JP2022058670A - Penetration electrode substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the adhesion of a conductive layer in a penetration hole on a penetration electrode substrate.

SOLUTION: A penetration electrode substrate includes a substrate with a penetration hole penetrating a first surface and a second surface, a first conductive layer provided to a part of the penetration hole on the first surface side, a second conductive layer provided to a part of the penetration hole on the second surface side apart from the first conductive layer, a third conductive layer connecting the first conductive layer and the second conductive layer, an insulating layer provided between the first conductive layer and a side wall of the penetration hole, between the second conductive layer and the side wall of the penetration hole, and between the third conductive layer and the side wall of the penetration hole, and including any of silicon nitride, silicon oxynitride, and an organic insulating material.

SELECTED DRAWING: Figure 13

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a through electrode substrate, a method for manufacturing the same, and a semiconductor device using the through electrode substrate.

In recent years, the development of three-dimensional mounting technology in which semiconductor chips forming integrated circuits are vertically stacked has been promoted. The three-dimensional mounting technology is a technology for reducing the occupied area of a semiconductor chip in the plane direction by laminating a plurality of semiconductor chips in the thickness direction of the semiconductor chip. Through silicon vias are used as three-dimensional wiring in such three-dimensional mounting technology. For example, Patent Document 1 discloses a technique in which a through hole is provided in a semiconductor chip, a through electrode is formed by filling the inside of the through hole with a conductive layer, and both sides of the semiconductor chip are electrically conductive. ..

However, in the invention (filling type) in which the conductive layer is filled inside the through hole disclosed in Patent Document 1, there is a problem that it takes time to fill the conductive layer inside the through hole. Therefore, for example, Patent Document 2 discloses an invention (non-filling type) that shortens the process and improves productivity by forming a conductive layer only on the side wall of the through hole.

Japanese Unexamined Patent Publication No. 2006-222138 Japanese Unexamined Patent Publication No. 2013-54213

The non-filled through silicon via disclosed in Patent Document 2 can shorten the process and improve productivity as compared with the filled silicon via disclosed in Patent Document 1. However, in the non-filled through silicon via, if the conductive layer is peeled off at the side wall of the through hole, conduction failure occurs, so that the adhesion between the side wall of the through hole and the conductive layer is important. In particular, with a through electrode having a high aspect ratio, it is difficult to ensure sufficient adhesion of the conductive layer formed on the side wall of the through hole, and further studies are required.

An object of the present invention is to improve the adhesion of the conductive layer in the through hole in the through electrode substrate.

The method for manufacturing a through electrode substrate according to an embodiment of the present invention has a first surface and a second surface opposite to the first surface, and a through hole penetrating the first surface and the second surface is provided. The formed substrate is prepared, a first conductive adhesive layer is formed on a part of the first surface side of the side wall of the first surface and the through hole by a sputtering method, and then the first conductive adhesive layer is formed. A second conductive adhesive layer is formed on the second surface and a part of the side wall of the through hole on the second surface side by a sputtering method, and is in contact with the first conductive adhesive layer and the second conductive adhesive layer, and the first. A seed layer is formed in contact with the side wall of the through hole exposed from the conductive adhesion layer and the second conductive adhesion layer, and the conductive layer is formed on the seed layer by electrolytic plating that feeds the seed layer.

According to this method for manufacturing the through electrode substrate, the adhesion of the conductive layer in the through hole in the through electrode substrate can be enhanced.

The method for manufacturing a through electrode substrate according to an embodiment of the present invention has a first surface and a second surface opposite to the first surface, and a through hole penetrating the first surface and the second surface is provided. The formed substrate is prepared, a first conductive adhesive layer is formed on a part of the first surface side of the side wall of the first surface and the through hole by a sputtering method, and then the first conductive adhesive layer is formed. A second conductive adhesive layer is formed on the second surface and a part of the side wall of the through hole on the second surface side by a sputtering method, and a third conductive adhesive layer is formed on the first conductive adhesive layer, and then the second. A fourth conductive adhesion layer is formed on the conductive adhesion layer, and the through holes are in contact with the third conductive adhesion layer and the fourth conductive adhesion layer and are exposed from the first to fourth conductive adhesion layers. A seed layer made of the same material as the third conductive adhesive layer and the fourth conductive adhesive layer, which are in contact with the side wall, is formed, and the conductive layer is formed on the seed layer by electrolytic plating that feeds the seed layer.

Further, in another preferred embodiment, the third conductive adhesion layer and the fourth conductive adhesion layer may be formed by a sputtering method.

According to this method for manufacturing the through electrode substrate, the adhesion of the conductive layer in the through hole in the through electrode substrate can be further enhanced.

Further, in another preferred embodiment, an insulating filler may be formed in the through hole in which the conductive layer is formed.

According to this method of manufacturing the through electrode substrate, the airtightness in the through hole can be improved.

Further, in another preferred embodiment, the seed layer may be formed by oblique vapor deposition.

According to this method for manufacturing a through electrode substrate, a seed layer can be formed on the side wall of the through hole between the first conductive adhesion layer and the second conductive adhesion layer even in the through hole having a high aspect ratio. ..

Further, in another preferred embodiment, in the oblique vapor deposition, the angle formed by the line parallel to the flight direction of the vapor-deposited material and the perpendicular line on the first surface may be 5 ° or more and 20 ° or less.

According to this method for manufacturing a through electrode substrate, a seed layer can be formed on the side wall of the through hole between the first conductive adhesion layer and the second conductive adhesion layer even in the through hole having a high aspect ratio. ..

The through electrode substrate according to an embodiment of the present invention has a first surface and a second surface opposite to the first surface, and is provided with a through hole penetrating the first surface and the second surface. The substrate, the first conductive adhesion layer arranged on the first surface and a part of the side wall of the through hole on the first surface side, and the second surface and a part of the side wall of the through hole on the second surface side. The second conductive adhesion layer, the seed layer arranged in contact with the first conductive adhesion layer, the second conductive adhesion layer and the side wall, and the conductive layer arranged on the seed layer are included.

According to this through electrode substrate, the adhesion of the conductive layer in the through hole in the through electrode substrate can be enhanced.

The through electrode substrate according to the embodiment of the present invention has a first surface and a second surface opposite to the first surface, and is provided with a through hole penetrating the first surface and the second surface. The substrate, the first conductive adhesive layer arranged on the first surface and a part of the side wall of the through hole on the first surface side, and the second surface and a part of the side wall of the through hole on the second surface side. A second conductive adhesion layer, a third conductive adhesion layer arranged on the first conductive adhesion layer, a fourth conductive adhesion layer arranged on the second conductive adhesion layer, and a third. A seed layer made of the same material as the third conductive adhesion layer and the fourth conductive adhesion layer, and a conductive layer arranged on the seed layer, which are arranged in contact with the conductive adhesion layer, the fourth conductive adhesion layer, and the side wall. And, including.

According to this through electrode substrate, the adhesion of the conductive layer in the through hole in the through electrode substrate can be further enhanced.

Further, in another preferred embodiment, the insulating filler may be arranged in the through hole in which the conductive layer is formed.

According to this through electrode substrate, the airtightness in the through hole can be improved.

A semiconductor device according to an embodiment of the present invention has the above-mentioned through silicon via substrate and two other substrates or chips that are laminated and electrically connected so as to arrange the through silicon via substrate in between.

The semiconductor device according to the embodiment of the present invention has the above-mentioned through silicon via substrate and another substrate or chip arranged side by side with the through silicon via substrate.

According to the present invention, the adhesion of the conductive layer in the through hole in the through electrode substrate can be improved.

It is a top view explaining the through electrode of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a flowchart explaining the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate provided with the through hole in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the insulating layer was formed in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the 1st conductive adhesion layer was formed from one side surface in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the 2nd conductive adhesion layer was formed from the other side surface in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the seed layer was formed from one side surface in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate which the seed layer was formed from the other side surface in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the conductive layer was formed in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate which the conductive layer was patterned in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the 1st photosensitive resin layer was formed in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the 2nd photosensitive resin layer was formed in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the 1st and 2nd photosensitive resin layers are patterned in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the cross section of the substrate in which the wiring layer was formed in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a figure which shows another example of the through hole of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a figure which shows another example of the through hole of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a figure which shows another example of the through hole of the through electrode substrate which concerns on 1st Embodiment of this invention. It is a schematic diagram of the film formation apparatus by diagonal vapor deposition in the manufacturing method of the through electrode substrate which concerns on 1st Embodiment of this invention. FIG. 3 is a schematic view showing a cross-sectional view of a through silicon via substrate in which a conductive layer is formed by diagonal vapor deposition in the method for manufacturing a through silicon via substrate according to the first embodiment of the present invention. It is a schematic diagram which shows the cross section of the substrate in which the conductive layer was formed in the manufacturing method of the through electrode substrate which concerns on 2nd Embodiment of this invention. It is a figure which shows the semiconductor device which concerns on 3rd Embodiment of this invention. It is a figure which shows another example of the semiconductor device which concerns on 3rd Embodiment of this invention. It is a figure which shows still another example of the semiconductor device which concerns on 3rd Embodiment of this invention.

<First Embodiment>
Hereinafter, a method for manufacturing a through-hole substrate according to the first embodiment of the present invention will be described in detail with reference to the drawings. The embodiments shown below are examples of the embodiments of the present invention, and the present invention is not limited to these embodiments. In the drawings referred to in the present embodiment, the same parts or parts having similar functions are designated by the same reference numerals or similar reference numerals, and the repeated description thereof may be omitted. Further, the dimensional ratio of the drawing may differ from the actual ratio for convenience of explanation, or a part of the configuration may be omitted from the drawing.

[Structure of Through Electrode Substrate 1]
FIG. 1 is a top view illustrating a through electrode of the through electrode substrate according to the first embodiment of the present invention. FIG. 13 shows a schematic cross-sectional view taken along the line AB of FIG. FIG. 1 is a view seen from the first surface 101 side of the substrate 100. First, the configuration of the through electrode substrate 1 will be described with reference to FIGS. 1 and 13.

In the substrate 100 in which the through hole 90 is formed, the through electrode substrate 1 electrically connects the first surface 101 side of the substrate 100 and the second surface 102 side opposite to the first surface through the through hole 90. Conductive layers 61, 62, 65 are formed to connect to the insulating layers 71, 72, 75, and first conductive adhesion layers 11, 15, 2nd between the conductive layers 61, 62, 65 and the substrate 100. Conductive adhesion layers 22, 25 and seed layers 31, 32, 35 are formed.

In the following description, the insulating layers 71, 72, and 75 are used to refer to those located on the first surface 101, the second surface 102, and the side wall of the through hole 90, respectively, and when they are not distinguished from each other. May be referred to as an insulating layer 70. The first conductive adhesive layers 11 and 15 are used to refer to those located on the first surface 101 and on the side wall of the through hole 90, respectively, and when they are not distinguished, the first conductive adhesive layer 10 is used. In some cases. Further, the second conductive adhesion layers 22 and 25 are used when referring to those located on the second surface 102 and on the side wall of the through hole 90, respectively, and when they are not distinguished, the second conductive adhesion layers 22 and 25 are used. It may be called layer 20.

The first conductive adhesive layer 10 and the second conductive adhesive layer 20 may be formed directly on the insulating layer 70, or may be formed via another intermediate layer (not shown). Further, the seed layers 31, 32, and 35 are used to refer to those located on the first surface 101, the second surface 102, and the side wall of the through hole 90, respectively, and when they are not distinguished, the seeds are used. It may be called layer 30. The first conductive adhesion layer 10, the second conductive adhesion layer 20, and the seed layer 30 may be provided so as to be in direct contact with each other, or may be formed via another intermediate layer (not shown). May be good. Further, the conductive layers 61, 62, and 65 are used to refer to those located on the first surface 101, the second surface 102, and the side wall of the through hole 90, respectively, and when they are not distinguished, they are conductive. It may be called layer 60.

Insulating layers 71, 72, and 75 are formed on the side walls of the first surface 101, the second surface 102, and the through hole 90, depending on the material of the substrate 100. Further, on the insulating layer 75, a first conductive adhesion layer 15 is formed on a part of the side wall of the through hole on the first surface side. Further, a second conductive adhesion layer 25 is formed on a part of the side wall of the through hole on the second surface side. The first conductive adhesion layer 15 and the second conductive adhesion layer 25 are separated in the vicinity of the center of the through hole in the illustrated example. Here, in FIG. 13, the ends of the first conductive adhesion layer 15 and the second conductive adhesion layer 25 are clear, but the ends of the first conductive adhesion layer 15 and the second conductive adhesion layer 25 are clear. Instead, for example, the shape may be such that the film thickness gradually decreases.

The first conductive contact layer 15 and the second conductive contact layer 25 separated near the center of the through hole are electrically connected by a seed layer 35 formed on these upper layers. The seed layer 35 is an insulating layer 75 on the side wall of the through hole exposed from the first conductive contact layer 15, the second conductive contact layer 25, the first conductive contact layer 15 and the second conductive contact layer 25. It is formed in contact with a part. Further, a conductive layer 65 is formed on the upper layer of the seed layer 35. The conductive layer 65 conducts the first surface 101 and the second surface 102 of the substrate 100. The conductive layers 61 and 62 may serve as wirings, lands, electrodes, and the like. The remaining portion in the through hole 90 (inside the conductive layer 65) is filled with the insulating filling member 85. The insulating filling member 85 can typically be made of an organic insulating material.

As shown in FIG. 13, the interlayer insulating layer 81 is formed on the first surface 101 of the substrate 100, and the interlayer insulating layer 82 is formed on the second surface 102 of the substrate 100. Two or more of the interlayer insulating layers 81 and 82 and the insulating filling member 85 may be made of the same material, or each may be made of a different material. In the following description, when each of the interlayer insulating layers 81 and 82 is not distinguished, it may be referred to as an interlayer insulating layer 80. In this example, the interlayer insulating layer 80 is directly formed on the first surface 101 and the second surface 102 of the substrate 100, but another structure (wiring, transistor, capacitor, coil, etc.) is formed between them. It may be included. Although the structure having the conductive layers 61 and 62 and the interlayer insulating layer 80 one by one is shown, the structure is not limited to this, and a structure in which two or more layers are laminated may be used.

The interlayer insulating layer 80 can be made of an organic insulating material, an inorganic insulating material, or the like. Further, the organic insulating material and the inorganic insulating material may be laminated and configured. The opening 111 is formed on the first surface 101 side of the substrate 100, and the opening 112 is formed on the second surface 102 side of the substrate 100. When each of the openings 111 and 112 is not distinguished, it may be referred to as an opening 110.

[Process flow of through electrode substrate 1]
FIG. 2 is a flowchart illustrating a method for manufacturing a through electrode substrate according to the first embodiment of the present invention. The method for manufacturing the through electrode substrate is a step of forming a through hole 90 penetrating the first surface 101 of the substrate 100 and the second surface 102 on the opposite side of the first surface 101 (step S201), the first surface 101. A step of forming the first conductive adhesion layer 10 from the side (step S202), a step of forming the second conductive adhesion layer 20 from the second surface 102 side (step S203), the first conductive adhesion layer 10 and the first. 2 A step of forming a seed layer 30 which is in contact with the conductive adhesion layer 20 and is arranged in contact with the side wall of the through hole 90 exposed from the first conductive adhesion layer 10 and the second conductive adhesion layer 20 (step S204). ), The step of forming the conductive layer 60 on the seed layer 30 (step S205), the step of etching the first conductive adhesive layer, the second conductive adhesive layer, the seed layer and the conductive layer to form a desired pattern. (Step S206) is provided. Hereinafter, each step will be described in order with reference to the drawings. It should be noted that this method for manufacturing the through electrode substrate does not prevent other steps from being included between the steps.

[Manufacturing method of through electrode substrate 1]
First, step S201 shown in FIG. 2 will be described with reference to FIGS. 3 and 4. FIG. 3 is a schematic view showing a cross section of a substrate provided with through holes in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. First, the substrate 100 is formed with a through hole 90 that penetrates the first surface 101 and the second surface 102.

In this example, the substrate 100 is a silicon substrate. In addition to silicon, the substrate 100 may be made of a silicon compound such as silicon carbide, a semiconductor such as gallium arsenide, quartz, glass, sapphire, or the like, or may be laminated. The thickness of the substrate 100 is not particularly limited, but is, for example, 100 μm to 800 μm.

The through hole 90 forms a mask (not shown) on one surface (for example, the first surface 101) of the substrate 100, and has RIE (Reactive Ion Etching) and DRIE (Deep RIE). It can be formed by dry etching processing such as ion etching), sandblasting, laser processing, and the like. Further, the through hole 90 is formed by forming a bottomed hole in the substrate that does not penetrate in the thickness direction, and then polishing and opening the surface opposite to one surface (for example, the second surface 102). May be good. The size of the opening of the through hole 90 is not particularly limited and may be, for example, 10 μm to 100 μm. Further, the shape of the through hole 90 is not limited and is typically circular, but may be rectangular or polygonal in addition to circular. Although it depends on the use of the through electrode substrate 1, for example, the aspect ratio of the through hole 90 is 5 or more, preferably 8 or more. The aspect ratio refers to a value obtained by dividing the value of the depth of the through hole 90 by the size of the opening of the through hole. One or more such through holes 90 are arranged on the substrate 100.

In each figure, the through hole 90 shows a straight shape in the thickness direction of the through electrode substrate 1, but the shape is not limited to this, and for example, the opening on the first surface 101 side as shown in FIG. 15 is the second surface 102. It may have a tapered shape larger than the opening on the side. Further, the shape is not limited to the tapered shape, and may be a concave shape in which the central portion of the through hole 90 is concave as shown in FIG. 16 or a convex shape in which the central portion of the through hole 90 is convex as shown in FIG. ..

FIG. 4 is a schematic view showing a cross section of a substrate on which an insulating layer is formed in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. As shown in FIG. 4, an insulating layer 70 (insulating layers 71, 72, 75) is formed on the substrate 100 shown in FIG. The insulating layer 70 may be formed at least on the side wall of the through hole 90.

The insulating layer 70 is a single-layer film made of one material selected from, for example, an inorganic insulating material such as silicon oxide, silicon nitride, silicon oxide, and an organic insulating material such as polyimide and benzocyclobutene, or 2 It may be a laminated film made of the above materials. The insulating layer 70 is formed by a CVD method (plasma CVD method, thermal CVD method, etc.), PVD method (vapor deposition method, sputtering method, etc.), thermal oxidation method, spray coating method, or the like. The thickness of the insulating layer 70 is not particularly limited as long as the desired insulating property can be obtained, but can be, for example, 0.5 μm to 5 μm. In addition, another structure may exist between the first surface 101 of the substrate 100 and the insulating layer 71. When the substrate is a substrate having insulating properties such as quartz, glass, and sapphire, the presence of the insulating layer 70 is optional.

Next, step S202 shown in FIG. 2 will be described with reference to FIG. FIG. 5 is a schematic view showing a cross section of a substrate on which a first conductive adhesion layer is formed from one side surface in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. The first conductive adhesion layer 10 is formed on the substrate 100 shown in FIG. The first conductive adhesive layer 10 is formed on the insulating layer 70 from the first surface 101 side. The first conductive adhesion layer 10 is formed by a sputtering method.

The sputtering method is a film forming method in which the film forming atoms reach the substrate with high energy, but in order to stabilize the discharge, for example, 0.1 to 1.0 Pa of Ar gas is applied in the chamber. Introduce to. The cluster of the film forming source sputtered by the ions of Ar gas has a high probability of colliding with Ar atom during flight, the traveling direction is changed, and the directivity of the cluster is lowered. As a result, when a film is formed from the first surface side of a through hole having a high aspect ratio such that the aspect ratio exceeds 5, the first film is formed on the side wall of the through hole as shown in FIG. The position of the end portion of the conductive adhesion layer 15 is a position less than half the depth of the through hole with respect to the first surface 101 side.

In the present invention, good adhesion can be obtained because the film-forming atoms that reach the substrate react with the base film with surplus energy by the sputtering method in which the film-forming atoms reach the substrate with high energy. .. When a film is formed by the sputtering method, a mixing layer in which the base atom and the film-forming atom are mixed is formed at the interface between the base film and the sputtering film, and the mixing layer causes good adhesion between the base film and the sputtering film. Is considered to be obtained.

Next, step S203 shown in FIG. 2 will be described with reference to FIG. FIG. 6 is a schematic view showing a cross section of a substrate on which a second conductive adhesion layer is formed from another side surface in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. The second conductive adhesion layer 20 (second conductive adhesion layers 22, 25) is formed on the substrate 100 shown in FIG. The second conductive adhesive layer 20 is formed on the insulating layer 70 from the second surface 102 side opposite to the first surface 101. The second conductive adhesion layer 20 is formed by a sputtering method in the same manner as the first conductive adhesion layer 10. As a result, as shown in FIG. 6, the position of the end portion of the second conductive adhesion layer 25 formed on the side wall of the through hole is less than half the depth of the through hole with respect to the second surface 102 side. It becomes a position, and the first conductive adhesion layer 15 and the second conductive adhesion layer 25 are separately formed on the side wall of the through hole. At this time, in the side wall of the through hole, the insulating layer 75 of the side wall of the through hole is exposed near the center of the first surface 101 and the second surface 102 in the depth direction of the through hole.

The first conductive adhesion layer 15 and the second conductive adhesion layer 25 have good adhesion to the underlying insulating layer 75, and are, for example, titanium (Ti), chromium (Cr), aluminum (Al), compounds thereof, or These alloys and the like can be used. The thickness of the first conductive adhesion layer 15 and the second conductive adhesion layer 25 is not particularly limited, but may be, for example, 50 nm to 400 nm. The first conductive adhesion layer 15 and the second conductive adhesion layer 25 may be made of the same material or may be different materials from each other.

In the first embodiment, an example in which a film having high adhesion is formed by a sputtering method has been described, but the present invention is not limited thereto. For example, good adhesion can be obtained by using a material that utilizes the reactivity with the base film. For example, when the undercoat is silicon oxide, good adhesion can be obtained by using a material having an enthalpy of oxide formation lower than that of silicon. For example, when titanium having a lower oxide formation enthalpy than silicon is formed on silicon oxide, the oxygen atom near the interface between silicon oxide and titanium tends to be titanium oxide, which is more stable than silicon oxide. It combines with titanium using the energy of the film. That is, since the interface between silicon oxide and titanium is scientifically bonded, good adhesion can be obtained. That is, good adhesion can be obtained by using a material in which the oxide or nitride of the conductive layer has a lower enthalpy of formation than the oxide or nitride of the base film as the material used as the conductive layer. It is thought that it can be done.

Next, step S204 shown in FIG. 2 will be described with reference to FIGS. 7 and 8. FIG. 7 is a schematic view showing a cross section of a substrate on which a seed layer is formed from one side surface in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. The seed layer 30 (seed layers 31, 35) is formed by diagonal vapor deposition. The detailed method of oblique vapor deposition will be described later (see FIGS. 19 and 20).

FIG. 8 is a schematic view showing a cross section of a substrate on which a seed layer is formed from other sides in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. Here, too, the seed layer 30 (seed layers 32 and 35) is formed by diagonal vapor deposition from the second surface side of the substrate by the same method as in FIG. 7. Subsequently, by performing diagonal vapor deposition from the second surface side as well, a seed layer 35 having a substantially uniform film thickness in the depth direction of the through hole is formed inside the through hole. Here, in the first embodiment, an example in which the seed layer 30 is formed by diagonal vapor deposition is shown, but the present invention is not limited to this, and for example, electroless plating or the like can be used. As a result, most of the seed layer 30 formed by a method other than the sputtering method is formed on the first conductive adhesion layer 15 and the second conductive adhesion layer 25 on the side wall of the through hole 90, thereby forming a lower layer. Adhesion is improved. Here, the seed layer 35 is formed so as to get over the stepped portion of the first conductive adhesion layer 15 and the second conductive adhesion layer 25. It is considered that the seed layer 35 and the first conductive adhesion layer 15 or the second conductive adhesion layer 25 come into contact with each other at the stepped portion to obtain an anchor effect and suppress the peeling of the seed layer 30.

Here, the seed layer 30 functions as a layer that supplies power by electrolytic plating when forming a conductive layer in a later step. The seed layer 30 is preferably made of the same material as the conductive layer, and copper (Cu), silver (Ag), gold (Au), or the like can be used. The film thickness of the seed layer 30 is not particularly limited, but may be, for example, in the range of 0.1 μm or more and 1.0 μm or less. It is preferably 600 nm or more and 900 nm or less. Within such a range, the film thickness of the conductive layer formed in the through hole 90 can be uniformly controlled.

Next, step S205 shown in FIG. 2 will be described with reference to FIG. FIG. 9 is a schematic view showing a cross section of a substrate on which the conductive layer 60 is formed in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. Although not shown, in order to obtain the structure shown in FIG. 9, first, a film-like resist called a photosensitive dry film resist is formed on both sides of the substrate 100 on which the seed layer 30 is formed, and the conductive layer is formed by photolithography. A mask is formed by opening the area to be formed. Next, the conductive layer 60 (conductive layers 61, 62, 65) as shown in FIG. 9 is formed by supplying power to the seed layer 30 and performing electrolytic plating with the mask on. As the material of the conductive layer, for example, Cu, Ag, Au or the like can be used. Among them, Cu is preferable because of its low material cost. By forming a thin film along the side wall of the through hole 90, the production efficiency is improved. The film thickness of the conductive layer 60 is not particularly limited, but may be, for example, in the range of 1 μm or more and 20 μm or less. It is preferably 3 μm or more and 15 μm or less. Within such a range, a through electrode having good conductivity can be obtained.

The conductive layer 60 may be formed on the side wall of the through hole 90 and the first or second surface of the substrate in separate steps, but the production efficiency can be improved by performing the above in an electrolytic plating step capable of forming the above at the same time. improves. Since the conductive layer is formed on the side wall of the through hole 90 and the first surface or the second surface of the substrate in the electrolytic plating step, the film thickness of the conductive layer at each location is substantially the same. After that, the mask is removed from the substrate 100. By the above steps, the structure shown in FIG. 9 can be obtained.

Next, step S206 shown in FIG. 2 will be described with reference to FIG. FIG. 10 is a schematic view showing a cross section of a substrate in which a conductive layer is patterned in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. The structure shown in FIG. 10 is obtained by etching the structure shown in FIG. 9 from the first surface side and the second surface side. Dry etching may be used for etching, or wet etching may be used. Dry etching has the advantage of shortening the process because the first conductive adhesion layer, the second conductive adhesion layer, and the seed layer can be etched at once, and the conductive layer 65 formed on the side wall of the through hole is formed. Since almost no etching is performed, the shape change of the conductive layer 65 can be suppressed. Further, wet etching has an advantage of shortening the process because the first surface and the second surface can be etched at the same time.

In the first embodiment, a method of forming a conductive layer after patterning has been described, but when the conductive layer 60 is not used, patterning may be performed after forming the seed layer 30.

FIG. 11 is a schematic view showing a cross section of a substrate on which a first photosensitive resin layer is formed in the method for manufacturing a through silicon via substrate according to the first embodiment of the present invention. The first photosensitive resin layer 89 is formed on the second surface 102 side of the substrate 100 shown in FIG. The first photosensitive resin layer 89 is formed by, for example, a laminating device or the like using a negative type dry film resist. A part of the first photosensitive resin layer 89 is partially introduced into the through hole 90. The dry film resist used is not limited to the negative type, but may be a positive type.

At this time, the opening on the second surface 102 side of the through hole 90 is closed by the first photosensitive resin layer 89. The first photosensitive resin layer 89 may be formed by using a material other than the dry film resist as long as it is formed so as to close the opening on the second surface 102 side of the through hole 90. It may be a liquid resist having a high viscosity (for example, 20 cp or more).

FIG. 12 is a schematic view showing a cross section of a substrate on which a second photosensitive resin layer is formed in the method for manufacturing a through silicon via substrate according to the first embodiment of the present invention. As shown in FIG. 12, a second photosensitive resin layer 88 is formed on the first surface 101 side of the substrate 100. The second photosensitive resin layer 88 is formed by, for example, a laminating device or the like using a negative type dry film resist. The dry film resist used is not limited to the negative type, but may be a positive type.

At this time, the surrounding environment of the substrate 100 is reduced to a reduced pressure (pressure lower than the atmospheric pressure) for laminating. As a result, the dry film resist of the second photosensitive resin layer 88 is introduced into the through hole 90 and comes into contact with the first photosensitive resin layer 89. As a result, the photosensitive resin layer is filled in the through hole 90, that is, the insulating filling member 85 is formed. In the state shown in FIG. 10, the portion remaining as a space in the through hole 90 (the portion surrounded by the conductive layer 65) is filled with the first photosensitive resin layer 89 and the second photosensitive resin layer 88. Will be done. Since the second photosensitive resin layer 88 is laminated while exhausting the gas in the through hole 90 under a reduced pressure state, it is possible to suppress the generation of voids and the like in the through hole 90. In addition, in this specification, the filling is not limited to the case where the space (void or the like) is completely eliminated, and does not exclude the case where a small amount of space remains inside the through hole 90.

When forming the second photosensitive resin layer 88, it is desirable that the pressure in the surrounding environment of the substrate 100 when laminating the dry film resist is as close to vacuum as possible. This facilitates the introduction of the dry film resist into the through hole 90. Not limited to the above method, the photosensitive resin layer may be formed on the first surface and the second surface after the through hole 90 is filled with the insulating material.

FIG. 13 is a schematic view showing a cross section of a substrate in which the first and second photosensitive resin layers are patterned in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. The first photosensitive resin layer 89 and the second photosensitive resin layer 88 formed on the substrate 100 of FIG. 12 are patterned by photolithography. As a result, as shown in FIG. 13, an opening 111 leading to the conductive layer 61 and an opening 112 leading to the conductive layer 62 are formed. After that, the photosensitive resin layer may be fired. FIG. 13 shows the interlayer insulating layer 80 (interlayer insulating layers 81 and 82) thus obtained from the photosensitive resin layer and the insulating filling member 85. The thickness of the interlayer insulating layer 80 on the first surface 101 and the second surface 102 of the substrate 100 is, for example, 10 μm to 100 μm, but may be thinner or thicker.

The through electrode substrate 1 manufactured as described above has a conductive layer (first conductive adhesive layer 15, second conductive adhesive layer 25, seed layer 35, conductive layer) formed along the side wall of the through hole 90. 65) allows the first surface 101 side and the second surface 102 side of the substrate 100 to be electrically connected. Further, by filling the inside of the through hole 90 with the insulating resin as described above, the manufacturing process can be shortened as compared with filling with a metal material by the electrolytic plating method, and the voids inside the through hole 90 can be shortened. It is also possible to suppress the occurrence.

FIG. 14 is a schematic view showing a cross section of a substrate on which a wiring layer is formed in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. The through silicon via substrate 1 manufactured as shown in FIG. 13 may be used to form the wiring layers 121 and 122 as shown in FIG. A wiring layer is formed on the through electrode substrate 1 shown in FIG. 13, and the wiring layers 121 and 122 are obtained by performing patterning on the wiring layer by photolithography. In addition, such a wiring layer may be multi-layered via an interlayer insulating film.

The wiring layers 121 and 122 thus obtained (usually the outermost wiring layer in the case of multi-layering) are used as connection terminals when connecting to another through electrode substrate 1 or the like.

[Method of forming the seed layer 30]
Here, the method of forming the seed layer 30 shown in FIGS. 7 and 8 will be described in detail. In the step of forming the seed layer 30, it is necessary to form a conductive layer inside a through hole having a high aspect ratio such that the aspect ratio exceeds 5, so that a film forming method having good film turning properties is required. be. As a method with good film turning property, for example, a method in which film growth occurs isotropically with respect to a growth surface such as an electroless plating method, or a method in which anisotropy such as oblique vapor deposition is high and a film forming source and a substrate are used. There is a method of forming a film with good rotation by positioning the film. Here, as an example, a film forming method by oblique vapor deposition will be described in detail. The diagonal vapor deposition is a vapor deposition set so that the vapor deposition material flying from the vapor deposition source reaches the surface of the substrate at an angle with respect to the perpendicular line on the surface of the substrate to be deposited.

FIG. 18 is a schematic view of a film forming apparatus by oblique vapor deposition in the method for manufacturing a through electrode substrate according to the first embodiment of the present invention. The film forming apparatus shown in FIG. 18 includes a vacuum chamber 150 that achieves a high vacuum for vapor deposition, a turbo molecular pump (TMP) 220, and a gate valve 222. The vacuum chamber 150 fixes the holder 141 and the holder 141 for fixing the substrate in a state where the angle 132 formed by the lines of the vapor deposition material is tilted at a constant angle 132 on the plane including the line parallel to the flight direction of the vapor-film deposition material and the vertical line 130 of the substrate. It is equipped with a rotary support column 140 for rotating the holder 141 while maintaining a constant angle 132, a pit 210 for holding the vapor deposition source 212, and an electron gun 200 for generating an electron beam 201 for evaporating the vapor deposition source 212.

During the vapor deposition, it is desirable to use TMP in a high vacuum state of, for example, 10 ^-3 to ^10-6 Pa in order to improve the straightness of the evaporated vapor-filmed material 214. When the vapor deposition is performed in such a high vacuum state, the vaporized vapor deposition material 214 collides with the gas molecules in the chamber at a lower probability, so that the change in the traveling direction due to scattering is reduced. As a result, the thin-film deposition material 214 reaches the substrate with extremely high straightness, so that sufficient coverage can be obtained even for a through hole having a high aspect ratio such that the aspect ratio exceeds 5. .. Further, by performing the vapor deposition while rotating the rotary support column 140 with the holder 141 tilted, the film can be uniformly formed in the circumferential direction of the through hole.

FIG. 19 is a schematic view showing a cross-sectional view of a through silicon via substrate in which a conductive layer is formed by oblique vapor deposition in the method for manufacturing a through silicon via substrate according to the first embodiment of the present invention. The thin-film vapor deposition material 214 evaporated by the electron beam 201 is incident on the substrate at a constant angle 132 with respect to the perpendicular line 130 of the substrate. The angle 132 may be determined by the aspect ratio of the through hole in which the vapor-deposited film is to be formed. For example, at least the end portion 79 of the space where the first conductive adhesion layer 15 and the second conductive adhesion layer 25 are separated. The angle should be set so as to reach. Preferably, for example, the angle may be set so as to reach the end portion 29 of the conductive layer inside the through hole formed on the opposite side of the surface to be vapor-deposited. Specifically, when performing diagonal vapor deposition on a through hole having an aspect ratio of 5, the angle between the vertical line and the first surface or the second surface of the substrate is 5 ° or more and 20 ° or less. A vapor-deposited film can be formed with good properties.

<Second Embodiment>
In the first embodiment, the first conductive adhesion layer 10 or the second conductive adhesion layer 20 is sandwiched between the insulating layer 70 and the seed layer 30 on the side wall of the through hole. In the second embodiment, a structure in which a plurality of layers are sandwiched between the insulating layer 70 and the seed layer 30 on the side wall of the through hole will be described.

FIG. 20 is a schematic view showing a cross section of a substrate on which a conductive layer is formed in the method for manufacturing a through electrode substrate according to the second embodiment of the present invention. The difference from FIG. 13 is that the third conductive adhesive layer 40 (third conductive adhesive layer 41, 42, 45) is formed between the first conductive adhesive layer 10 and the seed layer 30. 2. The fourth conductive adhesive layer 50 (fourth conductive adhesive layer 51, 52, 55) is formed between the conductive adhesive layer 20 and the seed layer 30.

The third conductive adhesion layer 40 and the fourth conductive adhesion layer 50 are preferably made of a material having good adhesion to the seed layer 30, preferably the same material as the seed layer 30. In this case, it can be considered that the third conductive adhesive layer 40 and the fourth conductive adhesive layer 50 also serve as a part of the seed layer. Further, it is desirable that the third conductive adhesion layer 40 has good adhesion to the first conductive adhesion layer 10 and the fourth conductive adhesion layer 50 has good adhesion to the second conductive adhesion layer 20. In the second embodiment, since the third conductive adhesion layer 40 and the fourth conductive adhesion layer 50 are formed by the sputtering method, the interface between the first conductive adhesion layer 10 and the third conductive adhesion layer 40 is formed. Good adhesion can be obtained. Similarly, good adhesion can be obtained at the interface between the second conductive adhesion layer 20 and the fourth conductive adhesion layer 50. This is a mixing layer of layers that are in contact with the interface between the first conductive adhesion layer 10 and the third conductive adhesion layer 40 and the interface between the second conductive adhesion layer 20 and the fourth conductive adhesion layer 50, respectively. Is considered to be formed. Further, when the third conductive adhesion layer 40, the fourth conductive adhesion layer 50 and the seed layer 30 are made of the same material, good adhesion can be obtained even at these interfaces.

<Third Embodiment>
In the third embodiment, the semiconductor device manufactured by using the through electrode substrate 1 in the first or second embodiment will be described.

FIG. 21 is a diagram showing a semiconductor device according to a third embodiment of the present invention. In the semiconductor device 1000, three through electrode substrates 300 (310, 320, 330) are laminated and connected to the LSI substrate 400. The through electrode substrate 310 has connection terminals 511 and 512 formed of, for example, a semiconductor element such as a DRAM and formed of wiring layers 121, 122 and the like. One or more of these through electrode substrates 300 may be a through electrode substrate made of a substrate made of glass, sapphire, or the like. The connection terminal 512 is connected to the connection terminal 500 of the LSI board 400 by a bump 610. The connection terminal 511 is connected to the connection terminal 522 of the through electrode substrate 320 by a bump 620. The connection terminals 521 of the through electrode substrate 320 and the connection terminals 532 of the through electrode substrate 330 are also connected by bumps 630. For the bump 600 (610, 620, 630), for example, a metal such as indium, copper, or gold is used.

When the through electrode substrates 1 are laminated, the number of layers is not limited to three, but may be two, or four or more. Further, in the connection between the through electrode substrate 1 and another substrate, not only the one using bumps but also other bonding techniques such as eutectic bonding may be used. Further, a polyimide, an epoxy resin or the like may be applied and fired to bond the through electrode substrate 1 to another substrate.

FIG. 22 is a diagram showing another example of the semiconductor device according to the third embodiment of the present invention. In the semiconductor device 1000 shown in FIG. 22, semiconductor chips (LSI chips) 410 and 420 such as a MEMS device, a CPU, and a memory, and a through electrode substrate 300 are laminated and connected to the LSI substrate 400.

A through electrode substrate 300 is arranged between the semiconductor chip 410 and the semiconductor chip 420, and is connected by bumps 640 and 650. A semiconductor chip 410 is placed on the LSI substrate 400, and the LSI substrate 400 and the semiconductor chip 420 are connected by a wire 700. In this example, the through silicon via substrate 300 is used as an interposer for stacking a plurality of semiconductor chips and mounting them three-dimensionally, and by stacking a plurality of semiconductor chips having different functions, a multifunctional semiconductor device is manufactured. can do. For example, by using the semiconductor chip 410 as a 3-axis acceleration sensor and the semiconductor chip 420 as a 2-axis magnetic sensor, it is possible to manufacture a semiconductor device in which a 5-axis motion sensor is realized by one module.

When the semiconductor chip is a sensor formed by a MEMS device or the like, the sensing result may be output by an analog signal. In this case, the low-pass filter, amplifier, and the like may also be formed on the semiconductor chip or the through electrode substrate 300.

FIG. 23 is a diagram showing another example of the semiconductor device according to the third embodiment of the present invention. The above two examples (FIGS. 21 and 22) were three-dimensional implementations, but in this example, they are applied to a combined implementation of two dimensions and three dimensions. In the example shown in FIG. 23, six through electrode substrates 300 (310 to 360) are laminated and connected to the LSI substrate 400. However, not only are all the through electrode substrates 300 stacked and arranged, but they are also arranged side by side in the in-plane direction of the substrate. One or more of these through electrode substrates 300 (310 to 360) may be a through electrode substrate made of a substrate made of glass, sapphire, or the like.

In the example of FIG. 23, the through electrode substrates 310 and 350 are connected on the LSI substrate 400, the through electrode substrates 320 and 340 are connected on the through electrode substrate 310, and the through electrode substrate 330 is connected on the through electrode substrate 320. , The through silicon via substrate 360 is connected on the through silicon via substrate 350. As in the example shown in FIG. 22, even if the through silicon via substrate 300 is used as an interposer for connecting a plurality of semiconductor chips, the two-dimensional and three-dimensional mounting can be performed in combination. For example, the through electrode substrate 330, 340, 360 and the like may be replaced with a semiconductor chip.

The semiconductor device 1000 manufactured as described above includes various devices such as mobile terminals (mobile phones, smartphones, notebook personal computers, etc.), information processing devices (desktop personal computers, servers, car navigation systems, etc.), home appliances, and the like. It is installed in electrical equipment.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

The first embodiment will be described with reference to FIG. 20 of the second embodiment. First, as the substrate 100, a silicon substrate having a thickness of 400 μm was prepared. Next, a resist pattern is formed on one surface of the silicon substrate (here, the first surface 101) by photolithography, and the silicon substrate is etched in the thickness direction by DRIE through the resist pattern to form a large number of through holes of φ50 μm. bottom. The aspect ratio of the through hole was 8.

After forming the through hole and removing the resist pattern, a silicon oxide film was formed on the surface of the silicon substrate and the side wall of the through hole by thermal oxidation. Here, thermal oxidation was performed by heat treatment at 1050 ° C. in an oxygen atmosphere to form a silicon oxide film having a diameter of 500 nm.

Next, from the first surface 101 side of the silicon substrate, Ti having good adhesion to the silicon oxide film formed on the silicon substrate was formed at 100 nm as the first conductive adhesion layer 10 by a sputtering method. Subsequently, 100 nm of Ti was formed as the second conductive adhesion layer 20 from the second surface 102 side of the silicon substrate by the sputtering method in the same manner as described above. Here, the sputtering method was performed by the DC magnetron sputtering method under the following conditions.
・ Target-board distance = 100 mm
・ Argon gas flow rate = 30 sccm
・ Chamber pressure = 0.5Pa
・ Electric power = 3kW
・ Film formation temperature = room temperature

Next, 100 nm of Cu was formed as the third conductive adhesion layer 40 by the sputtering method from the first surface 101 side of the silicon substrate. Subsequently, Cu was formed as the fourth conductive adhesion layer 50 from the second surface 102 side of the silicon substrate to a thickness of 100 nm by the sputtering method in the same manner as described above to form a sputter seed layer. Here, the sputtering method was performed by the DC magnetron sputtering method under the following conditions.
・ Target-board distance = 100 mm
・ Argon gas flow rate = 30 sccm
・ Chamber pressure = 0.3Pa
・ Electric power = 5kW
・ Film formation temperature = room temperature

Next, Cu was formed as a seed layer 30 at a thickness of 800 nm on the Cu formed by the sputtering method from the first surface 101 side of the silicon substrate to form a thin-film vapor deposition seed layer. Further, from the second surface 102 side of the silicon substrate, a thickness Cu of 800 nm was formed by diagonal vapor deposition in the same manner. At this time, the inclination of the silicon substrate was adjusted so that the angle formed by the line parallel to the flight direction of the vapor-filmed material and the perpendicular line of the silicon substrate was 8 °. The vapor deposition method was carried out under the following conditions.
・ Distance between vapor deposition source and substrate = 100 mm
・ Vacuum reaching pressure = 5 × 10 ^-4 Pa
-Angle between the line parallel to the flight direction of the vapor-filmed material and the perpendicular line of the substrate = 8 °

Next, a resist pattern for plating was formed on both sides of the silicon substrate so as to cover a region where the formation of a conductive film should be avoided in electrolytic plating described later. Then, Cu was formed with a thickness of 10 μm on the portion exposed from the resist pattern for plating by electrolytic plating to form a conductive film.

Then, after removing the resist pattern for plating, unnecessary vapor deposition seeds and sputter seed layers existing on both sides of the silicon substrate were sequentially removed. As a result, the through silicon via substrate shown in FIG. 20 was obtained.

When a continuity test was performed on the through electrode substrate obtained as described above, it was confirmed that proper continuity was ensured in the chip containing the 1024 through electrodes.

As described above, according to the first embodiment, in a through electrode substrate having a through hole having a high aspect ratio, it is possible to obtain a through electrode substrate having high adhesion of the conductive layer in the through hole.

1: Through electrode substrate 10, 11, 15: First conductive adhesion layer 20, 22, 25, 29: Second conductive adhesion layer 30, 31, 32, 35: Seed layer 40, 41, 42, 45: First 3 Conductive adhesion layers 50, 51, 52, 55: Fourth conductive adhesion layers 60, 61, 62, 65: Conductive layers 70, 71, 72, 85: Insulation layer 79: Ends 80, 81, 82: Layers Insulating layer 85: Insulating filling member 88: Second photosensitive resin layer 89: First photosensitive resin layer 90: Through hole 100: Substrate 101: First surface 102: Second surface 110, 111, 112: Opening Parts 121, 122: Wiring layer 130: Vertical wire 132: Angle formed by the vertical wire of the substrate and the vapor deposition direction 140: Rotating support column 141: Holder 150: Vacuum chamber 200: Electron gun 201: Electron beam 210: Thin film 212: Vapor deposition source 214 : Evaporated material 222: Gate valve 300, 310, 320, 330, 340, 350, 360: Through electrode substrate 400: LSI substrate 410, 420: Semiconductor chip 500, 511, 512, 521, 522, 531: Connection terminal 600, 610, 620, 630, 640, 650: Bump 700: Wire 1000: Semiconductor device

Claims (6)

A substrate having a through hole penetrating the first surface and the second surface,
A first conductive layer provided on a part of the first surface side of the through hole,
A second conductive layer provided on a part of the through hole on the second surface side, separated from the first conductive layer,
A third conductive layer connecting the first conductive layer and the second conductive layer,
It is provided between the first conductive layer and the side wall of the through hole, between the second conductive layer and the side wall of the through hole, and between the third conductive layer and the side wall of the through hole, and is nitrided. A through silicon via substrate having an insulating layer comprising any of silicon, silicon oxide nitride, and an organic insulating material. The through electrode substrate according to claim 1, wherein the third conductive layer is in contact with the insulating layer between the first conductive layer and the second conductive layer. The through electrode substrate according to claim 1 or 2, wherein the first conductive layer and the second conductive layer are in contact with the insulating layer. Any one of claims 1 to 3, wherein the third conductive layer is continuously provided between the first conductive layer and the second conductive layer, and connects the first conductive layer and the second conductive layer. The through electrode substrate according to 1. The through electrode substrate according to any one of claims 1 to 4, wherein the substrate is a semiconductor substrate. The invention according to any one of claims 1 to 4, further comprising an insulating material continuously arranged from the first surface side to the second surface side inside the through hole from the third conductive layer. Through electrode substrate.

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