U.S. patent application number 10/855161 was filed with the patent office on 2005-12-01 for wire-bonding method for chips with copper interconnects by introducing a thin layer.
Invention is credited to Chiu, Sang-Mao, Jeng, Yeau-Ren.
Application Number | 20050266672 10/855161 |
Document ID | / |
Family ID | 35206951 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050266672 |
Kind Code |
A1 |
Jeng, Yeau-Ren ; et
al. |
December 1, 2005 |
WIRE-BONDING METHOD FOR CHIPS WITH COPPER INTERCONNECTS BY
INTRODUCING A THIN LAYER
Abstract
A wire-bonding method for chips with copper interconnects by
introducing a thin layer is provided for solving the problem of
oxidizing a copper bonding-pad during bonding processing in order
not to deteriorate the bonding strength and yield rate thereof. The
wire-bonding method of the present invention comprises: a step for
providing a chip with a copper bonding-pad; another step for
providing an aqueous solution to form a Cuprous oxide thin layer on
the copper bonding-pad; and yet another step for setting a
plurality of copper interconnects on the copper bonding-pad and
providing an ultrasonic power for removing the Cuprous oxide layer
to have the interconnects bonded on the copper bonding-pad.
Inventors: |
Jeng, Yeau-Ren; (Tainan
City, TW) ; Chiu, Sang-Mao; (Da-Lin, TW) |
Correspondence
Address: |
SUPREME PATENT SERVICES
POST OFFICE BOX 2339
SARATOGA
CA
95070
US
|
Family ID: |
35206951 |
Appl. No.: |
10/855161 |
Filed: |
May 26, 2004 |
Current U.S.
Class: |
438/617 ;
257/E21.518; 257/E23.02 |
Current CPC
Class: |
H01L 2224/85205
20130101; H01L 24/03 20130101; H01L 2224/85048 20130101; H01L 24/48
20130101; H01L 2224/48247 20130101; H01L 2924/01006 20130101; H01L
2224/85181 20130101; H01L 2924/14 20130101; H01L 24/78 20130101;
H01L 2924/01018 20130101; H01L 2224/48647 20130101; H01L 2224/78301
20130101; H01L 24/85 20130101; H01L 2224/48465 20130101; H01L
2224/85205 20130101; H01L 2924/01029 20130101; H01L 2224/85181
20130101; H01L 2224/48465 20130101; H01L 2224/78301 20130101; H01L
2224/05647 20130101; H01L 2224/48465 20130101; H01L 2924/00
20130101; H01L 2224/48227 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; H01L 2924/00014 20130101; H01L 2224/48091
20130101; H01L 2924/00014 20130101; H01L 2224/48465 20130101; H01L
2224/48465 20130101; H01L 2224/48227 20130101; H01L 2924/00014
20130101; H01L 2224/45144 20130101; H01L 2924/00 20130101; H01L
2924/00014 20130101; H01L 2924/00 20130101; H01L 2924/00 20130101;
H01L 2224/04042 20130101; H01L 2224/48647 20130101; H01L 2924/01022
20130101; H01L 2224/85205 20130101; H01L 2924/30105 20130101; H01L
2224/45144 20130101; H01L 24/05 20130101; H01L 2224/48091 20130101;
H01L 2224/48465 20130101; H01L 2224/85045 20130101; H01L 2224/45144
20130101; H01L 2224/05647 20130101; H01L 2924/01033 20130101; H01L
2224/48247 20130101; H01L 2224/48465 20130101; H01L 2924/01082
20130101; H01L 2224/85375 20130101; H01L 2224/48091 20130101; H01L
24/45 20130101; H01L 2924/01005 20130101; H01L 2224/48227 20130101;
H01L 2924/01079 20130101; H01L 2924/01013 20130101 |
Class at
Publication: |
438/617 |
International
Class: |
H01L 021/44 |
Claims
What is claimed is:
1. A wire-bonding method for chips with copper interconnects by
introducing a thin layer, comprising following steps: (a) providing
a chip having a copper bonding-pad; (b) providing an aqueous
solution to react with the surface of the copper bonding-pad to
form a Cuprous oxide thin layer on the latter; and (c) setting a
plurality of copper interconnects on the copper bonding-pad and
providing an ultrasonic power for removing the Cuprous oxide thin
layer to have the copper interconnects bonded on the copper
bonding-pad, in which the pH value of the aqueous solution is
5-14.
2. The wire-bonding method according to claim 1, wherein the
reaction time of the aqueous solution and the surface of the copper
bonding-pad in step (b) is about 30-180 seconds.
3. The wire-bonding method according to claim 1, wherein the
Cuprous oxide thin layer is 10-500 .ANG. in thickness.
4. The wire-bonding method according to claim 1, wherein the
material of bonding wire is gold.
5. The wire-bonding method according to claim 1, wherein the step
(c) requires a wire bonder when bonding the copper
interconnects.
6. The wire-bonding method according to claim 5, wherein a step of
preheating up to 200-260.degree. C. is further included.
7. The wire-bonding method according to claim 1, wherein which a
step of connecting a bonding wire with a plurality of lead frames
after step (c) is further included.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the application field
regarding IC packaging, particularly to a wire-bonding method for
chips with copper interconnects by introducing a thin layer.
[0003] 2. The Prior Arts
[0004] In the VLSI (Very Large Scale Integration) era today, an IC
chip is made through several steps including wafer fabricating
process, wafer test, VLSI forming process, and finally, IC
packaging test.
[0005] The packaging test usually comprises a wafer attachment
process, a wire-bonding process, etc., in which the wire-bonding
process is conducted by a wire bonder for connecting a chip to a
plurality of pins with metallic interconnects under a
high-temperature and ultrasonic environment. The bonded
interconnects serve as a bridge for transmitting signal and/or
electric power between a chip and the external circuits. Since,
almost all the makers have made different efforts to try minimizing
the volume of chip as smaller as possible, and accompanying with
the scaling-down semiconductor devices, the RC constant of
interconnect is increased rapidly because the resistance of the
metal leading increases with decreasing line width and the
interconnect capacitance increases with decreasing spacing, hence,
a greater resistance and capacitance is inevitably resulted when
the width of wire and the space between lead wires in chip are
narrowed.
[0006] On the other hand, the performance of deep sub-micron
integrated circuit cannot be further improved since the delay of
signal in the interconnect would exceed the delay of signal in the
device. Therefore, it is necessary to use interconnects with better
conductivity to replace conventional Aluminum. Copper has been
identified as the best candidate due to its low resistivity, high
electromigration resistance and likely lower processing cost.
However, one of the disadvantages of copper is that copper is
readily oxidized at low temperature, and unlike the oxidation of
aluminum, the oxidation rate of copper is fast, and no
self-protective oxide layer forms to prevent further oxidation.
Such characteristic will deteriorate the effect in transmitting the
frictional power of ultrasonic vibrations to the surface of the
copper bonding-pad while bonding interconnects to the chip, so that
the efficiency for stripping the oxide layer off and obtaining
therethrough a smooth bonding on the surface of the copper
bonding-pad is retarded, and accordingly is the yield rate. Hence,
the key point for obtaining a good yield in the wire-bonding
process is to prevent the copper bonding-pad from being oxidized
rapidly owing to the temperature of a bonding interface.
[0007] For improvements, two ways have been suggested: (1) An
inertia gas (Ar) is applied to a chip during the wire-bonding
process to protect the surface thereof and lower down the
temperature to slow down oxidation. (2) A thin barrier layer, a
Titanium layer for example, is sputtered on the surface of a chip
to prevent oxidation of the copper-bonding pad. These ways are
capable of avoiding oxidation of the copper bonding-pad and
enhancing the strength of bonding points though, they are both
expensive and troublesome.
SUMMARY OF THE INVENTION
[0008] The primary object of the present invention is to provide a
wire-bonding method for chips with copper interconnects by
introducing a thin layer to prevent the problem of oxidizing a
copper bonding-pad during a bonding process.
[0009] The wire-bonding method for chips with copper interconnects
by introducing a thin layer comprises: providing a chip associated
with a copper bonding-pad; providing an aqueous solution to form a
Cuprous oxide thin layer on the copper bonding-pad; and setting
copper interconnects on the copper bonding-pad and providing an
ultrasonic power for removing the Cuprous oxide layer to have the
copper interconnects bonded on the copper bonding-pad.
[0010] The wire-bonding method for chips with copper interconnects
by introducing a thin layer is advantageous in that a Cuprous oxide
layer formed on the copper bonding-pad can prevent the pad from
being oxidized further, and the layer is removable by ultrasonic
power to ensure a better wire bonding.
[0011] With a proper control of pH value, the aqueous solution can
work to produce the Cuprous oxide layer on the copper bond-pad in a
low cost.
[0012] For more detailed information regarding advantages or
features of the present invention, at least one example of
preferred embodiment will be described below with reference to the
annexed drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The related drawings in connection with the detailed
description of the present invention to be made later are described
briefly as follows, in which:
[0014] FIGS. 1A and 1B are schematic views showing a chip, a
copper-bonding pad, and/or a thin layer of Cuprous oxide formed
thereon, subsequently; and
[0015] FIGS. 2A through 2H are schematic views showing a
wire-bonding method of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] As shown in FIG. 1A, a chip 101 is provided thereon with a
copper bonding-pad 102. The chemical reaction of copper in an
aqueous solution is known as:
CuCu.sup.++e.sup.- (1)
CuCu.sup.2++2e.sup.- (2)
2Cu.sup.++H.sub.2OCu.sub.2O+2H.sup.+ (3)
[0017] According to the principle of Le Chatelier, a system would
always react in such a way as to tend to counteract the original
alteration when the system is in equilibrium and one of the
factors, which determine the equilibrium point, is altered. It is
understood from reaction (3) that H.sup.+ is supposed to move to
the left side when its concentration is raised up. If the
concentration of H.sup.+ goes up, the aqueous solution is becoming
acidified and the pH value is lowered (the higher the H.sup.+, the
lower the pH value), or vice versa. Therefore, it is possible to
keep the reaction going toward the right hand to produce Cuprous
oxide (Cu.sub.2O) should the concentration of H.sup.+ is controlled
properly under a predetermined level. A preferred concentration of
H.sup.+ below 10.sup.-5M/L, or a pH value greater than 5, is found
by experiments.
[0018] As shown in FIG. 1B, an aqueous solution with a pH value
greater than 5 is provided to the upper surface of the copper
bonding-pad 102 for reaction, and then, after 30-180 seconds in
room temperature, the solution is removed away to form a thin layer
103 of Cuprous oxide (Cu.sub.2O) of 10-500 .ANG. in thickness
attached on the surface of the copper bonding-pad 102 for
protecting the copper bonding-pad 102 from being oxidized. Since
the created Cuprous oxide 103 is rigid and fragile, it can be
shocked and crushed easily by ultrasonic power and therefore
removed away to expose the copper bonding-pad 102.
[0019] The aqueous solution applied could be a solution of any kind
having a pH value between 5-14, including a weak acid, neutral,
weak alkaline, or active alkaline aqueous solution.
[0020] Moreover, there is no specified quantity of aqueous solution
to be provided on the surface of the copper bonding-pad 102, and it
is considered good enough as long as it can fully cover the surface
of the copper bonding-pad 102.
[0021] With reference to FIGS. 2A-2H, which show a wire-bonding
method in accordance with the present invention, a wire-penetrating
process of the wire-bonding method is shown in FIG. 2A, in which a
bonding wire 301 is guided to penetrate through a fixture 202 and a
steel cylinder 201, where the bonding wire 301 could be made of
gold.
[0022] FIG. 2B shows a ball-forming process of the wire-bonding
method, in which a spark 204 is ignited by an igniter 203 to hence
form a bonding ball 302.
[0023] FIG. 2C shows a positioning process of the wire-bonding
method, in which the chip 101 is located exactly under the steel
cylinder 201 in alignment with the copper bonding-pad 102. This
arrangement provides a preheat and ultrasonic environment, in which
the temperature range of the preheat environment is 200-260.degree.
C., and the rigid and fragile thin layer of Cuprous oxide (not
shown) on the copper bonding pad 102 can be removed easily by the
ultrasonic waves.
[0024] FIG. 2D shows a bonding process of the wire-bonding method
for a first bonding point, in which the steel cylinder 201 is moved
downwards to allow the bonding ball 302 to contact the copper
bonding-pad 102 to be bonded thereon.
[0025] FIG. 2E shows a rising process of the wire-bonding method
for the steel cylinder 201 to enable the bonding wire 301 to extend
an extra length owing to the unclosed fixture 202.
[0026] FIG. 2F shows a forming process of the wire-bonding method
for a bonding wire loop, in which the steel cylinder 201 is moved
above and aligned with a lead frame 401, and at this time, the
bonding wire 301 is dragged out to form a loop structure 303.
[0027] FIG. 2G shows a bonding process of the wire-bonding method
for a second bonding point, in which the steel cylinder 201
descends to allow the bonding wire 301 to contact with and get
bonded on the lead frame 401 to form the second bonding point.
[0028] FIG. 2H shows a wire-tearing process of the wire-bonding
method, in which the steel cylinder 201 rises to close up the
fixture 202, where the bonding wire 301 is torn and broken to have
the integral loop structure 303 of bonding wire completed.
[0029] In the above described, at least one preferred embodiment
has been described in detail with reference to the drawings
annexed, and it is apparent that numerous changes or modifications
may be made without departing from the true spirit and scope
thereof, as set forth in the claims below.
* * * * *