US20070080066A1

US20070080066A1 - Plating apparatus and manufacturing process for semiconductor device

Info

Publication number: US20070080066A1
Application number: US11/543,235
Authority: US
Inventors: Hiroaki Tachibana
Original assignee: NEC Electronics Corp
Current assignee: NEC Electronics Corp
Priority date: 2005-10-06
Filing date: 2006-10-05
Publication date: 2007-04-12
Also published as: CN1958868A; JP2007100185A

Abstract

The present invention is to provide a plating apparatus and a process for manufacturing a semiconductor device whereby passivation of an anode can be prevented and reduction in a current efficiency and a deposition rate of a plating film can be prevented. A plating apparatus 1 has a plating bath 11 which contains a plating solution; an anode 12 and a cathode 13 within the plating bath 11; and a switching control unit 16 which switches between a first state where a current is applied between a plating object 2 in contact with the plating solution and the anode 12 and a second state where a current is interrupted between the plating object 2 and the anode 12 while applying a current between the anode 12 and the cathode 13. The anode 12 is a soluble electrode containing a metal capable of being passivated.

Description

This application is based on Japanese patent application NO. 2005-293572, the content of which is incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a plating apparatus and a process for manufacturing a semiconductor device.
2. Description of the Related Art
Electroplating has been conventionally used in a variety of fields. For example, when forming a solder bump in a flip chip in a semiconductor device, a barrier metal layer is formed on a semiconductor chip by electroplating to prevent diffusion of solder components from the solder bump to an electrode on the semiconductor chip.
An exemplary electroplating apparatus for such electroplating is an electroplating apparatus 100 where an anode 101 and a pre-electrolysis electrode 102 are disposed in a plating bath (not shown) as shown in FIG. 7, (for example, see Japanese Patent Application No. 2003-129294).
In this electroplating apparatus 100, there are a switch unit 103 for conducting/interrupting between the pre-electrolysis electrode 102 and the anode 101 and the pre-electrolysis electrode 102 is removable from a circuit connecting the anode 101 to a plating object 2.
In such an electroplating apparatus 100, the pre-electrolysis electrode 102 is connected to the circuit connecting between the plating object 2 and the anode 101 and a current is applied from the anode 101 to the pre-electrolysis electrode 102 before the plating object 2 comes in contact with a plating solution.
Next, once the plating object 2 comes into contact with the plating solution, a current is distributed according to an area ratio between the pre-electrolysis electrode 102 and the plating object 2, so that a current is applied to between the pre-electrolysis electrode 102, the plating object 2 and the anode 101.
Subsequently, the pre-electrolysis electrode 102 is separated from the circuit connecting the anode 101 and the plating object 2 by the switch unit 103, to form a plating film over the plating object 2.
However, in the technique described in Japanese Patent Application No. 2003-129294, there is room for improvement with respect to the followings.
In the technique described in Japanese Patent Application No. 2003-129294, a plating film is formed on the plating object 2 to a desired thickness, and then the system is switched off to interrupt a current between the plating object 2 and the anode 101, and then the plating object 2 is removed from the plating solution.
Then, for plating a next plating object 2, the pre-electrolysis electrode 102 is connected to the circuit connecting the anode 101 and the plating object and subsequently the system is powered on.
After repeating this operation for plating the plating object 2, a current efficiency during plating of the plating object is reduced, leading to reduction in a deposition rate of the plating film.

SUMMARY OF THE INVENTION

One possible cause of reduction in a current efficiency is passivation of an anode surface. For forming a plating film, a high current is applied between the anode and the plating object. On the other hand, when removing the plating object from the plating solution after forming the plating film, a current is interrupted between the anode and the plating object.
Thus, after repeating application/interruption of a current, the anode surface would be oxidized during interruption of a current, leading to passivation of the anode.
According to an aspect of the present invention, there is provided a plating apparatus, comprising

- a plating bath which contains a plating solution;
- an anode and a cathode within the plating bath; and
- a switching control unit which switches between a first state where a current is applied between a plating object in contact with the plating solution and the anode and a second state where a current is interrupted between the plating object and the anode while applying a current between the anode and the cathode.

A preferred aspect of the anode is a soluble electrode containing a metal capable of being passivated.
In the plating apparatus according to the present invention, when forming a plating film on the plating object, a current is applied at least between the plating object and the anode by the switching control unit.
On the other hand, after completion of plating of the plating object, the current is interrupted between the plating object and the anode while applying a current between the anode and the cathode by the switching control unit.
As described above, in this invention, even after completion of plating of the plating object, the anode can be continuously dissolved without interrupting a current to the anode. Thus, passivation of the anode can be prevented and reduction in a current efficiency or a deposition rate of the plating film can be prevented.
In accordance with another aspect of the present invention, there is also provided a process for manufacturing a semiconductor device where a semiconductor substrate having a conductor film on or over its surface as a plating object is placed in a plating bath which is filled with a plating solution and in which an anode and a cathode are disposed and then a plating film is formed on the conductor film, comprising

- applying a current between the plating object and the anode by contacting the plating object with the plating solution; and
- interrupting the current between the plating object and the anode while applying a current between the anode and the cathode.

The process for manufacturing a semiconductor device as described above shows similar effects to those of the above plating apparatus.
That is, the process can prevent passivation of the anode and reduction in a current efficiency and in a deposition rate of the plating film can be prevented. Thus, the process for manufacturing a semiconductor device according to the present invention allows a semiconductor device to be efficiently produced.
The present invention can provide a plating apparatus and a process for manufacturing a semiconductor device which can prevent passivation of an anode and can prevent reduction in a current efficiency and a deposition rate of a plating film.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic view illustrating a plating apparatus according to one embodiment of the present invention;
FIG. 2 is a plan view showing a cathode in a plating apparatus;
FIG. 3 is a plan view showing a cathode in a plating apparatus;
FIG. 4 shows a current between an anode and a plating object, and a current between an anode and a cathode;
FIG. 5 shows a current between an anode and a plating object, and a current between an anode and a cathode;
FIG. 6 shows a relationship between the number of plating object processed and a thickness of a plating film in Comparative Example; and
FIG. 7 is a schematic view illustrating a conventional plating apparatus.
In the drawings, the symbols have the following meanings; 1: plating apparatus, 2: plating object, 11: plating bath, 12: anode, 13: cathode, 14: power source, 15: current control unit, 16: switching control unit, 17: storage unit, 100: plating apparatus, 101: anode, 102: pre-electrolysis electrode, 103: switch unit, 111: bottom face, 112: side face, 113: opening, 114: pipe, 131: through-hole, 161: switch unit, and 162: switch-unit driving controller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purpose.
There will be described preferred embodiments of the present invention with reference to the drawings.
FIG. 1 shows a plating apparatus 1 according to this embodiment.
There will be described a general configuration of the plating apparatus 1.
The plating apparatus 1 according to this embodiment comprises a plating bath 11 which contains a plating solution; an anode 12 and a cathode 13 within the plating bath 11; and a switching control unit 16 which switches between a first state where a current is applied between a plating object 2 in contact with the plating solution and the anode 12 and a second state where a current is interrupted between the plating object 2 and the anode 12 while applying a current between the anode 12 and the cathode 13. The anode 12 is a soluble electrode containing a metal which can be passivated.
Next, there will be detailed the plating apparatus 1.
The plating apparatus 1 according to this embodiment is an apparatus for electroplating.
The plating bath 11 in this plating apparatus 1 has a bottom face 111 and a side face 112 surrounding the periphery of the bottom face 111. The upper surface of the plating bath 11 which faces the bottom face 111 is open, where an opening 113 is formed. Through the opening 113, the plating object 2 (a semiconductor substrate on whose surface a conductor film is deposited) is inserted. The plating object 2 is held by a jig (unshown) and movable up and down in FIG. 1.
A supply pipe 114 for supplying a plating solution is connected to the bottom face 111 in the plating bath 11.
Outside of this plating bath 11, there is a overflow tank (unshown), into which the plating solution overflowing from the plating bath 11 is discharged as indicated by the arrow in FIG. 1.
The anode 12 is disposed in substantially parallel with the bottom face 111 of the plating bath 11 and is planar. This anode 12 is disposed in substantially parallel with the surface of the plating object 2 when the plating object 2 is inserted into the plating bath 11.
The anode 12 is a soluble electrode. This anode 12 contains a metal in whose surface a passivation film (oxide film) is formed after repeating current application and interruption of the anode 12 in the plating solution.
Examples of a metal capable of being passivated includes aluminum, nickel, cobalt, chromium, titanium, tantalum and niobium. The anode 12 may contain one or more of these metals.
Among others, the anode 12 preferably contains one or two metals selected from the group consisting of nickel, cobalt, chromium and titanium.
Since the anode 12 is a soluble electrode, the anode 12 may be made of a metal for a plating film; for example, when a nickel film is to be deposited on the plating object 2 as a plating film, the anode 12 is preferably made of nickel.
When a chromium film is to be deposited on the plating object 2 as a plating film, the anode 12 may be made of chromium.
Alternatively, the anode 12 may be made of an alloy containing a metal capable of being passivated and a metal incapable of being passivated.
When a given voltage is applied between the anode 12 and the plating object 2 or between the anode 12 and the cathode 13, a metal in the anode 12 is dissolved into the plating solution as metal ions. The metal ions receive electrons from the plating object 2 or the cathode 13, to form a plating film on the plating object 2 (a conductor film on or over a semiconductor substrate) or the cathode 13.
The plating film may be an alloy containing a plurality of metals (for example, an Ni—Co alloy and an Ni—Fe alloy).
The cathode 13 is disposed within the plating bath 11, facing the anode 12. When the plating object 2 is disposed within the plating bath 11, the cathode 13 is disposed between the plating object 2 and the anode 12.
The cathode 13 has a planar shape as shown in FIGS. 2 and 3, and has a plurality of through-holes 131. These through-holes 131 penetrate the surface of the anode 12 side and the surface of the plating object 2 side of the cathode 13.
There are no particular restrictions to the shape of the through-hole 131; for example, it may be rectangular as shown in FIG. 2 or circular as shown in FIG. 3.
The cathodes 13 in FIGS. 2 and 3 are substantially planar and circular. However, the outer shape of the cathode 13 is not limited to these, but may be, for example, planar and rectangular.
Although there are no particular restrictions to a material for the cathode 13, it is preferably an insoluble electrode and thus preferably made of a metal insoluble in a plating solution.
Examples of a material for the cathode 13 include, for example, graphite, platinum and ruthenium/platinum alloys.
Again, as shown in FIG. 1, the plating apparatus 1 has a power source 14. The power source 14 can be connected to the anode 12, the cathode 13 and the plating object 2. Specifically, the power source 14 and the anode 12 are mutually connected via a conducting wire. Each of the cathode 13 and the plating object 2 is connected with a conducting wire, and in an intersection of each conducting wire and a conducting wire from the anode 12, a switch unit 161 is formed.
To the plating object 2 is connected a conducting wire via a jig as described above.
To the power source 14 is connected a current control unit 15.
The current control unit 15 is disposed between the power source 14 and the anode 12, and controls currents between the plating object 2 and the anode 12 and between the anode 12 and the cathode 13. This current control unit 15 controls currents between the plating object 2 and the anode 12 and between the anode 12 and the cathode 13 in accordance with a given sequence stored in the storage unit 17 (for example, see FIG. 4).
The plating apparatus 1 of this embodiment has a switching control unit 16 having the switch unit 161 described above. This switching control unit 16 has the switch unit 161 and a switch-unit driving controller 162 which controls driving of the switch unit 161.
The switch-unit driving controller 162 switches connection of the switch unit 161 in accordance with switch timing stored in the storage unit 17.
By switching connection of the switch unit 161, the switch-unit driving controller 162 switches between a first state where a current is applied between the plating object 2 in contact with the plating solution and the anode 12 and a second state where a current is interrupted between the plating object 2 and the anode 12 while applying a current between the anode 12 and the cathode 13.
Next, there will be described a process for manufacturing a semiconductor device using such a plating apparatus 1.
First, a semiconductor substrate on whose surface a conductor film for electroplating is deposited is prepared as a plating object 2. The conductor film can be formed by sputtering or vapor deposition of Ti, Ni, Cu or the like.
A mask having a given pattern is applied over the semiconductor substrate on which the conductor film has been thus formed. In this embodiment, a plating film is formed on the conductor film exposed from the opening in this mask.
Next, the plating object 2 is pre-treated by, for example, washing, and then the plating object 2 is fit in a jig (unshown). Then, the jig is moved downward to immerse the plating object 2 in a plating solution filling in the plating bath 11. When a sensor (unshown) detects immersion of the plating object 2 in the plating solution, the switch-unit driving controller 162 requests the switch unit 161 to connect the anode 12 with the plating object 2. In response to the request, the switch unit 161 connects the anode 12 to the plating object 2.
After detection of the connection between the anode 12 and the plating object 2, the current control unit 15 controls a current supplied from the power source 14 in accordance with a sequence stored in the storage unit 17. Thus, a given current is applied between the plating object 2 and the anode 12.
It initiates plating, so that metal ions are dissolved into the plating solution from the anode 12. The metal ions receive electrons from the plating object 2 (the conductor film on or over a semiconductor substrate), so that a plating film is formed on the plating object 2.
In the plating apparatus 1, an elapsed time from initiation of plating is measured by a timer (unshown).
After a given time is elapsed from the initiation of plating based on the time measured by the timer and timing stored in the storage unit 17 (that is, after a plating film is formed to a desired thickness on the plating object 2), the switch-unit driving controller 162 requests the switch unit 161 to interrupt the connection between the anode 12 and the plating object 2 while connecting the anode 12 with the cathode 13.
Based on the time measured by the timer and a given sequence stored in the storage unit 17, the current control unit 15 controls a current from the power source 14.
Thus, the anode 12 and the cathode 13 are connected by the switch unit 161, so that a given current is applied between the anode 12 and the cathode 13.
Here, a current between the anode 12 and the cathode 13 is preferably lower than a current between the plating object 2 and the anode 12; for example, it is ½ or lower of the current between the plating object 2 and the anode 12 (see, FIG. 4).
That is, the current control unit 15 controls a current such that a current density in the anode 12 during stopping plating of the plating object 2 is lower than a current density in the anode 12 during plating of the plating object 2.
From the anode 12, metal ions are continuously dissolved and receive electrons from the cathode to form a plating film on the cathode 13.
The plating of the plating object 2 is terminated by interrupting connection between the anode 12 and the plating object 2 and connecting the anode 12 and the cathode 13. Then, the jig (not shown) and the plating object 2 are moved upward from the plating solution, and the plating object 2 is removed from the plating bath 11.
Then, the mask over the semiconductor substrate which is the plating object 2 is removed while the conductor film exposed after mask removal is peeled off. Thus, there can be provided a semiconductor device having a plating film as a barrier metal layer for a solder bump.
Subsequently, a next plating object 2 is fit to the jig and a plating film is formed over the plating object 2 as described above.
There will be described effects of this embodiment.
In this embodiment, when forming a plating film on the plating object 2, the plating object 2 is connected to the anode 12 and a current is applied between the plating object 2 and the anode 12.
On the other hand, after completion of plating of the plating object 2, the switching control unit 16 interrupts the current between the plating object 2 and the anode 12 while applying a current between the anode 12 and the cathode 13.
As described in this embodiment, even after completion of plating of the plating object 2, the anode 12 can be continuously dissolved since a current to the anode 12 is not interrupted. Thus, passivation of the anode 12 can be prevented and reduction in a current efficiency and a deposition rate of the plating film can be prevented.
When electroplating is conducted according to a conventional process (the process described in Japanese Patent Application No. 2003-129294), the anode is slowly passivated from its periphery. Thus, partial passivation of the anode makes it difficult to uniformly form a plating film on the plating object 2.
In contrast, this embodiment allows passivation of the anode 12 to be prevented and thus a plating film can be uniformly formed on the plating object 2.
When electroplating is conducted according to a conventional process (the process described in Japanese Patent Application No. 2003-129294), a deposition rate of the plating film is reduced as the anode is passivated. Therefore, it is necessary to extend a plating time as the deposition rate decreases, when the plating film is to be deposited to a desired thickness. However, it is troublesome to adjust a plating time as a deposition rate decreases.
In contrast, this embodiment can prevent passivation of the anode 12 and reduction in a deposition rate of the plating film, resulting in elimination of the need for adjusting a plating time.
This embodiment employs the cathode 13 in which a plurality of through-holes 131 are formed. Therefore, even when the cathode 13 is disposed between the anode 12 and the plating object 2, metal ions can move through the through-holes 131 formed in the cathode 13, so that a plating film can be reliably formed on the plating object 2.
Furthermore, in this embodiment, a current between the anode 12 and the cathode 13 during stopping plating of the plating object 2 is adjusted to be lower than a current between the plating object 2 and the anode 12 during forming the plating film on the plating object 2. It can avoid consumption of a large amount of metal in the anode 12 during stopping plating of the plating object 2.
The present invention is not limited to the above embodiment, and variations and modifications are intended to be encompassed by the present invention as long as the objectives of the invention can be achieved.
For example, although in the plating bath 11, the anode 12, the cathode 13 and the plating object 2 are disposed such that they are in substantially parallel with the bottom face 111 of the plating bath 11 in this embodiment, the anode 12, the cathode 13 and the plating object 2 may be, for example, disposed perpendicularly to the bottom face 111 of the plating bath 11.
In such a case, the plating object 2 may be plated while being placed between the anode 12 and the cathode 13. Thus, the cathode does not interfere with forming a plating film on the plating object 2, resulting in elimination of the need for forming through-holes in the cathode. It may lead to a simpler process for manufacturing the cathode.
Furthermore, the anode 12 may not be substantially parallel to the cathode 13. For example, the anode 12 and the cathode 13 may be disposed such that the surface of the anode 12 is oblique to the surface of the cathode 13, or alternatively the anode 12 and the cathode 13 may be disposed such that the surface of the anode 12 is perpendicular to the surface of the cathode 13.
In the above embodiment, a constant current is applied between the plating object 2 and the anode 12 as shown in FIG. 4, but for example, a current between the plating object 2 and the anode 12 may be increased stepwise as shown in FIG. 5.
The plating apparatus 1 can be used for forming a barrier metal layer for a solder bump on the semiconductor substrate as in the above embodiment, or for forming a plating film in, for example, a trench formed in the semiconductor substrate.
Furthermore, in addition to a semiconductor substrate, a plating object in which a conductor film is formed on a ceramic substrate may be plated. In addition to a substrate, other members such as accessories may be used to be plated as a plating object.
In the above embodiment, a current is interrupted between the anode 12 and the cathode 13 during plating the plating object 2, but a current may be applied between the anode 12 and the cathode 13.

EXAMPLES

There will be described an example of the present invention.

Example

A plating apparatus was prepared as described in the above embodiment and a plating object was plated as described in the above embodiment.
The plating object was a semiconductor substrate (Si substrate) on whose surface a conductor film (Ti film) was deposited.
An anode and a cathode were an Ni and a Pt electrodes, respectively.
A plating solution was a nickel sulfamate bath.
As described in the above embodiment, a current was applied between the plating object and the anode for a given time (5 min) during depositing a plating film on the plating object, and a current is interrupted between the plating object and the anode during stopping plating of the plating object while applying a current between the anode and the cathode.
A current between the anode and the cathode during stopping plating was lower than a current between the plating object and the anode during forming a plating film on the plating object.
Specifically, a current density in the anode was about 0.8 A/dm²during forming a plating film on the plating object, while a current density in the anode was less than 1 A/dm²(for example, 0.4 A/dm²) during stopping forming a plating film on the plating object.
After processing 150 plating objects, a current efficiency was not reduced.
Little variation was observed in a plating-film thickness on each plating object (a target value was 3.2 μm) as determined by a X-ray fluorescence spectrometer.

Comparative Example

A plating object was plated as described in Example, using a plating apparatus without a cathode or a switch unit. The plating apparatus in Comparative Example was as described in Example, except it does not have a cathode or a switch unit.
An anode was made of Ni and a plating solution was a nickel sulfamate bath.
During forming a plating film on a plating object, a current density in the anode was about 0.8 A/dm².
In Comparative Example, after plating each sheet of plating objects, a power source was turned off to interrupt a current between the plating object and the anode, and then the plating object was removed from the plating solution.
In the course of processing 150 plating objects as described above, a current efficiency was gradually reduced.
Determination of a plating-film thickness on the plating object indicated that as shown in FIG. 6, a plating-film thickness was reduced as the number of the processed objects increased, leading to significant variation in a plating-film thickness. FIG. 6 shows an average thickness of a plating film on one plating object.
It is apparent that the present invention is not limited to the above embodiment, that may be modified and changed without departing from the scope and spirit of the invention.

Claims

1. A plating apparatus, comprising

a plating bath which contains a plating solution;

an anode and a cathode within the plating bath; and

a switching control unit which switches between a first state where a current is applied between a plating object in contact with the plating solution and the anode and a second state where a current is interrupted between the plating object and the anode while applying a current between the anode and the cathode.

2. The plating apparatus as claimed in claim 1, wherein the anode is a soluble electrode containing a metal capable of being passivated.

3. The plating apparatus as claimed in claim 2, wherein the metal capable of being passivated is a metal selected from the group consisting of nickel, cobalt, chromium and titanium.

4. The plating apparatus as claimed in claim 1, wherein the cathode is disposed between the anode and the plating object when the plating object is placed within the plating bath; and

the cathode has through-holes penetrating the surfaces of the anode side and the plating object side.

5. The plating apparatus as claimed in claim 1, comprising a current control unit controlling a current between the plating object and the anode and a current between the anode and the cathode, wherein the current control unit controls a current such that a current between the anode and the cathode in the second state is lower than a current between the plating object and the anode in the first state.

6. A process for manufacturing a semiconductor device where a semiconductor substrate having a conductor film on or over its surface as a plating object is placed in a plating bath which is filled with a plating solution and in which an anode and a cathode are disposed and then a plating film is formed on the conductor film, comprising

applying a current between the plating object and the anode by contacting the plating object with the plating solution; and

interrupting the current between the plating object and the anode while applying a current between the anode and the cathode.