Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2002-07-17
2004-06-08
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S759000, C257S760000, C257S762000, C257S774000, C257S765000, C438S118000, C438S622000, C438S623000, C438S624000, C438S687000, C438S688000, C438S629000
Reexamination Certificate
active
06747355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a semiconductor device employing copper interconnects therein, and more particularly to a semiconductor device employing aluminum as bonding pads in addition to the copper interconnects to improve reliability of semiconductor device, and further a method for manufacturing the same.
2. Description of the Related Art
Generally, copper exhibits low resistance and provides high resistance against electromigration, and therefore, it becomes apparent that copper is the material of choice for interconnect lines and contacts in future generations including the subquarter-micron generation. At the same time, copper is essentially a material that is quite easily oxidized and easily enhances its oxidation due to moisture in air, and once when copper begins oxidation, the copper allows the oxidation to deeply progress into the inside of the copper without staying the surface layer thereof. For this reason, when a bonding pad is formed of a part of copper interconnects and an oxide layer is formed on a surface of the bonding pad, a bonding ball cannot be bonded to the bonding pad with sufficient adhesion strength. In addition, even when the bonding ball could successfully be bonded thereto, corrosion due to oxidation of copper would start from an exposed portion of the bonding pad, which portion is not covered by the bonding ball, and finally spread over the entire surface of the bonding pad. When formation of the corrosion is further enhanced, copper interconnects themselves are unfavorably corroded.
Accordingly, when copper is employed as an interconnects material, a bonding pad made of a material excluding copper and providing high resistance against oxidation is formed on an upper portion of copper interconnects, which technique is generally employed in this technical field. For example, Japanese Patent Application Laid-open No. 7(1995)-201909 discloses a technique in which a tungsten film is laminated on copper interconnects to form a bonding pad. Furthermore, Japanese Patent Application Laid-open No. 10(1998)-340920 discloses a technique in which a conductive film containing aluminum therein is laminated on copper interconnects to form a bonding pad. That is, in both the techniques disclosed in the above-stated publications, copper interconnects are covered by an insulation film and openings are formed in the insulation film to expose a part of the copper interconnects, and then, a conductive film made of tungsten, aluminum or the like is formed within each of the openings on the copper interconnects to thereby form a bonding pad.
However, according to the techniques disclosed in those publications, when a thickness of the insulation film covering the copper interconnects is made large, a film thickness of tungsten, aluminum or the like constituting the bonding pad becomes large, likely presenting performance and manufacturing problems. In particular, an insulation film consisting of a laminated structure having a copper diffusion barrier layer for preventing diffusion of copper and an insulation film is formed into a thick film, presenting a serious problem. For example,
FIGS. 1A through 1E
each illustrate a cross sectional view of an example in the order of manufacturing steps and the example is constructed by forming a bonding pad made of aluminum on copper interconnects.
Referring to
FIG. 1A
, a silicon oxide film
201
is formed on a surface of a semiconductor substrate (not shown) having elements such as transistors formed in a surface portion thereof and a trench
202
for an interconnect pattern is formed in the silicon oxide film
201
, and then, a barrier metal
203
is formed on an entire surface of a semiconductor device to fill the trench
202
with the barrier metal to prevent copper from diffusing into the oxide, and further, a copper film is formed thereon by a plating method or the like. Subsequently, the copper film on the silicon oxide film
201
is polished such as by a CMP (Chemical Mechanical Polishing) method to leave the copper film only within the trench
202
to thereby form a copper pad
205
that constitutes one piece structure together with copper interconnects (not shown).
Thereafter, as shown in
FIG. 1B
, a copper diffusion barrier layer
206
made of a silicon nitride film or the like and a silicon oxide film
207
are laminated to cover a surface of the above-stated copper pad
205
to thereby form an inter layer insulation film
208
. Then, an opening
209
is formed in the inter layer insulation film
208
to expose a part of the copper pad
205
.
Subsequently, as shown in
FIG. 1C
, a titanium nitride film
212
for preventing reaction between copper and aluminum, an aluminum film
213
and a titanium nitride film
214
for reducing reflectance of a surface of aluminum to make possible the application of photolithography technology in forming a fine interconnect pattern are formed in order.
Then, as shown in
FIG. 1D
, the titanium nitride film
214
, aluminum film
213
and titanium nitride film
212
are etched using a photolithography technique to thereby form an aluminum pad
213
made of the aluminum film
213
.
Furthermore, as shown in
FIG. 1E
, an insulating protection film
215
made of a silicon oxide film or the like is deposited on an entire surface of the semiconductor substrate. Thereafter, the insulating protection film
215
and the titanium nitride film
214
on the aluminum pad
213
are selectively etched and removed using a photolithography technique to expose a surface of the aluminum film
213
to thereby complete formation of bonding pad.
The conventional bonding pad constructed by forming the inter layer insulation film
208
consisting of a laminated structure having the copper diffusion barrier layer
206
for preventing copper diffusion from the copper pad
205
and the silicon oxide film
207
, and the insulating protection film
215
positioned on the inter layer insulation film includes the following problem. That is, since the inter layer insulation film
208
is formed on the copper pad
205
to resultantly have a large film thickness owing to its laminated structure and the aluminum pad
213
is formed so as to cover the opening
209
that is formed in the inter layer insulation film
208
, the aluminum pad
213
is forced to have a large step, which is formed by the opening
209
, and therefore, the step coverage of the aluminum pad
213
at the opening
209
is deteriorated, whereby the copper pad
205
under the aluminum pad
213
suffers from corrosion and/or oxidation due to leakage of moisture and/or oxygen through a portion corresponding to nonconformal step coverage of the aluminum pad
213
at the opening.
To prevent such problems, the technique disclosed in the above-described publication may be modified such that aluminum is formed within both the openings
209
and
216
that are respectively formed in the inter layer insulation film
208
and the insulating protection film
215
positioned thereon, thereby forming an aluminum pad. However, since a total thickness of the inter layer insulation film
208
and the insulating protection film
215
positioned thereon is large, the aluminum pad
213
is forcibly formed into an extremely thick film while making process time necessary for depositing aluminum into the openings
209
,
216
extremely long, unfavorably increasing manufacturing cost. The technique may also be modified such that aluminum is formed only within the opening
209
of the inter layer insulation film
208
to form an aluminum pad. However, the aluminum pad
213
formed as described above allows moisture or oxygen to leak through a nonconformal portion formed in the aluminum pad
213
to likely oxidize the copper pad
205
lying directly under the aluminum pad
213
, thereby causing the breaking of a part of copper interconnects which include the copper pad
205
as a part thereof and leading to degradation of reliability of a semiconductor device having such construction of bonding pad.
S
Abiru Takahisa
Hatano Keisuke
Huynh Andy
NEC Electronics Corporation
Nelms David
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