JP3326466B2 - Method for forming electrodes of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a bonding electrode suitable for so-called bare chip mounting, in which a semiconductor element such as a transistor, an IC or an LSI is mounted in a bare state without a package.

[0002]

2. Description of the Related Art In recent years, in response to demands for downsizing and high performance of electronic equipment, a surface mount type in which a bare chip is mounted on a tape-shaped insulating film having lead wiring and connected to leads instead of a conventional resin package. TCP that is a package
(Tape CarrierPackage) or a high-density packaging technology such as a flip-chip system in which a bare chip is directly mounted on a circuit board is increasingly required. In a semiconductor element used for these high-density mounting techniques, a projection electrode for bonding is required as an external electrode for making an electrical connection with the outside.

An example of a method for forming such a bump electrode for bonding will be described with reference to FIGS. 5 and 6. FIG.

FIG. 5 is a cross-sectional view of a semiconductor element near an Al electrode before a protruding electrode is formed by electroless plating. FIG. 6 is a process cross-sectional view showing a method of forming a protruding electrode by electroless plating. It is.

In these figures, 1 is a semiconductor device, 2
Is an Al electrode as an external electrode of the semiconductor element 1, 3 is a natural oxide film, 4 is a protective film such as a silicon nitride film formed so as to cover the edge of the Al electrode 2, 5 is a silicon oxide film, 6
Denotes a wafer, 7 denotes a Zn particle film, 8 denotes a Ni film, and 9 denotes an Au film.

First, FIG. 6A shows a wet etching process of the Al electrode 2 formed on the semiconductor element 1 of the wafer 6. In this step, the natural oxide film 3 formed on the surface of the Al electrode 2 is removed by immersing the wafer 6 in an aqueous solution of phosphoric acid or sodium hydroxide. After the removal of the natural oxide film 3, cleaning is performed with pure water kept at around room temperature.

When the device is left with the natural oxide film 3 removed,
Since the native oxide film 3 is formed on the Al electrode 2 again, as shown in FIG. 6B, a Zn particle film 7 is formed on the Al electrode 2 to prevent the natural oxide film 3 from being reformed. I do. The formation of the Zn particle film 7 is performed by immersing the Zn particle film 7 in an alkaline (pH 13 to 14) solution containing Zn at room temperature for about 30 seconds, and utilizing a substitution reaction between Al and Zn ions in the solution. To a thickness of 30 on the surface of the Al electrode 2.
This is for forming a Zn particle film 7 of about 0 to 500 °. After the formation of the Zn particle film 7, cleaning is performed with pure water kept near room temperature.

Next, as shown in FIG. 6C, a Ni film 8 is formed on the Al electrode 2 by an electroless plating method.

Specifically, immersion is performed for 2 to 5 minutes in an electroless Ni plating bath maintained at about 90 ° C., whereby the Zn particle film 7 is dissolved in the electroless Ni plating solution. , Ni is precipitated by a substitution reaction between Zn and Ni ions in the electroless Ni plating solution, and then Ni is self-precipitated on the Ni by a self-reduction reaction of the electroless Ni plating solution, and is deposited on the Al electrode 2 of the semiconductor element 1. About 0.7 to 1.2 μm Ni
A film 8 is formed.

Next, the wafer 6 is washed with pure water at room temperature, and thereafter, as shown in FIG. 6D, an Au film 9 is formed on the Ni film 8 by electroless plating. Specifically, in an electroless Au plating bath maintained at about 90 ° C., 4
The immersion is performed for about 0 minutes, and 0.2 μm is formed on the Ni film 8 by a substitution reaction between Ni and Au ions in the electroless Au plating solution.
An Au film 9 is formed.

The Au film 9 is formed by Ni
The film 8 alone has poor electrical connectivity due to the presence of the Ni oxide film, which is to be improved to enhance electrical connectivity.

The steps shown in FIGS. 6A to 6D are usually performed for each wafer.

In this manner, a Ni film 8 is formed on the Al electrode 2 which is an external electrode of the semiconductor element 1 by electroless plating, and an Au film 9 is further formed thereon by electroless plating. To form a projection electrode for bonding. When the semiconductor element 1 is mounted on a bare chip, the protruding electrodes are directly connected to a circuit board by flip chip mounting,
Alternatively, it is packaged in TCP.

[0014]

As described above, when the first and second metal films such as the Ni film and the Au film are formed on the Al electrode of the semiconductor element by the electroless plating method, the Al In many cases, a reactive plating solution is used. Therefore, when forming the second metal film on the first metal film formed on the Al electrode, the Al electrode and the first metal film are used.
If the plating solution for the second metal film is not prevented from entering the interface with the first metal film, the plating solution for the second metal film and the Al electrode may be used at the interface between the Al electrode and the first metal film. Reacts, and the adhesion between the Al electrode and the first metal film deteriorates, and the contact resistance increases.

However, in the electrode formation using the conventional electroless plating method as described above, when forming the first and second metal films on the Al electrodes of the semiconductor elements in wafer units, the number of steps required for forming the first and second metal films increases.
At a plating temperature of about 0 ° C. to 90 ° C., the wafer is warped. That is, due to the difference in the coefficient of thermal expansion of the materials laminated to form the semiconductor elements on the wafer, at the plating processing temperature, a warp occurs on the side of the wafer on which the semiconductor elements are formed, and in a state where the warp occurs, the metal is formed. A film will be formed.

Therefore, in the cleaning step at room temperature after the formation of the first metal film, since the substrate is not warped and returns to the original state, it is formed by electroless plating with the protective film 4 formed on the Al electrode. A minute gap is generated at the interface with the Ni film 8 as the first metal film, and the Au film 9 as the second metal film is formed.
Is formed by the electroless plating method, the plating solution of the Au film 9 penetrates through the minute gap, reacts with the Al electrode 2, and the adhesion between the Al electrode 2 and the Ni film 8 deteriorates. There is a problem that the value increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and a bonding electrode comprising at least two or more types of metal films is formed on an external electrode of a semiconductor element by an electroless plating method. An object of the method is to form an electrode having good adhesion and high connectivity.

[0018]

Means for Solving the Problems In order to solve the above problems, the present invention is configured as follows.

That is, in the method of forming an electrode of a semiconductor device according to the present invention, the protective film formed on the external electrode is formed by electroless plating due to the warpage of the wafer generated in the step of forming the metal film on the external electrode. In order to prevent the plating solution for the second metal film from penetrating from this gap and reacting with the external electrode, a small gap is formed at the interface with the first metal film. Wafer warpage in the processing process is constant, or warpage is forcibly prevented.
The gap created by the influence of the warpage is filled again by the plating method.

According to the present invention, it is possible to prevent the plating solution of the second metal film from entering the interface between the external electrode and the first metal film, thereby preventing the reaction between the plating solution and the external electrode. Thereby, the adhesion between the external electrode and the first metal film is improved, and an electrode having a small contact resistance value and high connectivity can be formed.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a method for forming an electrode by laminating at least two or more types of metal films on an external electrode of a semiconductor element by an electroless plating method. Electroless plating of the first metal film
Forming a first metal film by a metallization method;
Cleaning step of cleaning the semiconductor element on which the metal film is formed
And forming a second metal film by an electroless plating method.
Consists of a second metal film forming step, the treatment temperature in all the processing steps of at least said first metal film forming step to about the second metal film forming Engineering, which holds approximately equal temperature, The processing temperature in each of these steps
Since they are almost equal, the processing of each process can be
At the interface between the protective film and the first metal film.
No minute gaps are created and therefore the second gold
The plating solution for the metal film does not react with the external electrode.

According to a second aspect of the present invention, in the first aspect of the present invention, the substantially equal temperature is applied to the protective film covering an edge of the external electrode and the first film formed on the external electrode.
The temperature at which no gap is formed at the boundary portion with the metal film can reliably prevent the plating solution of the second metal film from reacting with the external electrode.

[0023]

According to a third aspect of the present invention, there is provided a method of forming an electrode by laminating at least two or more types of metal films on an external electrode of a semiconductor element by an electroless plating method. The deformation of the semiconductor element at the processing temperature to be formed is prevented by the reinforcing material, so that the semiconductor element does not warp in the step of forming the first metal film, and the external electrode can be returned to room temperature. There is no minute gap at the interface between the protective film formed thereon and the first metal film.
The plating solution for the second metal film does not react with the external electrode. In addition, the cleaning step after forming the metal film can be performed at a temperature around room temperature.

According to a fourth aspect of the present invention, there is provided a method of forming an electrode by laminating at least two or more types of metal films on an external electrode of a semiconductor element by an electroless plating method. Forming a first metal film by an electrolytic plating method, cleaning the semiconductor element on which the first metal film is formed at a temperature near room temperature, and forming a second metal film by an electroless plating method A first metal film forming step of forming the first metal film at a temperature higher than room temperature, and a first metal film forming step of forming the first metal film at a temperature near room temperature. And a second forming step of forming a first metal film.
When the semiconductor element is warped in the formation process and is returned to around room temperature, even if a minute gap is formed at the interface between the protective film formed on the external electrode and the first metal film, the temperature at around room temperature is reduced. In the second forming step, the first metal film is formed again to fill the gap, so that the plating solution for the second metal film does not react with the external electrode. In addition, the cleaning step after forming the first metal film can be performed at a temperature around room temperature.

[0026]

[0027]

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a cross-sectional view of a semiconductor device according to Embodiment 1 of the present invention, and FIG. 2 is a process cross-sectional view showing a method of forming electrodes of a semiconductor device in wafer units. There is a portion corresponding to the conventional example of FIGS. 5 and 6,
The same reference numerals are given. 2 (a) to 2 (c)
It shows the deformed state in the plating bath and the cleaning bath, respectively.

In the semiconductor device 1 of this embodiment, as shown in FIG. 1, a Ni film 8 as a first metal film is deposited on an external electrode Al electrode 2 by electroless plating. Is formed, and A is formed thereon as a second metal film.
u film 9 is deposited by an electroless plating method.
When the semiconductor element 1 shown in FIG. 1 is mounted on a bare chip, as in the prior art, the projecting electrode for bonding is directly connected to the circuit board by flip chip mounting, or
Is to be packaged.

Next, with reference to FIG. 2, a method of forming electrodes of a semiconductor element in wafer units according to the first embodiment of the present invention will be described in the order of steps.

First, FIG. 2A shows a wet etching process of the Al electrode 2 formed on the semiconductor element 1 on the wafer 6. In this step, the wafer 6
Is immersed in an aqueous solution of phosphoric acid or sodium hydroxide to remove a natural oxide film formed on the surface of the Al electrode 2. Thereafter, cleaning is performed with pure water maintained at around room temperature.

If the natural oxide film is left with the natural oxide film removed, a natural oxide film is formed on the Al electrode 2 again. Therefore, as shown in FIG.
The particle film 7 is formed to prevent the re-formation of the natural oxide film. The formation of the Zn particle film 7 is performed by immersing the Zn particle film 7 in an alkaline (pH 13 to 14) solution containing Zn at room temperature for about 30 seconds, and utilizing a substitution reaction between Al and Zn ions in the solution. To a thickness of 30 on the surface of the Al electrode 2.
This is for forming a Zn particle film 7 of about 0 to 500 °. After the formation of the Zn particle film 7, cleaning is performed with pure water kept near room temperature.

The above pretreatment steps are the same as in the above-mentioned conventional example.

Next, as shown in FIG. 2C, a Ni film 8 as a first metal film is formed on the Al electrode 2 by an electroless plating method.

Specifically, electroless Ni held at 90 ° C.
The immersion is performed in the plating bath 10 for 2 to 5 minutes, thereby dissolving the Zn particle film 7 in the electroless Ni plating solution, thereby causing a substitution reaction between Zn and Ni ions in the electroless Ni plating solution. After the deposition of Ni, the Ni is self-deposited on the Ni by a self-reduction reaction of the electroless Ni plating solution, and the Ni of about 0.7 to 1.2 μm is deposited on the Al electrode 2 of the semiconductor element 1.
A film 8 is formed.

Electroless Ni plating bath 1 at a processing temperature of 90 ° C.
0, as described above, due to the difference in the coefficient of thermal expansion of the material laminated to form the semiconductor element 1 on the wafer 6,
As shown in FIG. 2C, the semiconductor elements 1 on the wafer 6
Warpage occurs on the side of the formation surface of
An i film 8 is formed.

Next, as shown in FIG.
In 1, the wafer 6 is cleaned with pure water at 90 ° C. which is the same temperature as the electroless Ni plating bath 10. Specifically, FIG.
By performing the cleaning process after the electroless Ni plating process (c) using pure water maintained at 90 ° C., which is the same temperature as the electroless Ni plating bath 10, the warpage of the wafer 6 in the cleaning process can be reduced. The same state as the warpage when the wafer 6 is immersed in the plating bath 10 is maintained, whereby the warp is eliminated and the protective film 4 and the Ni film are removed as in the conventional example of cleaning with pure water at a temperature near room temperature. There is no generation of a minute gap at the interface with No. 8.

Next, as shown in FIG.
An Au film 9 is formed thereon by an electroless plating method. Specifically, in the electroless Au plating bath 12 held at the same 90 ° C. as the plating temperature and the cleaning temperature of the Ni film 8,
The immersion is performed for about 40 minutes, and 0.2 of the Ni film 8 is formed on the Ni film 8 by a substitution reaction between Ni and Au ions in the electroless Au plating solution.
A μm Au film 9 is formed.

As described above, since the wafer 6 is immersed in the electroless Au plating bath 12 at the same temperature as the plating temperature and the cleaning temperature of the Ni film 8, the warped state of the wafer 6 becomes the same, as in the case where the temperature is returned to around room temperature. No fine gap is formed at the interface between the protective film 4 and the Ni film 8.
Since the infiltration of the electroless Au plating solution into the interface between the electrode 2 and the Ni film 8 can be prevented, the electroless Au plating solution and the Al electrode 2 do not react with each other.
A protruding electrode having high adhesion to the film 8 and low contact resistance can be formed.

In this embodiment, the processing temperatures of the electroless plating process for Ni film 8, the cleaning process and the electroless plating process for Au film 9 are all set to the same temperature. As an embodiment of the present invention, the wafer 6
As long as the warp states are substantially the same and a gap is not generated at the boundary between the protective film 4 and the Ni film 8, the temperatures need not be the same, but may be approximately the same.

(Embodiment 2) Next, a method for forming an electrode of a semiconductor device according to Embodiment 2 of the present invention will be described with reference to FIG.

In the second embodiment, the protruding electrodes are formed in the same steps as in the conventional example described above, but at least in the plating step of forming the Ni film 8 on the Al electrodes 2 by the electroless plating method. The reinforcing member 13 for preventing the warpage of the wafer 6 is mounted on the wafer 6 for processing.

As shown in FIG. 3, the reinforcing member 13 is formed so as to extend from the back surface of the wafer 6 to the peripheral edge of the front surface. This prevents the wafer 6 from warping at the plating temperature.

The reinforcing material 13 is made of a corrosion-resistant material that does not deform at a temperature of about 80 ° C. to 90 ° C.
It is composed of tetrafluoroethylene or ceramic.

According to the electrode forming method of the second embodiment, in the plating process of the Ni film 8 in FIG. 2C of the first embodiment, the plating process is performed without warping the wafer 6 by the reinforcing member 13. After that, as in the conventional example, after returning to room temperature and washing with pure water at room temperature,
There is no minute gap at the interface between the protective film 4 and the Ni film 8. Therefore, in the plating process of the Au film 9, the infiltration of the electroless Au plating solution into the interface between the Al electrode 2 and the Ni film 8. Can be prevented, and a protruding electrode having high adhesion and low contact resistance can be formed.

Further, in the second embodiment, it is not necessary to perform the cleaning treatment after forming the Ni film 8 with pure water at a high temperature of about 90 ° C. Since pure water can be used, there is no need to raise the temperature of pure water.

The other structure is the same as that of the first embodiment.

The reinforcing material 13 may be used in the plating process of the Au film 9 as a matter of course.

Further, the shape of the reinforcing member 13 is not limited to the shape shown in FIG. 3, and for example, the back side and the front side of the wafer 6 may be formed by separate members, and both members may be connected by a connecting member. 6 may be prevented.

(Embodiment 3) Next, a method for forming an electrode of a semiconductor device according to Embodiment 3 of the present invention will be described with reference to FIG.

FIG. 4 is a process sectional view of a method for forming an electrode of a semiconductor device according to the third embodiment. Parts corresponding to the above-described embodiments are denoted by the same reference numerals.

First, FIG. 4A shows a wet etching step of the Al electrode 2 formed on the semiconductor element 1 on the wafer 6. In this step, the wafer 6
Is immersed in an aqueous solution of phosphoric acid or sodium hydroxide to remove a natural oxide film formed on the surface of the Al electrode 2. Thereafter, cleaning is performed with pure water maintained at around room temperature.

If the natural oxide film is left with the natural oxide film removed, a natural oxide film is formed again on the Al electrode 2. Therefore, as shown in FIG.
The particle film 7 is formed to prevent the re-formation of the natural oxide film. The formation of the Zn particle film 7 is performed by immersing the Zn particle film 7 in an alkaline (pH 13 to 14) solution containing Zn at room temperature for about 30 seconds, and utilizing a substitution reaction between Al and Zn ions in the solution. To a thickness of 30 on the surface of the Al electrode 2.
This is for forming a Zn particle film 7 of about 0 to 500 °. After the formation of the Zn particle film 7, cleaning is performed with pure water kept near room temperature.

Next, a Ni film as a first metal film is formed on the Al electrode 2 by electroless plating.
In this embodiment, the Ni film is formed by the first and second forming steps.

That is, as shown in FIG.
By an electroless plating method on the electrode 2 to form a first Ni layer _81.

Specifically, electroless Ni held at 90 ° C.
The Zn particle film 7 is immersed in the plating bath 10 for 2 to 5 minutes, thereby dissolving the Zn particle film 7 in the electroless Ni plating solution 10, thereby replacing Zn with Ni ions in the electroless Ni plating solution. After Ni is precipitated by the reaction, Ni is self-deposited on Ni by a self-reduction reaction of the electroless Ni plating solution,
On the Al electrode 2 of the semiconductor element 1 and forms a first Ni layer ₈₁ of about 0.7～1.2Myuemu.

Electroless Ni plating bath 1 at processing temperature of 90 ° C.
Among 0, the wafer 6 is warped on the upper surface direction to form a Ni film ₈₁ in a state this where warped.

The above steps are basically the same as in the first embodiment.

In the first embodiment, the subsequent cleaning process is performed with pure water at 90 ° C., whereas in the third embodiment, as shown in FIG. Similarly, cleaning is performed with pure water at room temperature in the cleaning tank 14.

[0061] In this room the cleaning process, in order to return to the original lost warpage of the wafer 6, to yield a fine gap 15 at the interface between the first Ni layer ₈₁ and the protective film 4 of the semiconductor element 1 become. In the conventional example, in a state where the gap 15 occurs, but the formation of the Au film 9 by electroless plating, in this third embodiment, as shown in FIG. 4 (e), first Ni layer 8 ₁ Above, a second time near room temperature
A Ni film 8 ₂ formed by electroless plating.

That is, the temperature of the wafer 6 is set to room temperature,
First the interface gap 15 between the Ni film ₈₁ and the protective film 4, electroless Ni near room caused by returning the warp based on
The second Ni layer 8 by dipping in the plating bath 16 ₂
Is formed, thereby filling the gap 15.

Specifically, electroless Ni held at 27 ° C.
Plating bath 16 immersed for 30 minutes in, forming a second Ni layer ₈₂ of 0.05~0.1μm on the first NI8 ₁ film.

[0064] After forming the second Ni layer _82, it is cleaned with pure water maintained at room temperature.

Next, as shown in FIG.
_An Au film 9 is formed on ₂ by an electroless plating method. Specifically, in an electroless Au plating bath 12 kept at 90 ° C., subjected to immersion of about 40 minutes, by substitution reaction between Ni and Au ions electroless Au plating solution on the Ni film 8 ₂ 0 An Au film 9 having a thickness of 0.2 μm is formed.

[0066] In the second Ni layer ₈₂ of the forming step in FIG. 4 (c), the the gap 15 is embedded, A
In the plating treatment step of u film 9, intrusion of an electroless Au plating solution into the interface of Al electrode 2 and the Ni film ₈₁ is prevented,
A highly adhesive metal film can be formed on the surface of the Al electrode 2 very easily.

Further, in the third embodiment, it is not necessary to perform the cleaning treatment after forming the Ni film with pure water at a high temperature of about 90 ° C. as in the first embodiment, Pure water can be used.

(Other Embodiments) In each of the above embodiments, although the Ni film is used as the first metal film,
As another embodiment of the present invention, instead of the Ni film, Cu
Although a film, a Pd film, or an Au film may be used, and in each of the above-described embodiments, an Au film is used as the second metal film. However, as another embodiment of the present invention, instead of the Au film, , Cu film or Pd film may be used.

In each of the above embodiments, an Al electrode is used as an external electrode. However, in another embodiment of the present invention, a Pt electrode or an Ag electrode is used instead of an Al electrode.
Electrodes may be used.

In each of the above embodiments, the external electrode is
Although two types of metal films are formed, three or more types of metal films such as In may be further formed as another embodiment of the present invention.

The processing conditions such as the processing temperature and the processing time in each processing step are not limited to the above-described embodiment.

[0072]

As described above, according to the present invention, when a metal film such as a Ni film or an Au film is formed on an external electrode such as an Al electrode by an electroless plating method, the processing temperatures are substantially equal. By maintaining the wafer at a constant temperature by maintaining the temperature, or by preventing the wafer from being warped by a reinforcing material, and further by forming the first metal film at two different plating processing temperatures, Since the intrusion of the plating solution of the second metal film from the gap between the first metal film and the protective film is completely prevented, it is possible to form an electrode having good adhesion and low contact resistance and high connectivity. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a process sectional view according to Embodiment 1 of the present invention;

FIG. 3 is a cross-sectional view of a state where a reinforcing member according to Embodiment 2 of the present invention is mounted.

FIG. 4 is a process sectional view according to Embodiment 3 of the present invention;

FIG. 5 is a sectional view of a conventional semiconductor device.

FIG. 6 is a process sectional view of a conventional semiconductor device by an electroless plating method.

[Explanation of symbols]

1 semiconductor element 2 Al electrodes 8, 8 _1, 8 ₂ Ni film 9 Au film 6 wafers 10, 16 an electroless Ni plating bath 11, 14 cleaning tank 12 an electroless Au plating bath 13 stiffener 15 gap

Continuation of the front page (56) References JP-A-7-263493 (JP, A) JP-A-6-140409 (JP, A) JP-A-8-264541 (JP, A) JP-A-6-232136 (JP) , A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01L 21/60

Claims (4)

(57) [Claims] 1. A method for forming an electrode by laminating at least two types of metal films on an external electrode of a semiconductor element by an electroless plating method, wherein the first metal film is formed by an electroless plating method. One
A metal film forming step; and a semiconductor having the first metal film formed thereon.
A cleaning step of cleaning the body element, and electrolessizing the second metal film.
And a second metal film forming step formed by an etching method.
Ri, at least the second metal from the first metal film forming step
The treatment temperature in all the processing steps up as Shokumaku formed Engineering, electrode forming method of a semiconductor device characterized by retaining substantially the same temperature. 2. The substantially equal temperature is a temperature at which no gap is formed at a boundary between a protective film covering an edge of the external electrode and the first metal film formed on the external electrode. 2. The method for forming an electrode of a semiconductor device according to claim 1. 3. A method of forming an electrode by laminating at least two or more types of metal films on an external electrode of a semiconductor element by an electroless plating method, wherein the semiconductor is formed at a processing temperature for forming at least a first metal film. A method for forming an electrode of a semiconductor device, wherein the deformation of the device is prevented by a reinforcing material. 4. A method for forming an electrode by laminating at least two types of metal films on an external electrode of a semiconductor element by electroless plating, wherein the first metal film is formed by electroless plating. A first metal film forming step, a cleaning step of cleaning the semiconductor element on which the first metal film is formed at a temperature around room temperature, and a second metal film forming of forming a second metal film by electroless plating The first metal film forming step includes a first forming step of forming the first metal film at a temperature higher than room temperature, and a second forming step of forming the first metal film at a temperature near room temperature. And a method of forming an electrode of a semiconductor device.