JP4225005B2 - Method for forming wiring using electrolytic plating - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming wiring using electrolytic plating, and can be applied to, for example, formation of rewiring of a CSP (chip size package).
[0002]
[Prior art]
A conventional general wiring forming method will be described by taking a wafer level CSP as an example. In the wafer level CSP, in the semiconductor manufacturing process, the solder bumps are formed in the wafer state without cutting the chips, and the completed wafer is diced into chips.
[0003]
FIG. 5 is a schematic cross-sectional view of a main part of the wafer level CSP, and FIGS. 6A and 6B are schematic cross-sectional views showing a conventional process for forming rewiring in the wafer level CSP.
[0004]
As shown in FIG. 5, the extraction electrode 12 of the semiconductor substrate 10 and the solder bump 40 are electrically connected by a rewiring 30. The method for forming the rewiring 30 is as follows.
[0005]
First, a semiconductor element such as a transistor, a wiring 11 made of aluminum or the like, an extraction electrode 12 and the like are formed on the semiconductor substrate 10 by a normal semiconductor process, and the semiconductor element and the wiring 11 are protected on the semiconductor substrate 10. A passivation film 13 is formed.
[0006]
An interlayer film 14 made of polyimide or the like is formed on the passivation film 13, and then the interlayer film 14 is removed by etching or the like above the extraction electrode 12 on the substrate 10 to form an opening 15 (interlayer). Film formation step).
[0007]
Next, a seed layer 16 formed by sputtering such as Cr or Cu is formed on the entire surface of the interlayer film 14 including the extraction electrode 12 exposed from the opening 15 (seed layer forming step).
[0008]
Next, as shown in FIG. 6A, a resist 20 having an opening 21 in a portion of the surface of the seed layer 16 where the rewiring 30 is to be formed is patterned by exposure and etching (resist formation). Step) A rewiring 30 is formed on the surface of the seed layer 16 exposed from the opening 21 of the resist 20 by an electrolytic plating method (wiring forming step).
[0009]
Thereafter, the resist is removed using a stripping solution or the like (resist removing step), and the seed layer 16 in a portion where the resist is removed is etched and removed using an etching solution such as an acid (seed layer etching step). Thus, the rewiring 30 is formed together with the remaining seed layer 16.
[0010]
Thereafter, as shown in FIG. 6B, a protective film 50 made of polyimide or the like is formed on the semiconductor substrate 10 (protective film forming step). As shown in FIG. 5, the protective film 50 is formed in a state where a connection portion with the solder bump 40 in the rewiring 30 is opened.
[0011]
Then, solder bumps 40 are formed using a technique such as printing or solder balls, and the rewiring 30 and the solder bumps 40 are electrically and mechanically connected through the openings 51 of the protective film 50 (solder bump formation). Process). Thus, the CSP structure shown in FIG. 5 is completed. After that, dicing is performed.
[0012]
[Problems to be solved by the invention]
However, for example, when the CSP has a power IC with a built-in power element that allows a large current to flow, it is necessary to increase the thickness of the wiring for the purpose of securing the current capacity of the wiring and reducing the wiring resistance. . For example, in the wafer level CSP, the film thickness of the rewiring 30 is set to about 6 to 12 μm.
[0013]
Therefore, as shown in FIG. 6B, the thickness (hereinafter referred to as coverage thickness) 50a of the portion of the protective film 50 formed on the shoulder 30a of the rewiring 30 is thin. . For example, when the conductive foreign matter K adheres to this portion, the insulation reliability between the adjacent rewirings 30 decreases.
[0014]
In order to avoid this, conventionally, there is a method in which the protective film 50 is applied and formed twice to increase the film thickness of the protective film itself to ensure the coverage film thickness. It will be connected. There is also a method of forming the protective film 50 thick by increasing the viscosity of the protective film.
[0015]
In view of this, it is conceivable to form a metal wiring by electrolytic plating and then etching the metal wiring so that the shoulder portion of the wiring is tapered or rounded. In this way, since the shoulder portion of the wiring flares toward the outer periphery, when the protective film is formed thereon, the coverage film thickness 50a can be secured.
[0016]
However, in this case, in order to form a taper on the shoulder portion of the thick metal wiring, there are problems that it takes a considerable time for the etching process, and the film thickness and width of the wiring are reduced by the etching.
[0017]
In view of the above problems, an object of the present invention is to form a taper (including an R shape) at the shoulder portion of the wiring simultaneously with the formation of the wiring by electrolytic plating in the wiring forming method using electrolytic plating.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, in the wiring forming method for forming the wiring (30) using electrolytic plating on one surface of the substrate (10), the wiring is formed on one surface of the substrate. Forming a resist (20) having an opening (21) at a site to be formed, forming a wiring by electrolytic plating on one surface of the substrate exposed from the opening, and then removing the resist In the step of forming the resist, in the step of forming the resist, the end surface of the opening in the resist is formed into a tapered shape that expands from below to above, so that the shoulder portion of the wiring is formed in an arc shape in the step of forming the wiring It is characterized by.
[0019]
According to this, by forming the resist in such a tapered shape, when the wiring is formed by electroplating, the wiring is formed in an arc shape on the tapered surface of the resist, and this arc-shaped portion is the shoulder of the wiring. Part. Therefore, according to the present invention, at the same time when the wiring is formed by electrolytic plating, a taper close to the R shape can be formed on the shoulder portion of the wiring.
[0023]
According to a second aspect of the present invention, in the method for forming a wiring according to the first aspect , in the step of forming the resist, the tapered shape of the resist is formed in an arc shape, and the invention according to the third aspect of the present invention. Then, in the method for forming a wiring according to claim 1 or 2 , in the step of forming the wiring, the wiring is formed thinner than the thickness of the resist. According to a fourth aspect of the present invention, in the wiring forming method for forming the wiring (30) on one surface of the substrate (10) using electrolytic plating, the wiring is formed on the surface of the substrate on which the wiring is to be formed. A step of forming a resist (20) having an opening (21), a step of forming wiring on one surface of the substrate exposed from the opening by an electrolytic plating method, and a step of removing the resist thereafter. In the step of forming the resist, the thickness of the resist is made thinner than the thickness of the wiring to be formed by electrolytic plating. In the step of forming the wiring, the wiring is formed thicker than the thickness of the resist, and the wiring is resisted. by also be formed to protrude over the edge of the opening of, and forming a shoulder portion of the wiring in a circular arc shape.
[0024]
According to this, by forming the resist thinner than the thickness of the wiring to be formed, when the wiring is formed by electrolytic plating, the resist exceeds the height of the resist and protrudes over the edge of the opening. The wiring portion to be formed is formed in a circular arc shape spreading toward the outer periphery. This arc-shaped portion becomes the shoulder portion of the wiring.
[0025]
Therefore, according to the present invention, in the method for forming a wiring using electrolytic plating, a taper can be formed on the shoulder portion of the wiring simultaneously with the formation of the wiring by electrolytic plating.
[0026]
In addition, the code | symbol in the parenthesis of each said means is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described below. Although not limited, in this embodiment, an example in which the wiring formed by electrolytic plating is applied to rewiring of a wafer level CSP will be described.
[0028]
The basic configuration of the CSP according to this embodiment is the same as the configuration shown in FIG. Although there are some overlapping parts, the basic configuration of the CSP of this embodiment will be described with reference to FIG.
[0029]
The semiconductor substrate 10 is composed of a silicon substrate or the like, and semiconductor elements such as transistors (not shown) are formed on the semiconductor substrate 10. Further, on one surface side of the semiconductor substrate 10, wirings 11 and lead electrodes (pads) 12 made of aluminum or the like that are electrically connected to the semiconductor element are formed.
[0030]
On one surface of the semiconductor substrate 10, a passivation film 13 made of a silicon nitride film that covers and protects the semiconductor element and the wiring 11 is formed. Here, the passivation film 13 is opened on the extraction electrode 12. The semiconductor element, the wiring 11, the extraction electrode 12, and the passivation film 13 can be formed by a known semiconductor process.
[0031]
An interlayer film 14 made of an insulating film material is formed on the passivation film 13. The interlayer film 14 plays a role of stress relaxation between the upper rewiring 30 and the semiconductor substrate 10, and can be formed by applying and curing polyimide or the like, for example. Further, the interlayer film 14 is removed by etching or the like above the extraction electrode 12 to form an opening 15.
[0032]
A rewiring 30 made of a material containing metal is formed in a predetermined pattern on the interlayer film 14 via the seed layer 16. The rewiring 30 is necessary to electrically connect the solder bumps 40 and the extraction electrodes 12 that are aligned and arranged at a predetermined pitch in the CSP.
[0033]
The seed layer 16 is a base for the rewiring 30, and a film of Cu, Cr, or the like can be formed by a sputtering method or the like. The seed layer 16 has a pattern that matches the rewiring 30.
[0034]
The rewiring 30 is electrically connected to the extraction electrode 12 through the opening 15 of the interlayer film 14, and has a predetermined wiring pattern from the opening 15 of the interlayer film 14 to the portion where the solder bump 40 is disposed. It extends.
[0035]
The rewiring 30 is a wiring formed by using electrolytic plating. For example, the rewiring 30 may have a multilayer structure in which plating layers such as Cu, Ni, and Au are laminated from the base side or a single-layer wiring structure such as Cu. it can.
[0036]
A protective film 50 made of an insulating film such as polyimide is formed on the rewiring 30 and the interlayer film 14. An opening 51 is formed in a predetermined portion of the protective film 50 on the rewiring 30, and the rewiring 30 and the solder bump 40 are electrically and mechanically connected through the opening 51. .
[0037]
Here, FIG. 1 shows a detailed cross-sectional configuration of the rewiring 30 of the present embodiment. FIG. 1 shows a cross section of a portion of the rewiring 30 covered with a protective film along a direction orthogonal to the longitudinal direction of the rewiring 30. A rewiring 30 is formed on the seed layer 16, and a shoulder 30a of the rewiring 30 has a tapered shape close to an R shape.
[0038]
An example of the film thickness dimension of each part is given. The film thickness T1 of the rewiring 30 including the seed layer 16 is, for example, 6 to 12 μm, the thickness T2 of the protective film 50 on the interlayer film 14 is about 5 μm, and the thickness T3 of the protective film 50 on the rewiring 30 is 3 to 3. About 4 μm, the film thickness (coverage film thickness) T4 of the protective film 50 on the shoulder 30a is secured to 1 μm or more.
[0039]
Such a wafer level CSP is mounted on a wiring board such as a printed board or a ceramic board on the solder bump 40 side, and is mounted on the wiring board by reflowing the solder bump 40.
[0040]
In addition, as described in the section of “Prior Art”, the CSP of this embodiment performs interlayer film formation, seed layer formation, resist formation, wiring formation, resist formation on the semiconductor substrate 10 formed up to the passivation film 13. It can be manufactured by performing each step of removal, seed layer etching, and protective film formation.
[0041]
Here, the rewiring 30 having a taper formed on the shoulder 30a shown in FIG. 1 is formed as shown in FIGS. In general, there are the following three forming methods found by the present inventors.
[0042]
The first method shown in FIG. 2 is characterized in that, in the step of forming the resist 20, the end surface of the opening 21 in the resist 20 is tapered so as to expand from below to above.
[0043]
Here, the taper of the resist 20 can be formed by making the exposure amount larger than the target value when patterning the resist made of a material such as an acrylic resin by exposure and etching using a photolithographic technique. . The taper of the resist can also be formed by shortening the development and etching time after exposing the resist.
[0044]
For example, the taper shape of FIG. 2 can be achieved by over-exposing a negative resist such as a synthetic rubber type, and can be easily formed by under-developing a phenol novolac type positive resist. Is possible.
[0045]
According to the first method, by forming the resist 20 in such a tapered shape, when the rewiring 30 is formed by electrolytic plating, the plating film that becomes the rewiring 30 on the tapered surface of the resist 20 is a circle. Form it in an arc. This arc-shaped portion becomes the shoulder portion 30 a of the rewiring 30. Thus, at the same time when the rewiring 30 is formed by electrolytic plating, a taper close to an R shape can be formed on the shoulder 30a of the rewiring 30.
[0046]
In the second method shown in FIG. 3, in the step of forming the resist 20, a film resist is used as the resist 20 so that the end surface of the opening 21 in the resist 20 has a tapered shape that expands from the top to the bottom. It is what.
[0047]
The inventors use a film resist made of a photosensitive resin film (for example, acrylic methacrylic ester polymer) or the like as the resist 20, and this is etched using a developer made of an aqueous solution of Na ₂ CO ₃ (sodium carbonate) or the like. By doing so, it was experimentally confirmed that the end surface of the opening 21 in the resist 20 can be formed into a tapered shape that expands from the top to the bottom.
[0048]
More specifically, an acrylic dry film resist is used, the focus of projection exposure is set near the surface, underexposure is performed, and development is performed over, so that the end surface of the opening 21 in the resist 20 is lowered from above. It was experimentally confirmed that the taper shape can be expanded toward.
[0049]
As shown in FIG. 3, in this second method, the rewiring 30 is formed by electrolytic plating by performing electroplating using the resist 20 whose end face of the opening 21 has such a tapered shape as a mask. At the same time, the shoulder 30a of the rewiring 30 can be tapered.
[0050]
In the third method shown in FIG. 4, in the step of forming the resist 20, the step of forming the rewiring 30 by making the thickness of the resist 20 thinner than the thickness of the rewiring 30 to be formed by electrolytic plating. Then, the rewiring 30 is formed so as to protrude beyond the edge of the opening 21 of the resist 20 by forming the rewiring 30 thicker than the thickness of the resist 20. .
[0051]
According to this, when the rewiring 30 is formed by electrolytic plating, the portion of the rewiring 30 that exceeds the height of the resist 20 and protrudes on the edge of the opening 21 spreads toward the outer periphery. It will be formed in an arc shape. This arc-shaped portion becomes the shoulder portion 30 a of the rewiring 30.
[0052]
Therefore, also by this third method, the shoulder 30a of the rewiring 30 can be tapered at the same time as the rewiring 30 is formed by electrolytic plating.
[0053]
As described above, in the present embodiment, the step of forming the resist 20 having the opening 21 at the portion where the wiring 30 is to be formed on the one surface of the substrate 10, and the one surface of the substrate 10 exposed from the opening 21. By adopting any one of the first to third methods in the method for forming the wiring 30 including the step of forming the wiring 30 by electrolytic plating and the step of removing the resist 20 thereafter. At the same time that 30 is formed by electrolytic plating, a taper can be formed on the shoulder 30 a of the wiring 30.
[0054]
In addition, by forming the protective film 50 on the wiring 30 having the shoulder 30a having a tapered shape (including the R shape) in this way, insulation reliability and the like can be ensured, that is, sufficient protective film characteristics can be secured. Can achieve a sufficient coverage film thickness.
[0055]
It has been experimentally confirmed that the taper can be formed on the shoulder 30a of the wiring 30 by increasing the current density at the time of electrolytic plating from the standard condition. For example, by increasing the current density to about 3 to 4 A / sd from the standard condition, the thickness of the rewiring 30 is about 0.5 to 0.7 μm thinner than the center of the wiring. Can be.
[0056]
Thereby, the taper can be formed on the shoulder 30a of the rewiring 30, and the coverage film thickness of the protective film 50 formed thereon can be set to 1 μm or more.
[0057]
The present invention can be applied to any wiring forming method using electrolytic plating other than CSP rewiring. For example, the present invention can also be applied to a wiring made of a plating film formed by performing electrolytic plating on a copper foil wiring on a printed board.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cross-sectional shape of a wiring according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing a first method for forming a wiring in the embodiment.
FIG. 3 is a schematic cross-sectional view showing a second method of forming a wiring in the embodiment.
FIG. 4 is a schematic cross-sectional view showing a third method for forming a wiring in the embodiment.
FIG. 5 is a schematic cross-sectional view showing a main part of a wafer level CSP.
FIG. 6 is a diagram illustrating a conventional method for forming a wiring.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate, 20 ... Resist, 21 ... Opening, 30 ... Rewiring.

Claims (4)

In the wiring formation method of forming the wiring (30) using electrolytic plating on one surface of the substrate (10),
Forming a resist (20) having an opening (21) at a site where the wiring is to be formed on one surface of the substrate;
Forming the wiring by electrolytic plating on one surface of the substrate exposed from the opening;
Thereafter, the step of removing the resist,
In the step of forming the resist, by forming the end surface of the opening in the resist into a tapered shape that expands from below to above, the shoulder of the wiring is formed in an arc shape in the step of forming the wiring. A method of forming a wiring characterized by the above. The resist in the step of forming a method for forming a wiring according to claim 1, characterized in that forming said resist tapered arcuately. In the step of forming the wiring, the method for forming a wiring according to claim 1 or 2, characterized by forming the wiring thinner than the thickness of the resist. In the wiring formation method of forming the wiring (30) using electrolytic plating on one surface of the substrate (10),
Forming a resist (20) having an opening (21) at a site where the wiring is to be formed on one surface of the substrate;
Forming the wiring by electrolytic plating on one surface of the substrate exposed from the opening;
Thereafter, the step of removing the resist,
In the step of forming the resist, the thickness of the resist is made thinner than the thickness of the wiring to be formed by the electrolytic plating method,
The wiring in the step of forming, said wire thicker than the thickness of the resist is formed, by forming the wiring protrudes also on the edge of the opening of the resist, the shoulder of the front Symbol wiring Is formed in an arc shape .

Images