KR20060003163A - Forming method of electroless ni bump with ni displacement plate - Google Patents

Abstract

The present invention relates to a bump forming method using an electroless nickel substitution plating layer.

This bump forming method according to the present invention includes a degreasing step of removing an oxide film on the surface of an aluminum pad of a wafer on which a passivation layer is formed; Neutralizing treatment to neutralize a surface of the aluminum pad in an alkaline state in the degreasing step; A nickel displacement plating step of forming a nickel displacement plating layer on the surface of the aluminum pad; An electroless nickel plating step of forming nickel bumps by electroless plating on the surface of the aluminum pad; An Au-immersion step of forming a gold plating layer by electroless plating on the surface of the nickel bumps to prevent oxidation of nickel.

According to the bump forming method using the electroless nickel substitution plating layer of the present invention, the problem of thinning the height of the silicon wafer in the bumping process is solved.

Description

Forming method of electroless Ni bump with Ni displacement plate

1 is a schematic diagram illustrating a method of forming nickel bumps through a conventional jinkate process,

2 is a flowchart showing each step of the method for forming an electroless nickel bump using the nickel displacement plating layer according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10: aluminum pad 12: passivation layer

14 silicon wafer 16: zinc ion group

18: nickel plating layer 20: gold plating layer

S1: Degreasing Step S2: Neutralization Treatment Step

S3: Nickel Displacement Plating Step

S4: electroless nickel plating step S5: gold-emulsion step

The present invention relates to a method for forming nickel bumps of a semiconductor chip, and more particularly, to a method for forming nickel bumps using a nickel displacement plating layer.

As a method of electrically connecting a semiconductor element to a board | substrate, the connection system by wire bonding using a metal wire is common. The wire bonding method is a method of connecting a pad of a semiconductor device and a substrate with a metal wire. However, as the performance of semiconductor chips has been greatly improved and the frequency has become high and miniaturized, the number of input / output pins of semiconductor devices has increased and a connection method with higher connection density has been required. As the demand for high performance and high density mounting is further accelerated, flip chip bonding technology has emerged.

Flip chip bonding method has been developed in recent years because of the excellent electrical performance and has the advantage of significantly reducing the size of the product, which is a metal medium that can be connected to the connection terminal with the substrate on the aluminum pad of the chip A bump is formed and connected to the substrate using ACF or NCP.

In the flip chip bonding method, bumps must be formed on the pads of the chip. The bumps are formed by vacuum deposition, screen printing using solder paste, a method using wire bonding, and an electroplating method. And electroless-plating.

These methods are selected and used in consideration of the characteristics and advantages of each method, and is one of the most widely used method of forming bumps by electroless plating.                         

The bump formation method using the electroless plating method is a technique for selectively forming bumps on an aluminum pad after a predetermined time by depositing a wafer in a plating solution, which has advantages of excellent selectivity and low cost.

FIG. 1 illustrates a method of forming a bump by an electroless nickel plating method including a gating process among various conventional bump forming methods as described above. As a first step, in the process shown by a in FIG. 1, the passivation layer 12 is formed to expose the aluminum pad 10 on top of the silicon wafer 14 on which the aluminum pad 10 is formed.

As a subsequent step, as shown by b in FIG. 1, the surface of the exposed aluminum pad 10 is activated. The activation process is to adsorb the zinc (Zn) ion group 16 on the surface of the aluminum pad 10 to roughen the surface of the aluminum pad 10. The zinc ion group is used as a nucleus in plating, and this process is called a zincate treatment.

On the surface active layer subjected to the gating treatment as described above, as shown in Fig. 1C, the nickel plating layer 18 is formed through electroless plating to form nickel bumps. Subsequently, as illustrated in FIG. 1D, gold (Au) is plated on the nickel plating layer to generate a gold plating layer 20 to form nickel / gold bumps.

The conventional nickel bump forming method through the electroless nickel plating method uses an oxidation / reduction reaction to remove metal ions from the metal to be plated, and does not require an expensive plating apparatus such as electroplating in the plating layer production. The bump can be formed by a simple operation, and has a merit of being superior to the bump formed by other plating methods in terms of flatness.

However, the electroless nickel bump formation method has the following problems.

First, as a result of a series of processes, the aluminum pad is increasingly etched and thinned, which may cause large defects in which the silicon wafer is exposed.

Second, for the same reason as the first problem, in order to perform a smooth bump forming process using the conventional bump forming method, the height of the aluminum pad of the wafer must be higher than an appropriate level, which causes another problem of increasing the wafer manufacturing cost.

Third, a defect in which the silicon wafer is exposed may occur due to the gating process, and thus, another problem that the manufacturing cost increases by increasing the height of the aluminum pad of the wafer is prevented.

Fourth, unlike the electroplating method, the electroless nickel bump formation method including the conventional jingate treatment process has a slow reaction rate and a large effect of material transfer, so that a technique for controlling the plating reaction such as temperature pH, stirring, and additives is more effective than electroplating. Since there is a difficult disadvantage, there is a problem that can be applied mainly to products having a relatively small number of electrode pads rather than products having a large number of electrode pads.

The present invention is to solve the above problems, to provide a method for forming an electroless nickel bump to prevent the silicon wafer is exposed to a thin thickness of the aluminum pad during the gating process.

Another object of the present invention is to provide a method for forming an electroless nickel bump, which can eliminate segregation of zinc particles generated in the conventional gating process.

It is still another object of the present invention to provide an electroless nickel bump forming method which prevents an oxide layer from being formed on a layer of an aluminum pad so that the adhesion of nickel plating is lowered.

In order to achieve the above object, the nickel bump forming method using the nickel displacement plating layer according to an embodiment of the present invention, degreasing to remove the oxide film on the surface of the aluminum pad of the wafer on which the passivation layer is formed. A neutralization treatment step of neutralizing the surface of the aluminum pad which is in an alkali state in the degreasing step, a nickel displacement plating step of forming a nickel displacement plating layer on the surface of the aluminum pad, and the aluminum. An electroless nickel plating step of forming nickel bumps by electroless plating on the pad surface, and an Au-immersion forming a gold plating layer by electroless plating on the surface of the nickel bumps to prevent oxidation of nickel. Steps.

Here, it is preferable to further include a washing step for washing the surface of the aluminum pad after each step in which a chemical reaction occurs.                     

In addition, the washing step is preferably performed by de-ionize water purged with N ₂ gas.

On the other hand, the neutralization treatment step is preferably carried out by HF.

In addition, the nickel displacement plating step is performed by a plating solution containing NiSO ₄ .6H ₂ O at a concentration of 0.05 mol / dm ³ and H ₂ NCH ₂ COOH at a concentration of 0.20 mol / dm ³ substantially. It is preferable.

In addition, the nickel displacement plating step is preferably carried out at a temperature of substantially 60 ℃ and a pH of pH 9.0 substantially.

In addition, the nickel displacement plating step is preferably performed in the state of stirring N ₂ .

The electroless nickel plating step of substantially 0.05mol / dm ³ in a concentration of ₄ · 6H ₂ O and NiSO substantially 0.15mol / dm ³ concentration of H ₂ NCH ₂ COOH, and a substantially 0.30mol / dm ³ of It is preferably carried out with a plating liquid containing a concentration of NaH ₂ PO ₂ H ₂ O.

Here, the electroless nickel plating step is preferably carried out at a temperature of substantially 60 ℃ and an acidity of pH 8.0 substantially.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.                     

 2 is a flowchart showing in sequence the main steps of the method for forming a nickel bump using a nickel displacement plating layer according to an embodiment of the present invention.

Referring to the drawings, the bump forming method of the present invention includes a degreasing step (S1) for removing an oxide film on the surface of an aluminum pad of a wafer on which a passivation layer is formed, and an alkali state in the degreasing step (S1). Neutralization treatment step (S2) of neutralizing the surface of the aluminum pad, a nickel displacement plating step (S3) of forming a nickel displacement plating layer on the surface of the aluminum pad, and an electroless treatment on the surface of the aluminum pad. Electroless nickel plating step (S4) to form a nickel bump by plating, and an Au-immersion step of forming a gold plating layer by electroless plating on the surface of the nickel bump to prevent oxidation of nickel ( S5).

While describing this in more detail in each step, the same reference numerals are used for the same components as those of the conventional nickel bump forming method. Degreasing the surface of the aluminum pad as part of the step of cleaning the aluminum pad, with the side of the aluminum pad 10 partially exposed at the top of the silicon wafer 14 covered with the passivation layer 12. The degreasing step S1 is performed.

The degreasing step (S1) is a process of removing the oxide film on the surface of the aluminum pad as an alkaline solution, the operation may be performed using a commercially available degreasing solvent.

The surface of the aluminum pad 10 subjected to the degreasing step (S1) is alkaline. In order to neutralize the aluminum pads having this biased acidity, a neutralization treatment step S2 is performed to neutralize the surface of the aluminum pad with an acid.

After the neutralization treatment step (S2) of the surface of the aluminum pad is neutralized without being biased toward either acidic or alkaline, to form a nickel displacement plating layer to improve the contact when forming nickel bumps Nickel displacement plating step S3 is performed.

Compared with the prior art described above, the jincate process shown in FIG. 1A is a process of activating a surface for nickel substitution plating on the aluminum pad 10, that is, oxidation and reduction reactions occur simultaneously on the aluminum surface. As the aluminum is dissolved and zinc is substituted in place, the zinc particles adhere to the aluminum surface. Substituted zinc acts as a nucleus in a subsequent nickel plating process, and according to the amount of zinc substituted, This will affect the adhesion of aluminum.

In order to prevent the reliability of the electroless nickel bumps from being degraded by the thickness reduction of the aluminum metal caused by the zinc casting process, the present invention does not perform the zinc casting process and instead forms a nickel displacement plating layer. The nickel plating is carried out on the surface of the aluminum pad by performing the cement plating step (S3).

That is, in the present invention, the thickness of the aluminum pad is reduced by performing the nickel displacement plating step (S3) of forming a substitution plating with electroless nickel instead of the gating process performed in the conventional nickel bump forming method. While preventing, it serves as a pretreatment process for the subsequent step of plating the electroless nickel to form nickel bumps.

After performing the nickel displacement plating step (S3), an electroless nickel plating step (S4) is performed on the aluminum pad having the surface pretreated to form nickel bumps by performing electroless nickel plating.

Through the electroless nickel plating step S4, the nickel plating layer 18 is formed to a predetermined thickness on portions of the surface of the aluminum pad except for the portion protected by the passivation layer, thereby forming bumps. In this case, electroless nickel plating is a kind of self-catalyzed reduction plating, in which a wafer is deposited in a solution in which a nickel salt and a soluble reducing agent coexist, whereby electrons released by oxidation of the reducing agent are transferred to metal ions to form a nickel film. .

At this time, since the aluminum surface to be plated acts as a catalyst for the reaction of the reducing agent, the plating reaction is selectively limited to the aluminum surface. The reaction is continued while the composition of the solution is kept constant, thereby allowing plating of a desired thickness over time.

For example, nickel precipitation response when sodium hypophosphite (NaH 2 PO 2 H 2 O) reducing agent is used is as shown in the following formula (1).

Equation _{^{(1) Ni 2+ + 2H 2}} PO 2+ 2H 2 O → Ni + 2H 2 PO3 - + H 2 + 2H +

After the electroless nickel plating step S4 is performed as described above, the gold plating layer 20 is formed through the Au-immersion step S5. The gold-emulsion step S5 is a self-limiting process in which growth stops when a predetermined thickness, for example, a thickness of about 0.15 to 0.25 micrometer is reached. This thin layer of gold serves to prevent the oxidation of nickel. Through this process, the bumps are formed at a predetermined height.

On the other hand, in the process of each step as described above, after the process involving the chemical reaction is washed with water to wash the site where the chemical reaction occurred. That is, after the degreasing step S1, the neutralization treatment step S2, the nickel displacement plating step S3, the electroless nickel plating step S4, and the gold-emulsion step S5, respectively, The washing process is performed.

The water used for this washing process is de-ionize water. However, deionized water used in the washing process is used by purging with N ₂ gas (injecting an inert gas into a flammable gas or steam to lower oxygen concentration below the minimum oxygen concentration (MOC)) before the process operation. This pershing process is performed to remove dissolved oxygen dissolved in deionized water and to prevent re-oxidation of aluminum.

On the other hand, such a washing process is preferably carried out at room temperature.

The chemicals and process conditions used in each step are shown in Table 1 below. Table 1 below shows the optimum values obtained by the experiment. Therefore, the conditions of the process and the chemicals used are not necessarily limited to the values shown in Table 1 below, and modifications may be made within the range that can be optimized by experiment.

Table 1

fair medicine Process conditions Degreasing Step Degreasing Solution Room temperature Washing steps Pershing with N ₂ gas Room temperature Neutralization Treatment Steps 1% HF Room temperature Nickel Displacement Plating Step NiSO ₄ · 6H ₂ O 0.05 mol / dm ³ H ₂ NCH ₂ COOH 0.20 mol / dm ³ 60 ℃ pH 9.0 N2 No stirring cycle Electroless nickel plating step _{NiSO 4 · 6H 2 O 0.05mol /} dm 3 H 2 NCH 2 COOH 0.15mol / dm 3 NaH 2 PO 2 · H 2 O 0.30mol / dm 3 60 ℃ pH 8.0 No stirring No circulation

The degreasing solution used in the degreasing step S1 may use an alkaline general commercial degreasing solution product.

As shown in Table 1, the nickel displacement plating step (S3) is NiSO ₄ · 6H ₂ O at a concentration of 0.05 mol / dm ³ and H ₂ NCH ₂ COOH at a concentration of 0.20 mol / dm ³ substantially It is preferably performed by a plating liquid containing.

At this time, the nickel displacement plating step (S3) is preferably carried out at a temperature of substantially 60 ℃ and a pH of pH 9.0 substantially. Also, the nickel displacement plating step is performed while N ₂ is stirred.

On the other hand, the electroless nickel plating step (S4) is substantially 0.05mol / dm ³ in a concentration of ₄ · 6H ₂ O and NiSO substantially 0.15mol / dm ³ of a concentration of H ₂ NCH ₂ COOH, and substantially 0.30 It is preferably carried out with a plating solution containing NaH ₂ PO ₂ H ₂ O at a concentration of mol / dm ³ . Wherein the electroless nickel plating step (S4) is preferably carried out at a temperature of substantially 60 ℃ and a pH of pH 8.0 substantially.

According to the electroless nickel bump forming method using the nickel displacement plating layer as described above, the following effects can be obtained.

First, the problem that the silicon wafer is exposed by thinning the aluminum pad during bump formation is eliminated.

Second, since the thickness of the aluminum pad does not decrease, there is no need to increase the thickness of the aluminum pad more than necessary in consideration of this, and thus there is an advantage of reducing manufacturing costs.

Third, since the oxide layer is removed from the surface of the aluminum pad, the adhesion of nickel plating is improved, thereby increasing the reliability of the bump forming process.

While the invention has been described with reference to the embodiments shown in the accompanying drawings, it will be understood that various modifications and other embodiments are possible to those skilled in the art. Therefore, the protection scope of the present invention will be defined by the appended claims.

Claims (9)

Degreasing to remove an oxide film on the surface of the aluminum pad of the wafer on which the passivation layer is formed; Neutralizing treatment to neutralize a surface of the aluminum pad in an alkaline state in the degreasing step; A nickel displacement plating step of forming a nickel displacement plating layer on the surface of the aluminum pad; An electroless nickel plating step of forming nickel bumps by electroless plating on the aluminum pad surface; A method of forming an electroless nickel bump using a nickel displacement plating layer, comprising: an Au-immersion step of forming a gold plating layer on the surface of the nickel bumps by electroless plating to prevent oxidation of nickel. The method of claim 1, A method of forming an electroless nickel bump using a nickel displacement plating layer, further comprising a washing step of washing the surface of the aluminum pad after each step in which a chemical reaction occurs. The method of claim 2, The washing step is performed by de-ionize water purged with N ₂ gas, characterized in that the electroless nickel bump forming method using a nickel displacement plating layer. The method of claim 1, The neutralization treatment step, characterized in that performed by HF, electroless nickel bump forming method using a nickel displacement plating layer. The method of claim 1, The nickel displacement plating step is performed by a plating solution containing NiSO ₄ .6H ₂ O at a concentration of 0.05 mol / dm ³ and H ₂ NCH ₂ COOH at a concentration of 0.20 mol / dm ³ . An electroless nickel bump forming method using a nickel displacement plating layer. The method of claim 5, Wherein said nickel displacement plating step is performed at a temperature of substantially 60 ° C. and an acidity of substantially pH 9.0. The method of claim 5, The nickel displacement plating step is performed in a state in which N ₂ is stirred, electroless nickel bump forming method using a nickel displacement plating layer. The method of claim 1, The electroless nickel plating step of substantially 0.05mol / dm ³ in a concentration of ₄ · 6H ₂ O and NiSO substantially 0.15mol / dm ³ concentration of H ₂ NCH ₂ COOH, and a substantially 0.30mol / dm ³ of A method of forming an electroless nickel bump using a nickel displacement plating layer, characterized in that it is performed by a plating solution containing NaH ₂ PO ₂ · H ₂ O at a concentration. The method of claim 8, Wherein the electroless nickel plating step is performed at a temperature of substantially 60 ° C. and an acidity of substantially pH 8.0.

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