Bump fabrication method

Details Bump fabrication method Bump fabrication method

2003-02-24

2004-04-13

Pert, Evan (Department: 2829)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

Reexamination Certificate

active

06720244

ABSTRACT:

BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to bump fabrication, and in particular, a bump fabrication method to increase the wettability of wetting layer of the under bump metallurgy (UBM) layer.
2. Description of the Related Art
In IC packaging technology, the first level package is the connection of chips to carrier. The common types of package are, for example, wire bonding, tape automatic bonding (TAB), flip chip (F/C), etc. However, in either TAB or F/C, in the course of bonding chips to the carrier, a bump has to be made on the pad of the wafer, and the bump is used as an electrical media for the chips and the carrier. The common types of bump, generally, are solder bump, gold bump, conductive polymer bump and polymer bump. Among all these, the solder bump is most widely applied.
FIGS. 1A
to
1
F there is show a conventional solder bump fabrication method. As shown in
FIG. 1A
, the active surface
112
of the wafer
110
is provided with a passivation layer
114
and a plurality of bonding pads
116
(only one shown).
The passivation layer
114
exposes the bonding pad
116
on the top of the active surface
112
. Next, as shown in
FIG. 1B
, evaporation, sputter or plating method is used to form an under bump metallurgy (UBM) layer
120
on the bonding pad
116
.
Next, as shown in
FIG. 1C
, a patterned masking layer
130
is formed on the active surface
112
of the wafer
110
, using a plurality of openings
132
(one has been shown) on the masking layer
130
, exposing the UBM layer
120
. Next, as shown in
FIG. 1D
, a printing method is used to fill solder paste
140
into the space formed by the openings
132
and the UBM layer
120
. After that, as shown in
FIG. 1E
, a re-flow process is performed such that the solder paste
140
is finally formed into a bump
142
having a ball shape.
Lastly, the masking layer
130
is removed, exposing the bump
142
on the active surface
112
of the wafer
110
.
Referring to
1
C to
1
E, the UBM layer
120
generally comprises a wetting layer
122
, a barrier layer
124
and an adhesion layer
126
. The wetting layer
122
is used to bond with the bump
142
, and thus, the wetting layer
122
must possess excellent wettability so as to provide better bonding between the bump
142
and the wetting layer
122
. Besides, the material of the solder paste
140
includes tin (Sn), and there is excellent bonding between copper (Cu) and tin. Thus, in the course of forming the UBM layer
120
, generally, copper is used as material for the wetting layer
122
.
In view of the above, as copper and oxygen in the air can be easily oxidized to form copper oxide, however, the bonding between copper oxide and tin is poor. Thus, when copper is used as material for the wetting layer
122
, in order to remove copper oxide formed on the wetting layer
122
, the unoxidized copper underneath is exposed so as to increase the wettability of the wetting layer
122
. As shown in
FIG. 1C
, in a conventional method, plasma ashing
150
is used to remove the copper oxide formed on the wetting layer
122
so as to expose the unoxidized copper. However, in the conventional method where plasma ashing
150
is used to remove the copper oxide of the wetting layer
122
, if solder paste
140
has not filled the opening
132
on time to perform a re-flow process to form a bump, when the copper of the wetting layer
122
comes in contact with oxygen, copper will again oxidize to form copper oxide.
SUMMARY OF INVENTION
Accordingly, it is an object of the present invention to provide a bump fabrication method, wherein after the bonding pad of a wafer is formed with a UBM layer, and before the bump is formed on the UBM layer, plasma ashing is employed in sequence to remove the oxidized region of the wetting layer, exposing the unoxidized region, and after that, on the wetting layer of the UBM layer a flux film is formed instantaneously.
This can prevent the wetting layer from being oxidized again, and in the course of re-flow process, the oxidized region of the wetting layer is reduced, improving the wettability of bump on the wetting layer.
An aspect of the present invention is to provide a bump fabrication method comprising the steps of providing a wafer having an active surface and a plurality of bonding pads distributed on the active surface; respectively forming into an under bump metallurgy layer onto the bonding pads, wherein at least each of the under bump metallurgy layers includes at least a wetting layer positioned at the topmost layer of the under bump metallurgy layer; patterning a masking layer on the active surface wherein the masking layer has a plurality of openings to expose the wetting layer with oxidized region thereon; removing the oxidized region of the wetting layer using plasma ashing process; fully forming a flux film on the active layer, wherein at least a portion of the flux film covers the wetting layer; filling a solder paste into the openings; performing a re-flow process to form a plurality of bumps after the solder paste melts so that the flux film removes the oxidized region of the wetting layer; and removing the masking layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.


REFERENCES:
patent: 6617237 (2003-09-01), Tong et al.

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