Patent Application
20160293334
The present invention relates to a thin film capacitor in which a vertical cross section has an uneven structure.
A thin film capacitor serving as an electronic component is disclosed in, for example, Patent Literature 1 (Japanese Unexamined Patent Publication No. 2002-26266). Also, a trench capacitor having a three-dimensional structure so that a surface area per unit area increases in semiconductor integration technology is proposed as a structure for achieving a capacitor constituting a memory with high capacity (Patent Literature 2: Specification of U.S. Pat. No. 6,740,922). Also, there has been an attempt to apply this three-dimensional structure to electronic components other than memories (Patent Literature 3: Japanese Unexamined Patent Publication No. H6-325970).
However, characteristics of a thin film capacitor may easily deteriorate in a thin film capacitor having a size reduced by providing an uneven surface structure as an electronic component. The present invention has been made in view of this problem and an objective of the invention is to provide a thin film capacitor capable of suppressing characteristic deterioration.
In a first type of thin film capacitor, a lower electrode has an uneven surface structure of a vertical cross section in a thickness direction (Z) of a substrate, an upper electrode has an uneven surface structure of a vertical cross section in the thickness direction of the substrate, a projecting portion of the upper electrode projecting to a lower electrode side is positioned in a gap between projecting portions of the lower electrode, the lower electrode includes Cu as a main component, and a Young's modulus ESS of the substrate 1, a Young's modulus ESC of a stress adjustment layer, and a Young's modulus ELE of the lower electrode satisfy the relational expressions ELE<ESC and ESS<ESC.
In a second type of thin film capacitor, the distal end of the projecting portion of the lower electrode has corner portions of radii R1 of curvature for which centers C1a and C1b of curvature are positioned inside the projecting portion. Here, the radius R1 of curvature and a thickness td of a dielectric thin film satisfy the relational expression 0.4×td≦R1≦20×td. When the radius R1 of curvature is less than 0.4 times the thickness td of the dielectric thin film, the antenna effect increases and an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film occurs while an element is used. When the radius R1 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but malfunctions such as concentration of an electric field due to a crystalline grain boundary of the electrode occurring in the corner portion occur.
In a third type of thin film capacitor, the thin film capacitor in which a dielectric thin film is interposed between a lower electrode and an upper electrode includes a first terminal provided in the lower electrode and a second terminal provided in the upper electrode, wherein the lower electrode has an uneven surface structure. A ridge line of the projecting portion of the uneven surface structure extends in a direction (X-axis direction) from the first terminal to the second terminal. In this case, equivalent series resistance (ESR) of the X-axis direction decreases and therefore the loss of the thin film capacitor decreases and stability increases.
First, an overview of a first type of invention will be described.
In the first type of invention, a thin film capacitor of a first aspect is a thin film capacitor including: a substrate; a stress adjustment layer formed on a main surface of the substrate; a lower electrode formed on the stress adjustment layer; a dielectric thin film configured to cover the lower electrode; and an upper electrode formed on the dielectric thin film, wherein the lower electrode has an uneven surface structure of a vertical cross section in a thickness direction of the substrate, wherein the upper electrode has an uneven surface structure of a vertical cross section in a thickness direction of the substrate, wherein a projecting portion of the upper electrode projecting to a lower electrode side is positioned in a gap between projecting portions of the lower electrode, wherein the lower electrode includes Cu as a main component, and wherein a Young's modulus ESS of the substrate, a Young's modulus ESC of the stress adjustment layer, and a Young's modulus ELE of the lower electrode satisfy the relational expressions ELE<ESC and ESS<ESC.
According to this thin film capacitor, the deformation of the lower electrode is suppressed because the stress adjustment layer is harder (has a higher Young's modulus) than the lower electrode and the substrate for supporting the lower electrode among the above-described three elements, and thus the damage associated with the deformation of the dielectric thin film adjacent to the lower electrode, and the characteristic deterioration associated with the damage can be suppressed.
In the thin film capacitor of a second aspect, a linear expansion coefficient αSS of the substrate, a linear expansion coefficient αSC of the stress adjustment layer, and a linear expansion coefficient αLE of the lower electrode satisfy the relational expressions αSC<αLE and αSC<αSS.
In this case, because thermal expansion of the substrate or the lower electrode is suppressed due to a decrease in the linear expansion coefficient of the stress adjustment layer even when thermal expansion occurs in the substrate or the lower electrode, the deformation of the lower electrode due to a change in a temperature decreases and the damage of the dielectric thin film adjacent to the substrate or the lower electrode and the characteristic deterioration associated with the damage can be suppressed.
In the thin film capacitor of a third aspect, a heat conductivity λSS of the substrate, a heat conductivity λSC of the stress adjustment layer, and a heat conductivity λLE of the lower electrode satisfy the relational expressions λSC<λSS and λSC<λLE.
In this case, because the heat conductivity of the stress adjustment layer is small even when the change in the temperature occurs in the substrate or the lower electrode, the deformation of the lower electrode decreases due to the suppression of the heat conduction of the substrate and the lower electrode and the suppression of the occurrence of linear expansion and the damage of the dielectric thin film adjacent to the substrate and the lower electrode and the characteristic deterioration according to the damage can be suppressed. In particular, the effect tends to be large in terms of the fact that the change in the temperature in a substrate having a relatively large volume does not affect the lower electrode.
In the thin film capacitor of a fourth aspect, the lower electrode includes: a common electrode part extending in parallel to a main surface of the substrate; and a plurality of projecting portions extending to project away from the substrate from the common electrode part, the thin film capacitor includes: a protective film configured to cover the upper electrode; a dummy electrode formed on the stress adjustment layer; and a lower contact electrode formed on the common electrode part of the lower electrode, the dielectric thin film, the upper electrode, and a first connection electrode are positioned on the dummy electrode, the lower contact electrode in contact with the common electrode part and a second connection electrode are positioned on the common electrode part of the lower electrode via an opening provided in the dielectric thin film, the dummy electrode has the same thickness as the common electrode part of the lower electrode, the first connection electrode is positioned within a first contact hole provided in the protective film, and the second connection electrode is positioned within a second contact hole provided in the protective film.
In the case of this structure, because the dummy electrode has the same thickness as the common electrode part of the lower electrode, heights of the first connection electrode and the second connection electrode in the thickness direction can be approximately the same and the thin-film capacitor of a flat structure can be formed.
According to the thin film capacitor of these aspects, it is possible to suppress characteristic deterioration by providing the stress adjustment layer of a predetermined condition.
Hereinafter, the thin film capacitor according to the embodiment related to the first type of invention will be described. Also, the same reference signs are assigned to the same elements and redundant description thereof will be omitted. Also, an XYZ three-dimensional orthogonal coordinate system is set and the thickness direction of the substrate is assumed to be the Z-axis direction.
This thin film capacitor includes a substrate 1, a stress adjustment layer 2 formed on a main surface (XY plane) of the substrate 1, a lower electrode 4 formed on the stress adjustment layer 2 via a base layer 3, a dielectric thin film 5 configured to cover the lower electrode 4, and an upper electrode 6 formed on the dielectric thin film 5.
A main part of the thin film capacitor is constituted of the lower electrode 4, the upper electrode 6, and the dielectric thin film 5 positioned between the lower electrode 4 and the upper electrode 6.
The lower electrode 4 includes the common electrode part 4a extending in parallel to the main surface of the substrate 1 and a plurality of projecting portions 4b extending to project from the common electrode part 4a away from the substrate 1. Likewise, the upper electrode 6 includes a common electrode part 6a extending in parallel to the main surface of the substrate 1 and a plurality of projecting portions 6b extending to project from the common electrode part 6a toward the substrate 1. Also, the upper electrode 6 has a contact portion 6c for enabling the connection electrode to come in contact with an external terminal.
The lower electrode 4 has an uneven surface structure of a vertical cross section (XZ plane) in the thickness direction of the substrate 1 and has a comb tooth shape. Likewise, the upper electrode 6 has an uneven surface structure of a vertical cross section (XZ plane) in the thickness direction of the substrate 1 and has a comb tooth shape. The projecting portion 6b projecting to the lower electrode side of the upper electrode 6 is positioned in a gap between the projecting portions 4b of the lower electrode 4 and a structure in which comb teeth face each other and engaged with each other is a trench structure in the vertical cross section and increases capacitance per unit area.
This thin film capacitor includes a protective film 7 configured to cover the upper electrode 6, a dummy electrode 4D formed on the stress adjustment layer 2, and a lower contact electrode 6D formed on the common electrode part 4a of the lower electrode 4 and in contact with the common electrode part 4a. The dummy electrode 4D is formed simultaneously with the common electrode part 4a of the lower electrode and the lower contact electrode 6D is formed simultaneously with the upper electrode 6.
On the left in
Also, the first connection electrode 8a is positioned within a first contact hole Ha provided in the protective film 7 and the second connection electrode 8b is positioned within a second contact hole Hb provided in the protective film 7.
In the case of this structure, because the dummy electrode 4D has the same thickness as the common electrode part 4a of the lower electrode 4, heights of the first connection electrode 8a and the second connection electrode 8b in the thickness direction can be approximately the same and a thin film capacitor of a flat structure can be formed.
A contact electrode and/or an under bump metal 9a are in contact with the first connection electrode 8a and are positioned on the first connection electrode 8a. A contact electrode and/or an under bump metal 9b are in contact with the second connection electrode 8b and are positioned on the second connection electrode 8b. Bumps 10a and 10b are arranged on the under bump metals 9a and 9b, respectively.
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The under bump metal 9a and the under bump metal 9b serving as conductive pads are provided on the first connection electrode 8a and the second connection electrode 8b. These can function as contact electrodes and the under bump metal can be further provided on the contact electrode using a different material. Bumps 10a and 10b are arranged on the under bump metals 9a and 9b, respectively. Cu, Ni, and Au can be used as materials of the under bump metal or the contact electrode. These can be stacked or mixed for use for each material. Preferably, it is possible to perform plating of Ni and Au on Cu.
Also, if the vertical cross section has the uneven surface structure, various types are considered as the structure of the lower electrode 4. Also, a plurality of thin film capacitors like that described above can be formed on a single wafer and can be separately used by performing dicing individually or for a desired group.
In the case of the structure of
In the case of the structure of
In the case of the structure of
In the case of the structure of
In the case of the structure of
In the case of the structure of
The structure illustrated in
Next, the material of each element described above will be described.
The lower electrode 4 includes Cu as a main component. Also, the lower electrode 4 is assumed to be Cu of 100 (atm %). The upper electrode 6 also includes Cu as the main component. These can also be constituted of the same material or different materials. In this example, these are assumed to have the same material and the same physical properties. The substrate 1 is made of Si and the stress adjustment layer 2 is made of silicon nitride.
In this case, the Young's modulus ESS of the substrate 1, the Young's modulus ESC of the stress adjustment layer 2, and the Young's modulus ELE of the lower electrode 4 satisfy the following relational expressions.
Relational expressions:
ELE<ESC
ESS<ESC
According to this thin film capacitor, the deformation of the lower electrode 4 is suppressed because the stress adjustment layer 2 is harder than the softest lower electrode 4 and the substrate 1 for supporting the lower electrode 4 (has a higher Young's modulus) among the above-described three elements, and the damage associated with the deformation of the dielectric thin film 5 adjacent to the lower electrode and the characteristic deterioration associated with the damage can be suppressed.
The dielectric thin film 5 is made of Al2O3, but another dielectric material (insulating material) can be used. The Young's modulus of Al2O3 is 370. Cu, Si, SiNx, and Al2O3 are arranged in ascending order of Young's modulus. When the Young's modulus of the dielectric thin film is high and its damage is suppressed, the present invention is more effective. Characteristic data of each element is as shown in the chart of
Also, Cu is used as an electrode material, but a metal material illustrated in
Also, GaAs, SiC, Ge, or Ga can be used as a material constituting the substrate in addition to Si as illustrated in
As illustrated in
Also, a linear expansion coefficient αSS of the substrate 1, a linear expansion coefficient αSC of the stress adjustment layer 2, and a linear expansion coefficient αLE of the lower electrode 4 satisfy the following relational expressions.
Relational expressions:
αSC<αLE
αSC<αSS
In this case, because the linear expansion coefficient of the stress adjustment layer is small even when thermal expansion occurs in the substrate or the lower electrode, the deformation of the lower electrode due to a change in a temperature decreases due to the suppression of thermal expansion of the substrate or the lower electrode and the damage of the dielectric thin film adjacent to the substrate or the lower electrode and the characteristic deterioration associated with the damage can be suppressed.
In the third thin film capacitor, it is preferable that a heat conductivity λSS of the substrate, a heat conductivity λSC of the stress adjustment layer, and a heat conductivity λLE of the lower electrode satisfy the following relational expressions.
Relational expressions:
λSC<λSS
λSC<λLE
In this case, because the heat conductivity of the stress adjustment layer decreases even when the change in the temperature occurs in the substrate or the lower electrode, the deformation of the lower electrode decreases due to the suppression of the heat conduction of the substrate and the lower electrode and the suppression of the occurrence of linear expansion, and the damage of the dielectric thin film adjacent to the substrate and the lower electrode and the characteristic deterioration according to the damage can be suppressed. In particular, the effect tends to be large in terms of the fact that the change in the temperature in a substrate having a relatively large volume does not affect the lower electrode.
The effect based on the above relational expressions was confirmed not only logically as described above but also though experiments.
A plurality of capacitors like that illustrated in
In Embodiment 1, Si was used as the substrate, SiNx was used as the stress adjustment layer, and Cu was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In Embodiment 2, Si was used as the substrate, SiNx was used as the stress adjustment layer, and Al was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In Embodiment 3, Si was used as the substrate, SiNx was used as the stress adjustment layer, and Ni was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In Embodiment 4, Si was used as the substrate, Al2O3 was used as the stress adjustment layer, and Cu was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In Embodiment 5, Si was used as the substrate, Al2O3 was used as the stress adjustment layer, and Al was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In Embodiment 6, Si was used as the substrate, ZrO2 was used as the stress adjustment layer, and Cu was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In Embodiment 7, Si was used as the substrate, SiO2 was used as the stress adjustment layer, and Al was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In Embodiment 8, ZrO2 was used as the substrate, AlN was used as the stress adjustment layer, and Cu was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In Embodiment 9, Si was used as the substrate, AlN was used as the stress adjustment layer, and Ni was used as the lower electrode. In this case, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied.
In comparative example 1, Si was used as the substrate, ZrO2 was used as the stress adjustment layer, and Ni was used as the lower electrode.
In comparative example 2, Si was used as the substrate, SiO2 was used as the stress adjustment layer, and Cu was used as the lower electrode.
In comparative example 3, Al2O3 was used as the substrate, SiO2 was used as the stress adjustment layer, and Cu was used as the lower electrode.
In comparative example 4, polyethylene terephthalate (PET) was used as the substrate, SiO2 was used as the stress adjustment layer, and Cu was used as the lower electrode.
In comparative example 5, Si was used as the substrate, polyimide was used as the stress adjustment layer, and Cu was used as the lower electrode.
In comparative examples 1 to 6, unlike embodiments 1 to 6, the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are not satisfied.
1000 samples were prepared for each experiment example and a voltage of 30 V was continuously applied between the upper and lower electrodes under an environment of 85% humidity and a temperature of 85° C. After the environmental test for 24 hours, a sample having an insulation resistance of 1011Ω or more was designated as a normal product and a sample having an insulation resistance of less than 1011Ω was designated as a defective product.
In embodiment 1, the number of normal products among the 1000 samples was 983. In embodiment 2, the number of normal products among the 1000 samples was 956. In embodiment 3, the number of normal products among the 1000 samples was 970. In embodiment 4, the number of normal products among the 1000 samples was 898. In embodiment 5, the number of normal products among the 1000 samples was 908. In embodiment 6, the number of normal products among the 1000 samples was 913. In embodiment 7, the number of normal products among the 1000 samples was 943. In embodiment 8, the number of normal products among the 1000 samples was 622. In embodiment 9, the number of normal products among the 1000 samples was 570. In comparative example 1, the number of normal products among the 1000 samples was 201. In comparative example 2, the number of normal products among the 1000 samples was 128. In comparative example 3, the number of normal products among the 1000 samples was 108. In comparative example 4, the number of normal products among the 1000 samples was 89. In comparative example 5, the number of normal products among the 1000 samples was 63.
As described above, when the relational expressions ELE<ESC and ESS<ESC related to Young's modulus E are satisfied as shown in data of embodiments 1 to 9, it can be seen that the environmental tolerance increases more than those of comparative examples 1 to 5 which do not satisfy these relational expressions.
The relational expressions αSC<αLE and αSC<αSS related to the linear expansion coefficient α are satisfied in embodiments 1 to 8 and are not satisfied in embodiment 9. Also, the relational expressions αSC<αLE and αSC<αSS related to the linear expansion coefficient α are satisfied in comparative examples 1 to 4 and are not satisfied in comparative example 5.
As illustrated in
The relational expressions λSC<λSS and λSC<λLE related to the heat conductivities 2 are satisfied in embodiments 1 to 7 and are not satisfied in embodiments 8 and 9. Also, the relational expressions λSC<λSS and λSC<λLE related to the heat conductivities λ are satisfied in comparative examples 1 to 3 and comparative example 5 and are not satisfied in comparative example 4.
As illustrated in
As described above, it is possible to increase capacitance because the thin film capacitor having an uneven surface structure is a structure in which an area opposite to the electrode in a unit volume increases. On the other hand, because the electrode is subdivided, the strength is degraded, a mechanical force generated by a temperature increase during mounting or an environment during actual use is transferred to a dielectric layer and the dielectric layer may be destroyed. In this embodiment, this destruction is suppressed. A lower electrode in which the shape of the vertical cross section is a comb tooth or slit shape or a lower electrode in which the shape of the vertical cross section is a shape including a pin or hole can be used as the uneven surface structure of the lower electrode, and the structures of the lower electrode and the upper electrode can also be replaced with each other.
As described above, it is possible to suppress stress accumulation for the dielectric thin film and suppress the characteristic deterioration by satisfying the above-described predetermined conditions.
Next, an overview of a second type of invention will be described.
In the second type of invention, a thin film capacitor of a first aspect is a thin film capacitor including: a substrate; an insulating layer formed on a main surface of the substrate; a lower electrode formed on the insulating layer; a dielectric thin film configured to cover the lower electrode; and an upper electrode formed on the dielectric thin film, wherein the lower electrode has an uneven surface structure of a vertical cross section in a thickness direction of the substrate, wherein the upper electrode has an uneven surface structure of a vertical cross section in a thickness direction of the substrate, wherein a projecting portion of the upper electrode projecting to a lower electrode side is positioned in a gap between projecting portions of the lower electrode, wherein, when an XYZ three-dimensional coordinate system is set, the main surface is an XY plane, and a direction in which a plurality of projecting portions of the lower electrode are arranged is designated as an X-axis direction, a distal end of the projecting portion of the lower electrode within the XZ plane has a corner portion with a radius R1 of curvature in which a center of curvature is positioned inside the projecting portion, and wherein the radius R1 of curvature and a thickness td of the dielectric thin film satisfy the relational expression 0.4×td≦R1≦20×td.
When the radius R1 of curvature is less than 0.4 times the thickness td of the dielectric thin film according to the thin film capacitor, the antenna effect increases, an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film occurs while an element is used. When the radius R1 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but the corner portion of the above-described projecting portion is formed to be more gentle than necessary, the stress applied in the in-plane direction of the dielectric thin film in the in-plane direction of the corner portion increases, and cracks tend to be introduced into a crystalline grain boundary of the dielectric thin film. Also, because a crystalline grain boundary density of the electrode in the above-described corner portion becomes rough to the extent that the electric field tends to concentrate, the concentration of an electric field due to a crystalline grain boundary of the lower electrode tends to occur.
In the thin film capacitor of a second aspect, a proximal end of the projecting portion of the lower electrode within the XZ plane has a corner portion with a radius R2 of curvature in which a center of curvature is positioned outside the projecting portion, and the radius R2 of curvature and the thickness td of the dielectric thin film satisfy the relational expression 0.4×td≦R2≦20×td.
The recess portion between proximal ends of the lower electrode is opposite to a distal end of the downward projecting portion of the upper electrode. Therefore, the influence of the electric field on the dielectric thin film interposed between the lower electrode and the upper electrode similarly occurs in the distal end of the projecting portion in the lower electrode and the proximal end.
That is, when the radius R2 of curvature is less than 0.4 times the thickness td of the dielectric thin film even in the proximal end, the antenna effect increases, an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film occurs while an element is used. When the radius R2 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but malfunctions such as the stress applied in the in-plane direction of the dielectric thin film in the in-plane direction of the corner portion increasing and cracks are introduced into the dielectric thin film or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion occur.
The condition for satisfying the above-described radius of curvature is not satisfied only within the XZ plane, so that the concentration of the electric field also similarly occurs in the periphery of the corner portion within the YZ plane from a point of view of the concentration of the electric field based on a shape for the corner portion.
Therefore, in the thin film capacitor of a third aspect, the distal end of the projecting portion of the lower electrode within the YZ plane has a corner portion with a radius R3 of curvature in which a center of curvature is positioned inside the projecting portion, and the radius R3 of curvature and the thickness td of the dielectric thin film satisfy the relational expression 0.4×td≦R3≦20×td.
Thereby, when the radius R3 of curvature is less than 0.4 times the thickness td of the dielectric thin film even in the YZ plane as described above, the antenna effect increases, an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film occurs while an element is used. When the radius R3 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but malfunctions such as the stress applied in the in-plane direction of the dielectric thin film in the in-plane direction of the corner portion increasing and cracks tending to be introduced into the dielectric thin film or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion occur.
Likewise, a similar structure to the case of the XZ plane is provided in the proximal end of the projecting portion within the YZ plane and therefore the similar actions and effects occur.
That is, in the thin film capacitor of a fourth aspect, the distal end of the projecting portion of the lower electrode within the YZ plane has a corner portion with a radius R4 of curvature in which a center of curvature is positioned outside the projecting portion, and the radius R4 of curvature and the thickness td of the dielectric thin film satisfy the relational expression 0.4×td≦R4≦20×td.
Thereby, when the radius R4 of curvature is less than 0.4 times the thickness td of the dielectric thin film even in the YZ plane as described above, the antenna effect increases, an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film occurs while an element is used. When the radius R4 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but malfunctions such as the stress applied in the in-plane direction of the dielectric thin film in the in-plane direction of the corner portion increasing and cracks tending to be introduced into the dielectric thin film or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion occur
Also, in the thin film capacitor of a fifth aspect, it is further preferable that the relational expression 0.5×td≦R1≦10×td be satisfied in relation to a value of the above-described R1. In this case, the internal defect of the dielectric thin film is suppressed more than in the case of the above-described range of R1 and malfunctions such as cracks tending to be introduced into the dielectric thin film due to stress in the in-plane direction of the dielectric thin film in the corner portion or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion are also reduced.
Also, in the thin film capacitor of a sixth aspect, it is further preferable that the relational expression 0.5×td≦R2≦10×td be satisfied in relation to a value of the above-described R1. In this case, the internal defect of the dielectric thin film is suppressed more than in the case of the above-described range of R1 and malfunctions such as cracks tending to be introduced into the dielectric thin film due to stress in the in-plane direction of the dielectric thin film in the corner portion or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion are also reduced.
In the thin film capacitor of a seventh aspect, the insulating layer is a stress adjustment layer, and the Young's modulus of the stress adjustment layer is greater than the Young's modulus of the substrate and greater than the Young's modulus of the lower electrode. When the Young's modulus of the stress adjustment layer is relatively higher than the others, mechanical distortion of the lower electrode is suppressed and therefore mechanical destruction of the dielectric thin film is suppressed. When the mechanical stress is applied to the dielectric thin film even in a state in which the internal defect slightly occurs, the dielectric thin film deteriorates and a probability of a defective product increases. However, when the Young's modulus of the stress adjustment layer increases, the stress transfer for the dielectric thin film via the lower electrode is suppressed and the characteristic deterioration of the thin film capacitor can be suppressed.
Also, any conditions of the thin film capacitor described above can be combined. According to the thin film capacitor of the present invention, it is possible to suppress the characteristic deterioration.
Hereinafter, the thin film capacitor according to the embodiment of the second type of invention will be described. Also, the same reference signs are assigned to the same elements and redundant description thereof will be omitted. Also, an XYZ three-dimensional orthogonal coordinate system is set and the thickness direction of the substrate is assumed to be the Z-axis direction.
This thin film capacitor includes a substrate 1, an insulating layer 2 (stress adjustment layer 2) formed on a main surface (XY plane) of the substrate 1, a lower electrode 4 formed on the stress adjustment layer 2 via a base layer 3, a dielectric thin film 5 configured to cover the lower electrode 4, and an upper electrode 6 formed on the dielectric thin film 5.
A main part of the thin film capacitor is constituted of the lower electrode 4, the upper electrode 6, and the dielectric thin film 5 positioned between the lower electrode 4 and the upper electrode 6.
The lower electrode 4 includes the common electrode part 4a extending in parallel to the main surface of the substrate 1 and a plurality of projecting portions 4b extending to project from the common electrode part 4a away from the substrate 1. Likewise, the upper electrode 6 includes a common electrode part 6a extending in parallel to the main surface of the substrate 1 and a plurality of projecting portions 6b extending to project from the common electrode part 6a toward the substrate 1. Also, the upper electrode 6 has a contact portion 6c for enabling the connection electrode to come in contact with an external terminal.
The lower electrode 4 has an uneven surface structure of a vertical cross section (XZ plane) in the thickness direction of the substrate 1 and has a comb tooth shape. Likewise, the upper electrode 6 has an uneven surface structure of a vertical cross section (XZ plane) in the thickness direction of the substrate 1 and has a comb tooth shape. The projecting portion 6b projecting to the lower electrode side of the upper electrode 6 is positioned in a gap between the projecting portions 4b of the lower electrode 4 and a structure in which comb teeth face each other and engaged with each other is a trench structure in the vertical cross section and increases capacitance per unit area.
This thin film capacitor includes a protective film 7 configured to cover the upper electrode 6, a dummy electrode 4D formed on the stress adjustment layer 2, and a lower contact electrode 6D formed on the common electrode part 4a of the lower electrode 4 and in contact with the common electrode part 4a. The dummy electrode 4D is formed simultaneously with the common electrode part 4a of the lower electrode and the lower contact electrode 6D is formed simultaneously with the upper electrode 6.
On the left in
Also, the first connection electrode 8a is positioned within a first contact hole Ha provided in the protective film 7 and the second connection electrode 8b is positioned within a second contact hole Hb provided in the protective film 7.
In the case of this structure, because the dummy electrode 4D has the same thickness as the common electrode part 4a of the lower electrode 4, heights of the first connection electrode 8a and the second connection electrode 8b in the thickness direction can be approximately the same and a thin film capacitor of a flat structure can be formed.
A contact electrode and/or an under bump metal 9a are in contact with the first connection electrode 8a and are positioned on the first connection electrode 8a. A contact electrode and/or an under bump metal 9b are in contact with the second connection electrode 8b and are positioned on the second connection electrode 8b. Bumps 10a and 10b are arranged on the under bump metals 9a and 9b, respectively.
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The under bump metal 9a and the under bump metal 9b serving as conductive pads are provided on the first connection electrode 8a and the second connection electrode 8b. These can function as contact electrodes and the under bump metal can be further provided on the contact electrode using a different material. Bumps 10a and 10b are arranged on the under bump metals 9a and 9b, respectively. Cu, Ni, and Au can be used as materials of the under bump metal or the contact electrode. These can be stacked or mixed for use for each material. Preferably, it is possible to perform plating of Ni and Au on Cu.
Also, if the vertical cross section has the uneven surface structure, various types are considered as the structure of the lower electrode 4. Also, a plurality of thin film capacitors like that described above can be formed on a single wafer and can be separately used by performing dicing individually or for a desired group.
In the case of the structure of
In the case of the structure of
In the case of the structure of
In the case of the structure of
In the case of the structure of
In the case of the structure of
The structure illustrated in
Next, the material of each element described above will be described.
The lower electrode 4 includes Cu as a main component. Also, the lower electrode 4 is assumed to be Cu of 100 (atm %). The upper electrode 6 also includes Cu as the main component. These can also be constituted of the same material or different materials. In this example, these are assumed to have the same material and the same physical properties. The substrate 1 is made of Si and the stress adjustment layer 2 is made of silicon nitride.
In this case, the Young's modulus ESS of the substrate 1, the Young's modulus ESC of the stress adjustment layer 2, and the Young's modulus ELE of the lower electrode 4 satisfy the following relational expressions.
Relational expressions:
ELE<ESC
ESS<ESC
According to this thin film capacitor, the deformation of the lower electrode 4 is suppressed because the stress adjustment layer 2 is harder than the softest lower electrode 4 and the substrate 1 for supporting the lower electrode 4 (has a higher Young's modulus) among the above-described three elements, and the damage associated with the deformation of the dielectric thin film 5 adjacent to the lower electrode and the characteristic deterioration associated with the damage can be suppressed.
The dielectric thin film 5 is made of Al2O3, but another dielectric material (insulating material) can be used. The Young's modulus of Al2O3 is 370. Cu, Si, SiNx, and Al2O3 are arranged in ascending order of Young's modulus. When Young's modulus of the dielectric thin film is high and its damage is suppressed, the present invention is more effective. Characteristic data of each element is as shown in the chart of
Also, Cu is used as an electrode material, but a metal material illustrated in
Also, GaAs, SiC, Ge, or Ga can be used as a material constituting the substrate in addition to Si as illustrated in
As illustrated in
Also, it is preferable that a linear expansion coefficient αSS of the substrate 1, a linear expansion coefficient αSC of the stress adjustment layer 2, and a linear expansion coefficient αLE of the lower electrode 4 satisfy the following relational expressions.
Relational expressions:
αSC<αLE
αSC<αSS
In this case, because the linear expansion coefficient of the stress adjustment layer is small even when thermal expansion occurs in the substrate or the lower electrode, the deformation of the lower electrode due to a change in a temperature decreases due to the suppression of thermal expansion of the substrate or the lower electrode and the damage of the dielectric thin film adjacent to the substrate or the lower electrode and the characteristic deterioration associated with the damage can be suppressed.
In the third thin film capacitor as well, it is preferable that a heat conductivity λSS of the substrate, a heat conductivity λSC of the stress adjustment layer, and a heat conductivity λLE of the lower electrode satisfy the following relational expressions.
Relational expressions:
λSC<λSS
λSC<λLE
In this case, because the heat conductivity of the stress adjustment layer decreases even when the change in the temperature occurs in the substrate or the lower electrode, the deformation of the lower electrode decreases due to the suppression of the heat conduction of the substrate and the lower electrode and the suppression of the occurrence of linear expansion, and the damage of the dielectric thin film adjacent to the substrate and the lower electrode and the characteristic deterioration according to the damage can be suppressed. In particular, the effect tends to be large in terms of the fact that the change in the temperature in a substrate having a relatively large volume does not affect the lower electrode.
In
Also, the metal can be etched with a suitable acid. For example, a sulfuric acid or hydrogen peroxide etching solution is well known as an etchant for copper, and the metal can be etched by merely sputtering metal atoms with a rare gas as dry etching using plasma or the like, but techniques of etching the metal while utilizing the oxidation of copper by employing a hydrocarbon gas or a halogen gas or incorporating oxygen therein are also well known.
After this process, a side surface of the projecting portion 4b is exposed by removing the mask M including a resist using an organic solvent or the like (
When the etching is performed as described above, a part of the top surface exposed during etching is deformed so that the corner portion positioned in the outer edge of the top surface of the projecting portion is formed in an arc shape within the XZ plane. Of course, the top surface is deformed so that the corner portion is formed in an arc shape even in the YZ plane. Also, when the projecting portion 4b is viewed in a direction vertical to the XZ plane or the YZ plane, the degree of deformation of the corner portion is left-right symmetry. Although the centers of curvature of the arcs of the corner portions in
The conditions of parameters for one projecting portion 4b within the XZ plane are as follows. Also, the thickness of the dielectric thin film 5 (see
First, the radius R1 of curvature of the corner portion satisfies 0.4×td≦R1≦20×td. In this example, 56 nm≦R1≦2800 nm when the range is represented by an absolute value because the thickness td of the dielectric thin film 5=140 nm.
According to this thin film capacitor, the antenna effect increases, an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film occurs while an element is used when the radius R1 of curvature is less than 0.4 times the thickness td of the dielectric thin film. When the radius R1 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but malfunctions such as the stress applied in the in-plane direction of the dielectric thin film in the corner portion increasing and cracks tending to be introduced into the dielectric thin film or the concentration of an electric field due to a crystalline grain boundary tending to occur in the corner portion occur.
More preferably, the radius R1 of curvature of the corner portion satisfies 0.5×td≦R1≦10×td. When this range is represented by an absolute value, 70 nm≦R1≦140 nm is given. In this case, the internal defect of the dielectric thin film is suppressed more than in the case of the above-described range of R1 and malfunctions such as cracks tending to be introduced into a crystalline grain boundary of the dielectric thin film due to stress in the in-plane direction of the dielectric thin film in the corner portion or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion are also reduced.
Also, because the thickness td of the dielectric thin film is constant, a downward projecting portion of the upper electrode 6 is formed along a shape of a recess portion between projecting portions 4b of the lower electrode and a recess portion recessed upward between the projecting portions 6b of the upper electrode is formed along a shape of the projecting portion 4b of the lower electrode (see
Next, a height H (4b) from the bottom surface of the recess portion adjacent to the projecting portion 4b and a height (thickness) H (4a) of the common electrode part 4a are included as parameters. As an example, H (4b)=8 μm is set and H (4a)=2 μm is set. A width within the XZ plane of the projecting portion 4b is W (4b) and the projecting portion 4b more projects to have a shape similar to an extended finger when an aspect ratio AR=H (4b)/W (4b) in the XZ plane of the projecting portion 4b more increases. A preferable range of the aspect ratio AR=H (4b)/W (4b) becomes 0.3≦AR≦10. This is because the stress applied in the in-plane direction of the dielectric thin film in the top portion of the projecting portion 4b occurs, cracks tend to be introduced into the dielectric thin film, and the concentration of the electric field due to the crystalline grain boundary of the electrode in the top portion occurs when the AR is less than a lower limit and because the projecting portion 4b serves as the antenna, the concentration of the electric field occurs in the top portion of the projecting portion 4b, and the destruction of the dielectric thin film may occur due to the material of the dielectric thin film when the AR exceeds an upper limit.
Although the corner portion of the proximal end of the projecting portion 4b within the XZ plane is not smooth and is discontinuously bent, a method of smoothly rounding the corner portion can be adopted.
In
Next, a side surface of the projecting portion 4b is exposed by removing the mask M including a resist using an organic solvent or the like (
Thereafter, a process of rounding corner portions for all exposed surfaces of the projecting portion 4b is performed. For example, a method (a sputtering method and a milling method) of rounding the corner portion of an outer edge of the top surface or the corner portion of the proximal end by causing a rare gas such as Ar to collide with the top surface, a method of rounding the corner portions of the surfaces by performing dry etching or wet etching on the corner portions, or the like is used. That is, the contour in the XZ section of the top surface has a shape in which a convex arc is formed at the top by removing a peripheral part of the projecting portion top surface more than a center part (
Also, the metal can be etched with a suitable acid. For example, a sulfuric acid or hydrogen peroxide etching solution is well known as an etchant for copper, and the metal can be etched by merely sputtering metal atoms with a rare gas as dry etching using plasma or the like, but techniques of etching the metal while utilizing the oxidation of copper by employing a hydrocarbon gas or a halogen gas or incorporating oxygen therein are also well known.
Also, before and/or after the process of
The projecting portion of
The conditions of parameters for the proximal end of one projecting portion 4b within the XZ plane are as follows.
First, the radius R2 of curvature of the corner portion of the left/right of the proximal end of the projecting portion 4b (radii of curvature in bottom portions of the recess portion positioned at both sides of the recess portion 4b) satisfies 0.4×td≦R2≦20×td. In this example, 56 nm≦R2≦2800 nm when the range is represented by an absolute value because the thickness td of the dielectric thin film 5=140 nm.
According to this thin film capacitor, the antenna effect increases and an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film in the vicinity of the proximal end occurs while an element is used when the radius R2 of curvature is less than 0.4 times the thickness td of the dielectric thin film. When the radius R2 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but malfunctions such as the stress applied in the in-plane direction of the dielectric thin film in the corner portion increasing and cracks tending to be introduced into the dielectric thin film or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion occur.
More preferably, the radius R2 of curvature of the corner portion satisfies 0.5×td≦R2≦10×td. When this range is represented by an absolute value, 70 nm≦R2≦140 nm is given. In this case, the internal defect of the dielectric thin film is suppressed more than in the case of the above-described range of R2 and malfunctions such as cracks tending to be introduced into the dielectric thin film due to stress in the in-plane direction of the dielectric thin film in the corner portion or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion are also reduced.
Also, because the thickness td of the dielectric thin film is constant, a downward projecting portion of the upper electrode 6 is formed along a shape of a recess portion between projecting portions 4b of the lower electrode and a recess portion recessed upward between the projecting portions 6b of the upper electrode is formed along a shape of the projecting portion 4b of the lower electrode (see
The section (YZ section) of
In etching in
The conditions of parameters for the proximal end of one projecting portion 4b within the XZ plane are as follows.
First, the radius R3 of curvature of the corner portion of the left/right of the distal end of the projecting portion 4b satisfies 0.4×td≦R3≦20×td. In this example, 56 nm≦R3≦2800 nm when the range is represented by an absolute value because the thickness td of the dielectric thin film 5=140 nm.
According to this thin film capacitor, the antenna effect increases and an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film occurs while an element is used when the radius R3 of curvature is less than 0.4 times the thickness td of the dielectric thin film. When the radius R3 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but malfunctions such as the stress applied in the in-plane direction of the dielectric thin film in the corner portion increasing and cracks tending to be introduced into the dielectric thin film or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion occur.
More preferably, the radius R3 of curvature of the corner portion satisfies 0.5×td≦R3≦10×td. When this range is represented by an absolute value, 70 nm≦R3≦140 nm is given. In this case, the internal defect of the dielectric thin film is suppressed more than in the case of the above-described range of R3 and malfunctions such as cracks tending to be introduced into the dielectric thin film due to stress in the in-plane direction of the dielectric thin film in the corner portion or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion are also reduced.
First, the radius R4 of curvature of the corner portion of the left/right of the proximal end of the projecting portion 4b satisfies 0.4×td≦R4≦20×td. In this example, 56 nm≦R4≦2800 nm when the range is represented by an absolute value because the thickness td of the dielectric thin film 5=140 nm.
According to this thin film capacitor, the antenna effect increases, an electric field is concentrated on the dielectric thin film, and an internal defect of the dielectric thin film in the vicinity of the proximal end occurs while an element is used when the radius R4 of curvature is less than 0.4 times the thickness td of the dielectric thin film. When the radius R4 of curvature is greater than 20 times the thickness td of the dielectric thin film, the antenna effect is degraded, but malfunctions such as the stress applied in the in-plane direction of the dielectric thin film in the corner portion increasing and cracks tending to be introduced into the dielectric thin film or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion occur.
More preferably, the radius R4 of curvature of the corner portion satisfies 0.5×td≦R4≦10×td. When this range is represented by an absolute value, 70 nm≦R4≦140 nm is given. In this case, the internal defect of the dielectric thin film is suppressed more than in the case of the above-described range of R4 and malfunctions such as cracks tending to be introduced into the dielectric thin film due to stress in the in-plane direction of the dielectric thin film in the corner portion or the concentration of an electric field due to a crystalline grain boundary of the electrode tending to occur in the corner portion are also reduced.
Also, the length of the projecting portion 4b in the Y-axis direction in the YZ plane is set to L (4b). An aspect ratio AR′=H (4b)/L (4b) in the YZ plane of the projecting portion 4b is not particularly limited. However, the capacitance per unit area increases if a height H (4b) increases and the mechanical strength of the Y-axis direction increases as the length L (4b) increases. Also, a plurality of projecting portions 4b can be arranged on dots in the Y-axis direction. In this case, the length L (4b) decreases, and the capacitance per unit area increases.
Embodiments 1 to 22 and comparative examples 1 to 4 are shown. TYPE 1 indicates the case in which a position at which the corner portion is rounded is only a distal end as illustrated in
The common electrode part 4a and the projecting portion 4b are made of Cu and grown by a plating method. In this etching, using a 5 wt % aqueous solution of ferric chloride and using alumina formed by an ALD method as the dielectric thin film 5, an upper electrode made of Cu was formed thereon by a sputtering method.
Also, H (4a)=2 μm, H (4b)=8 μm, W (4b)=4 μm, L (4b)=112 μm, and td=140 nm.
The plurality of thin film capacitors described above were formed within a single chip and the tolerance of each capacitor was measured. A Y-axis direction length (width) of the manufactured thin film capacitor is 0.1 mm and an X-axis direction length (length) is 0.4 mm. 1000 samples of each example were formed on the same Si wafer. The thickness of the wafer (substrate) is 2 mm, the thickness of the stress adjustment layer is 1 μm, and a material of the dielectric thin film sandwiched between the upper electrode and the lower electrode is Al2O3 manufactured by an ALD method and has a thickness of 140 nm (1400 Å). Materials of the upper electrode and the lower electrode are the same, the thicknesses of the common electrode parts thereof are the same (2 μm), the pitch of the uneven surface structure is 4 μm, the height H of the projecting portion in each uneven surface structure is 8 μm, the material of the protective film configured to cover the upper electrode is polyimide, and the plating of Ni and Au is performed on Cu for the connection electrode passing through the inside of the protective film, a contact electrode positioned at a termination end of the connection electrode, or the under bump metal. These electrodes were prepared using a plating method.
1000 samples were prepared for each experiment example and a voltage of 30 V was continuously applied between the upper and lower electrodes under an environment of 85% humidity and a temperature of 85° C. After the environmental test for 24 hours, a sample having an insulation resistance of 1011Ω or more was designated as a normal product and a sample having an insulation resistance of less than 1011Ω was designated as a defective product.
Etching was performed so that the radii R1, R2, R3, and R4 of curvature of the examples were substantially the same. A 5 wt % aqueous solution of ferric chloride was used and an etching time was 45 sec to 100 sec. An etching rate of a thickness direction of the substrate can be controlled by means of a temperature of an etching agent, the adjustment of an etching time, a pressure by ultrasonic waves, or the like, and an etching rate of a direction vertical to the thickness direction can be controlled by the adjustment of an aqueous solution concentration of an etching agent. In embodiments 1 to 22 including TYPE 1 and TYPE 2, at least the radii R1 and R3 of curvature of corner portions of the distal end satisfy 0.4×td≦R1≦20×td and 0.4×td≦R3≦20×td. In this case, a result indicated that the number of normal products among 1000 samples was 619 to 978. In the cases of comparative examples 1 to 4, the number of normal products was less than or equal to 500 after 24 hours. Therefore, it can be seen that the embodiment is superior to the comparative example.
Also, TYPE 1 is embodiments 1, 2, 5, 7, 9, 11, 13, 15, 20, 21, and 22 and TYPE 2 is embodiments 3, 4, 6, 8, 10, 12, 14, 16, 17, 18, and 19. Comparative examples 1 to 5 were set as TYPE 1.
In the case of TYPE 2 (embodiments 3, 4, 6, 8, 10, 12, 14, 16, 17, and 18), a ratio of normal products increases more than in thin film capacitors of TYPE 1 (embodiments 1, 2, 5, 7, 9, 11, 13, 15, 20, 21, and 22) having the same radius of curvature. Therefore, it can be seen that TYPE 2 is superior to TYPE 1.
In the case of embodiments 5 to 16 (0.5×td≦radius of curvature≦10×td), the number of normal products is 760 to 945. In this case, the number of normal products is greater than the number of normal products (619 to 756) in the cases of embodiments 1 to 4 and embodiments 17 to 22 (0.4×td≦radius of curvature≦0.45×td and 12.1×td≦radius of curvature≦20.6×td). Therefore, it is further preferable that the radius of curvature be (0.5×td≦radius of curvature≦10×td).
As described above, it is possible to increase capacitance because the thin film capacitor having an uneven surface structure is a structure in which an area opposite to the electrode in a unit volume increases. On the other hand, because the electrode is subdivided, the strength is degraded, a mechanical force generated by a temperature increase during mounting or an environment during actual use is transferred to a dielectric layer and the dielectric layer may be destroyed. In this embodiment, this destruction is suppressed. A lower electrode in which the shape of the vertical cross section is a comb tooth or slit shape or a lower electrode in which the shape of the vertical cross section is a shape including a pin or hole can be used as the uneven surface structure of the lower electrode, and the structures of the lower electrode and the upper electrode can also be replaced with each other.
As described above, it is possible to suppress stress accumulation for the dielectric thin film and suppress the characteristic deterioration by satisfying the above-described predetermined conditions.
Next, an overview of a third type of invention will be described.
In the third type of invention, a thin film capacitor of a first aspect is a thin film capacitor including: a substrate; an insulating layer formed on a main surface of the substrate; a lower electrode formed on the insulating layer; a dielectric thin film configured to cover the lower electrode; an upper electrode formed on the dielectric thin film; a first terminal provided in the lower electrode; and a second terminal provided in the upper electrode, wherein, when an XYZ three-dimensional coordinate system is set, the main surface is an XY plane, and a direction in which the first terminal and the second terminal are connected is designated as an X-axis, the lower electrode has an uneven surface structure and a longitudinal direction of a top surface of the projecting portion of the uneven surface structure is in the X-axis direction.
According to this thin film capacitor, it is possible to increase the capacitance per unit area because the lower electrode has an uneven surface structure. When a bias voltage is applied between a first terminal and a second terminal, charge is accumulated in the thin film capacitor. When the applied voltage is an alternating current voltage, an alternating current flows between the terminals. Here, equivalent series resistance (ESR) of the thin film capacitor is considered. Also, the ESR is given as the square root of Z2−X2 when impedance Z and equivalent reactance X are used.
The ESR increases when a resistance length is long and decreases when the resistance length is short. However, when the ESR increases, the loss of power based on resistance occurs and a circuit operation may be unstable. Therefore, it is preferable to decrease the ESR. When the ESR is low, a Q value of the thin film capacitor becomes high.
In this thin film capacitor, the longitudinal direction of the top surface of the projecting portion of the uneven surface structure is in the X-axis direction (a direction in which the terminals are connected). This structure has lower ESR than when the longitudinal direction of the top surface extends along the Y axis. Therefore, according to the thin film capacitor, the ESR becomes low, the loss can be reduced, and the operation can be stable.
In a second thin film capacitor, the width of the projecting portion of the lower electrode in a Y-axis direction narrows from a proximal end to a distal end.
In this case, the impedance decreases and the ESR also decreases. The cause of this is not always clear, but the mutual inductance within the above-described lower electrode is considered to decrease. A structure in which the longitudinal direction of the top surface extends along the X axis is equivalent to a structure in which a plurality of signal lines are placed in parallel. Also, a high-frequency signal applied to the above-described lower electrode of the thin film capacitor of the present invention tends to be concentrated on each top surface edge of the projecting portion. Thus, the mutual inductance occurs between signals concentrated on each top surface edge in the above-described lower electrode. According to a structure in which a width in the Y-axis direction is narrowed from the proximal end to the distal end, a top surface edge interval between one projecting portion and another projecting portion is widened. Simultaneously, the angle of the top surface edge becomes gentle and the concentration of a signal is mitigated. Thus, the mutual inductance occurring between a plurality of projecting portions of the lower electrode decreases. Therefore, the loss can be further reduced and the operation can be stable.
In a third thin film capacitor, when a ratio between a Y-axis direction width W1 of the proximal end of the projecting portion of the lower electrode and a Y-axis direction width W2 of the distal end of the projecting portion of the lower electrode is RW=W1/W2, the ratio RW satisfies the relational expression 1.2≦RW≦1.9.
When RW is less than 1.2, the impedance increases, the current of an electrode surface is unlikely to flow, and there is room for improvement in the reduction of the ESR because the concentration of the high-frequency signal in the top surface edge portion of the above-described projecting portion is excessively large and it is difficult to decrease the mutual impedance between projecting portions of the lower electrode. When RW is greater than 1.9, the concentration of the signal is mitigated in the projecting portion, but signal propagation from one projecting portion to another projecting portion tends to occur. Because impedance occurs due to this signal propagation in a horizontal direction, there is also room for improvement in the reduction of the ESR.
According to the thin film capacitor of the present invention, it is possible to decrease loss and increase stability.
Hereinafter, the thin film capacitor according to the embodiment related to the third type of invention will be described. Also, the same reference signs are assigned to the same elements and redundant description thereof will be omitted. Also, an XYZ three-dimensional orthogonal coordinate system is set and the thickness direction of the substrate is assumed to be the Z-axis direction.
This thin film capacitor includes a substrate 1, an insulating layer 2 (stress adjustment layer 2) formed on a main surface (XY plane) of the substrate 1, a lower electrode 4 formed on the stress adjustment layer 2 via a base layer 3, a dielectric thin film 5 configured to cover the lower electrode 4, and an upper electrode 6 formed on the dielectric thin film 5.
A main part of the thin film capacitor is constituted of the lower electrode 4, the upper electrode 6, and the dielectric thin film 5 positioned between the lower electrode 4 and the upper electrode 6.
The lower electrode 4 includes the common electrode part 4a extending in parallel to the main surface of the substrate 1 and a plurality of projecting portions 4b extending to project from the common electrode part 4a away from the substrate 1. Also, the longitudinal direction of the top surface of the projecting portion 4b of the uneven surface structure is in the X-axis direction and the uneven surface structure is observed within the YZ section as illustrated in
The lower electrode 4 has an uneven surface structure of a vertical cross section (YZ plane) in the thickness direction of the substrate 1 and has a comb tooth shape as illustrated in
This thin film capacitor includes a protective film 7 configured to cover the upper electrode 6, a dummy electrode 4D formed on the stress adjustment layer 2, and a lower contact electrode 6D formed on the common electrode part 4a of the lower electrode 4 and in contact with the common electrode part 4a. The dummy electrode 4D is formed simultaneously with the common electrode part 4a of the lower electrode and the lower contact electrode 6D is formed simultaneously with the upper electrode 6.
On the left in
Also, the second terminal 8a is positioned within a first contact hole Ha provided in the protective film 7 and the first terminal 8b is positioned within a second contact hole Hb provided in the protective film 7.
In the case of this structure, because the dummy electrode 4D has the same thickness as the common electrode part 4a of the lower electrode 4, heights of the second terminal 8a and the first terminal 8b in the thickness direction can be approximately the same and a thin film capacitor of a flat structure can be formed.
A contact electrode and/or an under bump metal 9a are in contact with the second terminal 8a and are positioned on the second terminal 8a. A contact electrode and/or an under bump metal 9b are in contact with the first terminal 8b and are positioned on the first terminal 8b. Bumps 10a and 10b are arranged on the under bump metals 9a and 9b, respectively.
First, as in
Next, as in
Thereafter, as in
Next, as in
Next, as in
Next, as in
Next, as in
Thereafter, as in
Next, as in
The under bump metal 9a and the under bump metal 9b serving as conductive pads are provided on the second terminal 8a and the first terminal 8b. These can function as contact electrodes and the under bump metal can be further provided on the contact electrode using a different material. Bumps 10a and 10b are arranged on the under bump metals 9a and 9b, respectively. Cu, Ni, and Au can be used as materials of the under bump metal or the contact electrode. These can be stacked or mixed for use for each material. Preferably, it is possible to perform plating of Ni and Au on Cu.
Also, if the vertical cross section has the uneven surface structure, various types are considered as the structure of the lower electrode 4. Also, a plurality of thin film capacitors like that described above can be formed on a single wafer and can be separately used by performing dicing individually or for a desired group.
In the case of the structure of
In the case of the structure of
The case of the structure of
In the case of the structure of
In the case of the structure of
The case of the structure of
The structure illustrated in
Next, the material of each element described above will be described.
The lower electrode 4 includes Cu as a main component. Also, the lower electrode 4 is assumed to be Cu of 100 (atm %). The upper electrode 6 also includes Cu as the main component. These can also be constituted of the same material or different materials. In this example, these are assumed to have the same material and the same physical properties. The substrate 1 is made of Si and the stress adjustment layer 2 is made of silicon nitride.
In this case, the Young's modulus ESS of the substrate 1, the Young's modulus ESC of the stress adjustment layer 2, and the Young's modulus ELE of the lower electrode 4 satisfy the following relational expressions.
Relational expressions:
ELE<ESC
ESS<ESC
According to this thin film capacitor, the deformation of the lower electrode 4 is suppressed because the stress adjustment layer 2 is harder than the softest lower electrode 4 and the substrate 1 for supporting the lower electrode 4 (has a higher Young's modulus) among the above-described three elements, and the damage associated with the deformation of the dielectric thin film 5 adjacent to the lower electrode and the characteristic deterioration associated with the damage can be suppressed.
The dielectric thin film 5 is made of Al2O3, but another dielectric material (insulating material) can be used. The Young's modulus of Al2O3 is 370. Cu, Si, SiNx, and Al2O3 are arranged in ascending order of Young's modulus. When the Young's modulus of the dielectric thin film is high and its damage is suppressed, the present invention is more effective. Characteristic data of each element is as shown in the chart of
Also, Cu is used as an electrode material, but a metal material illustrated in
Also, GaAs, SiC, Ge, or Ga can be used as a material constituting the substrate in addition to Si as illustrated in
As illustrated in
Also, a linear expansion coefficient αSS of the substrate 1, a linear expansion coefficient αSC of the stress adjustment layer 2, and a linear expansion coefficient αLE of the lower electrode 4 satisfy the following relational expressions.
Relational expressions:
αSC<αLE
αSC<αSS
In this case, because the linear expansion coefficient of the stress adjustment layer is small even when thermal expansion occurs in the substrate or the lower electrode, the deformation of the lower electrode due to a change in a temperature decreases due to the suppression of thermal expansion of the substrate or the lower electrode, the damage of the dielectric thin film adjacent to the substrate or the lower electrode, and the characteristic deterioration associated with the damage can be suppressed.
In the third thin film capacitor as well, it is preferable that a heat conductivity λSS of the substrate, a heat conductivity λSC of the stress adjustment layer, and a heat conductivity λLE of the lower electrode satisfy the following relational expressions.
Relational expressions:
λSC<λSS
λSC<λLE
In this case, because the heat conductivity of the stress adjustment layer is small even when the change in the temperature occurs in the substrate or the lower electrode, the deformation of the lower electrode due to the change in the temperature decreases due to the suppression of the heat conduction of the substrate and the lower electrode and the suppression of the occurrence of linear expansion and the damage of the dielectric thin film adjacent to the substrate and the lower electrode and the characteristic deterioration according to the damage can be suppressed. In particular, the effect tends to be large in terms of the fact that the change in the temperature in a substrate having a relatively large volume does not affect the lower electrode.
The thin film capacitor is different from the thin film capacitors illustrated in
Also, a structure obtained by improving a shape of a projecting portion was also considered in addition to the comparative examples.
In the projecting portion 4b of the lower electrode, the width in the Y-axis direction is narrowed in the direction (+Z axis direction) from the proximal end to the distal end. In this case, because it is possible to decrease mutual impedance occurring between a plurality of projecting portions of the lower electrode, the impedance decreases and the ESR also decreases. Therefore, the loss can be further reduced and the operation can be stable.
Also, when a ratio between a Y-axis direction width W1 of the proximal end of the projecting portion 4b of the lower electrode and a Y-axis direction width W2 of the distal end of the projecting portion 4b of the lower electrode is RW=W1/W2, the ratio RW satisfies the following relational expression.
1.2≦RW≦1.9
Also, when the corner portion of the projecting portion has the radius of curvature, the median of its arc is set as a reference position when the width W1 or W2 is defined. When RW is less than 1.2, the impedance increases, the current of an electrode surface is unlikely to flow, and there is room for improvement in the reduction of the ESR because the concentration of the high-frequency signal in the top surface edge portion of the above-described projecting portion is excessively large and it is difficult to decrease the mutual impedance between projecting portions of the lower electrode. When RW is greater than 1.9, a signal component tends to move between projecting portions of the lower electrode as in a planar thin film capacitor. Because impedance occurs due to this signal propagation in a horizontal direction, the ESR also decreases.
When a tapered shape is formed, the projecting portion 4b of the lower electrode is processed in
Next, a side surface of the projecting portion 4b is exposed by removing the mask including a resist using organic solvent or the like.
Thereafter, a process of etching all exposed surfaces of the projecting portion 4b is performed. For example, a tapered shape can be formed using a method (a sputtering method and a milling method) of rounding the corner portion of an outer edge of the top surface or the corner portion of the proximal end by causing a rare gas such as Ar to collide with the top surface or by performing dry etching or wet etching thereon.
Also, the metal can be etched with a suitable acid. For example, a sulfuric acid or hydrogen peroxide etching solution is well known as an etchant for copper, and the metal can be etched by merely sputtering metal atoms with a rare gas as dry etching using plasma or the like, but techniques of etching the metal while utilizing the oxidation of copper by employing a hydrocarbon gas or a halogen gas or incorporating oxygen therein are also well known.
Hereinafter, experiment examples (an embodiment and a comparative example) in the third type of invention will be described. The following experiments were performed.
The common electrode part 4a and the projecting portion 4b are made of Cu and grown by a plating method. In this etching, using a 5 wt % aqueous solution of ferric chloride and using alumina formed by an ALD method as the dielectric thin film 5 having a thickness of 140 nm, an upper electrode made of Cu was formed thereon by a sputtering method. Also, the thickness of the common electrode part 4a was set to 2 μm and the height of the projecting portion 4b was set to 8 μm. The pitch of the Y-axis direction of the uneven surface structure is 4 μm, the material of the protective film configured to cover the upper electrode is polyimide, and the plating of Ni and Au is performed on Cu for the connection electrode passing through the inside of the protective film, a contact electrode positioned at a termination end of the connection electrode, or the under bump metal. These electrodes were prepared using a plating method. The Y-axis direction length (width) of the manufactured thin film capacitor is 0.1 mm and the X-axis direction length (length) is 0.4 mm. Also, lengths between both ends in the X-axis direction of both the projecting portion 4b and the projecting portion 6b are 210 μm regardless of the presence/absence of separation.
Also, a process of tapering the projecting portion 4b was performed using a composite processing method of immersion into a 0.5 wt % aqueous solution of ferric chloride after Ar ion etching.
The thin film capacitor illustrated in
The thin film capacitor illustrated in
The thin film capacitor illustrated in
The thin film capacitor illustrated in
The thin film capacitor illustrated in
The thin film capacitor illustrated in
The thin film capacitor illustrated in
Embodiment 1: Q value=1050 (center separation type of projecting portion: RW=1)
Embodiment 2: Q value=1220 (continuation type of projecting portion: RW=1)
Embodiment 3: Q value=1450 (tapered shape of projecting portion: RW=1.5)
Embodiment 4: Q value=1370 (tapered shape of projecting portion: RW=1.2)
Embodiment 5: Q value=1320 (tapered shape of projecting portion: RW=1.9)
Embodiment 6: Q value=1255 (tapered shape of projecting portion: RW=1.05)
Embodiment 7: Q value=1230 (tapered shape of projecting portion: RW=2.2)
Comparative Example 1: Q value=164 (RW=1 in the type of
Also, the Q value was measured at 100 MHz. The Q value increases as the ESR decreases and is excellent from a point of view of loss and stability.
Embodiments 1 to 7 have higher Q values than comparative example 1, and embodiment 2 having a continuous projecting portion has a higher Q value than embodiment 1 having a separated projecting portion. Further, embodiments 3 to 7 having a tapered shape have higher Q values than embodiment 1 and embodiment 2. Further, embodiments 3 to 5 in which the ratio RW of the tapered shape is greater than or equal to 1.2 and less than or equal to 1.9 have higher Q values than embodiments 6 and 7 outside of this range.
As described above, the above-described thin film capacitor includes: a substrate 1; a stress adjustment layer 2 (insulating layer) formed on a main surface of the substrate 1; a lower electrode 4 formed on the stress adjustment layer 2; a dielectric thin film 5 configured to cover the lower electrode 4; an upper electrode 6 formed on the dielectric thin film 5; a first terminal 8b provided in the lower electrode 4; and a second terminal 8a provided in the upper electrode 6, wherein, when an XYZ three-dimensional coordinate system is set, the main surface of the substrate is an XY plane, and a direction in which the first terminal 8b and the second terminal 8a are connected is designated as an X-axis, the lower electrode 4 has an uneven surface structure and a longitudinal direction of a top surface of the projecting portion 4b of the uneven surface structure is in the X-axis direction.
According to this thin film capacitor, it is possible to increase the capacitance per unit area because the lower electrode has an uneven surface structure. When a bias voltage is applied between the first terminal 8b and the second terminal 8a, charge is accumulated in the thin film capacitor. When the applied voltage is an alternating current voltage, an alternating current flows between the terminals. When the ESR increases, the loss of power based on resistance may occur and the circuit operation may be unstable. Therefore, it is preferable to decrease the ESR. When the ESR decreases, the Q value of the thin film capacitor becomes high.
In this thin film capacitor, the longitudinal direction of the top surface of the projecting portion of the uneven surface structure is in the X-axis direction (a direction connected between the terminals). This structure has lower ESR than when the longitudinal direction of the top surface extends along the Y axis. Therefore, according to the thin film capacitor, the ESR becomes low, the loss can be reduced, and the operation can be stable.
Also, when the width in the Y-axis direction is narrowed in a direction from the proximal end to the distal end in the projecting portion of the lower electrode, the improvement of the Q value (decrease of ESR) is observed. In particular, when the tapering ratio satisfies 1.2≦RW≦1.9, this improvement effect is significant.
As described above, it is possible to increase capacitance because the thin film capacitor having an uneven surface structure is a structure in which an area opposite to the electrode in a unit volume increases. On the other hand, because the electrode is subdivided, the strength is degraded, a mechanical force generated by a temperature increase during mounting or an environment during actual use is transferred to a dielectric layer and the dielectric layer may be destroyed. In this embodiment, this destruction is suppressed. A lower electrode in which the shape of the vertical cross section is a comb tooth or slit shape or a lower electrode in which the shape of the vertical cross section is a shape including a pin or hole can be used as the uneven surface structure of the lower electrode, and the structures of the lower electrode and the upper electrode can also be replaced with each other.
As described above, it is possible to suppress stress accumulation for the dielectric thin film and suppress the characteristic deterioration by satisfying the above-described predetermined conditions. Also, it is possible to provide a thin film capacitor having small loss and high stability.
As described above, the lower electrode 4 can have various types of uneven surface structures. The upper electrode 6 can also have various types of uneven surface structures. A projecting portion projecting to the lower electrode side of the upper electrode 6 can be positioned in the gap between projecting portions of the lower electrode 4. The lower electrode 4 contains Cu as the main component. The Young's moduli of the substrate 1, the stress adjustment layer 2, and the lower electrode 4 have a specific relation. In addition, corner portions of the radii R1 of curvature positioned inside the projecting portion 4b have a specific relation. Any elements described above can be used in combination and it is possible to suppress the decrease of mechanical strength, the occurrence of loss, and/or instability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-073872 | Mar 2015 | JP | national |
| 2015-073886 | Mar 2015 | JP | national |
| 2015-073957 | Mar 2015 | JP | national |
