Patent Application
20100015362
1. Technical Field
Example embodiments relate to the fabricating of components, electrodes and wiring patterns of semiconductor devices, PCBs, semiconductor packages and the like. More particularly example embodiments relate to an apparatus for electroless plating and to a method of electroless plating.
2. Description of the Related Art
Nowadays, the electronic information industry centers on the development of the high-density mounting of semiconductor devices, such as those used in cellular phones, personal data assistants (PDAs) and so on. An electrically and physically stable connection between minute pad electrodes of the semiconductor devices and wiring on a substrate is required to achieve the high-density mounting. A metal contact layer has been suggested to provide such an electrically and physically stable connection. The metal contact layer is a layer of gold, nickel or nickel-gold plated on the pad electrodes. In this respect, the metal contact layer must have a uniform thickness if the connection is to be strong and reliable. To this end, the metal contact layer is generally formed using electroless plating.
Electroless plating is a method of plating a base metal with a second metal using a solution of ions of the second metal. Unlike electrolytic plating which uses electric current to facilitate the plating process, electroless plating is facilitated using a reducing agent. Accordingly electroless plating does not require a power source (as does electrolytic plating) and hence, the circuitry of the semiconductor device is less likely to be damaged during the plating process.
However, the plating solution imposes limitations on the type of base metal that can be employed, and forming a metal layer having a sufficient thickness using electroless plating is relatively time consuming. In addition, the surface structure of the metal layer may be rough and the metal layer may include some surface defects. For example, when nickel is plated with gold using electroless plating, the surface of the nickel-gold layer is excessively rough and non-uniform because of the substitution reaction of nickel with gold. Accordingly, the bond between nickel-gold contact layers and other elements, such as solder balls, can be weak.
Example embodiments of the present invention provide an apparatus for electroless plating capable of rapidly plating an object.
Likewise, example embodiments of the present invention provide an electroless method of rapidly and uniformly plating an object.
Example embodiments of the present invention provide a method of manufacturing a ball grid array (BGA) printed circuit board (PCB) using electroless plating.
According one aspect of the present invention, there is provided an apparatus for electroless plating includes a plating bath and a magnetic field generator associated therewith. The plating bath contains an aqueous metal salt solution producing metal ions and in which an object to be plated is immersed. The magnetic field generated by the magnetic field generator causes the metal ions in the solution to concentrate at a surface of the immersed object. The magnetic field generator may be provided below the plating bath. Alternatively, the magnetic field generator may be disposed alongside the plating bath. The magnetic field generator may be a permanent magnet or an electromagnet.
In the case of a permanent magnet, the north pole of the magnet faces the plating bath when the magnet is disposed outside the bath. Alternatively, the apparatus may include a transporting arm having a chuck for seizing the object, and operable to immerse the object into the aqueous metal salt solution. In this case, the magnetic field generator is integrated with the transporting arm so that the magnetic field passes through the object seized by the chuck of the arm.
According to another aspect of the present invention, there is provided a method of electroless plating which uses a magnetic field. An object to be plated is immersed in an aqueous metal salt solution. A magnetic field is generated for inducing and metal ions in the aqueous metal salt solution to concentrate at a surface of the object, and accumulate. A plated layer is formed by facilitating a (reduction) reaction that causes the metal ions concentrated at the surface of the object under the influence of the magnetic field to be adsorbed.
According another aspect of the present invention, there is provided a method of manufacturing a BGA PCB in which an electrode pad of the PCB is electrolessly plated using a magnetic filed. First, a metal wiring structure including a wire bonding pad and a solder ball pad is formed on a substrate. Then, a resist pattern having an aperture exposing the solder ball pad is formed. The substrate having the exposed solder ball pad is immersed into a first aqueous metal salt solution. A magnetic field is generated for inducing metal ions in the first aqueous metal salt solution to concentrate at a surface of the solder ball pad. A (reduction) reaction is facilitated that cause metal ions, concentrated at the surface of the bonding pad under the influence of the magnetic field to be adsorbed. As a result, a first bonding layer is formed on the solder ball pad.
The first aqueous metal salt solution may be an aqueous nickel salt solution. Thus, the solder ball pad may be nickel-plated.
According to another aspect of the present invention, the method of manufacturing a BGA PCB may further include the following steps. The substrate having the first bonding layer is immersed into a second aqueous metal salt solution. A magnetic field may be generated to induce metal ions in the second aqueous metal salt solution to concentrate at a surface of the first bonding layer. A second bonding layer may be formed by facilitating a (reduction) reaction which causes the first bonding layer to adsorb metal ions concentrated at the surface thereof under the influence of the magnetic field. Preferably, the second aqueous salt solution is an aqueous gold salt solution such that the solder ball pad becomes nickel-gold plated.
Example embodiments may be more clearly understood from the following detailed description of the preferred embodiments, i.e., non-limiting examples, thereof made in conjunction with the accompanying drawings.
This application claims priority under 35 U. S. C. §119 to Korean Patent Application No. 2008-70525, filed on Jul. 21, 2008 in the Korean Intellectual Property Office (KIPO), the contents of which are herein incorporated by reference in their entirety.
Various example embodiments will be described more fully hereinafter with reference to the accompanying drawings. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. Furthermore, like reference numerals designate like elements throughout the drawings.
Referring to
The plating bath 110 has a bottom, first and second side portions and an open top. A supply line 112 is connected to one of the side of the plating bath 110 at the top thereof for introducing the aqueous metal salt solution into the bath. A drain line 114 is connected to the other of side of the bath at the bottom thereof for discharging a waste aqueous metal salt solution. The aqueous metal salt solution contained in the plating bath 110 may be an aqueous nickel (Ni) salt solution, an aqueous gold (Au) salt solution, an aqueous silver (Ag) salt solution, or an aqueous cobalt (Co) salt solution. Also, the aqueous metal salt solution includes a reducing agent. The object 10 to be plated may be a printed circuit board (PCB) or a semiconductor substrate. Additionally, a support (not shown) for supporting the object 10 may be provided within the plating bath 110.
The magnetic field generator 120 may be provided at the lower portion of the plating bath 110 into which the object 10 is inserted. For example, when the object 10 is immersed into the aqueous metal salt solution and is oriented parallel to the bottom of the plating bath 110, the magnetic field generator 120 may be provided below the plating bath 110 so that the object 10 is vertically aligned with the magnetic field generator 120. In this case, the magnetic field generator 120 generates a magnetic field whose field lines pass through the object 10 from the bottom to the top thereof to induce the metal ions to concentrate at the surface of the object 10. For instance, the magnetic field generator 120 may generate a magnetic field of such a polarity that metal cations are concentrated on the surface of the object 10. In this example, the north pole of the permanent magnet faces the bottom surface of the object 10 to be plated. In the case of an electromagnet, the orientation of the coil of the magnet and the direction in which current is supplied through the coil are such that the direction or polarity of the magnetic field produced is the same as that of a permanent magnet whose north pole is oriented as shown in the figures. Also, the magnetic field generated by the magnetic field generator 120 can reduce the activation energy, i.e., to thereby increase the rate of the reaction caused by the reducing agent.
A method of forming a layer on the object 10 using the apparatus 100 for electroless plating will be described in detail, hereinafter.
A nickel aqueous metal solution for electroless plating is supplied into the plating bath 110 through supply line 112. The object 10 is immersed in the aqueous nickel solution and is oriented (supported) so that the bottom of the object 10 faces the bottom of the plating bath 110. A north pole of the magnetic field generator 120 faces the object 10.
Therefore, a magnetic field generated by the magnetic field generator 120 passes through the aqueous nickel solution and the object 10. The magnetic field also reduces the activation energy so that the reducing agent may more readily cause the reduction reaction that facilitates the plating process. Nickel cations thus concentrate on the surface of the object 10, rapidly accumulate and are rapidly adsorbed into the surface of the object 10. Thus, a thin nickel film is rapidly formed on the object 10.
Referring to
However, in this embodiment, the magnetic field generator 220 is disposed at a side of the plating bath 210. Also, the object 20 is supported within the bath such that the bottom thereof faces the side of the plating bath 210, and the magnetic field generator 220 faces the bottom of the object 20. The magnetic field generator 220 is operative to generate a magnetic field that passes through the object 20, and which magnetic field has a polarity that acts to attract the metal ions onto the surface of the object 20. For example, in the case in which the magnetic field generator 220 is a permanent magnet, the north pole of the magnet faces the surface of the immersed object 20 to be plated, and thus the surface becomes charged so that metal cations are attracted to the surface of the object 20.
Additionally, the heater 230 heats the aqueous metal salt solution contained in the plating bath 210 to a higher temperature than room temperature, so that the activity of the metal ions in the aqueous metal salt solution is increased and hence, the electroless plating rate is increased. The heater 230 may include a resistive wire (not shown) and a heat plate (not shown).
Hereinafter, a method of forming a layer on the surface of the object 20 using the apparatus 200 for electroless plating will be described in detail.
An aqueous gold salt solution for electroless plating is supplied into the plating bath 210 through supply line 212. The aqueous gold salt solution contained in the plating bath 210 is heated above room temperature by the heater 230. Also, the object 20 is immersed in the aqueous gold salt solution with the bottom thereof facing the side of the plating bath 210 where the magnetic field generator 220 is disposed outside the bath.
A magnetic field generated by the magnetic field generator 220 charges the surface of the object 20 and reduces the activation energy that must be overcome in order for the reducing agent to cause the reduction reaction that facilitates the plating process. As a result, a concentration of cations, i.e., gold ions, accumulate on the surface of the object 20 and are adsorbed by the surface of the object 20. Thus, a plated layer, i.e., a thin gold film, is formed on the object 20.
Referring to
The transporting arm 340 is operable to seize the object 30 by its bottom and/or side portions, and to move up and down to immerse the object 30 in the aqueous metal salt solution in the plating bath 310. The magnetic field generator 320 may be integrated with the transporting arm 340. In particular, the transporting arm 340 includes a chuck by which one side of the object 30 can be grasped when the object 30 is immersed in the aqueous metal salt solution, and the magnetic field generator 320 is affixed to the transporting arm 340 such that the magnetic field generator 320 face the side of the object 30 grasped by the chuck. In this case, the magnetic field generator 320 generates a magnetic field which passes through the object 30. In the case in which the magnetic field generator 320 is a permanent magnet, the north pole of the faces the object 30 immersed in the plating bath 310. As a result, cations, i.e., metal ions, in the solution concentrate at the surface of the object 30.
Hereinafter, a method of forming a layer on a surface of the object 30 using the apparatus 300 will be illustrated.
An aqueous silver metal salt solution for electroless plating is supplied into the plating bath 310 through supply line 312. The transporting arm 340 seizes the object 30, and positions the object 30 so that it is immersed in the aqueous silver salt solution contained in the plating bath 310. The magnetic field generator 320 generates a magnetic field to charge the surface of the object 30 and to reduce the activation energy that must be overcome by the reducing agent in the aqueous silver salt solution. As a result, the cations, i.e., the silver ions, become concentrated at the surface of the object 30, accumulated and are adsorbed into the surface of the object 30. Thus, a thin silver film is formed on the object 30.
According to the embodiments described above, a concentration of metal ions is formed on a surface of an object to be plated using a magnetic field. Therefore, a plated layer may be formed fast.
Characteristics of nickel-plated layers formed by electroless plating methods were evaluated. More particularly, a first nickel-plated layer A was formed by applying a magnetic field to an object immersed in an aqueous solution of nickel for about 7 minutes using the apparatus 100. A second nickel-plated layer B was formed using a conventional apparatus for about 7 minutes (i.e., by immersing an object in an aqueous solution of nickel without applying a magnetic field). The surfaces of the first and second nickel-plated layers A and B were inspected using a scanning electron microscope (SEM). The results are illustrated in
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The insulation patterned layer 430 may be formed by first forming an insulation layer, e.g., a silicon oxide layer, on the substrate 400 using a spin-coating process or a chemical vapor deposition (CVD) process. The insulation layer may then be planarized so as to have a planar upper surface. Next, an etching mask is formed on the insulation layer and a dry etching process is performed to remove a portion of the insulation layer exposed by the etching mask. As a result, the opening 432 is formed.
The conductive pattern exposed by the opening 232 may be the source/drain region 410 or the gate electrode 406. In the present embodiment, the source/drain region 410 is exposed by the opening 232. In the case in which the conductive pattern exposed by the opening 232 is to be the source/drain region 410, a portion of the source/drain region 410 may be etched along with the insulation layer, i.e., during the above-mentioned process in which the opening 432 is formed.
Referring to
The cobalt thin film 434 may be formed using one of the apparatuses 100, 200 and 300. For example, the substrate 400 is immersed into an aqueous cobalt salt solution including a reducing agent such as formaldehyde or hydrazine. A magnetic field is generated to concentrate the cobalt ions at the surface of the source/drain region 410 exposed by the opening 432. The cobalt ions concentrated at the surface of the source/drain region 410 by the magnetic field are then rapidly deposited on the source/drain region 410 as cobalt molecules. However, the cobalt molecules will not be deposited on the silicon oxide layer 430 due to the chemistry behind the electroless plating process. As a result, a cobalt layer is formed only on the exposed surface of the source/drain region 410.
Referring to
In one example embodiment, the cobalt silicide layer 436 is formed by a single silicidation process at a temperature of about 400° C. to 900° C. In another example, the cobalt silicide layer 436 is formed by a two-step silicidation process. In this example, the substrate 400 including the cobalt layer is thermally treated at a temperature of about 400° C. to 500° C. to form a preliminary cobalt silicide (CoSi) layer. Then, the preliminary cobalt silicide layer is thermally treated at a temperature of about 700° C. to 900° C. to produce the cobalt silicide layer (CoSi2) 436.
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In a specific example, the exposed surface of the pad to be plates is pre-treated to have a roughness (Ra) of about 0.5 μm≦Ra≦2.0 μm, preferably about 0.5 μm≦Ra≦1.5 μm, and more preferably about 0.5 μm≦Ra≦1.0 μm. The pre-treatment to reduce the surface roughness will enhance the ability of the nickel-gold-plated layer to bond to the pad.
After the pre-treatment, the CCL substrate 500 is immersed into an aqueous nickel salt solution, and the CCL substrate 500 is charged using the magnetic field generated by an electroless plating apparatus of the example embodiment. The cations, i.e., the nickel ions, are thus concentrated on the surface of the exposed bonding pad and the exposed solder ball pad, accumulate and are adsorbed onto the pads to form a nickel layer. Then the CCL substrate 500 having the nickel layer thereon is immersed into an aqueous gold salt solution, and charged using a magnetic field again. Accordingly, the cations, i.e., the gold ions, concentrate on the surface of the exposed nickel layer, accumulate and are adsorbed to form a gold layer. As a result, nickel-gold layer 505 is formed on the bonding pad and on the solder ball pad.
Referring to
In a conventional plating process which does not employ a magnetic field, forming a nickel-gold layer of a thickness of about 12 μm, necessary to achieve a high strength bond with the layer being plated, requires a long amount of time or the plating bath must maintained at a high temperature. However, the long processing time or high temperature required may allow for/cause the plating to be eluted by the solder resist or may result in overplating. In the electroless plating method in accordance with example embodiments, the plating can be formed very fast, e.g., at least twice as fast as the conventional method. Therefore, the above-described problems are not created and sufficient solder bond strength may be obtained.
Referring to
A second semiconductor package 700 may include substantially the same configuration and components as the first semiconductor package 600. That is, the second semiconductor package 700 may include a semiconductor pattern 710 having an opening 714 therethrough, an insulation layer 720 covering the semiconductor pattern 710, a wiring structure 730 electrically connected to a contact pad of a semiconductor device of the package, and a polymer insulation member 750 provided on the bottom of the second semiconductor pattern 710.
Referring to
A conductive filling material 690 may be injected into the space between the first and second semiconductor packages 600 and 700 so that the first and second semiconductor packages 600 and 700 are more firmly adhered to each other.
Referring to
According to example embodiments described above, metal ions in an aqueous metal salt solution are concentrated on an object to be plated using a magnetic field, and the activation energy that must be overcome by a reducing agent in the aqueous solution is reduced. Accordingly, a metal layer can be rapidly deposited on the object, and the surface roughness can be reduced. Furthermore, the thickness of the plating and the amount of the active metal ions may be controlled, and thus the plating may be formed on the object very fast.
Finally, although the example embodiments have been described with reference to the preferred embodiments thereof, the present invention may be embodied in other ways. Therefore, it is to be understood that the foregoing description is illustrative of the present invention and that the present invention is not limited to the specific embodiments disclosed. Rather, other embodiments and modifications of the disclosed embodiments may fall within the true spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0070525 | Jul 2008 | KR | national |
