Title: Manufacturing a bump electrode with roughened face
Abstract: The invention includes a semiconductor device, and a method for making the same, wherein bumps of a semiconductor chip and inner leads of a film tape carrier can be securely bonded to each other by thermal welding using a heating unit. A semiconductor wafer 50 is etched using a potassium iodide or ammonium iodide solution. By the etching, a barrier metal layer 48 is removed while the upper face of a bump 10 is simultaneously roughened and many prominences 12 are formed. The formation of the prominences 12 increases the surface area of the upper face of the bump 10 and improves the bonding between the bump 10 of the semiconductor chip and the lead of the film tape carrier.
Patent Number: 6,872,651 Issued on 03/29/2005 to Takano
| Inventors:
|
Takano; Michiyoshi (Okaya, JP)
|
| Assignee:
|
Seiko Epson Corporation (Tokyo, JP)
|
| Appl. No.:
|
445188 |
| Filed:
|
May 27, 2003 |
Foreign Application Priority Data
| Nov 18, 1999[JP] | 11-328467 |
| Current U.S. Class: |
438/613; 438/614; 257/737; 257/739 |
| Intern'l Class: |
H01L 021//44 |
| Field of Search: |
257/737-739,780
438/612,613,615
|
References Cited [Referenced By]
U.S. Patent Documents
| 5108950 | Apr., 1992 | Wakabayashi et al. | 438/614.
|
| 5487999 | Jan., 1996 | Farnworth | 216/18.
|
| 5545589 | Aug., 1996 | Tomura et al. | 438/119.
|
| 6084301 | Jul., 2000 | Chang et al. | 257/737.
|
| 6109507 | Aug., 2000 | Yagi et al. | 427/96.
|
| 6165820 | Dec., 2000 | Pace | 438/125.
|
| 6406991 | Jun., 2002 | Sugihara | 438/613.
|
| Foreign Patent Documents |
| 1-136354 | May., 1989 | JP.
| |
| 8-70019 | Mar., 1996 | JP.
| |
| 11-111761 | Apr., 1999 | JP.
| |
Primary Examiner: Elms; Richard
Assistant Examiner: Wilson; Christian D.
Attorney, Agent or Firm: Oliff & Berridge, PLC
Parent Case Text
This is a Divisional of application Ser. No. 09/714,944 filed Nov. 20, 2000
now abandoned. The entire disclosure of the prior application is hereby
incorporated by reference herein in its entirety.
Claims
What is claimed is:
1. A method for making a semiconductor device that includes a tape
substrate provided with a lead, and a semiconductor chip mounted onto the
tape substrate by thermal welding a bump formed on an active face of the
semiconductor chip with the lead, the method comprising the steps of:
roughening an upper face of the bump, thereby forming a plurality of
prominence on the upper face of the bump, the prominences having a height
of more than 1 .mu.m; and
thermally welding the bump to the lead.
2. The method for making a semiconductor device according to claim 1,
wherein the roughening step is performed while a barrier metal formed on a
semiconductor wafer provided with the semiconductor chip is simultaneously
removed.
3. The method for making a semiconductor device according to claim 1,
wherein the roughening step includes etching the upper face of the bump
with an iodide compound.
4. The method for making a semiconductor device according to claim 3,
wherein the iodine compound is potassium iodide or ammonium iodide.
5. The method for making a semiconductor device according to claim 2,
wherein the roughening step includes etching the upper face of the bump
with an iodide compound.
6. The method for making a semiconductor device according to claim 5,
wherein the iodine compound is potassium iodide or ammonium iodide.
7. A method for making a semiconductor device that includes a tape
substrate provided with a lead, and a semiconductor chip mounted onto the
tape substrate by thermal welding a bump formed on an active face of the
semiconductor chip with the lead, the method comprising the steps of:
roughening an upper face of the bump, thereby forming a plurality of
prominence on the upper face of the bump, the prominences having a height
of 1 to 5 .mu.m; and
thermally welding the bump to the lead.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a semiconductor device and a method for
making the same, and particularly to a semiconductor chip mounted onto a
tape substrate.
2. Description of Related Art
In the field of semiconductor devices, tape carrier packages (TCPs) are
well known as one type of bare-chip-mounted packages. FIG. 5 is a
schematic view of a film tape carrier. As shown in FIG. 5, the film tape
carrier 30 is generally formed by laminating a copper foil onto a
polyimide resin film, forming a circuit onto the copper foil, and plating
thereon using Sn or Au, as an oblong product before the product is
processed together with semiconductor devices. The lead comprises inner
leads 20 bonded to an Au bump formed on an electrode pad of the
semiconductor chip, and outer leads 36 integratedly formed with the inner
leads 20 and used for connection to an exterior.
A method for making a TCP by a gang bonding process which simultaneously
bonds all bumps to inner leads will now be described with reference to
FIG. 6. A semiconductor chip is placed in a position surrounded by a
device hole 32 on a stage (not shown in the drawing), and each bump of the
semiconductor chip and the corresponding inner lead are aligned so that
they are exactly bonded to each other. As shown in FIG. 6(1), a heating
unit 52, which is preliminarily heated to about 500.degree. C., is lowered
toward the bumps and the inner leads 20 so that the heating unit 52
presses the bumps and the inner leads 20 on the stage.
The heat from the heating unit facilitates the formation of an Au/Sn
eutectic alloy 46 shown in FIG. 6(2) by alloying the Au and the Sn plated
on the inner leads 20. The mounting of the semiconductor chip 40 onto the
film tape carrier 30 is completed by bonding the bumps to the inner leads
20 via the eutectic alloy 46. Next, unnecessary portions of the film tape
carrier 30 are removed by punching to prepare a TCP.
However, the bonding of the bumps to the inner leads of the semiconductor
chip using the heating unit has the following problems.
FIG. 4 is a schematic view showing a problem which occurs during mounting a
semiconductor chip by a conventional technique. As shown in FIG. 4, a bump
10 is formed on an electrode pad 42 of a semiconductor chip 40. Since the
periphery of the electrode pad 42 is covered by a passivation film 44 and
protrudes, the bump 10 formed on the passivation film 44 also protrudes at
the periphery and has an indented flat surface in the central portion.
When the inner lead 20 is put into contact with the bump 10, a gap 18 is
formed between the bump 10 and the inner lead 20 due to the protrusion.
Thus, the central portion of the bump 10 does not contribute to the
bonding of the bump 10 to the inner lead 20, in this state.
With reference to FIG. 6(2), in conventional thermal welding between the
bump 10 and the inner lead 20, a high load and a high temperature are
applied by the heating unit so that the Au/Sn eutectic alloy 46 is also
formed in the central portion of the bump 10.
However, the application of the high load and the high temperature causes
deforming and cracking of the inner lead and cracking of the passivation
film. Such phenomena result in unreliability of the semiconductor devices
as a product. Other problems, such as gas evolution from the film tape
carrier and a shortened life of the heating unit, also arise.
Accordingly, it is an object of the present invention to provide a
semiconductor device and a method for making the same in which bumps of a
semiconductor chip and leads of a tape substrate can be securely bonded to
each other by thermal welding using a heating unit.
SUMMARY OF THE INVENTION
The present invention includes a semiconductor device that includes a tape
substrate provided with a lead, and a semiconductor chip mounted onto the
tape substrate by thermal welding a bump formed on an active face of the
semiconductor chip with the lead. The upper face of the bump is roughened.
In the present invention having such a configuration, the upper face of the
bump is roughened so that the surface area increases compared to a case of
a flat upper face of the bump. Thus, the area contributing to the
formation of an Au/Sn eutectic alloy increases and the melted eutectic
alloy penetrates the gap between prominences by a capillary phenomenon,
ensuring bonding between the bump and the lead. Thus, high load and high
temperature are not required for bonding, and the occurrence of inner lead
cracking can be prevented.
In accordance with the above semiconductor device, prominences having a
height of 1 to 5 .mu.m are continuously formed on the upper face of the
bump.
In the present invention having such a configuration, the height of the
prominences formed by roughening the upper face of the bump is controlled
within a range which increases the surface area of the upper face of the
bump so as to contribute to the formation of the Au/Sn eutectic alloy and
to ensure sufficient bonding strength between the bump and the lead. Thus,
thermal welding between the bump and the lead are ensured.
It is preferable that the heights of the prominences on the upper face of
the bump be the same so that the prominences securely come into contact
with the lead to facilitate the formation of the Au/Sn eutectic alloy
between the prominences and the lead.
A method for making a semiconductor device that includes a tape substrate
provided with a lead, and a semiconductor chip mounted onto the tape
substrate by thermal welding a bump formed on an active face of the
semiconductor chip with the lead, includes the steps of roughening the
upper face of the bump, and thermally welding the bump to the lead.
In the present invention having such a configuration, the bump and the lead
are thermally welded after the upper face of the bump is roughened. Thus,
the surface area can be increased compared to a case of a flat upper face
of the bump. Thus, reliability of bonding between the bump and the lead
can be enhanced.
In accordance with the above method for making a semiconductor device, the
step for roughening is performed while a barrier metal formed on a
semiconductor wafer provided with the semiconductor chip is simultaneously
removed.
In the present invention having a such a configuration, the roughening step
and the step for removing the barrier metal in the wafer process are
simultaneously performed, and no additional process is required for
roughening.
In accordance with the method for making a semiconductor device, the
roughening treatment is performed by etching the upper face of the bump
with an iodide compound.
In the present invention having a such a configuration, soft etching of the
upper face of the bump is facilitated.
In accordance with the method for making a semiconductor device, the iodine
compound is potassium iodide or ammonium iodide.
In the present invention having such a configuration, desired projections
can be readily formed on the upper face of the bump.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 includes illustrative views of a method for making a semiconductor
device in accordance with an embodiment of the present invention, wherein
FIG. 1(1) is an illustrative view of the semiconductor chip before
roughening a bump of a semiconductor chip, and FIG. 1(2) is an
illustrative view after roughening.
FIG. 2 is an illustrative view of a bump after roughening treatment.
FIG. 3 is an illustrative chart showing the relationship between the height
of the prominence and the bonding strength of the bump and the inner lead.
FIG. 4 is a schematic view showing a problem which occurs during mounting
of a semiconductor chip by a conventional technique.
FIG. 5 is a schematic view of a film tape carrier.
FIG. 6 includes illustrative views of a method for thermally welding a bump
of a semiconductor chip to an inner lead of a film tape carrier, wherein
FIG. 6(1) is an illustrative view of a state of the bump and the inner
lead before thermal welding, and FIG. 6(2) is an illustrative view of a
state of the bump and the inner lead after thermal welding.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The semiconductor device and the method for making the same in accordance
with the present invention will now be described in detail based on the
preferred embodiments with reference to the attached drawings. Parts
corresponding to the parts described in the above conventional technology
are referred to as the same reference numerals, and the description for
these parts will be omitted. Moreover, descriptions, which are the same as
those in the above conventional technology, will be simplified.
FIG. 1 includes illustrative views of a method for making a semiconductor
device in accordance with an embodiment of the present invention, wherein
FIG. 1(1) is an illustrative view of the semiconductor chip before
roughening a bump of a semiconductor chip, and FIG. 1(2) is an
illustrative view after roughening. Moreover, FIG. 2 is an illustrative
view of a bump after roughening treatment. FIG. 3 is an illustrative chart
showing the relationship between the height of the prominence and the
bonding strength of the bump and the inner lead.
In this embodiment, prominences are formed on the upper face of the bump to
increase the surface area of the upper face so that the Au/Sn eutectic
alloy is readily formed by thermal welding using a gang bonding apparatus.
FIG. 1(1) shows a halfway stage of the wafer process. A passivation film 44
is formed on a semiconductor wafer 50 that is provided with a
semiconductor chip in a region other than an electrode pad 42. A barrier
metal layer 48 is formed over the passivation film 44 and the electrode
pad 42 above the entire semiconductor wafer 50. The barrier metal layer 48
includes two sub-layers. That is, a TiW sub-layer 48a is formed by
sputtering on the passivation film 44, and then an Au sub-layer 48b is
formed by plating on the TiW sub-layer 48a.
Next, a bump 10 is formed on the electrode pad 42. The bump 10 is formed by
applying a photoresist on the entire surface of the semiconductor wafer
50, and by removing the photoresist in a bump-forming portion by exposure
and development to form an opening, and then by plating Au in the opening.
The upper face of the bump 10 in this stage is slightly indented in the
central portion, as described above with reference to FIG. 3.
In this embodiment, the semiconductor wafer 50 is etched using a potassium
iodide or ammonium iodide solution. The etching, as shown in FIG. 1(2),
removes the barrier metal layer 48 and roughens the upper face of the bump
10 to form many prominences 12. The surface area of the bump 10
significantly increases compared to the surface area before etching. The
difference in height between the periphery and the central portion of the
bump 10 is considerably decreased due to the formation of the prominences
12.
When the bump 10 and the inner lead 20 are thermally welded using the
heating unit 52, as shown in FIG. 6(1), the area contributing to the
formation of the Au/Sn eutectic alloy significantly increases, and the
formation of the eutectic alloy is facilitated. In addition, the melt
eutectic alloy penetrates the gap of the prominences 12 by a capillary
phenomenon and adheres onto sloping faces 14 of the prominences 12 so as
to enhance the bonding between the bump 10 and the inner lead 20. Thus,
the bonding between the bump 10 and the inner lead 20 can be ensured even
if the heating unit 52 is set at a lower temperature compared to
conventional temperatures. Moreover, the difference in the height on the
upper face of the bump 10 is considerably decreased. Hence, the pressure
of the heating unit 52 can be reduced compared to the conventional cases.
The etching solution may be a solution containing an iodine compound or any
compound other than potassium iodide and ammonium iodide, as long as the
solution exhibits etching ability. Instead of Au, the bump 10 may be
formed of any material, such as Ni, in which Au is adhered to the surface
of the prominence. The prominences 12 may be formed by a mechanical
process, if possible, for example, by pressing the upper face of the bump
10 using a tool having an uneven surface or by buffing the upper face of
the bump 10 using such a tool. According to the mechanical process, the
heights of the prominences can be controlled within a predetermined range,
and the formation of the Au/Sn eutectic alloy is further facilitated for
the reasons described below.
The height of the prominence 12 depends on the type of the etching solution
used and the etching time. As shown in FIG. 2, individual heights are also
different, as shown by the lowest prominence 12a and the highest
prominence 12b. It is preferable that the difference in the height be
small as much as possible, because the formation of the An/Sn eutectic
alloy is promoted in proportion to the contact area during thermal welding
between the bump and the inner lead. In the case of a large difference in
the height of the prominences 12, prominences having lower heights are
still distant from the inner lead and thus do not contribute to the
formation of the Au/Sn eutectic alloy, even when the inner lead is pressed
by the heating unit.
Experimental results have been prepared regarding the heights of the
prominences 12, wherein the height A of the lowest prominence is 1 .mu.m
or more, and the height B of the highest prominence is less than 5 .mu.m.
The experimental results will now be described.
The present inventor has performed experiments regarding the relationship
between the heights of the prominences and the bonding strength of the
bump and the inner lead, and has obtained the data confirming the effects.
The results will now be described based on FIG. 3.
Term 1 in the table represents the surface roughness of the bump, that is,
the heights of the prominences on the upper face of the bump. The
description "0 to less than 1" represents all the heights of the
prominences lie within the range of 0 to 1. Term 2 represents the state of
the formation of the Au/Sn eutectic alloy, in which .largecircle.
indicates that the formation is satisfactory, .DELTA. indicates that the
formation is not so satisfactory, and X indicates that the formation is
unsatisfactory. Item 3 represents the bonding strength between the bump
and the inner liner, in which .largecircle. indicates that reliable
strength is obtained, .DELTA. indicates that strength is slightly
insufficient, and X indicates that strength is insufficient. Item 4
represents the comprehensive determination, in which .largecircle.
indicates that the reliable results are obtainable in the semiconductor
device, .DELTA. indicates that the slightly unreliable results are
obtainable in the semiconductor device, and X indicates that the
unreliable results are obtainable in the semiconductor device.
As shown in chart, the height of the most preferable height of the
prominence is within a range of 1 .mu.m to less than 5 .mu.m. A height of
the prominence of 0 .mu.m to less than 1 .mu.m is not substantially
different from a flat face of the bump, and thus, advantages by providing
the prominence are insufficient. A height of prominence of 5 .mu.m or more
results in a large distance between the base portion of the prominence and
the inner lead. Thus, the melted Au/Sn eutectic alloy is not adhered to
the vicinity of the base portion of the prominence and will not contribute
to an improvement in bonding strength.
As described above, in the semiconductor device and the method for making
the same in accordance with the embodiments of the present invention, the
upper face of the bump of the semiconductor chip is roughened to form
prominences. If the temperature and the pressure of the heating unit are
set to be lower than those in conventional processes, sufficient bonding
strength is achieved between the bump and the inner lead. Since the
removal of the barrier metal and the roughening of the upper face of the
bump are simultaneously performed, no additional step is required.
As described above, a semiconductor device in accordance with the invention
includes a tape substrate provided with a lead, and a semiconductor chip
mounted onto the tape substrate by thermal welding a bump formed on an
active face of the semiconductor chip with the lead. Thus, reliability of
the bonding between the semiconductor chip and the tape substrate can be
significantly improved by a simplified treatment in a wafer process.
Accordingly, the production cost of the semiconductor device can be
reduced.
*
