JPH06267775A - Manufacture of plate-type magnetic element - Google Patents

Abstract

PURPOSE:To provide a method for easily manufacturing a plane-type magnetic element excellent in property. CONSTITUTION:The manufacturing method has a process for forming a magnetic film 3 and an insulation film 4 on foundation substrates 1, 2, a process for forming foundation conductor film patterns 5, 6 which are wider than a line of a spiral coil 9 to be formed on the insulation film 4 or a process for forming a plating auxiliary electrode 12 electrically connected to the spiral coil 9 to be formed on the insulation film 4 through a contact hole, a process for forming an insulation film pattern 7 at a position corresponding to a space of the spiral coil 9 to be formed, a process for forming the spiral coil 9 by plating the foundation conductor film patterns 5, 6 with a coil conductor, and a process for forming an insulation film 10 and a magnetic film 11 on the spiral coil 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a planar magnetic element such as a planar inductor or a planar transformer.

[0002]

2. Description of the Related Art In recent years, miniaturization of various electronic devices has been actively promoted with the progress of integrated circuit technology typified by LSI. However, the tendency of the volume ratio of the power supply section in the entire device to increase has become remarkable. This is because the miniaturization and integration of magnetic components such as inductors and transformers, which are essential for the power supply, are significantly delayed compared to other components. recent years,
In order to solve this problem, a flat type magnetic element in which a flat coil and a magnetic material are combined has been proposed, and studies for improving its performance are being made.

Conventionally known planar inductors have a structure in which both sides of a spiral planar coil are sandwiched by insulating layers, and these both sides are sandwiched by magnetic materials. Similarly, as the plane transformer, a spiral side flat coil on the primary side and a spiral side flat coil on the secondary side are formed through an insulating layer, both sides of which are sandwiched by insulating layers, and both sides are made of a magnetic material. A sandwiched structure is known. The spiral plane coil may be composed of one layer of spiral coil conductor, or may be formed of two layers of spiral coil conductors formed on both surfaces of the insulating layer and connected so that the generated magnetic fields are the same.

Further, in order to further miniaturize the planar magnetic element, it is also considered to manufacture it by using a thin film process similar to the semiconductor manufacturing process. Of this process, forming a planar coil is an important step. The shape of the plane coil is preferably spiral as described above. This is because the use of the spiral coil increases the inductance, resulting in a higher quality factor Q of the element. According to Kawabe et al.
The inductance L of the spiral coil-magnetic film laminated type planar inductor is expressed by the following equation (“Planar”).
Inductor "; K. Kawabe et a
l. , IEEE Trans. Mag. Vol. 20,
No. 5,1984, pp. 1804).

[0005]

[Equation 1]

As is clear from this equation, the inductance L is proportional to the square of the number of turns N. Therefore, in order to obtain a practical level of inductance L, it is necessary to increase the number of turns N, and as a result, the total length of the spiral coil becomes long.

In order to obtain a spiral coil having a high quality factor, it is preferable to set some parameters to optimum values when manufacturing the coil. Important parameters are (1) coil film thickness, (2) coil line width / space width, (3) coil electrical resistance, (4) spiral coil outer dimensions, (5) planar inductor outer dimensions. And so on. For parameters other than (2), optimum conditions are almost determined according to the operating frequency of the coil. Therefore, the optimal relationship between the line width (δ) of the coil and the space width (s) of (2) will be described below.

5 (a) and 5 (b) respectively show a predetermined inductance (in a plane) in which the horizontal axis represents the line width (δ) and the vertical axis represents the space (s) width of the spiral coil forming the planar inductor. It is a figure which shows the conditions which can obtain L) and coil resistance (R). (A) in the figure is the product of magnetic permeability of magnetic material and thickness of magnetic material μ _s · t = 100
0 μm, (b) is the case of μ _s · t = 5000 μm. In each case, the dimension w of one side of the outer shape of the magnetic material is 5 mm, and the dimension a _o of one side of the outer shape of the spiral coil.
= 5 mm (equal to the outer dimension w of the magnetic body), the dimension a _i of one side of the spiral coil a _i = 0.2 mm, the number of turns of the spiral coil N = 10, the thickness of the coil conductor t _c = 1
0 μm, gap between magnetic bodies g = 12 μm. Here, the practical line / space (δ / s) range of the coil is Nδ + (N−1) s ≦ (w−a _i ) / 2. Under the above conditions, 10δ + 9s ≦ 2400 μm.

As is apparent from FIG. 5, the inductance L changes variously depending on the values of δ and s. On the other hand, the coil resistance R decreases as s decreases and δ increases. That is, the influence of δ and s is more remarkable in R than in L.
Since the Q value of the inductor is proportional to L / R, in order to increase it, δ and s are determined in the vicinity of s → 0 (or δ / p → 1, where p is the coil pitch and p = δ + s). Is important.

FIG. 6 shows the δ / p dependence of L / R. The vertical axis is L / R normalized by L / R (δ / p → 1), that is, the value of L / R when δ / p approaches 1. Further, in this figure, the outer dimensions of the magnetic body: w = 1 to 5 mm, the inner dimensions of the spiral coil: a _i = 0.2 mm, the outer dimensions of the spiral coil: a _o = 0.9 w, and the transmittance and thickness of the magnetic body. Product of: μ _s · t = 10 ³ -10
^Four μm

The area containing all the values obtained by calculation for the various cases of is shown by the shaded area. L / R is maximum when δ / p is 1, and decreases when δ / p becomes smaller. From this fact, similar to the conclusion of FIG. 5, in order to obtain a planar inductor with a high Q value, δ / p = 1
It is important to determine the coil line width (δ) / space width (s) in the vicinity.

On the other hand, the coil of the planar inductor
Thickness should be at least the frequency band used and the coil conductor
To the extent of skin depth determined by the electrical resistance of the material
Must be set. This skin depth d is generally
It is represented by a formula. d = (ρ / πμf)^1/2  Where ρ is the specific resistance, μ is the relative permeability, and f is the frequency.
It

FIG. 7 shows the relationship between the specific resistance of the coil conductor and the skin depth, using the operating frequency as a parameter. Figure 7
As shown in, the skin depth has a positive correlation with the resistivity of the coil. Therefore, if the specific resistance of the coil conductor is reduced, the required coil film thickness can be reduced, so that the aspect ratio (coil space width / coil space width /
The coil film thickness) can be reduced.

For example, when Al having a specific resistance of 2.7 μΩ · cm is used as the coil conductor material, the thickness of the coil conductor is 20 to 30 μm at the operating frequency of several tens MHz. If the thickness of the coil conductor is set to about 30 μm and the space width of the coil is reduced to obtain a Q value close to the theoretical value, the aspect ratio of the groove in the space portion is 10 to 10
It will be 0.

At present, etching a conductive film with such a high aspect ratio is a chemical etching technique (CD
Both E and RIE) and physical etching techniques (ion beam etching) are difficult. Also, as the aspect ratio of the coil space formed by etching becomes higher, it becomes more difficult to fill the insulating film. For example, in a normal chemical vapor deposition method (CVD method) or physical vapor deposition method (sputtering method or vacuum deposition method), when the aspect ratio of the coil space exceeds 2, it is not possible to fill the insulating film. It will be possible.

Therefore, if Cu having a specific resistance of 1.7 μΩ · cm can be used as the coil conductor material, the requirement for the aspect ratio can be reduced. However, it is not possible to form a spiral coil by selectively etching Cu having a large film thickness using a photolithography technique.

A problem also occurs when the spiral coil made of Cu is formed by using the electrolytic plating method.
Conventionally, the following method has been used to form a spiral coil using an electrolytic plating method. First, a magnetic film and an insulating film are formed on a base substrate, and a base conductor film and an insulating film pattern corresponding to a coil space are formed on the insulating film. Then, the substrate on which the base conductor film serving as one of the electrodes is formed and the counter electrode are immersed in an electrolytic bath, a voltage is applied between the electrodes, and a conductor made of Cu is formed by electrolysis. After that, the insulating film pattern in the coil space portion is removed, and the underlying conductor film in the coil space portion is removed by ion milling or the like to form a spiral coil, and the insulating film is filled again. However, in this case, when the aspect ratio of the coil space exceeds 2, it becomes impossible to fill the insulating film.

A magnetic film and an insulating film are formed on the underlying substrate, and an underlying conductor film pattern having the same width as the line width of the spiral coil and an insulating film pattern corresponding to the coil space are formed on the insulating film. Then, a spiral coil made of Cu is formed by electrolysis. In this case, it is not necessary to fill the insulating film again. However, as described above, if the number of turns of the coil is increased to obtain a practical level of inductance, the total length of the coil becomes longer. In this case, since the resistance of the underlying conductor film pattern is large, the voltage drop is remarkable at the position farther from the contact point with the electrode from the power supply. As a result, the plating growth rate varies depending on the position of the underlying conductor film pattern, making it difficult to make the plating film thickness (coil film thickness) uniform over the entire length of the coil.

For example, as the underlying conductor film, Cu (0.5 μm)
m) / Nb (0.1 μm), line width 20 μm,
When a spiral coil made of Cu having a total length of 87 mm and a target thickness of 4 μm is formed, the film thickness variation is about 10%. Furthermore, when the total length is 120 mm, the film thickness variation is less than 20%. When the spiral coil has a large variation in film thickness as described above, the magnetic flux distribution of the planar magnetic element becomes non-uniform, and further, a loss is increased due to a local demagnetizing field of the upper magnetic film.

[0020]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method capable of manufacturing a planar magnetic element having good characteristics by a very simple process.

[0021]

According to the method of manufacturing a flat magnetic element of the first invention of the present application, a step of forming a magnetic film and an insulating film on a base substrate and a line width of a flat coil to be formed are used. A step of forming a wide base conductor film pattern, a step of forming an insulating film pattern at a position corresponding to the space of the plane coil to be formed, and a coil conductor being plated on the base conductor film pattern to form a plane coil. The method is characterized by including a step of forming and an step of forming an insulating film and a magnetic film on the planar coil.

In the method of manufacturing a flat magnetic element according to the second aspect of the present invention, a step of forming a magnetic film and an insulating film on a base substrate and a plating auxiliary electrode for conducting a desired portion of a base conductor film pattern to be formed are provided. A step of forming, an step of forming an insulating film and selectively etching to form a contact hole, and a step of forming a base conductor film pattern connected to the plating auxiliary electrode through the contact hole on the insulating film, A step of forming an insulating film pattern in a portion corresponding to the space of the planar coil to be formed, a step of plating a coil conductor on the underlying conductor film pattern to form a planar coil, an insulating film on the planar coil, and And a step of forming a magnetic film. Hereinafter, the method of the first invention of the present application will be described in more detail.

First, an underlying conductor film pattern having a width wider than the line width of the planar coil is formed on the insulating film formed on the magnetic film on the underlying substrate so as to correspond to the planar coil to be formed. The substrate is not particularly limited, and a semiconductor substrate such as Si or GaAs, an insulating substrate or the like is used. The magnetic film may be formed on the surface of the semiconductor substrate via an insulating film, or may be formed directly on the insulating substrate. The magnetic film is preferably formed of various magnetic alloys by a thin film forming technique such as sputtering or vapor deposition. The buffer layer may be formed before the magnetic film is formed. Further, an insulating film is formed on this magnetic film.

Next, an underlying conductor film pattern wider than the line width of the plane coil to be formed is formed. The material of the base conductor film is appropriately selected according to the conductor material forming the planar coil. The base conductor film may be a single layer or a plurality of layers. The width of the underlying conductor film pattern is preferably as wide as possible than the line width of the flat coil to be formed. This is because the larger the width of the underlying conductor film pattern, the larger its cross-sectional area and the smaller its electrical resistance.

Next, an insulating film pattern is formed at a position corresponding to the space of the planar coil to be formed. The insulating film formed corresponding to the coil space preferably has a small relative permittivity in order to reduce the line capacitance of the coil. Examples of the material of the insulating film include various oxides, nitrides, fluorides, fluororesins, hydrocarbon-based polymer compounds, polysilane and the like. A typical material is SiO ₂ ,
Examples include Si _x N _y , CaF ₂ , polyimide, and Cytop. Examples of the method for forming the insulating film include a vapor deposition method such as a CVD method and a sputtering method, and a method of applying an insulating material using a spinner and thermally curing it. The insulating film thus formed is patterned so as to form a space for the planar coil. As a patterning method, it is preferable to use an etching method having large anisotropy. Specifically, the chemical dry etching method (CD
E), reactive ion etching method (RIE), ion beam etching method and the like.

Further, a coil conductor is plated on the underlying conductor film pattern to form a planar coil. Examples of the conductor material forming the coil include Cu, Cu alloys, Au, Au alloys, Ag, and Ag alloys that can be electroplated, but are not limited thereto.

Finally, an insulating film and a magnetic film are formed on the plane coil. This insulating film needs to be thick enough to insulate the coil from the magnetic film. The thickness differs depending on the insulating film material. For example, when SiO ₂ is used, a thickness of about 1 μm is suitable when the operating voltage is 20V. The upper magnetic film is formed similarly to the lower magnetic film.

As described above, in the first invention of the present application, since the underlying conductor film pattern having a width wider than the line width of the planar coil to be formed is formed, its cross-sectional area becomes large and the electric resistance becomes larger than that of the conventional one. It is getting smaller. Therefore, at the time of electrolytic plating, the voltage drop is relatively small even at the position away from the contact point with the electrode from the power supply, and the film thickness variation of the plating film thickness (coil film thickness) can be reduced over the entire length of the coil. As a result, the magnetic flux distribution of the obtained planar magnetic element can be made uniform, and an increase in loss due to a local demagnetizing field of the upper magnetic film can be suppressed.

The method of the second invention of the present application will be described in more detail below. In the second invention of the present application, after the magnetic film and the insulating film are formed on the underlying substrate, the plating auxiliary electrode is formed so as to be electrically connected to a desired portion of the underlying conductor film pattern to be formed, and then the insulating film is formed. , Selectively etching to form contact holes. Next, an insulating film pattern, a plane coil, an insulating film and a magnetic film are sequentially formed in a portion corresponding to the space of the underlying conductor film pattern and the plane coil.

As described above, the plating auxiliary electrode is formed so as to be electrically connected to a desired portion of the underlying conductor film pattern to be formed. By providing such a plating auxiliary electrode, a voltage can be supplied to a plurality of locations of the underlying conductor film pattern during electrolysis, so that the voltage drop can be further reduced as compared with the first invention of the present application.
Although only one plating auxiliary electrode may be formed, it is preferable to form a plurality of electrodes. .

By using the method of the present invention as described above, it is possible to reduce the requirement for the aspect ratio of the coil space by forming a plane coil made of a conductive material having a low specific resistance by using the electrolytic plating method. Since the variation in film thickness can be reduced, it is possible to manufacture a flat magnetic element having excellent characteristics.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 FIGS. 1A to 1D show a manufacturing process of a planar inductor in this example.

After forming the thermal oxide film 2 on the Si substrate 1,
The lower magnetic film 3 is formed by rf magnetron sputtering. A SiO ₂ film 4 is formed on the lower magnetic film 3. On this SiO ₂ film 4, a Nb film 5 having a film thickness of 0.1 μm and a Cu film 6 having a film thickness of 0.55 μm are formed. The underlying conductor film is patterned by photolithography to have a spiral shape corresponding to the spiral coil to be formed, and the line width of the spiral coil (20 μm
m), a 35 μm wide underlying conductor film pattern is formed (FIG. 1A).

Next, the Cytop film 7 is formed on the entire surface by the CVD method. A resist 8 is formed on the cytop 7 so as to correspond to the space of the spiral coil to be formed. Using this resist 8 as a mask, the CYTOP film 7 is selectively etched by RIE to obtain a width of 20 μm.
A Cytop film pattern forming a coil space of m is formed to expose a part of the Cu film 6 (FIG. 1B).

Then, a Cu film 9 having a line width of 20 μm, which constitutes the spiral coil, is formed by electrolytic plating. The total length of the spiral coil formed in this embodiment is 1
It is 20 mm (FIG. 1 (c)).

Further, after removing the resist 8, a SiO ₂ film 10 is formed on the entire surface and is etched back to be flattened. Finally, the upper magnetic film 11 is formed by rf magnetron sputtering to manufacture a planar inductor (FIG. 1 (d)). The film thickness variation of the spiral coil formed by the method of the present embodiment is 8% or less, which can be significantly reduced from the conventional film thickness variation of less than 20%. Example 2 A manufacturing process of a planar inductor in this example will be described with reference to FIGS.

After forming the thermal oxide film 2 on the Si substrate 1,
The lower magnetic film 3 is formed by rf magnetron sputtering. A SiO ₂ film 4 is formed on the lower magnetic film 3. On the SiO ₂ film 4, Al is formed as a conductor film for a plating auxiliary electrode and patterned into a predetermined shape by photolithography to form four plating auxiliary electrodes 12 (FIG. 2A).

Next, a SiO ₂ film 13 is formed by the CVD method and selectively etched by photolithography to electrically connect the plating auxiliary electrode 12 and the underlying conductor film pattern formed in the next step. Contact holes are formed. An Nb film 5 having a film thickness of 0.1 μm and a Cu film 6 having a film thickness of 0.55 μm are formed thereon. These underlying conductor films are patterned by photolithography,
A ground conductor film pattern having a spiral shape corresponding to the spiral coil to be formed and having a width of 35 μm, which is wider than the line width (20 μm) of the spiral coil, is formed (FIG. 2B).

Next, the Cytop film 7 is formed on the entire surface by the CVD method. A resist 8 is formed on the cytop film 7 so as to correspond to the space of the spiral coil to be formed.
To form. Using this resist 8 as a mask, the CYTOP film 7 is selectively etched by RIE to obtain a width 20
A Cytop film pattern that forms a coil space of μm is formed to expose a part of the Cu film 6 (see FIG. 2).
(C)).

Then, a Cu film 9 having a line width of 20 μm, which constitutes the spiral coil, is formed by electrolytic plating. The total length of the spiral coil formed in this embodiment is 1
It is 20 mm (FIG. 2 (d)).

Further, after removing the resist 8, a SiO ₂ film 10 is formed on the entire surface and is etched back to be flattened. Finally, the upper magnetic film 11 is formed by rf magnetron sputtering to manufacture a planar inductor (FIGS. 2E and 3).

According to the method of the present embodiment, since the four plating auxiliary electrodes 12 are formed, the film thickness variation of the spiral coil is 5% or less, which can be further reduced as compared with the first embodiment. Even if only one plating auxiliary electrode is formed, a sufficient effect can be obtained.

Further, as shown in FIG. 4, if one end of the plating auxiliary electrode is formed so as to be connected to the internal terminal of the double spiral coil, the plating auxiliary electrode serves as a lead electrode of the internal terminal when used as an element. Can be used. Similarly, the plating auxiliary electrode can be used as a connecting electrode between the internal terminals of the double spiral coil. Further, when a part of the underlayer magnetic film is used as the auxiliary electrode, the manufacturing process can be reduced. It goes without saying that in the second invention of the present application, even when the underlying conductor film pattern has the same shape and width as the spiral coil pattern to be formed, there is an effect of suppressing the film thickness variation of the spiral coil.

[0044]

As described in detail above, according to the method of the present invention, it is possible to reduce the requirement for the aspect ratio of the coil space by forming a flat coil made of a conductive material having a low specific resistance by using the electrolytic plating method. Moreover, since the variation in film thickness of the plane coil can be reduced, a plane type magnetic element having excellent characteristics can be manufactured.

[Brief description of drawings]

1A to 1D are cross-sectional views showing a manufacturing process of a planar inductor according to a first embodiment of the present invention.

2A to 2E are cross-sectional views showing a manufacturing process of a planar inductor according to a second embodiment of the present invention.

FIG. 3 is an exploded perspective view of a planar inductor according to a second embodiment of the present invention.

FIG. 4 is a partially cutaway perspective view showing a planar inductor according to another embodiment of the present invention.

5 (a) and 5 (b) are predetermined inductances (L) in a plane in which the horizontal width is the line width (δ) of the spiral coil forming the planar inductor and the vertical axis is the space (s) width. FIG. 3 is a characteristic diagram showing conditions under which resistance (R) is obtained.

FIG. 6 is a characteristic diagram showing the δ / p dependence of L / R normalized by a value of δ / p → 1 for a planar inductor.

FIG. 7 is a diagram showing the relationship between the specific resistance of the coil and the skin depth with the operating frequency as a parameter.

[Explanation of symbols]

1 ... Si substrate, 2 ... Thermal oxide film, 3 ... Lower magnetic film, 4 ... S
iO ₂ film, 5 ... Nb film, 6 ... Cu film, 7 ... Cytop film, 8 ... Resist, 9 ... Cu film (spiral coil),
10 ... SiO ₂ film, 11 ... Upper magnetic film, 12 ... Plating auxiliary electrode, 13 ... SiO ₂ film.

Claims (2)

[Claims] 1. A step of forming a magnetic film and an insulating film on a base substrate, a step of forming a base conductor film pattern wider than a line width of a plane coil to be formed, and a space of the plane coil to be formed. A step of forming an insulating film pattern at a corresponding position; a step of plating a coil conductor on the underlying conductor film pattern to form a flat coil; and a step of forming an insulating film and a magnetic film on the flat coil. A method of manufacturing a planar magnetic element, comprising: 2. A step of forming a magnetic film and an insulating film on a base substrate, a step of forming a plating auxiliary electrode for conduction to a desired portion of a base conductor film pattern to be formed, and an insulating film being formed selectively. The step of etching to form a contact hole, the step of forming a base conductor film pattern connected to the plating auxiliary electrode through the contact hole on this insulating film, and the insulation corresponding to the space of the planar coil to be formed The method further comprises the steps of forming a film pattern, plating a coil conductor on the underlying conductor film pattern to form a planar coil, and forming an insulating film and a magnetic film on the planar coil. And a method for manufacturing a planar magnetic element.