JP3146672B2 - A thin-film laminated magnetic induction element and an electronic device using the same. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film magnetic induction device suitable for mounting on a chip of an integrated circuit device by utilizing a semiconductor manufacturing technique for making a switching power supply into one chip.

[0002]

2. Description of the Related Art Conventionally, small electronic devices such as chopper devices and switching power supplies have been constructed by combining passive elements such as inductors and transformers with active elements such as individual semiconductor elements and integrated circuits. The technological progress on the passive device side is lagging behind the rapid progress in the semiconductor technology on the device side.Especially, magnetic induction devices such as inductors and transformers are much larger in size than integrated circuit devices, so electronic devices It is the biggest bottleneck for miniaturization of. For this reason, various attempts have been made to increase the operating frequency of chopping and switching of the electronic device to 1 MHz or more to facilitate downsizing from the side, and also to improve the structure of the magnetic induction element itself.

For example, in the technique disclosed in Japanese Patent Application Laid-Open No. 61-219114, an inductor is constituted by a woven structure in which magnetic fibers are knitted with warp yarns and ultrafine copper wire with weft yarns. JP 1-1512
In the technology disclosed in Japanese Patent Application Laid-Open No. 11, the magnetic induction element is formed of a ceramic laminated structure. Japanese Patent Application Laid-Open No. 2-275606 discloses a planar inductor having a structure in which a coil is supported on a flexible film and sandwiched between magnetic sheets from both sides. Furthermore, Japanese Patent Application Laid-Open No. 1-276708 proposes that an inductor having a woven structure according to the above-mentioned Japanese Patent Application Laid-Open No. 61-219114 is formed of a thin film laminate.

[0004]

As can be seen from these prior arts, in order to reduce the size of the magnetic inductive element, the direction in which the individual elements are adapted to the structure, and whether the individual elements are directly mounted on the semiconductor chip for the active element or not. The latter direction is clearly advantageous in that the overall structure of the electronic device can be reduced in size and the labor of assembling such as surface mounting can be reduced as much as possible and rationalized. The techniques disclosed in Japanese Patent Application Laid-Open No. HEI 11-51211 and Japanese Patent Application Laid-Open No. 1-151211 are not very advantageous because they tend to downsize individual elements. The technology disclosed in Japanese Patent Application Laid-Open No. 2-275606 is essentially an individual element, but is considered suitable for mounting on a chip. However, it is not always easy to reduce the size to a size that can be mounted on a small chip of several to 10 mm square.
In addition, as long as it is an individual element, mounting work for connecting to a chip is indispensable. The technology of Japanese Patent Application Laid-Open No. 1-276708 can solve this point, but since it is originally a woven structure, it is necessary to mix a thin film conductor for a coil and a magnetic thin film for a magnetic circuit. Is rather cumbersome to manufacture.

In addition to the above problem, there is a problem that it is difficult to make the magnetic induction element have a high Q value in a high frequency region.
That is, conventionally, in order to reduce the size of the magnetic induction element, the operating frequency of the electronic device is first increased so that a predetermined reactance value can be obtained even with a small inductance value. Because the inductance value of the magnetic induction element is saturated and the resistance value increases due to the high-frequency loss of
The value becomes saturated or conversely decreases. For this reason, even if the operating frequency is increased, the physical size of the magnetic induction element cannot be reduced in order to maintain the Q value at a predetermined level. Based on this situation, the present invention has a thin film laminated structure suitable for being directly and easily formed on a chip of a semiconductor device such as an integrated circuit, and can maintain a high Q value even in a high frequency region. It is an object of the present invention to provide a magnetic induction element that can be used.

[0006]

According to the magnetic induction element of the present invention, the thin film conductor formed in the coil having a predetermined shape is formed by one or more coils.
A magnetic induction element having a thin film laminated structure sandwiched between a pair of magnetic thin films is divided into a plurality of unit elements, and the permeability of the magnetic thin film is divided.
When the magnetic susceptibility is μ, the thickness is tM, and the distance between both magnetic thin films is g,
In this case, the characteristic length λ on the magnetic circuit = (μ · g · tM / 2) ^1/2
Is set smaller than the planar outer size D of each unit element , and these unit elements are electrically interconnected to form one magnetic induction element, thereby achieving the above object.

[0007] The thin film conductor of the above configuration is formed of a metal having a high conductivity such as copper or aluminum, and is formed into a film having a thickness of several to several tens of μm and formed into a coil having a predetermined shape by etching. The coil shape at this time is preferably a spiral shape or a broken shape, and the former shape is particularly advantageous in the present invention. As the magnetic thin film, a ferromagnetic material having a high magnetic permeability and a soft magnetic property is used, and it is preferable to form a film having a thickness of 10 to several tens μm in an amorphous state by a sputtering method or the like. In addition,
_Assuming that the magnetic permeability of the magnetic thin film is μ, the interval between the pair of magnetic thin films is g, and the thickness of the magnetic thin film is t _M , the characteristic length λ of the magnetic circuit in the above configuration is, for example, λ = (μgt _M / 2) Given by ^1/2 . In order to maximize the Q value of the magnetic induction element in a high frequency region of 1 MHz or more, the outer size, for example, the diameter of each unit element constituting the magnetic induction element is set to be smaller than this characteristic length λ. It is particularly desirable to set it to a degree or less.

As described above, as a method of manufacturing a magnetic induction element having a thin film laminated structure including a thin film conductor and a pair of upper and lower magnetic thin films, a lower magnetic thin film is covered with a lower insulating film, and a lower insulating film is formed. An inter-turn insulating film is applied on the film and etched into a pattern corresponding to the gap between the turns of the coil of the thin-film conductor, and the thin-film conductor is formed on the lower insulating film and the inter-turn insulating film above the same level as the inter-turn insulating film. After the film is formed to a thickness less than that, the portion on the inter-turn insulating film is selectively removed by etching, and the thin-film conductor and the inter-turn insulating film are covered with the upper insulating film, and then the upper insulating film is formed thereon. It is advantageous to provide a magnetic thin film. It is preferable that the inter-turn insulation be made of a material different from that of the lower insulating film so as to provide etching selectivity. Further, it is advantageous to use a reactive ion etching method for the etching. is there.

[0009]

In the magnetic induction element of the present invention, a simple thin film in which a thin film conductor for a coil is sandwiched between a pair of magnetic thin films for a magnetic circuit from both sides so that it can be easily formed on a semiconductor chip by using a semiconductor process technology. Focusing on the fact that this structure can increase the Q value in the high-frequency region by drastically reducing the planar outer size of the structure from conventional wisdom, and using a plurality of compact magnetic induction elements Then, a high Q value can be obtained even in a high frequency region by dividing into unit elements each having a high Q value and then electrically connecting them to form one magnetic induction element. Hereinafter, this principle will be described with reference to FIG.

FIG. 1A shows a cross section of a magnetic induction element 20 having a structure in which a thin film conductor 22 formed in a spiral coil is sandwiched between a pair of upper and lower magnetic thin films 21.
Reference numeral 20 denotes a circular inductor having an outer size or diameter D. The electrical resistivity of the metal of the thin film conductor 22 is ρ, the film thickness is t _C , the number of turns of the spiral coil formed therefrom is n, the outer diameter is Do, the inner diameter is Di, the width of each turn is d, and the distance between turns is Assuming that the gap is s, the DC electric resistance R of the coil is as follows: R = (πρ / t _C ) · F _R (1) Here, F _R is a function of the size, shape, and number of turns of the coil. If p = d + s, F _R = n (Do + s−np)
/ D, or F _R = n (Di−s + np) / d, and if the average diameter of the coil is Dm, then F _R = n Dm / d.

On the other hand, in the magnetic circuit, when the magnetic permeability of the magnetic thin film 21 is μ, the film thickness is t _M , and the mutual interval is g, the characteristic length λ is, for example, λ = (μgt _M / 2) as described above. ) ^1/2 is given by (2), the inductance L of the magnetic induction unit 20 of FIG. 1 (a), expressed by _{L = (πμt M / 2)} · K · F L (3). Here, K is a coefficient determined by the characteristic length λ, the outer diameter size D, and the turn width d of the coil, and is given by K = (λ / d) / sin (D / λ) (4). F _L is a function corresponding to F _R in equation (1), and is a rather complicated equation including a hyperbolic function related to the characteristic length λ on the magnetic circuit side, dimensions and number of turns on the coil side (for example, IEEE, Magn. ., MAG-27, No.6, pp.709, 1991)
However, in order to avoid complication, it is simply represented by F _R here.

The coefficient K is most dominant with respect to the value of the inductance L except for the term (πμt _M / 2) in the above equation (3). In the present invention, the coefficient K is focused on this point. Set the outer diameter size D to be large. That is, if the outer diameter size D is set to be smaller than the characteristic length λ, for example, 1/10 or less, since sin (D / λ) = D / λ substantially holds, K = λ ² / dD, and It is understood that the smaller the D, the larger the K can be. Further, when the outer diameter size D is set to be sufficiently smaller than the characteristic length λ, the relationship of K · F _L = F _R is almost established, so that the Q value of the magnetic induction element 20 is determined by setting the angular frequency to ω and the frequency to ω. f is expressed by the following equation from equations (1) and (3).

Q = ωL / R = πf (μt _M ) (t _C / ρ) (5) In the magnetic induction element 20 actually formed on a semiconductor chip,
In the equation (2), the thickness t _M of the magnetic thin film 21 and the mutual distance g are several tens μm.
Since the magnetic permeability μ is 10 ⁴ , the characteristic length λ is about 1 mm. Therefore, the equation (5) holds when the outer diameter D is about 100 μm or less, but practically holds when the outer diameter D is about 1 mm or less. As can be seen from equation (5), the Q value does not substantially depend on the number of turns n and the turn width d of the coil, and in the case of the present invention in which the outer diameter D is set to be smaller than the characteristic length λ, the magnetic thin film 21 The Q value can be improved by increasing the film thickness t _M by using a material having a high magnetic permeability μ and increasing the film thickness t _C by using a material having a low electric resistivity ρ for the thin film conductor 22.

However, if the outer diameter D is small even if the Q value is high, it is difficult to obtain a sufficient inductance value L and a current capacity of the coil. Therefore, in the present invention, as shown in FIG. Is divided into a plurality of unit elements 30 and formed on the semiconductor chip 10, and interconnected in series, parallel or series-parallel as necessary. It should be noted that, even if the outer shape of each unit element 30 is made to be a square with good area efficiency in arrangement as shown in FIG. The advantages of the invention are obtained.

By the way, in the coil of the thin film conductor 22 shown in FIG. 1A, it is advantageous to make the interval s between turns as small as possible to make the winding pitch p close to the turn width d. For example, let p = d for simplicity, and set the inner diameter Di of the coil to 0.
Then, F _R in equation (1) is F _R = n · Dm as described above.
/ D, the average diameter Dm of the coil is Dm = nd, so that Fm
_R = n ² and the resistance R is proportional to n ² . On the other hand, as is well known, the inductance L is essentially proportional to n ² which is the square of the number of turns n of the coil, so that the Q value does not substantially depend on the number of turns n of the coil and can be expressed by, for example, equation (5). Such a high Q value can be realized. As described above, the gap s is as narrow as possible, and it is desirable that the gap s be as small as 1/10 or less of the film thickness t _C of the thin film conductor 22.
When the etching of 22 is made clear, the aspect ratio t _C / s at which stable etching can be performed is limited to 1, so that the gap s becomes equal to or greater than the film thickness t _C.

The method of manufacturing a magnetic induction element according to the present invention solves this problem. When manufacturing a magnetic induction element including a thin film conductor and a pair of upper and lower magnetic thin films as described in the preceding paragraph, first, a lower layer side is formed. After covering the magnetic thin film with the lower insulating film,
An inter-turn insulating film is formed on the lower insulating film and is etched at a low aspect ratio to form a pattern corresponding to the narrow gap s between turns of the coil. A thin film conductor for a coil is formed on the inter-turn insulating film to a thickness equal to or less than that of the inter-turn insulating film, and then subjected to simple etching to form a thin-film conductor from above the inter-turn insulating film. The removal is performed by a lift-off method. Thereafter, the thin film conductor and the inter-turn insulating film may be covered with the upper insulating film, and the upper magnetic thin film may be disposed thereon. According to the method of the present invention, the gap s can be made smaller than the film thickness t _{C of the} thin film conductor, and can be made one tenth or less of that by etching the inter-turn insulating film by the reactive ion etching method.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the magnetic induction element of the present invention will be described with reference to FIGS. 2 and 3, and an embodiment of a manufacturing method thereof will be described with reference to FIG. FIG. 2 is a sectional view showing a state in which two unit elements 30 constituting the above-described magnetic induction element 20 are formed on the semiconductor chip 10 side by side. As shown in the figure, a semiconductor chip 10 has, for example, a p-type semiconductor substrate 11 covered with an insulating film 12, and an aluminum wiring film 13 on the
Are connected to each other in a pattern connected in series in this example, and are connected to the n-type layer 11a diffused on the surface of the semiconductor substrate 11 in a window portion opened in a key portion of the insulating film 12, and a protective film is further formed thereon. The unit element 30 having a thin film laminated structure covered with 15 is formed on the protective film 15. In the example of the figure, the protective film
A flattening film 14 is provided below 15 to eliminate a step due to the wiring film 13.

Each unit element 30 has a thin-film conductor 33 formed in a spiral coil interposed between a lower magnetic thin film 31 and an upper magnetic thin film 36 with insulating films 32 and 35 interposed therebetween. The very narrow gap between them is opened by the method described with reference to FIG. 4, and the inner and outer ends of the coil are connected to the wiring film 13 through the window or notch of the lower magnetic thin film 31 and the window of the protective film 15. Connected to Further, a protective film 37 such as silicon nitride is covered so as to cover the upper magnetic thin film. Note that a flattening film 34 is provided at a key position below the upper insulating film 35 to fill a step formed by the lower magnetic thin film 31 and the thin film conductor 33.

The pair of magnetic thin films 31 and 36 has, for example, a magnetic permeability μ.
8000 about soft 78 Permalloy which was deposited in an amorphous state by sputtering, for example, a thickness t _M is 9μ
m, and the mutual interval g is 6 μm. The aforementioned characteristic length λ of the magnetic circuit in this case is 220 μm. Also, the thin film conductor 33
A copper electrical resistivity ρ is 3x10 ^-8 [Omega] m in, for example, a thickness t _C are 3 [mu] m. In this embodiment, the outer diameter D of each unit element 30 is set to 22 μm, which is one tenth of the characteristic length λ. Accordingly, the outer diameter Do of the coil is 20 μm, the inner diameter Di is 2 μm, the number of turns n is 3, and the number of turns is three. The pitch p is 3 μm and the gap s is
Each is set to 0.8 μm. When the unit elements 30 having such a setting are arranged side by side on the semiconductor chip 10 as shown in FIG. 1B and measured at a frequency f of 5 MHz, the DC resistance R per each unit element 30 is 0.19Ω, the inductance is L was 850 nH and Q value was 140, which was roughly in agreement with the values predicted from the above formulas.

FIG. 3 shows the results of measuring the inductance L and the Q value of the unit element 30 within a frequency range of 1 to 10 MHz. As can be seen, the inductance L is 10
There is a tendency to decrease slightly around MHz, but it is almost constant,
The Q value tends to be gradually saturated as the frequency f increases, but shows a sufficiently high value of 100 or more at 5 MHz or more. The unit element 30 is designed with a focus on the Q value of 5 MHz. The slope of the Q value with respect to the frequency f is determined by the magnetic permeability μ
When the electrical resistivity ρ of the thin film conductor 33 is constant, it depends on the product t _M t _C of the film thicknesses of the two, and a large product is suitable for a low frequency and a small product is suitable for a high frequency. This indicates that the magnetic induction element of the present invention is particularly advantageous for high frequencies.

Next, referring to FIG. 4, the main point of the method for manufacturing the magnetic induction element of the present invention will be described.
The process of forming 33 coils will be mainly described. Unit element
4 is formed while the semiconductor chip 10 is still in a wafer state. The lower magnetic thin film 31 of FIG. 2 is provided on the wafer 40 of FIG. It shall be covered with. The lower insulating film 32 is preferably made of, for example, thin silicon nitride other than silicon oxide. In the step of FIG. 4A, a silicon oxide film is formed on the entire surface of the wafer 40 and photoetching is performed to form an inter-turn insulation 35a having the same width as the above-mentioned gap s of 0.8 μm.

The silicon oxide film for the inter-turn insulation 35a is formed in an atmosphere of a mixed gas of silane and oxygen at a low temperature of about 350 ° C. since the aluminum wiring film 13 is already formed in the wafer 40. The film is preferably formed by a low pressure CVD method. Further, in the method of the present invention, the thickness of the thin film conductor 33 is set to be slightly larger than that of the thin film conductor 33, for example, 4 μm when the thickness t _C of the thin film conductor 33 is 3 μm. The etching of the silicon oxide film is of course performed by using a photoresist film as a mask. The reactive ion etching method is used to make the side face of the inter-turn insulation 35a vertical as shown in FIG. Is advantageous. At this time, C ₂ H ₆ is used as an etching gas in order to set anisotropic etching conditions.
And a mixed gas of CHF ₃ and its surrounding pressure is, for example, 1
It is good to be about 50Pa. According to the method of the present invention, the etching for forming the inter-turn insulating film 35a with a narrow width s can be easily and accurately performed with an aspect ratio of 1 or close to it as can be seen from the figure.

FIG. 4B shows a process of forming the thin film conductor 33. In this embodiment, copper is formed on the entire surface of the wafer 40 by sputtering or the like to a thickness t _C of 3 μm. At this time, a thin film conductor naturally adheres to the upper side of the inter-turn insulation 35a as indicated by 33a in the figure, but near the base overlapping the upper end portion of the inter-turn insulation 35a due to poor coverage of the metal step. The film thickness becomes very thin. In the subsequent step of FIG. 4C, the thin film conductor portion 33a on the inter-turn insulation 35a is removed by simple etching. This etching requires only a very short immersion of the wafer 40 in a desirably ultrasonic bath of, for example, a 5% hydrofluoric acid solution.
The etchant penetrates from the thin part of a and insulation between turns 35
Since the silicon oxide at the upper end of a is dissolved, the thin film conductor portion 33a thereon is selectively removed by peeling to obtain the state shown in FIG.

Further, in the step of FIG. 4D, after the etching solution is completely removed by washing the wafer 40 with water, a silicon oxide film is formed on the entire surface of the wafer 40 by the low-temperature CVD method in the same manner as described above. As described above, the upper insulating film 35 continuous with the inter-turn insulation 35a is formed. Thereafter, as shown in FIG. 2, an upper magnetic thin film 36 may be provided and covered with a protective film 37 such as silicon nitride to complete the unit element 30 or the magnetic induction element 20. According to the method of manufacturing the magnetic induction element described above, the gap s between turns of the coil formed from the thin film conductor 33 is formed sufficiently narrower than the film thickness t _C , the value of the resistance R is reduced, and the current capacity is reduced. Increase and its Q
Value can be increased.

In the above embodiment, the magnetic induction element has been described as an inductor having a single coil. However, the present invention can be applied to a transformer only by changing the number and shape of coils formed from a thin film conductor. Also, the coil is not limited to the spiral shape of the embodiment, and various shapes such as a broken shape can be adopted as long as it can be formed from a thin film conductor. Furthermore, the specific dimensions, shapes, structures, arrangements, and the like shown in the embodiments are merely examples, and appropriate changes and modifications are possible within the spirit of the present invention.

[0026]

According to the magnetic induction element of the present invention, a magnetic induction element having a thin film laminated structure in which a thin film conductor formed in a coil is sandwiched between a pair of magnetic thin films is divided into a plurality of unit elements.
The following effects can be obtained by setting the outer size of each unit element to be smaller than the characteristic length on the magnetic circuit and interconnecting the unit elements to form a magnetic induction element. (a) Focusing on the relationship between the Q value of the magnetic induction element and the characteristic length of the magnetic circuit, the magnetic induction element is composed of a plurality of unit elements each having an outer size smaller than the characteristic length, thereby achieving a high frequency of 1 MHz or more. Even in the region, a higher Q value than before can be achieved. (b) Since the unit elements constituting the magnetic induction element are much smaller than before, they can be easily fabricated on a semiconductor chip by using integrated circuit manufacturing technology, thereby enabling active elements and passive elements. It is possible to develop a miniaturized electronic device such as a one-chip chopper device or a switching power supply that integrates the above. (c) By changing the combination of the connection of the plurality of unit elements to the magnetic induction element, magnetic induction elements having various reactance values can be configured according to the application. (d) It is possible to easily select a frequency having a desired Q value based on the product of the film thickness of the thin film conductor and the magnetic thin film, so that it is possible to provide a magnetic induction element having various frequency characteristics, and to apply the applicable frequency to a higher frequency range than before. And further downsizing can be achieved.

Further, in the method of manufacturing a magnetic induction element according to the present invention, an inter-turn insulating film is formed on the lower insulating film covering the lower magnetic thin film and etched into a pattern for gaps between turns of the coil. Then, a thin film conductor is formed thereon with a film thickness equal to or less than the inter-turn insulation, and the upper portion of the inter-turn insulation is selectively removed by a very simple etching, so that the inter-turn insulation is reduced. Insulation is reduced to a fraction of the thickness of the thin film conductor by etching with a small aspect ratio
By forming the magnetic induction element with the following extremely narrow width, the Q value of the magnetic induction element can be improved and its current capacity can be increased.

[Brief description of the drawings]

FIG. 1 shows the principle of a magnetic induction element according to the present invention.
(a) is a sectional view thereof, and (b) is a top view of a part thereof formed on a semiconductor chip.

FIG. 2 is a partially enlarged sectional view showing an embodiment of the magnetic induction element of the present invention in a state where the unit element is built on a semiconductor chip.

FIG. 3 is a characteristic diagram showing the frequency dependence of the inductance and the Q value of the magnetic induction element of the present invention.

4 (a) and 4 (b) show an embodiment of a method for manufacturing a magnetic induction element according to the present invention in each of main steps, wherein FIG. 4 (a) shows a step of forming insulation between turns for a coil, and FIG. Film forming process,
FIG. 3C is a partially enlarged cross-sectional view of the wafer showing the state after the etching step, and FIG. 3D is the state after the step of forming the upper insulating film.

[Explanation of symbols]

10 Semiconductor chip in which magnetic induction element is built 20 Magnetic induction element 21 Magnetic thin film 22 Thin film conductor 30 Unit element constituting magnetic induction element 31 Lower magnetic thin film 32 Lower insulating film 33 Thin film conductor 35 Upper insulating film 35a Between turns Insulation 36 Upper magnetic thin film 40 Wafer on which semiconductor chip and magnetic induction element are built D Outside diameter or diameter of magnetic induction element or unit element s Gap between turns of coil or width of insulation between turns

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-280509 (JP, A) JP-A-3-276604 (JP, A) JP-A-3-201511 (JP, A) JP-A-4- 149810 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 17/00, 30/00 H01F 41/04, 41/12

Claims (5)

(57) [Claims] 1. A thin-film laminated magnetic induction element having a structure in which a thin-film conductor formed in a coil having a predetermined shape is sandwiched between a pair of magnetic thin films, wherein the magnetic induction element comprises a plurality of unit elements. And the magnetic thin film has a magnetic permeability of μ and a thickness of t
When the distance between M and both magnetic thin films is g,
The characteristic length λ = (μ · g · tM / 2) ^1/2 is the plane of each unit element.
Characterized in that they are set smaller than a typical outer size D , and these unit elements are electrically interconnected to form one magnetic induction element. 2. A thin-film laminated magnetic induction device according to claim 1, wherein the outer size of the unit element is set to about one tenth or less of the characteristic length λ of the magnetic circuit. . 3. The element according to claim 1, wherein the element is a single element.
A thin film having an outer size of 1 mm or less
Stacked magnetic induction element. 4. The thin film laminated magnetic induction device according to claim 1, wherein the thin film conductor is formed in a spiral coil. 5. The method according to claim 1, wherein the device according to claim 1 is mounted on a semiconductor chip.
An electronic device, wherein the electronic device is laminated.