Bump structure, method for producing bump structure, and joint structure

Abstract

In this bump structure and method for producing the bump structure, a bump layer is formed by electroless plating, thus eliminating the need to provide a seed layer, and enabling bump layers to be formed at high yield and low cost. Further, components in a plating solution are not prone to contaminate a bump layer as impurities, enabling high crystallinity to be achieved.

Description

Bump structure, method for manufacturing bump structure, and bonding structure

[0001] The present disclosure relates to a bump structure, a method for manufacturing a bump structure, and a bonding structure.

[0002] In semiconductor devices, a technique for forming a bump on an electrode pad to achieve electrical connection with an external device is known. Patent Document 1 below discloses a technique for forming a bump by electrolytic plating, and particularly discloses a method for manufacturing a bump using a resist film provided with an opening that defines a plating region.

[0003] Japanese Patent Application Laid-Open No. 2003-297867

[0004] In recent years, it has become difficult to form fine bumps by electrolytic plating in response to finer pitches and smaller bump diameters. Particularly when a resist film is used, it has been difficult to perform exposure and development without misalignment during patterning of the resist film, and to eliminate resist residue during etching. As a result, the yield may decrease.

[0005] An object of one aspect of the present disclosure is to provide a bump structure with improved yield, a method for manufacturing the bump structure, and a bonding structure.

[0006] A bump structure according to one aspect of the present disclosure includes: an electrode mainly composed of Cu formed on a base material; an insulating frame body that surrounds the periphery of the electrode on the base material and has an opening exposing the surface of the electrode; and a bump layer mainly composed of Cu formed on the surface of the electrode exposed from the opening of the frame body.

[0007] A method for manufacturing a bump structure according to one aspect of the present disclosure includes the steps of: preparing a base material in which, on a main surface thereof, an electrode mainly composed of Cu and an insulating frame body that surrounds the periphery of the electrode and has an opening exposing the surface of the electrode are formed; and forming a bump layer mainly composed of Cu on the surface of the electrode exposed from the opening of the frame body by electroless plating.

[0008] A bonding structure according to one aspect of the present disclosure includes the bump structure described above.

[0009] The inventors have newly discovered that when forming a bump layer mainly composed of Cu on an electrode mainly composed of Cu, as in the bump structure, method for manufacturing the bump structure, and joining structure described above, the bump can be formed by electroless plating without using a resist film. Therefore, with the above bump structure, method for manufacturing the bump structure, and joining structure, deviations in exposure and development during patterning of the resist film and resist residue during etching cannot occur, and a high yield can be achieved.

[0010] According to various aspects of this disclosure, a bump structure, a method for manufacturing a bump structure, and a joint structure are provided that improve yield.

[0011] This is a schematic cross-sectional view showing a bump structure according to one embodiment. This is a flowchart showing the procedure for manufacturing the bump structure shown in Figure 1. This is a diagram showing the steps for manufacturing the bump structure shown in Figure 1. This is a schematic cross-sectional view showing a joint structure equipped with the bump structure of Figure 1.

[0012] Embodiments of this disclosure will be described in detail below with reference to the attached drawings. In the description of the drawings, the same or equivalent elements will be denoted by the same reference numeral, and redundant descriptions will be omitted.

[0013] First, a bump structure 1 according to one embodiment will be described with reference to Figure 1. The bump structure 1 is composed of a bump layer 20 formed on an electrode pad 12 (electrode) formed on a flat main surface 10a of a substrate 10. The substrate 10 has insulating properties and may be, for example, a silicon substrate or an organic substrate.

[0014] The electrode pad 12 is in the form of a film and has a thickness of, for example, 0.5 to 2 μm (1 μm as an example). The electrode pad 12 can be made of a metal (pure Cu) or alloy (Cu alloy) mainly composed of Cu. The electrode pad 12 according to this embodiment is made of pure Cu. The electrode pad 12 can be formed by electroplating using, for example, a seed layer (not shown) provided on the main surface 10a of the substrate 10. The electrode pad 12 according to this embodiment has a circular outer shape with a diameter of 2 to 50 μm when viewed in plan (i.e., viewed from a direction perpendicular to the main surface 10a of the substrate 10).

[0015] On the main surface 10a of the substrate 10, the electrode pad 12 is surrounded by a frame 14. The frame 14 is insulating and can be made of a resist material containing, for example, an insulating resin. The frame 14 has an opening 14a through which the surface 12a of the electrode pad 12 is exposed. In this embodiment, the frame 14 is a perfect circle with a diameter of 1 to 50 μm (5 μm as an example) in plan view. Since the diameter of the opening 14a of the frame 14 is smaller than the diameter of the electrode pad 12, only a part of the surface 12a of the electrode pad 12 is exposed through the opening 14a, not the entire surface. The frame 14 may cover the entire outer edge of the electrode pad 12 or it may cover it partially. The opening 14a of the frame 14 may be elliptical or polygonal in plan view. If the opening 14a is a polygon in plan view, the average value of the distances between substantially opposite sides in the polygon can be considered as the diameter of the opening 14a.

[0016] The bump layer 20 integrally covers the electrode pad 12 and the frame 14. The bump layer 20 according to this embodiment is composed of an embedded portion 21 located within the opening 14a of the frame 14 and a main body portion 22 located above the upper surface 14b of the frame 14.

[0017] The embedded portion 21 is provided to fill the opening 14a of the frame 14 and has the same planar shape as the opening 14a of the frame 14. In other words, in this embodiment, the embedded portion 21 of the bump layer 20 has a circular planar shape, and more specifically, it is cylindrical.

[0018] The main body portion 22 is substantially dome-shaped, with its upper surface curved in a convex manner. In this embodiment, the main body portion 22 is a perfect circle with a diameter of 15 μm or less (8 μm as an example) in plan view. The main body portion 22 may be elliptical or polygonal in plan view. If the main body portion 22 is polygonal in plan view, the average value of the distances between substantially opposite sides in the polygon can be considered as the diameter of the main body portion 22. Since the diameter of the main body portion 22 is larger than the diameter of the opening 14a and the diameter of the embedded portion 21 of the frame 14, the main body portion 22 covers the upper surface 14b in the peripheral region of the opening 14a. The main body portion 22 may cover the entire peripheral region of the opening 14a or it may cover it partially. By designing the main body portion 22 of the bump layer 20 to have a diameter of 15 μm or less, the bump layer 20 can be made extremely small in diameter. This allows for miniaturization of the entire bump structure 1, thereby enabling a narrower pitch and higher density arrangement by bringing the bump structures 1 closer together.

[0019] The bump layer 20 is in direct contact with the surface 12a of the electrode pad 12. In other words, there are no other layers (for example, a seed layer) interposed on the surface 12a of the electrode pad 12 (the interface between the electrode pad 12 and the bump layer 20).

[0020] The bump layer 20 is made of a material mainly composed of Cu. The bump layer 20 according to this embodiment is substantially made of pure Cu. By making it a material mainly composed of Cu, a bump layer 20 with high conductivity can be obtained. The bump layer 20 is formed by electroless plating, as will be described later. Components (for example, Ni) contained in the plating solution used for this electroless plating may be included in trace amounts in the bump layer 20. The bump layer 20 has a thickness of, for example, 2 μm or more (4 μm as an example). By making the bump layer 20 bulky with a thickness of 2 μm or more, sufficient clearance can be secured during bonding.

[0021] The bump layer 20 is covered by a coating layer 24. Specifically, the coating layer 24 covers the surface (i.e., the convex curved surface) of the main body portion 22 of the bump layer 20. The coating layer 24 can function as an antioxidant film that suppresses oxidation of at least the surface of the main body portion 22 of the bump layer 20. The coating layer 24 has a thickness of, for example, 0.05 to 0.2 μm (0.1 μm as an example). The coating layer 24 according to this embodiment is made of a material mainly composed of Ag. The coating layer 24 may also be made of a material mainly composed of Au or Pd in ​​addition to Ag. If the thickness of the coating layer 24 is 0.05 μm, oxidation of the bump layer 20 can be sufficiently suppressed, and if it exceeds 0.2 μm, the formation time and formation cost will be extra (although the effect of oxidation suppression will not change).

[0022] Next, the manufacturing method of the bump structure 1 described above will be explained with reference to Figures 2 and 3.

[0023] When fabricating the bump structure 1, first, a base material 10 is prepared (step S1 in Figure 2). In this step, the electrode pads 12 and frame 14 may be placed on the main surface 10a of the base material 10, or a base material 10 may be brought in with the electrode pads 12 and frame 14 already placed on the main surface 10a. In this state, as shown in Figure 3(a), a portion of the surface of the electrode pads 12 is exposed through the opening 14a of the frame 14.

[0024] Before forming the bump layer 20 on the substrate 10, known pretreatments may be performed as needed. Examples of pretreatments include surface modification by excimer irradiation or plasma treatment, degreasing, and acid cleaning.

[0025] Next, a bump layer 20 is formed on the surface 12a of the electrode pad 12 in the area exposed from the opening 14a of the frame 14 (step S2 in Figure 2). In this step, the bump layer 20 is formed by reducing electroless plating. For this electroless plating, a plating solution containing a copper compound, a complexing agent, and a reducing agent is used, and buffering agents, antioxidants, surfactants, brighteners, etc. can be added as needed. From the viewpoint of improving the deposition rate of electroless plating, a plating solution containing Ni can be used. As a result, a dome-shaped bump layer 20 as shown in Figure 3(b) is obtained, in which case the surface 12a of the electrode pad 12 is directly covered by the bump layer 20 within the opening 14a, the opening 14a is completely filled by the embedded portion 21 of the bump layer 20, and the upper surface 14b in the peripheral region of the opening 14a is covered by the main body portion 22 of the bump layer 20.

[0026] Subsequently, a coating layer 24 is formed on the bump layer 20 (step S3 in Figure 2), completing the bump structure 1 shown in Figure 1. The coating layer 24 is formed by reducing electroless plating. For this electroless plating, a plating solution containing a silver compound, a complexing agent, and a reducing agent is used.

[0027] In the bump structure 1 and its manufacturing method described above, the bump layer 20 is formed by electroless plating. However, in the fine bump structure 1 described above, it is difficult to form the bump layer 20 by electroplating. Electroplating requires a seed layer, but it is difficult to pattern the seed layer with high positional accuracy in the narrow area of ​​the surface 12a of the electrode pad 12 surrounded by the frame 14. Even if it were possible to provide it, the resist used for patterning may become a residue, leading to a decrease in yield and an increase in costs.

[0028] In this embodiment, the bump layer 20 is formed by electroless plating, eliminating the need for a seed layer. This allows for the formation of the bump layer 20 in the fine bump structure 1 described above with high yield and low cost. When the bump layer 20 is formed by electroless plating, components in the plating solution are less likely to be mixed into the bump layer 20 as impurities compared to when it is formed by electrolytic plating, thus achieving high crystallinity. Furthermore, if the bump layer 20 is as fine as described above, a bump layer 20 with sufficient height can be formed by electroless plating.

[0029] Figure 4 shows a bump joint structure 100 comprising a pair of bump structures 1A and 1B similar to the bump structure 1 described above. In the bump joint structure 100, the first bump structure 1A provided on the first substrate 10A and the second bump structure 1B provided on the second substrate 10B are joined together and electrically connected to each other. The first substrate 10A may be, for example, an electronic component or a mounting substrate, and similarly, the second substrate 10B may also be an electronic component or a mounting substrate.

[0030] The first bump structure 1A and the second bump structure 1B can be joined by solid-phase diffusion bonding while facing each other. Solid-phase diffusion bonding is performed, for example, by pressing the first bump structure 1A and the second bump structure 1B against each other at a temperature below the melting point in a vacuum or an inert gas atmosphere. At this time, each bump layer 20 of the first bump structure 1A and the second bump structure 1B does not melt substantially, and their shape is substantially maintained before and after bonding. During solid-phase diffusion bonding, the coating layer 24 covering the surface of each bump layer 20 of the first bump structure 1A and the second bump structure 1B is fed out from the bonding interface 5, and at the bonding interface 5, the bump layer 20 of the first bump structure 1A and the bump layer 20 of the second bump structure 1B are in direct contact. Therefore, in the bump bonded structure 100, the bump layers 20 facing each other are joined at the bonding interface 5. The surface of the bump layer 20 other than the bonding interface 5 is covered by the coating layer 24 even after the first bump structure 1A and the second bump structure 1B are bonded together.

[0031] The joined first bump structure 1A and second bump structure 1B are integrally covered by a coating resin 102. The coating resin 102 has insulating properties and is composed of, for example, an epoxy resin or a polyurethane resin. If one of the base materials 10A and 10B is an electronic component and the other is a mounting substrate, the coating resin 102 may be an underfill material filled between the electronic component and the mounting substrate.

[0032] As can be understood from the above description, this specification discloses the following: [Appendix 1] A bump structure comprising: an electrode formed on a substrate, mainly composed of Cu; an insulating frame on the substrate surrounding the electrode and having an opening through which the surface of the electrode is exposed; and a bump layer formed on the surface of the electrode, mainly composed of Cu, exposed through the opening of the frame. [Appendix 2] The bump structure according to Appendix 1, further comprising a coating layer covering the surface of the bump layer, mainly composed of Ag, Au, or Pd. [Appendix 3] The bump structure according to Appendix 2, wherein the thickness of the coating layer is in the range of 0.05 to 0.2 μm. [Appendix 4] The bump structure according to any one of Appendixes 1 to 3, wherein the thickness of the bump layer is 2 μm or more. [Note 5] A method for manufacturing a bump structure, comprising the steps of: preparing a substrate on which an electrode mainly composed of Cu and an insulating frame surrounding the electrode and having an opening through which the surface of the electrode is exposed are formed; and forming a bump layer mainly composed of Cu on the surface of the electrode exposed from the opening of the frame by electroless plating. [Note 6] The method for manufacturing a bump structure according to Note 5, further comprising the step of covering the bump layer with a coating layer mainly composed of Ag, Au, or Pd. [Note 7] A joint structure comprising the bump structure according to any one of Notes 1 to 4.

[0033] 1, 1A, 1B... Bump structure, 10, 10A, 10B... Substrate, 12... Electrode pad, 14... Frame, 20... Bump layer, 24... Coating layer, S1 to S3... Process, 100... Bump joint structure.

Claims

1. A bump structure comprising: an electrode formed on a substrate, mainly composed of Cu; an insulating frame on the substrate surrounding the electrode and having an opening through which the surface of the electrode is exposed; and a bump layer formed on the surface of the electrode, mainly composed of Cu, which is exposed through the opening of the frame.

2. The bump structure according to claim 1, further comprising a coating layer covering the surface of the bump layer, the coating layer having Ag, Au, or Pd as its main component.

3. The bump structure according to claim 2, wherein the thickness of the coating layer is in the range of 0.05 to 0.2 μm.

4. The bump structure according to claim 1, wherein the thickness of the bump layer is 2 μm or more.

5. A method for manufacturing a bump structure, comprising the steps of: preparing a substrate on which an electrode mainly composed of Cu and an insulating frame surrounding the electrode and having an opening through which the surface of the electrode is exposed are formed; and forming a bump layer mainly composed of Cu on the surface of the electrode exposed through the opening of the frame by electroless plating.

6. The method for manufacturing a bump structure according to claim 5, further comprising the step of covering the bump layer with a coating layer mainly composed of Ag, Au, or Pd.

7. A joint structure comprising the bump structure described in any one of claims 1 to 4.

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