JP2001352040A - Semiconductor integrated circuit device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor integrated circuit device which obtains an inductor with a high Q-value, which suppresses eddy currents as an element which increases a coil resistance. SOLUTION: Firstly, a coil is divided into a plurality of coils. Consequently, local concentration of a magnetic field can be suppressed, and the coil resistance due to the eddy current can be reduced. Secondly, the coils are formed on different planes which are parallel to each other, and the resistivity of the coils themselves can be reduced. Although the two constitutions can be adopted independently of each other, the inductor having both constitutions can also be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar magnetic element used for various high-frequency components such as a choke coil for a switching power supply and a transformer.

[0002]

2. Description of the Related Art Recently, with the advent of the multimedia age, various portable electronic devices have been improved in the degree of integration of electronic circuits by LSI technology, the progress of component mounting technology, and the development of lithium batteries and nickel hydrogen batteries. With the advent of high-energy batteries, electronic devices have become more sophisticated, smaller,
Thinning and weight reduction are being promoted.

A switching power supply is used as a stabilizing power supply for the power supply of such electronic equipment. However, it is difficult to reduce the size and weight of such a switching power supply while maintaining high power conversion efficiency. And
Regarding the size, weight, and cost, the proportion of the total equipment in the apparatus is steadily increasing.
Therefore, recently, as a countermeasure, it has been considered to realize a reduction in size and weight by increasing the switching frequency of the power supply to enable use of power supply components such as small inductors, transformers, and capacitors.

When the switching frequency increases and reaches the GHz band, the absolute values of required inductance and capacitance become smaller assuming that the specifications of the circuit do not change. If an external component is used to cope with these factors, the parasitic capacitance and parasitic inductance associated with the connection between the IC and these elements cannot be ignored with respect to the capacitance and inductance of the external component. Therefore, in order to improve the accuracy of the IC, it is necessary to provide an inductor and a capacitor inside the IC.

[0005]

There is a Q factor (Quality Factor) as an index indicating the performance of an inductor.
This index is

[0006]

(Equation 1)

However, in order to obtain an inductor having a high Q value, it is necessary to increase L or reduce R. However, without increasing R, L
In order to increase, it is necessary to create a large area L,
The IC itself becomes large. In addition, the parasitic capacitance between the substrate and the conductor increases. Therefore, it is necessary to reduce R.

In view of the foregoing, it is an object of the present invention to reduce the high-frequency resistance of a coil and obtain an inductor having a high Q value.

[0009]

In order to solve the above-mentioned problems, the present invention relates to an inductor formed on an IC chip, in which irregularities are formed in the cross-sectional shape so as to increase the conductor surface length; In the inductor formed on the IC chip, the coil is divided into a plurality of parts and connected in parallel. In the inductor formed on the IC chip, the coil is formed on at least two or more different planes. In an inductor formed on an IC chip, a plurality of divided coils are formed on different planes.

[0010] The specific resistance at high frequencies of the coil constituting the inductor greatly depends on the conductor surface length of the coil cross section. Therefore, according to the above configuration, it is possible to increase the conductor surface length, and it is possible to suppress an increase in the specific resistance of the coil due to eddy current loss.

According to the above structure, by dividing the coil, the conductor surface area of the coil cross section can be further increased. In addition, it is possible to suppress components in the same plane as the coil forming surface, which is a main factor of the eddy current, and suppress an increase in coil resistance.

According to this, the component perpendicular to the coil forming surface is reduced as compared with the case where the magnetic flux distribution penetrating the coil is
In-plane components increase. This means that the component perpendicular to the coil forming surface of the eddy current increases and the component parallel thereto decreases. Since the eddy current loss is proportional to the square of the magnitude of the eddy current, the total eddy current loss is reduced. That is, the eddy current can be reduced by reducing the vertical magnetic flux component linked to the coil.

According to the present invention, not only the effect as described above can be obtained, but also the component perpendicular to the coil forming surface is reduced and the in-plane component becomes large as compared with the case where the magnetic flux distribution penetrating the coil is provided. . This means that the component of the eddy current perpendicular to the coil forming surface increases and the component parallel to the coil forming surface decreases. Since the eddy current loss is proportional to the square of the magnitude of the eddy current, the total eddy current loss is small. Therefore, the eddy current can be reduced by reducing the vertical magnetic flux component linked to the coil.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a detailed description will be given with reference to the drawings.

(First Embodiment) FIG. 1 is a plan view showing a first embodiment of the inductor of the present invention, and FIG. 2 is a sectional view taken along line AA '. As shown in FIG. 2, this inductor has a shape in which a central portion of a rectangular coil cross section is depressed, and the depth of the depressed portion is b.
This is smaller than the height H of the rectangle in the cross section of the inductor. This cross-sectional shape is formed by reflecting the surface shape of the interlayer insulating film formed below the wiring layer. Alternatively, the concavo-convex shape of FIG. 2 may be intentionally formed.

The effect of the sectional shape of the inductor will be described in comparison with the conventional coil structure shown in FIG. When an alternating current flows through the coil, the resistance increases due to the eddy current effect. The electric field inside the conductor due to the skin effect can be expressed by the following expression of the electric field strength at the position Z from the conductor surface.

[0017]

(Equation 2)

Δ: skin depth, μ: magnetic permeability of conductor,
σ: Conductivity of conductor, ω: Frequency of electric field In this equation, the imaginary part does not contribute to the electric field strength, and the effective value of the electric field is the real part. Assuming that the specific resistance at the conductor surface (Z = 0) is ρ, the effective specific resistance ρ _{Z at Z} is

[0019]

(Equation 3)

And becomes larger as Z increases.

Further, assuming that L> H in FIG. 2, the specific resistance ρ _{case2 of the} coil is:

[0022]

(Equation 4)

## EQU1 ## The term 2H + 2L indicates the conductor surface length of the coil surface. Here, when a current of 1 GHz is used for the wiring using aluminum, δ ≒ 3 μm, and the specific resistance greatly depends on the term of 2H + 2L. Comparing the specific resistances of the coils in the cross sections of FIG. 2 and FIG. 16, in the case of FIG. 2, the term of 2H + 2L in the above equation is 2
(2b + L + H)

[0024]

(Equation 5)

Only the specific resistance decreases. Where ρ _case1
Is the normal structure (Figure 16), ρ _case2 is the proposed structure (Figure 2)
Is the specific resistance.

Next, the effect obtained by the simulation for the first embodiment is shown in FIG. FIG. 3 shows that the material of the coil conductor is Al, the conductor width L is 10 μm, and the conductor thickness H is 1 μm.
m, the depth of the recess when the width a of the recess is 6 μm (b)
And the relationship between specific resistance. According to FIG. 3, since the specific resistance decreases in inverse proportion to the increase of b, the Q value of the inductor is greatly improved.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
FIG. 5 is a plan view of a coil divided into a plurality of parts according to the embodiment, and FIG. 5 is a cross-sectional view taken along line BB ′. In FIG. 5, the divided coils are illustrated as being in contact with each other on the opposing surfaces. However, in practice, each of the divided coils is located at a certain distance. 4 and 5, one coil is divided into three, but may be divided into two or four or more.

FIG. 6 shows the distribution of the magnetic field interlinking with the coil on the coil forming surface. The data in FIG. 6 is obtained by passing a current of 1 amp to a coil having a width of 10 μm, a distance between coils of 1 μm, a coil thickness of 2 μm, and a coil center distance of 8 μm. As shown in the figure, the magnetic field at the center of the coil has a maximum value,
It can be seen that the magnetic field becomes smaller toward the outside of the coil. It can also be seen that the magnetic field has a local maximum value in a certain portion of the coil. Since this magnetic field is a main cause of the generation of eddy current, the eddy current can be effectively suppressed by reducing the coil width.

Table 1 shows a comparison of the impedance between the inductor of FIG. 4 and the inductor of FIG.

[0030]

[Table 1]

As shown in Table 1, R _total is 2.9.
It can be seen that it is greatly improved from 6 to 2.60. As described above, the eddy current can be suppressed by dividing the coil.

(Third Embodiment) FIG. 7 shows a third embodiment of the present invention.
FIG. 8 is a plan view of a coil in which each of adjacent coils is formed on a plane different from each other, and FIG. 8 is a cross-sectional view taken along the line CC ′. FIG. 9 is a diagram showing the distribution of components of the eddy current in the direction parallel to the coil forming surface. FIG. 10 is a diagram showing the distribution of the lines of magnetic force of the coil shown in FIG.

In this embodiment, by alternately forming coil conductors on two planes having different heights, the magnetic flux distribution interlinking the coil changes as shown in FIG. Magnetic flux components are reduced, and the in-plane distribution is increased. As a result, the component of the eddy current perpendicular to the coil forming surface increases and the component parallel to the coil forming surface decreases. Since the eddy current loss is proportional to the square of the magnitude of the eddy current, the total eddy current loss is reduced. That is, the eddy current can be reduced by reducing the vertical magnetic flux component linked to the coil.

FIG. 9 showing the present embodiment shows, as an example, a structure in which Al coils having a width of 10 μm, a thickness of 2 μm, and a coil interval of 1 μm are alternately formed on two planes having a height difference of 2 μm. It is shown. Table 2 shows a comparison of impedance between the inductor having this cross-sectional structure and an inductor having a conventional cross-sectional structure.

[0035]

[Table 2]

As shown in FIG. 10, compared with the conventional structure,
A decrease in the component of the eddy current parallel to the coil forming surface is observed. Further, as shown in [Table 2], R _total was 2.94.
It can be seen that it has been improved from 2.75 to 2.75. This is because, as described above, in the present embodiment, by forming the components on different planes, the component perpendicular to the coil forming surface of the eddy current increases and the component parallel to the coil decreases, so that the entire coil It is considered that the eddy current is reduced.

(Fourth Embodiment) FIG. 11 shows a fourth embodiment of the present invention, in which a coil is divided into a plurality of parts and each of the divided coils is formed on a different plane. It is a figure and FIG. 12 is sectional drawing in DD '. In FIG. 12, the divided coils are drawn so as to be in contact at the corners,
In practice, each of the split coils is at some distance. Further, in FIGS. 11 and 12, one coil is divided into three, but may be divided into two, or four.
It may be divided or more.

In this embodiment, as in the second embodiment, since the conductor surface length becomes longer, it is expected that the effects of the second embodiment will be satisfied. In addition, two different heights
By alternately forming the coil conductors on the two planes, the magnetic flux distribution linked to the coil changes, the magnetic flux component perpendicular to the coil forming surface is reduced, and the in-plane distribution is increased. As a result, the component of the eddy current perpendicular to the coil forming surface increases and the component parallel to the coil forming surface decreases. Since the eddy current loss is proportional to the square of the magnitude of the eddy current, the total eddy current loss is reduced. That is, the eddy current can be reduced by reducing the vertical magnetic flux component linked to the coil.

FIG. 13 shows a distribution diagram of the magnetic field lines in the present embodiment. It can be seen that the lines of magnetic force are vertically asymmetric and the vertical component of the magnetic flux is small. Therefore, it is considered that the increase in the resistance value due to the eddy current is small.

An inductor having a sectional structure in which a coil having a coil width of 9 μm is divided into three parts as shown in FIG. 12 and formed on different planes, and an inductor having a conventional sectional structure as shown in FIG. Table 3 shows a comparison of the impedance, and FIG. 14 shows a comparison of the component of the eddy current in a direction perpendicular to the coil forming surface with the conventional structure.

[0041]

[Table 3]

As shown in FIG. 14, the peak value of the component of the eddy current in the direction parallel to the coil forming surface in the fourth embodiment is about 2/3, which is a large decrease. In addition, as shown in [Table 3], R _total
Has been improved from 2.96 to 2.45.
It can be seen that the embodiment is improved more than the embodiment. This is considered to be due to the fact that, in the present embodiment, not only the coils are divided but also formed on different planes, as described above.

As described above, by dividing the coil,
Since the conductor surface length increases, the specific resistance of the coil decreases. Furthermore, since the divided coils are formed on different planes, eddy currents can be suppressed, so that the resistance of the coils can be reduced, and a large reduction in coil resistance can be realized as a whole. .

FIG. 15 shows a method of manufacturing the inductor according to the fourth embodiment. First, as shown in FIG. 15A, the first coil 1 is patterned by patterning the same layer as the first wiring layer on the surface of the insulating film (first insulating film) on the semiconductor substrate.
0 is formed. Then, as shown in FIG.
A first interlayer insulating film 11 is formed on the coil 10 of FIG.

After the formation of the first interlayer insulating film 11, a contact hole 13 (through hole) is opened so that the end of the first coil is exposed. After the opening, the second coil 12 is formed by patterning the same layer as the second wiring layer on the surface of the first interlayer insulating film 11 as shown in FIG.
At this time, the contact hole 13 is filled with the same layer as the second wiring layer.

In this manufacturing method, the first coil is patterned using the same pattern mask as the first wiring layer, and the second coil is patterned using the same pattern mask as the second wiring layer. Therefore, it is possible to manufacture a semiconductor device having a structure in which an inductor is mounted on a semiconductor chip without increasing the number of steps.

[0047]

According to the present invention, the coil resistance can be suppressed, and a high Q value inductor can be obtained.

[Brief description of the drawings]

FIG. 1 is a top view of an inductor according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line AA ′ of FIG.

FIG. 3 is a view showing a specific resistance of the inductor of FIG. 1;

FIG. 4 is a top view of the inductor according to the second embodiment of the present invention.

FIG. 5 is a sectional view taken along the line BB ′ of FIG. 4;

FIG. 6 is a distribution diagram of a magnetic field interlinking a coil on a coil forming surface.

FIG. 7 is a top view of the inductor according to the third embodiment of the present invention.

FIG. 8 is a sectional view taken along the line CC ′ of FIG. 8;

9 is a diagram showing a component of an eddy current generated in the inductor shown in FIG. 8 in a direction parallel to a coil forming surface.

FIG. 10 is a view showing a distribution of magnetic lines of force of the inductor shown in FIG. 8;

FIG. 11 is a top view of the inductor according to the fourth embodiment of the present invention.

FIG. 12 is a sectional view taken along line DD ′ of FIG. 11;

FIG. 13 is a view showing a distribution of lines of magnetic force of the inductor shown in FIG. 11;

FIG. 14 is a diagram illustrating a component of an eddy current generated in the inductor illustrated in FIG. 11 in a direction parallel to a coil formation surface.

FIG. 15 is a diagram illustrating a method of manufacturing the inductor according to the fourth embodiment of the present invention.

FIG. 16 is a sectional view of a conventional inductor.

FIG. 17 is a view showing a distribution of magnetic lines of force of a conventional inductor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 1st coil 11 1st interlayer insulating film 12 2nd coil 13 Contact hole

Claims (7)

[Claims] 1. A semiconductor integrated circuit device, comprising: a semiconductor integrated circuit; and an inductor having an uneven surface formed to correspond to the unevenness of an upper surface of the semiconductor integrated circuit. 2. The inductor according to claim 1, wherein the inductor is formed with irregularities so as to have a large surface area.
13. The semiconductor integrated circuit device according to claim 1. 3. The semiconductor integrated circuit device according to claim 1, wherein the inductor is formed using a wiring layer having a multilayer wiring structure in the semiconductor integrated circuit. 4. A semiconductor integrated circuit device comprising: a semiconductor integrated circuit; and an inductor in which one coil is divided into a plurality of coils. 5. The semiconductor integrated circuit device according to claim 4, wherein each divided coil of the inductor is formed on at least two or more different planes. 6. The semiconductor integrated circuit device according to claim 5, wherein the inductor is formed on a plane different from an adjacent coil among the divided coils. 7. A step of forming a first conductor layer on a surface of a first insulating film formed on a semiconductor integrated circuit; and etching the first conductor layer to form a first wiring layer and a first wiring layer. Forming a second insulating film on the first wiring layer and the first coil; and forming the second insulating layer so that both end surfaces of the first coil are exposed. Forming a through hole in the film; forming a second conductor layer on the surface of the second insulating film; etching the second conductor layer to form a second wiring layer and a second coil Forming a first coil and connecting both ends of the first coil to the second coil. A method of manufacturing a semiconductor integrated circuit device, comprising: