THIN-FILM DEVICE AND METHOD OF
MANUFACTURING SAME
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention
[0002] The present invention relates to a thin-film device comprising a lower conductor layer, a dielectric film and an upper conductor layer that are stacked, and to a method of manufacturing such a thin-film device. [0003] 2. Description of the Related Art [0004] With increasing demands for reductions in dimensions and thickness of high frequency electronic apparatuses such as cellular phones, reductions in dimensions and profile of electronic components mounted on the high frequency electronic apparatuses have been sought. Some of the electronic components comprise capacitors. Each capacitor typically incorporates a dielectric layer and a pair of conductor layers disposed to sandwich the dielectric layer. [0005] To achieve reductions in dimensions and profile of an electronic component comprising a capacitor, important factors are a reduction in area of a region in which the pair of conductor layers are opposed to each other with the dielectric layer disposed in between and a reduction in the number of layers making up the capacitor. Basically, in prior art, a material having a high permittivity is used as a dielectric material forming the dielectric layer and the thickness of the dielectric layer is reduced to achieve a reduction in area of the above-mentioned region and a reduction in the number of the layers making up the capacitor.
[0006] As conventional electronic components comprising capacitors, a thin-film capacitor disclosed in Japanese Published Patent Application (hereinafter referred to as JP-A) 2003-347155 and a thin-film capacitor element disclosed in JP-A2003-17366 are known. The thin-film capacitor disclosed in JP-A 2003-347155 incorporates a lower electrode layer, a dielectric layer and an upper electrode layer formed one by one on a substrate through the use of thin-film forming techniques. The thin-film capacitor element disclosed in JP-A 2003-17366 incorporates a lower electrode, a dielectric layer and an upper electrode formed one by one on a substrate through the use of thin-film forming techniques. JP-A 2003-17366 discloses a technique in which the top surface of the lower electrode and that of an insulator layer disposed around the lower electrode are flattened and the dielectric layer is formed on the flattened top surfaces. An electronic component formed through thinfilm forming techniques such as the above-mentioned thinfilm capacitor and thin-film capacitor element is called a thin-film device in the present patent application. [0007] JP-A 2002-93952 discloses a substrate for electronic components, the substrate comprising: an insulating substrate; a base electrode formed on the insulating substrate by a thin-film forming method; an Ni plating film having a thickness of 0.5 to 1.0 (im and formed on the base electrode; and a second plating film formed on the Ni plating film and made of a metal having a better solderability than Ni. [0008] For a thin-film device comprising a capacitor, since the dielectric layer is formed through thin-film forming techniques, it is possible to reduce the thickness of the dielectric layer and to thereby reduce the profile of the thin-film device. However, if the thickness of the dielectric layer is reduced in the thin-film device comprising a capacitor, there arise problems that the characteristics of the
capacitor become different from those intended, the withstand voltage of the capacitor is reduced, and variations in withstand voltage of the capacitor among products are increased. These problems will now be described in detail with reference to FIG. 12.
[0009] FIG. 12 is a cross-sectional view illustrating an example of configuration of a thin-film device comprising a capacitor. The thin-film device of FIG. 12 comprises: a lower conductor layer 102 disposed on a substrate 101; a dielectric layer 103 disposed on the substrate 101 and the lower conductor layer 102; and an upper conductor layer 104 disposed in a region sandwiching the dielectric layer 103 with the lower conductor layer 102. The thin-film device is fabricated by forming the lower conductor layer 102, the dielectric layer 103 and the upper conductor layer 104 in this order on the substrate 101 through the use of thin-film forming techniques.
[0010] In the thin-film device of FIG. 12, it is required that the lower conductor layer 102 have a certain thickness so that it is possible to feed a sufficient current thereto. Therefore, for example, electroplating is used to form the lower conductor layer 102. In electroplating, metallic ions having reached the surface of an object to be plated receive electrons and are thereby reduced to metal and taken into a metallic crystal lattice, so that the metallic crystal grows. If this process of metallic crystal growth reaches completion, the plating film reaches an equilibrium state. However, immediately after the plating film is formed, there may exist portions that have not reached the equilibrium state wherein the above-mentioned process of metallic crystal growth has not completed. Considering a case of forming a copper plating film by way of example, there may exist unreacted residual substances such as cupric sulfate, phosphorus, chlorine and sodium in the above-mentioned portions of the plating film that have not reached the equilibrium state. If the dielectric layer 103 is formed on the lower conductor layer 102 containing such residual substances, the residual substances in the lower conductor layer 102 may diffuse into the dielectric layer 103. As a result, there is a possibility that the characteristics of the dielectric layer 103 such as permittivity and dielectric loss tangent may change to become different from those intended. Possible consequences are that: the characteristics of the capacitor may become different from those intended; withstand voltage of the capacitor may be reduced due to a reduction in insulation of the dielectric layer 103; and variations in characteristics and withstand voltage of the capacitor among products may increase.
[0011] If the dielectric layer 103 is formed on the lower conductor layer 102 including portions that have not reached the equilibrium state, the lower conductor layer 102 is heated in the course of forming the dielectric layer 103, which may cause a change in the state of the portions of the lower conductor layer 102 that have not reached the equilibrium state. As a result, the surface roughness of the top surface of the lower conductor layer 102 touching the dielectric layer 103 may be increased. If the surface roughness of the top surface of the lower conductor layer 102 is thus increased, the thickness of the dielectric layer 103 is made nonuniform. Consequently, a portion that is extremely small in thickness develops in the dielectric layer 103, and insulation in the portion is degraded, which may result in an extreme reduction in withstand voltage of the capacitor. In such a case, a short-circuit failure of the capacitor resulting
from a puncture of the dielectric layer 103, for example, is likely to occur. Furthermore, if the thickness of the dielectric layer 103 is nonuniform, variations in withstand voltage of the capacitor among products are increased. [0012] In a case in which the thin-film device comprising a capacitor is designed for high frequency applications, if the surface roughness of the top surface of the lower conductor layer 102 is great, the skin resistance of the lower conductor layer 102 increases, and the signal transmission characteristic of the lower conductor layer 102 may be thereby degraded.
[0013] No measures to solve the foregoing problems are disclosed in any of JP-A 2003-347155, JP-A 2003-17366 and JP-A 2002-93952. The foregoing problems apply not only to thin-film devices comprising capacitors but also to thin-film devices in general each comprising a lower conductor layer, a dielectric film and an upper conductor layer that are stacked.
OBJECT AND SUMMARY OF THE INVENTION
[0014] It is an object of the invention to provide a thin-film device comprising a lower conductor layer, a dielectric film and an upper conductor layer that are stacked, the thin-film device being capable of preventing changes in characteristics of the dielectric film and a reduction in uniformity of the thickness of the dielectric film resulting from portions of the lower conductor layer that have not reached an equilibrium state, and to provide a method of manufacturing such a thin-film device.
[0015] A thin-film device of the invention comprises: a lower conductor layer; a dielectric film disposed on the lower conductor layer; and an upper conductor layer disposed on the dielectric film.
[0016] In the thin-film device of the invention, the lower conductor layer incorporates: a first layer made of a metal; and a second layer made of a metal and disposed between the first layer and the dielectric film. The grain diameter of a metallic crystal of the second layer is smaller than that of the first layer.
[0017] In the thin-film device of the invention, the grain diameter of the metallic crystal of the second layer of the lower conductor layer is smaller than that of the first layer of the lower conductor layer. Such a relationship can be achieved by, for example, forming the first layer by electroplating and forming the second layer by physical vapor deposition or chemical vapor deposition. In this case, the second layer is in a nearly equilibrium state as it is formed. [0018] A method of manufacturing the thin-film device of the invention comprises the steps of: forming the first layer by electroplating; forming the second layer on the first layer by physical vapor deposition or chemical vapor deposition; forming the dielectric film on the second layer; and forming the upper conductor layer on the dielectric film. [0019] According to the method of manufacturing the thin-film device of the invention, the first layer of the lower conductor layer is formed by electroplating, and the second layer of the lower conductor layer is formed by physical vapor deposition or chemical vapor deposition. The second layer formed by such a process is in a nearly equilibrium state as it is formed.
[0020] In the method of the invention, the grain diameter of the metallic crystal of the second layer may be smaller than that of the first layer.
[0021] In the thin-film device of the invention or the method of manufacturing the same, the surface roughness in maximum height of the top surface of the second layer may be smaller than that of the top surface of the first layer. [0022] In the thin-film device of the invention or the method of manufacturing the same, the dielectric film may have a thickness that falls within a range of 0.02 to 1 urn inclusive.
[0023] In the thin-film device of the invention or the method of manufacturing the same, the metal forming the first layer may contain any of Cu, Ag and Al, and the metal forming the second layer may contain any of Cu, Ag, Al, Cr, Ti, Ni, Ni—Cr and Au.
[0024] In the thin-film device of the invention or the method of manufacturing the same, the lower conductor layer, the dielectric film and the upper conductor layer may constitute a capacitor.
[0025] According to the thin-film device of the invention, the lower conductor layer incorporates: the first layer made of a metal; and the second layer made of a metal and disposed between the first layer and the dielectric film. The grain diameter of the metallic crystal of the second layer is smaller than that of the first layer. Such a relationship can be achieved by, for example, forming the first layer by electroplating and forming the second layer by physical vapor deposition or chemical vapor deposition. As a result, the second layer is in a nearly equilibrium state as it is formed. According to the invention, it is thereby possible to prevent changes in characteristics of the dielectric film and a reduction in uniformity of the thickness of the dielectric film resulting from portions of the lower conductor layer that have not reached an equilibrium state. [0026] According to the method of manufacturing the thin-film device of the invention, the first layer of the lower conductor layer is formed by electroplating, and the second layer is formed by physical vapor deposition or chemical vapor deposition. The second layer formed by such a process is in a nearly equilibrium state as it is formed. According to the invention, it is thereby possible to prevent changes in characteristics of the dielectric film and a reduction in uniformity of the thickness of the dielectric film resulting from portions of the lower conductor layer that have not reached an equilibrium state.
[0027] Other and further objects, features and advantages of the invention will appear more fully from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a cross-sectional view of a thin-film device of an embodiment of the invention. [0029] FIG. 2 is a cross-sectional view illustrating a step of a method of manufacturing the thin-film device of the embodiment of the invention.
[0030] FIG. 3 is a cross-sectional view illustrating a step that follows the step of FIG. 2.
[0031] FIG. 4 is a cross-sectional view illustrating a step that follows the step of FIG. 3.
[0032] FIG. 5 is a cross-sectional view illustrating a step that follows the step of FIG. 4.
[0033] FIG. 6 is a cross-sectional view illustrating a step that follows the step of FIG. 5.
[0034] FIG. 7 is a cross-sectional view illustrating a step that follows the step of FIG. 6.
[0035] FIG. 8 is a cross-sectional view illustrating a step that follows the step of FIG. 7.
[0036] FIG. 9 is a cross-sectional view illustrating a step that follows the step of FIG. 8.
[0037] FIG. 10 is a cross-sectional view illustrating a step that follows the step of FIG. 9.
[0038] FIG. 11 is a cross-sectional view illustrating a step that follows the step of FIG. 10.
[0039] FIG. 12 is a cross-sectional view illustrating an example of configuration of a thin-film device comprising a capacitor.
DESCRIPTION OF A PREFERRED
EMBODIMENT
[0040] A preferred embodiment of the invention will now
be described with reference to the accompanying drawings.
Reference is now made to FIG. 1 to describe a thin-film
device of an embodiment of the invention. FIG. 1 is a
cross-sectional view of the thin-film device of the embodi-
ment. As shown in FIG. 1, the thin-film device 1 of the
embodiment comprises: a substrate 2; a flattening film 3
made of an insulating material and disposed on the substrate
2; and a capacitor 4 provided on the flattening film 3. The
capacitor 4 incorporates: a lower conductor layer 10 dis-
posed on the flattening film 3; a dielectric film 20 disposed
on the lower conductor layer 10; and an upper conductor
layer 30 disposed on the dielectric film 20.
[0041] Each of the lower conductor layer 10 and the upper
conductor layer 30 is patterned into a specific shape. The
dielectric film 20 is disposed to cover the top and side
surfaces of the lower conductor layer 10 and the top surface
of the flattening film 3. The upper conductor layer 30 is
disposed in a region sandwiching the dielectric film 20 with
the lower conductor layer 10. The lower conductor layer 10
and the upper conductor layer 30 make up a pair of elec-
trodes opposed to each other with the dielectric film 20
disposed in between in the capacitor 4.
[0042] The substrate 2 is made of an insulating material (a
dielectric material). The insulating material forming the
substrate 2 may be an inorganic material or an organic
material. The insulating material forming the substrate 2
may be A1203, for example. The substrate 2 may be made of
a semiconductor material.
[0043] The insulating material forming the flattening film 3 may be an inorganic material or an organic material. An inorganic material forming the flattening film 3 is A1203, for example. When an inorganic material is used as the material of the flattening film, it is preferred to form the flattening film 3 by physical vapor deposition (PVD) or chemical vapor deposition (CVD). An organic material forming the flattening film 3 may be a resin, for example. In this case, the resin may be either a thermoplastic resin or a thermosetting resin. When an organic material such as a resin is used as the material of the flattening film 3, it is preferred that the organic material to form the flattening film 3 be applied to the top of the substrate 2 while the material exhibits fluidity, and then the organic material be hardened to form the flattening film 3. The flattening film 3 may be made of a spin-on-glass (SOG) film. The flattening film 3 may be formed through an ink-jet technique. [0044] The surface roughness in maximum height Rz of the top surface of the flattening film 3 is smaller than the surface roughness in maximum height Rz of the top surface of the substrate 2. The surface roughness in maximum height
Rz is one of parameters indicating the surface roughness and is defined as a sum of the maximum value of the peak and the maximum value of the valley of a contour curve of a unit length. The thickness of the flattening film 3 preferably falls within a range of 0.01 to 50 urn inclusive. [0045] If the surface roughness of the top surface of the substrate 2 is sufficiently small, the lower conductor layer 10 may be disposed directly on the substrate 2 without providing the flattening film 3.
[0046] The lower conductor layer 10 incorporates: an electrode film 11 made of a metal and disposed on the flattening film 3; a first layer 12 made of a metal and disposed on the electrode film 11; and a second layer 13 made of a metal and disposed between the first layer 12 and the dielectric film 20. The grain diameter of the metallic crystal of the second layer 13 is smaller than that of the first layer 12. In addition, it is preferred that the surface roughness in maximum height Rz of the top surface of the second layer 13 be smaller than that of the top surface of the first layer 12.
[0047] The metal forming the first layer 12 contains any of Cu, Ag and Al, for example. The metal forming the second layer 13 contains any of Cu, Ag, Al, Cr, Ti, Ni, Ni—Cr and Au, for example.
[0048] The first layer 12 is formed by electroplating. The electrode film 11 is used as an electrode for forming the first layer 12 by electroplating. The second layer 13 is formed by PVD or CVD.
[0049] The dielectric film 20 is made of a dielectric material. The dielectric material forming the dielectric film 20 is preferably an inorganic material. The dielectric material forming the dielectric film 20 may be any of A1203, Si N3 and Si02, for example.
[0050] The upper conductor layer 30 has a configuration the same as that of the lower conductor layer 10, for example. That is, the upper conductor layer 30 incorporates: an electrode film 31 made of a metal and disposed on the dielectric film 20; a first layer 32 made of a metal and disposed on the electrode film 31; and a second layer 33 made of a metal and disposed between the first layer 32 and the dielectric film 20. The grain diameter of the metallic crystal of the second layer 33 is smaller than that of the first layer 32. In addition, it is preferred that the surface roughness in maximum height Rz of the top surface of the second layer 33 be smaller than that of the top surface of the first layer 32. It is not necessarily required that the upper conductor layer 30 have a configuration the same as that of the lower conductor layer 10 if it is not necessary to stack a dielectric layer on the upper conductor layer 30. For example, it is not always necessary that the upper conductor layer 30 incorporate the second layer 33. [0051] The metals forming the first layer 32 and the second layer 33 and the methods of forming the first layer 32 and the second layer 33 are the same as those for the first layer 12 and the second layer 13 of the lower conductor layer 10.
[0052] The thickness of the dielectric film 20 is smaller than that of the lower conductor layer 10 and preferably falls within a range of 0.02 to 1 urn inclusive, for example, and more preferably a range of 0.05 to 0.5 urn inclusive. The thickness of the lower conductor layer 10 preferably falls within a range of 5 to 10 urn inclusive. The thickness of the upper conductor layer 30 preferably falls within a range of 5 to 10 um inclusive.
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