U.S. patent application number 10/061710 was filed with the patent office on 2003-03-06 for etch mask.
Invention is credited to Irino, Satoshi, Kurahashi, Nobuhiko, Toyosaki, Koichi, Tsukiji, Naoki.
Application Number | 20030042223 10/061710 |
Document ID | / |
Family ID | 26608654 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030042223 |
Kind Code |
A1 |
Toyosaki, Koichi ; et
al. |
March 6, 2003 |
Etch mask
Abstract
Provided is a etch mask that prevents the separation of the etch
mask which occurs in the vicinity of an end portion of a material
to be etched during etching step. The etch mask is one formed on a
surface of a material to be etched and comprising collected linear
masks. A portion of a linear mask positioned in the vicinity of an
end portion of the material to be etched becomes a wider portion as
compared with the remaining portion or a zigzag portion. As
required, the middle portion of the linear mask also becomes a
wider portion or a zigzag portion.
Inventors: |
Toyosaki, Koichi; (Tokyo,
JP) ; Kurahashi, Nobuhiko; (Tokyo, JP) ;
Irino, Satoshi; (Tokyo, JP) ; Tsukiji, Naoki;
(Tokyo, JP) |
Correspondence
Address: |
COUDERT BROTHERS LLP
Third Floor
600 Beach Street
San Francisco
CA
94109
US
|
Family ID: |
26608654 |
Appl. No.: |
10/061710 |
Filed: |
January 30, 2002 |
Current U.S.
Class: |
216/2 ;
257/E21.486 |
Current CPC
Class: |
H01L 21/467 20130101;
H01S 5/12 20130101 |
Class at
Publication: |
216/2 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2001 |
JP |
2001-23897 |
Oct 18, 2001 |
JP |
2001-321061 |
Claims
What is claimed is:
1. An etch mask on a material to be etched comprising: an elongated
portion, where the width of said elongated portion is measured
substantially perpendicular to the direction of elongation; and an
end member connected to said elongated portion, where the width of
said elongated portion adjacent to said end member is an end width,
where said end member has a maximum extent measured in the
direction of said end width, and where said maximum extent of said
end member is greater than said end width.
2. The mask pattern of claim 1, where said end member is a first
end member and further including a second end member on a material
to be etched and connected to said elongated portion, where the
width of said elongated portion adjacent to said second end member
is a second end width, where said second end member has a maximum
extent measured in the direction of said second end width, and
where said maximum extent of said second member is greater than
said second end width.
3. The mask pattern of claim 1, wherein said elongated portion is a
first elongated portion, and further including a second elongated
portion on a material to be etched and connected to said end
member, where the width of said second elongated portion is
measured substantially perpendicular to the direction of
elongation, where the width of said second elongated portion
adjacent to said end member is a second end width, and where said
maximum extent of said end member is greater than said end
width.
4. The mask pattern of claim 1, wherein said maximum extent of said
end member is at least twice than said end width.
5. The mask pattern of claim 1, wherein said end member is adjacent
to the edge of the material.
6. The mask pattern of claim 1, wherein said first end member has
an end member length measured perpendicular to said end width, and
wherein said end member covers an area on the material to be etched
that is greater than the product of said end width and said end
member length.
7. The mask pattern of claim 1, wherein said end member describes a
shape on the material to be etch, and where said shape is a circle,
a square, or a zigzag.
8. The mask pattern of claim 7, wherein said shape is a zigzag,
where said zigzag has a total elongated length, and where the total
elongated length of said zigzag is at least twice said end
width.
9. The mask pattern of claim 1, wherein said material to be etched
includes a semiconductor material or an insulating material.
10. The mask pattern of claim 1, wherein said etch mask is silicon
nitride, silicon oxide, silicon oxynitride, or photo-sensitive
resist.
11. The mask pattern of claim 2, wherein said elongated portion is
a rectangular portion extending from said first end to said second
end.
12. An etch mask comprising a plurality of mask patterns as in
claim 2, wherein each of said directions of elongation are
substantially parallel.
13. The etch mask of claim 12, wherein said etch mask is a
stripe-shaped etch mask or a diffraction grating-shaped etch
mask.
14. The etch mask of claim 12, wherein at least one of said
plurality of said first and second end members are adjacent to an
edge of said material.
15. A mask pattern comprising: a plurality of portions on a
material to be etched, said plurality of portions including two end
portions, and an elongated portion disposed between said two end
portions, where the width of said elongated portion is measured
substantially perpendicular to the direction of elongation, where
in the vicinity of said two end portions, said elongated portion
has an end width, said end portion has a maximum extent measured in
the direction of said end width, and where said maximum extent is
greater than said end width.
16. The mask pattern of claim 15, wherein said maximum extent is at
least twice than said end width.
17. The mask pattern of claim 15, wherein at least one of said two
end members is adjacent to the edge of the material.
18. The mask pattern of claim 15, wherein said end portion has an
end member length measured perpendicular to said end width, and
wherein said end member covers an area on the material to be etched
that is greater than the product of said end width and said end
member length.
19. The mask pattern of claim 15, wherein said end member describes
a shape on the material to be etch, and where said shape is a
circle, a square, or a zigzag.
20. The mask pattern of claim 19, wherein said shape is a zigzag,
where said zigzag has a total elongated length, and where the total
elongated length of said zigzag is at least twice said end
width.
21. The mask pattern of claim 15, wherein said material to be
etched includes a semiconductor material or an insulating
material.
22. The mask pattern of claim 15, wherein said etch mask is silicon
nitride, silicon oxide, silicon oxynitride, or photo-sensitive
resist.
23. The mask pattern of claim 16, wherein said elongated portion is
a rectangular portion.
24. An etch mask comprising a plurality of mask patterns as in
claim 15, wherein each of said directions of elongation are
substantially parallel.
25. The etch mask of claim 24, wherein said etch mask is a
stripe-shaped etch mask or a diffraction grating-shaped etch
mask.
26. The etch mask of claim 25, wherein each of the plurality of
said two end portions are adjacent to an edge of said material.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an etch mask which is
formed on a surface of a material to be etched, and more
specifically to an etch mask, particularly a stripe-shaped etch
mask or a diffraction grating-shaped etch mask, useful in forming a
required pattern on a semiconductor device.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to the formation of an etch
mask on a substrate. As one example of such an etch mask, FIG. 1
shows a prior art etch mask 2a having a predetermined pattern and
formed on a surface 1a of a precursor device 1. The prior art mask
2a is stripe-shaped, with a plurality of linear, parallel masks 2b
each having a predetermined line width and length. The surface of
the masked precursor device 1 is then etched according to the mask
pattern. The etch mask 2a is then removed, and another
semiconductor material, which may include but is not limited to
InP, GaAs, AlGaAs, GaP, InGaAs, AlInGaP, InGaP, GaInAsP, GaN, ZnSe,
or CdTe, is laminated thereon as required.
[0003] A major problem in semiconductor fabrication is the failure
of the mask during processing. Specifically, if etch mask 2a
separates from the surface 1a of the precursor device 1 by peeling,
delaminating or some other process, or tears or is cut, then the
semiconductor material positioned below the disturbed mask portion
could be exposed to etchant, and the integrity or functioning of
the resultant device could be jeopardized.
[0004] The separation or breakage of etch mask 2a may occur due to
various factors. If an oxide layer is formed on surface 1a prior to
masking the surface, then the mask material, such as a photoresist,
may not properly bond or attach to the surface. Semiconductor
surfaces are typically treated with hydrogen peroxide or other
agents to remove oxide layers and prepare the surface prior to
masking. Improper photolithography processing is another cause of
separation or breakage of an etch mask. Yet another cause of
separation is damage to the mask during etching.
[0005] These problems with the prior art can be addressed by means
of appropriate previous treating of a surface of the precursor
device, appropriate photolithography developing, and appropriate
control of the etching. Despite these precautions, the separation
of etch masks during etching continues to be a problem.
[0006] One problem that has been particularly difficult to solve is
the separation of the etch mask during etching that results from
excessive etching. In particular, isotropic etching of substrate
material near the edge of the mask can result in undesirable
modifications of the surface morphology and can weaken the bond
between mask and substrate. This is illustrated in FIG. 2, which is
a cross-sectional view taken along the line II-II in FIG. 1. As
shown by the horizontal arrow, etching perpendicular to the surface
of precursor device 1 can reduce the contact area between mask 2b
and that device. This may result in separation of the semiconductor
material positioned just below etch mask 2a in the vicinity 1A, and
as a result etch mask 2a can lift away from the precursor
device.
[0007] Separation of an etch mask may damage the semiconductor
device beyond repair for its intended use. Thus for the structure
illustrated in FIG. 1, separation of the mask may limit the
usefulness of surrounding areas or even the entire device, and
further processing may result in a defective product. Detection of
potentially defective products is difficult, and usually does not
occur until later in the manufacturing process. The delay and
additional processing results in an increase in manufacturing
costs.
[0008] As described above, the separation of etch masks in
manufacturing of a semiconductor device has been a serious
problem.
[0009] Japanese Unexamined Patent Publication No. Hei. 9-232682
discloses one method that addresses the problem of separation. The
etching process of that method is performed by the use of a etch
mask in which all ends of the adjacent linear mask 2b have been
connected and integrated as shown in prior art FIG. 3, or with an
etch mask in which a linear mask perpendicular to all linear masks
2b has been provided on each linear mask 2b shown in FIG. 3, as
shown in prior art FIG. 4.
[0010] However effective these techniques are in the prevention of
separation of the etch mask, other problems result from its use.
One problem that may occur from the use of an etch mask is a
variation in etch rate. At the point where adjacent linear masks
are connected to each other, a smooth flow of etchant is
suppressed. The resultant variation in etch rate can result in an
unacceptable variation of the dimensional accuracy of the
device.
[0011] Another problem is defectiveness in layer formation when
another semiconductor material has been laminated as a layer after
etching. For example, in the manufacturing of a light-emitting
semiconductor device, when a mesa stripe formed by etching is
formed as a current contracted portion, a current blocking layer
needs to be grown on the side of this current contracted portion,
that is, an etched portion. However, a desired current blocking
layer is difficult to grow in the periphery where adjacent linear
masks are connected to each other, that is, an end portion of the
mesa stripe.
SUMMARY OF THE INVENTION
[0012] An aspect of the present invention is to provide an etch
mask that can prevent separation of the etch mask in the vicinity
of an end portion of an etch mask.
[0013] To attain the above-mentioned aspect, the present invention
provides a etch mask formed on a surface of a material to be etched
comprising collected linear masks, where a portion of the linear
mask in the vicinity of an end portion of the etch mask or in the
vicinity of an end portion of the material to be etched has a wider
portion or a zigzag-shaped portion as compared with the remaining
portions.
[0014] It is one aspect of the present invention to provide an etch
mask on a material to be etched comprising an elongated portion,
and an end member connected to said elongated portion, where the
width of said elongated portion adjacent to said end member is an
end width, where said end member has a maximum extent measured in
the direction of said end width, and where said maximum extent of
said end member is greater than said end width.
[0015] It is another aspect of the present invention to provide a
mask pattern comprising a plurality of portions on a material to be
etched, said plurality of portions including two end portions, and
an elongated portion disposed between said two end portions, where
in the vicinity of said two end portions, said elongated portion
has an end width, said end portion has a maximum extent measured in
the direction of said end width, and where said maximum extent is
greater than said end width.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a partial top plan view showing one example 2a of
a conventional stripe-shaped etch mask;
[0017] FIG. 2 is a partial cross-sectional view taken along the
line II-II in FIG. 1;
[0018] FIG. 3 is a top plan view of an etch mask disclosed in
Japanese Unexamined Patent Publication No. Hei. 9-232682;
[0019] FIG. 4 is a top plan view of another etch mask disclosed in
Japanese Unexamined Patent Publication No. Hei. 9-232682;
[0020] FIG. 5 is a partial top plan view showing one example 12a of
a stripe-shaped etch mask according to the present invention;
[0021] FIG. 6 is a partially enlarged view in the vicinity of an
end portion of the etch mask 12a;
[0022] FIG. 7 is a schematic diagram showing the etch mask 12a of
the present invention with a material to be etched;
[0023] FIG. 8 is a partial top plan view showing another example
22a of a stripe-shaped etch mask according to the present
invention;
[0024] FIG. 9 is a partial top plan view showing another
stripe-shaped etch mask 32a according to the present invention;
[0025] FIG. 10 is a partial top plan view showing still another
stripe-shaped etch mask 32a according to the present invention;
[0026] FIG. 11 is a sequence of cross-sectional views showing the
procedures of forming a mesa stripe on a surface of a material to
be etched using the stripe-shaped etch mask of the present
invention;
[0027] FIG. 12 is a partially cutaway perspective view showing a
laminated structure of a DFB laser device;
[0028] FIG. 13 is a sequence of cross-sectional views showing the
procedures of forming a diffraction grating of a semiconductor
substrate; and
[0029] FIG. 14 is a partial top plan view showing an example of a
diffraction grating-shaped etch mask according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] One example of a etch mask 12a according to the present
invention will be described with reference to FIGS. 5 and 6, which
show a partial top plan view showing an etch mask 12a formed on a
surface 1a of a material 1 to be etched.
[0031] Reference to the material to be etched in the present
invention refers to material having a surface with an etch mask
covering at least a portion of the surface. Material to be etched
includes for example, a semiconductor material, an insulating
material, and a conducting material. Further, the material to be
etched includes a precursor device in which various semiconductor
materials have been laminated on a substrate.
[0032] Etch mask 12a comprises a plurality of linear masks 12b,
each having predetermined line widths and lengths and separations,
and formed on a surface of the material 1. The pattern of etch mask
12a shown in the Figures are illustrative, and are not meant to
limit the claims of the present invention.
[0033] As shown in FIGS. 5 and 6, etch mask 12a in the vicinity 1A
of an end portion of the material 1 has a wider portion 12c. The
area of wider portion 12c selected to provide protection from
separation due to undercutting as described in the prior art.
[0034] In one embodiment, the width W of wider portion 12c is wider
than a line width Ws of another portion of the linear mask 12b, as
shown in FIG. 6. FIG. 7 shows the extent of undercutting due to
isotropic etching as dashed lines. Even after undercutting of mask
12c, a material Id remains in contact with the mask. The greater
contact area near the end of mask 12c acts to inhibit or prevent
separation of the mask from material 1. Accordingly, the separation
of the entire wider portion 12c from the surface of the material 1
to be etched does not occur often. To allow such effects to occur,
it is preferable that the width W of the wider portion 12c be two
times or more as large as the line width Ws of another portion.
[0035] The size of wider portion 12c is limited by some practical
considerations. When the wider portion 12c is too wide, the spacing
between masks 12b increases and the number of the linear masks 12b
which can be formed on the surface of material 1 becomes small.
Also, the wider portion 12c may suppress the smooth flow of etchant
in the vicinity of the wider portion 12c. If crystalline growth is
subsequently preformed on material 1 then the width of the mask may
affect deposition as well. Thus, for example, for MOCVD, a line 5
.mu.m width Ws and a 100 .mu.m width W disturbs the distribution of
deposition precursors to the extent that it is difficult to get a
good crystal quality using MOCVD method.
[0036] The shape of materials 1 to be etched may include a circular
shape, a rectangular shape and the like. Further, the kinds of the
materials 1 to be etched may include, but are not limited to, InP
based semiconductors, GaAs based semiconductors, and GaP based
semiconductors, insulating materials such as sapphire, quartz,
diamond, and SiN, and various conducting materials.
[0037] When the material 1 to be etched is a laminated structure of
semiconductor materials, it may be comprised of a single layer or a
plurality of layers. The laminated materials may include, but are
not limited to, a III-V group compound semiconductor and/or a II-VI
group compound semiconductor such as InP, GaAs, AlGaAs, GaP,
InGaAs, AlInGaP, GaInP, GaInAsP, GaN, ZnSe and CdTe.
[0038] Additionally, the material of the above-mentioned etch mask
12a may include, but is not limited to, any one of silicon nitride,
silicon oxide, silicon oxynitride and photo-sensitive resist is
preferable. Any one of these materials can be easily applied to the
formation of the etch mask 12a of the present invention, and the
reliability thereof is high.
[0039] FIG. 8 is a partial top plan view showing an example of
another etch mask 22a according to the present invention. Etch mask
22a comprises a plurality of collected linear masks 22b and is
formed on a surface of the material 1 to be etched. And portions in
each linear mask 22b positioned in the vicinity 1A of end portions
of the material 1 have wider portions 22c.
[0040] In addition to wider portions 22c at the ends of mask 22b,
as described previously, etch mask 22a has an additional wider
portion 22d disposed between the ends of the mask. In the
embodiment shown in FIG. 8, wider portion 22d equally divides the
linear mask in the longitudinal direction.
[0041] The positions and number of wider portions 22d are
appropriately selected so that the separation of etch mask 22a can
be prevented. The formation of such wider portions 22d can enhance
the adhesion force between the etch mask 22a and the material 1 to
be etched just below the etch mask 22a by increasing the contact
area there between even in a case where the line width of each
linear mask 22b is small.
[0042] FIG. 9 is a partial top plan view showing an example 32a of
another etch mask embodiment of the present invention. This etch
mask 32a has a plurality of linear masks 32b each having zigzag
shapes in a top plan view in portions 32c positioned in the
vicinity 1A of the end portions of the material 1 to be etched.
Specifically, the end 32c of the etch mask 32a is formed such that
the mask end having the same width as the line width Ws of the
linear mask 32b is folded zigzag from side to side a plurality of
times (the zigzag is shown as being folded three times, as an
example, in FIG. 9).
[0043] The total elongated length of the zigzag portion in the end
32c, that is the length obtained by the addition of lengths of all
zigzag portions, is longer than the linear distance (L.sub.0) of
the linear mask 32b and the end portion of the etch mask 32a. In
other words, the contact area between the end 32c and the material
1 to be etched becomes larger than that in a case the associated
end is linear-shaped.
[0044] Etching of etch mask 32a advances from the end portion of
the etch mask during the etching process, decreasing the contact
area between mask and material to be etched. However, the contact
area per unit length in the end 32c is larger than that of a simple
linear shape, providing additional resistance of separation. At the
same time, the advance of he separation is stopped at the folded
portions in the zigzag portions. As a result, the separation of
etch mask 32a is suppressed.
[0045] A preferred etch mask 32a shape that is effective in
suppressing separation is one with a total elongated length of the
zigzag portions 32c that is two or more times the line width Ws of
the linear mask 32b.
[0046] As with the previous embodiments, there are some limitations
on the size of the end or enlarged portions. If the total elongated
length of the zigzag portions is too long, the length of the linear
masks 32b that can be formed on the entire surface of the material
1 to be etched becomes to short to be useful. Further, since a
smooth flow of etchant in the vicinity of the folded portions is
suppressed, which may present processing uniformity problems. As
discussed previously, the subsequent deposition may be affected as
well, though the zigzag portion 32c tends to have less of an effect
on deposition than does the wider portion 12c.
[0047] Additional variations on the zigzag mask are possible. Thus,
for example, a middle portion of the linear mask may be modified to
include a zigzag portion, as shown in FIG. 10.
[0048] In addition to the above-mentioned formation of a mesa
stripe, the mask of present invention can be used in the
preparation of a diffraction grating in a distributed feedback
(DFB) laser device, will be described.
[0049] A typical mesa stripe width is usually 1 .mu.m to several
tens .mu.m level. However, the period of the diffraction grating
formed in the DFB laser device is usually several hundreds of
nanometers level, and the line width of one linear mask may be in
the range of several tens nanometers to several hundreds
nanometers.
[0050] The separation phenomenon of the mesa stripe etch mask
almost occurs during etching steps after the etch mask has been
formed. However, since the line width of the etch mask used in the
formation of a diffraction grating is significantly narrow, the
adhesion properties between an etch mask and a semiconductor
substrate is deteriorated and such problems often occur that the
associated etch mask is separated even in the steps of forming the
etch mask.
[0051] When an etch mask for a diffraction grating is formed, a
negative resist is applied to a semiconductor substrate (a material
to be etched) and usually subjected to heat treatment, and then a
desired pattern of a diffraction grating is patterning-exposed with
an electron beam drawing device. After that, the patterning-exposed
portion is cross-linking-cured and is subjected to a developing
process by an alkali solution so that non-patterned portions are
removed by dissolution to form a diffraction grating-shaped stripe
of resist.
[0052] Finally, dry etching is conducted, for example, and a
diffraction grating having a desired period and a line width is
patterned on a semiconductor substrate (a material to be
etched).
[0053] In this series of formation processes, the resist is etched
by an alkali solution during the above-mentioned developing, and
the dissolution of the resist advances from an end of the resist.
Separation of the resist thus proceeds from the end of the
resist.
[0054] As explained above, an etch mask having a wider portion or a
zigzag portion near its end is effective in suppressing separation
of the resist and greatly improves the ability to form diffraction
gratings and other devices. In particular, separation is prevented
by increasing the width of the wider portion or by lengthening the
zigzag portion. However, if the width of the wider portion is too
wide, the width becomes larger than a desired period of the
diffraction grating. Accordingly, the end portions of the resists
(linear masks) become close to each other or connected to each
other and proper etching in the later dry etching steps is
suppressed and further, desired crystalline growth is not conducted
in the later layer laminating steps. Further, if the length of the
zigzag portion is too long, an appropriate diffraction grating
cannot be formed. For such reasons, the upper limits are properly
determined.
EXAMPLES
Examples 1 to 8 and Comparative Examples 1 and 2
[0055] By the use of an etch mask according to the present
invention, a mesa stripe was formed as follows. First, as shown in
FIG. 11(a), a surface of a material 1 to be etched having a
semiconductor laminate structure containing an active layer was
sufficiently subjected to a pretreatment. Typical pretreatment
includes an acid bath, followed by a rinse and drying with nitrogen
gas. Acid baths can include on or more of phosphoric acid,
hydrochloric acid, and sulfuric acid. Then a 100 nm thick SiN.sub.x
film 2 was formed by a plasma CVD process.
[0056] After pretreatment, a known photoresist was applied onto the
SiN.sub.x film 2 to form a 1.5 .mu.m thick resist film 3 (FIG.
11(b)). Then, by applying a known photolithography technique to the
resist film 3, resist masks 3a corresponding to the etch mask 12a
or 22a shown FIG. 5 or 8 respectively in the top plan view were
patterned (FIG. 11(c)). Subsequently, as shown in FIG. 11(d), an
SiN.sub.x film 2 positioned at a portion other than just below the
resist mask 3a was etched by an RIE (Reactive Ion Etching) process
and the entire resist mask 3a was removed whereby various
stripe-shaped mask bodies 12a (22a) shown in Table 1 were formed on
the surface 1a of the material 1 to be etched (FIG. 11(e)).
[0057] Then, the resultant structure was transferred to an etching
step and exposed material portions, which were not covered with
stripe-shaped mask bodies 12a (22a), were etched to form mesa
stripes (current contracted portions) on the surface of a substrate
(FIG. 11(f)).
[0058] The state of separation in the stripe-shaped mask bodies 12a
(22a) was inspected immediately after the etching step. The
inspection results are shown in Table 1 together with the size
factors of the linear masks.
[0059] As apparent from Table 1, the separation or peeling of the
etch mask is significantly reduced or does not occur at all for
stripe-shaped mask bodies 12a (22a) having wider portions. Slight
separation was found only in a linear mask having no wider portion
in its middle portion. As explained above, the usefulness of
forming a wider portion in the middle portion of the mask is
clear.
1 TABLE 1 Presence or Size factors of linear masks absence of wider
Width of wider portion in Line width of portion in the State(*) of
the vicinity of end linear mask middle portion of separation just
after portion (W:.mu.m) (Ws:.mu.m) W/Ws linear mask etching step
Comp. example 1 4.5 4.5 1 Absent 10-20% separated Comp. example 2
3.0 3.0 1 Absent 10-30% separated Example 1 9.0 4.5 2 Absent Not
separated Example 2 9.0 4.5 2 Present Not separated Example 3 6.0
3.0 2 Absent Not separated Example 4 6.0 3.0 2 Present Not
separated Example 5 6.75 4.5 1.5 Absent 5% or less separated
Example 6 6.75 4.5 1.5 Present 2% or less separated Example 7 4.5
3.0 1.5 Absent 7% or less separated Example 8 4.5 3.0 1.5 Present
3% or less separated (*)indicated by the percentage of the number
of separated mask bodies to the number of mask bodies formed
Examples 9 to 18 and Comparative Examples 3 to 6
[0060] To form a DFB laser device shown in FIG. 12, an n-InP buffer
layer 42, an MQW-SCH layer 43, and an under portion 44A of a spacer
layer of p-InP were sequentially laminated on an n-InP substrate
41, and diffraction gratings were formed on the under portion 44A
of the spacer layer as will be described later. Note that a
laminated structure from the substrate 41 to the under portion 44A
of the spacer layer is referred to as a material 1 to be
etched.
[0061] As shown in FIG. 13(a), an about 100 nm thick electron beam
drawing negative-type resist 4 was applied onto the material 1 to
be etched with a spin coater, followed by heat treatment.
[0062] Then, by the use of an electron beam drawing device, a
diffraction grating pattern was drawn on the negative-type resist 4
as shown in FIG. 13(b). The resultant drawn pattern is shown in
FIG. 14. After that a predetermined heat treatment and developing
process were performed, and portions of a unexposed resist were
removed to expose the surfaces 1a of the material to be etched as
shown in FIG. 13(c). Then, dry etching was conducted to pattern a
diffraction grating 5 as shown in FIG. 13(d).
[0063] The size factors of the resultant diffraction grating 5 are
shown in Table 2. Also the state of peeling or separation of a
resist (etch mask) just after a developing process is also shown in
Table 2.
[0064] As apparent from Table 2, separation is reduced more
significantly than in Examples 3 to 6, with wider portions having
little or no separation. Specifically, when the width (Wy) of the
wider portion is set to two times or more the line width (Wx) of
the linear mask, no separation occurs.
2 TABLE 2 Size factors of linear masks Width of wider Pitch between
Line width of portion in the diffraction Length of State(*) of
linear mask vicinity of end gratings linear mask separation just
after (Wx:nm) portion (Wy:nm) (Wz:nm) (Wp:.mu.m) etching step Comp.
example 3 100 100 300 20 About 20% separated Comp. example 4 50 50
300 20 80% or more separated Comp. example 5 100 100 500 20 About
20% separated Comp. example 6 50 50 500 20 80% or more separated
Example 9 100 150 300 20 None Example 10 100 200 300 20 None
Example 11 50 75 300 20 5% or less separated Example 12 50 100 300
20 None Example 13 50 150 300 20 None Example 14 100 150 500 20
None Example 15 100 200 500 20 None Example 16 50 75 500 20 5% or
less separated Example 17 50 100 500 20 None Example 18 50 150 500
20 None (*)indicated by the percentage of the number of separated
mask bodies to the number of mask bodies formed
[0065] While the above examples describe the use of a dry etching
process, wet etching may be used. If the etchant of wet etching
does not chemically react on the negative resist, then no SiN.sub.x
underlayer may be required. If the wet etchant chemically reacts
with the negative resist, then a SiN.sub.x underlayer may be
required. As an example of processing in this case, the mask is
prepared by photolithography. A dry RIE step is then used to etch
the SiN.sub.x layer, followed by wet etching of the patterned
substrate.
Examples 19 to 26 and Comparative Examples 7 and 8
[0066] Various stripe-shaped mask bodies were formed on a material
to be etched in the same manner as in Examples 1 to 8, except that
the etch mask was the etch mask 32a shown in FIG. 9 and the etch
mask shown in FIG. 10. The resultant structure was transferred to
an etching step. Then, the exposed portions not covered with the
stripe-shaped etch mask were etched to form mesa stripes (current
contracted portions) on the surface of a substrate.
[0067] The state of peeling or separation in the stripe-shaped mask
bodies was inspected just after the etching step. The inspection
results are shown in Table 3 together with the size factors of the
linear masks.
[0068] As apparent from Table 3, the separation of the etch mask
was significantly reduced or did not occur at all for stripe-shaped
mask bodies having zigzag portions.
3 TABLE 3 Size factors of linear masks Presence or absence Line
width of Total elongated of wider portion in State(*) of linear
mask length of the zigzag the middle portion of separation just
after (Ws:.mu.m) portions (L:.mu.m) L/Ws linear mask etching step
Comp. example 7 4.5 -- -- Absent 10-20% separated Comp. example 8
3.0 -- -- Absent 10-30% separated Example 19 3.0 6.0 2 Absent 2% or
less separated Example 20 3.0 6.0 2 Present Not separated Example
21 3.0 15.0 5 Absent Not separated Example 22 3.0 15.0 5 Present
Not separated Example 23 4.5 9.0 2 Absent 2% or less separate
Example 24 4.5 9.0 2 Present Not separated Example 25 4.5 22.5 5
Absent Not separated Example 26 4.5 22.5 5 Present Not separated
(*)indicated by the percentage of the number of separated mask
bodies to the number of mask bodies formed
[0069] After the etching process, all mask bodies were transferred
to a cleaning step and the state of separation in the mask bodies
just after the cleaning step was inspected. Slight separation was
observed only in a linear mask having no wider portion at the
middle portion. Based on the fact, as explained above, the
usefulness of forming a zigzag portion in the middle portion of the
mask is clear. As described above, according to the etch mask of
the present invention, by forming a wider portion or a zigzag
portion in a linear mask positioned in the vicinity of an end
portion of a material to be etched, or if necessary by forming a
wider portion or a zigzag portion in at least one portion other
than the portion in the vicinity of the end portion, the separation
of the etch mask in an etching step and the following cleaning step
can be prevented, and at the same time, the occurrence of etching
variations in the etching step and the layer defects in the layer
laminating step after the etching step can be prevented.
[0070] By the above-described effects, the yield in manufacturing
the semiconductor device can be enhanced and the cost reduction
(working man-hour, costs in members and the inspection costs) can
be realized. Further, an array-structured device comprised of a
plurality of mesa stripes and a diffraction grating-built in DFB
laser device can be also stably manufactured.
* * * * *