Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Bump leads
Reexamination Certificate
2001-10-05
2004-06-08
Kielin, Erik J. (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Bump leads
C257S750000, C257S753000, C257S766000, C257S773000, C257S780000
Reexamination Certificate
active
06747351
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor device having a protrusive electrode and manufacturing method of the same, and more particularly it relates to a semiconductor device with a protrusive electrode to connect the device and other devices electrically, and manufacturing method thereof.
BACKGROUND OF THE INVENTION
Today, for an electrode pad made of Al (aluminum) or mainly made of Al (will be referred to as electrode pad) on semiconductor substrates, electroless plating is used as one of the methods to form a protrusive electrode that electrically connects the electrode pad and other devices.
The electroless plating can omit steps such as:
a sputtering step that is required to form a barrier metal layer and an electrode in a step of plating;
a photo step that is needed for a pattern formation of a protrusive electrode; and
an etching step that eliminates a resist that is used in the step of pattern formation and a barrier metal that is used in the plating step.
Comparing with an electrolytic plating, the electroless plating can form the electrode pad with fewer steps. So the electroless plating has attracted attention as a method that enables to reduce costs as well as shorten delivery times.
The electroless plating is a method to selectively form a protrusive electrode made of Ni (nickel) or a Ni alloy (will be referred to as protrusive electrode) on the electrode pad. In this process, if an oxide film exists on the surface of the electrode pad, it deeply influences the form and reliability of the protrusive electrode, since the protrusive electrode cannot be formed uniformly on the electrode pad.
Therefore, before doing the electroless plating, the oxide film on the surface of the electrode pad is removed by sodium hydroxide, phosphoric acid, etc., to form a protrusive electrode in good and desired shape. However, a microscopic gap is formed between the protrusive electrode and the protective coat, because the protrusive electrode is developed from the surface of the electrode pad and not chemically joined with the protective coat on the semiconductor substrate.
Referring to FIGS.
5
(
a
) through
5
(
d
), the following description will discuss one example of methods to form a protrusive electrode on a electrode pad by the electroless plating.
FIGS.
5
(
a
) through
5
(
d
) are sectional process drawings of a method to form a protrusive electrode on the electrode pad made of Al or mainly made of Al through a commonly used electroless plating.
FIG.
5
(
a
); On a surface of an electrode pad
22
made of Al or mainly made of Al which is formed on a semiconductor substrate
21
, there is an area that is not covered with a protective coat
24
. The figure is a section view which shows a step to remove an oxide film
23
that is formed on the uncovered area described above. In this step, the oxide film
23
is completely removed using sodium hydroxide, phosphoric acid, etc. By the way, a formation of an insulating film on the surface of the semiconductor substrate
21
is omitted from the figure.
The oxide film
23
will be formed on the electrode pad
22
again, if the electrode pad
22
from which the oxide film
23
is removed is left as it is. Thus, as the FIG.
5
(
b
) shows, a Zn film
25
is formed on the electrode pad
22
to prevent the re-formation of the oxide film
23
. A process to form the Zn film
25
uniformly on the surface of the electrode pad
22
(zincate process) is a preliminary step to form a protrusive electrode
26
(see FIG.
5
(
c
)) by the electroless plating that precipitates Ni or a Ni alloy (will be referred to as Ni). The zincate process is carried out as follows; the electrode pad
22
is dipped into an alkaline solution that contains Zn, and displacement reaction is occurred between Al in the electrode pad
22
and Zn ions in the solution.
FIG.
5
(
c
) is a sectional view that shows a step to form the protrusive electrode
26
through the electroless plating that precipitates Ni. The plating by Ni through the use of the electroless plating is done as the electrode pad
22
on which the Zn film
25
is evenly formed is dipped into electroless Ni plating liquid. On account of this, Zn in the Zn film
25
dissolves in the electroless Ni plating liquid and the displacement reaction between Zn and Ni ions in the electroless Ni plating liquid occurs, then Ni is precipitated on the electrode pad
22
. Once Ni that becomes a nucleus is precipitated on the electrode pad
22
, due to an autocatalytic reaction (self-reduction reaction) of the electroless Ni plating liquid, Ni is self-precipitated on Ni, and the protrusive electrode
26
is formed.
Since the Zn film
25
is evenly formed in the zincate process as above, Ni uniformly grow on the electrode pad
22
and the protrusive electrode
26
which is well-shaped and small grain size is obtained. However, since the protective coat
24
and the protrusive electrode
26
are not chemically joined, a microscopic gap
27
is formed between these two.
FIG.
5
(
d
) is a sectional view that shows a step to form an immersion Au film
28
on the protrusive electrode
26
by immersion Au plating. The immersion Au plating is done by dipping the electrode pad
22
, on which the protrusive electrode
26
is formed, into an immersion Au plating liquid. In this manner, as the figure shows, the immersion Au film
28
is formed on the surface of the protrusive electrode
26
. By the way, to prevent corrosion of the electrode pad
22
in a subsequent step of electroless Au plating, the surface of the protrusive electrode
26
must be covered by the immersion Au film
28
, by this immersion Au plating.
However, due to extreme narrowness of the gap
27
between the protective coat
24
and the protrusive electrode
26
, it is difficult to remove the electroless Ni plating liquid from the gap
27
. If the immersion Au plating is done on condition that the electroless Ni plating liquid still remains in the gap
27
, the immersion Au plating liquid cannot enter the gap
27
adequately. Thus the immersion Au film
28
that formed in the area where the protective coat
24
faces the surface of the protrusive electrode
26
becomes defective, and leaves areas not plated by the immersion Au film
28
on the surface of the protrusive electrode
26
.
In a conventional method of this process, areas not plated by the immersion Au film
28
remain on the surface of the protrusive electrode
26
, because the microscopic gap
27
between the protective coat
24
and the protrusive electrode
26
is formed. Therefore, in a subsequent step:
an adhesion between the electrode pad
22
and the protrusive electrode
26
becomes poor, because the electroless Au plating liquid enters the gap
27
and the electrode pad
22
is corroded; and
reliability of the semiconductor device becomes significantly lower, owing to a seepage of the electroless Au plating liquid from the protrusive electrode
26
.
So, an object of the present invention is to offer a highly reliable semiconductor device with good adhesion between an electrode pad and a protrusive electrode and the manufacturing method of the device, by completely covering the surface of the protrusive electrode with a defect-free film that is formed on the surface of the protrusive electrode.
By the way, as a method to form an electrode for a semiconductor element, to resolve a problem that a microscopic gap between a protective coat and a metal film (a protrusive electrode) which is formed due to warpage of a wafer, Japanese Laid-Open Patent Application No. 10-125682/1998 (Tokukaihei 10-125682; published on May 15, 1998) discloses:
{circle around (1)} a technique to reduce warpage of the wafer due to the difference of temperature, caused as a plating step and a washing step are done at the same temperature;
{circle around (2)} a technique to reduce warpage of the wafer by attaching a reinforcing frame; and
{circle around (3)} a technique to carry out Ni plating again at room temperature.
However, what the invention disclosed in the application above intends
Asazu Takuro
Ono Atsushi
Yamaguchi Shinji
Hogans David L.
Kielin Erik J.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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