Title: Transfer of optical element patterns on a same side of a substrate already having a feature thereon
Abstract: A passive optical element is transferred into a substrate already having features with a vertical dimension thereon. The features may be another passive optical element, an active optical element, a dichroic layer, a dielectric layer, alignment features, metal portions. A protective layer is provided over the feature during the transfer of the optical element. One or more of these processes may be performed on a wafer level.
Patent Number: 6,869,754 Issued on 03/22/2005 to Suleski, et al.
| Inventors:
|
Suleski; Thomas J. (Charlotte, NC);
Boye; Robert Russell (Charlotte, NC);
Delaney; William (Charlotte, NC);
Miller; Harris (Charlotte, NC);
Morris; James (Charlotte, NC);
Han; Hongtao (Mooresville, NC);
Mathews; Jay (Huntersville, NC)
|
| Assignee:
|
Digital Optics Corp. (Charlotte, NC)
|
| Appl. No.:
|
994867 |
| Filed:
|
November 28, 2001 |
| Current U.S. Class: |
430/321; 216/24; 216/26 |
| Intern'l Class: |
G02B 027//42 |
| Field of Search: |
430/321
216/24,26
|
References Cited [Referenced By]
U.S. Patent Documents
| 5024726 | Jun., 1991 | Fujiwara | 216/24.
|
| 5225039 | Jul., 1993 | Ohguri | 216/24.
|
| 5286338 | Feb., 1994 | Feldblum.
| |
| 5575878 | Nov., 1996 | Cox.
| |
| 5687155 | Nov., 1997 | Fukakusa et al.
| |
| 5835458 | Nov., 1998 | Bischel et al.
| |
| 6124974 | Sep., 2000 | Burger.
| |
| Foreign Patent Documents |
| 8-082704 | Mar., 1996 | JP.
| |
| 2000-235105 | Aug., 2000 | JP.
| |
Other References
Patent Abstracts of Japan, vol. 011, No. 293 (P-619), Sep. 22, 1987, & JP
62 088149 A (Hitachi Ltd.).
Nussbaum, et al., *, Proceedings of the SPIE, vol. 3226, pp. 32-43, (1997).
*Entitled: "Refractive and diffractive elements for micro-optical systems".
Ferstl, et al., **, Ann. Report 1998, Heinrich-Hertz-Institute fur
Nachrichtentechnik, 109-112, 1999.
**Entitled: "Commercial Fabrication of Micro-Structures and Micro-Optical
Elements for Research . . . ".
Stern, ***, Microelectronic Engineering, vol. 34, No. 3-4, pp. 299-319,
(Dec. 1, 1997).
***Entitled: "Pattern transfer for diffractive and refractive microoptics".
Montamedi, et al., ****, Opt.Eng. 36(5): 1282-1297 (May 1997).
****Entitled: "Micro-opto-electro-mechanical devices and on-chip
processing".
Wu, et al, "Micromechanical Photonic Integrated . . . ", IEICE Trans.
Electron, vol. E83C:903-911 Jun. 2000.
|
Primary Examiner: McPherson; John A.
Attorney, Agent or Firm: Morse; Susan S.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. .sctn.119(e) to
U.S. Provisional Application Ser. No. 60/330,504 entitled "Transfer of
Optical Element Patterns on a Same Side of a Substrate Already Having a
Feature Thereon" filed Oct. 23, 2001, the entire contents of which are
hereby incorporated by reference for all purposes.
Claims
What is claimed is:
1. A method of forming a refractive optical element on a first surface of a
substrate already having diffractive optical element thereon, the method
comprising:
creating a pattern for the refractive optical element on the first surface
of the substrate, in a separate portion of the substrate from the
diffractive optical element;
providing a protective layer over the diffractive optical element;
transferring the pattern into the substrate using an analog etch to form
the refractive optical element, the protective layer protecting the
diffractive optical element during the transferring; and
removing the protective layer.
2. The method as claimed in claim 1, wherein the providing the protective
layer includes providing a layer more resistant to the analog etch than
the pattern.
3. The method as claimed in claim 1, wherein the providing the protective
layer includes providing a layer of a same material as the pattern that is
thicker than the pattern.
4. The method as claimed in claim 1, wherein the providing the protective
layer includes providing a layer less resistant to the analog etch than
the pattern, the layer being thicker than the pattern.
5. The method as claimed in claim 1, wherein the providing the protective
layer includes providing a layer having a same material as the substrate.
6. The method as claimed in claim 1, wherein the creating and providing are
simultaneous.
7. The method as claimed in claim 1, wherein the creating occurs after the
providing.
8. The method as claimed in claim 1, wherein the removing occurs during the
transferring.
9. The method as claimed in claim 1, further comprising stabilizing the
pattern.
10. The method as claimed in claim 1, wherein the creating the pattern for
the refractive optical element includes reflowing photoresist.
11. The method as claimed in claim 10, wherein the providing the protective
layer includes providing a layer which maintains substantially all of its
vertical dimension during the reflowing.
12. The method as claimed in claim 1, wherein the providing a protective
layer includes providing a lift off layer over a region in which the
refractive optical element is to be formed, providing the protective layer
over the first surface, and lifting off the protective layer in the
region.
13. The method as claimed in claim 1, further comprising alignment feature
on the first surface.
14. The method as claimed in claim 1, further comprising electro-optical
elements on the first surface.
15. The method as claimed in claim 1, further comprising metal portions on
the first surface.
16. The method as claimed in claim 1, further comprising one of dichroic
portions and dielectric portions on the first surface.
17. The method as claimed in claim 1, wherein the providing the protective
layer includes die bonding protective portions over the diffractive
optical element.
18. A method of making different optical elements on a first surface of a
substrate, the method comprising:
forming a refractive optical element on the first surface of the substrate;
creating a pattern for a diffractive optical element on the first surface
of the substrate, in a separate portion of the substrate from the
refractive optical element;
providing a protective layer over the refractive optical element;
transferring the pattern into the substrate to form the diffractive optical
element, the protective layer protecting the refractive optical element
during the transferring; and
removing the protective layer.
19. The method as claimed in claim 18, wherein the providing the protective
layer includes providing a layer more resistant to the etch than the
pattern.
20. The method as claimed in claim 18, wherein the providing the protective
layer includes providing a layer of a same material as the pattern that is
thicker than the pattern.
21. The method as claimed in claim 18, wherein the providing the protective
layer includes providing a layer less resistant to the etch than the
pattern, the layer being thicker than the pattern.
22. The method as claimed in claimed 18, wherein the providing the
protective layer includes providing a layer having a same material as the
substrate.
23. The method as claimed in claim 18, wherein the creating occurs after
the providing.
24. The method as claimed in claim 18, wherein the removing occurs during
the transferring.
25. The method as claimed in claim 18, further comprising stabilizing the
pattern.
26. The method as claimed in claim 18, wherein the creating the pattern for
the diffractive optical element includes coating the first surface with a
photoresist.
27. The method as claimed in claim 26, wherein the providing the protective
layer is achieved with the coating.
28. The method as claimed in claim 26, wherein the coating includes one of
spray coating and solvent assisted coating.
29. The method as claimed in claim 26, wherein the providing the protective
layer includes die bonding protective portions over the refractive optical
element.
30. A method of making different optical elements on a first surface of a
substrate, the method comprising:
forming a diffractive optical element on the first surface of the
substrate;
creating a pattern for a refractive optical element on the first surface of
the substrate, in a separate portion of the substrate from the diffractive
optical element;
providing a protective layer over the diffractive optical element;
transferring the pattern into the substrate to form the refractive optical
element, the
protective layer protecting the diffractive optical element during the
transferring; and removing the protective layer.
31. The method as claimed in claim 30, wherein the creating the pattern for
the refractive optical element includes reflowing photoresist.
Description
FIELD OF THE INVENTION
The present invention is directed to formation of optical elements etched
into a same side of a substrate having a feature thereon, more
particularly using patterning, masking and/or reflow techniques.
BACKGROUND OF THE INVENTION
Fabrication of both refractive and diffractive optical elements on the same
side of a wafer is desirable for numerous applications. However, known
wafer level creation techniques do not allow for high fidelity patterning
of both refractive and diffractive optical elements on the same side of
the wafer.
For example, if the diffractive optical element is created first, the
creation of the refractive optical element will degrade the fidelity of
the diffractive optical element. This degradation is due to the etching of
the diffractive optical element further into the substrate that occurs
during the etching of the refractive optical element.
If the refractive optical element is created first, then the high fidelity
diffractive optical elements are severely degraded. Also, the topology of
the refractive optical element will not allow a high quality thin
photoresist layer to be spun onto the substrate. Such a high quality,
i.e., uniform, thin photoresist layer is also needed to insure the
creation of high fidelity diffractive optical elements. One possible
solution is the use of spray coating and projection patterning, but this
is not as practical as spinning the photoresist.
Thus, current lithographic techniques do not permit high fidelity
patterning of both refractive and diffractive optical elements when both
are to be provided on the same side of the wafer.
More generally, the above problem arises when a pattern is to be etched
into a same surface already containing features which would be affected by
the etch process. The larger, i.e., deeper, the feature to be etched, the
more likely the etch process will effect the other features already
present.
SUMMARY OF THE INVENTION
The present invention is therefore directed to providing a method of
forming an optical element pattern to be etched on a surface having
features already thereon, and the structures formed thereby, which
substantially overcomes at least one of the above disadvantages.
It is an object of the present invention to create both refractive and
diffractive optical elements in the same side of the substrate.
It is another object of the present invention to preserve features, e.g.,
alignment features, metallization features, active optical elements,
passive optical elements, already on a surface while etching an optical
element into the surface.
These and other objects of the present invention will become more readily
apparent from the detailed description given hereinafter. However, it
should be understood that the detailed description and specific examples,
while indicating the preferred embodiments of the invention, are given by
way of illustration only, since various changes and modifications within
the spirit and scope of the invention will become apparent to those
skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, aspects and advantages will be described
with reference to the drawings, in which:
FIG. 1 is a flow chart of a general overview of the present invention;
FIGS. 2A-2H illustrate the process for forming a diffractive optical
element and a refractive optical element on a same surface according to an
embodiment of the present invention;
FIG. 3 illustrates a manner of protecting features on a substrate prior to
transfer of a pattern into the substrate in accordance with the present
invention;
FIGS. 4A-4C illustrate different manners of protecting features on a
substrate prior to transfer of a pattern into the substrate in accordance
with the present invention; and
FIGS. 5A-5C illustrate different manners of protecting features on a
substrate prior to transfer of a pattern into the substrate in accordance
with the present invention;
DETAILED DESCRIPTION
In the following description, for purposes of explanation and not
limitation, specific details are set forth in order to provide a thorough
understanding of the present invention. However, it will be apparent to
one skilled in the art that the present invention may be practiced in
other embodiments that depart from these specific details. In other
instances, detailed descriptions of well-known devices and methods are
omitted so as not to obscure the description of the present invention with
unnecessary details. As used herein, the term "wafer" is to mean any
substrate on which a plurality of components are formed which are to be
separated to some degree, either individually or as arrays, prior to final
use.
The method for forming an optical element on a surface already having
features thereon is shown in the flow chart of FIG. 1. Generally, a
pattern for forming an optical element is created in a known manner on a
surface already having features thereon in step 10. These features may be
any structure to be preserved either for functioning in the finished
system or for use in further processing, e.g., alignment features. The
pattern may be formed in any variety of manners, e.g., using a binary
mask, a gray scale mask, stamping, ink jet printing, direct writing. It is
then determined in step 12 whether the etching of the pattern would effect
the features on the surface. As used herein, etching is to mean any manner
of transferring the pattern into the substrate, e.g., plasma etching, dry
etching, ion milling, wet etching. If not, for example, if the height of
the pattern to be transferred to the surface is very small, e.g., at least
an order of magnitude less, compared with that of the features on the
surface, or otherwise does not adversely effect the features, then the
flow proceeds directly to the etch 16. More typically, the etch will
adversely effect the features, and the features that will be effected are
protected in step 14, and then the etch is performed in step 16. After the
etch at step 16 is completed, it is determined whether the protection
provided in step 14 still remains on the features at step 18. If not, the
creation is complete. If protection remains, this protection is removed at
step 19, before completion. It is noted that step 10 and step 14 may be
performed simultaneously or their order may be reversed. Further, some of
the patterning and protecting in steps 10 and 14 may be performed within
these steps.
A specific example of the method is shown in FIGS. 2A-2H. It is noted that
the size of the substrate and the relative size of the diffractives in
these figures are only increased to show the additional detail, not due to
any of the processes. A blank substrate 20 is shown in FIG. 2A. The blank
substrate 20 is patterned in any conventional manner to form a diffractive
145 optical element 22 thereon, as shown in FIG. 2B. A protective layer is
then provided over the diffractive optical element 22. This protective
layer should be resistant to the etching to be performed in transferring
the refractive structure into the substrate 20. The protective layer
should also be able to be removed by a process that does not affect the
substrate material.
In the specific example shown here, a lift-off photoresist layer 24 is
patterned to be on the non-diffractive optical element portion of the
substrate 20, as shown in FIG. 2C. A resistant material 26 is then
provided over the substrate 20, as shown in FIG. 2D. The photoresist 24 is
then lifted off the non-diffractive optical element portion of the
substrate 20, taking the unneeded portion of the resistant material 26
with it. A resultant protective layer 28 covering the diffractive optical
element 22 is shown in FIG. 2E. Other manners of patterning the resistant
material 26, such as using a mask, may also be employed to form the
protective layer 28.
Refractive structures 27 which are to be transferred into the substrate 20
are then formed on the substrate 20 as shown in FIG. 2F. These refractive
structures 27 may be formed in conventional manners, e.g., patterning
photoresist and reflowing the photoresist, using gray scale masks,
stamping or direct write. The refractive structures 27 are then
transferred into the substrate 20, using a process which may not
completely remove the protective layer 28, to form the refractive optical
elements 29 as shown in FIG. 2G. Finally, the protective layer 28 is
removed, resulting in refractive and diffractive optical elements being
formed on the same side of the substrate 20.
The protection of the features already present on the surface at step 14
may be realized in a number of manners, depending upon the pattern to be
etched, the etching to be performed, and the features to be protected. For
example, if the feature is below or a flat layer on the surface to be
etched, a protective material that is resistant to the etch process, but
may be removed from the surface without affecting the underlying
structure, may be bonded over the features to be protected. In the example
shown in FIG. 3, a substrate 30 has a diffractive structure 32 therein and
a patterned layer 34, e.g., a metal, an anti-reflection coating, a thin
film filter, a dielectric layer, a dichroic layer, which is to remain on
the surface of the substrate. It is noted that metal may serve an optical
function, e.g., an aperture stop, a reflector, and/or an electrical
function, e.g., input, output or contact. These features 32, 34 are
covered by protective portions 36. This may be realized using a die bonder
for individual protective portions or may be realized using a wafer of the
protective material with holes therethrough to permit the etching of a
pattern for a refractive optical element 38. Alignment tolerances may be
realized by oversizing the protective portions. The pattern for a
refractive optical element 38 is formed on the substrate, e.g., before the
protective portions are provided. One possible material for the protective
portions is CaF.sub.2, which is resistant to fluorine and oxygen, which
are commonly used in etching. CaF.sub.2 may be wet etched in ammonium
fluoride, which does not damage the underlying substrate, when the
substrate is, for example, fused silica or silicon.
Alternatively, the protection may be provided by patterning a protective
material, e.g., photoresist, over the features. This protective layer may
be the same photoresist layer to be used in the formation of the optical
element, as shown in FIGS. 4A and 4B. In FIG. 4A, a photoresist layer 44
is provided, e.g., screen printed, sprayed, spin coated, or plated, over a
refractive optical element 42 on a substrate 40. This photoresist layer 44
is then patterned and etched to form a diffractive optical element. The
refractive element 42 is protected during etch by the photoresist layer
44. In FIG. 4B, a photoresist layer 46 used to form a refractive optical
element is also patterned to remain over the feature 45, here a
diffractive optical element, to form a protective photoresist 48. The
photoresist pattern 46 is then reflowed to form the lens. The protective
photoresist 48 over the feature 45 is also reflowed. Then, the protective
photoresist 48 on the feature 45 is etched away as the refractive optical
pattern is etched into the substrate 40. Any remaining protective portion
may be removed, e.g., by chemical etching.
However, when the protective photoresist 48 covering the feature 45 is
larger, i.e., wider, than the pattern 46 for the refractive optical
element while having the same thickness, reflow may result in a lower
profile for the protective photoresist 48 over the feature 45 than that
for the refractive optical element 46. Then, when etched, the protective
photoresist 48 over the feature 45 is removed before the etch of the
refractive optical element is complete. Thus, the feature 45 may still be
damaged during the transfer. One solution to this problem would be to use
a gray scale mask or other technique to leave a thicker photoresist over
the feature, so that after reflow, sufficient height remains that the
feature is protected during etch. However, using a reflowed protective
photoresist also can result in undesired etching around the outer regions
of the protective photoresist.
A solution to this is shown in FIG. 4C, in which a protective photoresist
48 and a refractive photoresist are provided and patterned in either order
on the substrate 40. Here, the protective photoresist 48 is a photoresist
which does not reflow under the same conditions as the refractive
photoresist 46. So, when the substrate 40 is subjected to reflow, only the
refractive photoresist 46 reflows. The refractive photoresist 46 and the
protective photoresist 48 may have the same etch rate, so most of the
protective photoresist 48 may have been removed after the etch of the
refractive photoresist 46 is complete. Any subsequent complete removal of
the protective photoresist may be realized. Alternatively, the refractive
pattern could be formed using techniques that do not require reflow, e.g.,
gray scale masks, stamping, to eliminate the attendant problems of a
reflowed protective photoresist.
Another solution to this problem is shown in FIG. 5A, in which further
photoresist 58 is provided over reflowed protective photoresist 54
covering the feature 55 on the substrate 50. The refractive photoresist
pattern 56 may be silated, or otherwise stabilized, to allow for the
additional photoresist 58 to be patterned without affecting the refractive
pattern 56.
Another solution is shown in FIG. 5B, in which a protective photoresist
layer 58 is patterned to cover a feature 55 on a substrate 50, and then
another photoresist layer 54 in which the refractive pattern is to be
formed is provided over this layer, e.g., by spinning, and again patterned
to remain over the first protective layer 58 and to serve as the
refractive pattern 56. After the refractive pattern 56 is reflowed,
sufficient protection remains over the feature 55 to protect it during
etch. The first protective photoresist may be the same photoresist, may be
a photoresist which is more resistant to the etch than the photoresist, or
may be less resistant to the etch than the refractive photoresist 56. If
the protective photoresist layer 58 is less or equally resistant to the
etch, sufficient height of the protective photoresist 58 would need to be
provided. It is noted that providing a thicker protective layer than the
refractive pattern may distort the transfer of the refractive photoresist,
due to loading during etching. Further, if the photoresists are different,
once the photoresist layer 54 over the feature 55 is etched away, the etch
selectivity shifts dramatically, effecting the transfer of the refractive
element 56.
Yet another solution is shown in FIG. 5C, where a protective photoresist 58
is to provided over a feature 55 on the substrate 50 after the photoresist
56 for the refractive element has been patterned, reflowed, and
stabilized, if necessary. Again, the protective photoresist 58 may be the
same photoresist, may be a photoresist which is more resistant to the etch
than the photoresist, or may be less or equally resistant to the etch than
the refractive photoresist layer 56. If the protective photoresist layer
58 is less resistant to the etch, sufficient height of the protective
photoresist 58 would need to be provided to insure protection of the
feature 55.
At least one of the above steps in the process, e.g., the formation of the
pattern, the provision of protection, and the transfer of the pattern, is
performed on a wafer level. The wafer may then be diced to form individual
systems.
It will be obvious that the invention may be varied in a plurality of ways.
Such variations are not to be regarded as a departure from the scope of
the invention. All such modifications as would be obvious to one skilled
in the art are intended to be included within the scope of the present
invention.
*
