JP3431321B2 - Bump forming method - Google Patents

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Industrial applications Conventional technology (Fig. 2) Problems to be Solved by the Invention (FIG. 2) Means for Solving the Problems (FIGS. 1 and 2) Action (Figs. 1 and 2) Example (FIGS. 1 and 2) The invention's effect

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump forming method,
For example, IC (Integrated Circuit) chips and LSI (La
It is suitable for application when forming a protruding electrode (so-called bump) on each external electrode (pad) formed on the circuit surface of a semiconductor element such as a rge scale IC).

[0003]

2. Description of the Related Art Conventionally, in this type of semiconductor device, bumps are formed on each pad by the following procedure. That is, as shown in FIG. 2A, first, on each pad 2 formed by using aluminum or the like on the circuit surface of the wafer 1A of the semiconductor element 1, chromium having good adhesion to the pad 2 and solder, An intermediate metal layer 3 made of a copper and silver is formed, and then a metal mask 4 having openings 4A corresponding to the pads 2 is formed on the wafer 1.
After being placed on the circuit surface of A, lead and tin, which are solder materials, are sequentially deposited on each intermediate metal layer 3 through each opening 4A of the metal mask 4 to deposit the lead deposition film 5 and tin deposition. The film 6 is laminated.

At this time, the lead vapor deposition film 5 and the tin vapor deposition film 6 are usually slightly wider than the intermediate metal layer 3 in consideration of the size of the bumps to be formed, and thus the protective film layer 7 forming the surface of the wafer 1A. The size is such that it slightly protrudes on the upper surface. Next, as shown in FIG. 2B, the metal mask 4 is removed from the wafer 1A to remove unnecessary lead vapor deposition film 5 and tin vapor deposition film 6, and then the wafer 1A is passed through a reflow furnace to remove each lead vapor deposition film 5 The lead and tin forming the tin vapor deposition film 6 are heated and melted to be uniformly mixed and alloyed. The solder formed at this time is spherically united on each intermediate metal layer 3 due to its surface tension. As a result, bumps can be formed on each of the pads 2 of the wafer 1A with high adhesion through the intermediate metal layer 3.

[0005]

By the way, in such a bump forming process, normally, lead is deposited on the intermediate metal layers 3 and around the intermediate metal layers 3 at a vapor deposition rate of about 30 [nm / SEC]. Deposited on layer 7. However, if lead is vapor-deposited on the wafer 1A at such a vapor deposition rate, new lead is sequentially supplied before the thermal energy of vapor-deposited lead is radiated. Thermal energy may be accumulated in the lead vapor deposition film 5 formed on the film layer 7, and as a result, the protective film layer 7 may be damaged.

In such a case, since the adhesion between the protective film layer 7 of the wafer 1A and the lead vapor deposition film 5 is increased, the lead vapor deposition film 5 is difficult to be peeled off from the protective film layer 7 easily. The lead which forms the lead vapor deposition film 5 on the film layer 7 and the tin which forms the tin vapor deposition film 6 on the protective film layer 7 are mixed and alloyed to form a solder, which forms the intermediate metal layer 3 The lead of the lead vapor deposition layer 5 formed above and the tin vapor deposition layer 6 formed on the intermediate metal layer 3 are mixed and cannot be integrated with the bump 8 formed by alloying. As shown in C), a small amount of solder 9 remains on the protective film layer 7 of the wafer 1A, which causes a problem that the yield after the reflow is deteriorated.

In order to solve such a problem, the conventional method shown in FIG.
As shown in (D), a method of forming a coating layer 10 made of a glass material or the like having a weak adhesion to solder on the protective film layer 7 around the intermediate metal layer 3 is widely used. However, according to this method, the wafer 1
Since it is necessary to provide a process for forming the coating layer 10 on A, the bump forming process becomes complicated.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a bump forming method which facilitates bump formation and has a high yield.

[0009]

In order to solve such a problem, in the present invention, the bump forming position (3) on the surface of the bump forming object (1) and the bump forming position (3) on the surface of the bump forming object (1) ( 3) After sequentially depositing a predetermined substance (5, 6) on the periphery, heat and melt the deposited predetermined substance (5, 6) so that the bump formation target (1) is on the bump formation position (3). In the bump forming method for forming bumps (8) on a substrate, among the materials of the bumps (8), bumps are formed on the bump forming positions (3) on the surface of the bump forming object (1) and on the surface of the bump forming object (1). Position (3) 1 around
The predetermined substance (5) to be vapor-deposited at the beginning is applied at a first vapor deposition rate at which it is difficult for the surface around the bump formation position (3) of the bump formation target (1) and the predetermined substance (5) to adhere to each other ,
Evaporate to a second thickness that is less than the desired first thickness
The first step and the predetermined substance (5) from the first vapor deposition rate
Which has a larger second deposition rate and is deposited up to the first thickness.
The second step and the second step are provided.

Further, in the present invention, the bump forming object (1) is a semiconductor device, and the bump forming position (3)
Is a pad (2) formed on the circuit surface of the semiconductor device.
I made it.

Further, in the present invention, the predetermined substance (5)
Is lead, and the deposition rate is such that lead is deposited at a thickness of about 10 nm per second.

[0012]

[0013]

[Function] Of the materials of the bump (8), the first on the bump forming position (3) on the surface of the bump forming target (1) and on the periphery of the bump forming position (3) on the bump forming target (1). The predetermined substance (5) to be vapor-deposited on the first target is deposited at a first vapor deposition rate at which it is difficult for the surface around the bump formation position (3) of the bump formation target (1) and the predetermined substance (5) to come into close contact with each other.
It vapor-deposited to the second thickness thinner than the target first thickness.
Then, the predetermined substance (5) is added to the first vapor deposition rate higher than the first vapor deposition rate.
Since the vapor deposition is performed to the first thickness at the vapor deposition rate of 2, the predetermined substance (5) vapor-deposited around the bump formation position (3) on the surface of the bump formation target (1) in the subsequent reflow step is the bump. It can be easily peeled from the surface of the object (3) to be formed.

Accordingly, the material of the bump (8) laminated on the surface of the bump forming object (1) is laminated on the bump forming position (3) on the surface of the bump forming object (1) during the reflow process. Since the material of the bump (8) and the bump forming position (3) are integrated together, a residue of the bump (8) is generated around the bump forming position (3) on the surface of the bump forming object (1). And the bump formation position of the bump formation target (1) without forming the coating layer (10) around the bump formation position (3) on the surface of the bump formation target (1) as is conventionally done. (3) The bumps (8) can be formed on the bumps, and thus a bump forming method with a high yield that can facilitate bump formation can be realized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

1 (A) to 1 (D), in which parts corresponding to those in FIGS. 2 (A) to 2 (D) are denoted by the same reference numerals, show a method of forming solder bumps according to the present invention. Figure 1
As in (A), the intermediate metal layer 3 is formed on each pad 2 of the wafer 1A of the semiconductor element 1 in the same manner as the conventional one. Subsequently, the metal mask 4 is placed on the wafer 1A, and lead is deposited on the intermediate metal layers 3 and the protective film layer 7 around the intermediate metal layers 3 through the openings 4A of the metal mask 4 at a normal vapor deposition rate. Wafer 1 slower than (30-50 [nm / sec])
The first lead vapor-deposited film 2 is formed by vapor-depositing the lead vapor-deposited film at a first vapor-deposition rate that does not easily adhere to A.
Form 0.

Then, as shown in FIG. 1B, the first lead vapor-deposited film 20 is formed on the first lead vapor-deposited film 20 through the opening 4A of the metal mask 4,
The second lead vapor deposition film 21 is formed by depositing lead at a second vapor deposition rate higher than the vapor deposition rate of. At this time, the thickness of the second lead vapor deposition film 21 is selected so that the total thickness of the first and second lead vapor deposition films 20 and 21 is the same as the intended thickness of the lead vapor deposition film. Then, tin is vapor-deposited on the second lead vapor deposition film 21 through the opening 4A of the metal mask 4 at a predetermined vapor deposition rate to form the tin vapor deposition film 22 on the second lead vapor deposition film 21.

Further, thereafter, as shown in FIG. 1C, the metal mask 4 is removed from the wafer 1A, and then the wafer 1A is passed through a reflow furnace, so that the intermediate metal layer 3 and the intermediate metal layer 3 are removed. Lead and tin forming the first and second lead vapor deposition films 20 and 21 formed around are heated and melted, mixed, and alloyed. Thus, as shown in FIG. 1D, the solder formed by mixing and alloying lead and tin vapor deposited on each intermediate metal layer 3 and around the intermediate metal layer 3 is formed on each intermediate metal layer by surface tension. The bumps 8 can be formed on each of the pads 2 by interposing the intermediate metal layer 3 on the pads 2.

In the case of this embodiment, in the step of forming the first lead vapor-deposited film 20, lead is deposited on each intermediate metal layer 3 of the wafer 1A and each of these intermediate metal layers at a deposition rate of about 10 [nm / sec]. (3) The vapor deposition is sequentially performed on the surrounding protective film layer 7 until the thickness becomes about 1 [μm]. In this case, the film thickness of the first and second lead vapor deposition films 20 and 21 may be controlled by, for example, performing vapor deposition of lead while monitoring using a film thickness monitor.

In the above-mentioned structure, in this bump forming method, the intermediate metal layer 3 formed on each pad 2 of the wafer 1A and the protective film layer 7 around the intermediate metal layer 3 are deposited at a normal evaporation rate. The first lead vapor deposition film 20 is formed by vapor-depositing lead at a slower first vapor deposition rate, and then, after forming the first lead vapor deposition film 20, at a second vapor deposition rate higher than the first vapor deposition rate. The second lead vapor deposition film 21 is formed by depositing lead. In this case, the first vapor deposition rate for forming the first lead vapor deposition film 20 is selected so that the protective film layer 7 of the wafer 1A and vapor-deposited lead are difficult to adhere to each other. The first lead vapor deposition film 20 formed on the protective film layer 7 around the layer 3 is easily peeled off from the protective film layer 7.

Therefore, in the reflow process performed between FIGS. 1C and 1D, the first and second lead vapor deposition films 20 formed on the protective film layer 7 around each intermediate metal layer 3 are formed. Two
1 and the tin forming the tin vapor deposition layer 22 formed on the protective film layer 7 around each intermediate metal layer 3 are mixed and alloyed to form solder on each intermediate metal layer 3. The lead forming the first and second lead vapor-deposited films 20 and 21 and the tin forming the tin vapor-deposited film 22 are mixed and alloyed with each other, and integrated with the solder to form a lump by the surface tension. It tends to be a sphere, and thus the solder is not left on the protective film layer 7 around each intermediate metal layer 3 and the bumps 8 are formed on each intermediate metal layer 3.
Can be formed.

Therefore, according to this solder bump forming method, for example, each intermediate metal layer 3 of the wafer 1A is conventionally used.
The coating layer 10 is provided on the surrounding protective film layer 7 (FIG. 1D).
The solder 9 (see FIG.
The bumps 8 can be formed on the intermediate metal layer 3 without leaving (C)), and thus the yield after reflow can be improved. Further, after the first lead vapor deposition film 20 is formed, the second lead vapor deposition film 21 is formed at the second vapor deposition rate higher than the first vapor deposition rate.
The bumps 8 can be formed on the pads 2 of the wafer 1A in a shorter time than when the second lead vapor deposition film 21 is formed at the same first vapor deposition rate as the first lead vapor deposition film 20.

According to the above construction, when lead is vapor-deposited on the intermediate metal layer 3 formed on each pad 2 of the wafer 1A and on the protective film layer 7 around each intermediate metal layer 3, the protection is performed. The step of forming a lead vapor deposition film formed by vapor depositing lead on the film layer 7 is divided into two steps, and in the first step, the first lead vapor deposition film is formed in which lead is smaller than the normal vapor deposition rate. 20 is vapor-deposited at a first vapor deposition rate that makes it difficult to adhere to the protective film layer 7 and is thinner than the final thickness of the lead vapor-deposited film, and at the second stage, the second vapor deposition is faster than the first vapor deposition rate.
Since the second lead vapor deposition film 21 is formed by depositing lead on the first lead vapor deposition film 20 at the vapor deposition rate of 1, each intermediate metal formed on each pad 2 of the wafer 1A The bumps 8 are formed on the layer 3 without the solder 9 (FIG. 1C) remaining on the protective film layer 7 around each intermediate metal layer 3.
Can be formed, and thus a bump forming method with a good yield that facilitates bump formation can be realized.

In the above embodiment, the wafer 1
10 [nm / sec on each intermediate metal layer 3 formed on each pad 2 of A and on the protective film layer 7 around each intermediate metal layer 3
], The case where the first lead vapor deposition film 20 is formed is described, but the present invention is not limited to this, and the point is that lead is vapor-deposited on the protective film layer 7 around each intermediate metal layer 3. If the vapor deposition rate at which the first lead vapor deposition film 20 formed by the above is difficult to adhere, the first vapor deposition rate may be a size other than 10 [nm / sec]. .

Further, in the above-mentioned embodiment, the case where the present invention is applied to the step of forming the bumps 8 on each pad 2 of the wafer 1A has been described, but the present invention is not limited to this and, for example, printing is performed. It can also be applied to the case where bumps are formed on electrodes of a wiring board or other electronic components.

Further, in the above-described embodiment, a step of forming a lead vapor deposition film on each intermediate metal layer 3 formed on each pad 2 of the wafer 1A and on the protective film layer 7 around each intermediate metal layer 3 is described. Although the case where the process is performed in two stages has been described, the present invention is not limited to this, and the process is performed in two or more stages, and each stage is thinner than the final target thickness of the lead vapor deposition film. The lead vapor deposition film may be sequentially laminated. Even in this case, if the lead vapor deposition film of the bottom layer is formed at a vapor deposition rate that is smaller than the normal vapor deposition rate and that makes it difficult for the protective film layer 7 around each intermediate metal layer 3 and lead to adhere to each other, The same effect as the embodiment can be obtained.

Further, in the above-mentioned embodiment, lead is vapor-deposited first on each intermediate metal layer 3 formed on each pad 2 of the wafer 1A and on the protective film layer 7 around each intermediate metal layer 3. However, the present invention is not limited to this, and tin is first deposited on each intermediate metal layer 3 and on the protective film layer 7 around each intermediate metal layer 3 to form tin. The vapor-deposited film 22 may be formed, and in this case also, tin is vapor-deposited at a vapor deposition rate at which it is difficult for the tin to adhere to the protective film layer 7 around each intermediate metal layer 3 similarly to the embodiment. The effect can be obtained.

Further, in the above-mentioned embodiment, the case where the present invention is applied to forming the bumps 8 made of solder on the intermediate metal layers 3 formed on the pads 2 of the wafer 1A will be described. However, the present invention is not limited to this, and bumps made of a material other than solder may be used on the respective intermediate metal layers 3 formed on the pads 2 of the wafer 1A and around these intermediate metal layers 3. Protective film layer 7
It can also be applied to a case of forming by performing reflow after sequentially vapor-depositing on top. Also in this case, among the substances to be the material for the bumps, the substance that is deposited first on each intermediate metal layer 3 and on the protective film layer 7 around each of these intermediate metal layers 3 is the protective film of the wafer 1A. The vapor deposition may be performed at a vapor deposition rate that makes it difficult for the layer 7 to come into close contact with the layer 7.

[0029]

As described above, according to the present invention, the predetermined substance is sequentially deposited on the bump formation position on the surface of the bump formation target and on the periphery of the bump formation position on the surface of the bump formation target, and then the predetermined deposition is performed. In a bump forming method of forming a bump on a bump forming position of a bump forming target by heating and melting a substance, in a bump material, a bump forming position on a bump forming target surface and a bump forming target surface The first predetermined substance to be vapor-deposited on the periphery of the bump forming position is the first vapor deposition rate at which the surface around the bump forming position of the object on which the bump is formed and the predetermined substance are hard to be adhered to each other , and
Vapor deposition up to the second thickness, which is thinner than the final intended first thickness
And the first step of performing the predetermined substance at a rate higher than the first deposition rate.
A second vapor deposition to a first thickness at a large second vapor deposition rate.
By providing the step of (1) and (2), it is possible to form the coating layer on the surface of the bump forming object without forming a residue of the bump around the bump forming position on the surface of the bump forming object, and to form the coating layer on the surface of the bump forming object as conventionally performed. The bumps can be formed on the bump formation positions of the bump formation target without forming the bumps around the positions, and thus a bump formation method with a good yield that facilitates the bump formation can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining a bump forming method to which a bump forming method according to an embodiment is applied.

FIG. 2 is a cross-sectional view for explaining a conventional bump forming method.

[Explanation of symbols]

1 ... Semiconductor element, 1A ... Wafer, 2 ... Pad,
3 ... Intermediate metal layer, 7 ... Protective film layer, 8 ... Bump,
5, 20, 21 ... Lead vapor deposition film, 6, 22 ... Tin vapor deposition film.

Claims (3)

(57) [Claims] 1. A method of depositing a predetermined substance on a bump formation position on a surface of a bump formation target and on the periphery of the bump formation position on the surface of the bump formation target, and then melting the deposited predetermined substance by heating. In the bump forming method for forming a bump on the bump forming position of the bump forming target, the bumps on the bump forming position on the surface of the bump forming target and on the surface of the bump forming target of the material of the bump are formed. The first substance to be vapor-deposited on the periphery of the formation position is the first vapor deposition rate at which the surface around the bump formation position of the object to be bumped and the predetermined substance are hard to adhere to each other, and the final purpose is The second thinner than the first thickness
And a second step in which the predetermined substance is deposited at a rate higher than the first deposition rate.
And a second step of vapor-depositing to the first thickness at the vapor-deposition rate. Wherein said bump forming object becomes a semiconductor device, the bump forming position, according to claim 1, characterized in that in pads formed on the circuit surface of the semiconductor device <br / > Bump forming method. 3. The bump forming method according to claim 1, wherein the predetermined substance is lead, and the vapor deposition rate is a vapor deposition rate at which the lead is vapor-deposited at a thickness of about 10 [nm] per second. .