Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Ball or nail head type contact – lead – or bond
Reexamination Certificate
2002-01-29
2002-09-17
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Ball or nail head type contact, lead, or bond
C257S781000, C438S613000
Reexamination Certificate
active
06452281
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to Japanese application No.
2001-019950
filed on Jan. 29, 2001, whose priority is claimed under 35 USC §119, the disclosure of which is incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and a fabrication process therefor. More particularly, the invention relates to a semiconductor integrated circuit which has a plurality of bump electrodes having a uniform height, and to a fabrication process therefor.
2. Description of the Related Art
In the fields of cellular phones and mobile information terminals in the electronic information industry, attempts have recently been made to increase the integration density of semiconductor devices. For a higher integration density, it is necessary to stably establish electrical and physical connections between minute electrode pads on a semiconductor device and interconnections on a substrate mounted with the semiconductor device.
One exemplary method for the establishment of the connections is to form gold bumps on electrode pads of the semiconductor device. Plating methods are generally employed for the formation of the gold bumps on the semiconductor device. The plating methods are broadly classified into two categories: an electroless plating method and an electrolytic plating method.
In the electroless plating method, a metal of a metal base to be plated is chemically replaced with a metal contained in a plating liquid. Therefore, the electroless plating method is advantageous in that equipment such as a plating power source is not required. However, possible combinations of the metal base and the plating liquid are limited, and a plating rate is relatively low. Therefore, the electroless plating method is not suitable for formation of a metal film having a thickness of ten-odd micrometers to several tens of micrometers as required for the formation of the bumps on the semiconductor device.
In the electrolytic plating method, on the other hand, the plating is electrochemically achieved by passing an electric current through a metal base to be plated and a plating liquid. Therefore, the electrolytic plating method can be applied to a combination of the metal base and the plating liquid to which the aforesaid electroless plating method cannot be applied. In the electrolytic plating method, the plating electric current increases the plating rate as compared with the electroless plating method, and a metal film having a thickness of several tens of micrometers can easily be formed. Therefore, the electrolytic plating method is suitable for the formation of the bumps on the semiconductor integrated circuit.
Next, a bump formation process employing the electrolytic plating method will briefly be described.
A metal base film is first formed on an insulating film provided on a semiconductor substrate (herein referred to as “wafer”). Then, a photoresist film is formed on the metal base film, and openings are formed in the photo resist film by a photo lithography technique to expose predetermined portions of the metal base film, i.e., in bump electrode formation areas. Thereafter, a plating electric current is supplied to the metal base film, whereby a metal is deposited on the exposed portions of the metal base film for formation of bump electrodes. There are three conventionally known methods for the supply of the plating electric current.
In a first conventional method, an opening for connection of a plating electrode (herein referred to as “cathode electrode”) is formed in the photoresist film in a peripheral area of the wafer when the photoresist film is formed on the metal base film, and then the cathode electrode is connected to the metal base film through the opening. Alternatively, the photoresist film is removed by piercing the photo resist film with the cathode electrode for the connection of the cathode electrode to the metal base film.
More specifically, electrode pads
23
are provided on an insulating film
22
on a wafer
21
, and the wafer is covered with a protective film
24
which has openings on the electrode pads
23
in bump electrode formation areas A as shown in
FIG. 5. A
metal base film
25
is formed over the resulting wafer, and a photoresist film
26
is formed on the metal base film
25
. Further, openings are formed in the photoresist film
26
in the bump electrode formation areas A.
The photoresist film
26
is pierced with a cathode electrode
28
for electrical connection of the cathode electrode
28
to the metal base film
25
(though not shown, an opening may be formed in the photoresist film
26
for connection of the cathode electrode to the metal base film).
In turn, the resulting wafer
21
is set in a plating device
101
as shown in FIG.
6
. The wafer
21
is supported by the cathode electrode
28
with a bump electrode formation surface thereof facing downward to be opposed to an anode electrode
10
.
In the plating device
101
, a plating liquid
9
is fountained from an inner lower side of the device toward the bump formation surface of the wafer
21
, and discharged from the periphery of the wafer
21
to the outside.
In this state, a voltage is applied between the anode electrode
10
and the cathode electrode
28
connected to the metal base film
25
on the wafer
21
, whereby a plating electric current is supplied to the metal base film
25
for formation of bump electrodes
27
(see FIG.
5
).
In a second conventional method, a cathode electrode is connected to a portion of the metal base film on a side surface of the wafer (see, for example, Japanese Unexamined Patent Publication No. 1-110751 (1989)) in view of the fact that the metal base film is formed not only on the bump electrode formation surface but also on the side surfaces of the wafer.
More specifically, a metal base film
35
is formed on a bump electrode formation surface and side surfaces of a wafer
31
, and a cathode electrode
38
is electrically connected to a portion of the metal base film on the side surface of the wafer as shown in FIG.
7
. Thereafter, the resulting wafer is subjected to the plating process in substantially the same manner as in the first method in the aforesaid plating device
101
(See FIG.
6
).
In a third conventional method, a metal film electrically connected to the metal base film is formed on a back surface of the wafer, and a cathode electrode is connected to the metal film on the back surface of the wafer (see, for example, Japanese Unexamined Patent Publication No. 3-54829 (1991)).
More specifically, a metal base film
45
is formed as covering a bump electrode formation surface and side surfaces of a wafer
41
, and a metal film
46
is formed on a back surface of the wafer
41
so as to be electrically connected to the metal base film on the side surface of the wafer. A cathode electrode
48
is electrically connected to the metal film
46
. Thereafter, the resulting wafer is subjected to the plating process in substantially the same manner as in the first method in the aforesaid plating device
101
(see FIG.
6
).
In the first conventional method, the plating liquid penetrates through the opening provided for the cathode electrode connection during the plating process in the electrolytic plating device, so that the plating electric current is unevenly supplied to an area other than the bump electrode formation areas. Therefore, a metallization layer is uselessly formed in the unintended area by the plating, and the resulting bump electrodes are nonuniform in height.
Where the photoresist film is pierced with the cathode electrode to be removed, it is difficult to control the removal of the photoresist film. If the removal of the photoresist film is excessive, the aforesaid problem occurs. If the removal of the photoresist film is insufficient, an electrical connection cannot sufficiently be established between the cathode electrode and the metal base film, resulting in uneven supply of the plating electric c
Clark Sheila V.
Nixon & Vanderhye P.C.
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