U.S. patent application number 09/774216 was filed with the patent office on 2002-08-08 for optical membrane singulation process utilizing backside and frontside protective coating during die saw.
Invention is credited to Le, Minh Van, Wong, Jo-Ey.
Application Number | 20020106871 09/774216 |
Document ID | / |
Family ID | 25100574 |
Filed Date | 2002-08-08 |
United States Patent
Application |
20020106871 |
Kind Code |
A1 |
Le, Minh Van ; et
al. |
August 8, 2002 |
OPTICAL MEMBRANE SINGULATION PROCESS UTILIZING BACKSIDE AND
FRONTSIDE PROTECTIVE COATING DURING DIE SAW
Abstract
A process for singulating MOEMS optical devices from a precursor
structure, in which the precursor structure comprises device
material, having movable optical structures, and handle material,
through which optical ports are formed to provide for optical
access to the movable optical structures. The process comprises
coating a frontside and a backside of the precursor structure with
protection material. The precursor structure is then attached to a
substrate such as dicing tape and the precursor structure separated
into individual optical devices by a process, including die sawing.
Thereafter, the optical devices are removed from the tape and the
protection material removed from the optical devices.
Inventors: |
Le, Minh Van; (Methuen,
MA) ; Wong, Jo-Ey; (Brookline, MA) |
Correspondence
Address: |
J GRANT HOUSTON
AXSUN TECHNOLOGIES INC
1 FORTUNE DRIVE
BILLERICA
MA
01821
US
|
Family ID: |
25100574 |
Appl. No.: |
09/774216 |
Filed: |
January 30, 2001 |
Current U.S.
Class: |
438/465 |
Current CPC
Class: |
H01L 21/67092 20130101;
G02B 26/0841 20130101; H01L 21/67132 20130101; B81C 1/00896
20130101 |
Class at
Publication: |
438/465 |
International
Class: |
H01L 021/301 |
Claims
What is claimed is:
1. A process for singulating MOEMS optical devices from a precursor
structure, which comprises device material, in which movable
optical structures are formed, and handle material, through which
optical ports are formed to provide optical access to the movable
optical structures, the process comprising: coating a frontside and
a backside of the precursor structure with protection material;
attaching the precursor structure to a substrate; separating the
precursor structure into individual optical devices by a process
including die sawing; removing the optical devices from the tape;
and removing the protection material from the optical devices.
2. A MOEMS singulation process as claimed in claim 1, wherein the
step of coating the frontside and the backside of the precursor
structure comprises spraying the protection material on both the
frontside and the backside of the precursor structure.
3. A MOEMS singulation process as claimed in claim 1, wherein the
step of coating the frontside and the backside of the precursor
structure comprises coating with a photoresist material.
4. A MOEMS singulation process as claimed in claim 3, wherein the
step of removing the protection layer comprises dissolving the
photoresist layer in a circulated bath.
5. A MOEMS singulation process as claimed in claim 4, wherein the
bath contains acetone.
6. A MOEMS singulation process as claimed in claim 1, wherein the
step of coating the frontside and the backside of the precursor
structure comprises depositing protection material into the optical
ports in the backside of the precursor material.
7. A MOEMS singulation process as claimed in claim 1, wherein the
step of removing the protection layer comprises dissolving the
protection layer.
8. A MOEMS singulation process as claimed in claim 1, wherein the
step of separating the precursor structure into the individual
optical devices comprises die sawing completely through the handle
material and the device material.
9. A MOEMS singulation process as claimed in claim 1, wherein the
step of separating the precursor structure into the individual
optical devices comprises: die sawing through the device material
and partially through the handle material; and then cleaving the
precursor structure into the individual optical devices.
10. A MOEMS singulation process as claimed in claim 1, wherein the
substrate is dicing tape.
11. A MOEMS singulation process as claimed in claim 1, wherein the
step of coating the frontside and a backside of the precursor
structure is performed after the step of attaching the precursor
structure to the substrate.
12. A MOEMS singulation process as claimed in claim 1, wherein the
step of removing the optical devices from the substrate comprises
manipulating the optical devices with a pick-and-place machine.
13. A MOEMS singulation process as claimed in claim 1, wherein the
step of removing the optical devices from the substrate is
performed after reducing a level of adhesion between the optical
devices and the substrate.
14. A MOEMS singulation process as claimed in claim 13, further
comprising exposing the substrate to ultraviolet light to reduce
the adhesion.
15. A MOEMS singulation process as claimed in claim 1, wherein: the
step of removing the optical devices from the substrate comprises
placing the optical devices into a waffle pack jig; and the step of
removing the protection material from the optical devices comprises
removing the protection material while the optical devices are in
the waffle pack jig.
16. A MOEMS singulation process as claimed in claim 15, wherein the
waffle pack jig comprises fluid ports in each device cell for
facilitating removal of the protection material.
17. A processing jig for singulated MOEMS devices, comprising: a
waffle pack comprising an array of cells for receiving singulated
MOEMS devices; a top for retaining the MOEMS devices in the
respective cells; and fluid ports in the device cells for
facilitating fluid circulation through the cells.
18. A processing jig as claimed in claim 17, wherein the top
comprises fluid ports for facilitating fluid circulation through
the cells.
19. A processing jig as claimed in claim 17, wherein the jig
comprises lateral fluid ports for facilitating fluid circulation
between the cells.
Description
BACKGROUND OF THE INVENTION
[0001] Micro electromechanical systems (MEMS), and specifically,
microoptical electromechanical systems (MOEMS), are typically
fabricated at the wafer and/or sub-wafer level. Hundreds of devices
are typically manufactured on a single 4-inch or 6-inch wafer, for
example. Sometimes these wafers are cut into multi-device coupons
for further processing before the MOEMS optical devices are finally
singulated into the individual device dies.
[0002] Because MEMS devices typically include cantilevered features
and/or deflectable surfaces, provisions must be made for protecting
devices during the singulation process. Singulation is a relatively
violent process that typically includes sawing and/or cleaving a
precursor structure comprising multiple MEMS devices into
individual MEMS device dies. These steps of sawing and cleaving,
and possibly etching, produce particulate matter that can interfere
with the operation of the MEMS devices.
[0003] Various strategies have been proposed for protecting MEMS
devices, such as accelerometers during singulation. The strategies
typically combine a combination of frontside and/or backside sawing
and/or etching. Sometimes water-soluble protective coatings are
deposited over the MEMS structure and then later partially removed
during a die sawing process. In still other examples, special
two-layer dicing tape systems are used that encapsulate the MEMS
structure for the die sawing process.
SUMMARY OF THE INVENTION
[0004] Existing singulation technology assumes that the MEMS device
structure is only present on one side of the precursor structure.
This is true for common MEMS accelerometers. For MOEMS devices,
however, this assumption can sometimes be invalid. Optical ports
are sometimes desirable or required through the backside of the
MOEMS device to provide for transmission through the device.
Existing singulation technology does not address this device
configuration, since the particulate can enter the MOEMS device
from both sides of the wafer. Moreover, attempts to perform some
aspects of the singulation process prior to the release of the
membrane, for example, yield new problems associated with
electrostatic charge accumulation, during optical coating
deposition, on to electrically isolated device dies. This can
result in membrane snap-on the handle wafer material and its
stiction adhesion.
[0005] In general, according to one aspect, the present invention
is directed to a process for singulating MOEMS optical devices from
a precursor structure. This precursor structure comprises device
material, in which movable optical structures are formed, and
handle material, through which optical ports are formed to provide
for optical access to the movable optical structures. The inventive
process comprises coating a frontside and a backside of the
precursor structure with protection material. The precursor
structure is then attached to substrate, which is typically a
dicing tape, and the precursor structure separated into individual
optical devices by a process, including die sawing. Thereafter, the
optical devices are removed from the tape and the protection
material removed from the optical devices.
[0006] In the preferred embodiment, the step of coating the
frontside and the backside of the precursor structure comprises
spraying the protection material on both the frontside and the
backside of the structure. Preferably, a photo-resist material is
used, which is later removed by dissolving the photo-resist layer
in a bath. In one implementation, the bath is acetone. Also,
circulation is preferably employed so that, as particulate matter
is freed from the precursor structure due to the dissolving of the
protection material, the particulate matter is swept away.
[0007] In the preferred embodiment, the precursor structure is
separated into the individual optical devices by die sawing
completely through the handle material and device material. In
other implementations, however, die sawing is performed partially
through the handle material and then cleaving through the remaining
material to completely singulate the optical devices.
[0008] Also, according to the preferred embodiment, the dicing tape
is UV (ultra-violet) curable, with the frontside and backside of
the precursor structure being coated prior to attaching the
precursor structure to the dicing tape. Consequently, the adhesion
of the dicing tape is reduced through LTV exposure. The singulated
devices are then placed into a waffle pack jig for the subsequent
removal of the protection material.
[0009] In general, according to another aspect, the invention also
features a processing jig for singulated MOEMS devices. This jig
has the form of a waffle pack comprising an array of cells for
receiving singulated optical devices. A top is placed over the
waffle pack to retain the MOEMS devices in their respective cells.
Fluid ports are provided in each device cell for facilitating fluid
circulation through the cells.
[0010] The above and other features of the invention including
various novel details of construction and combinations of parts,
and other advantages, will now be more particularly described with
reference to the accompanying drawings and pointed out in the
claims. It will be understood that the particular method and device
embodying the invention are shown by way of illustration and not as
a limitation of the invention. The principles and features of this
invention may be employed in various and numerous embodiments
without departing from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the accompanying drawings, reference characters refer to
the same parts throughout the different views. The drawings are not
necessarily to scale; emphasis has instead been placed upon
illustrating the principles of the invention. Of the drawings:
[0012] FIG. 1 is a perspective view of a MOEMS optical device
including an optical membrane to which the present invention is
applicable in one example;
[0013] FIG. 2 is a perspective view showing the backside of the
MOEMS optical device;
[0014] FIG. 3 is a plan view of a wafer precursor structure for
MOEMS optical devices;
[0015] FIG. 4 is a top plan view showing coupon-level layout of the
MOEMS optical devices on a precursor structure;
[0016] FIG. 5 is a flow diagram illustrating the inventive
singulation process;
[0017] FIG. 6 is a schematic cross sectional view illustrating the
backside and frontside coating of the MOEMS optical device with the
protection material;
[0018] FIG. 7 is a top plan view with partial cut-away showing the
processing jig for singulated MOEMS devices according to the
present invention;
[0019] FIG. 8 is a detailed view of a cell for containing a
singulated MOEMS device;
[0020] FIG. 9 is a cross-sectional view of this single device cell;
and
[0021] FIG. 10 is a pin for registration between the waffle pack
base and the top.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] FIG. 1 shows a frontside of a singulated MOEMS optical
device 10 to which the present invention is applicable in one
example.
[0023] Generally, the optical device comprises device material 12.
A moveable optical structure 14 has been formed in this device
material 12. Specifically, in the illustrated example, a
deflectable membrane 16, i.e., the release structure, is capable
without-of-plane deflection.
[0024] The membrane 16 is attached to the remainder of the device
material via tethers 18. In the illustrated example, a highly
reflecting (HR) dot 20 is deposited at the center of the membrane
16. Device material 12 is provided on handle material 22 with an
intervening sacrificial, insulating layer 21 that is removed from
underneath the membrane 16 to provide for its release and
consequent out-of-plane actuation.
[0025] The deflection of the membrane 14 is controlled by an
electrostatic drive cavity between the device material 12 and the
handle material 22.
[0026] FIG. 2 shows the backside of the optical device 10.
Specifically, an optical port 30 has been formed in the handle
material 22. This optical port preferably extends all the way
through the handle material 22 so that the optical membrane 16 can
be observed from this backside view.
[0027] FIG. 3 shows a wafer precursor structure 110 on which
multiple optical devices 10 are fabricated. In this example,
multiple optical devices 10 are manufactured on a single wafer
simultaneously.
[0028] FIG. 4 shows a coupon-size portion 110' of the wafer. This
view better shows the separate device dies 10 and their associated
optical membrane 16. As shown, according to one feature, ball bumps
or solder balls 60 have been added to each device die 10 at this
wafer level process stage. These ball bumps 16 can be used to
solder bond the individual devices 10 to mounting structures or
alternatively to solder bond another optical device, such as a
concave mirror to the device die 10 to form a Fabry-Perot filter,
for example.
[0029] FIG. 5 is a process diagram illustrating the inventive
process for singulating the optical devices.
[0030] Specifically, in step 210, the frontside and backside of the
precursor structure 110, 110', containing the multiple optical
devices are coated with a protection material. In the preferred
embodiment, this protection material is a photo-resist.
[0031] FIG. 6 shows the process of coating. In the preferred
embodiment, the resist protection material 610 is sprayed on both
sides of the precursor structure 110. Specifically, this
photo-resist 610 forms a photo-resist layer 612 that fills into the
optical ports 30 of the individual optical devices 10 from the
backside. Further, the photo-resist on the frontside fills into
voids 24 that define the flexures 18 or tethers and generally forms
a frontside layer 614 that coats over the membrane 20 and the
surrounding frontside features.
[0032] Returning to FIG. 5, after the step of coating the
protection material on the frontside and backside, the precursor
structure 110 is attached to dicing tape.
[0033] In the preferred embodiment, a UV curable dicing tape is
used.
[0034] In step 214, the precursor structure 110, which is attached
to the dicing tape, is then singulated into the separate optical
devices 10. This is accomplished by die sawing completely through
the handle material 22 and the device material 12. With current die
saw technology, the devices can be singulated with kerfs that are
located with an accuracy of +/- 1.5 micrometers.
[0035] In step 216, the individual devices 10 are removed from the
dicing tape, preferably by a pick-and-place machine. In some
implementations, the adhesion between the dicing tape and the
singulated optical devices are decreased by UV exposure of the
dicing tape to reduce its adhesion.
[0036] Thereafter, in a final step, the protection material is
removed from the singulated optical devices in step 218.
[0037] FIG. 7 shows a plan view of a processing jig 700 for
singulated MOEMS devices. Specifically, the singulated optical
devices 10 are placed into a processing jig where the protection
material is preferably dissolved in an circulated bath in one
implementation of step 218.
[0038] Specifically, in one embodiment, the processing jig 700
comprises a base 710 and a top 712. Specifically, the base portion
710 is in the form of a waffle pack, comprising an array of cells
714 for receiving individual, singulated MOEMS devices.
[0039] FIG. 8 shows the details of one of these cells 714.
Specifically, the cell comprises a center port 716 that passes
entirely through the waffle pack base 710. In the illustrated
example, this port is 1.6 millimeters (mm) in diameter. Side
retaining blocks 718 are located on either lateral side of the port
716. These retaining blocks 718 are approximately 1 mm wide and 1.2
mm tall in the illustrated implementation. Top and bottom retaining
blocks 720 are provided above and below the fluid port 16. These
top and bottom retaining blocks are approximately 2 mm wide and 1
mm in depth. Thus, the void of the cell that receives the device or
chip 10 is less than 4 mm square or approximately 2.8 mm wide and
2.0 mm tall.
[0040] FIG. 9 is a cross sectional view of the exemplary cell 714.
Specifically, the view shows the port 716 and the cross-sections of
the top and bottom retaining blocks 720.
[0041] In the preferred embodiment, the waffle top 712 has a
corresponding array of fluid ports 730. The waffle top comprises
registration holes 732 that mate with registration pins 734 on the
waffle bottom 710 so that the fluid ports 730 of the top 712 are
aligned over the fluid ports 716 of the base 710.
[0042] FIG. 10 illustrates one of these registration pins 734. A 1
mm shoulder 736 surrounding the pins enables the waffle top 712 to
be spaced away from the waffle bottom 710 by approximately one
millimeter, which corresponds to the 1 mm height of the side and
top block 718, 720.
[0043] As a result, when the singulated devices are separately
placed in each one of the cells 714 and the top 712 secured on the
waffle base 710, the devices are retained within their respective
cells by the blocks 718, 720. Fluid ports 730 and 716, however,
allow circulating acetone to attack the photoresist protection
layer on the devices 10 while simultaneously allowing the acetone,
containing any particulate matter, to be washed away.
[0044] Further, acetone circulates through lateral fluid ports that
extend between the top 712 and the waffle bottom 710 and further
between the blocks 718 and 720 thereby allowing effective
particulate matter wash-out in the bath.
[0045] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *