JPH1174298A - Formation of solder bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form void-free solder bumps. SOLUTION: A method for forming solder bumps comprises a process for forming an electrode 5 on a substrate 1, a process for forming a surface protective film 6 which covers the electrode 5, and a process for forming an insulating mask 7 having an opening 7a above the partial region of the electrode on the protective film 6. The method also comprises a process for exposing the electrode 7 on the bottom of the opening 7a by selectively removing the protective film 6 exposed on the bottom of the opening 7a by using a mask 7, a process for plating the exposed surface of the electrode on the bottom of the opening 7a with solder 9 by performing electroplating by using the electrode 5 as a cathode, and a process for etching off the mask 7. In addition, the method also comprises a process for etching off the protective film 6 extended outwards from the opening 7a, and a process for forming a solder bump 9a on the electrode 5 by melting the solder 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a solder bump by plating a solder on an electrode provided on the surface of a substrate and melting the plated solder.

2. Description of the Related Art Solder bumps are widely used in mounting technology for semiconductor devices such as flip bonding of semiconductor chips or ball array packages. The solder bumps are formed by plating the electrodes provided on one surface of the semiconductor chip or package with a resist having an opening for exposing the electrodes as a mask, and then removing the resist mask by etching. After that, it is formed by a process of melting the solder to form a solder bump welded on the electrode.

[0003] In order to secure the reliability of a semiconductor device, a sufficient adhesion strength and a sufficiently low contact resistance are required for welding such an electrode to a solder bump. Therefore, there is a need for a method of forming a solder bump that can bond an electrode and a solder bump with high adhesive strength and low contact resistance.

[0004]

2. Description of the Related Art A conventional method for forming a solder bump will be described below with reference to an embodiment in which a solder bump is formed on a flip chip. 3 and 4 are sectional process diagrams (part 1) and (part 2) of a conventional example of the present invention, respectively, showing a process of forming solder bumps on a semiconductor chip.

Referring to FIG. 3A, a semiconductor chip is used as a base 1, and an aluminum wiring 2 for leading out an internal circuit of the semiconductor chip is formed on the surface of the base. Further, an insulating film 3 made of, for example, a silicon oxide film having an opening 3a exposing the upper surface of the wiring 2 is provided on the base 1 and the wiring 2.

Referring to FIG. 3B, the solder bumps are formed by sequentially depositing an insulating film 3 and an adhesion layer 4 made of Ti and a Ni layer covering the opening 3a of the insulating film 3 by sputtering. Thereafter, the Ni layer is removed by etching, leaving the Ni layer extending on the insulating film 3 near the bottom surface of the opening 3a and the vicinity of the opening 3a, thereby forming a Ni electrode 5 for plating.

Next, referring to FIG. 3 (c), a resist is applied to the entire surface of the substrate 1, an opening 7a for exposing the electrode 5 is opened in the resist by photolithography, and a plating mask 7 is formed. I do. The opening 7a is provided in an internal region on the upper surface of the electrode 5 so that the outside of the electrode 5 is not plated with solder. Therefore, the electrode upper surface 5a around the electrode 5
Is covered with a resist mask 7. Next, a negative voltage is applied to the adhesion layer 4, and a Ni plating layer 8 that covers the exposed surface of the electrode 5 exposed on the bottom surface of the opening 7a is deposited by electroplating using the electrode 5 as a cathode.

Next, referring to FIG.
Is applied to the Ni plating layer 8 by electroplating using the electrode 5 as a cathode to fill the opening 7a with the solder 9 reaching the upper surface of the mask 7 around the opening 7a.
Is deposited.

Next, referring to FIG.
Is removed by etching, a mushroom-shaped solder 9 is formed on the upper surface of the electrode 5. Next, referring to FIG. 4F, using the Ni electrode 5 and the solder 9 as a mask, Ti
The portion of the adhesive layer 4 made of, which is exposed outside the electrode 5, is removed by etching.

Next, referring to FIG. 4 (g), the temperature is raised to melt the solder 9 to form a solder bump 9a welded on the electrode 5. However, since the electrode upper surface 5a around the electrode 5 covered with the resist mask 7 is not sufficiently cleaned even after the mask is removed, the wettability of the solder deteriorates,
When the solder 9 is melted, the gas trapped in this portion is not effectively eliminated, and remains as a void 10 on the electrode upper surface 5a around the electrode 5 after the formation of the solder bump.

The presence of the voids 10 may reduce the bonding strength of the solder bumps, or may cause the voids to expand during the mounting process of the semiconductor device using the solder bumps, thereby breaking the bonding of the solder bumps.

[0012]

As described above, in the conventional method of forming a solder bump by directly forming a mask on an electrode and solder-plating, the electrode upper surface 5a around the electrode 5 covered by the mask 7 is used. In addition, there is a problem that voids are generated and the bonding strength of the solder bumps and the reliability of bonding by the solder bumps are deteriorated.

The present invention provides a method for forming a solder bump which prevents contamination of the electrode surface by a mask material and prevents voids from being formed on the electrode by providing a surface protective film between the electrode and the mask. The purpose is to:

[0014]

FIG. 1 is an explanatory view of the principle of the present invention, showing a process of forming a solder bump of a semiconductor device. FIG. 2 is a sectional process view of an embodiment of the present invention.
4 shows a cross section near a solder bump formation region of a semiconductor device.

Referring to FIGS. 1 and 2, the method of forming a solder bump according to the first aspect of the present invention comprises the steps of forming an electrode 5 on a substrate 1 and then protecting a surface of at least the electrode 5. Forming a film 6, and then forming the surface protective film 6
A step of forming an insulating mask 7 having an opening 7a formed on a partial region of the electrode 5 and then etching the surface protective film 6 using the mask 7 as an etching mask. A step of selectively removing the surface protective film 6 exposed on the bottom surface to expose the electrode 5 on the bottom surface of the opening 7a, and then performing electroplating using the electrode 5 as a cathode to form the bottom surface of the opening 7a. A step of plating solder 9 on the exposed surface of the electrode 5, a step of etching and removing the mask 7, and a step of removing the surface protective film 6 extending outside the opening 7 a. And a step of forming a solder bump 9a on the electrode 5 by melting the solder 9 and forming a solder bump 9a on the electrode 5. The method is described with reference to FIG. A step of forming an electrode 5 on the body 1, a step of forming a conductive surface protective film 6 covering at least the electrode 5, and a partial area of the electrode 5 on the surface protective film 6. A step of forming an insulating mask 7 having an opening 7a formed thereon, and then soldering on the exposed surface of the surface protective film 6 exposed on the bottom surface of the opening 7a by electroplating using the electrode 5 as a cathode. 9; a step of etching and removing the mask 7; a step of etching and removing the surface protective film 6 extending outside the opening 7a; F. Forming a solder bump 9a on the electrode 5 by melting. The third configuration is a method of forming a solder bump of the first or second configuration. The mask 7 is made of resist. And a fourth configuration is the method of forming a solder bump according to the first, second, or third configuration, wherein the surface protective film 6 is made of copper or a copper alloy, and the electrode 5 is , Nickel or a nickel alloy.

In the present invention, an electrode 5 is first formed on a base 1 with reference to FIG. Next, FIG.
Referring to, a surface protection film 6 covering the electrode 5 is formed on the base 1. The surface protective film 6 is formed at least on the entire surface of the electrode 5, but does not have to extend on the base 1 outside the electrode 5 if necessary. The material of the surface protective film 6 is
The electrode 5 is selected from materials having etching selectivity with respect to the material of the electrode 5 and having sufficient wettability with respect to solder after the surface protective film 6 is removed by etching. The surface protection film 6 can be made of Cu or Cu alloy for the electrode 5 made of, for example, Ti or Ni or an alloy thereof. Further, the surface protection film 6 can be made of a resin, for example, a resist. The etching selectivity of the surface protective film 6 with respect to the mask 7 is not always essential.

Next, referring to FIG. 1C, an insulating mask material, for example, a resist is deposited on the entire surface of the substrate 1,
An opening 7a is opened on the electrode 5 to form a mask 7 for selective plating.
To form This opening is formed in an internal region on the upper surface of the electrode 5 so that the opening 7a does not protrude outside the electrode 5.
Next, when the surface protective film 6 is insulative, and if necessary, the surface protective film 6 exposed on the bottom surface of the opening 7a is removed by etching. If the surface protection film 6 is conductive and does not need to be removed, the surface protection film 6 on the bottom surface of the opening 7a can be left without being etched as shown in FIG. Next, the solder 9 is plated using the electrode 5 as a cathode.

Next, referring to FIG.
Is removed by etching. For this etching, an appropriate etching method is selected according to the mask material, and is performed by, for example, ashing of the resist or dissolution in a chemical solution.

Next, referring to FIG.
Is used as an etching mask, the solder 9 is removed after the mask 7 is removed.
The surface protection film 6 exposed outside the formation region is removed by etching. Next, referring to FIG. 1 (f), the solder 9 is melted by heating and heating to form a solder bump 9 a on the electrode 5.

In the structure of the present invention described above, since the surface protective film 6 is interposed between the electrode 5 and the mask and the surface of the electrode 5 does not directly contact the mask 7, the surface of the electrode 5 is No contamination by residues after removal. In addition, the surface of the electrode 5 after removing the surface protective film 6 has good wettability to solder. Therefore, the molten solder 9 flows and covers the entire exposed surface of the electrode 5 without fail.
Gas is not retained on the surface of the electrode 5. Therefore, no void is generated on the surface of the electrode 5.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to an embodiment in which the present invention is applied to formation of a solder bump of a flip chip.

Referring to FIG. 2 (a), the chip has a silicon chip as a base 1 and an aluminum wiring 2 which is a wiring for leading out an internal circuit of the chip is formed on the surface thereof. An insulating film 3 made of a SiO ₂ film is provided. First, the insulating film 3 on the wiring 2
In addition, an opening 3 having a diameter of 80 μm,
Open a. Next, an adhesion layer 4 made of a 300 nm thick Ti layer and a 300 nm thick Ni layer are sequentially deposited by sputtering. Next, the Ni layer deposited by sputtering is etched with a 20% by weight nitric acid aqueous solution using a resist mask (not shown) to form a plating electrode 5 having a diameter of 100 μm and made of a Ni layer concentric with the opening 3a. The adhesion layer 4 is provided to improve the adhesion of the Ni electrode 5 and to provide a supply path for plating current to the electrode 5. The electrode 5 composed of a Ni layer deposited by sputtering is provided for use as a solder plating electrode and for improving the adhesive strength of Ni plating deposited thereon.

Next, a surface protective film 6 made of a Cu layer having a thickness of 100 nm is deposited on the entire surface of the substrate 1 by sputtering. Next, referring to FIG. 2 (b), a resist is applied to the entire surface of the base 1, and an opening 7a having a diameter of 80 μm is formed in the resist concentrically with the electrode 5 by photolithography to form a resist. The resist mask 7 is used. Then,
20% by weight of the surface protective film 6 exposed on the bottom of the opening 7a
Of ammonium persulfate aqueous solution as an etchant, and removed by etching at room temperature for 20 seconds. This surface protective film 6
This is because when Cu, which is a component of the surface protective film 6, remains in the solder bump formation region, Cu forms a compound with the solder to lower the bonding strength and increase the electrical resistance. Therefore, when such a problem does not occur, it is not necessary to remove the surface protection film 6.

Next, referring to FIG. 2C, a Ni plating layer 8 having a thickness of 2 μm is deposited on the exposed surface of the electrode 5 exposed on the bottom surface of the opening 7a by electroplating using the electrode 5 as a cathode. . The Ni plating layer 8 is provided as a diffusion barrier for solder. The voltage to the electrode 5 is supplied through the Ti adhesion layer 4 as a current path.

Next, a 40 μm thick Pb-5 wt% Sn solder 9 is plated on the Ni plating layer 8 by electroplating using the electrode 5 as a cathode. The solder opening 7a is completely buried, and thereafter, extends over the upper surface of the mask 7 near the opening 7a and is deposited in a semicircular shape. As a result, a mushroom-shaped cross section is exhibited.

Next, referring to FIG. 2D, the resist mask 7 is removed by etching. Next, the surface protective film 6 exposed by removing the resist mask 7 is coated with 20% by weight.
Of ammonium persulfate aqueous solution as an etchant, and removed by etching at room temperature for 20 seconds. As a result, the electrode upper surface 5a around the electrode 5 and the upper surface of the adhesion layer 4 are exposed.

Next, referring to FIG. 2E, the adhesion layer 4 exposed outside the electrode 5 is removed by etching for 5 minutes using a 0.5% hydrofluoric acid aqueous solution as an etchant. At this time, the thickness of the insulating film 3 to be etched is generally negligible compared to the thickness of the entire insulating film 3. Next, the temperature is raised to 250 ° C. to melt the solder 9 and form a solder bump 9 a having a diameter of 70 to 100 μm on the electrode 5.

In the solder bump 9a formed according to the present embodiment, the electrode upper surface 5 around the electrode 5 is formed by the transmission X-ray method.
No void was observed in a. On the other hand, in the conventional solder bump formed under the same conditions and dimensions except that the surface protective film 6 is not provided, the electrode upper surface 5 around the electrode 5 is formed.
A void of several tens μm was often observed in a.

[0029]

As described above, according to the present invention, the deterioration of the wettability of the solder on the electrode surface due to the mask material can be prevented by the surface protective film provided between the electrode and the mask. Therefore, it is possible to provide a method for forming a solder bump having a high bonding strength and a small electric resistance, thereby greatly contributing to the improvement of the reliability of the semiconductor device.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a sectional process view of an embodiment of the present invention.

FIG. 3 is a sectional process view of a conventional example (part 1).

FIG. 4 is a sectional view of a conventional example (part 2).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2 Wiring 3 Insulating film 3a, 7a Opening 4 Adhesion layer 5 Electrode 5a Electrode upper surface of peripheral part 6 Surface protective film 7 Mask 8 Ni plating layer 9 Solder 9a Solder bump 10 Void

Claims (4)

[Claims] A step of forming an electrode on a substrate, a step of forming a surface protective film covering at least the electrode, and forming an opening on the surface protective film over a partial region of the electrode. A step of forming the opened insulating mask, and then, by etching the surface protective film using the mask as an etching mask, the surface protective film exposed on the bottom surface of the opening is selectively removed. By exposing the electrode on the bottom surface, and then electroplating using the electrode as a cathode,
Plating a solder on the exposed surface of the electrode exposed on the bottom surface of the opening, then etching and removing the mask, and then etching the surface protective film extending outside the opening. A method for forming a solder bump, comprising: a step of removing; and a step of subsequently melting the solder to form a solder bump on the electrode. 2. A step of forming an electrode on a substrate, a step of forming a conductive surface protective film covering at least the electrode, and a step of forming an electrode on a partial region of the electrode on the surface protective film. Forming an insulating mask having an opening in the opening, and then plating the solder on the exposed surface of the surface protective film exposed on the bottom of the opening by electroplating using the electrode as a cathode; Next, a step of etching and removing the mask, a step of etching and removing the surface protective film extending outside the opening, and then, melting the solder to form a solder bump on the electrode. Forming a solder bump. 3. The method according to claim 1, wherein the mask is made of a resist. 4. A solder bump forming method according to claim 1, wherein said surface protection film is made of copper or a copper alloy, and said electrode is made of nickel or a nickel alloy. Method of forming bump.