U.S. patent application number 12/021210 was filed with the patent office on 2008-10-16 for angle control of multi-cavity molded components for mems and nems group assembly.
This patent application is currently assigned to Metadigm LLC. Invention is credited to Victory B. Kley.
Application Number | 20080254570 12/021210 |
Document ID | / |
Family ID | 38973863 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080254570 |
Kind Code |
A1 |
Kley; Victory B. |
October 16, 2008 |
ANGLE CONTROL OF MULTI-CAVITY MOLDED COMPONENTS FOR MEMS AND NEMS
GROUP ASSEMBLY
Abstract
A method of making a mold includes forming spaced mold cavities
in a mold body. The mold cavities include geometrically similar
portions, but have respective depths below an initial reference
surface that vary as a function of position along a particular
direction. The mold cavities can be formed using anisotropic
etching of preferred crystal directions in single crystal materials
such as silicon. A portion of the mold material adjacent the
initial reference surface is removed to expose a new reference
surface at a tilt angle with respect to the initial reference
surface. The modified mold cavities have their respective axes at a
new desired tilt angle relative to the new reference surface.
Inventors: |
Kley; Victory B.; (Berkeley,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Metadigm LLC
Berkeley
CA
|
Family ID: |
38973863 |
Appl. No.: |
12/021210 |
Filed: |
January 28, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11048611 |
Jan 31, 2005 |
7323111 |
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12021210 |
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11046526 |
Jan 28, 2005 |
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11048611 |
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60601274 |
Aug 12, 2004 |
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60544053 |
Feb 11, 2004 |
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60540940 |
Jan 30, 2004 |
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Current U.S.
Class: |
438/105 ;
249/114.1 |
Current CPC
Class: |
B81C 99/009 20130101;
B81C 99/004 20130101; B81C 1/00547 20130101; B81C 99/0085 20130101;
B81C 2203/054 20130101; B81C 3/005 20130101 |
Class at
Publication: |
438/105 ;
249/114.1 |
International
Class: |
H01L 21/00 20060101
H01L021/00 |
Claims
1-14. (canceled)
15. The structured use of a constant change in part depth when
creating molded or growth molded otherwise identical in at least
one structural element parts for a multiple cavity mold such that a
plane can intersect the lowermost portion of said parts, said plane
being the tilt angle plane of the final mold opening with respect
to the geometry of the parts.
16. The invention of claim 15 in which the mold is subsequently
machined or ground so as to form a new mold with the plane angle at
the mold opening.
17. The mold or growth mold of claim 15 on which a barrier film has
been attached which can prevent the etching process to free up the
molded part from causing damage to the bond or other structures
attached to the part of adjacent to it.
18. A mold in which the part is released by patterning the mold on
the back side away from the part side such that the minimum
material is removed sufficient to free up the part while supporting
the structure and any barrier film designed to limit the
distribution of the etchant.
19-22. (canceled)
23. An alignment system for bonding two wafers at specific bond
points with a material which has a specific bonding or welding
temperature with a combination of two more sets of self-terminated
pits and alignment shapes such that at or near the bond pressure
and temperature the bondable elements are brought into contact by
the deformation of the alignment shape or deformable coating or
both.
24. An assembly means for bonding wafers of parts in which one set
are cantilevers such that a preformed jig is used to support the
cantilevers for the bonding step.
25. A method as in 24 in which the combination of the jig and the
wafer carrying bondable elements to be joined to a cantilever cause
the cantilever to bend up or down creating a wedge of the bond
material and leaving the part with a characteristic angle due to
the bond wedge.
26-28. (canceled)
29. A molded or inserted material means in which a first means is
used to mold a base part and then the wafer is prepared by any
means including grinding, polishing, compress, or chemical etch and
a new pattern etched into the side opposite the first molded parts
and/or inserted parts so that these parts form a seed source to
fill up the cavities etched on the opposite side from the beginning
parts so as to form an complex integral assembly suitable for wafer
scale assembly or other use.
30. The method as in 29 wherein the parts are made of
polycrystalline or single crystal diamond and the wafers are
silicon.
31. The method of 29 in which the etched cavities are decreased in
diameter by growth of a native oxide by any means on the
silicon.
32. The method of 29 in which a diamond material is first cleaned
by use of a SF6 plasma gas etch to remove any remanant silicon
carbide.
33. The method of 29 in which the part material is boron nitride,
or silicon nitride or silicon carbide.
34-41. (canceled)
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 11/048,611, filed Jan. 31, 2005, issuing as U.S. Pat. No.
7,323,111 on Jan. 29, 2008 of Victor B. Kley for "Angle Control of
Multi-Cavity Molded Components for MEMS and NEMS Group Assembly,"
the entire disclosure of which is incorporated by reference
[0002] U.S. patent application Ser. No. 11/048,611 is a
continuation-in-part of U.S. patent application Ser. No.
11/046,526, filed Jan. 28, 2005, now abandoned, of Victor B. Kley
for "Angle Control of Multi-Cavity Molded Components for MEMS and
NEMS Group Assembly," the entire disclosure of which is
incorporated by reference
[0003] U.S. patent application Ser. No. 11/046,526 claims priority
to the following three provisional applications, the entire
disclosures of which are incorporated by reference: [0004] U.S.
Provisional Patent Application No. 60/540,940, filed Jan. 30, 2004
of Victor B. Kley for "Angle Control of Multi-Cavity Molded
Components for MEMS and NEMS Group Assembly"; [0005] U.S.
Provisional Patent Application No. 60/544,053, filed Feb. 11, 2004
of Victor B. Kley for "Angle Control of Multi-Cavity Molded
Components for MEMS and NEMS Group Assembly"; and [0006] U.S.
Provisional Patent Application No. 60/601,274, filed Aug. 12, 2004
of Victor B. Kley for "Angle Control of Multi-Cavity Molded
Components for MEMS and NEMS Group Assembly."
BACKGROUND OF THE INVENTION
[0007] The present invention relates generally to techniques for
molding parts and/or assembling parts and/or releasing parts from
molds, including the manufacture and processes for manufacture and
assembly of wafer molded and mold grown parts and their assembly on
a wafer scale to other parts for NEMS and MEMS. The present
invention relates more specifically to techniques for molding parts
using block multi-cavity molds and assembling these parts by a
mold-to-mold or mold-to-lithographically-constructed-part (or
machine) technique,
[0008] In the description that follows, reference will often be
made to diamond as the material being molded. It should be
understood that in general, the techniques apply to a variety of
other special materials (including cubic boron nitride, silicon
carbide, silicon nitride, titanium carbide, titanium nitride,
quartz, glass, silicon oxides, chrome and other metals, metal
carbides, nitrides, and magnetic and optical materials). Therefore,
references to "the diamond" or "the diamond tip" should be read
broadly unless the context suggests that diamond's unique
properties should limit the reference to diamond.
[0009] The use of silicon and other materials to mold or act as
growth substrates for diamond and other refractory or special
materials has been taught in earlier patent applications and issued
patents by this inventor, more particularly U.S. Pat. Nos.
6,144,028, 6,252,226, 6,337,479, 6,339,217, the entire disclosures
of which are incorporated by reference.
SUMMARY OF THE INVENTION
[0010] The present invention provides techniques, which while of
general applicability, find particular applicability to production
process for wafer-to-wafer assembly. Thus the invention provides
techniques for the precise assembly of semiconductor wafers used to
mold diamond or other special materials to other structures such as
cantilevers made of silicon, precision metal parts, glass or quartz
parts subject to semiconductor, MEMS, NEMS and related precision
manufacturing techniques.
[0011] While the specific embodiments generally contemplate molded
articles that are grown in the mold, various aspects of the
invention apply to other types of molded articles, regardless of
how the molded article is formed in the mold. Further, while some
embodiments exploit the use of self-terminating (also sometimes
referred to as self-limiting) etch processes, various aspects of
the invention do not require such etch processes.
Setting Bond Angles of Molded Parts
[0012] An aspect of the invention provides a technique for setting
a complex bond angle between the molded or mold grown part and the
structure to which it will be assembled as part of a group
assembly. The technique is typically limited only by the size of
the starting mold (diameter and thickness). A method of making a
mold includes forming a plurality of spaced mold cavities in a mold
body having an initial reference surface. The mold cavities include
geometrically similar portions, but have respective depths below
(into) the initial reference surface that vary as a function of
position along a particular direction along the initial reference
surface. The mold cavities can be considered to be characterized by
a respective plurality of parallel reference axes that are at a
particular initial angle (e.g., perpendicular) to the initial
reference surface. In some embodiments, the mold cavities are
formed using anisotropic etching of preferred crystal directions in
single crystal materials such as silicon.
[0013] The mold body is then modified by removing a portion of the
mold material adjacent the initial reference surface to expose a
new reference surface at a tilt angle with respect to the initial
reference surface, with the mold cavities now being modified mold
cavities. The modified mold cavities are now characterized by
having their respective axes at a new desired tilt angle relative
to the new reference surface. Further, the variation in depth as a
function of position is chosen so that the modified mold cavities
have the same respective depths.
[0014] When silicon or any crystal material which forms useful
atomically accurate surfaces by an etching process is used the
angular axis of this structure such a self-terminated pit may be
selected by using materials such as silicon cut at a particular
angle with respect to crystal axis.
Facilitating Mold Release and Providing In-Situ Inspection
[0015] An aspect of the invention provides techniques for releasing
a molded part or parts from the mold, possibly after bonding the
molded part(s) to a support structure on the mold side of the mold
wafer. In short, techniques provide for etching from the opposite
side from the mold side, i.e., from the backside, to provide what
is referred to as a release pit.
[0016] In some embodiments, a small amount of mold material is left
near the base of the molded part to protect the support structure
from etch fluid or plasma. This amount is small enough to allow the
molded part to be separated from the remaining portions of the mold
material without requiring excessive force. Where the molded parts
have not been bonded to a support structure, the small amount of
mold material near the base of the molded parts supports the molded
parts, with the remaining portions of the mold material providing
protection. In some embodiments, the release pit is
self-terminating, in cooperation with the base of the molded
part.
[0017] In other embodiments, one or more films of silicon oxides,
silicon nitrides, or other materials are deposited on the mold side
or the supporting structure to which the molded parts are bonded,
and act as an etch barrier to protect the supporting structure. In
one set of embodiments, the etch barrier layer is provided by a
layer of silicon dioxide bonding two wafers of silicon. A pattern
etch of the mold side silicon surface is used to create a breakaway
groove around the molded part, permitting a lowering of the
breakaway force along with a precise limitation of the breakaway
pattern of the silicon.
[0018] An aspect of the invention permits the in-situ examination
of four sides of the molded part by imaging the reflection of the
sides of the molded part in the highly reflective and precise mold
sides of the release pit.
Alignment and Bonding of Molded Parts to Support Structure
[0019] An aspect of the invention provides a technique for aligning
a pair of wafers having respective bond sites. Each wafer is
provided with a plurality of alignment pits, with the pits on one
wafer being registered to the pits on the other wafer. An alignment
structure such as a ball is placed in each pit of one of the
wafers. The alignment structures and/or one or more of the
alignment pit surfaces are sufficiently resilient that as the two
wafers are pressed together, the alignment structures align the
wafers. For example, where copper balls are used as the alignment
structures, they deform as the bond sites on the two wafers come
into contact and can be welded or soldered under heat and
pressure.
[0020] Another aspect of the invention provides an aligned support
for small structures such as cantilevers when being assembled or
bonded with another wafer carrying rigidly held structures such as
diamond tips. When being so used the cantilevers can be displaced
away from the bond point by the pressure of the other wafer and by
differential strains bending the cantilever at the bond
temperature. To overcome this limitation a jig or form is provided
with alignment structures that act to stop the released cantilevers
and hold them even with their normal (or neutral) position in the
cantilever-bearing wafer, or above or below this normal position to
set a net positive or negative angle which may serve as the angle
offset for the tip-cantilever assembly by creating a wedge of
bonding material between the cantilever and the tip or contribute
to this offset.
Molding Complex Shapes
[0021] Another aspect of the invention provides for using an
initial molded part as a seed for further growth through a backside
pit. After the initial molded part is formed in a mold cavity on
the mold side of the wafer, a pit of desired configuration is
formed on the backside to expose the end of the initial molded part
closest to the backside. Further material (e.g., diamond, silicon
nitride, cubic boron nitride) is grown using the exposed end of the
initial molded part. This way, a molded part not otherwise easily
achievable with a single mold or growth operation is achieved. For
example, very small diameter shapes on the ends of larger shapes
(the initial molded parts) can be obtained.
[0022] Another aspect of the invention provides for using an
initial molded part as a seed for further growth through a backside
pit. In this case, the growth is not confined to a narrow pit, but
rather electric fields are used to control the growth in an angled
backside pit.
Ejection from Mold
[0023] Another aspect of the invention provides techniques for
ejecting molded parts from the mold. In embodiments, the mold wafer
with molded parts formed therein has been subjected to a backside
etch to leave a small amount of mold material surrounding the base
of the molded part and the molded part substantially exposed from
the backside. One version uses an ejection tool having protrusions
that are aligned with a suitable feature on the molded parts. The
ejection tool is positioned so the protrusions engage the molded
parts, and then moved a controlled distance to rupture the mold
material retaining the molded part(s). Another version uses
hydraulic pressure to eject the molded parts from the mold. A
source of hydraulic fluid is sealed to the backside of the wafer
and pressurized to rupture the mold material retaining the molded
part(s).
Workpiece Alignment
[0024] An aspect of the invention provides an alignment wafer
configuration that facilitates the fabrication of aligned parts.
This process assumes a workpiece having a shaped end, which when
severed from the major portion of the workpiece, will define a
small part. The preshaped end of the workpiece may be oriented in
crystal axis to align the shape as a cutting edge with a preferred
axis for that cutting operation such as <100> or <110>
or <111> or any particular precise crystal orientation
desired. Multiple such workpieces are contemplated.
[0025] One side of the alignment wafer (corresponding in some sense
to the mold side) is formed with a recess that conforms to the
shaped end of the workpiece, but the other side of the wafer
(corresponding in some sense to the back side) is formed with a
recess so that the end of the workpiece, when it is inserted into
the mold-side recess, passes into the backside recess, but is
stopped before it extends past the backside. Multiple such
workpieces are inserted into corresponding mold-side recesses, and
they are then all cut in place by the operation of one focused
laser cut or abrasive wire or chemical etch. These aligned parts
can then be prepared for bonding to another wafer with
corresponding support structures, or can be removed from the
alignment wafer for such further handling as desired.
[0026] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings.
[0027] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIGS. 1A and 1B are schematic top and cross-sectional views
of a mold wafer in an early stage of mold fabrication;
[0029] FIGS. 2A and 2B are schematic top and cross-sectional views
of the mold wafer at a later stage of mold fabrication;
[0030] FIGS. 3A and 3B are schematic top and cross-sectional views
of the mold wafer at a generally final stage of mold
fabrication;
[0031] FIGS. 4A and 4B are schematic top and cross-sectional views
of an early stage of release of a mold wafer from an array of
molded parts;
[0032] FIGS. 4C and 4D are schematic cross-sectional views of later
stages of the release;
[0033] FIGS. 5A and 5C are schematic cross-sectional views of the
release of a mold wafer from a molded part;
[0034] FIG. 5B is a schematic cross-sectional view of the molded
part taken through line 5B-5B of FIG. 5A;
[0035] FIG. 5D is a schematic top view of the mold wafer and molded
part at the stage of the wafer shown in FIG. 5C, illustrating the
opportunity to inspect four sides of the molded part before it is
finally released from the mold;
[0036] FIGS. 6A-6E are schematic cross-sectional views showing the
fabrication of a mold wafer with a breakaway, and the molding and
releasing of a molded part in an embodiment of the present
invention;
[0037] FIG. 6F is a schematic bottom view of the mold wafer and
molded part;
[0038] FIGS. 7A-7C are schematic cross-sectional views showing an
alignment and bonding technique in an embodiment of the present
invention;
[0039] FIG. 7D is a schematic cross-sectional view showing a
variation on the embodiment shown in FIGS. 7A-7C;
[0040] FIG. 8 is a schematic cross-sectional view of an assembly
jig for aligning and bonding wafers;
[0041] FIGS. 9A-9C show schematically an alternative way to bond
tips where a desired tilt angle is established at the time of
bonding;
[0042] FIGS. 10A-10D show schematic the molding of a shape where a
first molded part is used as a seed for additional growth to form a
more complex part;
[0043] FIGS. 11A and 11B are schematics showing mechanically
ejecting molded parts from a mold;
[0044] FIGS. 12A-12C are schematics showing hydraulically ejecting
molded parts from a mold;
[0045] FIGS. 13A-13C are schematic cross-sectional views showing
the alignment and separation of a small part from a larger
workpiece.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Overview and Terminology
[0046] In general, the invention provides techniques related to
molded objects, typically using mold wafers. In the context of this
application, the term "molding" is intended to cover growing
objects in a mold as well as otherwise introducing material into a
mold cavity or onto a mold surface. Thus the term "molded part" is
intended to cover mold-grown parts, and vice versa.
[0047] In its various aspects, the invention provides techniques
for one or more of: setting a complex bond angle limited only by
the size of the starting mold (diameter and thickness); removing
the silicon or other mold material while maintaining support for a
film or other barrier that protects susceptible structures on the
mating part to be bonded; inspecting molded parts while they are
still in the mold; aligning parts to be bonded (e.g., a wafer mold
of containing molded parts to a wafer of structures to which the
molded parts are to be bonded; ejecting molded parts from a mold;
forming specialized shapes by molding from both sides of a mold
wafer; using films of silicon oxides, silicon nitrides, or other
materials to act as an etch barrier to protect structures to which
the molded parts are mounted; and/or
[0048] In a particular embodiment, the molded parts are diamond (or
one of the other special materials noted above) and are assembled
onto cantilevers for use in a scanning probe microscope (SPM) or
other use similar use such as nano-indentation and nanomachining.
These cantilevers in general are tilted at a fixed angle with
respect to surface they scan, typically 3 degrees to 15 degrees. In
some implementations, the diamond is grown into the mold as a
single crystal, while in other implementations, the diamond is
grown into mold shapes as oriented polycrystalline material.
[0049] Additionally, while particular embodiments use silicon
wafers for the mold, techniques according to different aspects of
the invention may be used in connection with other mold materials
such as sapphire, quartz, or alumina. If necessary wafers,
especially wafers used for assembly jigs and the like, can be
overcoated with an anti-wear and anti-stick film such as silicon
nitride
[0050] In portions of the description that follows, references will
be made to directions such as up and down. The invention is not
limited to any orientations or directions unless specifically
noted, and references to directions or orientations are with
respect to the figures and are for convenience only.
Setting Bond Angles of Molded Parts
[0051] In this section, the formation of a mold body with mold
cavities at a desired angle with respect to a reference surface
will be described. In an illustrative embodiment, the mold cavities
will be four-sided pyramids with their axes at an angle to a
reference surface. In the embodiment described below, the mold
cavities are created in a semiconductor wafer using known
photolithographic processing techniques. As a matter of
nomenclature, the side of the wafer in which mold cavities have
been formed is sometimes referred to as the mold side, and the
other side is sometimes referred to as the backside.
[0052] FIGS. 1A and 1B are schematic top and cross-sectional views
of a mold wafer 10 in an early stage of mold fabrication. The
drawing is not to scale, with the thickness of the wafer and the
spacing and size of various features greatly exaggerated Mold wafer
10, portions of which will define the mold body, is shown with top
and bottom surfaces 15a and 15b, respectively. In these figures,
the top surface will, after suitable processing to be described,
become the mold surface.
[0053] In a specific embodiment, the wafer is a 1-0-0 silicon wafer
with top surface 15a defining an initial reference surface, which
for a 1-0-0 wafer is parallel to the {100} planes. The mold wafer
has an etch stop layer 20 of silicon oxide that has been
lithographically patterned to form a plurality of openings 25 that
expose bare silicon. Openings 25, which will help define the mold
cavities, are not of uniform size, but rather are have
geometrically similar shapes (squares in the illustrated
embodiment) with a size that varies as a function of position on
the wafer. In particular, the squares can be seen as decreasing in
size moving from left to right.
[0054] FIGS. 2A and 2B are schematic top and cross-sectional views
of mold wafer 10 at a later stage of mold fabrication. At this
stage, the patterned side of the wafer has been subjected to an
anisotropic etch to produce cavities 30 in the wafer that will
further help define the mold cavities. As is well known, potassium
hydroxide (KOH) preferentially etches in the <100> and
<110> directions relative to the <111> direction, in
single-crystal silicon, thereby creating an anisotropic etch.
[0055] Where the etch stop pattern exposes bare silicon squares,
and an etchant such as potassium hydroxide is used, the etch will
self-terminate as a pyramid, ending in a point with the depth of
the pyramid depending precisely on the starting size of the square.
(In the case where the etch stop pattern would expose non-square
silicon rectangles, the etch would self terminate to a house roof
shape with quadrilateral faces forming the main roof and triangular
faces forming the ends, with a knife edge taking the place of the
single point of the pyramid. The length of the knife edge is
precisely related to the amount the rectangle departs from a
square, limiting to the point for a perfect square.)
[0056] Thus in this particular example, cavities 30 are
geometrically similar pyramids having respective square bases (in
the plane of top surface 15a) and respective apices opposite the
centers of the respective squares. The depth and base of each
pyramid relative to the initial reference surface vary as a
function of position along a particular direction along the initial
reference surface. More generally, the cavities can be considered
to include geometrically similar portions, but have respective
depths below (into) the initial reference surface that vary as a
function of position along a particular direction along the initial
reference surface. These cavities are further characterized by a
respective plurality of parallel reference axes that are at a
particular initial angle to the initial reference surface (top
surface 15a).
[0057] FIGS. 3A and 3B are schematic top and cross-sectional views
of the mold wafer at a generally final stage of mold fabrication.
At this stage, the mold body has been modified, as designated by
the reference numeral 10', with the original wafer 10 and cavities
30 shown in phantom. The main functional modification is the
removal of a portion 35a of the mold material adjacent the initial
reference surface to expose a new reference surface 40a at a
desired tilt angle .theta. with respect to initial reference
surface 15a, with the mold cavities, designated 30', now being
modified mold cavities. The modified mold cavities are now
characterized by having their respective axes at the desired tilt
angle .theta. relative to the new reference surface 40a. Further,
the variation in depth of the original cavities 30 as a function of
position is chosen so that the modified mold cavities 30' have the
same respective depths.
[0058] In the specific illustrated embodiment, the mold body has
been additionally modified (a) by removing a portion 35b of the
mold material adjacent the initial lower surface 15b to expose a
new lower surface 40b, and (b) by removing peripheral portions of
the wafer. Where new lower surface 40b is also at the desired tilt
angle .theta. with respect to initial lower surface 15b, the upper
and lower surfaces are parallel to each other. This step is also
referred to as a grind-back step.
[0059] Once the mold has been fabricated as described above,
diamond or any other material may be grown or otherwise introduced
into the mold, to provide a plurality of molded parts having
desired tilt angles to the reference surface of the mold body.
However, various techniques to be described below, including mold
release, in-situ inspection, and wafer alignment techniques, can be
used with other types of molds or with molds fabricated using other
methods.
[0060] The above technique for providing mold cavities whose axes
are tilted with respect to the mold surface has the advantage that
a standard wafer (e.g., a 1-0-0 silicon wafer) can be used. In an
alternative embodiment, suitable only for self-terminating shapes,
the wafer material is cut from the single crystal boule at the
desired tilt angle with respect to {100} to obtain the desired tilt
angle. In the other uses such as dry or isotropic etching in which
the mold is prepared without regard for crystal orientation, the
additional grind-back step discussed above is a requirement
regardless of the actual crystal axis of the wafer.
Facilitating Mold Release and Providing In-Situ Inspection
[0061] Use of Backside Etch Pits for Release
[0062] FIGS. 4A and 4B are schematic top and cross-sectional views
of an early stage of mold release according to an embodiment of the
present invention. For purposes of example, mold wafer 10' shown in
FIGS. 3A and 3B is shown in FIGS. 4A and 4B as having been used as
a mold to form molded parts 45, which have been aligned with and
bonded to a separate support structure 50. In the case where the
molded parts are SPM tips, the separate structure can be a wafer of
cantilevers, or can be any other structure to which such tips might
be advantageously bonded. The techniques for facilitating mold
release do not depend on the molded parts having been bonded to
support structures, but would also be workable for molded parts
that have not been so bonded.
[0063] The mold with parts 45 and structure 50 is shown as having
been flipped over relative to the orientation of FIGS. 3A and 3B.
Thus the backside is the upper surface in these figures. The
backside of the mold wafer has been provided with an etch barrier
layer 55, which may be silicon oxide or silicon nitride, that has
been lithographically patterned to form a plurality of openings 60
that expose bare silicon. Molded parts 45 are shown in phantom in
FIG. 4A. Since the mold of FIG. 3B has, by design, the crystalline
axes tilted with respect to the mold surfaces, openings 60 are
offset from the bases of the molded parts to account for the tilt.
If the mold had been fabricated from a wafer solely by anisotropic
etching without the subsequent removal of material to provide a new
tilted reference surface, openings 60 would most likely be centered
relative to the bases of the molded parts.
[0064] FIG. 4C shows the result of subjecting the patterned
backside of mold wafer 10' to an anisotropic etch using an
anisotropic etch process that is analogous to the etch process with
which the mold cavities were formed. In order to facilitate removal
of the mold material, openings 60 should be large enough relative
to the thickness of the mold material to permit a sufficiently deep
etch since the etch is self-terminating. The result of this etch is
a series of etch pits 65, which are referred to as release
pits.
[0065] FIG. 4D shows the result of separating the residual mold
material from molded parts 45 and support structure 50.
[0066] It is typically desired to protect support structure 50 from
the etch fluid or plasma; this can be accomplished in a number of
ways. One approach is providing an etch stop coating to the mold
side of the mold wafer and molded parts before bonding them to the
support structure, and/or providing an etch stop coating to the
support structure before it is bonded to the mold wafer and molded
parts. This is a viable approach as long as the etch stop coating
does not interfere with the bonding process. Other, and sometimes
preferred, approaches will be discussed below with reference to
FIGS. 5A-5D and 6A-6B.
[0067] Use of Self-Terminating Backside Etch Pits for Release
[0068] FIGS. 5A-5C illustrate a technique that exploits the
self-terminating property of some etch processes as applied to some
mold materials (e.g., a potassium hydroxide etch as applied to
1-0-0 silicon wafers). In one set of embodiments, openings 60 are
sized to form a self-terminated etch pit (release pit) with sloped
sides using an anisotropic etch process that is analogous to the
etch process with which the mold cavities were formed.
[0069] FIG. 5A is a schematic cross-sectional view of a portion of
a mold wafer 70 (say a 1-0-0 wafer) which has been used as a mold
to form one or more molded parts 75. Mold wafer 70 is shown as
having been provided with an etch barrier layer 80, e.g., a layer
of silicon oxide, that has been lithographically patterned to form
one or more openings 85 that expose bare silicon over the molded
part(s). While the technique could be used with a mold wafer having
surfaces at a tilt angle relative to the {100} planes, such as
described above, the technique has wider application.
[0070] FIG. 5B is a cross-sectional view of molded part 70 taken
through line 5B-5B of FIG. 5A. In this particular example, for
illustrative purposes, the molded part has a jagged outline in one
plane, but a rectangular outline in the perpendicular plane, as if
extruded. The base of the molded part is a truncated four-sided
pyramid, in a specific case having angles of 54.7.degree. relative
to the base (corresponding to the characteristic angle formed by
the anisotropic etch.
[0071] FIG. 5C shows the result of subjecting the patterned side of
mold wafer 70 to an anisotropic etch that forms a self-terminating
release pit 90 with walls 95. In this embodiment, the size of
opening(s) 85 is chosen so that the etch self terminates before
reaching the bottom of the wafer. This leaves a small amount of the
mold material 100 surrounding and overlying the outer portion of
the molded part's base (see enlarged inset). The thickness of mold
material 100 at the edge of the molded part's base is small enough
to allow moderate mechanical force to cause the mold material to
fracture without compromising the bond. The thickness of mold
material 100 is large enough, however, to protect the support
structure from the etchant fluid or plasma without requiring a
separate protective layer.
[0072] In the specific case where the molded part's geometry is
defined by the nature of the anisotropic etch process (mold
material and anisotropy parameters), it is straightforward to make
the release etch self-terminating. To extend the technique to a
general class of molded shapes, one need only provide that the
molded part's base forms part of a self-terminated shape. Further,
mold wafer 70, at the stage of processing shown in FIG. 5D,
provides a convenient way to store and/or transport the molded
parts prior to mounting them on a support structure.
[0073] In the particular case of a diamond pyramidal tip formed and
bonded to a 50-micron thick cantilever, the pyramidal depression
(65, 90) is etched to release the diamond such that the etch
terminates on the molded part itself, and stops at 5 microns from
going completely through the mold wafer. This method has the added
advantage that the rectangle or square etch region can be chosen
exactly to match the measured thickness of the wafer so as to
obtain exactly the remainder thickness appropriate to the use.
[0074] FIG. 5D is a top view of mold wafer 70 and molded part 75 at
the stage of the wafer shown in FIG. 5C, illustrating the
opportunity to inspect four sides of the molded part before it is
finally released from the mold. Walls 95 of release pit 90 have the
property, particularly in a 1-0-0 silicon wafer (and partially off
axis-single crystal silicon), of being highly reflective optically.
Thus each of the pit walls forms a virtual image 75' of the side of
molded part facing that pit wall. Thus by suitable focus of a
standard incident light microscope the side of the molded part
facing the pit wall is visible in reflection from the wall and
indeed in many cases all four pits walls show a visible image of
the molded side from that view. Thus with one image all four sides
of the molded part may be viewed and/or inspected at once.
[0075] Use of Backside Release Pit with Etch Stop Layer and
Mold-Side Breakaway Groove
[0076] FIGS. 6A-6E are schematic cross-sectional views showing the
fabrication of a mold wafer 110 with a narrow breakaway groove 115,
and the molding and releasing of a molded part 120 in another
embodiment of the present invention. The upper surface of the mold
wafer is the backside in FIGS. 6A-6E. As can be seen in FIG. 6A,
the mold wafer comprises an upper wafer 125 and a lower wafer 130
(device layer), which are bonded together by a silicon oxide layer
135 (shown as a heavy line). The upper wafer is relatively thick
and provides most of the volume of the mold cavity. Oxide layer 135
acts as an etch stop layer for the mold release as will be further
described. Upper wafer 125 is provided with an etch barrier layer
140 on the backside, which corresponds generally to etch barrier
layer 55 (shown in FIGS. 4A-4C) and etch barrier layer 80 (shown in
FIGS. 5A and 5C). For simplicity, etch barrier layer is shown as
having been formed early in the process, but it may be provided at
other stages.
[0077] FIG. 6B shows lower wafer 130 having been subject to process
steps that result in two features, namely a mold opening 145 and
breakaway groove 115 surrounding mold opening 145. A representative
process is as follows. First the bottom wafer is patterned and
etched part of the way through to define the breakaway groove. The
depth is selected to require a desired breakaway force to fracture
wafer 130 along the groove. A typical groove would be on the order
of 3 to 4 times the depth, and a typical depth would be on the
order of 20 microns on a 40-micron thick device layer. Then the
groove is protected from further etching by a suitable resist (not
shown). Lower wafer 130 is then provided with an etch-resistant
layer that is patterned to define mold opening 145, and the exposed
silicon is dry etched to oxide layer 135.
[0078] FIG. 6C shows the exposed oxide in mold opening 145 having
been etched with an oxide-selective etchant such as dilute
hydrofluoric acid or buffered oxide etch (BOE) to expose the
silicon in the mold opening, This is followed by an anisotropic
etch (e.g., potassium hydroxide) to form a mold cavity 150.
[0079] FIG. 6D shows molded part 120 having been formed by growing
diamond, silicon nitride, silicon carbide, or other appropriate
material in the mold cavity. FIG. 6D also shows an opening 155
having been formed in etch barrier layer 140.
[0080] FIG. 6E shows the effect of etching the portion of wafer 125
exposed by opening 155. This is preferably an anisotropic etch
along the lines of the etch used to etch the mold cavity, as was
described in connection with the embodiments shown in FIGS. 4A-4C
and FIGS. 5A and 5C. The result is a release pit 160 surrounding
molded part 120 and extending down to and being limited by oxide
layer 135, which as mentioned above acts as an etch stop layer.
[0081] FIG. 6F is a bottom view showing breakaway groove 115 (shown
with cross-hatching), the base of molded part 120, and surrounding
portions of the lower surface of lower wafer 130. At this point,
processed mold wafer 110 with molded part(s) 120 can be stored or
transported with the remaining surrounding portions of the mold
wafer providing support and protection for the molded part(s) until
such time as bonding the molded part(s) to a support structure is
desired.
[0082] As mentioned above, molding diamond in silicon wafer molds
is only an example. As further examples, for this and other
embodiments, the silicon or sapphire or quartz or alumina mold
material for original molding of the diamond or silicon nitride or
silicon carbide may be prepared on a silicon or other material
wafer in which a stop layer is incorporated such as silicon oxide,
carbide or nitride or other material well known in the art. This
layer may then be used as a stop layer when back etching a release
pit around the molded part.
Alignment and Bonding of Molded Parts to Support Structure
[0083] Captured Alignment Structures
[0084] FIGS. 7A-7C are schematic cross-sectional views showing a
technique in an embodiment of the present invention for aligning a
pair of wafers 170 and 175 having respective pluralities of bond
sites 180 and 185. The bond sites on one wafer may, for example, be
associated with molded parts such as cantilever tips, while the
bond sites on the other wafer may be associated with cantilevers or
other support structures. The technique does not depend on the
particular form of bonding, but for purposes of illustration, the
bond sites may be occupied by lithographically patterned sandwiches
of titanium-nickel-copper, with the facing copper surfaces
effecting a weld when subjected to pressure and heat. For
simplicity, the molded parts are not shown.
[0085] To facilitate alignment, each wafer is provided with a set
of alignment pits, designated with reference numerals 190 and 195
for wafers 170 and 175, respectively. Each set of alignment pits
has two or more (typically three to six) pits disposed along the
edges of the wafer. Two such pits are shown for each wafer. In the
embodiment of FIGS. 7A-7C, the alignment pits are self-terminated
cavities, such as those created for the mold cavities by
anisotropic etching as described above. These alignment pits are
generally larger is size than at least some types of molded parts.
For example, the alignment pits might have dimensions on the order
of hundreds of microns while the molded parts may have dimensions
on the order of tens of microns.
[0086] An alignment structure such as a precision ball 200 is place
in each of alignment pits 195. The ball may be made of copper,
silver, or some other deformable material. FIG. 7A shows the wafers
spaced from each other by an arbitrary distance. FIG. 7B shows the
wafers having been brought close enough so that balls 200 are
seated in pits 190 and 195. The balls and alignment pits are sized
relative to each other such that when the balls are seated in the
upper and lower pits, the bond sites do not touch. While dimensions
are not critical, a representative embodiment has balls having
diameters of 254.+-.1 microns, with the pits being sized to leave a
space of 20 microns between the wafers when the balls are seated in
the alignment pits.
[0087] FIG. 7C shows the wafers having been brought together under
pressure and heat. The balls deform while maintaining the
alignment, thereby ensuring that bond sites 180 and 190 are
precisely registered as they come in contact and are welded
together.
[0088] FIG. 7D shows an alternative arrangement where the lower
pits are self-terminating shapes as noted above, but the upper
pits, designated 190', are etched relatively shallow rectangular
cavities with vertical sidewalls. A depth of 50 microns is typical,
and the balls and lower alignment pits are sized accordingly to
leave a 20-micron separation between the wafers when the balls
contact the upper and lower alignment pits.
[0089] In an alternative arrangement, suitable for use with either
of the two geometries described above is to use non-deforming
balls, such as stainless steel, silicon nitride, silicon carbide
(or other hard material), and provide one or both sets of alignment
pits with a coating of a thermally softenable material (e.g.,
copper, silver, or tin) to allow the wafers to come together after
the balls are seated in the upper and lower pits. In yet another
arrangement, deformable coatings in the pits and deformable balls
are used.
[0090] Jig with Alignment Posts
[0091] FIG. 8 is a schematic cross-sectional view of an assembly
jig for aligning and bonding wafers, such as wafers 170 and 175
described above in connection with FIGS. 7A-7D. The jig includes a
base 205 that supports the two wafers to be aligned and a weight
210. The base has a number of posts 215 (e.g., three, two of which
are shown) that are made of a suitable material like sapphire and
sized and positioned in correspondence with through holes in the
wafers to be aligned. Since it is generally desired to place the
aligned wafers in a furnace for bonding, base 205 and weight 210
preferably have similar coefficients of thermal expansion (CTE) to
the wafers. Thus silicon would be the preferred material for use
with silicon wafers. Weight 210 is shown as having recesses to
accommodate the posts, but could also have recesses. The jig thus
allows the wafers to move as required in z while maintaining
alignment in x and y to complete the bond in the desired
manner.
[0092] The jig can be used as the sole alignment mechanism or it
can be used in conjunction with a mechanism described above in
connection with FIGS. 7A-7D. In the latter instance, the jig could
provide a relatively coarse alignment, with the balls in the pits
providing the fine alignment.
[0093] Alignment with Tilt Angle Set During Bonding
[0094] FIGS. 9A-9C show an alternative way to bond tips where a
desired tilt angle is established at the time of bonding. Each
figure has three parts; the left part shows a setup for a normal
bond angle, the middle part shows a setup for one direction of
tilt, while the right part shows a setup for the other direction of
tilt. Cantilevers 220 are shown with bond material 225 (e.g.,
exposed copper for welding, a solder material, or a resin
material). Three different support structures 230, 232, and 235 are
shown. The support structures have respective lower land surfaces
240, 242, and 245 for engaging the base of the cantilever, and
respective upper land surfaces 250, 252, and 255 for engaging the
bottom of the arm of the cantilever. The support structures differ
from each other by having their respective upper land surfaces 250,
252, and 255 at different heights above their respective lower land
surfaces 240, 242, and 245.
[0095] FIG. 9A shows the cantilevers above the support structures.
FIG. 9B shows the cantilevers seated on the respective lower land
surfaces of the support structures with a downward force having
been exerted on the cantilevers. It will be noticed that the
cantilever arm engages upper land surface 250 without bending the
cantilever; the cantilever arm engages upper land surface 252
before the base engages lower land surface 242, so that the arm is
bent upwardly; the cantilever base engages lower land surface 245
before the cantilever arm engages upper land surface 255, thereby
leaving a gap. Molded parts 260 in mold wafers 265 are to be bonded
to the cantilevers, and for this purpose have bond material 270 on
their bottom surfaces.
[0096] FIG. 9C shows the mold wafers having been pressed down on
the cantilevers. The cantilever in the left part of the figure
remains horizontal, so the molded part is bonded with no nominal
tilt between its bottom surface and the top of the cantilever arm
surface. The cantilever in the middle part of the figure has been
tilted upwardly by the excess height of upper land surface 252, so
the molded part is bonded with a nominal tilt between its bottom
surface and the top of the cantilever arm surface. The cantilever
arm in the right part of the figure has remained spaced from upper
land surface 255 and is forced down against upper land surface 255
so that it curves downwardly, so the molded part is bonded with a
nominal tilt between its bottom surface and the top of the
cantilever arm surface, but in the opposite direction from the
molded part in the middle part of the figure. Thus, support
structures 230, 232, and 235, by virtue of their different upper
land surface heights, leave horizontal, lift, or lower the
cantilever end. This causes the bond material to form an even slab,
or to wedge wide to the right or left. Since molded part 260 is
rigidly held and unreleased from mold wafer 265 during the bonding,
when the part is released and the cantilever free to return to its
relaxed state, the part will lean toward or away from the base of
the cantilever.
Molding Complex Shapes
[0097] Cylindrical Backside Pit as Secondary Mold
[0098] FIGS. 10A-10D show the molding of a shape where an initial
molded part 280 (e.g., diamond) is used as a seed for additional
growth in a backside etch pit to form a more complex part 285. Only
one such initial part is shown, but it is understood that the
technique would normally be applied to a wafer of such parts. FIG.
11A shows molded part 280 in a mold wafer 290 as might have been
achieved according to various of the embodiments discussed above.
The mold is shown as having been ground and/or polished to a new
total thickness and a small pit 295 of arbitrary shape (typically
consistent with that available in microlithography) has been made
such that it terminates at part 280.
[0099] FIG. 10B shows a native oxide layer 300 having been grown on
the walls of pit 295, thus possibly making it narrower than is
normally available with conventional microlithography. FIG. 10C
shows diamond having been grown inside the narrowed pit with molded
part 280 acting as a seed, resulting in the more complex molded
part 285. FIG. 10D shows the wafer surrounding molded part 285
having been removed as described above in connection with FIGS.
4A-4D by the formation of a release pit 305.
[0100] While this technique is not limited to specific dimensions
or process parameters, a specific example will be described. After
the initial molded part has been formed in cavities in a silicon
wafer, the wafer is ground (or the wafer and/or cavities were sized
before the molding steps) so that a few microns remain between the
molded diamond and opposite side of the wafer. This side is then
processed by methods well known in the art including REI etching to
make shaped cavities extending down to and/or around the molded
diamond part. In particular shapes may be etched including very
small diameter shapes typically as small as 200 nm or less and the
wall of the resultant shape may be oxidized to substantially reduce
the diameter by twice the oxide thickness.
[0101] Thus in a typical arrangement a 200-nm hole 1 micron deep
etched in silicon may be oxidized to a thickness on the wall of the
hole of 2-30 nm, resulting in a hole having a diameter of 196-140
nm opening ending at the point of a four sided molded pyramid
formed by growing diamond in an etch terminated silicon mold. The
extremely slow silicon oxide growth rate means that it is easy to
control pits made at the limits of lithography (today about 50 nm
to create open diameters as small as 1 or 2 nm).
[0102] The molded diamond point (or alternately a single crystal
diamond mechanically embedded in the silicon) then serves as a seed
or start point for the growth of diamond the length of the 1 micron
shaft to form an integrated molded diamond structure consisting of
a pyramid with an integral small diameter molded diamond shape. In
preparation before growth of the oxide, the cavity and diamond tip
may be etched or chemically cleaned with a silicon carbide etchant
(such as a SF6 dry etch) to insure that any remnant carbide formed
in the molding process does not interfere with diamond growth. It
is important to note that by using the molded or single crystal
diamond at the bottom of the cavity as the ONLY seed, CVD or
thermal diamond or other seed based diamond growth techniques will
not grow diamond elsewhere and will grow in the shaft from the
bottom of the diamond terminated shaft to the top.
[0103] After the molded diamond in the small diameter shape is
grown, the oxide is etched (or chemically removed or subjected to a
CMP (chemical mechanical polish) operation), then lithographically
exposed to make self-terminated pits which partially or fully clear
the pyramidal diamond or seed single crystal diamond. A straight
wall or flat topped (shaft end away from the pyramidal diamond or
seed diamond can end in a flattened structure of diamond greater in
at least one direction then the radius of the shaft structure is
particularly well suited to use in AGN, AFM, STM, and other SPM or
SPM-related techniques.
[0104] Growth in Angled Backside Pit
[0105] In yet another embodiment an angled backside pit is made
around a previously molded conductive part (e.g., a self-terminated
silicon pit mold of diamond, which due to its dopant or contents of
sp2 graphitic carbon is conductive). The molded part is connected
to voltage source and is charged by the source to be negative with
respect to carbon ion species in the plasma of an MPCVD or hot
filament or other kind of bulk diamond growth system. Further the
bulk silicon mold and previously molded part (e.g., pyramidal
diamond form) may be maintained at a temperature such that growth
is principally promoted at the sharp edge, tip, or point of the
molded part by heat differential maintained by the hot plasma heat
transfer to the molded part.
[0106] Either latter method may be used alone or in combination to
promote rapid growth at the tip of the molded part. Growth is
further promoted in this method by the large volume of plasma feed
gas able to circulate around the exposed pyramidal tip of diamond.
Additionally the bulk silicon may be electrically charged positive
with respect to the diamond pyramidal tip by grounding or
maintaining a further positive differential voltage. Alternatively
a material like tungsten may be coated on the back surface of the
silicon mold and the positive voltage or ground may be applied to
it while using low conductivity silicon as the mold. Similarly the
latter methods may be used on diamond molded forms from sapphire or
other substrates similarly prepared and then etched to expose all
or part of the molded diamond.
[0107] In an embodiment, after the pyramidal or other shape mold
pit is prepared, a diamond-like-carbon (DLC) seed layer is coated
at high vacuum onto such a wafer from a carbon plasma in a vacuum
arc in which the back or handle side of the wafer is fully grounded
or even charged negatively with respect to carbon plasma. This can
be done by placing a conductive coating (such as aluminum) on the
back side and arranging the grounded or negatively charged
connection to this side. Additionally the device or silicon layer
on top of the stop layer (said silicon relatively thin compared to
the handle side and meant to provide mechanical support for the
molded part in wafer scale bonding or shipping of the part may be
kept at a positive charge or grounded with respect to the handle
side bias voltage. A further advantage is the ability to pattern
the device layer and etch it such that the formed molded part after
the backside etch can be easily removed by mechanical extraction
from the mold wafer, while in shipment this breakaway structure
prevents inadvertent movement or release of the part.
Ejection from Mold
[0108] Embodiments of the present invention provide techniques for
ejecting molded parts from molds. These embodiments build on the
techniques for etching release pits from the backside of the mold
wafer
[0109] Mechanical Ejection
[0110] FIGS. 11A and 11B are schematics of an apparatus for
mechanically ejecting molded parts 310 from a mold 315. The molded
parts are shown as having been bonded to support structures 320
with bond material 325. In a specific example, the molded parts are
diamond tips, and the support structures are silicon cantilevers
that have already been released from their wafer so that they are
free to flex. As can be seen, the backside of mold has been etched
to form self-terminating release pits 330 that end at a depth
slightly less than the mold thickness, leaving a small amount of
material around the bases of the molded objects.
[0111] FIG. 11A shows the pre-ejection state. Mold 315 (with molded
parts 310 and support structures 320) is supported on a base 350
(analogous to base 205 in FIG. 8) with posts 355 (analogous to
posts 215 in FIG. 8). Base 350 is formed with recesses 360 to clear
support structures 320 (and, to the extent that the molded parts
and their support structures are free, to receive the released
molded parts after ejection from the mold).
[0112] The apparatus comprises, in addition to base 350 and posts
355, a plate 370 having a plurality of projections 375 configured
to engage the ends of the molded parts. Plate 370 includes holes to
allow the plate to slide along the posts. The projections are sized
relative to the plate and the thickness of the mold above the ends
of the molded parts so that the projections engage the molded parts
while the plate remains a short distance 380 above the backside
surface of mold 315. A weight 390 with through holes 395 (recesses
would also work) configured to clear posts 355 is shown poised to
be lowered onto plate 370.
[0113] FIG. 11B shows the state once plate 380 has been lowered
onto plate 370. The weight pushes down on plate 370, whose
projections 375 exert enough force to break the small amount of
mold material around the bases of molded parts 310, and plate 370
comes to rest on mold 315. The distance of travel is limited to
prevent damage to the released molded parts and support structures.
For example, if support structures 320 are cantilevers that are
free to flex, this ensures that the cantilevers are not flexed
beyond their limits. In a specific embodiment, plate 370 is a wafer
and projections 375 are lithographically formed. They may be coated
with silicon nitride.
[0114] Hydraulic Ejection
[0115] FIGS. 12A-12C are schematics of an apparatus for
hydraulically ejecting molded parts from a mold. FIG. 12A shows a
mold with molded parts. As an example, the molded parts are shown
as the complex parts made as described in connection with FIGS.
10A-10D, and as such, the molded parts are designated with
reference numeral 285 and the mold with reference numeral 290.
Again, the backside of the mold has been etched to form release
pits 305. The hydraulic approach has special advantages for shapes
where the upper portion may not be able to withstand the force
necessary to release the molded parts using a mechanical force
against the top of the molded part. However, the hydraulic approach
is applicable to a wide variety of shapes.
[0116] FIG. 12B shows a chamber 400 as having been disposed and
sealed on the backside of mold 290, and a volume of fluid having
been introduced into the reservoir defined by chamber 400 and
release pits 305 surrounding molded parts 285. The figure shows a
plunger 410 poised above the seals. The fluid is preferably
de-ionized water, although other liquids such as alcohols, oils,
and unhardened resists might be used under appropriate
circumstances.
[0117] FIG. 12C shows plunger 410 having been inserted into the
reservoir and moved downwardly, thereby exerting sufficient
hydraulic force to break the small amount of mold material at the
bases of the molded parts. It is noted that a small amount of force
on the plunger translates to a magnified force at the bottom of the
reservoir due to the much smaller surface area. Plunger 410 is
configured for a controlled travel before it engages the top
portions of chamber 400. The plunger may be actuated by any
convenient mechanism such as a hydraulic pump, a membrane or
collapsible chamber, or compressed gas or compressed air such that
the pressure is adequate to break or release the part from the
mold.
Workpiece Alignment
[0118] FIGS. 13A-13C are schematic cross-sectional views showing
the alignment and separation of a small part 450 from a larger
workpiece 455. In an example, the workpiece consists of
single-crystal lapped diamond which is oriented in crystal axis to
align the shape as a cutting edge with a preferred axis for that
cutting operation, such as <100> or <110> or
<111> or any particular precise crystal orientation
appropriate.
[0119] FIG. 13A shows a wafer 460 is provided with a number of
recesses 465, each recess having an upper portion 470 and a lower
portion 475. Thus the wafer is configured to accept multiple
workpieces. Each recess's upper portion 470 is configured to accept
a respective workpiece 455 and allow an end portion of the
workpiece to pass entirely through the upper portion extend into
the recess's lower portion 475, but not exit the bottom surface of
the wafer. Each recess's lower portion 475 is configured as a
relatively large relief.
[0120] FIG. 13B shows multiple workpieces inserted into respective
recesses. As can be seen, the very ends of the workpieces are
located within the lower portions of the recesses, and are
protected by the mold material surrounding the recesses. The figure
also shows schematically a parting operation, denoted by an arrow
480, for cutting all the workpieces along a plane 485, denoted by a
dashed line. This parting operation may be effected by any
convenient mechanism such as a laser cut, an abrasive or lapping
cut with a wire or wheel, a chemical etch, or a focused ion
beam.
[0121] FIG. 13C shows the ends of the workpieces, defining small
parts 450, remaining in the wafer while the larger portions 490 of
the workpieces having been removed from the vicinity of the wafer.
The removed larger portions can have their ends ground or reduced
by CMP or other lapping operation to form new workpieces from which
the ends can be separated as just described. With the small parts
still in the wafer, the entire surface may be given a CMP treatment
and/or grind and/or lapping operation such that bond surfaces are
smoothed and prepared for coating steps for good adhesion to a
metal bond element. In this form these small parts may then be
assembled as described above into a complete series of bonded
assemblies. The small parts may also be released from wafer 460 and
later used with a shaker table or fluid flow system so that they
self align into pits or recesses of another alignment wafer.
Conclusion
[0122] In conclusion it can be seen that the invention provides one
or more advantageous techniques, usable individually or in various
combinations. These techniques include: [0123] the structured use
of a constant change in part depth when creating molded or growth
molded otherwise identical in at least one structural element parts
for a multiple cavity mold such that a plane can intersect the
lowermost portion of the parts, the plane being the tilt angle
plane of the final mold opening with respect to the geometry of the
parts (including the possibilities that the mold is subsequently
machined or ground so as to form a new mold with the plane angle at
the mold opening and/or a barrier film has been attached which can
prevent the etching process to free up the molded part from causing
damage to the bond or other structures attached to the part of
adjacent to it); and/or [0124] a mold in which the part is released
by patterning the mold on the back side away from the part side
such that the minimum material is removed sufficient to free up the
part while supporting the structure and any barrier film designed
to limit the distribution of the etchant; and/or [0125] the use of
off-axis single crystal mold so as to form a self-terminated pit or
structure with a tilt established by the crystal axis; and/or
[0126] a method of release in which the release etch process is
self-terminating on the molded structure itself such that a
specific remnant mold material remains and creates a seal to
control etchant contamination or dispersal; and/or [0127] a mold in
which the mold material is removed from most of the part with
sufficient material remaining to maintain a barrier to the mold
etchant or mold material removal process; and/or [0128] inspection
or viewing for any purpose of the molded part in the reflective
surfaces formed by the removal of the mold material; and/or [0129]
an alignment system for bonding two wafers at specific bond points
with a material which has a specific bonding or welding temperature
with a combination of two more sets of self-terminated pits and
alignment shapes such that at or near the bond pressure and
temperature the bondable elements are brought into contact by the
deformation of the alignment shape or deformable coating or both;
and/or [0130] an assembly means for bonding wafers of parts in
which one set are cantilevers such that a preformed jig is used to
support the cantilevers for the bonding step (including the
possibility of the combination of the jig and the wafer carrying
bondable elements to be joined to a cantilever cause the cantilever
to bend up or down creating a wedge of the bond material and
leaving the part with a characteristic angle due to the bond
wedge); and/or [0131] a wafer with preshaped pits and any insertion
means whereby tool parts loose or on a workpiece are inserted into
the wafer, trimmed or released to remain in place and the wafer is
then prepared and used for wafer to wafer assembly of the parts;
and/or [0132] a molded or inserted material means in which a first
means is used to mold a base part and then the wafer is prepared by
any means including grinding, polishing, compress, or chemical etch
and a new pattern etched into the side opposite the first molded
parts and/or inserted parts so that these parts form a seed source
to fill up the cavities etched on the opposite side from the
beginning parts so as to form an complex integral assembly suitable
for wafer scale assembly or other use (including the possibility
that the parts are made of polycrystalline or single crystal
diamond and the wafers are silicon and/or that the etched cavities
are decreased in diameter by growth of a native oxide on the
silicon and/or that a diamond material is first cleaned by use of a
SF6 plasma gas etch to remove any remanant silicon carbide; and/or
[0133] methods in which the formed diamond, silicon nitride, or
silicon carbide molded part is charged negatively with respect to
carbon and/or silicon and/or nitrogen ion species in the feed gas;
and/or [0134] methods in which the surrounding mold backside is
charged positively or grounded with respect to the seed ion species
(including the possibility that a thermal gradient is maintained to
promote differential preferred rates at point or knife edge
structures on the molded part); and/or [0135] methods of
selectively molding diamond, silicon nitride, and silicon carbide
in which a stop layer is used to control the depth of the back etch
of the mold material; and/or [0136] mold seed growth preparation in
which the stop layer permits differential charging of etched first
molded structure such that seed species are attracted to either the
handle or device side of the electrically biased mold form; and/or
[0137] device side etched patterns in the mold material on the thin
or device side of the etch stop layer such that the part may be
easily removed from the mold assemble at the end of the process;
and/or
[0138] While the above is a complete description of specific
embodiments of the invention, the above description should not be
taken as limiting the scope of the invention as defined by the
claims.
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