Isolator

Abstract

To provide an isolator achieving an improvement in dielectric breakdown voltage between a primary side and a secondary side.SOLUTION: An isolator includes a first coil at a primary side, a second coil at a secondary side, a first insulating film, and a primary side conductor electrically connected to the primary side. The second coil is provided above the first coil, and magnetically coupled to the first coil. The first insulating film is provided on the first coil, and the second coil is embedded in the surface of the first insulating film, on a side opposite to the first coil. The primary side conductor is embedded in any position away from the second coil on the surface side of the first insulating film. The first insulating film has a plurality of island-shaped projections provided between the second coil and the primary side conductor, on the surface side. The plurality of island-shaped projections are disposed such that a creepage distance along the surface of the first insulating film, from the second coil to the primary side conductor in any direction, is longer than a direct distance therebetween in the direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments relate to an isolator. [Background technology]

[0002] In an isolator that transmits signals via magnetic coupling between two coils, it is important to maintain a high dielectric breakdown voltage between the primary and secondary sides. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-182223 Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiments provide an isolator with improved dielectric breakdown voltage between the primary side and the secondary side. [Means for solving the problem]

[0005] The isolator according to the embodiment includes a first coil on a primary side, a second coil on a secondary side, a first insulating film, and a primary conductor electrically connected to the primary side. The second coil is provided above the first coil and magnetically coupled to the first coil. The first insulating film is provided on the first coil, and the second coil is embedded in the surface of the first insulating film opposite the first coil. The primary conductor is embedded in the surface side of the first insulating film at a position spaced apart from the second coil. The first insulating film has a plurality of island-shaped protrusions provided between the second coil and the primary conductor on the surface side. The plurality of island-shaped protrusions are arranged so that the creepage distance along the surface of the first insulating film in any direction from the second coil to the primary conductor is longer than the linear distance in that direction from the second coil to the primary conductor. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an isolator according to an embodiment. [Figure 2] 1A and 1B are schematic diagrams illustrating the structure of an isolator according to an embodiment. [Figure 3] FIG. 1 is a schematic plan view showing an isolator according to an embodiment. [Figure 4] 5A to 5C are schematic cross-sectional views illustrating a manufacturing process of the isolator according to the embodiment. [Figure 5] FIG. 10 is a schematic plan view showing the structure of an isolator according to a modified example of the embodiment. [Figure 6] FIG. 10 is a schematic plan view showing an isolator according to another modified example of the embodiment. [Figure 7] FIG. 10 is a schematic cross-sectional view showing an isolator according to another modified example of the embodiment. [Figure 8] FIG. 10 is a schematic plan view showing an isolator according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments will be described with reference to the drawings. Identical parts in the drawings are assigned the same numbers, and detailed descriptions thereof will be omitted as appropriate, and different parts will be described. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc., are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing.

[0008] Furthermore, the arrangement and configuration of each part will be explained using the X-axis, Y-axis, and Z-axis shown in each figure. The X-axis, Y-axis, and Z-axis are mutually perpendicular and represent the X-direction, Y-direction, and Z-direction, respectively. In addition, the Z-direction may be explained as upward and the opposite direction as downward.

[0009] 1 is a schematic cross-sectional view showing an isolator 1 according to an embodiment. The isolator 1 includes a first coil 10 on the primary side, a second coil 20 on the secondary side, and a primary conductor 30 electrically connected to a primary circuit including the first coil 10. The isolator 1 transmits signals from the primary side to the secondary side via magnetic coupling between the first coil 10 and the second coil 20. The first coil 10 and the second coil 20 are spiral planar coils (see FIG. 3).

[0010] The primary conductor 30 is disposed at the same level as the second coil 20 in a direction from the first coil 10 to the second coil 20, for example, in the Z direction. The primary conductor 30 is provided, for example, as an external terminal for supplying a reference potential to the primary circuit.

[0011] 1, the isolator 1 further includes another primary-side conductor 40, a first insulating film 50, a second insulating film 60, a third insulating film 70, and a semiconductor substrate SS. The semiconductor substrate SS is made of, for example, silicon. The first insulating film 50, the second insulating film 60, and the third insulating film 70 are stacked on the semiconductor substrate SS.

[0012] The primary conductor 40 is provided at the same level as the first coil 10 in the Z direction. The primary conductor 40 is electrically connected to the first coil 10, for example, via wiring or a circuit (not shown) (see FIG. 7). The primary conductor 40 is electrically connected to the primary conductor 30 on the front surface side via a connecting conductor 35.

[0013] The first insulating film 50 is provided on the first coil 10. The first insulating film 50 is, for example, a silicon oxide film. The first insulating film 50 is provided between the first coil 10 and the second coil 20. The first insulating film 50 has a thickness that electrically insulates the second coil 20 from the first coil 10 and provides a desired dielectric breakdown voltage between the first coil 10 and the second coil 20. The first insulating film 50 extends between the primary side conductor 30 and the primary side conductor 40. The connecting conductor 35 is, for example, a contact plug that extends in the first insulating film 50. The connecting conductor 35 is, for example, a conductor containing a metal such as copper.

[0014] The second coil 20 is provided on the surface of the first insulating film 50 opposite to the first coil. The second coil 20 is, for example, embedded in the first insulating film 50. The second coil is, for example, a conductor containing a metal such as copper.

[0015] The second insulating film 60 is provided on the first insulating film 50. The second insulating film 60 covers the second coil 20 and the primary side conductor 30. The second insulating film 60 is, for example, a silicon oxide film. The second insulating film 60 may have a different composition from the first insulating film 50.

[0016] The third insulating film 70 is provided between the semiconductor substrate SS and the first insulating film 50. The third insulating film 70 is, for example, a silicon oxide film. The first coil 10 and the primary side conductor 40 are each embedded in the third insulating film 70 between the first insulating film 50 and the third insulating film 70. The first coil 10 and the primary side conductor 40 are, for example, conductors containing a metal such as copper.

[0017] 1, the first coil 10 and the primary side circuit (not shown) are electrically insulated from the second coil 20 on the secondary side by a first insulating film 50. The dielectric breakdown voltage between the primary side and the secondary side is ensured by widening the distance VD from the first coil 10 to the second coil 20 and the linear distance HD from the primary side conductor 30 to the second coil 20.

[0018] However, the breakdown voltage between the primary side and the secondary side decreases when an interface with low electrical resistance exists between the first insulating film 50 and the second insulating film 60. For example, if there is a defect such as the presence of foreign matter or mobile ions between the first insulating film 50 and the second insulating film 60 due to the manufacturing process, or a decrease in the breakdown voltage due to initial deposits during the formation of the second insulating film 60, the breakdown voltage between the primary side and the secondary side decreases.

[0019] For example, in insulating films deposited using chemical vapor deposition (CVD), initial deposits of several tens of nanometers in thickness may have different compositions and crystallinity, which may result in a decrease in dielectric breakdown voltage. Such initial deposition layers can be identified, for example, by the contrast of a transmission electron microscope (TEM) image of the insulating film cross section.

[0020] In contrast, in the isolator 1 according to the embodiment, a plurality of island-shaped protrusions IP are provided between the second coil 20 and the primary-side conductor 30. The island-shaped protrusions IP are provided, for example, on the surface of the first insulating film 50. This makes the creepage distance from the second coil 20 along the surface of the first insulating film 50 to the primary-side conductor 30 longer than the linear distance HD, thereby increasing the electrical resistance at the interface between the first insulating film 50 and the second insulating film 60.

[0021] 2 is a schematic diagram showing the structure of the isolator 1 according to the embodiment, and is a schematic plan view showing the shape and arrangement of the island-shaped protrusions IP in a plane parallel to the boundary between the first insulating film 50 and the second insulating film 60.

[0022] 2, the planar shape of the island-shaped protrusions IP is, for example, a regular hexagon. By arranging adjacent island-shaped protrusions IP in the closest proximity, a planar tessellation can be achieved in the area where multiple island-shaped protrusions are provided. Furthermore, the planar shape of the island-shaped protrusions according to the embodiment is not limited to this example, and may be, for example, a polygon other than a regular hexagon or a circle.

[0023] 3 is a schematic plan view showing the isolator 1 according to the embodiment, and is a schematic diagram showing the surface of the first insulating film 50. As shown in FIG.

[0024] As shown in FIG. 3, the second coil 20 is a spiral planar coil. The second coil 20 has connection pads 23 and 25 at both ends. The second coil 20 is electrically connected to an external circuit or another secondary coil, for example, via metal wires bonded to the connection pads 23 and 25. The first coil 10 is also a planar coil and has a shape similar to that of the second coil 20 below the second coil 20. The planar shape of the second coil 20 is not limited to a circle and may be, for example, a polygon.

[0025] The island-shaped protrusions IP are arranged, for example, in an area surrounding the second coil 20. The primary conductor 30 can be arranged at any of positions P1 to P3 outside the area where the island-shaped protrusions IP are arranged. The island-shaped protrusions IP can make the creepage distance from the second coil 20 to any of positions P1 to P3 where the primary conductor 30 is arranged longer than the linear distance HD therebetween. That is, as shown by the arrows in FIG. 3 , the creepage distance from the second coil 20 to each of positions P1 to P3 can be made longer than the linear distance HD in any direction along the surface of the first insulating film 50.

[0026] 4(a) to 4(c) are schematic cross-sectional views illustrating a manufacturing process of the isolator according to the embodiment, and are schematic views illustrating a process of forming island-shaped protrusions.

[0027] 4(a), after the second coil 20 is formed in the first insulating film 50, an etching mask EM is formed on the surface of the first insulating film 50. The primary side conductor 30 is formed in a portion not shown.

[0028] The etching mask EM is, for example, a photoresist. The etching mask EM is patterned, for example, by photolithography. In the region where the island-shaped protrusion IP is to be formed, the etching mask EM is patterned, for example, into a regular hexagon.

[0029] As shown in FIG. 4(b), the first insulating film 50 is selectively etched to form island-shaped protrusions IP. The first insulating film 50 is selectively removed by, for example, dry etching. During this process, the etching mask EM is also etched, and the island-shaped protrusions IP are formed into a shape having, for example, inclined side surfaces.

[0030] As shown in FIG. 4(c), the etching mask EM is removed. The etching mask EM is removed by, for example, ashing. The height of the island-shaped protrusion IP is, for example, smaller than the thickness TC of the second coil 20 in the Z direction. The inclination angle θ of the side surface of the island-shaped protrusion IP with respect to a plane including the bottom surfaces between adjacent island-shaped protrusions IP is, for example, larger than 45°. This allows the creepage distance SD along the surface of the first insulating film 50 to be increased.

[0031] The method for manufacturing the island-shaped protrusions IP is not limited to the above example. For example, fine island-shaped protrusions may be formed by roughening the surface of the first insulating film 50. For example, irregular and randomly shaped protrusions can be formed on the surface of the insulating film by liquid-phase etching or the like. Such a protrusion-recess structure preferably has a step of, for example, several hundred nanometers, and the area ratio of the protrusions is approximately 50%. A protrusion-recess structure having a step of several tens of nanometers is also effective, and in combination with the improvement in adhesion described below, a good dielectric breakdown voltage can be obtained.

[0032] 5(a) to 5(c) are schematic plan views showing the structure of an isolator according to a modified example of the embodiment. 5(a) and 5(b) are schematic views showing an example of the arrangement of island-shaped protrusions IP according to a comparative example. 5(c) is a schematic view showing an example of the arrangement of island-shaped protrusions IP according to the embodiment.

[0033] In the example shown in FIG. 5(a), island-shaped protrusions IP having a rectangular planar shape are arranged. The island-shaped protrusions IP are arranged, for example, at equal intervals in the X and Y directions. Therefore, linear short-circuit paths SPX and SPY exist between adjacent island-shaped protrusions IP in the X and Y directions, respectively. The short-circuit paths SPX and SPY do not intersect with any of the island-shaped protrusions IP. Therefore, the creepage distance along the short-circuit paths SPX and SPY is the same as the linear distance HD.

[0034] The example shown in Figure 5(b) shows an arrangement in which the island-shaped protrusions IP are arranged periodically in the X direction with their phases shifted. That is, the island-shaped protrusions IP are arranged so that the period of their arrangement in the X direction is shifted alternately in the Y direction. This eliminates the short-circuit paths SPY in the Y direction, but the short-circuit paths SPX in the X direction remain.

[0035] As shown in Fig. 5(c), polygonal island-shaped protrusions IP of different sizes may be arranged. That is, an island-shaped protrusion IP with a larger size in the Y direction is added to the arrangement shown in Fig. 5(b). This also makes it possible to eliminate short-circuit paths SPX in the X direction.

[0036] In this way, by arranging a plurality of island-shaped protrusions IP having polygonal planar shapes of different sizes, it is possible to realize an arrangement in which the creepage distance is longer than the linear distance HD in any direction.

[0037] FIG. 6 is a schematic plan view showing an isolator 2 according to another modified example of the embodiment. FIG. 6 is a schematic view showing the surface of a first insulating film 50. In this example, a plurality of second coils 20 are provided on the secondary side. The plurality of second coils 20 are connected in series, for example, via metal wires (not shown). The plurality of second coils 20 are also magnetically coupled to the plurality of first coils 10 arranged below. Furthermore, the second coils 20 may be connected to each other at their outermost peripheries, and may have the same or opposite winding directions.

[0038] 6 shows four second coils 20, but this is not meant to be limiting. The number of second coils 20 arranged on the secondary side is arbitrary, and at least two second coils 20 are provided.

[0039] As shown in Fig. 6, the primary conductor 30 is arranged to surround the plurality of second coils 20. A plurality of island-shaped protrusions IP (not shown) are provided between the primary conductor 30 and each of the second coils 20 (see Fig. 3). The island-shaped protrusions IP are arranged so that the creepage distance from each of the second coils 20 to the primary conductor 30 is longer than the linear distance therebetween in any direction.

[0040] For example, Fig. 8 is a schematic plan view showing an isolator 3 according to a comparative example. In the isolator 3, a plurality of grooves 50G are provided on the surface side of the first insulating film 50. The plurality of grooves 50G are provided between each of the plurality of second coils 20 and the primary conductor 30 so as to surround the plurality of second coils 20. Even with this configuration, the creepage distance from each of the second coils 20 to the primary conductor 30 can be made longer than the linear distance HD. However, providing the plurality of grooves 50G between each of the second coils 20 and the primary conductor 30 requires a large area therebetween.

[0041] In the isolator 2 according to the embodiment, a plurality of island-shaped protrusions IP can be provided without increasing the space between each of the second coils 20 and the primary conductor 30. Furthermore, the arrangement of the island-shaped protrusions IP does not depend on the shape and arrangement of the second coils 20 and the primary conductor 30. In other words, the island-shaped protrusions IP according to the embodiment are suitable for miniaturizing the isolator 2 and offer a high degree of freedom in arrangement.

[0042] 7 is a schematic cross-sectional view showing an isolator 2 according to another modified example of the embodiment, taken along line AA in FIG.

[0043] 7, the first insulating film 50 has a stacked structure including a first film 51, a second film 53, a third film 55, and a fourth film 57. The second insulating film 60 includes a first film 61, a second film 63, and a third film 65. The third insulating film 70 includes a first film 73 and a second film 75.

[0044] The first film 51 of the first insulating film 50 is, for example, a silicon carbonitride film (SiCN film) formed by using PCVD (Plasma Enhanced Chemical Vapor Deposition). The first film 51 is provided on the third insulating film 70. The first film 51 suppresses diffusion of metal atoms from the first coil 10 and the primary side conductor 40 into the first insulating film 50.

[0045] The second film 53 is, for example, a silicon oxide film formed by using CVD (Chemical Vapor Deposition). The second film 53 is provided on the first film 51. The second film 53 is located between the first coil 10 and the second coil 20, and has a thickness that can ensure a dielectric breakdown voltage therebetween. The second film 53 has a thickness in the Z direction of, for example, 5 micrometers or more.

[0046] The third film 55 is, for example, a silicon nitride film formed by PCVD. The third film 55 is provided on the second film 53. Furthermore, a fourth film 57 is provided on the third film 55. The fourth film 57 is, for example, a silicon oxide film formed by PCVD.

[0047] The second coil 20 is embedded in the fourth film 57. In the process of forming the second coil 20, the third film 55 functions as an etching stop film. That is, when a groove for embedding the second coil 20 and the primary side conductor 30 is formed in the fourth film 57, the third film 55 prevents over-etching that reaches the second film 53.

[0048] The first film 61 of the second insulating film 60 is provided on the first insulating film 50. The first film 61 is, for example, a SiCN film. The first film 61 suppresses diffusion of metal atoms of the second coil 20 and the primary side conductor 30.

[0049] The second film 63 is provided on the first film 61. The second film 63 is, for example, a silicon oxide film formed by using CVD. The second film 63 is formed so as to cover the second coil 20.

[0050] The third film 65 is provided on the second film 63 and the first film 61. The third film 65 is provided between the second coil 20 and the primary side conductor 30 so as to be in contact with the first film 61. The third film 65 is, for example, a silicon oxide film formed using PCVD.

[0051] The first film 73 of the third insulating film 70 is provided on the semiconductor substrate SS. The first film 73 is, for example, a silicon oxide film formed by CVD. The first film 73 is formed as an interlayer insulating film.

[0052] The second film 75 is provided on the first film 73. The second film 75 is, for example, a silicon oxide film formed by PCVD. The first coil 10 and the primary conductor 40 are embedded in the second film 75.

[0053] As shown in FIG. 7, the isolator 2 further includes a drive circuit DC. The drive circuit DC operates the first coil 10. The drive circuit DC is provided on the front surface side of the semiconductor substrate SS. The first film 73 of the third insulating film 70 includes multilayer wiring of the drive circuit DC. The primary conductor 40 is electrically connected to the first coil 10 via, for example, the drive circuit DC.

[0054] In the isolator 2, an island-shaped protrusion IP is provided on the surface of the fourth film 57 of the first insulating film 50. This allows the creepage distance at the interface between the fourth film 57 of the first insulating film 50 and the first film 61 of the second insulating film 60 and the interface between the first film 61 of the second insulating film 60 and the third film 65 of the second insulating film 60 to be longer than the linear distance HD. This allows the breakdown voltage between the second coil 20 and the primary-side conductor 30 to be increased.

[0055] Furthermore, the adhesion at the interface between the fourth film 57 of the first insulating film 50 and the first film 61 of the second insulating film 60 is improved, making it possible to disperse stress, for example, from the sealing resin, during repeated temperature tests such as TCT. That is, the multiple protrusions increase the creepage distance and ensure interface stability through improved adhesion. Furthermore, by configuring the first film 61 of the second insulating film 60 to have a smaller linear expansion coefficient than the third film 65 of the second insulating film and the fourth film 57 of the first insulating film 50, and by configuring the first film 61 of the second insulating film 60 to have a thinner film thickness than the third film 65 and the fourth film 57 of the first insulating film 50, the effect of stress relaxation at the interface between the fourth film 57 of the first insulating film 50 and the first film 61 of the second insulating film 60, and at the interface between the first film 61 of the second insulating film 60 and the third film 65 of the second insulating film 60, can be improved. In other words, by sandwiching a thin film (first film 61 of second insulating film 60) between thick films (fourth film 57 of first insulating film 50 and third film 65 of second insulating film) having a different linear expansion coefficient from that of the thin film, the island-like structure increases the creepage distance and improves adhesion, thereby achieving a higher breakdown voltage.

[0056] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0057] 1, 2, 3...isolator, 10...first coil, 20...second coil, 23, 25...connection pad, 30, 40...primary side conductor, 35...connection conductor, 50...first insulating film, 50G...groove, 51, 61, 73...first film, 53, 63, 75...second film, 55, 65...third film, 57...fourth film, 60...second insulating film, 70...third insulating film, DC...drive circuit, EM...etching mask, IP...island-shaped convex portion, SPX, SPY...short circuit path

Claims

1. a first coil on the primary side; a second coil on a secondary side provided above the first coil and magnetically coupled to the first coil; a first insulating film provided on the first coil, the second coil being embedded in a surface opposite to the first coil; a primary-side conductor embedded in the front surface side of the first insulating film at a position spaced apart from the second coil and electrically connected to the primary side; Equipped with the first insulating film has, on the front surface side, a plurality of island-shaped protrusions provided between the second coil and the primary-side conductor, the plurality of island-shaped protrusions are arranged such that a creepage distance along a surface of the first insulating film in any direction from the second coil to the primary conductor is longer than a linear distance in the direction from the second coil to the primary conductor, a second insulating film covering at least a portion of the second coil and the primary conductor; a third insulating film provided between the first insulating film and the second insulating film and having a composition different from that of the first insulating film and the second insulating film; Furthermore, The isolator, wherein the first insulating film and the second insulating film have the same composition.

2. a first coil on the primary side; a second coil on a secondary side provided above the first coil and magnetically coupled to the first coil; a first insulating film provided on the first coil, the second coil being embedded in a surface opposite to the first coil; a primary-side conductor embedded in the front surface side of the first insulating film at a position spaced apart from the second coil and electrically connected to the primary side; Equipped with the first insulating film has, on the front surface side, a plurality of island-shaped protrusions provided between the second coil and the primary-side conductor, the plurality of island-shaped protrusions are arranged such that a creepage distance along a surface of the first insulating film in any direction from the second coil to the primary conductor is longer than a linear distance in the direction from the second coil to the primary conductor, a plurality of pairs of the first coil and the second coil; The primary conductor is arranged to surround the second coils.

3. a plurality of pairs of the first coil and the second coil; The isolator according to claim 1 , wherein the primary conductor is provided so as to surround the second coils.

4. 4. The isolator according to claim 1, wherein the island-shaped protrusion includes polygons of different sizes in a plane along the surface of the first insulating film.

5. 4. The isolator according to claim 1, wherein the island-shaped protrusions are each hexagonal in a plane along the surface of the first insulating film and are arranged closest to each other.

6. 6. The isolator according to claim 1, wherein the primary side reference potential is supplied to the primary side conductor.

7. 7. The isolator according to claim 1, wherein the height of the island-shaped protrusion in the direction from the first coil toward the second coil is smaller than the thickness of the second coil.

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