U.S. patent application number 09/885518 was filed with the patent office on 2001-10-25 for optical module for optical transmission and manufacturing process therefor.
This patent application is currently assigned to NEC Corporation. Invention is credited to Itoh, Masataka, Kitamura, Naoki, Sasaki, Junichi.
Application Number | 20010033718 09/885518 |
Document ID | / |
Family ID | 14983845 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033718 |
Kind Code |
A1 |
Sasaki, Junichi ; et
al. |
October 25, 2001 |
Optical module for optical transmission and manufacturing process
therefor
Abstract
The integrity of a solder jointing pad, which is used to mount
an optical module, is enhanced by avoiding exposure to high
temperatures used in the formation of an accompanying optical wave
guide. The enhanced integrity of the solder jointing pad permits a
mounting solder bump to be evenly distributed on the pad, which
improves mounting position characteristics. The solder jointing
pads are elongated in shape and arranged in parallel and
perpendicular orientation with respect to an optical transmission
path in the optical module. The enhanced integrity of the solder
jointing pads permits a precise amount of solder to be introduced
to the pads when mounting the optical module. The optical module
can then be precisely positioned simply by varying the amount of
solder introduced to the solder jointing pads. The optical device
can be positioned with high accuracy by taking advantage of the
self-alignment action which occurs between the molten solder bumps
and the solder jointing pads. The optical module can thus be
precisely positioned during manufacturing, without the need for
additional adjustments.
Inventors: |
Sasaki, Junichi; (Minato-ku,
JP) ; Itoh, Masataka; (Minato-ku, JP) ;
Kitamura, Naoki; (Minato-ku, JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Assignee: |
NEC Corporation
|
Family ID: |
14983845 |
Appl. No.: |
09/885518 |
Filed: |
June 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09885518 |
Jun 20, 2001 |
|
|
|
09081322 |
May 19, 1998 |
|
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Current U.S.
Class: |
385/88 ;
385/49 |
Current CPC
Class: |
G02B 6/423 20130101;
G02B 6/42 20130101; G02B 6/4232 20130101 |
Class at
Publication: |
385/88 ;
385/49 |
International
Class: |
G02B 006/42 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 1997 |
JP |
128399/1997 |
Claims
What is claimed is:
1. An optical module for optical transmission comprising: a
substrate with an optical waveguide; and an optical device located
opposite to a section of the optical waveguide, wherein said
optical device is secured by a solder bump on a solder joint pad,
said solder joint pad being formed on non-solder jointing
metallization formed on the substrate.
2. The optical module as set forth in claim 1, wherein said optical
device comprises a solder joint pad for joining the solder
bump.
3. The optical module as set forth in claim 1, wherein said solder
joint pads on the substrate and the optical device are constituted
by a plurality of elongated pads including pads parallel to the
optical waveguide with their longitudinal side and those
perpendicular to the optical waveguide with their longitudinal
side, respectively.
4. The optical module as set forth in claim 1, wherein the
non-solder jointing metallization is formed by WSi.
5. The optical module as set forth in claim 1, wherein said solder
joint pads contains either one of Au or Pt.
6. The optical module as set forth in claim 1, wherein the solder
bump is AuSn alloy.
7. A process for manufacturing an optical module comprising:
forming non-solder jointing metallization on a substrate; forming
an optical waveguide on the substrate after said non-solder
jointing metallization is formed; removing a portion of said
optical waveguide; forming a solder joint pad on said non-solder
jointing metallization; and installing an optical device on said
solder joint pad through a solder bump.
8. The process for manufacturing an optical module as set forth in
claim 7, wherein the step of removing a part of the optical
waveguide comprises the step of forming an end surface of the
optical waveguide by removing a part of the optical waveguide.
9. The process for manufacturing an optical module as set forth in
claim 8, wherein the solder joint pad formed on the non-solder
jointing metallization is formed at a location opposite to the end
surface of the optical waveguide.
10. The process for manufacturing an optical module as set forth in
claim 7, further comprising the step of forming a solder joint pad
on an optical device.
11. The process for manufacturing an optical module as set forth in
claim 7, wherein the step of installing an optical device on the
solder joint pad through a solder bump comprises the steps of
jointing a solder piece on the solder joint pad through
thermocompression bonding, placing the optical device so that the
solder joint pad of the optical device is positioned on said solder
piece, and melting said solder bump.
12. The process for manufacturing an optical module as set forth in
claim 11, wherein, in the thermocompression step, a solder alloy
sheet is stamped out by a punch and die, the solder piece being on
the solder joint pad of the substrate as it is.
13. The process for manufacturing an optical module as set forth in
claim 11, wherein melting of the solder bump is performed in one or
more gasses selected from nitrogen, hydrogen, and inert gas.
14. The process for manufacturing an optical module as set forth in
claim 7, further comprising the steps of forming a groove in the
substrate, and installing fiber optics in said groove.
15. The process for manufacturing an optical module as set forth in
claim 14, further comprising the steps of forming an oxide film on
the substrate, and removing the oxide film on a region on the
substrate where the groove is formed.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
09/081,322, filed May 19, 1998 in the name of Junichi Sasaki et al.
and entitled "OPTICAL MODULE FOR OPTICAL TRANSMISSION AND
MANUFACTURING PROCESS THEREFOR."
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an optical module in which
optical devices, such as a light emitting device and a light
receiving device, are integrated with an optical transmission
patent, such as obtained with fiber optics and optical waveguides,
and a process for manufacturing the same.
[0003] In an optical module used in optical communication, the
optical devices and the optical transmission path included in the
module must be closely positioned. Close positioning of the devices
assures that an optical signal is accurately transmitted between
the optical devices and the optical transmission path.
[0004] Japanese Patent Application Laid-Open No. 8-179154 discloses
a process for manufacturing such an optical module at a low cost.
The disclosed process permits optical devices to be mounted in
self-alignment by utilizing the surface tension of a solder bump.
In this process, as a first step, a metallized solder joint pad is
formed on a silicon substrate with photolithography technology. In
the next step, silicon is deposited on the substrate, and patterned
to form a planar optical waveguide. Then, formed on the solder
joint pad on the substrate is a solder bump on which a
semiconductor laser chip formed with a solder joint pad is mounted.
Subsequently, the solder bump is made molten so that the
semiconductor laser chip is joined to the silicon substrate. The
semiconductor laser chip is automatically positioned at a
predetermined junction position by a self-alignment effect based on
the surface tension of the molten solder bump.
[0005] In the process, the optical waveguide and the solder joint
pad must be formed using a continuous photolithography process to
accurately establish a relative position of the optical waveguide
and the solder joint pad formed on the silicon substrate. To this
end, the optical waveguide is formed at a high temperature of
800.degree. C. or more by a silicon deposition process after the
solder joint pad is formed on the substrate. However, if the
metallized solder joint pad is exposed to a high temperature during
formation of the optical waveguide, it deteriorates and is
difficult to join to the solder joint pad. In addition, since the
solder joint pad is of a minute size, and directly formed on the
silicon substrate, it tends to easily peel off the substrate when
subjected to a high temperature. Therefore, positioning the
semiconductor laser chip by self-alignment using the solder bump is
difficult to attain accurately.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to eliminate the above
problem, and to provide an optical module which can be accurately
and reliably manufactured at a low cost, and to provide a
manufacturing process for the same.
[0007] The optical module of the present invention comprises a
substrate with an optical waveguide, and an optical device located
opposite to a section of the optical waveguide, wherein the optical
device is secured by a solder bump on a solder joint pad. The
solder joint pad is formed on non-solder jointing metallization on
the substrate. The optical device has a solder joint pad for
joining the solder bump. The solder joint pads on the substrate and
the optical device are preferably a plurality of elongated pads,
including pads parallel to the optical waveguide with their
longitudinal side, and pads perpendicular to the optical waveguide
with their longitudinal side, respectively.
[0008] The process for manufacturing the optical module of the
present invention comprises the steps of forming non-solder
jointing metallization on a substrate, forming an optical waveguide
on the substrate formed with the non-solder jointing metallization,
removing a part of the optical waveguide, forming a solder joint
pad on the non-solder jointing metallization, and installing an
optical device on the solder joint pad through a solder bump.
[0009] According to the present invention, since the solder joint
pad on the substrate is formed on the non-solder jointing
metallization after the optical waveguide is formed, and is not
subject to a high temperature, the solder laser chip is accurately
positioned by the self-alignment effect of the solder bump on the
solder joint pad.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The above and other objects, features and advantages of the
present invention will become apparent from the following detailed
description when taken with the accompanying drawings in which:
[0011] FIG. 1A through 1C are a plan view, a front view and a
sectional view of a conventional optical module respectively;
[0012] FIGS. 2A through 2E are side views showing formation of the
optical module of the present invention up to the step of forming a
solder joint pad on a substrate according to a manufacturing
process of the present invention;
[0013] FIGS. 3A through 3E are side views showing formation of the
optical module of the present invention up to the step of
introducing a semiconductor laser chip on the solder joint pad
according to a manufacturing process of the present invention;
[0014] FIGS. 4A through 4C are side views showing the process for
manufacturing an optical module with another arrangement; and
[0015] FIGS. 5A through 5E are side views showing the process for
manufacturing an optical module with still another arrangement.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0016] A conventional optical module is shown in FIGS. 1A through
1C. As shown in these figures, a plurality of solder joint pads 2
are formed on a silicon substrate 1 in such a manner that they are
longitudinally orthogonal to the silicon substrate 1. Formed on
these solder joint pads 2 are solder bumps 3 on each of which a
solder joint pad 9 for a semiconductor laser chip 5 is mounted. An
optical waveguide 6 is formed on the other side of the silicon
substrate 1 through deposition of silicon. As shown in these
figures, an active layer 8 of the semiconductor laser chip 5 is
formed to be linear with the optical axis 7 of the optical
waveguide 6. In the optical module with such arrangement, when the
optical waveguide 6 is formed, the solder joint pad 2 already
formed on the silicon substrate 1 is subject to a high temperature,
which causes solder joint pad 2 to deteriorate. This makes it
difficult to accurately position the semiconductor laser chip based
on the self-alignment effect achieved with the solder bump.
[0017] Referring now to FIGS. 2A-2E, a series of schematic views
show the optical module according to the present invention in
various stages of the manufacturing process. in FIG. 2A, a WSi
layer 4 is first formed and patterned as non-solder joining
metallization on the silicon substrate 1. Then, a lower clad layer
12 and a core layer 13 of the optical waveguide consisting of
quartz are sequentially deposited on the surface of the silicon
substrate 1, and form a part of the optical waveguide through
photolithography and etching.
[0018] Subsequently, as shown in FIG. 2B, an upper clad layer 14 is
deposited on the entire surface. In the following step, as shown in
FIG. 2C, the deposited layers 12, 13 and 14 are etched and removed
from an area where the semiconductor laser chip is to be mounted,
to expose an end surface of the optical waveguide. In the following
step D, as shown in FIG. 2D, a metal layer 15 is formed on the
entire surface. Then, a part of the metal layer 15 is patterned
through photolithography and etching, and formed on the WSi layer 4
as a solder joint pad 2 on the substrate. A plurality of solder
joint pads 2 are formed. Each of the solder joint pads 2 is formed
in an elongated shape. A number of the solder joint pads 2 are
formed longitudinally parallel to the optical waveguide 6, while
others are formed longitudinally perpendicular to the optical
waveguide 6. Photoresist is sprayed on the silicon substrate for
patterning the metal layer 15 using photolithography. In addition,
a stepper exposure system is employed to permit photolithography to
be performed on a substrate with a step. The optical waveguide 6
positioned relative to the solder joint pad 2 on the substrate
through a matching mask photoprocess.
[0019] Then, as shown in FIGS. 3A through 3E, the semiconductor
laser chip 5 is formed on the solder joint pad 2 on the substrate.
FIG. 3A shows the step of forming a solder bump 3 consisting of
AuSn on the solder joint pad 2. In this step, an AuSn sheet 16 is
stamped by a miniature punch 17 and die 18. The stamped AuSn piece
is thermally compressed on the solder joint pad 2 on the substrate
as it is. At the stage where the solder bump 3 is formed, an oxide
film on the surface of the solder bump 3 can be molten and removed
by adding flux. Then, as shown in FIG. 3B, a plurality of solder
joint pads 9 on the optical device and the semiconductor laser chip
5 are mounted on the solder bumps 3 which correspond to the solder
joint pads 2, the semiconductor laser chip 5 being previously
formed with an active layer 8 for emitting light. Thereafter, when
the silicon substrate 1 is heated in a nitrogen atmosphere, the
solder bump 3 is molten. The molten solder bump 3 spreads over the
entire surfaces of both solder joint pads 2 and 9 on the substrate
and optical devices. As shown in FIGS. 3C and 3D, the molten solder
places both solder joint pads 2 and 9 at predetermined positions by
the self-alignment action due to its surface tension. As show in
FIGS. 3E, this action accurately positions the semiconductor laser
chip 5 at a predetermined location on the silicon substrate 1.
[0020] Here, since the WSi layer does not have wettability, the
solder bump 3 wets and spreads only over the solder joint pad 2. In
addition, since the solder joint pads 2 and 9 are elongated, the
molten solder bump exerts a self-alignment action in a direction
perpendicular to the longitudinal direction of the pad. Therefore,
since here a plurality of pads 2 and 9 are longitudinally oriented
parallel and perpendicular to the optical waveguide 6, the
self-alignment effect of the solder bump acts in a parallel and
perpendicular direction to the optical waveguide 6. Consequently,
the relative plane position between the active layer 8 of the
semiconductor laser chip 5 and the optical waveguide 6 is
established in a desired positional relationship. In addition, the
semiconductor laser chip 5 is positionable at a height which
depends on the volume of solder used to form the solder bump 3. If
the volume of the solder bump 3 is controlled to a predetermined
value, active layer 8 of the semiconductor laser chip 5 can be
aligned with the optical axis 7 of the optical waveguide 6. The
light emitted from the semiconductor laser chip 5 can then be
incident on the optical waveguide 6. Since the solder joint pad 2
is formed after the optical waveguide 6 is formed on the silicon
substrate 1, the solder joint pad 2 is not subjected to high
temperatures which would cause the solder joint pad 2 to
deteriorate. The later formation of the solder pad 2 permits the
optical waveguide 6 to be formed with a high temperature process of
800.degree. C. or more, as with a quartz type optical waveguide.
Therefore, it becomes possible to form a pad with stable quality,
on which a solder bump 3 can be reliably formed. In addition, the
piece of solder is stamped out from the solder sheet with a
miniature punch 17 and die 18 is secured on the solder joint pad 2.
Unlike vapor deposition or plating, forming the AuSn alloy solder
bump from a stamped sheet allows the solder bump 3 to be formed in
a proper amorphous composition rapidly and at low cost.
[0021] Since the solder joint pad 2 on the substrate is formed on
the non-solder jointing WSi film 4, it can be formed with higher
adhesion that in a case where it is directly formed on silicon. WSi
is a material which can sufficiently withstand the high temperature
necessary for forming the waveguide. Since the WSi film 4 is
provided in a step previous to the step of forming the waveguide 6,
patterning can be easily performed. In the above process, the
solder bump 3 is remolten in a nitrogen atmosphere, thereby
preventing oxidation of the solder bump 3. An inert gas such as
argon can also be similarly used to prevent oxidation. In addition,
hydrogen gas can be used to reduce oxide films on the solder bump
3, so that the molten solder can well wet and spread over the
solder joint pad 2 on the optical device, to enhance joint
properties and the self-alignment effect on the optical device. In
addition, when Au or Pt is used as the material for the respective
solder joint pads 2 and 9 on the substrate and optical device, an
oxide film will not form as easily on the surface of the pad. Thus,
the solder bump 3 can well wet and spread over the solder joint pad
2 to provide a desirable self-alignment action.
[0022] FIGS. 4A through 4C show an example of an alternate
manufacturing process according to the present invention. FIG. 4A
shows an arrangement in which a middle section of the optical
waveguide 6 is etched, and the WSi layer 4 is formed on the etched
section. This arrangement is achieved by the process described
above to form a first optical waveguide 21 and a second optical
waveguide 22. Then, as shown in FIG. 4B, a plurality of the solder
joint pads 2 are formed on the WSi layer 4 to have an elongated
shape. The longitudinal axes are arranged to be parallel and
perpendicular to the respective first and second optical waveguides
21 and 22. Subsequently, as shown in FIG. 4C, a semiconductor
optical amplifier device 23 is mounted on the solder joint pad 2 on
the substrate using the self-alignment effect of the solder bump 3
which avoids the need to adjust the optical axis. That is, the
active layer 8 of the semiconductor optical amplifier device 23
aligns with the optical axis 7 of the first an second optical
waveguides 21 and 22. The resultant optical amplifier module
permits the optical amplifier device 23 to amplify light propagated
over the first optical waveguide 21, and to project the light on
the second waveguide 22.
[0023] FIGS. 5A through 5E show a manufacturing process for an
optical amplifier module in which light propagated over an optical
waveguide is amplified by an optical amplifier device, and
projected onto an optical fiber. First, as in FIG. 5A, the WSi
layer 4, the optical waveguide 6 consisting of quartz and the
solder joint pad 2 are formed on the silicon substrate 1 along with
the oxide film 31. Then, as shown in FIG. 5B, the oxide film 31 is
etched and removed to expose silicon at a region on which the fiber
optics 34 is mounted in a subsequent step. Subsequently, as shown
in FIG. 5C, etching is performed on a surface region of the silicon
substrate 1 to form a V-groove 32. Moreover, as shown in FIG. 5D,
the surface of the silicon substrate 1 is cut at an end of the
V-groove 32 to form a slit 33 for positioning the end plane of the
optical fiber. Finally, as shown in FIG. 5E, the solder bump 3 is
formed on the solder joint pad 2, on which the semiconductor
optical amplifier device 23 is mounted using the solder joint pad
9. Then, the solder bump 3 is made molten, and the semiconductor
optical amplifier device 23 is joined to the silicon substrate 1 in
self-alignment through the solder bump 3, which avoids the need to
adjust the optical axis. Then, the optical fiber 34 is positioned
by the V-groove 32 and the slit 33, and secured on the silicon
substrate 1 with adhesives. Once positioned as described, the
active layer 8 of the semiconductor optical amplifier device 23,
and the optical axis 7 of the optical waveguide 6 and the optical
fiber are all aligned. The resulting optical amplifier module
permits the optical amplifier device 23 to amplify light propagated
over the optical waveguide 6 and to project the light onto the
optical fiber 34.
[0024] The above embodiment contemplates use of the semiconductor
leaser chip 5 and the semiconductor optical amplifier device 23 as
the optical device, but another optical device such as a waveguide
type light receiving device or a semiconductor optical modulator
device may be used. The solder bump is indicated as made of AuSn,
but may be implemented by other solder materials such as AuSi or
AuGe. In addition, another material may be used in place of WSi as
long as it a material with good adhesion with the substrate and the
solder joint pad, and with no solder wettability. Moreover, an
optical divider, optical switch or the like may be used in place of
the optical waveguide 6. Alternatively, the optical device and the
optical waveguide 6 are not limited to a single core structure, but
a multi-core optical device or optical waveguide may be used. In
addition, according to the present invention, a spot-size converter
may be provided in the optical input/output section of the optical
device. Usually, when an optical device such as a semiconductor
laser is coupled to an optical waveguide, a coupling loss in mode
fields is experienced. Use of the spot-size converter helps reduce
such losses, whereby highly efficient coupling can be attained.
Conversely, even when the spot-size converter section is not
provided on the optical device, a lens may be provided on the end
of the optical fiber or optical waveguide. Use of a lens also
reduces differences experienced in mode fields, so that highly
efficient coupling can be attained. In addition, when the optical
fiber is secured by adhesives, it may have a groove or hole to
provide the adhesives with an escape path in the middle section of
the V-groove.
[0025] In addition, in the above example, the films of the solder
joint pad formed on the substrate are constituted in an order of
titanium-platinum-gold from the silicon substrate. Furthermore, the
solder joint pad has a rounded contour in dimensions of 140 .mu.m
long and 25 .mu.m wide, with a thickness of 0.7 .mu.m. The bump
height after joining is 18 .mu.m including the thickness of both
solder joint pads on the substrate and the optical device. The
heating temperature is 300.degree. C. for reflow of the joint. In
forming the solder bump, the AuSn sheet solder has a thickness of
20 .mu.m, the punch has a diameter of 60 .mu.m, and stamping is
performed with the AuSn sheet solder heated to 180.degree. C., and
the silicon substrate heated to 150.degree. C. The optical
waveguide has a lower clad layer 19 .mu.m thick, a core layer 6
.mu.m thick, an upper clad layer of 20 .mu.m, a size of 6
.mu.m.times.6 .mu.m, and a height of 22 .mu.m from the silicon
substrate surface to the center of the optical waveguide. When an
optical fiber is used, the fiber has a diameter of 125 .mu.m, the
mode field has a diameter of 9.5 .mu.m, the V-groove has a width of
122 .mu.m and a depth of 50 .mu.m or more, and the oxide film which
becomes the mask layer when forming the V-groove by etching has a
thickness of 0.5 .mu.m or more.
[0026] As described above, according to the optical module and its
manufacturing process, the solder joint pad is formed after the
optical waveguide is formed on the substrate, and it thus becomes
possible to form a stable solder joint pad. In addition, adhesion
of the solder joint pad is enhanced by providing the solder joint
pad on the non-solder jointing metallization, whereby reliable bump
mounting can be attained. Therefore, it becomes possible to
construct a reliable and low cost optical module which does not
require adjustment of an optical axis due to the self-alignment
effect of the solder bump.
[0027] While the present invention has been described in connection
with certain preferred embodiments, it is to be understood that the
subject matter encompassed b the present invention is not limited
to those specific embodiments. On the contrary, it is intended to
include all alternatives, modifications, and equivalents as can be
included within the spirit and scope of the following claims.
* * * * *