JPH088259A - Manufacture of semiconductor electrode - Google Patents

Abstract

PURPOSE:To ensure the strength of junction between a copper bump and a solder layer and the durability and strength of electrodes with reliability, by controlling the concentration of sulfur in the copper bump to a specified value or below. CONSTITUTION:A solder layer 231, 232 is placed on circuit conductors 251, 252 formed on the surface of a ceramic substrate 24. Heat is applied to melt the solder 231, 232 so that copper bumps 221, 222 will be mechanically and electrically connected with the circuit conductors 251, 252 on the ceramic substrate 24 through the solder 231, 232. When the concentration of sulfur in the copper bumps is set to 50ppm or below, it is possible to form semiconductor electrodes without degradation in endurance and strength. The solder bath used is composed of 50g/l of copper sulfate and sulfuric acid, each and 60ppm of chlorine with additive concentration varied as required. This ensures the strength of junction between the copper bumps and the solder layer and the durability and strength of the electrodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a flip-chip IC electrode, that is, a semiconductor electrode, in which durability bumps are less deteriorated by forming highly pure copper bumps on a semiconductor wafer.

[0002]

2. Description of the Related Art In a flip chip IC, a protruding electrode is formed at a lead-out terminal portion corresponding to a circuit element on a semiconductor chip on which circuit elements are integrated, and circuit wiring is provided through this electrode. It is configured by being connected to a substrate made of a ceramic or the like. Here, the protruding electrode formed on the semiconductor chip is known as a bump electrode, and FIG. 4 shows a sectional configuration of the bump electrode portion.

That is, bumps 12 are formed so as to project from the surface of a semiconductor chip 11 on which circuit elements are integrated, and the bumps 12 and the conductor circuit 14 formed on the surface of a ceramic substrate 13 are It is designed to be mechanically and electrically connected by the solder 15. The bumps 12 are composed of a metal having a good solder wettability, for example, a material such as gold, silver, or copper, and copper is generally used when cost is taken into consideration. By semiconductor chip
11 Protrudingly formed at a predetermined position on the surface.

However, the bumps 12 thus formed by electrolytic plating are connected to the conductor circuits 14 on the surface of the ceramic substrate 13 via the solders 15 at 100 ° C.
If left in the above high temperature for a long time, the tin contained in the solder 15 will form an alloy with the copper forming the bump 12, so that the connection between the bump 12 and the solder 15 may become defective. Have a problem.

In order to deal with such a problem of poor connection,
It is conceivable to form the bump 12 made of copper sufficiently thick in consideration of the copper-tin diffusion film thickness. But,
When the thickness of the bump 12 is set to about 20 to 30 μm, the growth amount of the copper-tin diffusion layer becomes 20 μm or less, and the problem of connection failure is solved, but the bonding between the semiconductor chip 11 and the ceramic substrate 13 is solved. The strength, that is, the electrode strength, becomes half or less of the initial strength, which is a standard for guaranteeing durability. Therefore, it becomes unsuitable for use especially in a high temperature environment.

A copper bump 12 as shown in FIG.
In the electrode structure that is connected to the conductor circuit 14 of the ceramic substrate 13 via the, when this is left for 1000 hours in a high temperature environment of, for example, 150 ° C., copper that forms the bump 12 and tin contained in the solder 15 Interdiffuse to form a copper-tin diffusion (alloy) layer 16. When microscopically observing the vicinity of the diffusion layer 16 thus formed, it was confirmed that a large number of voids 17 were formed at the boundary portion between the copper bump 12 and the diffusion layer 16, and at the same time, these voids 17 were formed. It was confirmed that sulfur was segregated inside the.

As a result of scrutinizing the process in which the voids 17 are formed and the sulfur is segregated inside the voids 17,
When electrolytic plating is performed to form 12, the co-deposited sulfur in the film segregates on the bumps 12 made of copper when left in a high-temperature environment, resulting in minute amounts of copper-tin interdiffusion. It was found that the voids grow and the durability strength is lowered.

Here, the electrolytic copper plating for forming the bumps 12 uses an acidic plating bath having low toxicity. In order to bring about brightening by electro-depositing on the plating film during this electrolytic plating. Further, a sulfur-containing organic substance such as dimercaptobenzothiazole and a polymer surfactant such as polyethylene glycol which is adsorbed on the plating interface to improve the uniformity of the coating are simultaneously added to the plating bath. Then, the sulfur contained in the sulfur-containing organic substance, which is an additive to the plating bath, is segregated and has a great influence on the durability strength of the electrode.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and in a bump formed by copper plating, particularly the bonding strength between the copper bump and the solder layer is reliably ensured. Thus, it is an object of the present invention to provide a method for manufacturing a semiconductor electrode that ensures the durability of the electrode and ensures sufficient reliability even in a high temperature environment.

[0010]

A method of manufacturing a semiconductor electrode according to the present invention forms a copper bump by electrolytic plating using a mask having an opening corresponding to a bump electrode forming region on a semiconductor chip surface. Then, a solder layer is formed on the copper bumps formed in the bump forming step. In the bump forming step by the electroplating, the amount of sulfur eutectoid is controlled to 50 ppm or less depending on the content of the sulfur-containing organic substance which is an impurity contained in the plating bath. For this reason, for example, the plating bath is composed of a copper sulfate bath, and when the sulfur-containing organic substance and the polymer are added to the plating bath as an additive, the content of the sulfur-containing organic substance is controlled to 0.5 vol% or less. I am trying to do it.

[0011]

In the method of manufacturing a semiconductor electrode having such a structure, paying attention to the fact that the sulfur component co-deposited in the copper plating film has an influence on the decrease in the durability strength of the electrode.
Based on the relationship between the sulfur concentration in the copper bumps and the durability strength of the electrode when left in a high temperature environment, the sulfur concentration in the copper bumps is set to 50 ppm or less to form a semiconductor electrode with little decrease in electrode durability strength. I found that I could do it. Then, the content of the sulfur-containing organic substance in the additive to the electrolytic plating bath is optimized to reduce the sulfur concentration in the copper bumps, and the durability of the electrode is reduced even when left in a high temperature environment for a long time. As a result, a highly reliable semiconductor electrode is formed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a resist mask is first formed on the surface of a semiconductor chip 21 on which circuit elements are integrally formed, and openings are formed in this mask in correspondence with the electrode lead-out portions of the circuit elements formed on the semiconductor chip 21. Has been done. Then, partial copper plating is applied to the surface of the semiconductor chip 21 corresponding to the openings from above the resist mask to form copper bumps 221 and 222 in a protruding manner. In this case, the copper bump 221
The plating time is controlled so that the thickness of each of the electrodes 222 and 222 is 35 μm. When the copper bumps 221 and 222 are formed by plating in this way, unnecessary portions such as a resist mask are removed by etching, and the solder bumps 231 and 232 on the tops of the copper bumps 221 and 222 protruding from the surface of the semiconductor chip 21 respectively. Form the layers. Here, the composition of the solders 231 and 232 was Sn 40%.

After the copper bumps 221 and 222 and the layers of the solders 231 and 232 are formed on the copper bumps 221 and 222 in this manner, the cleaned and cut semiconductor chip 21 is assembled and integrated with the ceramic substrate 24. That is, the layers of solder 231 and 232 are contacted on the circuit conductor 25 formed on the surface of the ceramic substrate 24, heat is applied to melt the solders 231 and 232, and the copper bumps 221 and 222 are soldered to the solders 231 and 232. And the circuit conductors 251 and 252 of the ceramic substrate 24 are mechanically and electrically bonded to each other.

Looking at the relationship between the sulfur concentration in the copper bumps and the electrode durability strength, paying attention to the fact that the sulfur component co-deposited in the copper plating film affects the reduction of the electrode durability strength. As shown in FIG. That is, when the sulfur concentration in the copper bumps is set to 50 ppm or less, it is possible to form a semiconductor electrode with a small decrease in durability strength.

Considering a copper plating process for forming such copper bumps 221 and 222, in this copper plating process, an acidic copper plating bath having low toxicity is used and 2 A / d is used.
It is carried out under a current density of about m ² . At this time, the plating bath used contains copper sulfate and sulfuric acid at 50 g / liter each,
And chlorine of 60 ppm, and the concentration of the additive is appropriately changed.

Example in which copper bumps 221 and 222 are formed by applying a commercially available acidic copper plating additive (main components: dimercaptobenzothiazole and polyethylene glycol) used for plating through-holes of a printed circuit board as an additive Will be described.

FIG. 3 shows the relationship between the sulfur-containing organic substance (dimercaptobenzothiazole etc.) in the plating bath and the concentration of sulfur co-deposited in the copper bump when such an additive is used. The amount of sulfur eutectoid tends to increase with an increase in the concentration of the sulfur-containing organic substance in the plating bath.
When such an additive is used, if the concentration of the sulfur-containing organic substance in the plating bath is controlled to 0.5 vol% or less, it is possible to suppress the deterioration of the durability strength of the electrode.

The additive is controlled by the user, and is replenished in the plating bath in a timely manner according to the amount of consumption. Generally, the concentration of the sulfur-containing organic substance in the plating bath tends to gradually rise with time as compared with the time of the initial construction bath, and therefore the concentration of the sulfur-containing organic substance in the plating bath is maintained at 0.5 vol% or less. In order to reduce the concentration of the sulfur-containing organic substance, the predetermined plating bath may be updated little by little in a specified cycle (for example, about 1 to 2 months). In this case, the hardness of the formed copper bump can monitor the sulfur concentration and the eutectoid sulfur concentration in the plating bath.

The function of the sulfur-containing organic compound added to the plating bath is that the sulfur in this additive is taken into the copper plating film as copper sulfide to densify the copper crystals and make the film glossy. To give. In the copper plating step for forming the copper bumps as shown in the embodiment, such an effect of giving luster is not always necessary. Therefore, only polymeric surfactants (polyethylene glycol, etc.) that have the effect of removing the sulfur-containing organic substances from the above-mentioned commercially available additives that are added to the prescribed plating bath and ensuring the uniformity of the plating film May be applied as an additive.

In this case, the co-deposition of sulfur in the copper bumps is 10 ppm or less, and the decrease in electrode durability strength can be sufficiently suppressed. In addition, since there is no organic sulfur component in the plating bath, it is not necessary to consider the fluctuation of the sulfur concentration in the plating bath, the plating bath management becomes easy, and the plating bath renewal cycle is, for example, one year. You can do more than that.

[0021]

As described above, according to the method of manufacturing a semiconductor electrode of the present invention, in the additive to the plating bath, the relationship between the sulfur-containing organic substance in the plating bath and the sulfur concentration in the copper bump is grasped. And the amount of co-deposition of sulfur is 50ppm
By controlling so as to be controlled below, particularly in the bump formed by copper plating, the bonding strength between the copper bump and the solder layer is surely ensured, and the durability strength of the electrode is surely obtained. In this way, sufficient reliability is secured even in a high temperature environment.

[Brief description of drawings]

FIG. 1 is a sectional view illustrating an electrode structure of a semiconductor device including a copper bump formed by a manufacturing method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a sulfur concentration in a copper bump and electrode durability strength.

FIG. 3 is a diagram showing a relationship between a sulfur-containing organic substance concentration in a plating bath and a sulfur concentration in a copper bump.

FIG. 4 is a diagram illustrating a bump electrode provided in a conventional semiconductor device.

[Explanation of symbols]

21 ... Semiconductor chip, 221, 222 ... Copper bump, 231, 232
… Solder, 24… Ceramic substrate, 251, 252… Circuit conductor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Motoki Ito 1-1, Showa-cho, Kariya city, Aichi Prefecture Nihon Denso Co., Ltd. (72) Inventor Motoaki Hyodo 1-1-chome, Showa town, Kariya city, Aichi prefecture Sozo Co., Ltd.

Claims (3)

[Claims] 1. A bump forming step of forming a copper bump on a terminal lead-out surface of a semiconductor chip by electrolytic plating through a pattern mask having openings corresponding to bump electrode forming regions, and a bump forming step. And a step of forming a solder layer on the copper bumps, wherein in the bump forming step, the content of sulfur-containing organic matter, which is an impurity contained in the plating bath, results in a co-deposition amount of sulfur. A method for manufacturing a semiconductor electrode, which is controlled to 50 ppm or less. 2. The plating bath is composed of copper sulfate and a copper sulfate bath containing sulfuric acid, and a sulfur-containing organic substance and a polymer are added to the plating bath as an additive. The method for manufacturing a semiconductor electrode according to claim 1, wherein the content is controlled to 0.5 vol% or less. 3. The method of manufacturing a semiconductor electrode according to claim 2, wherein the plating bath is renewed at a specified cycle so that the content of the sulfur-containing organic material is maintained at 0.5 vol% or less.