JP2007165343A - Thin film transistor, and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film transistor having high withstand voltage of about 5 kv by forming a recess in a semiconductor substrate, and forming an intermediate insulating film between a lower coil and an upper coil so that the recess is filled with the film. <P>SOLUTION: In the thin film transistor 101, the lower coil 104 and the upper coil 106 are oppositely arranged on a silicon oxide film 103 formed on a silicon substrate 11 through an intermediate insulating film 105. The lower coil 104 is formed at a base of the recess 102 arranged in the silicon substrate 11. The intermediate insulating film 105 is formed so that the recess 102 is filled with the film. The upper coil 106 is formed on the intermediate insulating film 105. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thin film transformer formed by arranging a lower coil and an upper coil on a semiconductor substrate so as to face each other with an intermediate insulating film therebetween, and a method for manufacturing the same, and in particular, between the lower coil and the upper coil. The present invention relates to a thin film transformer that requires high withstand voltage and a method for manufacturing the same.

Conventionally, a photocoupler that transmits a signal using light by combining a light emitting element and a light receiving element is known. Recently, a coupler that transmits a signal using magnetism has been developed. Magnetic couplers have attracted attention because they have the same or better characteristics than photocouplers, and have the advantages of low power consumption, high data rate, and low price.

As shown in FIG. 6, the schematic configuration of a semiconductor device as a coupler using such magnetism includes driver IC chips 1 and 2 for encoding / decoding input / output signals, and converting input signals to magnetism and outputting them. A semiconductor chip 3 (hereinafter simply referred to as a thin film transformer) on which a thin film transformer that transmits to the side is formed. Normally, the driver ICs 1 and 2 and the thin film transformer 3 are thus formed on separate semiconductor chips.

In FIG. 6, 1 is an input side driver IC chip, 2 is an output side driver IC chip, 3 is a thin film transformer, 4 is a mold resin, 5 is an Au wire, and 6 is a lead.

An example of a conventional thin film transformer will be described with reference to FIG. FIG. 7A is a plan view, and FIG. 7B is a cross-sectional view taken along line AA in FIG. 7A.

In FIG. 7, 10 is a conventional thin film transformer, 11 is a silicon substrate, 12a, 12b and 12c are silicon oxide films, 13 is a lower side (primary side) coil, and 13a and 13b are lower side (primary side) coils. Both ends, 14 is an upper (secondary side) coil, and 14a and 14b are both ends of an upper (secondary side) coil.

In this example, the primary coil is used as the lower coil, and the secondary coil is used as the upper coil.

In the conventional thin film transformer 10, a lower (primary side) coil 13 is formed on a silicon oxide film 12 a formed on the surface of a silicon substrate 11. Further, an upper (secondary) coil 14 is formed through a silicon oxide film 12b formed thereon. Then, the top is covered with a silicon oxide film 12c as a cover film.

Here, the thicknesses of the silicon oxide films 12a, 12b and 12c and the thicknesses of the lower / upper (first and second) coils 13 and 14 made of Al are 2 μm, respectively.

In addition, the planar shape of the lower / upper (upper and lower) coils 13 and 14 is spiral to increase the inductance per coil length (or area), and is formed at positions corresponding to each other.

In such a thin film transformer 10, when a current flows through the lower (primary) coil 13, and the current is changed, the magnetic field around the lower (primary) coil 13 changes. Secondary side) An electromotive force is generated in the coil 14, and signal transmission using magnetism can be performed.

Next, a method for manufacturing the thin film transformer 10 as described above will be described with reference to FIG.

First, a silicon oxide film 12a (thickness 2 μm) is formed on the surface of the silicon substrate 11 by a thermal oxidation method.

Next, after a metal film (thickness 2 μm) made of Al is formed on the silicon oxide film 12a by sputtering, photolithography and etching are performed, and a predetermined spiral lower (primary) coil is formed. 13 is formed.

Next, a silicon oxide film 12b (thickness 2 μm) as an intermediate insulating film is formed thereon by a CVD method.

Thereafter, the upper (secondary side) coil 14 (thickness: 2 μm) is formed in the same manner as the lower (primary side) coil 13.

Next, a silicon oxide film 12c (thickness 2 μm) as a cover film is formed on the upper (secondary side) coil 14 by a CVD method.

Finally, both ends 13a and 13b of the lower (primary) coil 13 and both ends 14a and 14b of the upper (secondary) coil 14 can be electrically connected to form upper silicon oxide films 12b and 12c. The thin film transformer 10 is formed by removing by performing photolithography and etching. (For example, refer to Patent Document 1).

Japanese Patent No. 3141562 FIG.

However, in the thin film transformer as described above, since the intermediate insulating film between the lower coil and the upper coil is formed of a thin silicon oxide film of about 2 μm, a higher insulation breakdown voltage (for example, about 5 kv) is required. In the case of a thin film transformer, it is necessary to form the intermediate insulating film to be thicker (for example, about 20 μm).

The thin film transformer of the present invention is a thin film transformer formed by disposing a lower coil and an upper coil opposite to each other with an intermediate insulating film on a semiconductor substrate, and the lower coil is provided on the semiconductor substrate. The thin film transformer is formed at the bottom of the recess, the intermediate insulating film is formed so as to fill the recess, and the upper coil is formed on the intermediate insulating film.

A method for manufacturing a thin film transformer of the present invention is a method for manufacturing a thin film transformer formed by disposing a lower coil and an upper coil on a semiconductor substrate with an intermediate insulating film therebetween.
Forming a recess in the semiconductor substrate;
Forming a lower coil at the bottom of the recess;
Applying a liquid insulating material to the surface of the semiconductor substrate and filling the recesses, and then curing the liquid insulating material;
And a step of forming an upper coil on the intermediate insulating film.

  According to the thin film transformer and the method of manufacturing the same of the present invention, the recess is formed in the semiconductor substrate, and the recess is embedded to form the intermediate insulating film between the lower coil and the upper coil. Thus, an intermediate insulating film having sufficient thickness and flatness can be obtained with good moldability, and as a result, a thin film transformer having a high withstand voltage of about 5 kv can be formed.

  The present invention aims at forming a thin film transformer for high withstand voltage with an intermediate insulating film having a stable and sufficient thickness and flatness, and a recess is formed in a semiconductor substrate, and a lower coil is formed at the bottom thereof. Then, the intermediate insulating film is formed so as to fill the concave portion, and the upper coil is formed thereon.

An example of the thin film transformer of the present invention will be described with reference to FIGS. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line BB in FIG. FIG. 2 is an exploded perspective view of a main part of a connection portion between the lower coil and the lead portion. The same parts as those in FIG.

1 and 2, 101 is a thin film transformer of the present invention, 11 is a silicon substrate, 102 is a recess, 103 is a two-layer silicon oxide film as a first insulating film, 103a is a lower layer film, 103b is an upper layer film, 104 is a lower side (primary side) coil, 104a and 104b are lead portions having a bonding pad at the tip, 105 is an intermediate insulating film, 106 is an upper (secondary side) coil, and 106a and 106b have a bonding pad at the tip. A lead portion 107 is an opening provided in the upper layer film, and 108 is a silicon oxide film as a cover film.

In this example, the primary coil is used as the lower coil, and the secondary coil is used as the upper coil.

A recess 102 (depth 22 μm) is provided on the surface of the silicon substrate 11 of the thin film transformer 101 of the present invention. A silicon oxide film 103 as a first insulating film is formed on the surface of the silicon substrate 11 including the inner surface of the recess 102. The silicon substrate 11 is a silicon substrate having a crystal axis of (100).

A spiral lower (primary) coil 104 (thickness 2 μm) made of Al is formed at the bottom of the recess 102.

Here, the silicon oxide film 103 is composed of two layers of a lower layer film 103a (thickness 1 μm) and an upper layer film 103b (thickness 1 μm). A lead-out portion 104 a (thickness 2 μm) from the inner end of the lower (primary) coil 104 is formed between the lower layer film 103 a and the upper layer film 103 b, and the lower (primary side) coil 104. It is electrically connected to the lower (primary side) coil 104 through an opening 107 provided in the upper layer film 103b at the inner end position.

It should be noted that at the intersection of the lead portion 104a and the lower (primary) coil 104, the lower (primary) coil 104 is lifted by the thickness of the lead portion 104a, but there is no problem. Is a level.

An intermediate insulating film 105 made of polyimide resin is formed on the lower (primary) coil 104 so as to bury the concave portion 102.

Further, an upper (secondary side) coil 106 is formed on the intermediate insulating film 105.

Here, the depth of the recess 102 is determined by the thickness of the intermediate insulating film 105 determined by the depth between the lower (primary) coil 104 and the upper (secondary) coil 106. The depth is such a thickness that a breakdown voltage can be obtained. (When the depth of the recess 102 is 22 μm and the thickness of the lower (primary) coil 104 is 2 μm, the thickness of the intermediate insulating film 105 is 20 μm (= 22 μm−2 μm).

Moreover, the recessed part 102 has a side wall which has the taper opened upwards. The lead portions 104 a and 104 b from the inner end and the outer end of the lower (primary) coil 104 are drawn to the main surface of the silicon substrate 11 along the tapered side walls. Bonding pads are integrally formed at the leading ends of the lead portions 104a and 104b.

On the other hand, the lead-out portion 106 a at the inner end of the upper (secondary) coil 106 is positioned at the inner end of the upper (secondary) coil 106 on the surface of the intermediate insulating film 105 flush with the main surface of the silicon substrate 11. It is formed as a bonding pad. The lead-out portion 106b from the outer end is pulled out as it is to a predetermined position on the main surface of the silicon substrate 11, and a bonding pad is integrally formed at the tip portion.

A silicon oxide film 108 (thickness: 1 μm) is formed as a cover film having an opening only on the bonding pad.

In such a thin film transformer 101, when a current is passed through the lower (primary side) coil 104, and the current is changed, the magnetic field around the lower (primary side) coil 104 changes. Secondary side) An electromotive force is generated in the coil 106, and signal transmission using magnetism can be performed.

Next, a method for manufacturing the thin film transformer 101 as described above will be described with reference to FIGS. 3 and 4 are cross-sectional views schematically showing the manufacturing flow of the thin film transformer.

First, as shown in FIG. 3A, a recess 102 (depth 22 μm) is formed on the surface of the silicon substrate 11, and a lower insulating film of the first insulating film is formed on the surface of the silicon substrate 11 including the inner surface of the recess 102. A silicon oxide film (thickness 1 μm) as 103a is formed by a thermal oxidation method.

Here, as a method for forming the recess 102, anisotropic etching is performed on the silicon substrate 11 having a crystal axis of (100) using an alkaline etchant such as a KOH (potassium hydroxide) aqueous solution. According to this method, in addition to obtaining the bottom surface of the flat recess 102, a tapered side wall extending toward the opening portion due to the crystal orientation of the silicon substrate 11 is obtained. This tapered side wall is suitable for forming the lower (primary side) coil lead-out portion to the main surface of the silicon substrate 11.

Next, as shown in FIG. 3B, a lead-out portion 104a from the inner end of the lower (primary) coil 104 is formed on the lower layer film 103a. As a forming method, a metal film (thickness 2 μm) made of Al is formed by a sputtering method, and then photolithography and etching are performed to form a lead-out portion 104a having a bonding pad at the tip.

Next, as shown in FIG. 3C, a silicon oxide film (thickness: 1 μm) is formed as an upper film 103b of the first insulating film thereon by a CVD method. In this way, by forming the lead-out portion 104a between the lower layer film 103a and the upper layer film 103b, insulation from the coil portion of the lower (primary side) coil formed on the upper layer film 103b is secured. To do.

Next, as shown in FIG. 4D, the upper layer film 103b at the position of the inner end of the lower (primary) coil to be formed is subjected to photolithography and etching to form the opening 107. To do.

Next, as shown in FIG. 4E, the lower (primary) coil 104 is formed. As a forming method, a metal film (thickness: 2 μm) made of Al is formed by a sputtering method, and then photolithography and etching are performed to form a predetermined spiral coil.

At that time, the inner end of the lower (primary) coil 104 and the lead-out portion 104a are electrically connected through the opening 107 at the same time. Further, the lead-out portion from the outer end of the lower (primary) coil 104 is drawn to a predetermined position on the main surface of the silicon substrate 11 along the tapered side wall. Then, a bonding pad is integrally formed at the leading end of the drawer portion.

Next, as shown in FIG. 4 (f), a liquid polyimide resin is applied as an insulating material to the surface of the silicon substrate 11 to fill the recesses 102. In the coating method, the silicon substrate 11 is adsorbed and held by a spin coater (not shown), and a liquid polyimide resin is rotated while being dropped onto the surface of the silicon substrate 11, and the polyimide resin is utilized by utilizing the centrifugal force generated by the rotation. Is uniformly spread over the entire surface of the silicon substrate 11. A liquid polyimide resin is suitable for filling the inside of the recess 102.

Thereafter, the polyimide resin is thermally cured. In addition, although demonstrated here with the thermosetting polyimide resin, the photosensitive polyimide resin may be sufficient.

Next, as shown in FIG. 5G, the intermediate insulating film 105 is formed by removing the cured polyimide resin to a height at which the concave portion 102 is buried, by CMP. As a result, the surface of the intermediate insulating film 105 and the main surface of the silicon substrate 11 are substantially flush.

Next, as shown in FIG. 5H, the upper (secondary) coil 106 is formed. As a forming method, a metal film (thickness: 2 μm) made of Al is formed by a sputtering method, and then photolithography and etching are performed to form a predetermined spiral coil.

Here, the lead-out portion 106 a at the inner end of the upper (secondary) coil 106 is formed as a bonding pad on the surface of the intermediate insulating film 105 as it is. Then, the lead-out portion from the outer end is pulled out to a predetermined position on the main surface of the silicon substrate 11 that is substantially flush. And the bonding pad is integrally formed in the front-end | tip part.

Finally, as shown in FIG. 5I, a silicon oxide film 108 (thickness 1 μm) as a cover film having only the bonding pad portion opened is formed by the CVD method, and the thin film transformer 101 is formed. .

In the above description, the lower (primary) coil and the upper (secondary) coil are formed by depositing a metal film on the surface of the silicon substrate 11 by sputtering, followed by photoresist and etching, and patterning. Explained how to do. However, in the case where it is difficult to apply a photoresist only by depositing only a metal film because the depth of the recess is deep, after depositing the metal film on the surface of the silicon substrate 11, the CVD method is used. A silicon oxide film or the like may be deposited on the metal film, and then patterned by applying a photoresist and an etching process.

In the above description, the sputtering method has been described as the method for forming the lower coil and the upper coil. However, it is needless to say that the present invention is not limited to this and a vacuum deposition method may be used. Moreover, although the method of removing the cured polyimide resin has been described by the CMP method, an etch back method may be used.

According to such a forming method, the liquid polyimide resin is formed on a flat surface without the need for multiple recoating steps and drying steps as compared with a method of recoating until a desired thickness is obtained. Stable thickness and flatness can be obtained. As a result, the thin film transformer 101 having a high withstand voltage of about 5 kv can be formed. Further, since all the bonding pads are formed on substantially the same plane, the bonding work at the time of assembly becomes easy.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a thin film transformer having an intermediate insulating film having a stable and sufficient thickness and flatness and requiring a high withstand voltage, and a manufacturing method thereof.

The top view and sectional drawing which show schematic structure of an example of the thin film transformer of this invention The principal part disassembled perspective view of the connection part of the lower coil and drawer | drawing-out part of the thin film transformer of this invention Sectional drawing which shows typically the manufacture flow of the thin film transformer of this invention Sectional drawing which shows typically the manufacture flow of the thin film transformer of this invention Sectional drawing which shows typically the manufacture flow of the thin film transformer of this invention Schematic configuration diagram of a semiconductor device as a coupler using magnetism A plan view and a cross-sectional view showing a schematic configuration of an example of a conventional thin film transformer

Explanation of symbols

1 Driver IC chip on the input side 2 Driver IC chip on the output side 3 Thin film transformer (semiconductor chip on which a thin film transformer is formed)
4 Mold resin 5 Au wire 6 Lead 10 Conventional thin film transformer 11 Silicon substrates 12a, 12b, 12c Silicon oxide film 13 Lower side (primary side) coils 13a, 13b Both ends 14 of lower side (primary side) coils Upper side (2 Secondary side) Coils 14a, 14b Both ends 101 of upper (secondary) coil Thin film transformer 102 of the present invention Recess 103 Silicon oxide film 103a as first insulating film Lower film 103b Upper film 104 Lower (primary) coil 104a, 104b Both ends 105 of the lower (primary) coil Intermediate insulating film 106 Upper (secondary) coils 106a, 106b Both ends 107 of the upper (secondary) coil Openings 108 Silicon oxide film as a cover film

Claims (12)

A thin film transformer formed by disposing a lower coil and an upper coil opposite to each other with an intermediate insulating film on a semiconductor substrate, wherein the lower coil is formed at the bottom of a recess provided in the semiconductor substrate. The thin film transformer is characterized in that the intermediate insulating film is formed so as to fill the recess, and the upper coil is formed on the intermediate insulating film. The thin film transformer according to claim 1, wherein the intermediate insulating film is made of polyimide resin. 3. The thin film transformer according to claim 1, wherein the semiconductor substrate is a silicon substrate having a crystal axis of (100). The concave portion has a tapered side wall extending toward the opening, and the lead-out portions from both ends of the lower coil are drawn to the main surface of the semiconductor substrate along the tapered side wall. 4. The thin film transformer according to claim 1, wherein the thin film transformer is characterized in that: When the lower coil is a spiral coil, the lower coil is formed on an insulating film formed of two layers, an upper layer film and a lower layer film, formed on the semiconductor substrate, and the inner end of the spiral coil. The lead-out portion is formed between the upper layer film and the lower layer film, and passes through the opening of the upper layer film provided at the position of the inner end of the spiral coil. The thin film transformer according to claim 4, wherein the thin film transformer is electrically connected to the thin film transformer. 6. The thin film transformer according to claim 4, wherein a wire bonding pad is integrally formed at a tip of each of the lower coil lead portion and the upper coil lead portion. A method of manufacturing a thin film transformer formed by arranging a lower coil and an upper coil opposite to each other with an intermediate insulating film on a semiconductor substrate,
Forming a recess in the semiconductor substrate;
Forming the lower coil at the bottom of the recess;
Applying a liquid insulating material to the surface of the semiconductor substrate and filling the recess, and then curing the liquid insulating material;
And a step of forming the upper coil on the intermediate insulating film. 8. The method of manufacturing a thin film transformer according to claim 7, wherein the intermediate insulating film is made of polyimide resin. In the method of forming the recess, the semiconductor substrate is a silicon substrate having a crystal axis of (100), and spreads toward the opening using anisotropic etching with an alkaline etchant such as a KOH (potassium hydroxide) aqueous solution. 9. The method of manufacturing a thin film transformer according to claim 7, wherein the thin film transformer is formed to have a tapered side wall. 10. The method of manufacturing a thin film transformer according to claim 9, wherein lead portions from both ends of the lower coil are led to the main surface of the semiconductor substrate along the tapered side wall. When the lower coil is a spiral coil, the lower coil is formed on an insulating film composed of an upper layer film and a lower layer film formed on the semiconductor substrate, and forming the insulating film Before the step of forming the lower coil,
First, forming the lower layer film,
Next, on the lower layer film, forming a conductor portion to be a lead portion from the inner end of the spiral coil;
Next, a step of forming the upper layer film thereon,
Next, a step of providing an opening at a position where an inner end of the spiral coil of the upper layer film is formed;
The method of manufacturing a thin film transformer according to claim 7, comprising: 12. The method of manufacturing a thin film transformer according to claim 10, wherein a wire bonding pad is integrally formed at a tip of each of the lower coil lead portion and the upper coil lead portion.

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