the main scanning motor 64.
On the other hand, in order to convey the paper 58 set in the paper feed cassette 59 to the lower side of the liquid ejection head 31, a paper feed roller 68 and a friction pad 69 for separating and feeding the paper 58 from the paper feed cassette 59 are provided. Yes. Further, a guide member 70 that guides the paper 58 and a transport roller 71 that reverses and transports the fed paper 58 are disposed. Furthermore, a conveyance roller 72 pressed against the peripheral surface of the conveyance roller 71 and a leading end roller 73 for defining a feed angle of the paper 58 from the conveyance roller 71 are provided. The transport roller 71 is rotationally driven through a gear train by a sub scanning motor (not shown).

  Corresponding to the range of movement of the carriage 55 in the main scanning direction, a printing receiving member 74, which is a sheet guide member, is provided to guide the sheet 58 fed from the transport roller 71 at a position below the liquid discharge head 31. Yes. On the downstream side of the printing receiving member 74 in the sheet conveyance direction, a conveyance roller 75 and a spur 76 that are rotationally driven to send out the sheet 58 in the sheet discharge direction are provided. Further, a discharge roller 77 and a spur 78 for sending the paper 58 to the discharge tray 61, and guide members 79 and 80 for forming a discharge path are provided.

In the above-described ink jet recording apparatus 54, the liquid ejection head 31 is driven according to the image signal while moving the carriage 55 during recording. Thus, ink is ejected onto the stopped paper 58 to record one line, and after that, the paper 58 is conveyed by a predetermined amount, and then the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the paper 58 has reached the recording area, the inkjet recording device 54 ends the recording operation and discharges the paper 58.
A recovery device 81 for recovering the ejection failure of the liquid ejection head 31 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 55. The recovery device 81 includes a cap unit, a suction unit, and a cleaning unit. The carriage 55 is moved to the recovery device 81 side during printing standby, and the liquid ejection head 31 is capped by the capping unit to keep the nozzles in a wet state, thereby preventing the occurrence of ejection failure due to ink drying. Further, by ejecting ink that is not related to recording during recording or the like, the ink viscosity of all the nozzles is made constant and a stable ejection state is maintained.

When a discharge failure occurs, the nozzle of the liquid discharge head 31 is sealed with a capping unit, and bubbles and the like are sucked out from the nozzle through the tube with a suction unit. Then, ink or dust adhered to the nozzle surface is removed by the cleaning means, and thereby the ejection failure is recovered. The sucked ink is discharged into a waste ink reservoir (not shown) provided at the lower part of the main body, and is absorbed and held by an ink absorber provided inside the waste ink reservoir.
Since the above-described ink jet recording apparatus 54 is equipped with the liquid discharge head 31 of the present invention, stable ink discharge characteristics can be obtained and image quality can be improved. In the above description, the liquid ejection head 31 ejects ink. However, the liquid droplets to which the present invention can be applied are not limited to ink. For example, the liquid ejection head may be used in an apparatus for ejecting a liquid resist for patterning. 31 may be applied. Further, the liquid discharge head 31 may be applied to an apparatus for discharging a gene analysis sample.

  In the above-described embodiment, the paper 58 is shown as a recording medium on which an image is formed. The paper 58 is not limited to recording paper, and includes thick paper, postcards, envelopes, plain paper, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like. As the recording medium other than paper, any material may be used as long as it is a sheet-like material capable of forming an image, such as an OHP sheet, an OHP film, or a resin film.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to such specific embodiments, and unless specifically limited by the above description, the present invention described in the claims is not limited. Various modifications and changes are possible within the scope of the gist. The effects described in the embodiments of the present invention are merely examples of the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

8 Silicon wafer substrate 31 Liquid discharge head 33 Ferroelectric element (piezoelectric element)
41 Ferroelectric film (piezoelectric)
54 Liquid discharge device

JP 2013-63580 A

Claims (5)

A process of applying a precursor liquid, drying, and thermal decomposition on the substrate on which the lower electrode is formed is repeated a plurality of times to form an amorphous film on the substrate, and then the amorphous film is subjected to high temperature treatment to be crystallized. In the method for forming a dielectric film,
A first step of mixing a plurality of types of the precursor liquids having different compositions, respectively, at different predetermined ratios depending on the number of times of application onto the substrate, and heating the mixed precursor liquids to a synthesis reaction temperature of the precursor liquids A ferroelectric film having a second step of performing, a third step of cooling the heated precursor liquid to a predetermined application temperature, and a fourth step of applying the cooled precursor liquid onto the substrate. Film forming method. The method for forming a ferroelectric film according to claim 1,
A method for forming a ferroelectric film, wherein a temperature at which the precursor liquid mixed in the second step is heated is higher than a highest temperature among synthesis reaction temperatures of the mixed precursor liquids.   A ferroelectric film formed by the method for forming a ferroelectric film according to claim 1.   A liquid discharge head manufactured using the ferroelectric film according to claim 3.   A liquid discharge apparatus manufactured using the ferroelectric film according to claim 3.

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