U.S. patent application number 12/222671 was filed with the patent office on 2009-02-26 for process to form a mold of nanoimprint technique for making diffraction grating for dfb-ld.
Invention is credited to Masaki Yanagisawa.
Application Number | 20090053656 12/222671 |
Document ID | / |
Family ID | 40382516 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090053656 |
Kind Code |
A1 |
Yanagisawa; Masaki |
February 26, 2009 |
Process to form a mold of nanoimprint technique for making
diffraction grating for DFB-LD
Abstract
A process using the nanoimprint technique to form the
diffraction grating for the DFB-LD is disclosed. The process
includes (a) coating a resist for the EB exposure on a dummy
substrate, (b) irradiating the resist as varying the acceleration
voltage, (c) forming a resist pattern by developing the irradiated
resist, (d) coating the SOG film on the patterned resist, (e)
attaching the silica substrate on the cured SOG film, and (f)
removing the dummy substrate with the resist from the SOG film and
the silica substrate. Using the mold thus formed, the diffraction
grating for the DFB-LD is formed by the nanoimprint technique.
Inventors: |
Yanagisawa; Masaki;
(Yokohama-shi, JP) |
Correspondence
Address: |
Michael A. Makuch, Esq.;Smith, Gambrell & Russell, LLP
Suite 800, 1850 M. Street
Washington
DC
20036
US
|
Family ID: |
40382516 |
Appl. No.: |
12/222671 |
Filed: |
August 13, 2008 |
Current U.S.
Class: |
430/323 ;
430/325 |
Current CPC
Class: |
G03F 7/2059 20130101;
H01S 5/1225 20130101; B82Y 40/00 20130101; H01S 5/2275 20130101;
G03F 7/0002 20130101; B82Y 10/00 20130101 |
Class at
Publication: |
430/323 ;
430/325 |
International
Class: |
G03F 7/20 20060101
G03F007/20; G03F 7/004 20060101 G03F007/004 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2007 |
JP |
2007-217512 |
Claims
1. A method to produce a mold for the nanoimprint technique, said
mold being used for fabricating a diffraction grating for a
distributed feedback laser diode, comprising steps of: (a) coating
a dummy substrate with a photo resist for the electron beam
lithograph; (b) irradiating said photo resist by electron beams as
varying an acceleration voltage of said electron beams; (c)
developing said irradiated resist to form a resist pattern; (d)
coating said resist pattern with a mold resin to be converted into
said mold; (e) curing said mold resin; and (f) removing said dummy
substrate and said resist pattern from said cured mold resin.
2. The method according to claim 1, wherein said resin to be
converted into said mold is a spin on glass film.
3. A method to produce a mold for the nanoimprint technique, said
mold being used for fabricating a diffraction grating for a
distributed feedback laser diode, comprising steps of: (a) coating
a substrate with a first resist for the electron beam lithography;
(b) irradiating a first limited region of said first photo resist
by electron beams; (c) developing said irradiated first photoresist
to prepare a first resist pattern; (d) etching said substrate under
a first condition with said patterned first photo resist as an
etching mask to form a first pattern on said substrate and removing
said patterned first photo resist after said etching; (e) coating
said substrate with a second photo resist for the electron beam
lithography; (f) irradiating a second limited region of said second
photo resist by electron beams, said second limited region being
different from said first limited region; (g) developing said
irradiated second photo resist to prepare a second resist pattern;
and (h) etching said substrate under a second condition different
from said first condition with said patterned second photo resist
as an etching mask to form a second pattern on said substrate and
removing said patterned second photo resist after said etching,
wherein said first pattern and said second pattern constitute at
least a potion of patterns provided in said mold.
4. The method according to claim 2, wherein said etching to form
said first pattern has a different process time from said etching
to form said second pattern.
5. A method to produce a mold for the nanoimprint technique, said
mold being used for fabricating a diffraction grating for a
distributed feedback laser diode and having a pattern for said
diffraction grating, comprising steps of: (a) coating a substrate
with a photosensitive film; (b) irradiating said photosensitive
film by electron beams as varying an acceleration voltage of said
electron beams; and (c) developing said irradiated photosensitive
film to form said pattern.
6. The method according to claim 5, wherein said photosensitive
film is made of spin on glass material.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention related to a process to form a mold,
for the nanoimprint technique, the mold having a pattern for the
diffraction grating, a process to form the diffraction grating and
a process to form the distributed feedback laser diode (hereafter
denoted as DFB-LD) with the diffraction grating.
[0003] 2. Related Prior Art
[0004] Conventionally, the diffraction grating for the DFB-LD has
been formed by, after preparing the resist pattern by the
interference lithography or the electron beam lithography (EB
lithography), etching the semiconductor material with resist
pattern as the etching mask. Recently, another technique to form
the diffraction grating has been known in which a mold having the
grating pattern is pressed against a resin to transfer the grating
pattern on this resin, which is often called as the nanoimprint
technique. Prior documents, such as the United States Patent U.S.
Pat. No. 7,165,957, and Journal of Vacuum Science and Technology,
vol. B14(6), pp. 4129-4133 (1996), have disclosed the nanoimprint
technique.
[0005] Because the interference lithography, or the EB lithography,
is inevitable to form the patterns with an uniform depth, that is,
the aspect ratio of the obtained patterns is uniform within a
wafer; accordingly, it is quite hard to modify the depth of the
diffraction grating in a limited portion thereof or to control the
depth of the resist patterns intentionally so as to compensate the
inhomogeneous etching rate within the wafer. Moreover, it is
further difficult to grade the duty ratio of the patterns
optionally within the wafer. Here, the duty ratio of the pattern
means the ratio of the width of the rib against the width of the
valley of the pattern. It is also hard or at least necessary for a
long time to distribute the pitch of the patterns optionally in the
wafer. Thus, the conventional technique of the interference
lithography fundamentally limits to the uniform resist patterns
within the wafer. That is, only one type of the patterns may be
realized in the single wafer by the conventional technique.
SUMMARY OF THE INVENTION
[0006] An aspect of the present invention relates to a process to
form a mold for the nanoimprint technique. This mold is used to
form the diffraction grating for the DFB-LD. The process includes:
(a) coating a dummy substrate with a photo resist for the electron
beam lithography; (b) irradiating the photo resist by electron
beams as varying the acceleration voltage of the electron beams;
(c) developing the irradiated resist to form a resist pattern; (d)
coating this resist pattern with a mold resin, which is to be
converted into the mold; (e) curing the mold resin; and (f)
removing the dummy substrate and the resist pattern from the cured
mold resin. The mold resin may be a spin on glass (SOG).
[0007] Because the irradiation of the electron beams are carried
out as varying its acceleration voltage, the resultant resist
pattern shows a non-uniform dimensions. For instance, the depth (or
the height), the duty ratio, the aspect ratio, the pitch and so on
of the pattern are varied within the dummy substrate. Accordingly,
the diffraction grating obtained by using thus prepared mold shows
the non-uniform characteristic.
[0008] Another process to form the mold according to the present
invention includes: (a)coating a substrate with a first photo
resist; (b) irradiating a first limited region of this first photo
resist by the electron beams; (c) developing the irradiated first
photo resist to prepare a first resist pattern; (d) etching the
substrate under a first condition with the patterned first photo
resist as the etching mask to form a first pattern on the substrate
and removing the patterned first photo resist after the etching;
(e) coating the substrate with a second photo resist for the
electron beam lithography; (f) irradiating a second limited region,
different from the first limited region, of the second photo resist
by the electron beams; (g) developing the irradiated second photo
resist to prepare a second resist pattern; and (h) etching the
substrate under a second condition different from the first
condition with the patterned second photo resist as the etching
mask to form a second pattern on the substrate and removing the
patterned second photo resist after the etching. The first pattern
and the second pattern each formed in the substrate constitute at
least a portion of patterns provided in the mold.
[0009] Still another process to form the mold according to the
present invention includes: (a) coating a substrate with a
photosensitive film; (b) irradiating the photosensitive film by
electron beams as varying the acceleration voltage of the electron
beams; and (c) developing the irradiated photosensitive film to
form a pattern for the diffraction grating. The photosensitive film
may be a spin on glass material.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIGS. 1A to 1C schematically illustrate the first process to
form the mold according to the invention;
[0011] FIGS. 2A to 2C schematically illustrate the first process
performed subsequent to FIG. 1C;
[0012] FIG. 3 images a mold viewed from a side where the patterns
are formed;
[0013] FIGS. 4A to 4D schematically illustrate the second process
to form the mold according to the invention;
[0014] FIGS. 5A to 5C schematically illustrate the second process
performed subsequent to FIG. 4D;
[0015] FIGS. 6A to 6C schematically illustrate the third process to
form the mold according to the invention;
[0016] FIGS. 7A to 7C schematically illustrate a process to form
the diffraction grating using the mold formed by any one of first
to third processes;
[0017] FIGS. 8A to 8C schematically illustrate a process to form
the diffraction grating performed subsequent to FIG. 7C;
[0018] FIGS. 9A to 9C schematically illustrate a process to form
the DFB-LD that provides the diffraction grating formed by the
process illustrated in FIGS. 7A to 8C; and
[0019] FIG. 10 is a perspective view, a portion of which is broken
to indicate the layer stacking, of the DFB-LD formed by the process
shown in FIGS. 9A to 9C.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] Next, preferred embodiments according to the present
invention will be described as referring to accompanying drawings.
In the description of the drawings, the same elements will be
referred by the same numerals or the same symbols without
overlapping explanations. Further, dimensions illustrated in the
drawings do not always reflect the practical one or that of the
descriptions. First, a method to prepare the mold will be
described.
[0021] (First Method to Prepare the Mold)
[0022] FIGS. 1A and 2C illustrate a process to prepare the mold 10
according to the first method. As illustrated in FIG. 1A, the
process coats a photo resist 102 for the electron beam (hereafter
denoted as EB) lithography on the dummy substrate 101, typically a
silicon substrate. The photo resist 102 may be a positive type
photo resist such as ZEP-520 provided from Zeon Corp.
[0023] Next, the electron beam EB irradiates on the surface 102a of
the photo resist 102 as varying the acceleration voltage, the
exposure dose, and the scanning patterns thereof (FIG. 1B). In FIG.
1B, the length of the arrowhead corresponds to the acceleration
voltage, while, the spans between the arrowheads denotes the
scanning width of the electron beams.
[0024] Developing the photo resist 102, we can obtain the resist
patterns 103 as illustrated in FIG. 1C. Because the irradiation of
the electron beam is carried out as varying the acceleration
voltage, the exposure dose and the scanning patterns, which varies
the irradiation depth and area of the electron beam, the resultant
patterns obtained in the photo resist 103 varies its depth, an
aspect ratio, a pattern pitch, and so on.
[0025] Next, the process coats the spin-on-glass (hereafter denoted
as SOG) film 104 on the patterned photo resist 103, as illustrated
in FIG. 2A. This SOG film 104 will be converted to the pattern 10A
of the mold 10, which will be described later.
[0026] Next, the silica substrate 106 is attached to the SOG film
104 with an adhesive 105 after the SOG film 104 is cured (FIG. 2B).
This silica substrate 106 will be the substrate 10B of the mold 10.
Subsequently, the dummy substrate 101 and the patterned resist 103
are removed; thus, the mold with the pattern 10A of the SOG film
104 on the silica substrate 10B is completed as illustrated in FIG.
2C.
[0027] FIG. 3 shows the mold 10 viewed from the side where the
pattern 10A is formed. The mold 10 provides a plurality of regions
each having particular patterns specific to the region, for
example, patterns in the regions, A to D, provide particular aspect
ratio of 1.0 to 2.5 with a step of 0.5, respectively. When the
irradiation of the electron beams is carried out as varying its
acceleration voltage, the depths (or the height) and the duty
ratios of patterns in each region, A to D, are different from each
other. Or, when the irradiation is carried out as varying the pitch
of the patterns, the pitch of the patterns in respective sections,
A to D, shows the different pitch. Here, the aspect ratio means a
ratio of the pattern width to the depth, the duty ratio means a
ratio of the pattern width to the pattern span, and the pitch means
the distance from one pattern in the top thereof to the next
pattern also in the top thereof.
[0028] According to the process thus described, the patterns 10A
formed on the mold 10 varies their depth, the duty ratio, the pitch
and so on reflecting the acceleration voltage of the electron
beams, the exposure dose and the scanning patterns. Accordingly,
using this mold 10 with various patterns of the depth, the duty
ratio, the pitch and so on for forming the diffraction grating for
the DFB-LD, diffraction gratings with various configurations may be
obtained within a semiconductor wafer.
[0029] (Second Method to Form Mold)
[0030] FIGS. 4A to 5C show a process to form a mold 11 according to
one embodiment of the invention.
[0031] First, the process coats a photo resist 112 for the electron
beam lithography on the substrate 111, typically a silicon
substrate, as illustrated in FIG. 4A. The photo resist 112 may be a
positive type photo resist such as ZEP-520 provided from Zeon
Corp.
[0032] Next, the electron beam EB irradiates on the surface 112a of
the photo resist 112. In this process, the acceleration voltage and
the exposure dose of the electron beam may be varied as those of
the first embodiment described above. Further, the process may
irradiate the electron beam such that the scanning patterns or the
pitch thereof has a predetermined distribution. Developing the
irradiated resist 112, we obtain the first resist pattern 113 as
shown in FIG. 4C.
[0033] Carrying out the first etching of the substrate 111 using
the first resist pattern 113 as the etching mask and subsequently
removing the resist 112, a first pattern 111a may be obtained with
the depth of dl on the substrate 111. The portion except for the
region P1 leaves no patterns because it is covered with the resist
112.
[0034] Next, the process coats the second resist 114 on the
substrate 111 with the first pattern 111a again as illustrate in
FIG. 5A. This second resist 114 may be the same with the first
resist 112. Subsequently, the process irradiates the electron beams
on a region P2 except for the first region P1. In this process, the
acceleration voltage and the exposure dose of the electron beams
may be varied in each irradiation, or the patterns to be irradiated
may have a preset distribution in the shape thereof.
[0035] Developing the second resist 114, the second pattern 115 as
illustrated in FIG. 5B may be obtained. Etching the substrate 111
with the second resist 115 as the etching mask and removing the
second resist 115, the second pattern 111b with a depth of d2 may
be obtained. The process conditions of the second etching may be
different from those of the first etching. In this process, the
region except for the region P2 is covered with second resist 115
and no patterns are left. Iterating the formation of the resist
patterns and the etching of the substrate 111 by distinguishable
conditions, the mold 11 according to the second method may be
obtained.
[0036] FIG. 3 shows the mold 11 viewed from the side where the
patterns, 111a and 111b, are formed, where each region forms
particular patterns specific to the region, for instance, patterns
in the region, A to D, provide particular aspect ratio of 1.0 to
2.5 by a step of 0.5, respectively. When the irradiation of the
electron beams is carried out as varying its acceleration voltage,
the depths (or the height) and the duty ratios of patterns in each
section, A to D, are different from each other. Or, when the
exposure is carried out as varying the pitch of the scanning
patterns, the pitch of the resultant patterns formed in the mold in
respective regions, A to D, shows the different pitches.
[0037] According to the second process described above, the
patterns 11A in respective regions provide the depth, d1 or d2
shown in FIG. 5C, specific to the region and different from the
other regions. Forming the diffraction grating using this mold 11
with the patterns 11A, the resultant gratings have different
characteristics within the wafer.
[0038] Moreover, using this mold 11 to form the diffraction grating
within the wafer, the process may avoid the iteration of the resist
coating, the irradiation on the resist, the developing, and the
removal of the resist to form the various gratings, which may
protect the wafer from the process damage, such as due to the
irradiation of the electron beams and the etching. As described
later, the process cost and the term thereof to form the pattern
for the diffraction grating by the nanoimprint technique using this
mold may be remarkably shortened, and the process damage applied to
the semiconductor material may be reduced.
[0039] (Third Method to Form Mold)
[0040] FIGS. 6A to 6C schematically illustrate the process to form
the mold 12 according to the third embodiment of the invention.
This process first coats the SOG film 122 on the silicon (Si)
substrate 121 by the spin coater (FIG. 6A). As described later, the
Si substrate 121 becomes the base 12B of the mold 12, while, the
SOG 122 converts the pattern 12A of the mold 12.
[0041] Next, the process irradiates the electron beams on the
surface 122a of the SOG film as varying its acceleration voltage or
the exposure dose, or varying the scanning patterns within the
substrate, as illustrated in FIG. 6B.
[0042] Subsequently, the process etches the irradiated SOG 122 by
the buffered fluoric acid to form the patterns 12A as shown in FIG.
6C. Since the irradiation of the electron beams is carried out as
varying the condition thereof, the penetration depth of the beams
into the SOG film 122 and the spreading width of the beams within
the SOG film 122 show variety, which results in the etched patterns
12A with various depths, duty ratios, pitches and so on. Thus, the
mold 12 is completed with the patterns 12A on the base 12B.
[0043] According to the method described above to form the mold 12,
the patterns 12A in the mold 12 varies the depth, the duty ratio,
the pitch and so on depending on the acceleration voltage and the
exposure doses of the electron beams, or the scanning patterns.
Such a mold 12 may vary the characteristic of the diffraction
grating to be formed by using the mold 12 within the semiconductor
wafer.
[0044] (Method to Form Diffraction Grating)
[0045] Next, a method to form the diffraction grating according to
an embodiment of the invention will be described. FIGS. 7A to 8C
schematically illustrate the process to form the grating.
[0046] First, the mold is prepared by at least one of the first to
third method aforementioned. The explanation explained below
assumes, for convenience's sake, that the mold 10 is formed by the
first method and provides the patterns 10A. The patterns 10A, as
already explained, have various depths, duty ratios, and the
pitches depending on the position.
[0047] Second, the nanoimprint technique is carried out. That is,
the mold 10 with the pattern 10A is pressed against the resist 21
on the semiconductor substrate 20 by the force F whose magnitude
may be estimated beforehand depending on the process conditions
(FIG. 7A). The substrate 20 may include semiconductor epitaxial
layers of the multiple quantum well (MQW) active layer and the
cladding layers.
[0048] Next, the resist 21 on the substrate 20 may be cured as the
mold 21 is pressed thereat, which forms the pattern 23 for the
diffraction grating in the cured resist 24. Various techniques may
be applicable to cure the resist 24, for instance, the ultra-violet
(UV) curing, which is often called as the optical nanoimprint
technique, or the thermal curing using the heat treatment, which is
often called as the thermal nanoimprint technique. In the optical
nanoimprint technique, the mold 10 is preferably made of material
with a high transmissivity for the ultraviolet rays, while, the
resist 21 is preferably a type of the UV-curable resist.
[0049] On the other hand, the thermal nanoimprint technique cures
the resist 21, which is once softened by raising the temperature
thereof, by cooing it down. Thus, the mold 10 is preferably made of
metal, typically nickel (Ni), while, the resist 21 is preferably
made of thermoplastic material with a glass transition
temperature.
[0050] Next, as illustrated in FIG. 7C, the process exfoliates the
mold 10 from the resist 24 with the patterns for the grating. As
already explained, the resist 24 has grooves with various depths
dependent on positions thereof.
[0051] FIG. 8A illustrates the process to etch the semiconductor
substrate 20 by the resist 24 with the patterns 23 as the etching
mask. The etching may be the reactive ion etching (RIE) whose
conditions are so selected that both the resist 24 and the
substrate 20 are etched.
[0052] Advancing the etching, the semiconductor substrate 20 in a
portion where the resist pattern 23 has a deeper groove is going to
be exposed, and the substrate 20 exposed in the bottom of the
groove is etched in a order that the resist pattern 23 has the
deeper groove by the further etching. Finally, the process forms
the diffraction grating 25 on the substrate 20, where the grating
25 has grooves with various depths depending on the resist pattern
23. That is, when the mold 10 provides the plural regions shown in
FIG. 3 and each region shows patterns specific to respective
regions, for instance, the pattern in the region provides an aspect
ratio specific to the region, the aspect ratio in the groove on the
substrate 20 reflects that of the resist pattern 23 and the mold 10
in respective regions. However, depending on the etching rate of
the resist 24 and that of the substrate 20, which is often called
as the selection ratio of the etching, the relative aspect ratio in
respective regions may be reflected in the pattern on the substrate
20 but the absolute value thereof are different from each other. In
other words, when the aspect ratios of the resist are 1.0 to 2.5
with 0.5 steps for the regions A to D, respectively, the aspect
ratios of the grooves on the substrate 20 may be 0.5 to 1.25 with
0.25 steps for the regions A to D, respectively. That is, the
aspect ratio of the grating 25 finally formed on the substrate 20
may be optionally varied by setting the selection ratio of the
etching. Finally, removing the resist 24 after completing the
etching, the diffraction grating 25 may be completed.
[0053] According to the process to form the diffraction grating 25
above described, the process applies the nanoimprint technique by
using the mold 10 with the pattern 10A, where the dimensions such
as the depth of the pattern varies therein. Accordingly, the
resultant diffraction grating 25 may vary the dimensions such as
the depth of the groove. The description above concentrates the
subject to be varied on the depth of the groove, but the process
may vary the other physical parameters such as the duty ratio, the
pitch, and so on.
[0054] The process thus described may be applicable to a case when
various types of the diffraction gratings are necessary. The
process may also be applicable to enhance the homogeneity of the
dimensions of the diffraction grating within a wafer. That is,
evaluating the inhomogeneity of the etching rate within the wafer
in advance, and forming mold 10 whose patterns, in particular, the
depth, the duty ratio, the pitch of the groove and so on, are
formed so as to compensate the inhomogeneity of the etching, the
resultant diffraction grating realizes improved homogeneity. As an
example, when the etching rate shows a concentric circular
distribution such that the rate in a peripheral portion of the
wafer is about 10% higher that that of the center portion, the
homogeneous diffraction grating 25 may be obtained through the
nanoimprint technique using the mold 10 with the grooves in the
peripheral portion of the wafer about 10% shallower than those in
the center portion.
[0055] Moreover, the present method mentioned above is also
applicable in a case where one diffraction grating built in the
device, for instance, in the single distributed feedback (DFB)
laser, has variety of dimensions. This enables to modify the
optical coupling coefficient between the active layer and the
diffraction grating within the device; accordingly, the optical
power distribution along the optical axis of the device becomes
controllable such that the homogeneous distribution of the optical
power is attained; accordingly, the device may suppress the
hole-burning effect along its optical axis.
[0056] (Process to Form DFB-LD)
[0057] Next, a process to form the DFB-LD according to one
embodiment of the present invention will be described. FIGS. 9A to
9C illustrate, in cross sections of the device, the process to form
the DFB-LD 40, while, FIG. 10 is a perspective view of the DFB-LD,
a portion of which is broken to show the layer structure thereof,
obtained through the process of the embodiment.
[0058] First, the process forms, on the semiconductor substrate 20,
a first cladding layer 30, a first separate optical confinement
(SCH) layer 31, an active layer 32, a second SCH layer 33, a layer
34, and a resist 21 in this order. Here, both SCH layers, 31 and
33, may be saved. Second, the mold 10 with the pattern 10A is
pressed against the resist 21 to transfer the pattern 10A on the
cured resist 24 (FIG. 9B). Etching the cured resist 24 and the
layer 34 according to the method described in FIGS. 8A to 8C, and
removing the resist 24 after the etching, the diffraction grating
shown in FIG. 9C may be obtained in the layer 34, which is often
called as the guiding layer.
[0059] Next, on the guiding layer 34 formed with the diffraction
grating 25 is grown with a second cladding layer with a refractive
index different from that of the guiding layer so as to bury the
diffraction grating 25. Subsequently, the second cladding layer,
the guiding layer 34, the second SCH layer 33, the active layer 32,
the first SCH layer and the first cladding layer 30 are wet-etched
to form the mesa. Further, the process buries thus formed mesa by
the burying layer 35, and on the second cladding layer and the
burying layer 35 are grown with the third cladding layer 36. This
third cladding layer 36 may be saved. On the third cladding layer
36, or on the second cladding layer and the burying layer 35, is
grown with the contact layer 37, and on the contact layer 37 is
formed with the upper electrode 38, while, the whole back surface
of the substrate 20 is formed with the lower electrode 39. Thus,
the DFB-LD 40 is completed.
[0060] The process to form the DFB-LD above described adopts the
nanoimprint technique using the mold 10 with the pattern whose
dimensions such as the pattern depth are non-uniform; accordingly,
the resultant diffraction grating may reflect this distributed
dimensions. Because the process of the invention may form the
diffraction gratings with various dimensions in a wafer, various
DFB-LD s 40 with different types of the is diffraction gratings may
be intermingled within the wafer, which shows a great advantage for
the multi-objective but low production.
[0061] When the etching to form the diffraction grating shows an
inhomogeneous rate within the wafer, the process may compensate the
inhomogeneous rate by using the mold with the imprint pattern 10A
whose dimensions are varied. In this case, because the depth of the
groove in the diffraction grating may be homogeneous, the DFB-LD
with this diffraction grating may also enhance its homogeneity.
[0062] Moreover, using the mold 10 with the imprint pattern 10A
with a non-uniform dimensions, the DFB-LD with the non-uniform
diffraction grating may be obtained. In this case, the optical
coupling coefficient between the diffraction grating and the active
layer varies within the device, the optical power distribution
along the optical axis may be modified, which effectively
suppresses the hole-burning effect.
* * * * *