JP2006033217A - Microstripline and characteristic impedance control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microstripline whose impedance control is facilitated, and to provide a characteristic impedance control method. <P>SOLUTION: The microstrip line 10 comprises a base 11, a ground metal 12 formed on the base 11, a dielectric layer 13 formed on the ground metal 12, and a signal wire 14 formed on the dielectric layer 13, wherein the width of the dielectric layer 13 is narrower than the width of the ground metal 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a microstrip line and a characteristic impedance control method, and can be used as, for example, a wiring line used in an electronic device, an optical device, and a module thereof.

  With the recent rapid increase in the speed of semiconductor electronic devices and semiconductor optical devices, the number of cases in which a microstrip line structure is used also in a wiring line formed on a semiconductor element has increased.

  FIG. 5 is a schematic cross-sectional structure diagram of an example of a conventional microstrip line. As shown in the figure, the microstrip line 50 includes a substrate 51, a ground metal 52 formed on the substrate 51, a dielectric layer 53 formed on the ground metal 52, and a dielectric layer 53. It has a structure in which a dielectric layer 53 is sandwiched between a ground metal 52 and a signal line 54.

  FIG. 6 is a schematic sectional view showing an example of a conventional microstrip line. As shown in the figure, the microstrip line 60 includes a ground metal 62, a dielectric layer 63 as a substrate formed on the ground metal 62, and a signal line 64 formed on the dielectric layer 63. Consists of. As a manufacturing method, the ground metal 62 and the signal line 64 are formed on the front and back surfaces of a relatively hard dielectric substrate (dielectric layer 63) by a method such as vapor deposition.

  The characteristic impedances of the microstrip lines 50 and 60 are the width of the signal lines 54 and 64, the gap between the signal lines 54 and 64 and the ground metal 52 and 62 (the thickness of the dielectric layers 53 and 63), and the signal lines 54 and 64, It is determined by the dielectric constant between the ground metals 52 and 62 (the dielectric constant of the dielectric layers 53 and 63). In the drawings, the “width” of each member refers to the length in the left-right direction in the drawings.

  Since the characteristic impedance of a high-frequency electric signal generation source or measuring instrument is generally 50Ω, the characteristic impedance of the semiconductor element itself or the wiring line on the semiconductor element is often designed to match 50Ω. . For this reason, a precise structure control process is required in order to realize good characteristics of the semiconductor element with respect to high-frequency signals.

  As this precise structure control process, when producing electrodes such as microstrip lines that become high-frequency lines, a process that generally keeps the substrate surface to be processed flat and facilitates ensuring pattern accuracy in the photolithography process. The procedure is adopted.

  For example, the ground metal 52, 62 is designed to have a large width, and the dielectric layers 53, 63 on the ground metal 52, 62 have the same width, so that it is easy to ensure the pattern accuracy of the signal lines 54, 64, which are the finest patterns. Process is adopted.

  In general, in the production of a microstrip line or the like, a technique of forming a signal line pattern or a ground metal pattern on the front and back surfaces of a dielectric layer is used, and as a result, conventional microstrip lines 50 and 60 are used. Has a structure in which the width of the dielectric layers 53 and 63 is the same as the width of the ground metals 52 and 62, or the width of the dielectric layers 53 and 63 is larger than the width of the ground metals 52 and 62 ( For example, see Non-Patent Document 1 and Patent Document 1 below.)

Eitaro Abe, “Microwave”, University of Tokyo Press, August 1992, p.39 Japanese Patent Laid-Open No. 05-129808

  However, in the conventional structure in which the width of the ground metal is equal to the width of the dielectric layer in the microstrip line, there is a problem that the characteristic control of the microstrip line and the manufacturing method are limited.

  For example, when a microstrip line having a characteristic impedance of 50Ω is formed in a wiring portion of a semiconductor element by a dielectric layer having a characteristic of a signal line having a width of 50 μm and a relative dielectric constant of 4, the thickness of the dielectric layer is about 25 μm. It becomes.

  In device fabrication that requires fine pattern formation, it is important to flatten the wafer surface so as to ensure accuracy in the photolithography process. As described above, for example, the thickness of the dielectric layer Is about 25 μm, the step difference from the electronic device and the optical device becomes large, and the subsequent process becomes difficult. For example, the accuracy of the signal line pattern formed on the dielectric layer is deteriorated, causing a problem that the characteristic impedance of the wiring line cannot be controlled.

  In addition, when the relative permittivity and the layer thickness of the dielectric layer are fixed, in order to control the characteristic impedance to be, for example, 50Ω, it is necessary to adjust the width of the signal line. As a result, the microwave loss of the signal line itself increases.

For example, when the dielectric layer is formed by sputtering such as SiO ₂ , the layer thickness can be precisely controlled. On the other hand, if the layer thickness is increased, cracks may occur. Can only be about 1 μm. In this case, in order to adjust the characteristic impedance to 50Ω, it is necessary to reduce the width of the signal line, which makes it difficult to control the width of the signal line and increases the microwave loss. Arise.

  On the other hand, in a microstrip line on an actual semiconductor device, a polyimide material or a BCB material is often used as a dielectric material from the viewpoint of easy process and relatively easy securing of a dielectric layer thickness. In this case, it is possible to increase the layer thickness, but because the accuracy control of the layer thickness is low, it is difficult to control the characteristic impedance, and it is difficult to increase the yield (reproducibility is difficult to ensure). Occurs.

  Also, in semiconductor optical devices obtained by cutting out elements by cleavage, it is common to polish the semiconductor substrate thinly to facilitate cleavage, but when the thickness of a dielectric layer such as polyimide is increased However, there is a problem that a stress difference between the substrate and the thick dielectric layer becomes large, the wafer is warped in the polishing process, and the substrate is cracked.

  The present invention has been made in view of the above situation, and provides a microstrip line and a characteristic impedance control method that facilitate control of characteristic impedance, improve yield, and suppress the possibility of cracks in a substrate polishing process. For the purpose.

The microstrip line according to the present invention that solves the above problems is as follows.
In a microstrip line in which a signal line and a ground metal are provided via a dielectric layer,
An effective dielectric constant between the signal line and the ground metal is adjusted by replacing a part of the dielectric layer with a material having a dielectric constant different from that of the dielectric layer. This is a microstrip line.

  Adjusting the effective dielectric constant by replacing a part of the dielectric layer with a material having a different dielectric constant means, for example, replacing the dielectric layer with a material having a dielectric constant lower than the dielectric constant of the dielectric layer. The effective dielectric constant is adjusted by decreasing the value or replacing the dielectric layer with a material having a dielectric constant higher than that of the dielectric layer. Further, for example, not only a part of the dielectric layer may be replaced with a solid material, but a part of the dielectric layer may be removed and replaced with a gas such as air.

In the microstrip line,
The microstrip line is characterized in that a part or the whole width of the dielectric layer is smaller than a width of the ground metal.

In the microstrip line,
The microstrip line is characterized in that the width of the dielectric layer is substantially the same as the width of the signal line.

In the microstrip line,
The microstrip line is characterized in that a width of the dielectric layer is smaller than a width of the signal line.

In the microstrip line,
The microstrip line has a characteristic impedance of 50Ω.

In the microstrip line,
The microstrip line is a microstrip line produced on a semiconductor substrate.

The characteristic impedance control method according to the present invention that solves the above problems is as follows.
A signal line and a ground metal are provided via a dielectric layer, and a microstrip line in which a part or the whole width of the dielectric layer is smaller than a width of the ground metal,
The characteristic impedance control method is characterized in that the characteristic impedance of the microstrip line is controlled by changing the width of the dielectric layer.

  The various inventions described above provide a microstrip line and a microstrip line that solve the above problems by controlling the effective dielectric constant of the dielectric layer, thereby giving freedom to the layer thickness of the dielectric layer and the line width of the signal line. This is a characteristic impedance control method.

  According to the microstrip line according to the present invention, it is possible to control the characteristic impedance even in a microstrip line in which the gap between the ground metal and the signal line cannot be sufficiently secured or the gap between the ground metal and the signal line is limited. Become.

  Further, since the width of the signal line can be increased under the same dielectric layer thickness, microwave loss can be reduced. In particular, in semiconductor electronic devices and semiconductor optical devices, the loss reduction effect is effective because the thickness of the dielectric layer in the microstrip line structure of the wiring portion may be limited. Further, since the width of the signal line with the finest pattern width can be made wider than before, the accuracy required for the process can be relaxed.

  Further, the characteristic impedance of the microstrip line can be controlled by using the structure of the microstrip line according to the present invention and removing the width of the dielectric layer by etching or the like (the impedance control method can be used). ). According to this control method, since the signal line is not damaged, the characteristic impedance of the line can be controlled without impairing the resistance of the signal line. In particular, the impedance can be adjusted even in a microstrip line or the like using an organic film whose layer thickness is difficult to control as a dielectric material. As a result, the product yield can be improved.

  Further, in the structure of the present invention in which the dielectric layer other than the periphery of the signal line is removed, even when a thick dielectric layer is formed, the dielectric layer does not exist on the entire surface of the substrate. In this manufacturing process, generation of warpage of the substrate based on stress during polishing and generation of cracks in the substrate can be suppressed, and high yield can be manufactured.

  Hereinafter, although an embodiment of the present invention is described in detail using a drawing, the present invention is not limited to this.

<First Embodiment>
FIG. 1 is a schematic cross-sectional structure diagram of the microstrip line according to the first embodiment. As shown in the figure, a microstrip line 10 according to the present embodiment includes a substrate 11, a ground metal 12 formed on the substrate 11, a dielectric layer 13 formed on the ground metal 12, The signal line 14 is formed on the dielectric layer 13. The width of the dielectric layer 13 is smaller than that of the ground metal 12.

<Second Embodiment>
FIG. 2 is a schematic cross-sectional structure diagram of the microstrip line according to the second embodiment. As shown in the figure, the microstrip line 20 according to the present embodiment includes a substrate 21, a ground metal 22 formed on the substrate 21, a dielectric layer 23 formed on the ground metal 22, Signal line 24 formed on dielectric layer 23, the width of dielectric layer 23 is smaller than the width of ground metal 22, and the width of dielectric layer 23 and the width of signal line 24 are equivalent. It has a structure.

<Third Embodiment>
FIG. 3 is a schematic sectional view of a microstrip line according to the third embodiment. As shown in the figure, a microstrip line 30 according to the present embodiment includes a substrate 31, a ground metal 32 formed on the substrate 31, a dielectric layer 33 formed on the ground metal 32, The signal line 34 is formed on the dielectric layer 33, the width of the dielectric layer 33 is smaller than the width of the ground metal 32, and the width of the dielectric layer 33 is larger than the width of the signal line 24. It has a small structure.

<Method for Producing Microstrip Line According to Embodiment>
FIG. 4 is a diagram for explaining a microstrip line manufacturing process according to the first embodiment. As shown in the figure, first, a ground metal 12 is formed on a substrate 11 (FIG. 1A), and a dielectric layer 13 having the same width as that of the ground metal 12 is further formed on the ground metal 12. '(Dielectric layer before width adjustment) was formed ((b) in the figure).

  In the present embodiment, polyimide is used as a dielectric material for forming the dielectric layer 13 ′, and after the polyimide material is applied onto the ground metal 12 by spin coating, the polyimide is baked and solidified to thereby control the layer thickness. A dielectric layer 13 ′ having was formed.

  Next, the signal line 14 was formed on the upper surface of the solidified dielectric layer 13 ′ (FIG. (C)), and a resist pattern 15 was formed so as to cover the signal line 14 (FIG. (D)).

Thereafter, by using the resist pattern 15 as a mask, the dielectric layer 13 ′ is subjected to dry etching such as O ₂ -RIE to remove unnecessary portions of the dielectric layer 13 ′ to have a desired width. A dielectric layer 13 was formed ((e) in the figure).

  Finally, by removing the resist pattern 15 covering the signal line 14, the microstrip structure 10 according to the first embodiment was manufactured ((f) in the figure).

  In the microstrip line manufacturing method described above, unnecessary portions of the dielectric layer 13 'are removed by dry etching using the resist pattern 15 formed over the signal line 14 as a mask. However, the signal line 14 itself is a metal mask. Therefore, dry etching may be performed. In this case, the microstrip line 20 according to the second embodiment shown in FIG. 2 can be produced.

Further, after forming the microstrip line 20 according to the second embodiment, further, for example, performs the process by O ₂ ashing or the like, by removing portions of the dielectric layer 23 immediately below the signal line 24, FIG. 3 The microstrip line 30 according to the third embodiment shown in FIG.

  In addition to the microstrip line manufacturing method described above, for example, the width of the dielectric layer may be controlled by photolithography by using photosensitive polyimide as the dielectric material.

<Impedance Control of Microstrip Line According to Embodiment>
Next, the results (see Table 1 below) of impedance control (trimming) using the microstrip line according to the embodiment will be described.

  The characteristic impedance of a microstrip line manufactured with a signal line width of 10 μm, a dielectric layer made of polyimide of 3 μm and a width of 200 μm (the width of the ground metal is 200 μm) is 39.65Ω based on evaluation by a network analyzer. It was estimated.

The wafer is further subjected to dry etching by O ₂ -RIE using the signal line as a mask, and when the width of the dielectric layer is set to 1 Oμm, which is the same as the width of the signal line, the characteristic impedance is 41.97Ω. It was.

Furthermore, when this wafer was post-treated with O ₂ asher and a weak alkaline solution, the width of the dielectric layer was about 5 μm, the characteristic impedance was 50.38Ω.

  As described above, it was found that the impedance can be easily controlled by changing the width of the dielectric layer, and the impedance can be adjusted even after the device is manufactured.

  By changing the width of the dielectric layer, the dielectric constant of air existing on the side of the layer can be used to reduce the effective dielectric constant for the signal line, and impedance control can be performed.

  In the case of a microstrip line manufactured with the same design as a conventional microstrip line, the thickness of the dielectric layer is 3 μm, the width is 200 μm (the width of the ground metal is the same), and the width of the signal line is about 7 μm. The characteristic impedance was about 50Ω, but the microwave loss of the signal line was 1.35 dB per mm.

  On the other hand, in the microstrip line according to the embodiment, when the thickness of the dielectric layer is 3 μm, the width is 5 μm (the width of the ground metal is 200 μm), and the width of the signal line is 10 μm, the microwave loss of the signal line Was 0.83 dB per mm, confirming the loss reduction effect of 0.52 dB compared to the conventional structure.

  That is, in the microstrip line according to the embodiment, the width of the signal line is increased even when the same characteristic impedance is obtained by reducing the effective dielectric constant by reducing the width of the dielectric layer. Therefore, the microwave loss can be reduced and the control of the width of the signal line can be facilitated.

  Needless to say, the microstrip line according to the embodiment has the same effect not only on a semiconductor substrate but also on an alumina substrate used for wiring in a module.

  The structure of the microstrip line according to the embodiment is configured by accurately manufacturing a microstrip line on a semiconductor substrate by a manufacturing process similar to the conventional one, and then removing the dielectric portion by dry etching such as RIE. Also good. This has the merit that the microstrip line according to the embodiment can be easily manufactured after following the conventional manufacturing process.

1 is a schematic cross-sectional structure diagram of a microstrip line according to a first embodiment. It is a schematic sectional structure figure of the microstrip line concerning a 2nd embodiment. It is a schematic sectional structure figure of the microstrip line concerning a 3rd embodiment. It is a figure explaining the production process of the microstrip line concerning a 1st embodiment. It is a schematic sectional drawing of an example of the conventional microstrip line. It is a schematic sectional drawing of an example of the conventional microstrip line.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Microstrip line 11 Board | substrate 12 Ground metal 13 Dielectric layer 13 'Dielectric layer before width adjustment 14 Signal line 15 Resist pattern

20, 30 Microstrip line 21, 31 Substrate 22, 32 Ground metal 23, 33 Dielectric layer 24, 34 Signal line

50, 60 Microstrip line 51 Substrate 52, 62 Ground metal 53, 63 Dielectric layer 54, 64 Signal line

Claims (7)

In a microstrip line in which a signal line and a ground metal are provided via a dielectric layer,
An effective dielectric constant between the signal line and the ground metal is adjusted by replacing a part of the dielectric layer with a material having a dielectric constant different from that of the dielectric layer. A microstrip line. In the microstrip line according to claim 1,
The microstrip line according to claim 1, wherein a width of a part or the whole of the dielectric layer is smaller than a width of the ground metal. In the microstrip line according to claim 1,
The width of the dielectric layer is substantially the same as the width of the signal line. In the microstrip line according to claim 1,
The width of the dielectric layer is smaller than the width of the signal line. In the microstrip line according to any one of claims 1 to 4,
A microstrip line having a characteristic impedance of 50Ω. The microstrip line according to any one of claims 1 to 5,
The microstrip line is manufactured on a semiconductor substrate. A signal line and a ground metal are provided via a dielectric layer, and a microstrip line in which a part or the whole width of the dielectric layer is smaller than a width of the ground metal,
A characteristic impedance control method, wherein the characteristic impedance of the microstrip line is controlled by changing the width of the dielectric layer.

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