Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2001-08-24
2003-02-11
Nguyen, Ha Tran (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S613000, C438S614000, C134S001200, C134S001300
Reexamination Certificate
active
06518162
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device. More specifically, the invention relates to a method for manufacturing a semiconductor device provided with protrudent electrodes used as an external wiring to make electrical connection with a conductive pattern formed on a circuit substrate.
BACKGROUND OF THE INVENTION
Recently, with advancement of smaller and higher-performance semiconductor devices, a semiconductor chip has been miniaturized and the number of terminals (connection terminals) has been increasing. In connection with this, pitches of the connection terminals are being made finer. A result of this is wide spreading use of packaging methods by which a semiconductor device is packaged in a tape carrier package (hereinbelow referred to as a TCP) by inner lead bonding (hereinbelow referred to as ILB) and packaged on a circuit substrate by direct flip-chip bonding with its face down. Further, like the ILB and the flip-chip bonding, the packaging methods by which fine pitch terminals can be connected at once regardless of the number of connection terminals are adopted by various semiconductors.
In order to realize these packaging methods, it is required to form a protrudent electrode (hereinbelow referred to as a bump) for connection on an electrode pad of a semiconductor chip.
Processes of manufacturing a bump in practical applications include a non-electrolytic bump process by which an Au (gold) bump or a solder bump is formed by electrolytic plating which utilizes electrocoating by electrolysis, and a wire bump process which utilizes wire bonding by metal fine lines.
The electrolytic plating bump process is advantageous because it provides high throughput by wafer batch processing, a large number of terminals, and finer pitch. However, the electrolytic plating bump process requires forming a barrier metal layer which is also used as a conductive film for electrolytic plating and forming a window in a bump forming portion by coating, exposuring, and developing a photoresist. Further, in the electrolytic plating bump process, since it is necessary to employ a step of forming the metal layer for electrolytic plating and a masking step using a photoresist for forming a bump selectively, the step of forming the bump is complicated. Further, in the electrolytic plating bump process, it is required to use such equipment as sputtering equipment and photo equipment other than electrolytic plating equipment. Thus, there is a problem that equipment investment becomes very large.
On the other hand, in the wire bump process, bumps are formed successively on respective electrode pads with wire bonder. Thus, in the wire bump process, throughput is low and it is difficult to increase the number of terminals. Further, in realizing finer pitch, while the limit of the pitch of the electrode pad in the electrolytic plating bump process is about bump width+5 &mgr;m (for example, when the bump width is 20 &mgr;m, the pitch width is 25 &mgr;m), the finest pitch of the electrode pad in the wire bump process is about 75 &mgr;m. Note that, since it is possible to form the bump only with the wire bonder in the wire bump process, there is an advantage that equipment investment can be suppressed.
As described above, semiconductor devices having a bump have been manufactured conventionally by making use of characteristics of the respective methods for forming a bump. However, recently, an non-electrolytic plating bump process is being developed as a new method for forming a bump.
The non-electrolytic plating bump process is to perform non-electrolytic plating selectively on an electrode pad made of or mainly made of Al (aluminum) which is formed on the semiconductor substrate in a semiconductor device. Further, in the non-electrolytic plating bump process, unlike the electrolytic bump process, it is not required to form a conductive film for plating by the sputter equipment or form a window using a photoresist in a bump forming portion by photo equipment. Thus, the process can be simplified and less equipment investment is required. Further, the non-electrolytic plating bump process can realize lower cost while having the advantageous characteristics of higher throughput by wafer batch processing, and finer pitches, which are common characteristics of plating bump processes.
Here, as the non-electrolytic plating bump process in the case where Ni (nickel) is used as the main component of the bump, Ni/Au plating bump process is described below with reference to FIG.
5
(
a
) to FIG.
5
(
e
).
First, as shown in FIG.
5
(
a
), an electrode pad
2
made of or mainly made of Al is formed on a semiconductor substrate
1
. Further, a protecting film
3
(insulating protecting film) having an insulating property is stacked on the electrode pad
2
so as to cover the electrode pad
2
. Next, a portion of an upper surface of the electrode pad
2
is exposed, for example, by etching a portion of the protecting film
3
on the electrode pad
2
. Thus, the protecting film
3
having an opening
3
a
on the electrode pad
2
is patterned.
Next, as shown in FIG.
5
(
b
), an oxide film
4
on the surface of the electrode pad
2
in the opening
3
a
of the protecting film
3
and a residual thin film (not shown) of the protecting film
3
are removed. Thereafter, a zincate process is performed by a substitution reaction of Al and Zn (zinc), and as shown in FIG.
5
(
c
), Al on the surface of the electrode pad
2
is substituted with Zn. Thus, a Zn layer
5
is formed on the surface of the electrode pad
2
.
Next, the semiconductor substrate
1
processed by the zincate process is immersed in a non-electrolytic plating solution to carry out the non-electrolytic plating process. For example, the semiconductor substrate
1
on which the Zn layer
5
is formed is immersed in a non-electrolytic Ni plating solution, so as to carry out the non-electrolytic Ni plating process by a non-electrolytic Ni plating reaction. In the non-electrolytic Ni plating reaction, first, Zn of the Zn layer
5
and Ni undergo a substitution reaction and Ni is deposited, thereby substituting Zn with Ni. Thereafter, as shown in FIG.
5
(
d
), Ni is deposited progressively by the self catalytic reaction in which the substituted Ni itself acts as a catalyst, thus forming an Ni bump
6
.
In the case where the bump is made of a material which forms an oxide film on its surface like the Ni bump
6
, an Au thin film is formed on the surface of the bump so as to prevent oxidation on the surface of the resulting bump.
In this case, after non-electrolytic Ni plating is finished, for example, displacing Au plating is performed so as to prevent oxidation on an Ni surface of the Ni bump
6
. Thus, as shown in FIG.
5
(
e
), Au is deposited on the Ni surface, and an Au layer
9
is formed on the Ni bump
6
. This completes the non-electrolytic Ni/Au plating bump process.
As described above, in forming the non-electrolytic Ni plating bump, it is not required to form a conductive film for plating by sputter equipment, or form a window in a bump forming portion using a photoresist by photo equipment. Thus, forming the non-electrolytic Ni plating bump has an advantage that less equipment investment is required. Further, since inexpensive Ni is used as a main material and throughput is good, forming the non-electrolytic Ni plating bump costs less than forming the Au bump by the electrolytic plating bump process.
However, as a result of study by the inventor of the present invention, it was found that the bump formed by the non-electrolytic plating bump process poses a problem in a pressure cooker test (hereinbelow referred to as PCT), which is an index of guaranteed quality.
In the non-electrolytic plating bump process, the non-electrolytic plating process is performed selectively only on the electrode pad
2
in the opening
3
a
of the protecting film
3
. Here, the reaction of the non-electrolytic Ni plating proceeds as the Zn (or Pd) of the Zn layer
5
which is formed by substitution with
Asazu Takuro
Yamaguchi Shinji
Nguyen Ha Tran
Nixon & Vanderhye P.C.
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