JP3709117B2 - Thin film electronic components and substrates - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film electronic component and a substrate, and more particularly to a thin film electronic component and a substrate for high frequency use suitably used for a thin film capacitor, a thin film inductor, a thin film filter, and the like.
[0002]
[Prior art]
In recent years, with the downsizing and high functionality of electronic devices, there has been an increasing demand for downsizing, thinning, and high frequency compatibility for electronic components installed in electronic devices. In particular, in a high-speed digital circuit of a computer that needs to process a large amount of information at high speed, even at the personal computer level, the clock frequency in the CPU chip is 200 MHz to 1 GHz, the clock frequency of the inter-chip bus is 75 MHz to 133 MHz, and so on. The speedup is remarkable.
[0003]
As the degree of integration of LSIs increases and the number of elements in a chip increases, the power supply voltage tends to decrease in order to reduce power consumption. As these IC circuits increase in speed, density, and voltage, passive components such as capacitors have become essential to exhibit excellent characteristics for high-frequency or high-speed pulses in conjunction with downsizing and large capacity. Yes.
[0004]
In addition to the electrical characteristics of the passive element itself, such as improvements in mounting accuracy due to the increase in the number of elements and reflow resistance due to component mounting, characteristics related to mounting (mounting accuracy, mounting reliability) It has been demanded at a high level.
[0005]
US Pat. No. 4,439,813 relates to a technique for reducing the inductance of a capacitor connection portion. In order to obtain an electrical signal from a lower electrode made of TiW, Ta, Al, Cu at the shortest distance, an insulating layer, an upper electrode, and a protective layer A thin film capacitor is disclosed in which a through hole is provided in a through hole, a BLM layer made of Cr / Cu / Au is formed on the inner surface of the through hole, and then a solder bump is formed on the BLM layer.
[0006]
[Problems to be solved by the invention]
When considering high frequency applications of passive components, materials with low loss at high frequencies are used as electrodes and conductors. Cu, Ni, Ag and Au can be considered as low-resistance electrode materials. However, Cu and Ni have problems with oxidation resistance, and it is necessary to process at a high temperature when forming a dielectric thin film or magnetic thin film. Such thin film capacitors and thin film inductors are difficult to use as electrodes.
[0007]
In addition, Ag is superior to Cu and Ni in terms of oxidation resistance, but there are problems of migration and reaction with the insulating layer, making it difficult to use as an electrode for thin film components with a thin insulating layer. It was.
[0008]
On the other hand, since Au has low resistance and good oxidation resistance and does not react with insulators and magnetic substances, it can be sufficiently used as an electrode for thin film capacitors and thin film inductors for high frequency applications.
[0009]
However, when Au electrodes are used to reduce the resistance of passive components, there are problems with connection strength and reflow resistance. That is, Au is usually more likely to react with solder as it is used as an adhesive layer with solder, and immediately forms an Au—Sn alloy. This Au—Sn alloy is a hard and brittle metal, and when a thick alloy layer is formed at the interface between the solder and the electrode, there is a problem that the adhesion strength of the external terminal made of solder deteriorates.
[0010]
Therefore, it is conceivable to form a solder diffusion prevention layer between the Au electrode and the external terminal made of solder. Conventionally, in the thin film formation method such as the sputtering method, a thin solder is required due to cost and residual stress. Since only the diffusion preventing layer could be formed, there was a problem that the solder diffused into the Au electrode due to a defect in the solder diffusion preventing layer and reacted with the Au electrode immediately below the solder diffusion preventing layer. That is, in a film formed by a thin film formation method such as sputtering, the crystal grains grow in the film thickness direction, so that the solder diffuses from the grain boundaries of the crystal grains, reacts with the Au electrodes, and shorts between the electrodes. Therefore, there arises a problem in reflow resistance such as characteristic deterioration due to disappearance of the Au electrode.
[0011]
Although it is possible to cope with such problems by increasing the thickness of the solder diffusion prevention layer, as described above, the cost becomes high, or deformation or the like occurs due to the residual stress of the film, and the thin film electronic component It was difficult to produce.
[0012]
It is an object of the present invention to provide a thin film electronic component and a substrate that can prevent the diffusion of solder by a thin solder diffusion preventing layer.
[0013]
[Means for Solving the Problems]
The thin film electronic component of the present invention includes a support substrate, a thin film element provided on the support substrate, having an insulator layer and an electrode layer, and connected to the electrode layer via a solder diffusion prevention layer, and is made of external solder. The solder diffusion preventing layer is formed by laminating two or more layers of the same material formed by a thin film forming method .
[0014]
Such a solder diffusion preventing layer is formed by sputtering, and it is effective that the electrode layer is made of Au.
[0015]
In the layer formed by the sputtering method in this manner, crystal grains grow in the layer thickness direction, and therefore a grain boundary exists between the crystal grains. In the present invention, by forming a solder diffusion prevention layer by laminating two or more of the same material layers, crystal grain formation positions are different between the same material layer in the first layer and the same material layer above it (discontinuous). ), The grain boundaries of crystal grains in the same material layer are not formed linearly in the thickness direction, but once become discontinuous at the interface, the grain boundaries of the first same material layer are the same material in the upper layer. Even if the first layer of the same material layer and the upper layer of the same material layer are connected to each other, they are connected by detours, and the diffusion path of the solder can be interrupted or lengthened. Even if it is a diffusion prevention layer, the diffusion of solder to the electrode layer made of Au can be suppressed, and the reflow resistance of the thin film electronic component in the reflow process can be improved.
[0016]
In the present invention, the thickness of the solder diffusion preventing layer is desirably 3 μm or less. Thus, by setting the thickness of the solder diffusion preventing layer to 3 μm or less, the cost can be reduced even when the thin film forming method is used, and damage due to residual stress can be prevented.
[0017]
Further, the substrate of the present invention is obtained by providing the above-described thin film electronic component on the surface of a base via its external terminal.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a thin film electronic component comprising the thin film capacitor of the present invention. This thin film capacitor has a thin film element A having an insulating layer 3 (dielectric thin film) and electrode layers 5 and 7 on a support substrate 1. Are provided. The electrode layers 5 and 7 are made of Au, and the insulator layer 3 is sandwiched between the electrode layers 5 and 7 to form a thin film element A (capacitive element).
[0019]
The insulator layer 3 constituting the dielectric thin film of the thin film capacitor may be a dielectric made of a perovskite type oxide crystal having a high relative dielectric constant in a high frequency region. For example, Pb (Mg, Nb) O ₃ type, Pb (Mg) , Nb) O ₃ —PbTiO ₃ system, Pb (Zr, Ti) O ₃ system, Pb (Mg, Nb) O ₃ —Pb (Zr, Ti) O ₃ system, (Pb, La) ZrTiO ₃ system, BaTiO ₃ It may be a system, (Sr, Ba) TiO ₃ system, or a compound in which other additives are added or substituted thereto, and is not particularly limited.
[0020]
The film thickness of the insulator layer 3 is preferably 0.3 to 1.0 μm in order to ensure high capacity and insulation. This is because when the thickness is smaller than 0.3 μm, the covering property is not good and the insulating property may be lowered, and when the thickness is larger than 1.0 μm, the capacity tends to be small. The film thickness of the insulator layer 3 is preferably 0.4 to 0.8 μm.
[0021]
The film thickness of the electrode layers 5 and 7 made of Au is preferably 0.3 to 0.5 μm in consideration of impedance in the high frequency region and film coverage. This is because when the electrode layers 5 and 7 are thinner than 0.3 μm, there is a possibility that a portion that is not partially covered may occur, and when thicker than 0.5 μm, the conductor layer in the high frequency region This is because the resistance of the conductor layer hardly changes in consideration of the skin effect.
[0022]
The protective layer 9 is for protecting the surface of the thin film capacitor, and is made of, for example, Si ₃ N ₄ , SiO ₂ , polyimide resin, BCB (benzocyclobutene), or the like.
[0023]
Here, the support substrate 1 is not particularly limited as it is selected from alumina, sapphire, aluminum nitride, MgO single crystal, SrTiO ₃ single crystal, surface silicon oxide, glass, quartz and the like.
[0024]
The thin film element A and the insulating layer non-formation region B where the insulating layer 3 is not formed are covered with a protective layer 9, and the protective layer 9 has a pair of external terminals 11a and 11b having different polarities made of solder bumps. Is provided protruding. These external terminals 11a and 11b are formed in through holes 13a and 13b formed in the protective layer 9 in the insulator layer non-forming region B. The external terminal 11 a is electrically connected to the lower electrode layer 5, and the external terminal 11 b is electrically connected to the upper electrode layer 7.
[0025]
The external terminals 11a and 11b are preferably made of at least two kinds of metals among Pb, Sn, Ag, In, Cu, Bi, Sb and Zn, and have a melting point and a eutectic temperature depending on the use of the thin film electronic component. Different materials may be selected. The external terminals 11a and 11b are formed using a known technique such as screen printing or ball mounter.
[0026]
The lower electrode layer 5 is annularly etched so as to surround the external terminal 11b, and is separated into a lower electrode layer 5a that forms a capacitor and a lower electrode layer 5b that does not form a capacitor.
[0027]
The upper electrode layer 7 is annularly etched on the insulator layer 3 so as to surround the external terminal 11a, and is separated into an upper electrode layer 7a that forms a capacitor and an upper electrode layer 7b that does not form a capacitor.
[0028]
A solder diffusion prevention layer 21 is formed on the upper electrode layer 7, and the formation range thereof is the same as that of the upper electrode layer 7. This solder diffusion prevention layer 21 is formed of two layers of the same material by sputtering. It is configured by stacking more than one layer.
[0029]
In this way, by forming the same material layer in two by sputtering, as shown in FIG. 2, the lower same material layer 21a and the upper same material layer 21b are formed, and the same material layers are formed. Crystal grains grow in the thickness direction in the layers 21a and 21b. The formation positions of the crystal grains are different and are discontinuous, and the grain boundary of the same material layer 21a is the crystal of the same material layer 21b. It is blocked by grains, or grain boundaries of crystal grains are not formed linearly in the thickness direction, and are once discontinuous at the interface. 2B is a cross-sectional view of the vicinity of the solder diffusion preventing layer 21. FIG. 2A is a partially enlarged view of FIG. 2B. In FIG. 2A, the white background is a crystal grain. The black part is the grain boundary, and here, the same material layer is formed twice by sputtering. After the first material layer is formed, the sputter discharge is stopped once or After putting the shutter between the deposition object and the same material layer by sputtering again, the solder diffusion preventing layer 21 in which two identical material layers are laminated is produced.
[0030]
The solder diffusion preventing layer 21 is made of one kind of metal selected from Ti, Cr, Ni, Cu, Pd, and Pt. The thickness of the solder diffusion preventing layer 21 is 3 μm or less in order to exhibit the function of the solder barrier. In particular, a thickness of 1 to 3 μm is desirable. In order to improve the adhesion between the solder diffusion preventing layer 21 and the upper electrode layer 7 made of Au, a known adhesion material such as Ti or Cr may be interposed therebetween. Needless to say, the solder diffusion preventing layer 21 may be formed by laminating two or more layers of the same material.
[0031]
As shown in FIG. 1, the solder adhesion layer 22 having good solder wettability is formed on the upper surface of the solder diffusion preventing layer 21 and in the insulating layer non-forming region B where the insulating layer 3 is not formed. Is formed. Examples of materials having good solder wettability include Ni—Cr and Au, and Au is particularly desirable. The film thickness of the solder adhesion layer 22 may be 0.01 to 0.05 μm in order to exhibit its function. Further, as shown in FIG. 1, it is desirable that the solder adhesion layer 22 be formed with a smaller area than the solder diffusion preventing layer 21 from the viewpoint of preventing the diffusion of solder to the upper electrode layer 7.
[0032]
The external terminal 11a is joined to the support substrate 1 through the lower electrode 5a, the upper electrode 7b, the solder diffusion preventing layer 21, and the solder adhesion layer 22, and the external terminal 11b is connected to the lower electrode 5b, the upper electrode 7a, The support substrate 1 is bonded via the solder diffusion preventing layer 21 and the solder adhesion layer 22.
[0033]
The thin-film electronic component configured as described above is used by connecting the external terminals 11a and 11b to the electrodes on the surface of the base (mother substrate).
[0034]
In the thin film electronic component configured as described above, since the electrode layers 5 and 7 made of Au having a small resistance are used as the electrode layers 5 and 7 of the thin film element A, the resistance at a high frequency can be reduced. High frequency can be promoted. Furthermore, since a high-permittivity perovskite oxide can be used as the insulator layer 3, a high-capacity thin film capacitor can be formed and impedance at high frequencies can be reduced.
[0035]
Even if the electrode layers 5 and 7 made of Au are used, the external terminals 11 a and 11 b are electrically connected to the electrode layers 5 and 7 through the solder diffusion prevention layer 21. , 7 can be prevented from forming an alloy layer, the deterioration of the adhesion strength of the external terminal 11 can be suppressed, and the solder component can be prevented from diffusing through the electrode layers 5 and 7 made of Au during reflow, Characteristic deterioration due to short-circuit between the electrode layers 5 and 7 and disappearance of the electrode layers 5 and 7 made of Au can be suppressed, and reflow resistance can be improved.
[0036]
In the present invention, the solder diffusion preventing layer 21 is divided into two portions by the sputtering method, and is composed of the same material layer 21a on the lower side and the same material layer 21b on the upper side. The crystal grains grow in the thickness direction, and the formation positions of the crystal grains are different and are discontinuous, and the grain boundaries of the same material layer 21a are blocked by the crystal grains of the same material layer 21b. Or the grain boundaries of the crystal grains are not formed linearly in the thickness direction, but are once discontinuous at the interface, and the solder diffusion path can be interrupted or lengthened. The diffusion of solder to the electrode layers 5 and 7 made of Au can be suppressed, and the reflow resistance of the thin film electronic component in the reflow process can be improved.
[0037]
In addition, the material of the electrode layers 5 and 7 in the present invention is a material made of Au that has low resistance, oxidation resistance at high temperature, and small reaction with the dielectric material. In order to increase the adhesion, an adhesion layer typified by Ti or Cr may be interposed between the electrode layers 5 and 7 and the support substrate 1.
[0038]
In the above example, the example in which the present invention is applied to a thin film capacitor has been described. However, the present invention is not limited to the above example. For example, a thin film inductor, a thin film LC filter, or a thin film composite component obtained by combining these components. You may apply to.
[0039]
In the above example, a single plate type in which one insulator layer is sandwiched between electrode layers is shown, but a thin film capacitor in which a plurality of insulator layers and electrode layers are alternately stacked may be used.
[0040]
In the above example, the example in which the solder adhesion layer 22 made of Au is formed has been described. However, depending on the material of the external terminal, for example, the external terminal made of a metal of Pb or Sn does not need to interpose the solder adhesion layer. Since it adheres to the solder diffusion preventing layer, it is possible to suppress deterioration of the adhesion strength of the external terminal.
[0041]
【Example】
The electrode layer, the solder diffusion preventing layer, and the solder adhesion layer were formed by DC sputtering, and the insulator layer was prepared by sol-gel method.
[0042]
First, a 10 nm adhesion layer made of Ti was formed on a support substrate made of alumina, and a 0.3 μm Au layer was formed on the upper surface of the adhesion layer to form a lower electrode layer. The lower electrode layer was patterned using photolithography technology.
[0043]
After the Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ —PbZrO ₃ coating solution synthesized by the sol-gel method is applied to the processed lower electrode layer using the spin coating method and dried. Heat treatment was performed at 380 ° C. and firing was performed at 810 ° C. to form an insulator layer made of Pb (Mg _1/3 Nb _2/3 ) O ₃ —PbTiO ₃ —PbZrO ₃ with a film thickness of 0.8 μm. Thereafter, through holes were formed in the insulator layer using a photolithography technique.
[0044]
Next, a 30 nm-thickness Ti layer is formed on the top surface of the insulator layer to form an adhesion layer, and a 0.3 μm-thickness Au layer is formed on the top surface of this adhesion layer to form an upper electrode layer. On the upper electrode layer, first, the same material layer composed of a Ni layer having a thickness of 1.5 μm is formed, and then the deposition is temporarily stopped, and then the same material layer composed of Ni is formed again, thereby forming a film having a thickness of 3 μm. A Ni layer was formed as a solder diffusion preventing layer, and a solder adhesion layer made of Au having a thickness of 0.01 μm was formed on the solder diffusion preventing layer. Thereafter, the upper electrode layer and the solder diffusion prevention layer were processed after processing the solder adhesion layer by using a photolithography technique.
[0045]
Thereafter, a photosensitive BCB was applied, exposed and developed to form a protective layer having a through hole having a diameter of about 100 μm and a depth of 4.0 μm so that the solder adhesion layer was exposed.
[0046]
Finally, by using screen printing, a high-temperature solder paste composed of 95% by weight of Pb and 5% by weight of Sn is transferred onto the processed solder diffusion prevention layer, reflowed, and external terminals are formed. A thin film capacitor as shown in 1 was obtained.
[0047]
The effective electrode area of the obtained thin film capacitor was 1.4 mm ² , and the capacitance at a frequency of 1 kHz was about 40 nF.
[0048]
A thin film capacitor of a comparative example was produced in the same manner as described above except that a 3 μm thick Ni layer (same material layer) was formed at a time to form a solder diffusion preventing layer by DC sputtering.
[0049]
About the obtained thin film capacitor, the ball shear strength of the external terminal was measured after each reflow using a shear strength tester, and the result is shown in FIG. The capacitance value of the thin film capacitor was measured after each reflow, and the result is shown in FIG.
[0050]
From FIG. 3, as a result of measuring the ball shear strength after repeated reflow treatment, in the comparative example in which a solder diffusion prevention layer having a film thickness of 3 μm was produced at once, the strength decreased by 10% in the first reflow, and in the second time In contrast to the initial strength of only about 70%, the thin film capacitor of the present invention is only about 5% lower than the initial even after the 10th reflow, and the strength deterioration of the external terminal is improved. I understand.
[0051]
From FIG. 4, in the sample of the comparative example, the electrostatic capacitance suddenly decreased from the third reflow, and a short circuit occurred at the seventh. This decrease in capacitance is due to a decrease in effective area of the electrode layer forming the capacitance due to diffusion of solder into the Au electrode layer. In addition, in the seventh time, it can be seen that conduction occurs because the electrode layers having different polarities are short-circuited by the diffusion of the solder.
[0052]
On the other hand, in the thin film capacitor of the present invention, since the capacitance hardly changed even after the 10th reflow, the stress due to the diffusion of the solder and the thermal contraction of the external terminal is hardly affected by the insulator layer. It can be seen that insulation is secured.
[0053]
Further, when a solder diffusion prevention layer made of a Ni layer having a thickness of 2 μm was formed by forming a Ni layer (same material layer) having a thickness of 1 μm in two steps, the thickness of the solder diffusion prevention layer described above was formed. It was confirmed that the same effect as in the case of 3 μm was exhibited.
[0054]
In addition, processes other than the composition of the solder bumps were similarly performed, and thin film capacitors having solder bumps of Pb95Sn5 solder, Sn-3.5Ag solder, and Sn-3Ag-0.7Cu solder were produced and evaluated in the same manner. Although the reflow temperature varies depending on the solder bump composition, the deterioration of adhesion strength and the behavior of capacitance are the same as the results for eutectic solder bumps, and the structure of the present invention has a great effect on reflow resistance. confirmed.
[0055]
【The invention's effect】
In the thin film electronic component of the present invention, by forming two or more of the same material layers to form a solder diffusion prevention layer, the formation positions of crystal grains are the same in the first material layer and the same material layer above it. Due to the difference (discontinuity), the grain boundaries of the crystal grains of the same material layer are not formed linearly in the thickness direction, but once become discontinuous at the interface, the grain boundaries of the first material layer of the same material layer Even if the upper same material layer is blocked by crystal grains, or the same material layer in the first layer and the upper material layer are connected, the solder diffusion path is interrupted or lengthened. Even if it is a thin solder diffusion prevention layer, the diffusion of solder to the electrode layer made of Au can be suppressed, and the reflow resistance of the thin film electronic component in the reflow process can be improved.
[0056]
In addition, when Ni is selected as the material for the solder diffusion prevention layer, the adhesion of the external terminals can be secured between the solder diffusion prevention layer and the external terminals without using Au, which is usually used as the adhesion layer of the external terminals, and as a result Further, there is no formation of an alloy between Au just below the solder diffusion preventing layer and Sn, which is one of solder materials, and it is possible to further suppress the deterioration of the adhesion strength of the external terminals.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a thin film electronic component of the present invention.
FIG. 2 shows a solder diffusion preventing layer, wherein (a) is a cross-sectional view of (b).
FIG. 3 is a graph showing the relationship between the number of reflows and the ball share strength.
FIG. 4 is a graph showing the relationship between the number of reflows and the capacitance.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Support substrate 3 ... Insulator layer 5 ... Lower electrode layer 7 ... Upper electrode layer 11a, 11b ... External terminal 21a, 21b ... Solder diffusion prevention layer A ... Thin film element

Claims (5)

A support substrate, a thin film element provided on the support substrate, having an insulator layer and an electrode layer, and connected to the electrode layer via a solder diffusion prevention layer, and having external terminals made of solder, and A thin film electronic component, wherein the solder diffusion preventing layer is formed by laminating two or more layers of the same material formed by a thin film forming method . The thin film electronic component according to claim 1, wherein the same material layer is formed by a sputtering method. 3. The thin film electronic component according to claim 1, wherein the electrode layer is made of Au. 4. The thin film electronic component according to claim 1, wherein the solder diffusion preventing layer has a thickness of 3 [mu] m or less. 5. A substrate comprising the thin film electronic component according to claim 1 provided on a surface of a base via an external terminal.

Images