JP2008166476A - Thin film transformer and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film transformer capable of easily improving energy conversion efficiency without an occupied area increased, and to provide its manufacturing method. <P>SOLUTION: A first coil conductor 4 comprising a vortical (a planar spiral) primary coil and a second coil conductor 6 comprising a secondary coil are formed in mutually facing laterally in insulating films of silicon oxide films 2, 5, 7 formed on a silicon substrate 1. The width of the coil conductors 4, 6 can be formed vertically to easily improve the energy conversion efficiency without the occupied area increased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin film transformer in which spiral thin film coils are opposed to each other and a method for manufacturing the same.

A thin film transformer formed on a semiconductor substrate such as silicon is known as a transformer that can be miniaturized because its coil is formed by a thin film formation technique, and is one of elements constituting a semiconductor integrated device or the like. Here, conductive wiring (conductor or semiconductor) is used for the coil, and the shape of the coil has a large inductance per length (or area) of the coil, that is, a large Q value (Q = ωL / R, ω : Angular frequency, L: Mutual inductance, R: Coil resistance) are formed in a spiral shape (planar coil shape). An example of the thin film transformer thus formed is shown in FIG.
5A and 5B are configuration diagrams of a conventional thin film transformer, in which FIG. 5A is a perspective view, and FIG. The silicon oxide film 12 is omitted in FIG. Further, the coil conductors 13 and 14 are drawn with the thickness omitted for simplicity.
In the thin film transformer, a silicon oxide film 12a having a thickness of 0.1 to 2 μm is formed on a silicon substrate 11, and a conductive metal material made of aluminum, copper, or the like is formed on the surface side by a sputtering method or a vacuum deposition method. It is formed as a metal film having a thickness of 1 to 5 μm. Thereafter, the metal film is transferred by lithography to the spiral pattern of the first coil conductor 13, and after an etching process, the first coil having a width of 10 to 100 μm and a wiring interval (distance between the coil conductors) of 10 to 100 μm. A conductor 13 is formed, and the first coil conductor 13 is spirally formed to form a primary coil. The pitch W of the first coil conductor 13 is a combination of the width of the coil conductor and the wiring interval, and the pitch of the second coil conductor 14 is the same.
Next, after a silicon oxide film 12b having a thickness of 0.1 to 3 μm is formed on the surface side, the second coil conductor 14 is formed to a thickness of 1 to 5 μm by the same method as the first coil conductor 13. A secondary coil is formed in the same pattern directly above the conductor 13, and a silicon oxide film 12 c having a thickness of 1 to 2 μm is formed on the surface side of the secondary coil. In this way, a thin film transformer composed of the first coil conductor 13 and the second coil conductor 14 embedded in the silicon oxide film 12 is formed.
Next, in order to form terminals that can electrically connect both ends of the first coil conductor 13 and both ends of the second coil conductor 14, silicon oxide films on the first and second coil conductors 13, 14 are formed. 12c is removed by lithography and etching processes to form a thin film transformer. In the thin film transformer of FIG. 5, the number of turns of the primary and secondary coils is 4, and the secondary coil is formed in the same pattern so as to face the primary coil in the vertical direction.

In the thin film transformer having such a configuration, for example, when a current flows through both ends of the primary coil and the current is changed, the magnetic field generated around the primary coil changes. A potential difference is generated in the secondary coil, and an electromotive force is generated in the secondary coil. Here, the induced electromotive force (induced current) generated in the secondary coil is proportional to the number of turns of the secondary coil.
Further, if the number of turns of the primary coil is large, the magnetic field generated around the primary coil is emphasized, so that a large electromotive force can be induced.

Thus, in a thin film transformer that obtains an electromotive force due to the effect of mutual inductance, if the number of coil turns between the primary and secondary coils increases, the magnetic field due to each coil wire is emphasized, and the amount of inductance increases. Since the coupling coefficient is also increased, the efficiency of energy conversion from the primary coil to the secondary coil is improved.
According to Patent Document 1, when creating a planar coil in a magnetic element typified by a planar inductor or the like, a pattern having a width equal to the coil conductor width to be fabricated in advance is prepared. Based on this, a coil conductor is formed on the underlying surface, and then a thin insulating layer is formed so as to cover the entire surface of the coil conductor portion, and finally the remaining space is filled with a metal material to produce a coil. It is disclosed that the thickness of the insulating film between adjacent coil conductors can be made very thin, and a planar inductor having a high Q value can be manufactured.

According to Patent Document 2, a step of forming an insulating film constituting a space between coil conductors on a magnetic film, a step of patterning the insulating film into a shape of a space between coil conductors, and a pattern of the insulating film as a conductor A step of surface modification so that the film can be selectively grown, a step of selectively filling a conductor film in a gap between the patterns of the insulating film to form a coil conductor, and a step of forming an insulating film on the entire surface. A high-performance planar magnetic element having a sufficiently thick coil conductor that can reduce the width of the space between the coil conductors by manufacturing a planar magnetic element in the process of forming a magnetic film on the insulating film Is disclosed in a very simple process.
JP-A-5-6832 JP-A-6-77072

  However, in the thin film transformer having the structure shown in FIG. 5 described above, if the number of turns of the primary coil and the secondary coil is increased, the area of the thin film transformer itself increases, which hinders miniaturization of the transformer. is there. In addition, an increase in the number of coil turns leads to an increase in the length of the coil wire, and in particular, in a thin film coil, the resistance value is very large compared to the resistance value of a general conducting wire. There is a problem that the increase may lead to an increase in energy loss, that is, a decrease in Q value that is a measure of energy conversion efficiency.

As described above, in the conventional thin film transformer, there is a trade-off relationship between an increase in the number of coil turns for the purpose of improving the energy conversion efficiency and a reduction in the size of the transformer. It has been pointed out that this could lead to a decline.
Moreover, although the said patent documents 1 and 2 have disclosed the thin film inductor, the concrete description regarding the thin film transformer is not made.

  An object of the present invention is to solve the above-described problems and provide a thin film transformer and a method for manufacturing the same that can easily improve energy conversion efficiency without expanding an occupied area.

In order to achieve the above object, a support substrate, a first insulating film formed on the support substrate, an elongated groove formed in the first insulating film, and a sidewall of the groove are formed. A first coil conductor and a second coil conductor formed in the groove through a second insulating film so as to face the first coil conductor are provided.
The support substrate may be a semiconductor substrate or an insulating substrate.

The planar shape of the groove may be a spiral shape (planar spiral shape).
The first coil conductor may be formed on a side wall and a bottom surface of the groove.
The insulating film may be a silicon oxide film, a polyimide film, or a resist film.
In addition, a pad electrode is connected to each end of the first coil conductor and the second coil conductor.

A step of forming a first insulating film on the support substrate and forming an elongated groove in the first insulating film;
Forming a first metal film on the first insulating film including the inside of the trench;
Removing the first metal film by anisotropic etching, leaving the first metal film on the side wall of the groove, and forming a first coil conductor;
Coating the first metal film with a second insulating film leaving the groove;
Covering the second insulating film with a second metal film and filling the groove with the second metal film;
Forming the second coil conductor by leaving the second metal film filled in the groove by a CMP method using the second insulating film as a stopper layer, and removing the second metal film at other locations;
It is set as a manufacturing method provided with.

A step of forming a first insulating film on the support substrate and forming an elongated groove in the first insulating film;
Forming a first metal film on the first insulating film including the inside of the trench;
Forming a first coil conductor by using the first insulating film as a stopper layer, leaving the first metal film on the sidewalls and bottom of the groove by CMP, and removing the first metal film at other locations;
Coating the surface and the first metal film in the groove with a second insulating film;
Covering the second insulating film with a second metal film and filling the groove with the second metal film;
Leaving the second metal film filled in the groove by CMP and removing the second metal film in other locations to form a second coil conductor;
It is set as a manufacturing method provided with.

The support substrate may be a semiconductor substrate, and the first insulating film and the second insulating film may be silicon oxide films.
In addition, after forming the second coil conductor, the surface is covered with a third insulating film, a contact hole is formed in the third insulating film, and an end portion of the first coil conductor and an end portion of the second coil conductor are formed. And a step of forming a pad electrode connected through a contact hole.

  According to the present invention, in the spiral thin film transformer, a groove is formed in the insulating film on the support substrate, and the primary coil and the secondary coil are formed in the groove without increasing the occupied area. , Energy conversion efficiency can be improved.

  Embodiments will be described in the following examples.

FIG. 1 is a configuration diagram of a thin film transformer according to a first embodiment of the present invention. FIG. 1 (a) is a plan view of an essential part, and FIG. 1 (b) is cut along line X1-X1 in FIG. 1 (a). It is principal part sectional drawing. The figure (a) is the principal part top view cut | disconnected by the X2-X2 line | wire of the figure (b).
A spiral (planar spiral) primary coil is formed in insulating films 2, 5, and 7 (these numbers are also attached to the silicon oxide film) made of a silicon oxide film formed on a silicon substrate 1 that is a semiconductor substrate. The first coil conductor 4 and the second coil conductor 6 constituting the secondary coil are formed so as to face each other in the lateral direction. This is obtained by forming the first coil conductor 4 and the second coil conductor 6 in the spiral groove 3 formed in the insulating film 2. The surface is covered with a silicon nitride film 8 as a protective film. The first coil conductor 4 has a width of 2.5 μm and a thickness of 0.5 μm, and the second coil conductor 6 has a width of 2.5 μm and a thickness of 1 μm. The distance between the first coil conductor 4 and the second coil conductor 6 is 0.2 μm, and the distance between the spirals is 1 μm. The first and second coil conductors 4 and 6 are made of, for example, copper. In this embodiment, the insulating film 2 is a silicon oxide film, but may be a polyimide film or a resist film. In the product of the present invention, the widths of the coil conductors 4 and 6 are in the vertical direction, and it is the thickness of the coil conductors 4 and 6 that affects the occupied area.

When the conventional thin film transformer shown in FIG. 5 is manufactured with the above-described coil specifications, in the conventional product, the pitch W of the coil conductors is the width of the coil conductor + the interval between the coil conductors (swirl interval) = 2.5 μm + 1 μm = 3.5 μm.
On the other hand, in the case of the present invention product, the pitch T of the first coil conductor 4 (or the second coil conductor 6) is the thickness of the first coil conductor 4 (1 μm) × 2 + the thickness of the second coil conductor 6 + the second. 1. The interval between the second coil conductors 4 and 6 (0.2 μm) × 2 + vortex interval = 1 μm + 1 μm + 0.4 μm + 1 μm = 3.4 μm. The occupied area of the conventional product is about the same, but the first and second coil conductors Since the overlap of 4 and 6 is larger, the Q value is larger than that of the conventional product.

Further, in order to increase the energy conversion efficiency, the width of the coil conductor can be increased by increasing the thickness of the insulating film 2 and deepening the groove, thereby easily increasing the energy conversion efficiency. However, as the insulating film 2 at that time, it is preferable to use a polyimide film, a resist film, or the like that can be larger than the silicon oxide film.
Further, since the silicon substrate 1 serves as a support substrate, when a polyimide film or a resist film is used for the insulating film 2, other than the silicon substrate, for example, an insulating magnetic substrate such as ferrite, plastics, etc. Alternatively, an insulating substrate may be used. When an insulating magnetic substrate is used, the magnetic flux density is increased, and the energy conversion efficiency can be increased compared to a silicon substrate or the like.

2A to 2C are process diagrams showing a method of manufacturing the thin film transformer of FIG. 1, and FIGS. 2A to 2C are cross-sectional views of main part manufacturing processes shown in the order of processes.
A silicon oxide film 2 having a thickness of 3 μm is formed on the surface side of the silicon substrate 1 by a CVD (Chemical Vapor Deposition) method, and a spiral groove having a width of 2.4 μm, an interval of 1 μm, and a depth of 2.5 μm is formed by lithography and etching. 3 is formed. Subsequently, copper having a thickness of 0.5 μm is formed on the silicon oxide film 3 by a sputtering method, and the copper is etched by anisotropic dry etching to leave copper on the side wall in the groove 3 and at the bottom. The copper other than the copper and the groove is removed to form the first coil conductor 4 constituting the primary coil (FIG. 1A).

  Next, the surface is covered with a silicon oxide film 5 having a thickness of 0.2 μm by a CVD method, and copper having a thickness of 0.5 μm is formed on the silicon oxide film 5 by a sputtering method. The recess 10 covered with the silicon oxide film 5 is filled with copper, and the silicon oxide film 5 is used as a stopper layer to remove the copper other than the copper filled in the recess 10 by CMP, leaving the copper in the recess 10 to form the secondary coil. The second coil conductor 6 to be formed is formed ((b) in the figure).

  Next, a silicon oxide film 7 having a thickness of 1 μm is formed by a CVD method, contact holes of primary coils and secondary coils at locations not shown are formed by lithography and etching, and titanium is formed by a sputtering method. Aluminum having a thickness of 1 μm is formed thereon. Subsequently, pad electrodes (not shown) of the primary coil and the secondary coil are formed by lithography and etching, and a silicon nitride film 8 having a thickness of 1 μm is formed by a CVD method. This silicon nitride film 8 serves as a surface protective film of the thin film transformer. Subsequently, a pad electrode portion (not shown) is opened by lithography and etching ((c) in the figure).

The spiral primary coil and secondary coil coil conductors 4 and 6 formed in this way are formed in the groove 3 so that the primary coils are opposed to both sides of the secondary coil. And the secondary coil overlap each other, the transmission efficiency is improved, the mutual inductance is increased, the Q value is improved, and the energy conversion efficiency can be increased as described above.
In this structure, the length of the coil conductors 4 and 6 in the substrate vertical direction (vertical direction in the drawing) (corresponding to the width of the coil conductors 4 and 6) is increased to overlap the primary coil and the secondary coil. As a result, the Q value can be improved without increasing the area. Further, by increasing the length of the coil conductor in the direction perpendicular to the substrate, the cross-sectional areas of the primary coil and the secondary coil are increased, and the coil resistance is also reduced.

FIGS. 3A and 3B are configuration diagrams of a thin film transformer according to the second embodiment of the present invention. FIG. 3A is a plan view of the main part, and FIG. 3B is cut along the X1-X1 line of FIG. It is principal part sectional drawing. The figure (a) is the principal part top view cut | disconnected by the X2-X2 line | wire of the figure (b).
The difference from FIG. 1 is that a copper film to be the first coil conductor 9 is also formed at the bottom of the groove 3. By doing so, the resistance value of the first coil conductor 9 can be made smaller than that of the first coil conductor 4 of the thin film transformer of FIG. 1, and the energy conversion efficiency can be increased.

4A to 4C are process diagrams showing a method of manufacturing the thin film transformer of FIG. 3, and FIGS. 4A to 4C are cross-sectional views of main part manufacturing processes shown in the order of processes.
A silicon oxide film 2 having a thickness of 3 μm is formed on the surface side of the silicon substrate 1 by CVD, and grooves 3 having a width of 2.4 μm, a spacing of 1 μm, and a depth of 2.5 μm are formed in a spiral shape by lithography and etching. Subsequently, copper having a thickness of 0.5 μm is formed on the silicon oxide film 2 by a sputtering method, copper other than the groove 3 is removed by a CMP method, and the side wall and the bottom copper in the groove 3 are left, A first coil conductor 9 constituting the primary coil is formed (FIG. 1A).
Next, the surface is covered with a silicon oxide film 5 having a thickness of 0.2 μm by a CVD method, and copper having a thickness of 0.5 μm is formed on the silicon oxide film 5 by a sputtering method. The concave portion 10 covered with the silicon oxide film 5 is filled with copper, and the silicon oxide film 5 is used as a stopper to remove the copper other than the copper filled in the concave portion 10 by CMP. The second coil conductor 6 is formed (FIG. 2B).

  Next, a silicon oxide film 7 having a thickness of 1 μm is formed by CVD, contact holes (not shown) of the primary coil and the secondary coil are formed by lithography and etching, titanium is formed by sputtering, Aluminum having a thickness of 1 μm is formed thereon. Subsequently, pad electrodes (not shown) of the primary coil and the secondary coil are formed by lithography and etching, and a silicon nitride film 8 having a thickness of 1 μm is formed by a CVD method. This silicon nitride film 8 serves as a surface protective film of the thin film transformer. Subsequently, a pad electrode portion (not shown) is opened by lithography and etching ((c) in the figure).

1A and 1B are configuration diagrams of a thin film transformer according to a first embodiment of the present invention, in which FIG. 1A is a plan view of a main part, and FIG. 1B is a cross-sectional view of a main part taken along line X1-X1 of FIG. It is process drawing which shows the manufacturing method of the thin film transformer of FIG. 1, (a)-(c) is principal part manufacturing process sectional drawing shown to process order It is a block diagram of the thin film transformer of 2nd Example of this invention, (a) is a principal part top view, (b) is principal part sectional drawing cut | disconnected by the X1-X1 line | wire of (a). FIGS. 4A to 4C are process diagrams illustrating a method for manufacturing the thin film transformer of FIG. 3, and FIGS. It is a block diagram of the conventional thin film transformer, (a) is a perspective view, (b) is principal part sectional drawing.

Explanation of symbols

1 Silicon substrate 2, 5, 7 Insulating film (the same number is given to the silicon oxide film)
3 Grooves 4 and 9 First coil conductor 6 Second coil conductor 8 Silicon nitride film 10 Recessed portion T pitch

Claims (10)

A supporting substrate; a first insulating film formed on the supporting substrate; an elongated groove formed in the first insulating film; a first coil conductor formed on a sidewall of the groove; And a second coil conductor formed so as to face the first coil conductor with a second insulating film interposed therebetween. The thin film transformer according to claim 1, wherein the support substrate is a semiconductor substrate or an insulating substrate. The thin film transformer according to claim 1, wherein the planar shape of the groove is a spiral shape. The thin film transformer according to claim 1, wherein the first coil conductor is formed on a side wall and a bottom surface of the groove. 3. The thin film transformer according to claim 1, wherein the insulating film is any one of a silicon oxide film, a polyimide film, and a resist film. The thin film transformer according to any one of claims 1 to 4, wherein a pad electrode is connected to each end of the first coil conductor and the second coil conductor. Forming a first insulating film on the support substrate and forming an elongated groove in the first insulating film;
Forming a first metal film on the first insulating film including the inside of the trench;
Removing the first metal film by anisotropic etching, leaving the first metal film on the side wall of the groove, and forming a first coil conductor;
Coating the first metal film with a second insulating film leaving the groove;
Covering the second insulating film with a second metal film and filling the groove with the second metal film;
Forming the second coil conductor by leaving the second metal film filled in the groove by a CMP method using the second insulating film as a stopper layer, and removing the second metal film at other locations;
A method of manufacturing a thin film transformer, comprising: Forming a first insulating film on the support substrate and forming an elongated groove in the first insulating film;
Forming a first metal film on the first insulating film including the inside of the trench;
Forming the first coil conductor by removing the third metal film at other locations while leaving the first metal film on the sidewall and bottom of the groove by CMP using the first insulating film as a stopper;
Coating the surface and the first metal film in the groove with a second insulating film;
Covering the second insulating film with a second metal film and filling the groove with the second metal film;
Leaving the second metal film filled in the groove by CMP and removing the second metal film in other locations to form a second coil conductor;
A method of manufacturing a thin film transformer, comprising: 9. The method of manufacturing a thin film transformer according to claim 7, wherein the supporting substrate is a semiconductor substrate, and the first insulating film and the second insulating film are silicon oxide films. After forming the second coil conductor, the surface is covered with a third insulating film, a contact hole is formed in the third insulating film, and contacts the end of the first coil conductor and the end of the second coil conductor. The method for manufacturing a thin film transformer according to any one of claims 7 to 9, further comprising a step of forming a pad electrode connected through a hole.

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