Patent Publication Number: US-2007095653-A1

Title: Method for manufacturing conductive complex oxide layer, and method for manufacturing laminated body having ferroelectric layer

Description:
The entire disclosure of Japanese Patent Application No. 2005-316968 filed Oct. 31, 2005 is expressly incorporated by reference herein.  
     BACKGROUND  
      1. Technical Field  
      The present invention relates to a method for manufacturing a conductive complex oxide layer, and a method for manufacturing a laminated body having a ferroelectric layer and a method for manufacturing a device to which the aforementioned method for manufacturing a conductive complex oxide is applied.  
      2. Related Art  
      As one of the methods for forming a film of conductive complex oxide expressed by a general formula of ABO 3 , a sputter method is known. The sputter method normally uses an atmosphere in which inert gas as discharge gas and oxygen as oxidizing gas exist together.  
     SUMMARY  
      In accordance with an advantage of some aspects of the present invention, it is possible to provide a method for manufacturing a conductive complex oxide layer by which a conductive complex oxide layer with excellent crystallinity can be obtained.  
      In accordance with another advantage of some aspects of the invention, it is possible to provide a method for manufacturing a laminated body having a ferroelectrlc layer to which the method for manufacturing a conductive complex oxide layer in accordance with the embodiment of the invention is applied.  
      In accordance with still another advantage of some aspects of the invention, it is possible to provide a method for manufacturing a device to which the method for manufacturing a laminated body in accordance with the embodiment of the invention is applied.  
      A method for manufacturing a conductive complex oxide layer in accordance with an embodiment of the invention includes the steps of: forming, above a base substrate, a first layer of conductive complex oxide expressed by a general formula of ABO 3  by first sputtering with first oxygen concentration, and forming, above the first layer of conductive complex oxide, a second layer of conductive complex oxide expressed by a general formula of ABO 3  by second sputtering at least with second oxygen concentration lower than the first oxygen concentration.  
      In the method for manufacturing a conductive complex oxide layer in accordance with the present embodiment of the invention, when a conductive complex oxide layer is formed by sputtering, a first sputtering step that is conduced with first oxygen concentration and a second sputtering step that is conducted at least with second oxygen concentration lower than the first oxygen concentration are conducted, whereby the conductive complex oxide layer with excellent crystallinity and surface morphology can be formed.  
      It is noted that, in the invention, the case where a specific layer B (hereafter referred to as a “layer B”) is provided above a specific layer A (hereafter referred to as a “layer A”) includes a case where the layer B is directly provided on the layer A, and a case where the layer B is provided over the layer A through another layer.  
      In the method for manufacturing a conductive complex oxide layer in accordance with an aspect of the present embodiment of the invention, the first sputtering may be conducted where inert gas and oxygen coexist.  
      In the method for manufacturing a conductive complex oxide layer in accordance with another aspect of the present embodiment of the invention, the first layer of conductive complex oxide and the second layer of conductive complex oxide may be composed of the same compound.  
      In the method for manufacturing a conductive complex oxide layer in accordance with another aspect of the present embodiment of the invention, the second sputtering may be conducted in an atmosphere that does not include oxygen.  
      In the method for manufacturing a conductive complex oxide layer in accordance with another aspect of the present embodiment of the invention, heat treatment may be conducted after the second layer of conductive complex oxide has been formed.  
      In the method for manufacturing a conductive complex oxide layer in accordance with the present embodiment of the invention, the element A may be at least one element selected from La, Ca, Sr, Mn, Ba and Re, and the element B may be at least one element selected from Ti, V, Sr, Cr, Fe, Co, Ni, Cu, Ru, Ir, Pb and Nd.  
      In the method for manufacturing a conductive complex oxide layer in accordance with the present embodiment of the invention, the element A may be La, and the element B may be Ni.  
      In the method for manufacturing a conductive complex oxide layer in accordance with the present embodiment of the invention, the sputtering may be RF sputtering.  
      A method for manufacturing a laminated body including a ferroelectric layer in accordance with another embodiment of the invention includes the steps of: forming, above a base substrate, a first layer of conductive complex oxide expressed by a general formula of ABO 3  by first sputtering with first oxygen concentration, forming above the first layer of conductive complex oxide, a second layer of conductive complex oxide expressed by a general formula of ABO 3  by second sputtering at least with second oxygen concentration lower than the first oxygen concentration, and forming a ferroelectric layer above the second layer of conductive complex oxide.  
      According to the method for manufacturing a laminated body in accordance with the present embodiment of the invention, a layer of conductive complex oxide with excellent characteristics can be obtained, such that the laminated body with excellent hysteresis characteristics and piezoelectric characteristics can be obtained.  
      The method for manufacturing a laminated body having a ferroelectric layer in accordance with an aspect of the present embodiment of the invention may include the step of forming a layer of conductive complex oxide expressed by a general formula of ABO 3  by sputtering above the ferroelectric layer.  
      In the method for manufacturing a laminated body having a ferroelectric layer in accordance with another aspect of the present embodiment of the invention, the step of forming the layer of conductive complex oxide may include the step of forming a third layer of conductive complex oxide expressed by a general formula of ABO 3  by third sputtering conducted with the first oxygen concentration, and the step of forming, above the third layer of conductive complex oxide, a fourth layer of conductive complex oxide expressed by a general formula of ABO 3  by fourth sputtering conducted at least with the second oxygen concentration having a lower oxygen concentration than the first oxygen concentration.  
      A method for manufacturing a laminated body having a ferroelectric layer in accordance with another embodiment of the invention includes the steps of: forming a ferroelectric layer above a base substrate, forming, above the ferroelectric layer, a first layer of conductive complex oxide expressed by a general formula of ABO 3  by first sputtering with first oxygen concentration, and forming, above the first layer of conductive complex oxide, a second layer of conductive complex oxide expressed by a general formula of ABO 3  by second sputtering at least with second oxygen concentration lower than the first oxygen concentration.  
      According to the method for manufacturing a laminated body in accordance with the present embodiment of the invention, a layer of conductive complex oxide with excellent characteristics can be obtained, and therefore a laminated body with excellent piezoelectric characteristics can be obtained.  
      A method for manufacturing a device in accordance with another embodiment of the invention includes the method for manufacturing a laminated body in accordance with the embodiment of the invention described above.  
      Devices to which the manufacturing method in accordance with the embodiment of the invention is applicable will be described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  schematically shows a step of a method for manufacturing a first laminated body in accordance with an embodiment of the invention.  
       FIG. 2  schematically shows a step of the method for manufacturing the first laminated body in accordance with the embodiment of the invention.  
       FIG. 3  schematically shows a step of the method for manufacturing the first laminated body in accordance with the embodiment of the invention.  
       FIG. 4  schematically shows a step of the method for manufacturing the first laminated body in accordance with the embodiment of the invention.  
       FIG. 5  schematically shows a step of the method for manufacturing the first laminated body in accordance with the embodiment of the invention.  
       FIG. 6  schematically shows a step of a method for manufacturing a second laminated body in accordance with an embodiment of the invention.  
       FIG. 7  shows results of X-ray analysis conducted on laminated bodies of an embodiment example and a comparison example.  
       FIG. 8  shows a surface morphology of the laminated body of the embodiment example.  
       FIG. 9  shows a surface morphology of the laminated body of the comparison example.  
       FIG. 10  shows results of X-ray analysis conducted on the laminated body of the embodiment example.  
       FIG. 11  shows hysteresis characteristics of capacitors in accordance with an embodiment example and a comparison example.  
       FIGS. 12A and 12B  schematically show a plan view and a cross-sectional view of a semiconductor device in accordance with an embodiment of the invention, respectively.  
       FIG. 13  schematically shows a cross-sectional view of a 1T1C type ferroelectric memory in accordance with an embodiment of the invention.  
       FIG. 14  shows an equivalent circuit of the ferroelectric memory shown in  FIG. 13 .  
       FIG. 15  shows a cross-sectional view schematically showing a piezoelectric element in accordance with an application example of an embodiment of the invention.  
       FIG. 16  shows a schematic structural view of an ink jet recording head in accordance with an application example of an embodiment of the invention.  
       FIG. 17  shows an exploded perspective view of an ink jet recording head in accordance with an embodiment of the invention.  
       FIG. 18  shows a schematic structural view of an ink jet printer in accordance with an application example of an embodiment of the invention.  
       FIG. 19  is a cross-sectional view of a surface acoustic wave element in accordance with an application example of an embodiment of the invention.  
       FIG. 20  is a perspective view of a frequency filter in accordance with an application example of an embodiment of the invention.  
       FIG. 21  is a perspective view of an oscillator in accordance with an application example of an embodiment of the invention. 
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      Preferred embodiments of the invention are described below in detail with reference to the accompanying drawings.  
      1. Method for Manufacturing First Laminated Body having Ferroelectric Layer  
      A method for manufacturing a first laminated body in accordance with an embodiment of the invention is described with reference to  FIGS. 1 through 5 .  FIGS. 1 through 3  schematically show steps of a method for manufacturing a conductive complex oxide layer in accordance with an embodiment of the invention.  
      (1) First, as shown in  FIG. 1 , a base substrate  1  is prepared In the illustrated example, the base substrate  1  is formed by successively laminating a silicon oxide layer  12 , a titanium oxide layer  14  and a platinum layer  16  on a silicon substrate  10 . For example, the base substrate  1  may be formed as follows.  
      The silicon oxide layer  12  is formed on the silicon substrate  10 . Then, the titanium oxide layer  14  is formed on the silicon oxide layer  12  by DC (direct current) sputtering or the like. The titanium oxide layer  14  can improve adhesion between the silicon oxide layer  12  and the platinum layer  16 . The titanium oxide layer  14  may have a film thickness of, for example, 10-40 nm. A titanium layer may be used instead of the titanium oxide layer  14 . Then, the platinum layer  16  is formed on the titanium oxide layer  14  by DC (direct current) sputtering or the like. The platinum layer  16  may have a film thickness of, for example, 50-200 nm. A layer of another platinum group metal may also be used instead of the platinum layer  16 .  
      The type of the base substrate  1  can be selected depending on the usage of a layer of conductive complex oxide. An insulating substrate, a semiconductor substrate or the like can be used as the base substrate  1 , and its structure is not particularly limited. As the insulating substrate, for example, a sapphire substrate, a plastic substrate, a glass substrate or the like can be used, As the semiconductor substrate, a silicon substrate, a germanium substrate, a TiO 2  substrate, a ZnO substrate, a NiO x  substrate or the like can be used. Also, the base substrate  1  may be formed with a single substrate or a laminated body in which at least one layer is laminated on a substrate.  
      (2) As shown in  FIG. 2 , a first layer of conductive complex oxide  20  of perovskite type expressed by a general formula ABO 3  is formed on the base substrate  1 .  
      In the general formula, the element A may be at least one element selected from La, Ca, Sr, Mn, Ba and Re, and the element B may be at least one element selected from Ti, V, Sr, Cr, Fe, Co, Ni, Cu, Ru, Ir, Pb and Nd. Also, as the layer of conductive complex oxide in accordance with an embodiment of the invention, LaCoO 3 , SrCoO 3 , La 1−x  Sr x  CoO 3  [where x and y is a rational number of 0-1, and the same applies to the following chemical formulas], such as, La (Sr) CoO 3  [where a metal in the brackets ( ) means a substitution metal, and the same applies to the following chemical formulas], LaMnO 3 , SrMnO 3 , La 1−x  Sr x  MnO 3 , such as, La (Sr) MnO 3 , LaNiO 3 , SrNiO 3 , La(Sr)NiO 3 , CaCoO 3 , La(Ca)CoO 3 , LaFeO 3 , SrFeO 3 , La(Sr)FeO 3 , La 1−x  Sr x Co 1−y  Fe y  O 3 , such as, La(Sr)Co(Fe)O 3  or La 1−x Sr x VO 3 , La 1−x Ca x FeO 3 , LaBaO 3 , LaMnO 3 , LaCuO 3 , LaTiO 3 , BaCeO 3 , BaTiO 3 , BaSnO 3 , BaPbO 3 , BaPb 1−x O 3 , CaCrO 3 , CaVO 3 , CaRuO 3 , SrIrO 3 , SrFeO 3 , SrVO 3 , SrRuO 3 , Sr(Pt)RuO 3 , SrTiO 3 , SrReO 3 , SrCeO 3 , SrCrO 3 , BaReO 3 , BaPb 1−x Bi x O 3 , CaTiO 3 , CaZrO 3 , CaRuO 3 , and CaTi 1−x Al x O 3  can be exemplified.  
      As the material of the first layer of conductive complex oxide  20  among the materials listed above, LaNiO 3  may be more preferably used. The first layer of conductive complex oxide  20  may suffice if it forms at least a layer, and its film thickness may be, for example, 40-100 nm without any particular limitation.  
      The first layer of conductive complex oxide  20  may be formed by RF sputtering (Radio Frequency Sputtering) (hereafter also referred to as “first sputtering”). The first sputtering may be conducted where inert gas and oxygen exist together. As the inert gas, argon may be used. The flow quantity ratio between argon and oxygen is not particularly limited, and the flow ratio of argon/oxygen may be, for example, 49/1-40/10. Also, the temperature of the base substrate  1  may be 200-500° C. The power for the sputtering may be selected depending on the type of the sputter apparatus and other conditions, and may be set to, for example, 1000-1500 W.  
      In the first sputtering, besides inert gas and oxygen, an atmosphere containing other gas such as reactive gas may be used depending on the requirements.  
      (3) As shown in  FIG. 3 , a second layer of perovskite type conductive complex oxide  22  expressed by a general formula of ABO 3  is formed on the first layer of conductive complex oxide  20 . As the material of the second layer of conductive complex oxide  22 , the same materials exemplified as the materials for the first layer of conductive complex oxide  20  may be listed. The second layer of conductive complex oxide  22  can be composed of the same compound as that of the first layer of conductive complex oxide  20 . As the material of the second layer of conductive complex oxide  22 , LaNiO 3  may more preferably be used. The film thickness of the second layer of conductive complex oxide  22  can be selected depending on the film thickness of a layer of conductive complex oxide  2  that is to be finally obtained without any particular limitation.  
      The second layer of conductive complex oxide  22  may be formed by RF sputtering (hereafter also referred to as “second sputtering”), like the first layer of conductive complex oxide  20 . In this step, the RF sputtering may be conducted in an atmosphere where inert gas and oxygen at least having a lower concentration than that of the first sputtering exist together. Also, in this step, the gas that is used for the RF sputtering may be composed of inert gas alone without any oxygen contained. Also, in the second sputtering, besides inert gas and oxygen, an atmosphere containing other gas such as reactive gas may be used depending on the requirements.  
      As the inert gas, argon may be used. The flow quantity ratio between argon and oxygen is not particularly limited if the conditions described above are satisfied, and the flow ratio of argon/oxygen may be, for example, 50/0-45/5. Also, the temperature of the base substrate  1 may be 200-500° C. The power for the sputtering may be selected depending on the type of the sputter apparatus and other conditions, and may be set to, for example, 1000-1500 W.  
      (4) Next, to improve the crystallinity of the first and second layers of conductive complex oxide  20  and  22 , a heat treatment is conducted. The heat treatment may be conducted differently depending on the material of the layer of conductive complex oxide and the like, and may be conducted at, for example, 500-800° C. The heat treatment may be conducted in an atmosphere containing at least one of argon and oxygen.  
      In this manner, when the layer of conductive complex oxide  2  is formed by RF sputtering, a first sputtering step which is conducted in an inert gas atmosphere such as an argon atmosphere with higher oxygen concentration, and a second sputtering step which is conducted in an inert gas atmosphere with a lower oxygen concentration than the first sputtering or without including oxygen are conducted. As a result, the layer of conductive complex oxide with excellent crystallinity and surface morphology can be formed, as it becomes clear from embodiment examples to be described below.  
      The layer of conductive complex oxide  2  having the first and second layers of conductive complex oxide  20  and  22  formed by the steps described above can be used as a conductive layer, an electrode or the like. For example, when a capacitor is to be obtained, the following steps (5) through (8) can be conducted.  
      (5) As shown in  FIG. 4 , a ferroelectric layer  3  is formed on the second layer of conductive complex oxide  22 . The type of the ferroelectric layer  3  may appropriately selected according to a device to be fabricated without any particular limitation. As the ferroelectric material of the ferroelectric layer  3 , perovskite type ferroelectrics, such as, for example, PZT (Pb (Zr, Ti) O 3 ), PZTN (Pb (Zr, Ti, Nb) O 3 ), SBT (SrBi 2  Ta 2  O 9 ), BST ((Ba, Sr) TiO 3 ), and KN (KNbO 3 ) may be exemplified.  
      The ferroelectric layer  3  may be formed by using any one of the known film forming methods without any particular limitation, such as, for example, a liquid method such as a sol-gel method, or a vapor phase method such as a CVD method, a MOCVD method or a sputter method.  
      (6) As shown in  FIG. 5 , a layer of conductive complex oxide  4  is formed on the ferroelectric layer  3 . In the illustrated example, the layer of conductive complex oxide  4  includes a third layer of conductive complex oxide  40  and a fourth layer of conductive complex oxide  42 . The third layer of conductive complex oxide  40  may be formed by a method similar to the method used for forming the first layer of conductive complex oxide  20  described above. Also, the fourth layer of conductive complex oxide  42  may be formed by a method similar to the method used for forming the second layer of conductive complex oxide  22  described above.  
      More concretely, as shown in  FIG. 5 , the third layer of perovskite type conductive complex oxide  40  expressed by a general formula of ABO 3  is formed on the ferroelectric layer  3 . The third layer of conductive complex oxide  40  may suffice if it forms at least a layer, and its film thickness may be, for example, 40-100 nm without any particular limitation.  
      The third layer of conductive complex oxide  40  may be formed by RF sputtering (hereafter referred to as “third sputtering”). Conditions of the sputtering are similar to the film forming conditions applied to the first layer of conductive complex oxide  20 , and therefore description of their details is omitted.  
      (7) Next, as shown in  FIG. 5 , the fourth layer of perovskite type conductive complex oxide  42  expressed by a general formula of ABO 3  is formed on the third layer of conductive complex oxide  40 . The film thickness of the fourth layer of conductive complex oxide  42  may be selected depending on the film thickness of the layer of conductive complex oxide  4  that is to be finally obtained, without any particular limitation.  
      The fourth layer of conductive complex oxide  42  may be formed by RF sputtering, like the second layer of conductive complex oxide  22 . Conditions of the sputtering are similar to the film forming conditions applied to the second layer of conductive complex oxide  22 , and therefore description of their details is omitted.  
      As the material of the third layer of conductive complex oxide  40  and the fourth layer of conductive complex oxide  42 , materials similar to those used for the first layer of conductive complex oxide  20  may be exemplified. Also, the third layer of conductive complex oxide  40  and the fourth layer of conductive complex oxide  42  may be composed of the same material.  
      (8) Next, to improve the crystallinity of the third and fourth layers of conductive complex oxide  40  and  42 , a heat treatment is conducted. The heat treatment may be conducted differently depending on the material of the layer of conductive complex oxide and the like, and may be conducted at, for example, 500-800° C. The heat treatment may be conducted in an atmosphere containing at least one of argon and oxygen.  
      The layer of conductive complex oxide  4  having the third and fourth layers of conductive complex oxide  40  and  42  formed by the steps described above has characteristics similar to those of the first and second layers of conductive complex oxide  20  and  22 , and can be used as a conductive layer or an electrode. Also, the layer of conductive complex oxide  4  as an upper electrode and the layer of conductive complex oxide  2  as a lower layer may be provided with generally the same structure, whereby the band gaps at interfaces between the upper and lower electrodes and the ferroelectric layer can be matched, such that superior capacitor characteristics, hysteresis characteristics and piezoelectric characteristics can be obtained.  
      The layer of conductive complex oxide  4  is not limited to a laminated body of the third and fourth layers of conductive complex oxide  40  and  42 , and may be composed of a single layer of conductive complex oxide. Also, the layer of conductive complex oxide  4  may be composed of a material different from the material composing the layer of conductive complex oxide  2 .  
      Through the steps described above, a capacitor composed of the layer of conductive complex oxide  2  as a lower electrode, the ferroelectric layer  3 , and the layer of conductive complex oxide  4  as an upper electrode can be formed on the base substrate  1 .  
      According to the present embodiment, the following characteristics can be obtained. p At least when the layer of conductive complex oxide  2  is formed by RF sputtering, a first sputtering step that is conduced in an inert gas atmosphere such as an argon atmosphere with a higher oxygen concentration, and a second sputtering step that is conducted in an argon atmosphere with an oxygen concentration lower than the first sputtering or in an argon atmosphere that does not contain oxygen are conducted, whereby the layer of conductive complex oxide with excellent crystallinity and surface morphology can be formed, as it becomes clear from embodiment examples to be described below.  
      Also, capacitors having the layer of conductive complex oxide  2  have excellent hysteresis characteristics and piezoelectric characteristics, and can be used for a variety of applications, such as, semiconductor memory devices, piezoelectric elements and the like, as described below.  
      2. Method For Manufacturing Second Laminated Body Having Ferroelectric Layer  
      A method for manufacturing a second laminated body in accordance with an embodiment of the invention is described with reference to  FIG. 6 .  FIG. 6  is a cross-sectional view schematically showing a step of the method for manufacturing the second laminated body. The present embodiment is different from the first laminated body in that a ferroelectric layer  3  and a layer of conductive complex oxide  1  are successively formed on a base substrate  1 .  
      (1) As shown in  FIG. 6 , a base substrate  1  is prepared. The base substrate  1 , in the illustrated embodiment, is formed with a silicon oxide layer  12 , a titanium oxide layer  14  and a platinum layer  16  successively deposited on a silicon substrate  10 . The base substrate  1  has a structure similar to that of the first laminated body, and therefore its detailed description is omitted. Also, the type of the base substrate  1  can be selected according to the usage of the layer of conductive complex oxide and the ferroelectric layer. The structure of the base substrate  1  is not particularly limited, and may be formed from an insulating substrate, a semiconductor substrate or the like. As the insulating substrate, for example, a sapphire substrate, a single crystal substrate (LiTaO 3 , LiNbO 3 , Li 2 B 4 O 7 ), a plastic substrate, a glass substrate or the like can be used. As the semiconductor substrate, a silicon substrate or the like can be used. Also, the base substrate  1  may be a single substrate, or a laminated body having a substrate and another layer laminated thereon.  
      (2) As shown in  FIG. 6 , a ferroelectric layer  3  is formed on the base substrate  1 . The type of ferroelectric layer  3  may be appropriately selected, without any particular limitation, depending on a device to be fabricated. As the ferroelectric material of the ferroelectric layer  3 , perovskite type ferroelectries, such as, for example, PZT (Pb(Zr, Ti)O 3 ), PZTN (Pb(Zr, Ti, Nb) O 3 ), SBT, BST, and KN (KNbO 3 ) can be exemplified.  
      The ferroelectric layer  3  may be formed by a known film forming method, without any particular limitation, such as, for example, a liquid phase method such as a sol-gel method, or a vapor phase method such as a CVD method, a sputter method or the like.  
      (3) As shown in  FIG. 6 , a first layer of perovskite type conductive complex oxide  20  expressed by a general formula of ABO 3  is formed on the ferroelectric layer  3 . As the material of the first layer of conductive complex oxide  20 , the same materials exemplified as the materials for the first layer of conductive complex oxide  20  shown in  FIG. 2  through  FIG. 5  may be listed. The first layer of conductive complex oxide  20  may form at least a layer, and its film thickness may be, for example, 40-100 nm without any particular limitation.  
      The first layer of conductive complex oxide  20  may be formed by RF sputtering (hereafter also referred to as “first sputtering”). The first sputtering may be conducted where inert gas and oxygen exist together. As the inert gas, argon may be used. The ratio between argon and oxygen is not particularly limited, and may be, for example, 49/1-40/10. Also, the temperature of the base substrate  1  may be 200-500° C. The power for the sputtering may be selected depending on the type of the sputter apparatus and other conditions, and may be set to, for example, 1000-1400 W.  
      (4) As shown in  FIG. 6 , a second layer of perovskite type conductive complex oxide  22  expressed by a general formula of ABO 3  is formed on the first layer of conductive complex oxide  20 . As the material of the second layer of conductive complex oxide  22 , the same materials exemplified as the materials for the second layer of conductive complex oxide  22  shown in  FIG. 3  through  FIG. 5  may be used. The film thickness of the second layer of conductive complex oxide  22  can be selected depending on the film thickness of a layer of conductive complex oxide  2  that is to be finally obtained, without any particular limitation.  
      The second layer of conductive complex oxide  22  may be formed by RF sputtering (hereafter also referred to as “second sputtering”), like the first layer of conductive complex oxide  20 . In this step, the RF sputtering may be conducted in an atmosphere where inert gas and oxygen having at least a lower concentration than the first sputtering exist together. Also, in this step, the gas that is used for the RF sputtering may be composed of inert gas alone without any oxygen contained. Also, in this step, the gas that is used for the RF sputtering may be inert gas alone, without oxygen contained.  
      As the inert gas, argon may be used. The flow quantity ratio between argon and oxygen is not particularly limited if the conditions described above are satisfied, and the flow ratio of argon/oxygen may be, for example, 50/0-40/10. Also, the temperature of the base substrate  1  may be 200-500° C. The power for the sputtering may be selected depending on the type of the sputter apparatus and other conditions, and may be set to, for example, 1000-1400 W.  
      (5) Next, to improve the crystallinity of the first and second layers of conductive complex oxide  20  and  22 , a heat treatment is conducted. The heat treatment may be conducted differently depending on the material of the layer of conductive complex oxide and the like, and may be conducted at, for example, 500-800° C. The heat treatment may be conducted in an atmosphere containing at least one of argon and oxygen.  
      The layer of conductive complex oxide  2  having the first and second layers of conductive complex oxide  20  and  22  formed in the steps described above can be used as a conductive layer, an electrode or the like.  
      By the steps described above, a laminated body having the ferroelectric layer  3  and the layer of conductive complex oxide  2  successively laminated on the base substrate  1  can be obtained.  
      According to the present embodiment, when the layer of conductive complex oxide  2  is formed by RF sputtering, a first sputtering step that is conducted in an inert gas atmosphere such as an argon atmosphere with a higher oxygen concentration and a second sputtering step that is conducted in an argon atmosphere with an oxygen concentration lower than the first sputtering or in an argon atmosphere that does not contain oxygen are conducted, whereby the layer of conductive complex oxide with excellent crystallinity and surface morphology can be formed, as it becomes clear from embodiment examples to be described below. Also, laminated bodies having the layer of conductive complex oxide  2  and the ferroelectric layer  3  can be used in a variety of applications that use surface acoustic waves, such as, surface acoustic wave elements, oscillators and the like, as described below.  
      3. EMBODIMENT EXAMPLES  
      Embodiment examples of the invention are described below, but the invention is not limited to the embodiments.  
      (a) As a sample of the embodiment example, a laminated body shown in  FIG. 3  was formed. More specifically, a first layer of LaNiO 3  as the first layer of conductive complex oxide  20  and a second layer of LaNiO 3  as the second layer of conductive complex oxide  22  were formed on a base substrate  1 .  
      As the base substrate  1 , a base substrate in which a silicon oxide layer  12 , a titanium oxide layer  14  and a platinum layer  14  are formed by the method described above on a silicon substrate  10  was used. As the first LaNiO 3  layer, a LaNiO 3  layer having a film thickness of 40 nm, which was formed by an RF sputter method under conditions with the power being 1500 W, the gas flow quantity ratio of argon/oxygen being 40/10, and the substrate temperature being 400° C., was used. As the sputter target, a LaNiO 3  (composition: stoichiometry) was used. As the second LaNiO 3  layer, a LaNiO 3  layer having a film thickness of 40 nm, which was formed by an RF sputter method under conditions with the power being 1500 W, the gas flow quantity ratio of argon/oxygen being 50/0, and the substrate temperature being 400° C., was used. As the sputter target, a LaNiO 3  (composition: stoichiometry) was used.  
      Also, a comparison sample having a base substrate  1  and a third LaNiO 3  layer formed thereon was used. As the third LaNiO 3  layer, a LaNiO 3  layer having a film thickness of 80 nm, which was formed under the same conditions as the film forming conditions applied for forming the first LaNiO 3  layer (with the power being 1500 W, the gas flow quantity ratio of argon/oxygen being 40/10, and the substrate temperature being 400° C.), was used.  
      Surfaces of the sample and the comparison sample obtained in the manner described above were observed by X-ray diffraction (2θ-measurement) and an electron microscope. The results are shown in  FIG. 7  through  FIG. 9 .  FIG. 7  shows the results of X-ray diffraction. In  FIG. 7 , the result of the sample of the embodiment example is indicated by the sign a, and the result of the sample of the comparison example is indicated by the sign b.  FIG. 8  shows the morphology of the sample of the embodiment example, and  FIG. 9  shows the morphology of the sample of the comparison example.  
      It was confirmed from the results obtained that, according to the sample of the embodiment example, the LaNiO 3  layer with outstanding ( 100 ) orientation and excellent surface morphology was obtained. Also, it was confirmed that, according to the sample of the comparison example, the LaNiO 3  layer with substantially weaker ( 100 ) orientation than the embodiment example and poorer surface morphology than the embodiment example was obtained.  
      (b) Next, the samples of the embodiment example were heat-treated in an argon atmosphere or an oxygen atmosphere to form samples, and X-ray diffraction measurement was conducted on the samples. The heat treatment was conducted at 800° C. for five minutes. The results are shown in  FIG. 10 . In  FIG. 10 , the sign a indicates the result of the sample of the embodiment example before heat treatment, the sign b indicates the result of the sample that was heat-treated in an oxygen atmosphere, and the sign c indicates the result of the sample that was heat-treated in an argon atmosphere. It is confirmed from  FIG. 10  that the ( 100 ) orientation became more pronounced by the heat treatment. Also, generally similar results were obtained with both of the samples heat-treated in an oxygen atmosphere and an argon atmosphere.  
      (c) A capacitor was formed using the sample that had been heat-treated and obtained in the embodiment example (b) described above. More concretely, a PZT layer as a ferroelectric layer was formed on the LaNiO 3  layer, and a platinum layer was further formed on the PZT layer. The PZT layer was formed by a sol-gel method. The sample is referred to as a “capacitor sample.” Also, as a sample for comparison, a capacitor sample for comparison was obtained in a similar manner as the sample of the embodiment example except that a LaNiO 3  layer was not formed. Hysteresis characteristics of the capacitor samples were obtained. The results are shown in  FIG. 11 . In  FIG. 11 , the sign a indicates the hysteresis characteristic of the capacitor sample of the embodiment example, and the sign b indicates the hysteresis characteristic of the capacitor sample of the comparison example.  
      It is confirmed from  FIG. 11  that the sample of the embodiment example has better hysteresis characteristic than that of the sample of the comparison example.  
      4. Devices  
      Devices in accordance with an embodiment of the invention include parts having a laminated body obtained by the method for manufacturing a laminated body having a ferroelectric layer in accordance with the embodiment of the invention, and electronic devices having the aforementioned parts. Examples of the devices to which the method for manufacturing a device in accordance with the embodiment of the invention is applicable are described below.  
      4.1. Semiconductor Element  
      Next, a semiconductor element including a laminated body obtained by the manufacturing method in accordance with an embodiment of the invention is described. In the present embodiment, a ferroelectric memory device including a ferroelectric capacitor, which is an example of a semiconductor element, is described as an example.  
       FIG. 12A  and  FIG. 12B  are views schematically showing a ferroelectric memory device  1000  having a laminated body obtained by the manufacturing method in accordance with the present embodiment described above. It is noted that  FIG. 12A  shows a plane configuration of the ferroelectric memory device  1000 , and  FIG. 12B  is a cross-sectional view taken along a line I-I in  FIG. 12A .  
      The ferroelectric memory device  1000  has a memory cell array  200  and a peripheral circuit section  300 , as shown in  FIG. 12A . The memory cell array  200  includes lower electrodes (word lines)  210  for selection of rows, and upper electrodes (bit lines)  220  for selection of columns, which are disposed orthogonal to one another. Also, the lower electrodes  210  and the upper electrodes  220  are arranged in stripes composed of a plurality of line shaped signal electrodes. It is noted that the signal electrodes can be for ed such that the lower electrodes  210  may define bit lines, and the upper electrodes  220  may define word lines. The peripheral circuit section  300  includes various circuits that selectively write or read information in or from the above-described memory cell array  200  and, for example, is formed from a first driving circuit  310  to control the lower electrodes  210  selectively, a second driving circuit  320  to control the upper electrodes  220  selectively, and a signal detection circuit such as a sense amplifier (omitted in the figure) and the like.  
      As shown in  FIG. 12B , a ferroelectric layer  215  is disposed between the lower electrodes  210  and the upper electrodes  220 . In the memory cell array  200 , memory cells that function as ferroelectric capacitors  230  are formed in areas where the lower electrodes  210  and the upper electrodes  220  intersect one another.  
      The ferroelectric capacitor  230  can be formed by the method for forming a laminated body in accordance with an embodiment of the invention. In other words, at least the lower electrode  210  and the ferroelectric layer  215  can be formed by a manufacturing method in accordance with an embodiment of the invention, for example, the method for manufacturing a first laminated body. The lower electrode  210  may be composed of a layer of conductive complex oxide  2  (having a first layer of conductive complex oxide  20  and a second layer of conductive complex oxide  22 ) shown in  FIG. 2  through  FIG. 5 , and the ferroelectric layer  215  is composed of a ferroelectric layer  3  shown in  FIG. 5 . Also, the upper electrode  22  may be composed of a layer of conductive complex oxide  4  shown in  FIG. 5 . Furthermore, a first interlayer dielectric layer  420  corresponds to the base substrate  1  shown in  FIG. 5 . The interlayer dielectric layer  420  may have a barrier layer (not shown) at its topmost layer.  
      The ferroelectric layer  215  may only have to be disposed between areas where at least the lower electrodes  210  and the upper electrodes  220  are intersecting one another.  
      Also, the peripheral circuit section  300  includes MOS transistors  330  formed on the semiconductor substrate  400 , as shown in  FIG. 12B . The MOS transistor  330  has a gate insulation film  332 , a gate electrode  334 , and source/drain regions  336 . The MOS transistors  330  are isolated from one another by an element isolation area  410 . A first interlayer dielectric film  420  is formed on the semiconductor substrate  400  on which the MOS transistor  330  is formed. Further, the peripheral circuit section  300  and the memory cell array  200  are electrically connected to one another by wiring layers  450 . Furthermore, the ferroelectric memory device  1000  is provided with a second interlayer dielectric film  430  and an insulating protective layer  440 .  
      FIG,  13  shows a structural drawing of a 1T1C type ferroelectric memory device  500  as another example of a semiconductor device.  FIG. 14  is an equivalent circuit diagram of the ferroelectric memory device  500 .  
      As shown in  FIG. 13 , the ferroelectric memory device  500  is a memory element having a structure similar to that of a DRAM, which is formed from a capacitor  504  ( 1 C) composed of a lower electrode  501 , an upper electrode  502  that is connected to a plate line and a ferroelectric layer  503 , and a switching transistor element  507  ( 1 T), having source/drain electrodes, one of them being connected to a data line  505 , and a gate electrode  506  that is connected to a word line. The 1T1C type memory can perform writing and reading at high-speeds at 100 ns or less, and because written data is nonvolatile, it is promising as the replacement of SRAM.  
      At least the lower electrode  501  and the ferroelectric layer  503 , and further the upper electrode  502  if necessary, of the ferroelectric memory device  500  may be formed by the method for manufacturing a first laminated body in accordance with the embodiment of the invention. The lower electrode  501  is composed of the layer of conductive complex oxide  2  (having the first layer of conductive complex oxide  20  and the second layer of conductive complex oxide  22 ) shown in  FIG. 2  through  FIG. 5 , and the ferroelectric layer  503  may be composed of the ferroelectric layer  3  shown in  FIG. 5 . Also, the upper electrode  502  may be composed of the layer of conductive complex oxide  4  shown in  FIG. 5 .  
      The semiconductor device in accordance with the present embodiment can also be applied to 2T2C type ferroelectric memory devices and the like without being limited to the above.  
      4.2. Piezoelectric Element  
      Next, an example in which the method for manufacturing a laminated body in accordance with the embodiment of the invention is applied to a method for manufacturing a piezoelectric element is described.  
       FIG. 15  is a cross-sectional view of a piezoelectric element having a laminated body (a first laminated body) formed by the manufacturing method in accordance with the embodiment of the invention. The piezoelectric element includes a base substrate  1 , a lower electrode  2  formed on the base substrate  1 , a piezoelectric layer  3  formed on the lower electrode  2 , and an upper electrode  4  formed on the piezoelectric layer  3 .  FIG. 15  corresponds to  FIG. 5 .  
      In other words, at least the lower electrode  2  and the piezoelectric layer (a ferroelectric layer)  3 , and further the upper electrode  4  if necessary, of the piezoelectric element shown in  FIG. 15  can be formed by the method for manufacturing a first laminated body in accordance with the embodiment of the invention. The lower electrode  2  is composed of the layer of conductive complex oxide  2  (including the first layer of conductive complex oxide  20  and the second layer of conductive complex oxide  22 ) shown in  FIG. 2  through  FIG. 55  and the piezoelectric layer  3  is composed of the ferroelectric layer  3  shown in  FIG. 5 . Also, the upper electrode  4  may be composed of the layer of conductive complex oxide  4  shown in  FIG. 5 .  
      The base substrate  1  may be composed of a single-crystal silicon substrate with a ( 110 ) orientation and a thermal oxidation film formed on the surface of the single-crystal silicon substrate. By processing the base substrate  1 , the base substrate  1  can have ink cavities  521  in an ink jet recording head  50  as described below (see  FIG. 16 ).  
      4.3. Inkjet Recording Head  
      Next, an inkjet recording head in which the above-described piezoelectric element functions as a piezoelectric actuator, and an inkjet printer having the inkjet recording head are described.  FIG. 16  is a side cross-sectional view schematically showing a structure of the inkjet recording head in accordance with the present embodiment, and  FIG. 17  is an exploded perspective view of the inkjet recording head, which is shown upside down with respect to a state in normal use.  FIG. 18  shows an ink jet printer  700  that has the inkjet recording head in accordance with the present embodiment.  
      As shown in  FIG. 16  and  FIG. 17 , the inkjet recording head  50  includes a head main body (base substrate)  57  and piezoelectric sections  54  formed on the head main body  57 . The piezoelectric section  54  is provided with a piezoelectric element shown in  FIG. 15 , and the piezoelectric element is composed of a lower electrode  2 , a piezoelectric layer (ferroelectric layer)  3  and an upper electrode  4  successively laminated. The piezoelectric section  54  functions as a piezoelectric actuator in the inkjet recording head.  
      The head main body (base substrate)  57  is formed from a nozzle plate  51 , an ink chamber substrate  52 , and an elastic film  55 , which are housed in a housing  56 , thereby forming the ink jet recording head  50 .  
      Each of the piezoelectric sections is electrically connected to a piezoelectric element driving circuit (not shown), and is structured to operate (vibrate, deform) based on signals of the piezoelectric element driving circuit. In other words, each of the piezoelectric sections  54  functions as a vibration source (head actuator). The elastic film  55  vibrates (deforms) by vibrations (deformation) of the piezoelectric section  54 , and functions to instantaneously increase the inner pressure of the cavity  521 .  
      Although an ink jet recording head that discharges ink is described above as one example, the present embodiment is intended to be generally applicable to all liquid jet heads and liquid jet devices that use piezoelectric elements. As the liquid jet head, for example, a recording head used for an image recording device such as a printer, a color material jet head used to manufacture color filters of liquid crystal displays, and the like, an electrode raw material jet head used for forming electrodes of organic EL displays, FED (plane emission display), and the like, a bio-organic material jet head used for manufacturing biochips, and the like can be enumerated.  
      4.4. Surface Acoustic Wave Element  
      Next, an example of a surface acoustic wave element to which the method for manufacturing a laminated body (the method for manufacturing a second laminated body) in accordance with the embodiment of the invention is applied is described with reference to the accompanying drawings.  
       FIG. 19  is a cross-sectional view schematically showing a surface acoustic wave element  400  in accordance with the present embodiment.  
      The surface acoustic wave element  400  includes a substrate  11 , a piezoelectric layer  12  formed on the substrate  11 , and inter digital type electrodes (hereafter referred to as inter digital transducers or “IDT electrodes”)  18  and  19  formed on the piezoelectric layer  12 . The IDT electrodes  18  and  19  have predetermined patterns.  
      The surface acoustic wave element  400  in accordance with the present embodiment may be formed by using the method for manufacturing a laminated body (the method for manufacturing a second laminated body) in accordance with the embodiment of the invention, for example, as follows.  
      First, a piezoelectric layer  12  (corresponding to the ferroelectric layer  3  shown in  FIG. 6 ) is formed on a substrate  11  shown in  FIG. 16  (corresponding to the base substrate  1  shown in  FIG. 6 ). Then, first and second layers of conductive complex oxide  20  and  22  shown in  FIG. 6  are formed to thereby form a conductive layer (corresponding to the layer of conductive complex oxide  2 ). Then, by using known lithography technique and etching technique, the conductive layer (the layer of conductive complex oxide  2 ) is patterned to thereby form IDT electrodes  18  and  19  on the piezoelectric layer  12 .  
      4.5. Frequency Filter  
      Next, an example of a frequency filter to which the method for manufacturing a laminated body (the method for manufacturing a second laminated body) in accordance with the embodiment of the invention is applied is described with reference to the accompanying drawings.  FIG. 20  is a view schematically showing the frequency filter in accordance with the present embodiment.  
      As shown in  FIG. 20 , the frequency filter has a base substrate (laminated body)  140 . As the laminated body  140 , a laminated body similar to the one used in the surface acoustic wave element  400  described above may be used (see  FIG. 19 ). More specifically, the laminated body  140  includes a base substrate  11  and a piezoelectric layer  12  formed on the base substrate  11 , as shown in  FIG. 19 .  
      On an upper surface of the base substrate  140 , IDT electrodes  141  and  142  are formed. Acoustic absorber sections  143  and  144  are formed on the upper surface of the base substrate  140  in a manner to interpose the IDT electrodes  141  and  142 . The acoustic absorber sections  143  and  144  absorb surface acoustic waves propagating on the surface of the base substrate  140 . A high frequency signal source  145  is connected with the IDT electrode  141 , and a signal line is connected with the IDT electrode  142 . The laminated body  140  and the IDT electrodes  141  and  142  may be formed in a manner similar to the surface acoustic wave element  400  described above.  
      4.6. Oscillator  
      Next, an example of an oscillator to which the method for manufacturing a laminated body (the method for manufacturing a second laminated body) in accordance with the embodiment of the invention is applied is described with reference to the accompanying drawings.  FIG. 21  is a view schematically showing an oscillator in accordance with the present embodiment.  
      As shown in  FIG. 21 , the oscillator has a laminated body  150 . As the laminated body  150 , a laminated body similar to the one used in the surface acoustic wave element  400  described above (see  FIG. 9 ) may be used. In other words, the laminated body  150  has, as shown in  FIG. 19 , a base substrate  11  and a piezoelectric layer  12  formed on the base substrate  11 .  
      On an upper surface of the base substrate  150 , an IDT electrode  151  is formed. Furthermore, IDT electrodes  152  and  153  are formed in a manner to interpose the IDT electrode  151 . A high frequency signal source  154  is connected with one of comb teeth-shape electrodes  151   a  composing the IDT electrode  151 , and a signal line is connected with the other comb teeth-shape electrode  151   b.  It is noted that the IDT electrode  151  corresponds to an electric signal application electrode, while the IDT electrodes  152  and  153  correspond to resonating electrodes for resonating a specific frequency or a specific band frequency of the surface acoustic waves generated by the IDT electrode  151 . It is noted here that the laminated body  150  and the IDT electrodes  152  and  153  may be formed in a manner similar to the surface acoustic wave element  400  described above.  
      Also, the oscillator described above may be applied to a VCSO (Voltage Controlled SAW Oscillator).  
      The present invention is not limited to the embodiments described above, and many modifications can be made. For example, the present invention may include compositions that are substantially the same as the compositions described in the embodiments (for example, a composition with the same function, method and result, or a composition with the same objects and result). Also, the present invention includes compositions in which portions not essential in the compositions described in the embodiments are replaced with others. Also, the present invention includes compositions that achieve the same functions and effects or achieve the same objects of those of the compositions described in the embodiments. Furthermore, the present invention includes compositions that include publicly known technology added to the compositions described in the embodiments.