JP2006210589A - Thin film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film capacitor having a low parasitic resistance due to a lower electrode layer.
A lower electrode layer 22 formed on a support substrate 21, a dielectric layer 23 formed on the lower electrode layer 22, an upper electrode layer 24 formed on the dielectric layer 23, and a lower electrode A lower electrode layer 22 having a lower resistance than that of the lower electrode layer 22 connected to the layer 22, and the lower electrode layer 22 is thicker on the formation region side of the dielectric layer 23 and thinner on the outer side. The lead electrode 27b is a thin film capacitor connected in contact with the vertical surface of the stepped portion. Since the current path through the high-resistance lower electrode layer 22 can be made shorter than that of the conventional structure, a thin film capacitor having a small parasitic resistance and excellent electrical characteristics as a capacitor can be provided.
[Selection] Figure 1

Description

  The present invention relates to a thin film capacitor in which a dielectric layer is sandwiched between a lower electrode layer and an upper electrode layer, and more particularly to a thin film capacitor with reduced parasitic resistance.

  A thin film capacitor is known in which a lower electrode layer, a dielectric layer, and an upper electrode layer are sequentially formed on a support substrate, and the dielectric layer is sandwiched between the lower electrode layer and the upper electrode layer. In order to connect this thin film capacitor to an external circuit, a lower electrode layer and a lead electrode connected to the upper electrode layer are required (see, for example, Patent Document 1). A thin film capacitor having such a conventional lead electrode will be described.

  FIG. 8 is a cross-sectional view of an essential part showing an example of a conventional thin film capacitor having an extraction electrode. In the thin film capacitor shown in FIG. 8, a capacitor element is formed by sequentially laminating a lower electrode layer 2, a dielectric layer 3, and an upper electrode layer 4 on a support substrate 1, and a protective film 5 covering the capacitor element. Is formed. In this capacitive element, the lower electrode layer 2 is formed larger than the dielectric layer 3 and the upper electrode layer 4. An opening 6 a reaching the upper electrode layer 4 and a dielectric layer of the lower electrode layer 2 are formed in the protective film 5. 3 and an opening 6b reaching a region where the upper electrode layer 4 is absent. An extraction electrode 7a connected to the upper electrode layer 4 through the opening 6a and an extraction electrode 7b connected to the lower electrode layer 2 through the opening 6b are formed.

  According to such a configuration, since the surface where the lower electrode layer 2 and the extraction electrode 7b are in contact with the surface where the lower electrode layer 2 and the dielectric layer 3 are in contact with each other, the capacitance element The path of current flowing from the dielectric layer 3 through the lower electrode layer 2 to the extraction electrode 7b is, for example, paths f1 to f3 indicated by dashed arrows in FIG.

  Here, when the lower electrode layer 2 is formed of a material having a specific resistance larger than that of the extraction electrode 7b, the electric resistance of the path f1 having the shortest distance passing through the lower electrode layer 2 is minimized. Accordingly, it can be said that the path f1 is the path through which current flows most easily. However, it is impossible in principle that all of the current selectively flows only through the path f1, and actually, for example, the path f2 and the path f3 also pass.

  Therefore, as shown in FIG. 9 which is a cross-sectional view of the main part similar to FIG. 8, a general current path is divided into three parts of paths A1, B1, and C1, and defined as follows.

Path A1; a path from the surface where the dielectric layer 3 and the lower electrode layer 2 are in contact to a region included in the lower electrode layer 2 immediately below the extraction electrode 7b.

Path B1; a path from the region included in the lower electrode layer 2 directly below the extraction electrode 7b to the surface where the extraction electrode 7b and the lower electrode layer 2 are in contact with each other.

Path C1: A path from the contact surface between the extraction electrode 7b and the lower electrode layer 2 to the external circuit through the extraction electrode 7b.

The electrical resistances of the paths A1, B1, and C1 defined as described above are expressed as follows.
(A + b) × resistivity of lower electrode layer 2 / ΔS + c × resistivity of extraction electrode 7b / ΔS
It is expressed as Here, a, b, and c represent the lengths of the paths A1, B1, and C1, respectively.

  By the way, in order to obtain a large capacity with a small area in such a thin film capacitor, a crystalline dielectric material having a high dielectric constant in the dielectric layer 3, particularly strontium titanate, barium titanate, barium strontium titanate, titanate. It is generally known that a perovskite oxide dielectric material such as lead may be used.

  However, these high dielectric materials do not exhibit excellent dielectric properties unless the crystallinity is good. The crystallinity of the dielectric layer 3 is greatly influenced by the crystal lattice constant, crystal orientation, and the like of the material constituting the support substrate 1 and the lower electrode layer 2 existing below the dielectric layer 3. Among these, the lower electrode layer 2 located immediately below the dielectric layer 3 is particularly important. That is, the lower electrode layer 2 is required to have good lattice matching with the dielectric layer 3 and good surface morphology. Further, since the high dielectric film as described above is generally formed in a high temperature atmosphere, excellent heat resistance that can withstand this high temperature is also required.

  As a material satisfying these conditions, platinum, an oxide conductor, or the like is generally used as a material for forming the lower electrode layer 2. However, these are excellent in lattice matching with the dielectric layer 3 and heat resistance, but have a higher electric resistance than gold, copper, aluminum, etc., which are used as general electrode materials. It is unsuitable. However, in view of the crystallinity of the dielectric layer 3 as described above, it is necessary to use these materials even if the resistance is high.

As described above, in the conventional thin film capacitor, the lower electrode layer 2 having such a high specific resistance is used in the structure as shown in FIG.
Japanese Patent No. 3246274

  By the way, the resistance component parasitic on the thin film capacitor deteriorates the electrical characteristics of the capacitor. Therefore, the structure of the capacitive element is required to have a parasitic resistance as small as possible. Therefore, in a thin film capacitor using a material having a high specific resistance for the lower electrode layer 2, the length of the current path through the lower electrode layer 2 must be as short as possible.

  However, in the conventional thin film capacitor, as shown in FIG. 2, the current passes through the high resistance lower electrode layer 2 through a path having a length obtained by adding the distance between the path A1 and the path B1. However, the capacitance element has not been devised to reduce the parasitic resistance, and there has been a problem that the electrical characteristics as a capacitor such as a decrease in the Q value are deteriorated by the parasitic resistance.

  In addition, in a thin film capacitor configured by electrically connecting such conventional thin film capacitors in series for improving withstand voltage and the like, parasitic resistance is added as much as the capacitive elements are connected in series. There is a problem that the influence of the parasitic resistance due to the lower electrode layer 2 becomes more remarkable.

  The present invention has been made in view of such problems in the prior art, and an object of the present invention is to provide a thin film capacitor having a small parasitic resistance due to a lower electrode layer and excellent electrical characteristics as a capacitor. is there.

  The thin film capacitor of the present invention includes a lower electrode layer formed on a support substrate, a dielectric layer formed on the lower electrode layer, an upper electrode layer formed on the dielectric layer, and the lower electrode And a lower electrode layer having a lower resistance than the lower electrode layer connected to the lower electrode layer. The lower electrode layer has a stepped portion that is thicker on the dielectric layer forming region side and thinner on the outer side. And the extraction electrode is connected in contact with a vertical surface of the stepped portion.

  Further, the thin film capacitor of the present invention is characterized in that two or more thin film capacitors having the above-described configuration are connected in series.

  According to the thin film capacitor of the present invention, the lower electrode layer formed on the support substrate, the dielectric layer formed on the lower electrode layer, the upper electrode layer formed on the dielectric layer, The lower electrode layer is connected to the electrode layer and has a lower resistance than the lower electrode layer. The lower electrode layer has a stepped portion that is thick on the dielectric layer forming region side and thin on the outside. Since the extraction electrode is connected in contact with the vertical surface of the step portion of the lower electrode layer, the current path through the high resistance lower electrode layer should be shorter than that of the conventional structure. Therefore, a thin film capacitor with low parasitic resistance and excellent electrical characteristics as a capacitor can be provided.

  Further, according to the thin film capacitor of the present invention, since two or more thin film capacitors having the above-described configuration are connected in series, the current path through the high resistance lower electrode can be made shorter than that of the conventional structure. Therefore, a thin film capacitor with low parasitic resistance and excellent electrical characteristics as a capacitor can be provided. Therefore, in the case where two or more thin film capacitors functioning as a capacitive element are connected in series for improving withstand voltage, a thin film capacitor having a smaller parasitic resistance than the conventional one can be obtained.

  FIG. 1 is a cross-sectional view of an essential part showing an example of a first embodiment of a thin film capacitor of the present invention. As shown in FIG. 1, the thin film capacitor of the present invention includes a lower electrode layer 22 formed on a support substrate 21, a dielectric layer 23 formed on the lower electrode layer 22, and the dielectric layer 23. An upper electrode layer 24 formed on the upper electrode layer 24 and an extraction electrode 27b connected on the lower electrode layer 22 are provided.

  The lower electrode layer 22 is made of a platinum film or the like, and has a step portion that is thick on the formation region side of the dielectric layer 23 and thin on the outside thereof. Further, in the lower electrode layer 22 of this example, in addition to the region 22a having a high stepped portion on the side where the dielectric layer 23 is formed and the region 22b having a low stepped portion which is an outer region thereof, the lower region 22b A second step portion is further provided on the outer side to have a high region 22c. The lead electrode 27b is connected to the lower electrode layer 22 in contact with the vertical surface between the high region 22a and the low region 22b of the step portion of the lower electrode layer 22. Since the lead electrode 27b is connected to the lower electrode layer 22 in this way, the current path through the high-resistance lower electrode layer 22 can be made shorter than that of the conventional structure, so that the parasitic resistance Can be reduced as compared with the conventional one.

  For the lower electrode layer 22 in the thin film capacitor of the present invention, platinum, an oxide conductor, or the like may be used in consideration of compatibility with the dielectric layer 23, heat resistance, and the like.

  Further, as in this example, a second step portion is further provided outside the low region 22b of the lower electrode layer 22 to have a high region 22c, and the extraction electrode 27b is arranged vertically to the second step portion. Since the lower electrode layer 22 and the extraction electrode 27b are fixed in a bowl shape if they are connected so as to be in contact with the surface, the adhesion between the lower electrode layer 22 and the extraction electrode 27b is greatly improved. Can be improved. As a result, it is possible to supply a highly reliable thin film capacitor in which the extraction electrode layer 27b does not easily peel off due to thermal history or the like.

  Here, the fact that the parasitic resistance is smaller than that of the conventional thin film capacitor according to the thin film capacitor of the present invention will be described by showing a current path in the same cross-sectional view as FIG. 1 shown in FIG. In FIG. 2, the same parts as those in FIG.

In the example of the first embodiment of the thin film capacitor of the present invention shown in FIG. 1, for example, consider the current flowing through the paths A2, B2, and C2 as shown by broken arrows in FIG. At this time, the routes A2, B2, and C2 are the same trajectories as the routes A1, B1, and C1 shown in FIG. The electrical resistance of such paths A2, B2, C2 is
a × specific resistance of lower electrode layer 22 / ΔS + (b + c) × specific resistance of extraction electrode 27b / ΔS
Compared with the conventional thin film capacitor shown in FIG. 8, ΔR = b × (specific resistance of lower electrode layer 22−specific resistance of lead electrode 27b) / ΔS
Can only be reduced. Here, a, b, and c represent the lengths of the paths A2, B2, and C2, respectively. The specific resistance of the lower electrode layer 22 is larger than the specific resistance of the extraction electrode 27b. Further, the possible range of the length b of the path B2 is b ≧ 0. Therefore, ΔR takes a positive value when b = 0 is not satisfied. This is the case in all the paths of the current flowing through the lower electrode layer 22 and the extraction electrode 27b except for the path where b = 0, that is, the path not including the path B2, as shown in FIG. It shows that the electric resistance is reduced as compared with the current path having the same locus in the structure. Further, in the present invention, the same electrode material as that used in the prior art can be used as the electrode material for forming the lower electrode layer 22 and the extraction electrode 27b. However, there is no increase compared to the conventional thin film capacitor. Furthermore, as described above, it is impossible in principle that the current selectively flows only through the path of b = 0.

  For the reasons described above, the parasitic resistance of the thin film capacitor of the present invention is smaller than that of a conventional thin film capacitor, and a thin film capacitor having excellent electrical characteristics as a capacitor can be obtained.

  In the thin film capacitor of the present invention, the thickness of the lower electrode layer 22 is, for example, 0.1 to 10 μm in the high stepped region 22a on the dielectric layer 23 forming region side, and the lower stepped portion is the outer region. In the region 22b, for example, 0.01 μm to 10 μm. If the lower electrode layer 22 is made thinner than 0.1 μm in the high region 22a, there is a possibility that continuity of electric characteristics such as variation in resistance in the surface may be secured. On the other hand, if the lower electrode layer 22 is made thicker than 10 μm, the support substrate 21 and There is a possibility that the adhesiveness of the support substrate 21 is lowered or the support substrate 21 is warped due to the stress of the lower electrode layer 22 due to the increase in thickness. On the other hand, in the low region 22b of the lower electrode layer 22, only the adhesion with the lead electrode 27b formed thereon and the adhesion with the support substrate 21 need to be considered, and the uniformity of electrical characteristics is taken into consideration. Since there is no need, the lower limit of the film thickness is determined within a range in which the film can be continuously formed. Further, the effect of the present invention is not essentially lost if the upper limit value of the film thickness of the low region 22b is smaller than the film thickness of the high region 22a. However, when the present invention is used for a capacitor used in a high frequency region, for example. If so, the difference between the high region 22a and the low region 22b is preferably about the same as the skin depth of the current passing through the lower electrode layer 22.

  In the thin film capacitor of the present invention, it is preferable to use a low-resistance material generally used as an electrode, such as gold, copper, aluminum, or an alloy thereof, for example, for the extraction electrodes 27a and 27b. In order to obtain the effect of the present invention, the specific resistance value of the material used for the extraction electrodes 27a and 27b must be smaller than the specific resistance value of the material used for the lower electrode layer 22.

  On the high region 22a, which is the formation region of the dielectric layer 23 of the lower electrode layer 22, is a dielectric layer 23 made of a barium strontium titanate film or the like, and an upper part made of a platinum film having a thickness of 0.1 to 10 μm, for example. The electrode layer 24 is formed, and the lower electrode layer 22, the dielectric layer 23, and the upper electrode layer 24 form a capacitive element. The thickness of the dielectric layer 23 is arbitrarily determined depending on the capacitance value desired for the element. The area of the dielectric layer 23 is preferably smaller than the high region 22 a of the lower electrode layer 22 and larger than the area of the upper electrode layer 24. The area of the upper electrode layer 24 is arbitrarily determined in accordance with the capacitance value desired for the element within a range not exceeding the area of the dielectric layer 23.

  For the dielectric layer 23, a crystalline dielectric material having a high dielectric constant, particularly a perovskite oxide dielectric material such as strontium titanate, barium titanate, barium strontium titanate, lead titanate or the like is used. desirable.

Also, the thickness range of the upper electrode layer 24 is determined in consideration of the uniformity of the electrical characteristics and the adhesion to the dielectric layer 23, as in the lower electrode layer 22.

  For the upper electrode layer 24 in the thin film capacitor of the present invention, it is desirable to use a chemically stable metal such as platinum or gold that is not easily oxidized.

  A protective film 25 is formed on the capacitor element. The protective film 25 has an opening 26a reaching the upper electrode layer 24 and an opening reaching the region of the lower electrode layer 22 where the dielectric layer 23 and the upper electrode layer 24 are absent. 26b is formed. An extraction electrode 27a connected to the upper electrode layer 24 through the opening 26a and an extraction electrode 27b connected to the lower electrode layer 22 through the opening 26b are formed. As shown in FIG. 1, in this example, the extraction electrode 27 b is lower than the lower electrode layer 22 in the region 22 b where the step portion of the lower electrode layer 22 is low and the vertical surface of the step portion of the lower electrode layer 22. Connected in contact with As a result, the current path passing through the high-resistance lower electrode layer 22 can be made shorter than that of the conventional structure, so that a thin film capacitor having a small parasitic resistance and excellent electrical characteristics as a capacitor can be obtained. It will be a thing.

  Next, an example of the manufacturing method of the thin film capacitor of the present invention will be described. 3 and 4 are cross-sectional views for explaining each step of the manufacturing method of the example of the first embodiment of the thin film capacitor of the present invention.

  First, as shown in FIG. 3, a first platinum film 22 ′ having a thickness of 0.1 to 10 μm is formed on a support substrate 21, a barium strontium titanate film 23 ′ is further formed thereon, and a thickness of 0.01 to 1 μm is further formed thereon. The second platinum film 24 'is continuously formed by using a sputtering method and laminated.

Next, a resist is applied onto the second platinum film 24 'and patterned, and then etching is performed using this as a mask to form the upper electrode layer 24. Next, after removing the resist, a new resist is applied and patterned so as to have a larger shape than the upper electrode layer 24. Using this as a mask, the barium strontium titanate film 23 ′ is etched. A dielectric layer 23 is formed and the resist is removed. Next, a new resist is applied to perform patterning so as to be larger than the dielectric layer 23, and the first platinum film 22 'is etched using this as a mask to form the lower electrode layer 22. . Then, after removing the resist, as shown in FIG. 4, a protective film 25 made of SiO _{2 is formed} on the entire upper surface by CVD.

  Next, a resist is applied on the protective film 25 and patterned, followed by etching to form an opening 26b in the protective film 25 reaching the lower electrode layer 22 in a region where the dielectric layer 23 is not formed. To do. Further, etching is performed through the opening 26b, the lower electrode layer 22 is etched so as to remain in a thickness of 0.01 to 1 μm, a thin region 22b is formed, the lower electrode layer 22 having a stepped portion is formed, and the resist is removed. .

  At this time, the etching of the lower electrode layer 22 may be performed using the resist mask used for forming the opening 26b as a mask without removing the resist mask, or the protective film 25a having the opening 26b formed by removing the resist. It may be performed as a mask.

  Next, after a resist is applied and patterned, etching is performed using the resist as a mask to form an opening 26a reaching the upper electrode layer 24 in the protective film 25, and then the resist is removed.

  Next, by forming lead electrodes 27a and 27b made of a gold alloy material or the like through openings 26a and 26b, the thin film capacitor of the present invention as shown in FIG. 1 can be formed.

  As described above, when the extraction electrode 27b is connected to the lower electrode layer 22 in contact with the vertical surface of the stepped portion provided in the lower electrode layer 22, the lower electrode layer 22 having a higher resistance than the extraction electrode 27b. Since the path of the current passing therethrough is shorter than the path passing through the lower electrode layer 2 in the conventional thin film capacitor having no stepped portion, a thin film capacitor having a small parasitic resistance can be obtained. Further, the etching of the lower electrode layer 22 for forming the stepped portion uses the resist when forming the protective film 25 or the protective film 25 formed with the openings 26a and 27b as a mask. Since the mask forming process for providing the stepped portion is not necessary, the processing steps required for forming the stepped portion can be minimized.

  In the first embodiment described above, platinum and gold alloy are used for the lower electrode layer 22 and the extraction electrodes 27a and 27b, respectively, but the specific resistance value of the material used for the extraction electrodes 27a and 27b is lower. Other metals, oxide conductors, or multilayer films thereof may be used as long as the specific resistance value of the material used for the film is low.

  In the first embodiment described above, barium strontium titanate is used for the dielectric layer 23, but other high dielectric materials may be used.

  Next, an example of the second embodiment of the thin film capacitor of the present invention will be described with reference to the drawings.

  FIG. 5 is a cross-sectional view of an essential part showing an example of the second embodiment of the thin film capacitor of the present invention. The same reference numerals are given to the same portions as in FIG. Only the parts different from the example of the first embodiment will be described below.

  As shown in FIG. 5, in this embodiment, the opening 26 b of the protective film 25 is larger than the region 22 b having a low step in the lower electrode layer 22. Thereby, when forming the opening 26b, the alignment with the lower electrode layer 22 does not have to be stricter than the example of the first embodiment shown in FIG. 1, and is very advantageous from the viewpoint of ease of processing. It becomes.

  The manufacturing method for the example of the present embodiment is the same as the manufacturing method of the example of the first embodiment described above, except for the resist patterning when the opening 26a is formed.

  Next, FIG. 6 is a cross-sectional view of an essential part showing an example of the third embodiment of the thin film capacitor of the present invention, and the same reference numerals are given to the same portions as in FIGS.

  In the third embodiment, since the upper electrode layer 24 has a thicker structure than the upper electrode layer 24 of the first embodiment, the number of steps can be reduced in the manufacturing process. Also, since the only difference between the third embodiment and the first embodiment is the structure of the upper electrode layer 24, the path of the current flowing through the lower electrode layer 22 is the same as that of the third embodiment and the first embodiment. The route is not different from that of the embodiment, and therefore the effect of the present invention is not impaired by selecting the structure of the third embodiment.

  The manufacturing process of the example of the third embodiment is the same as the manufacturing process of the example of the first embodiment described above until the step of forming the protective film 25 (see FIG. 4). In the subsequent manufacturing process, in the example of the first embodiment, an opening 26b is formed in the protective film 25, etching is performed to form the lower electrode layer 22 having a stepped portion, and then the opening 26a is formed in the protective film 25. Formed. On the other hand, in the example of the present embodiment, openings 26a and 26b are simultaneously formed in the protective film 25, and then etching is performed to form the lower electrode layer 22 having a stepped portion. At this time, since the opening 26a has already been formed on the upper electrode layer 24, the upper electrode layer 24 having a stepped portion is formed as shown in FIG. Thereafter, the manufacturing steps of the first to third embodiments are the same.

  In the example of the third embodiment, attention must be paid to the reduction in the film thickness of the upper electrode layer 24 due to etching in the manufacturing process, but the openings 26a and 26b can be simultaneously formed in the protective film 25. Therefore, the number of manufacturing steps can be reduced as compared with the example of the first embodiment, which is very advantageous.

  Next, FIG. 7 is a cross-sectional view of an essential part showing an example of the fourth embodiment of the thin film capacitor of the present invention. In FIG. 7, the same reference numerals are used for the same parts as in FIGS. Is attached.

  In the example of the fourth embodiment, two or more thin film capacitors Cap 1 and Cap 2 according to the example of the first embodiment are connected in series by a lead electrode 27. Here, the part which connected two pieces in series is shown. According to the thin film capacitor of the present invention, a thin film capacitor having a lower parasitic resistance than that of a conventional thin film capacitor is connected in series, so that a thin film capacitor having a smaller parasitic resistance than a thin film capacitor in which a conventional thin film capacitor is connected in series. Obtainable.

  It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

It is principal part sectional drawing which shows the example of 1st Embodiment of the thin film capacitor of this invention. It is principal part sectional drawing which shows the current pathway in the example of 1st Embodiment of the thin film capacitor of this invention. It is sectional drawing for demonstrating the manufacturing method of the example of 1st Embodiment of the thin film capacitor of this invention. It is sectional drawing for demonstrating the manufacturing method of the example of 1st Embodiment of the thin film capacitor of this invention. It is principal part sectional drawing which shows the example of 2nd Embodiment of the thin film capacitor of this invention. It is principal part sectional drawing which shows the example of 3rd Embodiment of the thin film capacitor of this invention. It is principal part sectional drawing which shows the example of 4th Embodiment of the thin film capacitor of this invention. It is sectional explanatory drawing of the conventional thin film capacitor. It is sectional explanatory drawing of the conventional thin film capacitor.

Explanation of symbols

21 ... Support substrate
22 ... Lower electrode layer
23 ・ ・ ・ Dielectric layer
24 ... Upper electrode layer
25 ... Protective film
27a, 27b ... extraction electrodes

Claims (2)

  A lower electrode layer formed on the support substrate; a dielectric layer formed on the lower electrode layer; an upper electrode layer formed on the dielectric layer; and the connected to the lower electrode layer A lower electrode layer having a lower resistance than the lower electrode layer, and the lower electrode layer has a step portion that is thicker on the dielectric layer forming region side and thinner on the outer side, and The electrode is connected in contact with a vertical surface of the step portion, and is a thin film capacitor.   2. A thin film capacitor comprising two or more thin film capacitors according to claim 1 connected in series.

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