JP3679275B2 - Transmission line manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transmission line that propagates a high-frequency signal formed on a semiconductor substrate and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, applications of millimeter wave frequency bands, which are unused frequency bands, have been proposed. In particular, the development of antennas and sensors has attracted attention. With the advancement of semiconductor devices that utilize this millimeter-wave frequency band and the demand for integration of microwave circuits, the advantages of such features as wide bandwidth, ease of mounting of circuit elements, and less influence of parasitic elements, Coplanar lines that are shaped waveguides have been proposed.
As one of them, Reference 1 (KJHerrick, TAschwarz and LPBKatehi, 'Si-Micromachined Copanar Waveguides for Use in High-Freqency Circuits', IEEE Trans. On Microwave Theory and Techniques, Vol. 46, No. 6, June, pp762- 768 (1998)).
[0003]
In the technique of this document 1, as shown in FIG. 10, a coplanar transmission line is formed on a silicon substrate 1001 having a high specific resistance. First, as shown in FIG. 10A, a signal line 1002 and a ground line 1003 made of a metal material are formed on a silicon substrate 1001 to have a film thickness of about 1 to 2 μm. The signal line 1002 and the ground line 1003 form a coplanar transmission line.
Next, as shown in FIG. 10B, the silicon substrate 1001 is selectively etched using the signal line 1002 and the ground line 1003 as a mask to form a groove 1004. Alternatively, as shown in FIG. 10C, the silicon substrate 1001 is selectively etched using the signal line 1002 and the ground line 1003 as a mask to form a groove 1005.
[0004]
In such a coplanar transmission line, a high-frequency signal propagating through the signal line causes transmission loss due to the presence of the silicon substrate. For this reason, by forming the grooves as described above, the air around the signal line is made a layer of air having a lower dielectric constant. However, in the technique of this document 1, the size of the groove is determined by the size of the wiring, and the size of the wiring and the size of the groove cannot be individually designed. There is a limit.
In addition, the shape and size of the groove affects the high-frequency signal in the transmission line and its transmission specification, but it is difficult to make the shape and size of the groove uniform in the process. is there.
[0005]
On the other hand, Reference 2 (M.Hirano, Y.Imai, I.Toyoda, K.Nishikawa, M.Tokumitsu and K.Asai, 'Three Dimensional Passive Elements for Compact GaAs MMICs', I EICE Trans. Electrpn., Vol. E76 -C, No. 6 June pp961-967 (1993)), there is a technique for forming a signal line and a ground line in a plate shape.
As shown in FIG. 11, a plate-like signal line 1102 and a ground line 1103 are placed on a substrate 1101 made of high-resistance GaAs so as to be orthogonal to the main surface of the substrate 1101. Further, the signal line 1102 and the ground line 1103 extend in a state parallel to a direction perpendicular to the plane. In this way, most of the periphery of the signal line 1102 is formed as an air layer so that transmission loss is further reduced.
[0006]
[Problems to be solved by the invention]
However, the above-described conventional technique has a problem that it is difficult to form a transmission line monolithically on the same substrate together with other antenna elements.
First, in the technique of Document 1, since the reproducibility of groove formation is difficult, when other elements are mounted at the same time, the quality of the transmission line greatly affects the yield of the entire apparatus. Therefore, if an attempt is made to produce a high-frequency device with a higher yield, the above-described coplanar transmission line and other elements will be individually produced. However, it has been very difficult to satisfy the demands for miniaturization and high performance with such individual formation.
[0007]
In general, active elements and the like are formed on a low-resistance semiconductor substrate. Therefore, if a high-resistance material is used for the substrate as in the techniques of Reference 1 and Reference 2 described above, At the same time, it was very difficult to form other elements.
The present invention has been made to solve the above-described problems, and is capable of suppressing transmission loss of a transmission line formed on a semiconductor substrate having a low resistance. With the goal.
[0008]
[Means for Solving the Problems]
The transmission line manufacturing method of the present invention comprises the following steps. First, an oxide film having two stripe-shaped openings extending in parallel with each other at a predetermined interval is formed on a semiconductor substrate, and the semiconductor substrate is etched using the oxide film as a mask. A first step of forming two grooves extending in parallel with each other at a predetermined interval. Next, after removing the oxide film, a second step of filling the two grooves with a sacrificial film to make the surface of the semiconductor substrate substantially flat. Next, a third step of forming a first metal thin film on the surface of the semiconductor substrate.
[0009]
In the following, first in the region of a predetermined width adjacent to the outer region and grooves sandwiched between two grooves on the metal thin film, a stripe shape extending in parallel along the grooves first and second Forming a resist pattern with openings, filling the openings by forming a second metal film by plating on the first metal thin film exposed at the bottoms of the first and second openings of the resist pattern, A fourth step of forming a signal line disposed in a region sandwiched between the grooves and a ground line disposed adjacent thereto; Next, a fifth step of removing the exposed region of the first metal thin film after removing the resist pattern. Next, a step of removing the sacrificial film after the fifth step.
The opening of the resist pattern is formed deeper than the width of the bottom of the opening.
As a result, the transmission path is formed in a plate-like shape, and the concentration of the electric field is concentrated on the side wall of the plate-like signal line.
[0010]
Under such circumstances, in the fourth step, the third opening is simultaneously formed in the resist pattern, and the second metal film is simultaneously formed on the first metal thin film exposed at the bottom of the third opening. And forming a sacrificial layer on the signal line, the ground line and the high-frequency element, covering the signal line, the ground line and the high-frequency element, and forming a sacrificial layer in a substantially flat surface, and the signal line and the high-frequency element. A seventh step of forming a connection port in a predetermined region of the sacrificial layer on the device; and a new step of forming a second metal thin film on the sacrificial layer including the connection premises and having an opening region between the connection ports An eighth resist pattern is formed, and a second metal film is selectively formed on the second metal thin film exposed at the bottom of the opening region by plating to form a connection portion for connecting the signal line and the high-frequency element. Process and new resist pattern And a ninth step of removing the exposed region of the second metal thin film after removal of the over down a new, sacrificial film was followed by removal after the ninth step with a sacrificial layer.
[0011]
In addition, the sacrificial film is formed by forming a photosensitive resin film on a semiconductor substrate having two grooves, and selectively irradiating the resin film with exposure light to develop the resin film on the upper part of the groove. The remaining resin film may be patterned by removing the portion protruding on the semiconductor substrate plane and planarizing the remaining resin film.
The resin film may be made of photosensitive polyimide. In plating, gold is formed by electroplating. Further, the planarization is performed by a chemical mechanical polishing method.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
Embodiment 1
The first embodiment of the present invention will be described below. In the first embodiment, as shown in the perspective view of FIG. 1, a transmission line including a signal line 102 and a ground line 103 is formed on a semiconductor substrate 101, and the semiconductor substrate 101 on both sides of the signal line 102 is formed on the semiconductor substrate 101. A groove 104 was formed so that a space existed. Further, the signal line 102 and the ground line 103 are disposed on the semiconductor substrate 101 via the metal thin film 105.
[0013]
Further, the signal line 102 and the ground line 103 are formed so that the area of the side surface adjacent to the bottom surface parallel to the main surface of the semiconductor substrate 101 is larger. That is, when a cross section perpendicular to the extending direction of the signal line 102 is viewed, the side (height) adjacent to the base is longer than the bottom.
In FIG. 1, the signal line 102 is in a state of being connected to an antenna structure (high-frequency element) 107 through a connection portion 106. The semiconductor substrate 101 is made of silicon having a specific resistance of 3 to 5Ω, and a microwave circuit (not shown) is formed in another region of the semiconductor substrate 101.
[0014]
Next, the manufacturing method of the transmission line in this Embodiment 1 is demonstrated.
First, as shown in FIG. 2A, an oxide film 201 is formed on a semiconductor substrate 101 made of silicon by a thermal oxidation method.
Next, as shown in FIG. 2B, the oxide film 201 is patterned by a known photolithography technique and etching technique to form a stripe-shaped opening 201a extending in a predetermined direction.
Next, as shown in FIG. 2C, the semiconductor substrate 101 was selectively etched by wet etching using the oxide film 201 in which the opening 201a was formed as a mask, so that the groove 104 was formed. In this wet etching, a potassium hydroxide aqueous solution was used as an etching solution.
[0015]
Next, the oxide film 201 was removed by etching using HF (hydrogen fluoride), so that the groove 104 was formed in the substrate 101 as shown in FIG. The depth of the groove 104 was about 10 μm. In FIG. 2, the cross-sectional shape of the groove 104 is V-shaped. However, the shape is not limited to this, and any shape may be used as long as a space can be formed.
Next, as shown in FIG. 2E, a sacrificial film 202 made of polyimide was formed so as to fill the groove 104. This was formed by applying polyimide to the surface of the semiconductor substrate 101 to form a polyimide film with a thickness of about 10 μm, and then planarizing and etching the polyimide film by a chemical mechanical polishing method.
[0016]
Next, as shown in FIG. 3F, a metal thin film 301 having a two-layer structure of a chromium layer and a gold layer was formed on a semiconductor substrate 101, and a resist pattern 302 was formed thereon. The metal thin film 301 was formed by vapor deposition of 0.1 μm each of chromium and gold. The resist pattern 302 is formed to a thickness of about 10 μm, and openings 302 a and 302 b and an opening 302 c extending in a direction parallel to the groove 104 are formed.
Next, as shown in FIG. 3G, the surface of the metal thin film 301 exposed at the bottoms of the openings 302a, 302b, 302c is plated with gold to a thickness of about 10 μm by electroplating, and the openings 302a, 302b. , 302 c are filled with the gold film 303.
[0017]
Next, after peeling off the resist pattern 302, the metal thin film 301 under the resist pattern 302 was selectively removed. In this method, first, the gold film portion of the metal thin film 301 is removed by etching using an etching solution made of an aqueous solution of iodine, ammonium iodide, and ethanol, and then the chromium film portion underneath is wet etched. It was performed by removing. In the etching of the gold film, the etching rate was about 0.05 μm per minute.
As a result, the signal line 102, the ground line 103, and the antenna structure 107 are formed on the semiconductor substrate 101 with the metal thin film 105 interposed therebetween as shown in FIG.
[0018]
Next, as shown in FIG. 3I, first, a sacrificial layer 304 made of an insulating material was formed on the semiconductor substrate 101 so as to bury the signal line 102, the ground line 103, and the antenna structure 107. The sacrificial layer 304 was formed by forming polyimide to a thickness of about 10 μm. Next, a connection port was formed at a predetermined position of the sacrificial layer 304, and a connection portion 106 for connecting the signal line 102 and the antenna structure 107 was formed through the connection port.
[0019]
The formation of the connection portion 106 is the same as the formation of the signal line 102 described above. First, a two-layer structure of a chromium layer and a gold layer is formed over the entire region including the sacrificial layer 304 with the connection port formed. A metal thin film was formed, and a resist pattern having a groove (opening region) in the connection portion 106 formation region was formed thereon. Next, the surface of the metal thin film exposed at the bottom of the groove was plated with gold by about 10 μm by electroplating, and the groove was filled with the plated gold film. Next, after removing the resist pattern, the metal thin film below the resist pattern, that is, the metal thin film in a region other than the gold structure formed by plating may be selectively removed.
[0020]
Next, the sacrificial layer 304 and the sacrificial film 202 are removed. This can be done by ashing them with oxygen plasma. As a result, as shown in FIG. 3J, the ground line 103, the antenna structure 107, and the connection portion 106 are formed in the semiconductor substrate 101 on both sides of the signal line 102 with the groove 101a. A state is obtained.
[0021]
As described above, in the first embodiment, first, the cross section of the signal line 102 and the ground line 103 is formed in a vertically long shape in a direction perpendicular to the main surface of the semiconductor substrate 101, and grooves are formed in the semiconductor substrate 101 on both sides of the signal line 102. 104 is provided. Since this is done, more space exists around the signal line 102, and the area of the semiconductor substrate 101 around the signal line 102 becomes relatively small. As a result, as shown below, according to this embodiment, transmission loss can be further reduced.
[0022]
First, as shown in FIG. 4, a coplanar transmission line (CPW) is formed on a semiconductor substrate 401 by a signal line 402 and a ground line 403 made of metal wiring having a film thickness of 3.5 μm, and shown in FIG. As described above, a transmission line (SCPW) including a signal line 502 and a ground line 503 made of a metal wiring having a thickness of 10 μm on the semiconductor substrate 501 will be considered.
FIG. 6 shows these transmission characteristics. In FIG. 6, the transmission characteristics of the transmission line in FIG. 4 are indicated by dotted lines, and the transmission characteristics of the transmission line in FIG. 5 are indicated by solid lines.
[0023]
As is clear from the transmission characteristics of FIG. 6, the transmission line in the form of a plate with a thick film (FIG. 5) is attenuated compared to the normal coplanar transmission line (FIG. 4). Good characteristics. By standing the line in a plate shape, the concentration of the electric field is concentrated on the side wall of the plate-like line, so that the transmission loss in the semiconductor substrate is suppressed. Therefore, the attenuation characteristic is better in FIG. .
[0024]
However, even in the transmission line of the form of FIG. 5, as the transmission line becomes longer, the loss increases as shown in FIG. In FIG. 7, the state of the propagated signal when the transmission line is 500 μm is shown by a dotted line, and the state of the propagated signal when the transmission line is 1000 μm is shown by a solid line.
As shown in FIG. 7 (a), in the transmission line of the form of FIG. 5, the amplitude is attenuated by 20.9% due to the difference in length of the transmission line between 500 μm and 1000 μm, and a delay of 4.11 ps is obtained. It has occurred.
[0025]
On the other hand, FIG. 7B shows the case of the transmission line in the first embodiment of the present invention shown in FIG. In the first embodiment, as shown in FIG. 7 (b), the amplitude is attenuated only by about 5% due to the difference in the length of the transmission line between 500 μm and 1000 μm, and the delay is reduced to 3.37 ps. doing.
As described above, according to the first embodiment, it is possible to configure a transmission line with low loss and excellent propagation characteristics on a semiconductor substrate on which a functional circuit such as an LSI can be formed. That is, a transmission line can be formed monolithically on the same substrate together with other high-frequency elements such as an antenna structure, and thus a highly integrated high-frequency circuit element structure can be easily realized.
[0026]
Embodiment 2
Next explained is the second embodiment of the invention. In the second embodiment, a transmission line is manufactured as follows.
First, in a manner similar to that described with reference to FIGS. 2A to 2D, the substrate 104 is formed with the groove 104 as shown in FIG. 8A. The depth of the groove 104 was about 10 μm.
Next, as shown in FIG. 8B, a resin film 801 made of photosensitive polyimide was formed to a thickness of about 10 μm on the entire surface. This photosensitive polyimide is made photosensitive by adding a positive photosensitive agent to a base resin made of a polybenzoxazole precursor.
[0027]
Next, as illustrated in FIG. 8C, ultraviolet light 803 is irradiated with the light shielding member 802 disposed on the upper part of the groove 104 to expose the resin film 801 other than the upper part of the groove 104. Then, the exposed resin film 801 is developed with an alkaline developer so that a development pattern 801a is formed on the groove 104 as shown in FIG.
Next, the development pattern 801a is heated and thermally cured, and then cut and polished by a chemical mechanical polishing method to flatten the polyimide so as to fill the groove 104 as shown in FIG. A sacrificial film 202 made of was formed.
[0028]
The subsequent steps are the same as those of the first embodiment described above. First, as shown in FIG. 8F, a metal thin film 301 having a two-layer structure of a chromium layer and a gold layer is formed on the semiconductor substrate 101. Then, a resist pattern 302 was formed thereon. The metal thin film 301 was formed by vapor deposition of 0.1 μm each of chromium and gold. The resist pattern 302 is formed to a thickness of about 10 μm, and the openings 302a and 302b and the opening 302c are formed.
Next, as shown in FIG. 9G, the surface of the metal thin film 301 exposed at the bottom of the openings 302a, 302b, 302c is plated with gold to a thickness of about 10 μm by electroplating, and the openings 302a, 302b. , 302 c are filled with the gold film 303.
[0029]
Next, after peeling off the resist pattern 302, the metal thin film 301 under the resist pattern 302 was selectively removed. In this method, first, the gold film portion of the metal thin film 301 is removed by etching using an etching solution made of an aqueous solution of iodine, ammonium iodide, and ethanol, and then the chromium film portion underneath is wet etched. It was performed by removing. In the etching of the gold film, the etching rate was about 0.05 μm per minute.
As a result, the signal line 102, the ground line 103, and the antenna structure 107 are formed on the semiconductor substrate 101 with the metal thin film 105 interposed therebetween as shown in FIG.
[0030]
Next, as shown in FIG. 9I, first, a sacrificial layer 304 made of an insulator is formed on the semiconductor substrate 101 so as to bury the signal line 102, the ground line 103, and the antenna structure 107. The sacrificial layer 304 was formed by forming polyimide to a thickness of about 10 μm. Next, a connection port was formed at a predetermined position of the sacrificial layer 304, and a connection portion 106 for connecting the signal line 102 and the antenna structure 107 was formed through the connection port.
[0031]
Next, if the sacrificial layer 304 and the sacrificial film 202 are removed using, for example, oxygen plasma, the semiconductor substrate 101 on both sides of the signal line 102 is provided with the grooves 101a as shown in FIG. The state in which the ground line 103, the antenna structure 107, and the connection portion 106 are formed is obtained in the same manner as in the first embodiment.
In the first and second embodiments, two ground lines are formed so as to sandwich the signal line. However, the number of ground lines may be one.
[0032]
【The invention's effect】
As described above, according to the present invention, first, an oxide film having two stripe-shaped openings extending in parallel with each other at a predetermined interval is formed on a semiconductor substrate, and this oxide film is used as a mask. By etching the semiconductor substrate, two grooves extending in parallel with each other at a predetermined interval are formed on the semiconductor substrate. Next, after removing the oxide film, the two trenches are filled with a sacrificial film to make the surface of the semiconductor substrate substantially flat. Next, a third step of forming a first metal thin film on the surface of the semiconductor substrate. Next, stripe-shaped first and second stripes extending in parallel along the groove into a region sandwiched between the two grooves on the first metal thin film and a region having a predetermined width adjacent to the outside of the groove. Forming a resist pattern having an opening, filling the opening by forming a second metal film by plating on the first metal thin film exposed at the bottom of the first and second openings of the resist pattern; A signal line disposed in a region sandwiched between the grooves and a ground line disposed adjacent thereto are formed. Next, after removing the resist pattern, the exposed region of the first metal thin film is removed. Next, the sacrificial film is removed after the fifth step. The opening of the resist pattern is formed deeper than the width of the bottom of the opening.
[0033]
Since as this, the transmission path is formed in the form of standing in a plate shape, electric field concentration is to concentrate on the side walls of the plate-shaped signal line. Since the groove is provided on both sides of the signal line, there is more space around the signal line, and the area of the semiconductor substrate around the signal line is relatively small. It becomes. As a result, according to the present invention, it is possible to obtain an excellent effect that transmission loss of a transmission line formed thereon can be suppressed even on a semiconductor substrate having low resistance.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing a configuration of a transmission line according to Embodiment 1 of the present invention.
FIG. 2 is a process diagram for explaining the transmission line manufacturing method according to the first embodiment;
3 is a process diagram for illustrating the manufacturing method of the transmission line in the first embodiment, following FIG. 2; FIG.
FIG. 4 is a configuration diagram showing a configuration of a conventional transmission line.
FIG. 5 is a configuration diagram showing another form of the transmission line.
6 is a characteristic diagram showing transmission characteristics of the transmission line shown in FIGS. 4 and 5. FIG.
7 is a characteristic diagram showing amplitude characteristics of the transmission line shown in FIG. 5 and the transmission line of the first embodiment. FIG.
FIG. 8 is a process diagram for describing the method of manufacturing the transmission line in the second embodiment.
FIG. 9 is a process diagram for illustrating the manufacturing method of the transmission line in the second embodiment, following FIG. 8;
FIG. 10 is a configuration diagram showing a configuration of a conventional transmission line.
FIG. 11 is a configuration diagram showing another form of a conventional transmission line.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Semiconductor substrate, 102 ... Signal line, 103 ... Ground line, 104 ... Groove, 105 ... Metal thin film, 106 ... Connection part, 107 ... Antenna structure.

Claims (6)

An oxide film having two stripe-shaped openings extending in parallel with each other at a predetermined interval is formed on a semiconductor substrate, and the semiconductor substrate is etched using the oxide film as a mask, thereby the semiconductor substrate A first step of forming two grooves extending in parallel with each other at a predetermined interval;
A second step of filling the two trenches with a sacrificial film after removing the oxide film to make the surface of the semiconductor substrate substantially flat;
A third step of forming a first metal thin film on the surface of the semiconductor substrate;
Striped first and second stripes extending in parallel along the groove into a region sandwiched between the two grooves on the first metal thin film and a region having a predetermined width adjacent to the outside of the groove. And forming a second metal film by plating on the first metal thin film exposed at the bottoms of the first and second openings of the resist pattern. And forming a signal line disposed in a region sandwiched by the groove and a ground line disposed adjacent thereto,
A fifth step of removing an exposed region of the first metal thin film after removing the resist pattern;
And at least a step of removing the sacrificial film after the fifth step,
The method of manufacturing a transmission line, wherein the opening of the resist pattern is formed deeper than the width of the bottom of the opening. In the manufacturing method of the transmission line of Claim 1,
In the fourth step, a third opening is simultaneously formed in the resist pattern, and the second metal film is simultaneously formed on the first metal thin film exposed at the bottom of the third opening. Forming a high-frequency element together with the signal line and the ground line;
A sixth step of covering the signal line, the ground line, and the high-frequency element, and forming a sacrificial layer in a substantially flat surface state;
A seventh step of forming connection ports respectively in predetermined regions of the sacrificial layer on the signal line and the high-frequency element;
A second metal thin film is formed on the sacrificial layer including the connection premises, a new resist pattern having an opening region extending between the connection ports is formed, and the second metal exposed at the bottom of the opening region An eighth step of selectively forming a second metal film on the thin film by plating to form a connection portion for connecting the signal line and the high-frequency element;
A ninth step of removing an exposed region of the second metal thin film after removing the new resist pattern;
The method of manufacturing a transmission line, wherein the sacrificial film is removed together with the sacrificial layer after the ninth step. In the manufacturing method of the transmission line of Claim 1 or 2,
The sacrificial film is formed by forming a photosensitive resin film on the semiconductor substrate on which the two grooves are formed, and selectively irradiating the resin film with exposure light to develop the resin film. A method for producing a transmission line, wherein the resin film is formed by patterning so that the resin film remains, and a portion of the remaining resin film protruding on the semiconductor substrate plane is removed and planarized. In the manufacturing method of the transmission line according to claim 3,
The method for manufacturing a transmission line, wherein the resin film is made of photosensitive polyimide. In the manufacturing method of the transmission line of any one of Claim 1 to 4,
In the plating, a gold is formed by an electroplating method. In the manufacturing method of the transmission line of Claim 3 or 4,
The method of manufacturing a transmission line, wherein the planarization is performed by a chemical mechanical polishing method.

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