KR20120064361A - An electroplating method and an electroplating apparatus - Google Patents

Abstract

The present invention relates to a plating method. Provided is a copper electroplating method that performs preliminary electroplating (first electroplating) to enhance via coverage before full electroplating (second electroplating) forming a circuit wiring pattern. Enhancing coverage in the via holes results in better via filling and no dimples. In addition, since the thickness variation of the circuit pattern can be reduced, it is possible to prevent a resistance or the like.

Description

Plating method and plating equipment {AN ELECTROPLATING METHOD AND AN ELECTROPLATING APPARATUS}

The present invention relates to a plating method and a plating apparatus, and more particularly, to a plating method and a plating apparatus excellent in via coverage and via filling.

BACKGROUND ART With the miniaturization, light weight, and high speed of electronic devices, high density of patterns on printed circuit boards is required. As a result, even a blind via connecting the interlayer interfaces is changed from a staggered via to a stack via. In stack vias, interlayer connection is very important in terms of via reliability, so via filling is an important measure of reliability. In addition, since the aspect ratio of blind vias is also diversified as products are diversified, it is necessary to establish stable via filling.

Generally, the structure of a copper pattern plating apparatus consists of three steps, an acid cleaner, pickling, and electroplating. Among these, the acid cleaner removes the organic substances remaining on the substrate and the dry film, and in the pickling, an acid treatment is performed to remove the oxide film present on the surface of the plated object.

Before electroplating, electroless plating is performed for the purpose of forming a seed layer. The copper layer also grows in the via after this process.

Via coverage is fine but reduced in thickness through the circuit pretreatment stage (sulfuric acid) until the pattern process, and the coverage of the bottom portion of the via is weakened when the copper pattern electroplating stage is reached.

If the copper pattern is electroplated in this state, via filling is incomplete and dimples are likely to occur in the vias. Such dimples reduce the contact area between vias, which in turn lowers the reliability of electronic components. There is this.

The present invention seeks to provide an electroplating method having excellent via coverage and via filling.

In one embodiment of the present invention, the electroless plating step of performing an electroless plating to form an electroless plating layer on the plated object; A first electroplating step of performing preliminary electroplating to form a first electroplating layer on the electroless plating layer; And a second electroplating step of applying a current higher than the current applied during the first electroplating to form a second electroplating layer on the first electroplating layer.

In addition, the plated object provides a plating method which is a wiring board on which via holes are formed.

In addition, the material of the electroless plating layer provides a plating method of copper, nickel or tin.

In addition, the thickness of the first electroplating layer provides a plating method of 3 to 5um.

The present invention also provides a plating method further comprising removing an organic material and an oxide film existing on the surface of the plated material before the electroless plating step.

In another embodiment of the present invention, an electroless plating tank for performing an electroless plating to form an electroless plating layer on the plated object; A first electroplating tank performing preliminary electroplating to form a first electroplating layer on the electroless plating layer; And a second electroplating tank configured to form a second electroplating layer on the first electroplating layer by applying a current higher than the current applied during the first electroplating.

In addition, the present invention provides a plating apparatus further comprising an acid cleaner tank for removing organic matter present on the surface of the plated material and an pickling tank for removing oxide film present on the surface of the plated material before the electroless plating tank.

According to the present invention, the via coverage and the via filling characteristics are excellent, thereby preventing the occurrence of dimples. In addition, the thickness variation of the circuit pattern can be reduced.

1 is a flowchart of a method of electroplating copper according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a wiring board on which via holes are formed which are changed by electroplating according to an embodiment of the present invention. FIG.
3 is a schematic view showing an arrangement of plating tanks of a plating apparatus according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Furthermore, embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

1 shows a flowchart of a plating method according to an embodiment of the present invention.

Plating method according to an embodiment of the present invention comprises the electroless plating step of performing an electroless plating to form an electroless plating layer on the plated object; A first electroplating step of performing preliminary electroplating to form a first electroplating layer on the electroless plating layer; And a second electroplating step of applying a current higher than the current applied during the first electroplating to form a second electroplating layer on the first electroplating layer.

Electroless plating is a method in which metal ions in an aqueous metal salt solution are self-catalytically reduced by the force of a reducing agent without receiving electrical energy from the outside, thereby depositing metal on the surface of the plated object. Also called chemical plating or autocatalyst plating. In other words, it is a surface treatment method of imparting conductivity by depositing a metal on the surface of a non-conductive material by chemical reduction reaction.

Electroplating is a method of covering an object's surface with a thin film of another metal using the principle of electrolysis. Also called electroplating.

For example, copper formed by electroless plating is also called chemical copper because it is formed by chemical methods. In contrast, copper formed by electrolysis or electroplating may be referred to as electrolytic copper or electrolytic copper.

The plated object may be an insulating material. It is because electroplating can be performed after forming a seed layer with electroconductivity by electroless plating.

Hereinafter, the present invention will be described in detail with the case of electroplating copper on the wiring board on which the via holes are formed.

2 illustrates a process of forming a circuit wiring pattern on a wiring board on which a via hole is formed according to an exemplary embodiment of the present invention.

FIG. 2A is a cross-sectional view before the wiring board 200 on which the via hole 100 is formed is plated. The wiring board may be an insulating material.

The via hole 100 refers to a hole selectively formed only in an interlayer portion necessary for electrical connection. The via hole 100 has a relatively large aspect ratio because of the recent trend toward higher integration of semiconductor chips.

Filling the via hole 100 with the pattern material is referred to as via filling, and it is preferable that the via filling property is excellent. If the via filling is poor, dimples may occur, thereby reducing the reliability of the product.

FIG. 2B is a cross-sectional view in which an electroless plating layer 210 is formed on a bottom portion, a side portion, and an upper surface of a wiring board of a via hole.

According to this embodiment, electroless plating is performed for the purpose of forming a seed layer before electroplating.

The plating solution may consist of CuSO ₄ , HCHO, NaOH and other stabilizers. In the composition of the plating solution, copper sulfate (copper sulfate: CuSO): Copper Sulphate), an alkali source, sodium hydroxide (caustic soda: NaOH: Caustic soda), a reducing agent, formaldehyde, and a chelating agent, Rochelle salt (potassium) Sodium tartaric acid) and trace amounts of compounds of stabilizers and malleable agents.

In order for the plating reaction to be continued, three reactions of copper precipitation, plating solution decomposition reaction, and stabilization reaction must be balanced. For this purpose, it is important to control the composition of the plating solution. In order to maintain the composition, proper supply of scarce components, mechanical agitation, and a plating system purifying system must be well operated.

In addition, there is a need for a filtration device for the by-products generated as a result of the reaction, by utilizing this can extend the use time of the plating liquid.

Electroless plating has an advantage that the plating layer has a dense and uniform thickness as compared with electroplating, and can be applied to various substrates such as plastics or organics as well as conductors. However, electroless plating is difficult to carry out and is not economical.

The reason why electroless plating is first performed before electroplating is that electroplating cannot be directly performed on the insulating layer when the plating is to be performed on the insulating layer. In other words, since the insulating layer does not flow electricity, electroplating performed using electricity cannot be performed.

Therefore, in order to conduct electroplating on the insulating layer, electroless plating should be performed before the electroplating to form an electrically conductive film on the surface of the insulating layer so that electricity can flow.

The electroless plating layer 210 is formed in the via hole inner wall and the wiring pattern groove by the electroless plating. The electroless plating layer 210 is also called a seed layer.

The electroless plating layer serves as an electrode in an electroplating process, and metal ions are continuously deposited on the electroless plating layer to grow a metal layer.

The metal constituting the electroless plating layer is preferably the same as the metal element to be electrodeposited on the surface of the plated object during electroplating, but it is not necessarily the same. This is because the electroless plating layer is sufficient to serve as an electrode in an electroplating process for filling via vias or filling pattern grooves, so it may be any material having electrical conductivity.

By electroless plating, electroless plating layers, such as copper, nickel, and tin, can be formed. It is preferable that an electroless plating layer is copper.

The electroless plating causes the electroless plating layer to grow in the via, and there is a difference in the thickness of the electroless plating layer formed on the top of the via inner wall and the bottom of the via inner wall. This is due to the difference in liquid flow and reactivity.

The ratio of the thickness of the electroless plating layer formed on the bottom of the inner wall of the via to the thickness of the electroless plating layer formed on the upper portion of the via inner wall is approximately 50 to 60%. That is, the thickness of the bottom portion of the via inner wall is 50 to 60% smaller than the top portion of the via inner wall.

As the thickness of the electroless plating layer at the bottom of the via inner wall is secured, it is advantageous to via filling, but the electroless plating layer cannot be grown indefinitely to secure coverage. Because increasing the thickness of the electroless plating layer increases the etching rate (E / R) in the Flash Etching process, which will be performed after copper pattern electroplating. Because.

FIG. 2 (c) is a cross-sectional view in which the first electroplating layer 220 is formed on the electroless plating layer 210, and FIG. 2 (d) is a second electroplating layer 230 formed on the first electroplating layer 220. It is a cross section.

According to this embodiment, the electroplating is divided into a first electroplating step and a second electroplating step to perform a total of two electroplatings.

Referring to the principle of electroplating is as follows. In other words, the metal (plating material) to be plated is used as the cathode, the metal to be electrodeposited is used as the anode, and is placed in an electrolytic solution containing ions of the metal to be electrodeposited, and energized by electrolysis. Metal ions are electrolytically deposited on the surface of the object.

Therefore, it is not easy to form an electroplating layer having good adhesion to an article having no electrical conductivity.

In this embodiment, 1st electroplating is a process of forming a thin metal layer on the electroless plating layer (seed layer) formed by electroless plating. Since the thickness of the metal layer formed by electroplating is proportional to the magnitude of the current, the electroplating is performed with a very weak current. The thin metal layer formed at this time is called a first electroplating layer.

By forming the first electroplating layer, via coverage is strengthened, and via coverage is strengthened, thereby making via filling excellent during second electroplating and preventing dimple defects from occurring.

The first electroplating layer formed by the first electroplating may be one of metals having electrical conductivity, such as copper, gold, silver, zinc, and tin. Copper is preferable for the first electroplating layer.

The thickness of the first electroplating layer may be 3 to 5um. Since the first electroplating is to prevent dimples during the second electroplating by reinforcing the via coverage, the first electroplating layer does not need to be too thick.

Hereinafter, the implementation of the first electroplating step will be described in detail.

In general, the copper pattern plating apparatus is composed of three stages: acid cleaner, pickling, and electroplating. There are five water washing stages between the acid cleaner and the pickling.

Change the structure as follows.

The fifth of the five water washers present between the acid cleaner and the pickling will perform the same function as the pickling. And pickling is replaced by electroplating so that the first electroplating is performed.

This allows preliminary first electroplating to enhance via coverage prior to entering full electroplating (second electroplating) forming a circuit pattern.

The acid cleaner removes the organic foreign matter remaining on the substrate and the dry film.

In the last 5th washing | cleaning end among the 5 washing | cleaning ends which were between an acid cleaner and pickling, the oxide film which exists on a wiring board is removed. It performs the same function as pickling.

The pickling stage is replaced by electroplating (first electroplating), where preliminary electroplating is carried out with a weak current prior to entering full-scale electroplating (second electroplating) forming a circuit pattern.

By performing preliminary first electroplating, via coverage can be strengthened and dimples that can occur in the second electroplating step can be prevented.

In this embodiment, 2nd electroplating is a process of filling a via hole and a wiring pattern groove | channel with electroconductive metals, such as copper and silver. Electroplating is carried out while flowing a larger current than that used in the first electroplating step. A metal is deposited on the first electroplating layer to fill via holes or pattern grooves.

After pickling, electroplating is performed for 80 minutes by direct current plating. There are six tanks in one bath and one rack in each bath. One rack holds four products. Therefore, copper electroplating is performed on 24 products in one bath.

According to the present embodiment, the method may further include removing the organic material and the oxide film existing on the surface of the plated material before the electroless plating step.

By acid treatment of the surface of the plated object with a 10% sulfuric acid solution, the organic material and the oxide film formed on the surface of the plated object can be removed.

When an organic material or an oxide film exists on the surface of a to-be-plated object, an electric current does not flow uniformly in the organic material or oxide film point, and metal ions which exist in a plating liquid do not precipitate uniformly, and a void may arise.

That is, because foreign matter or voids, etc. exist in the final electroplating layer, the resistance of the wiring pattern may increase or the wiring pattern may be peeled off.

2E is a cross-sectional view after removing the plating layer formed higher than the upper surface of the substrate by etching or the like.

The plating layer formed higher than the upper surface of the wiring board is removed to complete the copper wiring pattern. In addition, in order to protect the copper wiring from contamination due to foreign matters from the outside or from external physical shocks, etc., an insulating film or the like may be formed on the upper surface of the copper wiring pattern to completely cover the copper wiring pattern.

Figure 3 schematically shows the arrangement of the plating tank and the like of the plating apparatus according to an embodiment of the present invention.

The plating apparatus according to the present embodiment includes an electroless plating tank 330 which performs electroless plating to form an electroless plating layer on a plated object; A first electroplating tank 340 which performs preliminary electroplating to form a first electroplating layer on the electroless plating layer; And a second electroplating tank 341 forming a second electroplating layer on the first electroplating layer by applying a current higher than the current applied during the first electroplating.

The plating apparatus according to this embodiment has one electroless plating tank 330 and two electroplating tanks, that is, a first electroplating tank 340 and a second electroplating tank 341.

The electroless plating described above is performed in the electroless plating tank 330, the first electroplating is performed in the first electroplating tank 340, and the second electroplating is performed in the second electroplating tank 341. .

An acid cleaner tank 310 for removing organic matter present on the surface of the plated material before the electroless plating tank, and a pickling tank 320 for removing oxide film present on the surface of the plated material may be further included. .

In this embodiment, the object to be plated, the electroless plating, the first electroplating, the second electroplating, and the matters related thereto are the same as described above.

The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited only by the appended claims. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

Claims (7)

An electroless plating step of performing an electroless plating to form an electroless plating layer on a plated object;
A first electroplating step of performing preliminary electroplating to form a first electroplating layer on the electroless plating layer; And
A second electroplating step of applying a current higher than the current applied during the first electroplating to form a second electroplating layer on the first electroplating layer;
Plating method comprising a.
The method of claim 1,
The plating method is a plating substrate in which via holes are formed.
The method of claim 1,
The plating method of the electroless plating layer is copper, nickel or tin.
The method of claim 1,
The thickness of the first electroplating layer is a plating method of 3 to 5um.
The method of claim 1,
And removing the organic material and the oxide film existing on the surface of the plated material before the electroless plating step.
An electroless plating tank for performing an electroless plating to form an electroless plating layer on the plated object;
A first electroplating tank performing preliminary electroplating to form a first electroplating layer on the electroless plating layer; And
A second electroplating tank configured to form a second electroplating layer on the first electroplating layer by applying a current higher than the current applied during the first electroplating;
Plating apparatus comprising a.
The method of claim 6,
And an acid cleaner tank for removing organic matter present on the surface of the plated material before the electroless plating tank, and a pickling tank for removing an oxide film present on the surface of the plated material.

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