U.S. patent application number 11/273769 was filed with the patent office on 2006-03-23 for micromachined structures made by combined wet and dry etching.
This patent application is currently assigned to Shipley Company, L.L.C.. Invention is credited to Jasean Rasnake, Dan A. Steinberg.
Application Number | 20060060564 11/273769 |
Document ID | / |
Family ID | 27372965 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060060564 |
Kind Code |
A1 |
Steinberg; Dan A. ; et
al. |
March 23, 2006 |
Micromachined structures made by combined wet and dry etching
Abstract
A micromachined structure, comprising: a substrate; a first wet
etched pit disposed in the substrate; a second wet etched pit
disposed in the substrate, the second pit extending into the
substrate a greater depth than the first pit; and a dry pit
disposed between, and adjacent to, the first and second pits. Also
disclosed is a micromachined substrate comprising: a wet etched
pit; and a dry-etched hole disposed in the wet etched pit, wherein
the dry hole extends through the substrate.
Inventors: |
Steinberg; Dan A.;
(Blacksburg, VA) ; Rasnake; Jasean; (Blacksburg,
VA) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
P.O. BOX 55874
BOSTON
MA
02205
US
|
Assignee: |
Shipley Company, L.L.C.
|
Family ID: |
27372965 |
Appl. No.: |
11/273769 |
Filed: |
November 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10076858 |
Feb 14, 2002 |
6964804 |
|
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11273769 |
Nov 16, 2005 |
|
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60269011 |
Feb 14, 2001 |
|
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60269010 |
Feb 14, 2001 |
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Current U.S.
Class: |
216/41 ; 216/52;
219/94 |
Current CPC
Class: |
B81C 2201/0132 20130101;
B81B 2203/033 20130101; B81B 2203/0315 20130101; B81C 1/00103
20130101; G02B 6/3692 20130101; Y10T 428/249978 20150401; G02B
6/4204 20130101; Y10T 428/24355 20150115; B81C 2201/0133
20130101 |
Class at
Publication: |
216/041 ;
216/052; 219/094 |
International
Class: |
C23F 1/00 20060101
C23F001/00; B44C 1/22 20060101 B44C001/22; B23K 11/00 20060101
B23K011/00 |
Claims
1-14. (canceled)
15. A method for micromachining a substrate, comprising: providing
a hard mask on a selected portion of the substrate to provide a
region of the substrate without a hard mask; removing a portion of
the substrate adjacent the region without the hard mask using one
or more of ultrasonic drilling, laser etching, sawing and
electrochemical etching to provide a micromachined feature in the
substrate; and wet etching the substrate to provide a wet etched
feature adjacent to the micromachined feature.
16. The method according to claim 15, comprising providing a
fugitive material in the micromachined feature prior to wet etching
the substrate.
17. The method according to claim 16, wherein the fugitive material
comprises one or more of a polymer, wax, and photoresist.
Description
RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Patent Application Nos. 60/269,011 filed on Feb. 14,
2001 and 60/269,010 filed on Feb. 14, 2001, which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to micromachining.
More particularly, the present invention relates to a new method
for combining directional ion etching and anisotropic wet etching.
The present invention is particularly applicable to silicon
micromachining.
BACKGROUND OF THE INVENTION
[0003] Silicon optical bench chips often have anisotropically
etched grooves for holding optical fibers or other components.
Also, SiOB chips can have dicing saw cuts that function as fiber
stops, thereby providing passive longitudinal alignment for an
optical fiber. Such optical bench chips are well known in the
art.
[0004] In some cases, it is not desirable or practical to have
dicing saw cuts. Particularly, dicing saw cuts can be undesirable
because they typically must extend across an entire wafer. It would
be an advance in the art to provide fiber stops in optical bench
chips without requiring dicing saw cuts. Also, it would be an
advance in the art of micromachining to provide a wider array of
precision-made structures. Particularly, it would be advance to
combine multiple micromachining techniques to provide unusual,
useful structures.
SUMMARY OF THE INVENTION
[0005] The present invention provides a micromachined structure,
comprising: a substrate; a first wet etched pit disposed in the
substrate; a second wet etched pit disposed in the substrate, the
second pit extending into the substrate a greater depth than the
first pit; and a dry pit disposed between, and adjacent to, the
first and second pits. The present invention also provides a
micromachined substrate comprising: a wet etched pit; and a
dry-etched hole disposed in the wet etched pit, wherein the dry
hole extends through the substrate.
[0006] In a further aspect of the present invention, a method for
micromachining a substrate is provided, comprising: providing a
hard mask on a selected portion of the substrate to provide a
region of the substrate without a hard mask; removing a portion of
the substrate adjacent the region without the hard mask using one
or more of ultrasonic drilling, laser etching, sawing and
electrochemical etching to provide a micromachined feature in the
substrate; and wet etching the substrate to provide a wet etched
feature adjacent to the micromachined feature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The foregoing summary and the following detailed description
of the preferred embodiments of the present invention will be best
understood when read in conjunction with the appended drawings, in
which:
[0008] FIG. 1 illustrates a top view of an exemplary structure in
accordance with the present invention having two flat, planar
surfaces that are both parallel with the substrate surface and a
dry pit disposed between the planar surfaces;
[0009] FIG. 2 illustrates a cross-sectional view of the structure
of FIG. 1;
[0010] FIG. 3 illustrates the structure of FIG. 2 with a VCSEL
disposed on the deeper flat surface;
[0011] FIG. 4 illustrates a top view of another exemplary structure
in accordance with the present invention having two flat, planar
surfaces and a linear dry pit disposed between the planar
surfaces;
[0012] FIGS. 5 and 6 illustrate top views of further exemplary
structures in accordance with the present invention having two
flat, planar surfaces and a dry pit having curved boundaries
disposed between the planar surfaces;
[0013] FIG. 7 illustrates a top view of an exemplary structure in
accordance with the present invention having a V-groove with a
fiber stop and a wet-etched pit for retaining a ball lens;
[0014] FIG. 8 illustrates a top view of the structure of FIG. 7
with an optical fiber in the V-groove and a ball lens in the
pit;
[0015] FIGS. 9 and 10 illustrate a top view and a cross-sectional
view taken along the line A-A in FIG. 9, respectively, of an
exemplary structure in accordance with the present invention having
a wet etched pit disposed within another wet etched pit with a
ring-shaped dry pit disposed therebetween;
[0016] FIGS. 11 and 12 illustrate a top view and a cross-sectional
view taken along the line A-A in FIG. 11, respectively, of an
exemplary structure in accordance with the present invention having
a U-shaped dry pit disposed within a wet etched pit to provide a
wedge in the wet etched pit;
[0017] FIGS. 13 and 14 illustrate a top view and a cross-sectional
view taken along the line A-A in FIG. 13, respectively, of another
exemplary structure in accordance with the present invention having
a U-shaped dry pit disposed within a wet etched pit to provide a
wedge in the wet etched pit that lies below the surface of the
substrate;
[0018] FIGS. 15 and 16 illustrate a top view and a cross-sectional
view taken along the line A-A in FIG. 15, respectively, of an
exemplary structure in accordance with the present invention having
two U-shaped dry pits disposed within a wet etched pit to provide
two wedges in the wet etched pit;
[0019] FIG. 17 illustrates a top view of an exemplary structure in
accordance with the present invention having a plurality of wet
pits each having a micromachined hole disposed therethrough;
[0020] FIG. 18 illustrates a cross-sectional view of one of the wet
pits and through-holes of FIG. 17 taken along the line A-A in FIG.
17;
[0021] FIG. 19 illustrates a top view of an exemplary structure in
accordance with the present invention having a plurality of wet
pits each having an off-center micromachined hole disposed
therethrough;
[0022] FIG. 20 illustrates a top view of an exemplary structure in
accordance with the present invention having V-grooves with a
plurality of micromachined holes disposed therethrough;
[0023] FIGS. 21A-21H illustrate a method for making structures in
accordance with the present invention;
[0024] FIGS. 22A-21E illustrate additional, optional steps for use
with the method illustrated in FIGS. 21A-21H;
[0025] 23A-23G illustrate another method for making structures in
accordance with the present invention;
[0026] 24A-24G illustrate a further method for making structures in
accordance with the present invention; and
[0027] 25A-25E illustrate a yet further method for making
structures in accordance with the present invention.
DETAILED DESCRIPTION
[0028] The present invention provides novel micromachined
structures made by combined wet/dry etching. The structures can be
used in a variety of micromachined devices, including micro-optical
submounts and the like. For example, referring now to the figures,
wherein like elements are numbered alike throughout, FIGS. 1 and 2
illustrate an exemplary structure 100 in accordance with the
present invention comprising two wet pits 10, 20 disposed in a
substrate 40 with a dry pit 30 disposed between the two wet pits
10, 20. Each wet pit 10, 20 includes a corresponding flat, planar
surface 12, 22 that is parallel with an upper substrate surface 15.
As provided in the exemplary structure of FIGS. 1 and 2, the flat
surfaces 12, 22 may be located at different depths within the
substrate 40. For example, the flat surface 22 of the second wet
pit 20 may be deeper than flat surface 12 of the first wet pit 10.
As provided by the methods described below, the dry pit 30 is
desirably etched before the wet pits 10, 20, with the dry pit 30
being coated with a mask layer before the wet pits 10, 20 are
etched.
[0029] The structure 100 is particularly useful in an application
where a VCSEL or photodetector is disposed on the flat surface 22
of the second wet pit 20, because planar electrical connections 27
(e.g., wire bonds) can be made between the flat surface 12 of the
first wet pit 10 and the VCSEL 25, as illustrated in FIG. 3. Planar
electrical connections are desirable because they have better
characterized impedance characteristics than wire bonds that extend
between two different levels.
[0030] FIGS. 1-3 illustrate a first exemplary structure 100 in
accordance with the present invention. However, there are various
configurations of dry and wet pits that can provide wet pits that
have flat surfaces at different depths. For example, as illustrated
in FIG. 4, the dry pit 430 may comprise a straight line trench that
is disposed between two wet pits 410, 420 to provide flat surfaces
412, 422 disposed at different depths. The dry pit 430 maybe
created by dry-etching or a dicing saw cut, for example.
Alternatively, as shown in FIG. 5, the dry pit 530 may comprise
curved sidewall portions 538 disposed between two wet pits 510,
520. However, if the curved sidewall portions 638 are too tightly
curved, wedges 639 maybe formed between the wet pits 610, 620, as
illustrated in FIG. 6.
[0031] In another aspect of the present invention, a structure 700
for coupling an optical fiber 750 and a ball lens 760 is provided,
as illustrated in FIGS. 7 and 8. The structure 700 comprises a
V-groove 710 with a fiber stop 711 and a wet-etched pit 720 for a
ball lens 760.
[0032] In yet another aspect of the present invention, a structure
900 for use as a silicon optical bench can be provided, as
illustrated in FIGS. 9 and 10. An interior wet etched pit 910 can
be formed within an exterior wet etched pit 920 with a ring-shaped
dry pit 930 disposed therebetween. The exterior wet etched pit 920
can have a flat bottom surface 932. The interior wet pit 910 can
hold a ball lens, and the flat bottom surface 932 of the exterior
pit 930 can be used to hold optical devices such as switches or
filters.
[0033] In still another aspect of the present invention, a wedge
1190 is provided on the flat bottom 1115 of a wet etched pit 1110,
as illustrated in FIG. 11. In order to form the wedge 1190, a
U-shaped dry pit 1130 is dry etched or machined and coated with a
hard mask. As illustrated in FIGS. 13 and 14, the U-shaped dry pit
1330 may be shaped so that the size of the wedge 1390 may be
limited by the size of the U-shaped pit 1330. In this case, the top
corner 1392 of the wedge 1390 will be located below the substrate
surface 1315. In yet a further aspect of the invention, multiple
U-shaped areas 1590, 1591 can be combined to form a V-groove 1595
or similar shapes in a flat-bottom pit 1510, as shown in FIG.
15.
[0034] The present invention also provides a 2-D fiber array 1700,
as shown in FIGS. 17 and 18. The fiber array 1700 includes holes
1730 that are drilled or etched or machined (e.g., by reactive ion
etching, ultrasonic drilling, laser drilling, laser machining, or
electrodischarge machining) into a substrate 1740. The holes 1730
are then coated with a hard mask material (e.g., SiO.sub.2 or Si
nitride). Then, the substrate 1740 is wet-etched. The wet etching
step can form a wet pit 1710 around each hole 1730. Alternatively,
the wet pit can have the shape of a V-groove 2010 and can include a
row of holes 2030 disposed therein, as shown in FIG. 20. The
V-groove 2010 provides passive alignment in one direction when
aligning the optical fibers with the holes 2030.
[0035] The wet pit 1710 associated with each hole 1730 acts as a
funnel for guiding an optical fiber into the hole 1730. In this
way, the assembly process of a fiber array is simplified. It is
noted that the holes 1710 can be located off-center within each wet
pit 1730, as shown in FIG. 19. Having off-center holes can be
useful for locating the fibers in cases where the fibers are guided
into the holes from one direction (e.g., from the right side in
FIG, 19).
[0036] The present invention also provides several methods for
creating the above-described structures. For example, with to
reference FIGS. 21A-21H, a method in accordance with the present
invention is illustrated. First, a hard mask layer 2142 (e.g.,
nitride) is deposited and patterned on a substrate 2140, such as a
silicon wafer, FIG. 21A. The hard mask layer 2142 does not cover
areas of the substrate 2140 to be wet etched. The hard mask layer
2142 may partially cover areas to be machined (i.e., ultrasonically
drilled, electrochemically etched, sawed, etc.), provided that the
machining process can remove the hard mask material. Subsequently,
a coating 2144 of CVD oxide, PSG or BPSG is provided as shown in
FIG. 21B. Then, the machining process is performed to provide a pit
2110, FIG. 21C. The machining process can be any process that
removes substrate material. The machining process should be able to
cut through the hard mask layer 2142 and oxide layer 2144. After
the machining, a coating of CVD nitride 2146 is provided, as shown
in FIG. 21D. Next, nitride 2146 is removed from the top surface
2145 by planarization, FIG. 21E. Then the oxide 2144 is removed by
a dilute HF etch, for example, FIG. 21F, and the substrate 2140 is
wet etched, FIG. 21G. Finally, hard mask layer 2142 and CVD nitride
2146 is removed, FIG. 21H.
[0037] Optionally, after the step of FIG. 21D, the pit 2110 can be
filled with a fugitive mask material 2148 that resists nitride
etches (e.g., wax, polymer or photoresist), FIG. 22A. After filling
the pit 2110, the nitride layer 2146 on the upper surface 2145 is
removed by etching, FIG. 22B. Subsequently, the oxide layer 2144 is
etched away, FIG. 22C. Then the substrate 2140 is wet etched, FIG.
22D. Finally, the fugitive mask material 2148, nitride layer 2146,
and hard mask 2142 are removed, FIG. 22E.
[0038] Combined wet and dry etching can be performed according to a
number of different methods. The dry pit can be coated with CVD
nitride or oxide, or can be thermally oxidized. The present
invention can be used with silicon or other materials (e.g., GaAs)
that can be dry etched and wet etched (isotropic or anisotropic)
and can be conformally coated with a mask material.
[0039] For example, referring to FIGS. 23A-23G, another method in
accordance with the present invention is provided. First, an
SiO.sub.2 layer 2342 and a nitride layer 2344 are deposited and
patterned over a substrate 2340, such as a silicon wafer, to
provide the structure shown in FIG. 23A. The SiO.sub.2 layer 2342
should be thick enough to serve as a mask during the dry etch step
(e.g., the SiO.sub.2 layer 2342 can be about 2 microns thick for a
100 micron deep dry pit 2310). The patterns in the SiO.sub.2 layer
2342 and nitride determine the wet and dry etch areas as shown in
FIG. 23A. Next, the dry pit 2310 is formed. The dry pit 2310 can be
formed by reactive ion etching, plasma etching, ion milling or any
other directional process, FIG. 23B. Then, the substrate 2340 is
thermally oxidized to yield the structure shown in FIG. 23C. The
sidewalls are necessarily oxidized in this step to provide a
sidewall oxide 2312. The thermal oxidation step causes the
SiO.sub.2 layer 2342 to thicken in areas outside of the nitride
layer 2344. Afterwards, the nitride layer 2344 is removed, FIG.
23D, which can be done with a wet etch. A short duration oxide etch
(wet or dry) removes the SiO.sub.2 layer 2342 that was under the
nitride layer 2344 to yield the structure shown in FIG. 23E. The
other SiO.sub.2 layer areas not under the nitride layer 2344 remain
intact because they are thicker. Next, the substrate 2340 is expose
to an anisotropic wet etch to yield the structure shown in FIG.
23F. KOH should not be used because it will attack the SiO.sub.2
layer 2342. EDP or TMAH can be used because they will not attack
the SiO.sub.2 layer 2342 as strongly. Then, the SiO.sub.2 layer
2342 and sidewall oxide 2312 are optionally removed, which can be
done in a dilute HF etch, FIG. 23G.
[0040] Referring now to FIGS. 24A-24G, yet another method in
accordance with the present invention is provided. First, a nitride
layer 2442 is deposited and patterned on a substrate 2440, such as
a silicon wafer. Then an oxide layer 2444 is deposited and
patterned to yield the structure shown in FIG. 24A. The oxide layer
2444 can be thicker than the nitride layer 2442. The oxide layer
2444 can comprise PSG or BPSG, for example. The nitride and oxide
patterns determine the wet and dry areas as shown in FIG. 24A.
Next, the dry pit 2410 is etched, to yield the structure shown in
FIG. 24B, which can be done with RIE, ion milling or similar
processes. Then, the substrate is conformally coated with CVD
nitride 2446, resulting in the structure of FIG. 24C, where the dry
pit 2410 is coated with nitride 2446. The substrate 2440 is then
planarized or polished so that CVD nitride 2446 is removed from the
top surface, FIG. 24D. Then the oxide layer 2444 is removed, FIG.
24E, which can be done with dilute HF. The exposed areas of the
substrate 2440 are then Wet etched, to provide the structure shown
in FIG. 24F. This can be done with KOH since the mask is made of
nitride. Optionally, the nitride layer 2442 and CVD nitride 2446
are removed with etchant that does not damage the silicon, FIG.
24G.
[0041] Referring now to FIGS. 25A-25G, still another method in
accordance with the present invention is provided. A hard mask
layer 2504 that blocks oxide formation (e.g., silicon nitride) is
deposited and patterned over a substrate 2540, such as a silicon
wafer, followed by depositing and patterning a photoresist layer
2504, resulting in the structure of FIG. 25A with the dry and wet
etch areas defined as shown. The photoresist layer 2504 does not
need to cover the entire hard mask layer 2504. The portion of the
substrate 2540 exposed by the photoresist layer 2504 and hard mask
layer 2504 is dry etched, FIG. 25B. Then the photoresist layer 2504
is removed and the substrate 2540 oxidized to provide an oxide
layer 2506, as shown in FIG. 25C. Oxide will not grow under the
hard mask layer 2502. Next, the hard mask layer 2502 is removed,
FIG. 25D. Subsequently, the substrate 2540 is wet-etched with an
anisotropic etchant, resulting in the structure of FIG. 25E.
Optionally, the oxide layer 2506 can be removed after the wet
etch.
[0042] These and other advantages of the present invention will be
apparent to those skilled in the art from the foregoing
specification. Accordingly, it will be recognized by those skilled
in the art that changes or modifications may be made to the
above-described embodiments without departing from the broad
inventive concepts of the invention. It should therefore be
understood that this invention is not limited to the particular
embodiments described herein, but is intended to include all
changes and modifications that are within the scope and spirit of
the invention as set forth in the claims.
* * * * *