U.S. patent application number 10/866416 was filed with the patent office on 2005-12-15 for optical films and methods of making the same.
Invention is credited to Deng, Xuegong, Nikolov, Anguel N., Wang, Jian Jim.
Application Number | 20050275944 10/866416 |
Document ID | / |
Family ID | 35460243 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050275944 |
Kind Code |
A1 |
Wang, Jian Jim ; et
al. |
December 15, 2005 |
Optical films and methods of making the same
Abstract
Films for optical use, articles containing such films, methods
for making such films, and systems that utilize such films, are
disclosed.
Inventors: |
Wang, Jian Jim; (Orefield,
PA) ; Deng, Xuegong; (Piscataway, NJ) ;
Nikolov, Anguel N.; (Bridgewater, NJ) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
35460243 |
Appl. No.: |
10/866416 |
Filed: |
June 11, 2004 |
Current U.S.
Class: |
359/576 ;
264/1.31; 359/578; 427/162; 430/321 |
Current CPC
Class: |
G02B 5/18 20130101; G02B
5/3025 20130101; G02B 1/118 20130101; G02B 5/1809 20130101; G02F
1/13363 20130101; B82Y 20/00 20130101; G02B 1/113 20130101; G02B
5/1866 20130101; G02B 5/1857 20130101; G02B 5/3083 20130101 |
Class at
Publication: |
359/576 ;
430/321; 359/578; 427/162; 264/001.31 |
International
Class: |
B05D 005/06; B29D
011/00; G02B 005/18 |
Claims
What is claimed is:
1. A method, comprising: providing an article that includes a layer
of a first material, wherein the layer of the first material
includes at least one trench and wherein the layer is birefringent
for light of wavelength .lambda. propagating through the layer
along an axis, wherein .lambda. is between 150 nm and 2,000 nm; and
filling at least about 50% of a volume of the trench by
sequentially forming a plurality of monolayers of a second material
within the trench.
2. The method of claim 1, wherein the filling further comprises
forming one or more monolayers of a third material within the
trench, wherein the second and third materials are different.
3. The method of claim 2, wherein the monolayers of the second and
third materials form a nanolaminate material.
4. The method of claim 1, wherein at least about 80% of the volume
of the trench is filled by sequentially forming the plurality of
monolayers of the second material within the trench.
5. The method of claim 1, wherein at least about 90% of the volume
of the trench is filled by sequentially forming the plurality of
monolayers of the second material within the trench.
6. The method of claim 1, wherein at least about 99% of the volume
of the trench is filled by sequentially forming the plurality of
monolayers of the second material within the trench.
7. The method of claim 1, wherein the second material is different
from the first material.
8. The method of claim 1, wherein the layer of the first material
and the second material form a continuous layer.
9. The method of claim 1, wherein the article comprises additional
trenches formed in the surface of the layer of the first
material.
10. The method of claim 9, wherein the method further comprises
filling at least about 50% of a volume of each of the additional
trenches by sequentially forming a plurality of monolayers of the
second material within the additional trenches.
11. The method of claim 9, wherein the method further comprises
filling at least about 80% of a volume of each of the additional
trenches by sequentially forming a plurality of monolayers of the
second material within the additional trenches.
12. The method of claim 9, wherein the method further comprises
filling at least about 90% of a volume of each of the additional
trenches by sequentially forming a plurality of monolayers of the
second material within the additional trenches.
13. The method of claim 9, wherein the method further comprises
filling at least about 99% of a volume of each of the additional
trenches by sequentially forming a plurality of monolayers of the
second material within the additional trenches.
14. The method of claim 9, wherein the trenches are separated by
rows of the first material.
15. The method of claim 7, wherein the layer of the first material
forms a surface relief grating.
16. The method of claim 15, wherein the surface relief grating has
a grating period of about 500 nm or less.
17. The method of claim 7, wherein the trench is formed by etching
a continuous layer of the first material.
18. The method of claim 17, wherein the etching comprising reactive
ion etching.
19. The method of claim 1, wherein the trench is formed
lithographically.
20. The method of claim 19, wherein the trench is formed using
nano-imprint lithography.
21. The method of claim 20, wherein the nano-imprint lithography
includes forming a pattern in a thermoplastic material.
22. The method of claim 20, wherein the nano-imprint lithography
includes forming a pattern in a UV curable material.
23. The method of claim 19, wherein the trench is formed using
holographic lithography.
24. The method of claim 1, further comprising forming a layer of
the second material over the filled trench by sequentially forming
monolayers of the second material over the trench.
25. The method of claim 24, wherein the layer of the second
material has a surface with an arithmetic mean roughness of about
50 nm or less.
26. The method of claim 1, wherein the second material is a
dielectric material.
27. The method of claim 1, wherein forming the plurality of
monolayers of the second material comprises depositing a monolayer
of a precursor and exposing the monolayer of the precursor to a
reagent to provide a monolayer of the second material.
28. The method of claim 27, wherein the reagent chemically reacts
with the precursor to form the second material.
29. The method of claim 28, wherein the reagent oxidizes the
precursor to form the second material.
30. The method of claim 27, wherein depositing the monolayer of the
precursor comprises introducing a first gas comprising the
precursor into a chamber housing the article.
31. The method of claim 30, wherein a pressure of the first gas in
the chamber is about 0.01 to about 100 Torr while the monolayer of
the precursor is deposited.
32. The method of claim 30, wherein exposing the monolayer of the
precursor to the reagent comprises introducing a second gas
comprising the reagent into the chamber.
33. The method of claim 30, wherein a pressure of the second gas in
the chamber is about 0.01 to about 100 Torr while the monolayer of
the precursor is exposed to the reagent.
34. The method of claim 30, wherein a third gas is introduced into
the chamber after the first gas is introduced and prior to
introducing the second gas.
35. The method of claim 27, wherein the third gas is inert with
respect to the precursor.
36. The method of claim 27, wherein the third gas comprises at
least one gas selected from the group consisting of helium, argon,
nitrogen, neon, krypton, and xenon.
37. The method of claim 27, wherein the precursor is selected from
the group consisting of tris(tert-butoxy)silanol,
(CH.sub.3).sub.3Al, TiCl.sub.4, SiCl.sub.4, SiH.sub.2Cl.sub.2,
TaCl.sub.3, AlCl.sub.3, Hf-ethaoxide and Ta-ethaoxide.
38. The method of claim 1, wherein the trench has a width of about
1,000 nm or less.
39. The method of claim 1, wherein the trench has a depth of about
10 nm or more.
40. The method of claim 8, wherein the continuous layer is
birefringent for light of wavelength .lambda. propagating through
the continuous layer along an axis, wherein .lambda. is between 150
nm and 2,000 nm.
41. A method, comprising: forming a layer of a material on a
surface of a grating using atomic layer deposition.
42. The method of claim 41, wherein the grating is a surface relief
grating.
43. The method of claim 41, wherein the grating has a grating
period of about 2,000 nm or less.
44. The method of claim 1, further comprising forming a second
birefringent layer on the layer of the first material after filling
the trench.
45. The method of claim 44, wherein the second birefringent layer
comprises a plurality of trenches and forming the second
birefringent layer includes filling the plurality of trenches by
sequentially forming a plurality of monolayers of a third material
within the trenches of the second birefringent layer.
46. The method of claim 44, further comprising forming additional
birefringent layers on the second birefringent layer.
47. A method, comprising: forming an optical retardation film using
atomic layer deposition.
48. The method of claim 47, wherein the optical retardation film is
form birefringent.
49. An article, comprising: a continuous layer including rows of a
first material alternating with rows of a nanolaminate material,
wherein the continuous layer is birefringent for light of
wavelength .lambda. propagating through the continuous layer along
an axis, wherein .lambda. is between 150 nm and 2,000 nm.
50. The article of claim 49, further comprising at least one
antireflection film, wherein a surface of the article comprises a
surface of the antireflection film.
51. The article of claim 49, further comprising a layer of a third
material adjacent the continuous layer.
52. The article of claim 49, further comprising a layer of the
nanolaminate material adjacent the continuous layer.
53. The article of claim 49, wherein the layer of the nanolaminate
material adjacent the continuous layer has a surface with an
arithmetic mean roughness of about 50 nm or less.
54. The method of claim 49, wherein the layer of the nanolaminate
material adjacent the continuous layer has a surface with an
arithmetic mean roughness of about 20 nm or less.
55. The method of claim 49, wherein the layer of the nanolaminate
material adjacent the continuous layer has a surface with an
arithmetic mean roughness of about 10 nm or less.
56. The article of claim 49, wherein the nanolaminate material has
a refractive index of about 1.3 or more at .lambda..
57. The article of claim 49, wherein the nanolaminate material has
a refractive index of about 1.5 or more at .lambda..
58. The article of claim 49, wherein the nanolaminate material has
a refractive index of about 1.6 or more at .lambda..
59. The article of claim 49, wherein the nanolaminate material has
a refractive index of about 1.7 or more at .lambda..
60. The article of claim 49, wherein the nanolaminate material has
a refractive index of about 1.8 or more at .lambda..
61. The article of claim 49, wherein the nanolaminate material has
a refractive index of about 1.9 or more at .lambda..
62. The article of claim 49, wherein the nanolaminate material has
a refractive index of about 2.0 or more at .lambda..
63. The article of claim 49, wherein the nanolaminate material
comprises portions of a second material and portions of a third
material, wherein the second and third materials are different.
64. The article of claim 63, wherein the first and third materials
are the same.
65. The article of claim 49, wherein the nanolaminate material
comprises a dielectric material.
66. The article of claim 49, wherein the nanolaminate material
comprises an inorganic material.
67. The article of claim 49, wherein the nanolaminate material
comprises a metal.
68. The article of claim 49, wherein the nanolaminate material
comprises a material selected from a group consisting of SiO.sub.2,
SiN.sub.x, Si, Al.sub.2O.sub.3, ZrO.sub.2, Ta.sub.2O.sub.5,
TiO.sub.2, HfO.sub.2, Nb.sub.2O.sub.5, and MgF.sub.2.
69. The article of claim 49, wherein the first material is a
dielectric material.
70. The article of claim 49, wherein the first material is an
inorganic material.
71. The article of claim 49, wherein the first material is a
polymer.
72. The article of claim 49, wherein the first material is a
semiconductor.
73. The article of claim 49, wherein the first material is a
metal.
74. The article of claim 49, wherein the first material is selected
from a group consisting of SiO.sub.2, SiN.sub.x, Si,
Al.sub.2O.sub.3, ZrO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2, HfO.sub.2,
Nb.sub.2O.sub.5, and MgF.sub.2.
75. The article of claim 49, wherein the first material is a
glass.
76. The article of claim 49, wherein the continuous layer forms a
grating with a grating period of about 500 nm or less.
77. The article of claim 49, wherein the continuous layer forms a
grating with a grating period of about 200 nm or less.
78. The article of claim 49, wherein the continuous layer forms a
grating with a grating period of about 100 nm or less.
79. The article of claim 49, wherein the continuous layer forms a
grating with a grating period of about 50 nm or less.
80. The article of claim 49, wherein the rows of the first material
have a minimum width of about 500 nm or less.
81. The article of claim 49, wherein the rows of the first material
have a minimum width of about 200 nm or less.
82. The article of claim 49, wherein the rows of the first material
have a minimum width of about 100 nm or less.
83. The article of claim 49, wherein the rows of the first material
have a minimum width of about 50 nm or less.
84. The article of claim 49, wherein the rows of the first material
have a minimum width of about 20 nm or less.
85. The article of claim 49, wherein the rows of the first material
have a minimum width of about 10 nm or less.
86. The article of claim 49, wherein the rows of the first material
have a minimum width that is different than a minimum width of the
rows of the nanolaminate material.
87. The article of claim 49, wherein the rows of the first material
have a minimum width that is the same as a minimum width of the
rows of the nanolaminate material.
88. The article of claim 49, wherein a minimum width of each of the
rows of the first material is substantially the same.
89. The article of claim 49, wherein a minimum width of each of the
rows of the nanolaminate material is substantially the same.
90. The article of claim 49, wherein the continuous layer has a
thickness of about 15 nm or more.
91. The article of claim 49, wherein the continuous layer has a
thickness of about 100 nm or more.
92. The article of claim 49, wherein the continuous layer has a
thickness of about 200 nm or more.
93. The article of claim 49, wherein the continuous layer has a
thickness of about 300 nm or more.
94. The article of claim 49, wherein the continuous layer has a
thickness of about 500 nm or more.
95. The article of claim 49, wherein the continuous layer has a
thickness of about 1,000 nm or more.
96. The article of claim 49, wherein the continuous layer has a
thickness of about 1,500 nm or more.
97. The article of claim 49, wherein the layer has a thickness of
about 2,000 nm or more.
98. The article of claim 49, wherein the continuous layer has an
optical retardation of about 1 nm or more for light of wavelength
.lambda. propagating through the continuous layer along an axis,
wherein .lambda. is between 150 nm and 2,000 nm.
99. The article of claim 49, wherein the continuous layer has an
optical retardation of about 2 nm or more for light of wavelength
.lambda. propagating through the continuous layer along an axis,
wherein .lambda. is between 150 nm and 2,000 nm.
100. The article of claim 49, wherein the continuous layer has an
optical retardation of about 5 nm or more for light of wavelength
.lambda. propagating through the continuous layer along an axis,
wherein .lambda. is between 150 nm and 2,000 mm.
101. The article of claim 49, wherein the layer has an optical
retardation of about 10 nm or more for light of wavelength .lambda.
propagating through the composite layer along an axis, wherein
.lambda. is between 150=n and 2,000 nm.
102. The article of claim 49, wherein the layer has an optical
retardation of about 20 nm or more for light of wavelength .lambda.
propagating through the composite layer along an axis, wherein
.lambda. is between about 150 nm and about 2,000 nm.
103. The article of claim 49, wherein the layer has an optical
retardation of about 50 nm or more for light of wavelength .lambda.
propagating through the composite layer along an axis, wherein
.lambda. is between about 150 nm and about 2,000 nm.
104. The article of claim 49, wherein the layer has an optical
retardation of about 2,000 nm or less for light of wavelength
.lambda. propagating through the composite layer along an axis,
wherein .lambda. is between about 150 nm and about 2,000 nm.
105. The article of claim 49, wherein the layer has an optical
retardation of about 1,000 nm or less for light of wavelength
.lambda. propagating through the composite layer along an axis,
wherein .lambda. is between about 150 nm and about 2,000 mm.
106. The article of claim 49, wherein .lambda. is between about 400
nm and about 700 nm.
107. The article of claim 49, wherein .lambda. is between about 510
nm and about 570 mm.
108. The article of claim 49, wherein the continuous layer has an
optical retardation of about 4 nm or more for light of wavelength
.lambda. propagating through the continuous layer along an axis,
wherein .lambda. is between about 400 nm and about 700 nm.
109. The article of claim 49, further comprising a second
continuous layer including rows of a third material alternating
with rows of a second nanolaminate material, wherein the second
continuous layer is birefringent for light of wavelength .lambda.
propagating through the second continuous layer along the axis.
110. The article of claim 109, further comprising additional form
birefringent layers, wherein each of the form birefringent layers
are birefringent for light of wavelength .lambda. propagating
through each form birefringent layer along the axis.
111. An article, comprising: a form birefringent optical
retardation film comprising a nanolaminate material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.119
to U.S. Provisional Patent Application Ser. No. ______, entitled
"PRECISION OPTICAL RETARDERS AND WAVEPLATES AND THE METHOD FOR
MAKING THE SAME," and filed on Apr. 15, 2004, the entire contents
of which are hereby incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to optical films and related
articles, systems and methods.
BACKGROUND
[0003] Optical devices and optical systems are commonly used where
manipulation of light is desired. Examples of optical devices
include lenses, polarizers, optical filters, antireflection films,
retarders (e.g., quarter-waveplates), and beam splitters (e.g.,
polarizing and non-polarizing beam splitters).
SUMMARY
[0004] This invention relates to films for optical use, articles
containing such films, methods for making such films, and systems
that utilize such films.
[0005] In a first aspect, the invention features a method that
includes providing an article that includes a layer of a first
material, wherein the layer of the first material includes at least
one trench and wherein the layer is birefringent for light of
wavelength .lambda. propagating through the layer along an axis,
wherein .lambda. is between 150 nm and 2,000 nm, and filling at
least about 50% of a volume of the trench by sequentially forming a
plurality of monolayers of a second material within the trench.
[0006] In another aspect, the invention features a method that
includes forming a layer of a material on a surface of a grating
using atomic layer deposition.
[0007] In another aspect, the invention features a method that
includes forming an optical retardation film using atomic layer
deposition.
[0008] In another aspect, the invention features an article, which
includes a continuous layer including rows of a first material
alternating with rows of a nanolaminate material, wherein the
continuous layer is birefringent for light of wavelength .lambda.
propagating through the continuous layer along an axis, wherein
.lambda. is between 150 nm and 2,000 nm.
[0009] In another aspect, the invention features an article
including a form birefringent optical retardation film that
includes a nanolaminate material.
[0010] Embodiments of the invention can include one or more of the
following features.
[0011] The filling can further include forming one or more
monolayers of a third material within the trench, wherein the
second and third materials are different. The monolayers of the
second and third materials can form a nanolaminate material. At
least about 80% (e.g., at least about 90%, at least about 99%) of
the volume of the trench can be filled by sequentially forming the
plurality of monolayers of the second material within the trench.
The second material can be different from the first material. The
layer of the first material and the second material can form a
continuous layer. The continuous layer can be birefringent for
light of wavelength .lambda. propagating through the continuous
layer along an axis, wherein .lambda. is between 150 nm and 2,000
nm. The article can include additional trenches formed in the
surface of the layer of the first material. The method can further
include filling at least about 50% of a volume of each of the
additional trenches by sequentially forming a plurality of
monolayers of the second material within the additional trenches.
The method can further include filling at least about 80% (e.g., at
least about 90%, at least about 99%) of a volume of each of the
additional trenches by sequentially forming a plurality of
monolayers of the second material within the additional trenches.
The trenches can be separated by rows of the first material. The
layer of the first material can form a surface relief grating. The
surface relief grating can have a grating period of about 500 nm or
less (e.g., about 400 nm or less, about 300 mm or less, about 200
nm or less, about 100 nm or less).
[0012] The trench can be formed by etching (e.g., reactive ion
etching) a continuous layer of the first material. The trench can
be formed lithographically. For example, the trench can be formed
using nano-imprint lithography or holographic lithography. Where
the trench is formed using nano-imprint lithography, the
nano-imprint lithography can include forming a pattern in a
thermoplastic material. Alternatively, or additionally, the
nano-imprint lithography can include forming a pattern in a UV
curable material.
[0013] The method can further include forming a layer of the second
material over the filled trench by sequentially forming monolayers
of the second material over the trench. The layer of the second
material has a surface with an arithmetic mean roughness of about
50 nm or less (e.g., about 40 nm or less, about 30 nm or less,
about 20 mm or less, about 10 nm or less).
[0014] The second material can be a dielectric material. In some
embodiments, forming the plurality of monolayers of the second
material comprises depositing a monolayer of a precursor and
exposing the monolayer of the precursor to a reagent to provide a
monolayer of the second material. The reagent can chemically react
with the precursor to form the second material. For example, the
reagent can oxidize the precursor to form the second material.
Depositing the monolayer of the precursor can include introducing a
first gas comprising the precursor into a chamber housing the
article. A pressure of the first gas in the chamber can be about
0.01 to about 100 Torr while the monolayer of the precursor is
deposited. Exposing the monolayer of the precursor to the reagent
can include introducing a second gas comprising the reagent into
the chamber. A pressure of the second gas in the chamber can be
about 0.01 to about 100 Torr while the monolayer of the precursor
is exposed to the reagent. A third gas can be introduced into the
chamber after the first gas is introduced and prior to introducing
the second gas. The third gas can be inert with respect to the
precursor. The third gas can include at least one gas selected from
the group consisting of helium, argon, nitrogen, neon, krypton, and
xenon. The precursor can be selected from the group consisting of
tris(tert-butoxy)silanol, (CH.sub.3).sub.3Al, TiCl.sub.4,
SiCl.sub.4, SiH.sub.2Cl.sub.2, TaCl.sub.3, AlCl.sub.3, Hf-ethaoxide
and Ta-ethaoxide.
[0015] The trench can have a width of about 1,000 nm or less (e.g.,
about 900 mm or less, about 800 mm or less, about 700 nm or less,
about 600 nm or less, about 500 m or less, about 400 mm or less,
about 300 nm or less, about 200 nm or less). The trench can have a
depth of about 10 nm or more (e.g., about 20 nm or more, about 30 m
or more, about 40 nm or more, about 50 nm or more, about 75 m or
more, about 100 mm or more, about 150 nm or more, about 200 nm or
more, about 300 mm or more, about 400 nm or more, about 500 nm or
more, about 1,000 or more, about 1,500 nm or more, about 2,000 or
more).
[0016] The method can further include forming a second birefringent
layer on the layer of the first material after filling the trench.
The second birefringent layer can include a plurality of trenches
and forming the second birefringent layer includes filling the
plurality of trenches by sequentially forming a plurality of
monolayers of a third material within the trenches of the second
birefringent layer. The method can also include forming additional
birefringent layers on the second birefringent layer.
[0017] In certain embodiments, the grating can be a surface relief
grating. The grating can have a grating period of about 2,000 nm or
less (e.g., about 1,500 nm or less, about 1,000 or less, about 750
nm or less, about 500 nm or less, about 300 nm or less, about 200
nm or less).
[0018] The optical retardation film can be form birefringent.
[0019] The article can further include at least one antireflection
film, wherein a surface of the article comprises a surface of the
antireflection film. In some embodiments, the article also includes
a layer of a third material adjacent the continuous layer. The
article can include a layer of the nanolaminate material adjacent
the continuous layer. The layer of the nanolaminate material
adjacent the continuous layer can have a surface with an arithmetic
mean roughness of about 50 nm or less (e.g., about 40 nm or less,
about 30 nm or less, about 20 nm or less, about 10 nm or less). The
nanolaminate material can have a refractive index of about 1.3 or
more at .lambda. (e.g., about 1.4 or more, about 1.5 or more, about
1.6 or more, about 1.7 or more, about 1.8 or more, about 1.9 or
more, about 2.0 or more, about 2.1 or more). The first material can
have a refractive index of about 1.3 or more at .lambda. (e.g.,
about 1.4 or more, about 1.5 or more, about 1.6 or more, about 1.7
or more, about 1.8 or more, about 1.9 or more, about 2.0 or more,
about 2.1 or more). The nanolaminate material can include portions
of a second material and portions of a third material, wherein the
second and third materials are different. In some embodiments, the
first and third materials are the same.
[0020] The nanolaminate material can include a dielectric material,
an inorganic material, and/or a metal. The nanolaminate material
can include a material selected from a group consisting of
SiO.sub.2, SiN.sub.x, Si, Al.sub.2O.sub.3, ZrO.sub.2,
Ta.sub.2O.sub.5, TiO.sub.2, HfO.sub.2, Nb.sub.2O.sub.5, and
MgF.sub.2.
[0021] The first material can be a dielectric material, an
inorganic material, a glass, a polymer, a semiconductor, and/or a
metal. In certain embodiments, the first material is selected from
a group consisting of SiO.sub.2, SiN.sub.x, Si, Al.sub.2O.sub.3,
ZrO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2, HfO.sub.2; Nb.sub.2O.sub.5,
and MgF.sub.2.
[0022] The continuous layer can form a grating with a grating
period of about 500 nm or less (e.g., about 200 nm or less, about
100 nm or less, about 50 nm or less). The rows of the first
material can have a minimum width of about 500 nm or less (about
200 nm or less, about 100 nm or less, about 50 nm or less, about 20
nm or less, about 10 nm or less). The rows of the first material
can have a minimum width that is the same or different than a
minimum width of the rows of the nanolaminate material. A minimum
width of each of the rows of the first material can be
substantially the same. Alternatively, or additionally, a minimum
width of each of the rows of the nanolaminate material is
substantially the same.
[0023] The continuous layer has a thickness of about 15 nm or more
(e.g., about 30 nm or more, about 50 nm or more, about 75 nm or
more, about 100 nm or more, about 150 or more, about 200 nm or
more, about 300 nm or more, about 500 nm or more, about 1,000 nm or
more, about 1,500 nm or more, about 2,000 or more). In certain
embodiments, the continuous layer has an optical retardation of
about 1 nm or more (e.g., about 2 nm or more, about 5 nm or more,
about 10 nm or more, about 20 nm or more, about 50 nm or more) for
light of wavelength .lambda. propagating through the continuous
layer along an axis, wherein .lambda. is between 150 nm and 2,000
nm. The continuous layer can have an optical retardation of about
2,000 nm or less for light of wavelength .lambda. propagating
through the composite layer along an axis, wherein .lambda. is
between 200 nm and 2,000 nm. In some embodiments, .lambda. is
between about 400 nm and about 700 m (e.g., between about 510 nm
and about 570 nm). In some embodiments, the continuous layer has an
optical retardation of about 4 nm or more for light of wavelength
.lambda. propagating through the continuous layer along an axis,
wherein .lambda. is between about 400 nm and about 700 nm.
[0024] The article can include a second continuous layer including
rows of a third material alternating with rows of a second
nanolaminate material, wherein the second continuous layer is
birefringent for light of wavelength .lambda. propagating through
the second continuous layer along the axis. The article can further
include additional form the portion(s), thereby controlling the
birefringence. As an example, one or more portions of the layer can
be formed from a nanolaminate. The refractive index of the
nanolaminate can be tuned by selecting the proportion of two or
more different materials in the nanolaminate, which can be
controlled on a monolayer by monolayer basis where the nanolaminate
is formed using atomic layer deposition.
[0025] Alternatively, or additionally, precisely controlling the
structure of the layer can accurately control the birefringence of
a form birefringent layer. For example, using lithographic
techniques (e.g., electron beam lithography, nanoimprint
lithography, holographic lithography) to define the structure
(e.g., depth, width and profile of a grating) of a form
birefringent layer can allow for precise control of the
structure.
[0026] In certain embodiments, the retardance of optical retarders
can be precisely controlled. For example, the birefringence and/or
depth of a form birefringent layer in an optical retarder can be
precisely controlled to provide a desired retardance. As an
example, optical retarders can include one or more layers to
control the thickness of portions of a form birefringent layer in
the retarder, such as one or more etch stop layers.
[0027] In some embodiments, optical retarders have high
transmission at wavelengths of interest. For example, optical
retarders can include one or more antireflection films on one or
more interfaces that reduce reflection of light at wavelengths of
interest. Alternatively, or additionally, layers of optical
retarders can be formed from materials with relatively low
absorption at wavelengths of interest.
[0028] Other features, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0029] FIG. 1 is a perspective view of an embodiment of an optical
retarder.
[0030] FIGS. 2A-2J show steps in the manufacture of the optical
retarder shown in FIG. 1.
[0031] FIG. 3 is a schematic diagram of an atomic layer deposition
system.
[0032] FIG. 4 is a flow chart showing steps for forming a
nanolaminate using atomic layer deposition.
[0033] FIG. 5 is a cross-sectional view of another embodiment of an
optical retarder birefringent layers, wherein each of the form
birefringent layers are birefringent for light of wavelength
.lambda. propagating through each form birefringent layer along the
axis.
[0034] Embodiments of the invention may include one or more of the
following advantages.
[0035] In some embodiments, the article can be a relatively robust
optical retarder, that can have high transmission at wavelengths of
interest, and that have a retardation that can be precisely
controlled. Optical retarders can include one or more form
birefringent layers. Form birefringence results from sub-wavelength
structure in a medium, which can be achieved by arranging at least
two difference materials (e.g., optically isotropic materials) in
an alternating way. Form birefringence can result from
sub-wavelength grating structures, in which a medium has a periodic
modulation in its refractive index, where the period is
substantially less than the wavelength of interest. Since the
period is less than the wavelength of interest, substantially only
zero-order diffractions occur and all higher order diffractions
become evanescent (e.g., a beam at the wavelength of interest is
substantially transmitted and/or reflected). While the materials
composing the form birefringent media can be optically isotropic
(i.e., having an isotropic index of refraction), the media itself
will be optically anisotropic, giving rise to birefringence.
[0036] In some embodiments, optical retarders can include one or
more form birefringent layers that are formed of continuous
material, as opposed to, for example, having trenches filled with a
gas (e.g., air). Accordingly, the optical retarders can be more
mechanically robust than optical retarders that include
non-continuous layers (e.g., layers that include one or more
trenches filled with air).
[0037] In certain embodiments, continuous form birefringent layers
can be formed having relatively high aspect ratios between the
width and thickness of portions of the layers. As an example, high
aspect ratio trenches can be etched into a layer, and the trenches
subsequently filled using a conformal coating method (e.g., atomic
layer deposition) to provide a continuous form birefringent layer
having a relatively high aspect ratio.
[0038] The birefringence of optical retarders can be precisely
controlled. To achieve this, the refractive index of one or more
portions of a form birefringent layer in an optical retarder can,
for example, be tuned to a desired value by controlling the
composition of
[0039] FIG. 6 is a cross-sectional view of an embodiment of an
optical retarder including multiple retardation layers.
[0040] FIG. 7 is a cross-sectional view of a polarizer
incorporating an optical retarder.
[0041] FIG. 8 is a cross-sectional view of a liquid crystal display
incorporating an optical retarder.
[0042] FIG. 9A is a scanning electron micrograph of a
sub-wavelength grating prior to trench filling.
[0043] FIG. 9B is a scanning electron micrograph of the
sub-wavelength grating shown in FIG. 9A after trench filling.
[0044] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0045] Referring to FIG. 1, an embodiment of an optical retarder
100 includes a retardation layer 110 and two antireflection films
150 and 160. Optical retarder 100 also includes a substrate 140, an
etch stop layer 130, and a cap layer 120. Retardation layer 110 is
in the form of a grating and includes portions 111 having a first
refractive index and portions 112 having second refractive index.
Retardation layer 110 is birefringent for light of wavelength
.lambda. propagating along an axis 101, parallel to the z-axis of
the Cartesian coordinate system shown in FIG. 1. In general,
.lambda. is between about 150 nm and about 5,000 nm. In certain
embodiments, .lambda. corresponds to a wavelength within the
visible portion of the electromagnetic spectrum (e.g., from about
400 nm to about 700 nm).
[0046] Portions 111 and 112 extend along the y-direction, forming a
periodic structure consisting of a series of alternating rows
having different indices of refraction. The rows corresponding to
portions 111 have a width .LAMBDA..sub.111 in the x-direction,
while the rows corresponding to portions 112 have a width
.LAMBDA..sub.112 in the x-direction. The widths of the rows are
smaller than .lambda., resulting in retardation layer 110 being
form birefringent for light of wavelength .lambda. without
encountering significant high-order diffraction. Optical waves with
different polarization states propagate through retardation layer
110 with different phase shifts, which depend on the thickness of
retardation layer 110, the index of refraction of portions 111 and
112, and .LAMBDA..sub.111 and .LAMBDA..sub.112. Accordingly, these
parameters can be selected to provide a desired amount of
retardation to polarized light at .lambda..
[0047] Retardation layer 110 has a birefringence, .DELTA.n, which
corresponds to n.sub.e-n.sub.o, where n.sub.e, and n.sub.o are the
effective extraordinary and ordinary indices of refraction for
layer 110, respectively. For retardation layer 110, n.sub.e and
n.sub.o are given by: 1 n o 2 = 111 111 + 112 n 111 2 + 112 111 +
112 n 112 2 1 n e 2 = 111 111 + 112 1 n 111 2 + 112 111 + 112 1 n
112 2 . ( 1 )
[0048] In Eq. (1), n.sub.111 and n.sub.112 and .LAMBDA..sub.111 and
.LAMBDA..sub.112 refer to the refractive indices and thickness
(along the x-direction) of portions 111 and 112 respectively. In
general, the values of ne and n.sub.0 depend on n.sub.111,
n.sub.112, .LAMBDA..sub.111 and .LAMBDA..sub.112, and are between
n.sub.111 and n.sub.112. .LAMBDA..sub.111 and .LAMBDA..sub.112 can
be selected to provide a desired value of .DELTA.n based on the
values for n.sub.e and n.sub.o given by Eq. (1). Moreover, the
refractive indices n.sub.111 and n.sub.112, which depend on the
respective compositions of portions 111 and 112, can be selected to
provide a desired value of .DELTA.n. In some embodiments, .DELTA.n
is relatively large (e.g., about 0.1 or more, about 0.15 or more,
about 0.2 or more, about 0.3 or more, about 0.5 or more, about 1.0
or more, about 1.5 or more, about 2.0 or more). Alternatively, in
other embodiments, .DELTA.n is relatively small (e.g., about 0.05
or less, about 0.04 or less, about 0.03 or less, about 0.02 or
less, about 0.01 or less, about 0.005 or less, about 0.002 or less,
0.001 or less).
[0049] In general, the refractive index of portions 111 can be
about 1.3 or more (e.g., about 1.4 or more, about 1.5 or more,
about 1.6 or more, about 1.7 or more, about 1.8 or more, about 1.9
or more, about 2.0 or more, about 2.1 or more, about 2.2 or more).
Furthermore, in general, the refractive index of portions 112 can
be about 1.3 or more (e.g., about 1.4 or more, about 1.5 or more,
about 1.6 or more, about 1.7 or more, about 1.8 or more, about 1.9
or more, about 2.0 or more, about 2.1 or more, about 2.2 or
more).
[0050] In general, .LAMBDA..sub.111 can be about 0.2 .lambda. or
less (e.g., about 0.1 .lambda. or less, about 0.05 .lambda. or
less, about 0.04 .lambda. or less, about 0.03 .lambda. or less,
about 0.02 .lambda. or less, 0.01 .lambda. or less). For example,
in some embodiments, .LAMBDA..sub.111 is about 200 nm or less
(e.g., about 150 nm or less, about 100 nm or less, about 80 nm or
less, about 70 nm or less, about 60 nm or less, about 50 nm or
less, about 40 m or less, about 30 nm or less). Similarly,
.LAMBDA..sub.112 can be about 0.2 .lambda. or less (e.g., about 0.1
.lambda. or less, about 0.05 .lambda. or less, about 0.04 .lambda.
or less, about 0.03 .lambda. or less, about 0.02 .lambda. or less,
0.01 .lambda. or less). For example, in some embodiments,
.LAMBDA..sub.112 is about 200 nm or less (e.g., about 150 nm or
less, about 100 nm or less, about 80 nm or less, about 70 nm or
less, about 60 nm or less, about 50 nm or less, about 40 nm or
less, about 30 m or less). .LAMBDA..sub.111 and .LAMBDA..sub.112
can be the same as each other or different.
[0051] Along the x-axis, the refractive index of retardation layer
110 is periodic, with a period, .LAMBDA., corresponding to
.LAMBDA..sub.111+.LAMBDA..sub.112. In general, .LAMBDA. is less
than .lambda., such as about 0.5 .lambda. or less (e.g., about 0.3
.lambda. or less, about 0.2 .lambda. or less, about 0.1 .lambda. or
less, about 0.08 .lambda. or less, about 0.05 .lambda. or less,
about 0.04 .lambda. or less, about 0.03 .lambda. or less, about
0.02 .lambda. or less, 0.01 .lambda. or less). In some embodiments,
.LAMBDA. is about 500 nm or less (e.g., about 300 nm or less, about
200 m or less, about 100 nm or less, about 80 nm or less, about 60
m or less, about 50 nm or less, about 40 nm or less).
[0052] While retardation layer 110 is shown as having 19 portions,
in general, the number of portions in a retardation layer may vary
as desired. The number of portions depends on the period, A, and
the area required by the retarder's end use application. In some
embodiments, retardation layer 110 can have about 50 or more
portions (e.g., about 100 or more portions, about 500 or more
portions, about 1,000 or more portions, about 5,000 or more
portions, about 10,000 or more portions, about 50,000 or more
portions, about 100,000 or more portions, about 500,000 more
portions).
[0053] The thickness, d, of retardation layer 110 measured along
the z-axis can vary as desired. In general, the thickness of layer
110 is selected based on the refractive indices of portions 111 and
112 and the desired retardation of retardation layer 110 at
.lambda.. In some embodiments, d can be about 50 nm or more (e.g.,
about 75 nm or more, about 100 nm or more, about 125 nm or more,
about 150 nm or more, about 200 nm or more, about 250 nm or more,
about 300 nm or more, about 400 m or more, about 500 nm or more,
about 1,000 or more, such as about 2,000 nm).
[0054] The aspect ratio of retardation layer thickness, d, to
.LAMBDA..sub.111 and/or d to .LAMBDA..sub.112 can be relatively
high. For example d:.LAMBDA..sub.111 and/or d:.LAMBDA..sub.112 can
be about 2:1 or more (e.g., about 3:1 or more, about 4:1 or more,
about 5:1 or more, about 8:1 or more, about 10:1 or more).
[0055] The retardation of retardation layer 110 corresponds to the
product of the thickness of retardation layer 110, d, and .DELTA.n.
By selecting appropriate values for .DELTA.n and the layers
thickness, the retardation can vary as desired. In some
embodiments, the retardation of retardation layer 110 is about 50
nm or more (e.g., about 75 nm or more, about 100 nm or more, about
125 nm or more, about 150 nm or more, about 200 nm or more, about
250 nm or more, about 300 nm or more, about 400 nm or more, about
500 nm or more, about 1,000 or more, such as about 2,000 nm).
Alternatively, in other embodiments, the retardation is about 40 nm
or less (e.g., about 30 nm or less, about 20 nm or less, about 10
nm or less, about 5 m or less, about 2 nm or less). In some
embodiments, the retardation corresponds to .lambda./4 or
.lambda./2.
[0056] Retardation can also be expressed as a phase retardation,
.GAMMA., where 2 = 2 nd . ( 2 )
[0057] For example, quarter wave retardation corresponds to
.GAMMA.=.pi./2, while half wave retardation corresponds to
.GAMMA.=.pi.. In general, phase retardation may vary as desired. In
some embodiments, phase retardation may be about 2.pi. or less
(e.g., about 0.8 .pi. or less, about 0.7.pi. or less, about 0.6.pi.
or less, about 0.5.pi. or less, about 0.4.pi. or less, about
0.2.pi. or less, 0.2.pi. or less, about 0.1.pi. or less, about
0.05.pi. or less, 0.1.pi. or less). Alternatively, in other
embodiments, phase retardation of retardation layer 110 can be more
than 2 .pi. (e.g., about 3.pi. or more, about 4.pi. or more, about
5.pi. or more).
[0058] In general, the composition of portions 111 and 112 can vary
as desired. Portions 111 and/or 112 can include inorganic and/or
organic materials. Examples of inorganic materials include metals,
semiconductors, and inorganic dielectric materials (e.g., glass).
Examples of organic materials include polymers.
[0059] In some embodiments, portions 111 and/or portions 112
include one or more dielectric materials, such as dielectric oxides
(e.g., metal oxides), fluorides (e.g., metal fluorides), sulphides,
and/or nitrides (e.g., metal nitrides). Examples of oxides include
SiO.sub.2, Al.sub.2O.sub.3, Nb.sub.2O.sub.5, TiO.sub.2, ZrO.sub.2,
HfO.sub.2, SnO.sub.2, ZnO, ErO.sub.2, Sc.sub.2O.sub.3, and
Ta.sub.2O.sub.5. Examples of fluorides include MgF.sub.2. Other
examples include ZnS, SiN.sub.x, SiO.sub.yN.sub.x, AlN, TiN, and
HfN.
[0060] The compositions of portions 111 and 112 are typically
selected based on their optical properties and their compatibility
with the processes used to manufacture optical retarder 100 and
their compatibility with the materials used to form other layers of
optical retarder 100. The composition of portions 111 and/or
portions 112 can be selected to have particular refractive indices
at .lambda.. In general, the refractive index of portion 111 is
different from the refractive index or portion 112 at .lambda.. In
some embodiments, portions 111 or portions 112 are formed from a
material that has a relatively high index of refraction, such as
TiO.sub.2, which has a refractive index of about 2.35 at 632 nm, or
Ta.sub.2O.sub.5, which has a refractive index of 2.15 at 632 nm.
Alternatively, portions 111 or portions 112 can be formed from a
material that has a relatively low index of refraction. Examples of
low index materials include SiO.sub.2 and Al.sub.2O.sub.3, which
have refractive indices of 1.45 and 1.65 at 632 nm,
respectively.
[0061] In some embodiments, the composition of portions 111 and/or
portions 112 have a relatively low absorption at .lambda., so that
retardation layer 110 has a relatively low absorption at .lambda..
For example, retardation layer 110 can absorb about 5% or less of
radiation at .lambda. propagating along axis 101 (e.g., about 3% or
less, about 2% or less, about 1% or less, about 0.5% or less, about
0.2% or less, about 0.1% or less).
[0062] Portions 111 and/or portions 112 can be formed from a single
material or from multiple different materials. In some embodiments,
one or both of portions 111 and 112 are formed from a nanolaminate
material, which refers to materials that are composed of layers of
at least two different materials and the layers of at least one of
the materials are extremely thin (e.g., between one and about 10
monolayers thick). Optically, nanolaminate materials have a locally
homogeneous index of refraction that depends on the refractive
index of its constituent materials. Varying the amount of each
constituent material can vary the refractive index of a
nanolaminate. Examples of nanolaminate portions include portions
composed of SiO.sub.2 monolayers and TiO.sub.2 monolayers,
SiO.sub.2 monolayers and Ta.sub.2O.sub.5 monolayers, or
Al.sub.2O.sub.3 monolayers and TiO.sub.2 mono layers.
[0063] Portions 111 and/or portions 112 can include crystalline,
semi-crystalline, and/or amorphous portions. Typically, an
amorphous material is optically isotropic and may transmit light
better than portions that are partially or mostly crystalline. As
an example, in some embodiments, both portions 111 and 112 are
formed from amorphous materials, such as amorphous dielectric
materials (e.g., amorphous TiO.sub.2 or SiO.sub.2). Alternatively,
in certain embodiments, portions 111 are formed from a crystalline
or semi-crystalline material (e.g., crystalline or semi-crystalline
Si), while portions 112 are formed from an amorphous material
(e.g., an amorphous dielectric material, such as TiO.sub.2 or
SiO.sub.2).
[0064] Referring now to other layers in optical retarder 100, in
general, substrate 140 provides mechanical support to optical
retarder 100. In certain embodiments, substrate 140 is transparent
to light at wavelength .lambda., transmitting substantially all
light impinging thereon at wavelength .lambda. (e.g., about 90% or
more, about 95% or more, about 97% or more, about 99% or more,
about 99.5% or more).
[0065] In general, substrate 140 can be formed from any material
compatible with the manufacturing processes used to produce
retarder 100 that can support the other layers. In certain
embodiments, substrate 140 is formed from a glass, such as BK7
(available from Abrisa Corporation), borosilicate glass (e.g.,
pyrex available from Corning), aluminosilicate glass (e.g., C1737
available from Corning), or quartz/fused silica. In some
embodiments, substrate 140 can be formed from a crystalline
material, such as a non-linear optical crystal (e.g., LiNbO.sub.3
or a magneto-optical rotator, such as garnett) or a crystalline (or
semicrystalline) semiconductor (e.g., Si, InP, or GaAs). Substrate
140 can also be formed from an inorganic material, such as a
polymer (e.g., a plastic).
[0066] Etch stop layer 130 is formed from a material resistant to
etching processes used to etch the material(s) from which portions
112 are formed (see discussion below). The material(s) forming etch
stop layer 130 should also be compatible with substrate 140 and
with the materials forming retardation layer 110. Examples of
materials that can form etch stop layer 130 include HfO.sub.2,
SiO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2, SiN.sub.x, or metals (e.g.,
Cr, Ti, Ni).
[0067] The thickness of etch stop layer 130 can be varied as
desired. Typically, etch stop layer 130 is sufficiently thick to
prevent significant etching of substrate 140, but should not be so
thick as to adversely impact the optical performance of optical
retarder 100. In some embodiments, etch stop layer is about 500 nm
or less (e.g., about 250 nm or less, about 100 nm or less, about 75
nm or less, about 50 nm or less, about 40 nm or less, about 30 nm
or less, about 20 nm or less).
[0068] Cap layer 120 is typically formed from the same material(s)
as portions 111 of retardation layer 110 and provides a surface 121
onto which additional layers, such as the layers forming
antireflection film 150, can be deposited. Surface 121 can be
substantially planar.
[0069] Antireflection films 150 and 160 can reduce the reflectance
of light of wavelength .lambda. impinging on and exiting optical
retarder 100. Antireflection film 150 and 160 generally include one
or more layers of different refractive index. As an example, one or
both of antireflection films 150 and 160 can be formed from four
alternating high and low index layers. The high index layers can be
formed from TiO.sub.2 or Ta.sub.2O.sub.5 and the low index layers
can be formed from SiO.sub.2 or MgF.sub.2. The antireflection films
can be broadband antireflection films or narrowband antireflection
films.
[0070] In some embodiments, optical retarder 100 has a reflectance
of about 5% or less of light impinging thereon at wavelength
.lambda. (e.g., about 3% or less, about 2% or less, about 1% or
less, about 0.5% or less, about 0.2% or less). Furthermore, optical
retarder 100 can have high transmission of light of wavelength
.lambda.. For example, optical retarder can transmit about 95% or
more of light impinging thereon at wavelength .lambda. (e.g., about
98% or more, about 99% or more, about 99.5% or more).
[0071] In general, optical retarder 100 can be prepared as desired.
FIGS. 2A-2J show different phases of an example of a preparation
process. Initially, substrate 140 is provided, as shown in FIG. 2A.
Surface 141 of substrate 140 can be polished and/or cleaned (e.g.,
by exposing the substrate to one or more solvents, acids, and/or
baking the substrate).
[0072] Referring to FIG. 2B, etch stop layer 130 is deposited on
surface 141 of substrate 140. The material forming etch stop layer
130 can be formed using one of a variety of techniques, including
sputtering (e.g., radio frequency sputtering), evaporating (e.g.,
electron beam evaporation, ion assisted deposition (LAD) electron
beam evaporation), or chemical vapor deposition (CVD) such as
plasma enhanced CVD (PECVD), ALD, or by oxidization. As an example,
a layer of HfO.sub.2 can be deposited on substrate 140 by _IAD
electron beam evaporation.
[0073] Referring to FIG. 2C, an intermediate layer 210 is then
deposited on surface 131 of etch stop layer 130. Portions 112 are
etched from intermediate layer 210, so intermediation layer 210 is
formed from the material used for portions 112. The material
forming intermediate layer 210 can be deposited using one of a
variety of techniques, including sputtering (e.g., radio frequency
sputtering), evaporating (e.g., election beam evaporation), or
chemical vapor deposition (CVD) (e.g., plasma enhanced CVD). As an
example, a layer of SiO.sub.2 can be deposited on etch stop layer
130 by sputtering (e.g., radio frequency sputtering), CVD (e.g.,
plasma enhanced CVD), or electron beam evaporation (e.g., LAD
electron beam deposition). The thickness of intermediate layer 210
is selected based on the desired thickness of retardation layer
110.
[0074] Intermediate layer 210 is processed to provide portions 112
of retardation layer 110 using lithographic techniques. For
example, portions 112 can be formed from intermediate layer 210
using electron beam lithography or photolithograpy (e.g., using a
photomask or using holographic techniques). In some embodiments,
portions 112 are formed using nano-imprint lithography. Referring
to FIG. 2D, nano-imprint lithography includes forming a layer 220
of a resist on surface 211 of intermediate layer 210. The resist
can be polymethylmethacrylate (PMMA) or polystyrene (PS), for
example. Referring to FIG. 2E, a pattern is impressed into resist
layer 220 using a mold. The patterned resist layer 220 includes
thin portions 221 and thick portions 222. Patterned resist layer
220 is then etched (e.g., by oxygen reactive ion etching (RIE)),
removing thin portions 221 to expose portions 224 of surface 211 of
intermediate layer 210, as shown in FIG. 2F. Thick portions 222 are
also etched, but are not completely removed. Accordingly, portions
223 of resist remain on surface 211 after etching.
[0075] Referring to FIG. 2G, the exposed portions of intermediate
layer 210 are subsequently etched, forming trenches 212 in
intermediate layer 210. The unetched portions of intermediate layer
210 correspond to portions 112 of retardation layer 110.
Intermediate layer 210 can be etched using, for example, reactive
ion etching, ion beam etching, sputtering etching, chemical
assisted ion beam etching (CAIBE), or wet etching. The exposed
portions of intermediate layer 210 are etched down to etch stop
layer 130, which is formed from a material resistant to the etching
method. Accordingly, the depth of trenches 212 formed by etching is
the same as the thickness of portions 112. After etching trenches
212, residual resist 223 is removed from portions 112. Resist can
be removed by rinsing the article in a solvent (e.g., an organic
solvent, such as acetone or alcohol), by O.sub.2 plasma ashing,
O.sub.2 RIE, or ozone cleaning.
[0076] Referring to FIG. 2I, after removing residual resist,
material is deposited onto the article, filling trenches 212 and
forming cap layer 120. The filled trenches correspond to portions
111 of retardation layer 110. Material can be deposited onto the
article in a variety of ways, including sputtering, electron beam
evaporation, CVD (e.g., high density CVD) or atomic layer
deposition (ALD). Note that where cap layer 120 is formed and
trenches 212 are filled during the same deposition step, portions
111 and cap layer 120 are formed from a continuous portion of
material.
[0077] Finally, antireflection films 150 and 160 are deposited onto
surface 121 of cap layer 120 and surface 142 of substrate 140,
respectively: Materials forming the antireflection films can be
deposited onto the article by sputtering, electron beam
evaporation, or ALD, for example.
[0078] As mentioned previously, in some embodiments, portions 111
of retardation layer 110, cap layer 120, and/or one or both of
antireflection films 150 and 160 are prepared using atomic layer
deposition (ALD). For example, referring to FIG. 3, an ALD system
300 is used to fill trenches 212 of an intermediate article 301
(composed of substrate 140, cap layer 130, and portions 112) with a
nanolaminate multilayer film, forming portions 111 and cap layer
120. Deposition of the nanolaminate multilayer film occurs
monolayer by monolayer, providing substantial control over the
composition and thickness of the films. During deposition of a
monolayer, vapors of a precursor are introduced into the chamber
and are adsorbed onto exposed surfaces of portions 112, etch stop
layer surface 131 or previously deposited monolayers adjacent these
surfaces. Subsequently, a reactant is introduced into the chamber
that reacts chemically with the adsorbed precursor, forming a
monolayer of a desired material. The self-limiting nature of the
chemical reaction on the surface can provide precise control of
film thickness and large-area uniformity of the deposited layer.
Moreover, the non-directional adsorption of precursor onto each
exposed surface provides for uniform deposition of material onto
the exposed surfaces, regardless of the orientation of the surface
relative to chamber 110. Accordingly, the layers of the
nanolaminate film conform to the shape of the trenches of
intermediate article 301.
[0079] ALD system 300 includes a reaction chamber 310, which is
connected to sources 350, 360, 370, 380, and 390 via a manifold
330. Sources 350, 360, 370, 380, and 390 are connected to manifold
330 via supply lines 351, 361, 371, 381, and 391, respectively.
Valves 352, 362, 372, 382, and 392 regulate the flow of gases from
sources 350, 360, 370, 380, and 390, respectively. Sources 350 and
380 contain a first and second precursor, respectively, while
sources 360 and 390 include a first reagent and second reagent,
respectively. Source 370 contains a carrier gas, which is
constantly flowed through chamber 310 during the deposition process
transporting precursors and reagents to article 301, while
transporting reaction byproducts away from the substrate.
Precursors and reagents are introduced into chamber 310 by mixing
with the carrier gas in manifold 330. Gases are exhausted from
chamber 310 via an exit port 345. A pump 340 exhausts gases from
chamber 310 via an exit port 345. Pump 340 is connected to exit
port 345 via a tube 346.
[0080] ALD system 300 includes a temperature controller 395, which
controls the temperature of chamber 310. During deposition,
temperature controller 395 elevates the temperature of article 301
above room temperature. In general, the temperature should be
sufficiently high to facilitate a rapid reaction between precursors
and reagents, but should not damage the substrate. In some
embodiments, the temperature of article 301 can be about
500.degree. C. or less (e.g., about 400.degree. C. or less, about
300.degree. C. or less, about 200.degree. C. or less, about
150.degree. C. or less, about 125.degree. C. or less, about
100.degree. C. or less).
[0081] Typically, the temperature should not vary significantly
between different portions of article 301. Large temperature
variations can cause variations in the reaction rate between the
precursors and reagents at different portions of the substrate,
which can cause variations in the thickness and/or morphology of
the deposited layers. In some embodiments, the temperature between
different portions of the deposition surfaces can vary by about
40.degree. C. or less (e.g., about 30.degree. C. or less, about
20.degree. C. or less, about 10.degree. C. or less, about 5.degree.
C. or less).
[0082] Deposition process parameters are controlled and
synchronized by an electronic controller 399. Electronic controller
399 is in communication with temperature controller 395; pump 340;
and valves 352, 362, 372, 382, and 392. Electronic controller 399
also includes a user interface, from which an operator can set
deposition process parameters, monitor the deposition process, and
otherwise interact with system 300.
[0083] Referring to FIG. 4, the ALD process is started (410) when
system 300 introduces the first precursor from source 350 into
chamber 310 by mixing it with carrier gas from source 370 (420). A
monolayer of the first precursor is adsorbed onto exposed surfaces
of article 301, and residual precursor is purged from chamber 310
by the continuous flow of carrier gas through the chamber (430).
Next, the system introduces a first reagent from source 360 into
chamber 310 via manifold 330 (440). The first reagent reacts with
the monolayer of the first precursor, forming a monolayer of the
first material. As for the first precursor, the flow of carrier gas
purges residual reagent from the chamber (450). Steps 420 through
460 are repeated until the layer of the first material reaches a
desired thickness (460).
[0084] In embodiments where the films are a single layer of
material, the process ceases once the layer of first material
reaches the desired thickness (470). However, for a nanolaminate
film, the system introduces a second precursor into chamber 310
through manifold 330 (380). A monolayer of the second precursor is
adsorbed onto the exposed surfaces of the deposited layer of first
material and carrier gas purges the chamber of residual precursor
(490). The system then introduces the second reagent from source
380 into chamber 310 via manifold 330. The second reagent reacts
with the monolayer of the second precursor, forming a monolayer of
the second material (500). Flow of carrier gas through the chamber
purges residual reagent (510). Steps 580 through 510 are repeated
until the layer of the second material reaches a desired thickness
(520).
[0085] Additional layers of the first and second materials are
deposited by repeating steps 520 through 530. Once the desired
number of layers are formed (e.g., the trenches are filled and/or
cap layer has a desired thickness), the process terminates (540),
and the coated article is removed from chamber 310.
[0086] Although the precursor is introduced into the chamber before
the reagent during each cycle in the process described above, in
other examples the reagent can be introduced before the precursor.
The order in which the precursor and reagent are introduced can be
selected based on their interactions with the exposed surfaces. For
example, where the bonding energy between the precursor and the
surface is higher than the bonding energy between the reagent and
the surface, the precursor can be introduced before the reagent.
Alternatively, if the binding energy of the reagent is higher, the
reagent can be introduced before the precursor.
[0087] The thickness of each monolayer generally depends on a
number of factors. For example, the thickness of each monolayer can
depend on the type of material being deposited. Materials composed
of larger molecules may result in thicker monolayers compared to
materials composed of smaller molecules.
[0088] The temperature of the article can also affect the monolayer
thickness. For example, for some precursors, a higher temperate can
reduce adsorption of a precursor onto a surface during a deposition
cycle, resulting in a thinner monolayer than would be formed if the
substrate temperature were lower.
[0089] The type or precursor and type of reagent, as well as the
precursor and reagent dosing can also affect monolayer thickness.
In some embodiments, monolayers of a material can be deposited with
a particular precursor, but with different reagents, resulting in
different monolayer thickness for each combination. Similarly,
monolayers of a material formed from different precursors can
result in different monolayer thickness for the different
precursors.
[0090] Examples of other factors which may affect monolayer
thickness include purge duration, residence time of the precursor
at the coated surface, pressure in the reactor, physical geometry
of the reactor, and possible effects from the byproducts on the
deposited material. An example of where the byproducts affect the
film thickness are where a byproduct etches the deposited material.
For example, HCl is a byproduct when depositing TiO.sub.2 using a
TiCl.sub.4 precursor and water as a reagent. HCl can etch the
deposited TiO.sub.2 before it is exhausted. Etching will reduce the
thickness of the deposited monolayer, and can result in a varying
monolayer thickness across the substrate if certain portions of the
substrate are exposed to HCl longer than other portions (e.g.,
portions of the substrate closer to the exhaust may be exposed to
byproducts longer than portions of the substrate further from the
exhaust).
[0091] Typically, monolayer thickness is between about 0.1 nm and
about five nm. For example, the thickness of one or more of the
deposited monolayers can be about 0.2 nm or more (e.g., about 0.3
nm or more, about 0.5 nm or more). In some embodiments, the
thickness of one or more of the deposited monolayers can be about
three nm or less (e.g., about two nm, about one nm or less, about
0.8 nm or less, about 0.5 nm or less).
[0092] The average deposited monolayer thickness may be determined
by depositing a preset number of monolayers on a substrate to
provide a layer of a material. Subsequently, the thickness of the
deposited layer is measured (e.g., by ellipsometry, electron
microscopy, or some other method). The average deposited monolayer
thickness can then be determined as the measured layer thickness
divided by the number of deposition cycles. The average deposited
monolayer thickness may correspond to a theoretical monolayer
thickness. The theoretical monolayer thickness refers to a
characteristic dimension of a molecule composing the monolayer,
which can be calculated from the material's bulk density and the
molecules molecular weight. For example, an estimate of the
monolayer thickness for SiO.sub.2 is .about.0.37 nm. The thickness
is estimated as the cube root of a formula unit of amorphous
SiO.sub.2 with density of 2.0 grams per cubic centimeter.
[0093] In some embodiments, average deposited monolayer thickness
can correspond to a fraction of a theoretical monolayer thickness
(e.g., about 0.2 of the theoretical monolayer thickness, about 0.3
of the theoretical monolayer thickness, about 0.4 of the
theoretical monolayer thickness, about 0.5 of the theoretical
monolayer thickness, about 0.6 of the theoretical monolayer
thickness, about 0.7 of the theoretical monolayer thickness, about
0.8 of the theoretical monolayer thickness, about 0.9 of the
theoretical monolayer thickness). Alternatively, the average
deposited monolayer thickness can correspond to more than one
theoretical monolayer thickness up to about 30 times the
theoretical monolayer thickness (e.g., about twice or more than the
theoretical monolayer thickness, about three time or more than the
theoretical monolayer thickness, about five times or more than the
theoretical monolayer thickness, about eight times or more than the
theoretical monolayer thickness, about 10 times or more than the
theoretical monolayer thickness, about 20 times or more than the
theoretical monolayer thickness).
[0094] During the deposition process, the pressure in chamber 310
can be maintained at substantially constant pressure, or can vary.
Controlling the flow rate of carrier gas through the chamber
generally controls the pressure. In general, the pressure should be
sufficiently high to allow the precursor to saturate the surface
with chemisorbed species, the reagent to react completely with the
surface species left by the precursor and leave behind reactive
sites for the next cycle of the precursor. If the chamber pressure
is too low, which may occur if the dosing of precursor and/or
reagent is too low, and/or if the pump rate is too high, the
surfaces may not be saturated by the precursors and the reactions
may not be self limited. This can result in an uneven thickness in
the deposited layers. Furthermore, the chamber pressure should not
be so high as to hinder the removal of the reaction products
generated by the reaction of the precursor and reagent. Residual
byproducts may interfere with the saturation of the surface when
the next dose of precursor is introduced into the chamber. In some
embodiments, the chamber pressure is maintained between about 0.01
Torr and about 100 Torr (e.g., between about 0.1 Torr and about 20
Torr, between about 0.5 Torr and 10 Torr, such as about 1
Torr).
[0095] Generally, the amount of precursor and/or reagent introduced
during each cycle can be selected according to the size of the
chamber, the area of the exposed substrate surfaces, and/or the
chamber pressure. The amount of precursor and/or reagent introduced
during each cycle can be determined empirically.
[0096] The amount of precursor and/or reagent introduced during
each cycle can be controlled by the timing of the opening and
closing of valves 352, 362, 382, and 392. The amount of precursor
or reagent introduced corresponds to the amount of time each valve
is open each cycle. The valves should open for sufficiently long to
introduce enough precursor to provide adequate monolayer coverage
of the substrate surfaces. Similarly, the amount of reagent
introduced during each cycle should be sufficient to react with
substantially all precursor deposited on the exposed surfaces.
Introducing more precursor and/or reagent than is necessary can
extend the cycle time and/or waste precursor and/or reagent. In
some embodiments, the precursor dose corresponds to opening the
appropriate valve for between about 0.1 seconds and about five
seconds each cycle (e.g., about 0.2 seconds or more, about 0.3
seconds or more, about 0.4 seconds or more, about 0.5 seconds or
more, about 0.6 seconds or more, about 0.8 seconds or more, about
one second or more). Similarly, the reagent dose can correspond to
opening the appropriate valve for between about 0.1 seconds and
about five seconds each cycle (e.g., about 0.2 seconds or more,
about 0.3 seconds or more, about 0.4 seconds or more, about 0.5
seconds or more, about 0.6 seconds or more, about 0.8 seconds or
more, about one second or more).
[0097] The time between precursor and reagent doses corresponds to
the purge. The duration of each purge should be sufficiently long
to remove residual precursor or reagent from the chamber, but if it
is longer than this it can increase the cycle time without benefit.
The duration of different purges in each cycle can be the same or
can vary. In some embodiments, the duration of a purge is about 0.1
seconds or more (e.g., about 0.2 seconds or more, about 0.3 seconds
or more, about 0.4 seconds or more, about 0.5 seconds or more,
about 0.6 seconds or more, about 0.8 seconds or more, about one
second or more, about 1.5 seconds or more, about two seconds or
more). Generally, the duration of a purge is about 10 seconds or
less (e.g., about eight seconds or less, about five seconds or
less, about four seconds or less, about three seconds or less).
[0098] The time between introducing successive doses of precursor
corresponds to the cycle time. The cycle time can be the same or
different for cycles depositing monolayers of different materials.
Moreover, the cycle time can be the same or different for cycles
depositing monolayers of the same material, but using different
precursors and/or different reagents. In some embodiments, the
cycle time can be about 20 seconds or less (e.g., about 15 seconds
or less, about 12 seconds or less, about 10 seconds or less, about
8 seconds or less, about 7 seconds or less, about 6 seconds or
less, about 5 seconds or less, about 4 seconds or less, about 3
seconds or less). Reducing the cycle time can reduce the time of
the deposition process.
[0099] The precursors are generally selected to be compatible with
the ALD process, and to provide the desired deposition materials
upon reaction with a reagent. In addition, the precursors and
materials should be compatible with the material on which they are
deposited (e.g., with the substrate material or the material
forming the previously deposited layer). Examples of precursors
include chlorides (e.g., metal chlorides), such as TiCl.sub.4,
SiCl.sub.4, SiH.sub.2Cl.sub.2, TaCl.sub.3, HfCl.sub.4, InCl.sub.3
and AlCl.sub.3. In some embodiments, organic compounds can be used
as a precursor (e.g., Ti-ethaOxide, Ta-ethaOxide, Nb-ethaOxide).
Another example of an organic compound precursor is
(CH.sub.3).sub.3Al.
[0100] The reagents are also generally selected to be compatible
with the ALD process, and are selected based on the chemistry of
the precursor and material. For example, where the material is an
oxide, the reagent can be an oxidizing agent. Examples of suitable
oxidizing agents include water, hydrogen peroxide, oxygen, ozone,
(CH.sub.3).sub.3Al, and various alcohols (e.g., Ethyl alcohol
CH.sub.3OH). Water, for example, is a suitable reagent for
oxidizing precursors such as TiCl.sub.4 to obtain TiO.sub.2,
AlCl.sub.3 to obtain Al.sub.2O.sub.3, and Ta-ethaoxide to obtain
Ta.sub.2O.sub.5, Nb-ethaoxide to obtain Nb.sub.2O.sub.5, HfCl.sub.4
to obtain HfO.sub.2, ZrCl.sub.4 to obtain ZrO.sub.2, and InCl.sub.3
to obtain In.sub.2O.sub.3. In each case, HCl is produced as a
byproduct. In some embodiments, (CH.sub.3).sub.3Al can be used to
oxidize silanol to provide SiO.sub.2.
[0101] While certain embodiments have been described, the
invention, in general, is not so limited. For example, while
optical retarder 100 (see FIG. 1) shows a specific configuration of
different layers, other embodiments can include additional or fewer
layers. For example, in certain embodiments optical retarders need
not include one or both of antireflection films 150 and 160. In
some embodiments, optical retarders can include additional
antireflection films (e.g., between substrate layer 140 and etch
stop layer 130). Embodiments can also include protective layers,
such as hardcoat layers (e.g., hardcoat polymers) on one or both of
antireflection films 150 and 160. In certain embodiments, optical
retarders need not include a cap layer. For example, the cap layer,
which forms while filling trenches between portions 112, can be
removed once portions 111 are formed. The cap layer can be removed
by, e.g., chemical mechanical polishing or etching.
[0102] Referring to FIG. 5, in some embodiments, an optical
retarder 600 is formed by partially etching trenches directly into
a substrate layer, and subsequently filling the trenches to provide
a continuous retardation layer 610. Optical retarder 600 also
includes a cap layer 620, and a base layer 630, which corresponds
to an unetched portion of the original substrate layer. An
antireflection film 640 is deposited on surface 621 of cap layer
602, and a second antireflection film 650 is deposited on surface
631 of base layer 630.
[0103] In certain embodiments, optical retarders can be formed from
more than one retardation layer. For example, referring to FIG. 6,
an optical retarder 800 includes four retardation layers 810, 820,
830, and 840. Optical retarder 800 also includes a substrate layer
801, an etch stop layer 805, and cap layers 811, 821, 831, and
841.
[0104] Retardation layers 810, 820, 830, and 840 can have the same
retardation for a beam of light having wavelength .lambda., or can
have different retardations.
[0105] Optical retarder 800 can be prepared using methods disclosed
herein. For example, each retardation layer and its corresponding
cap layer can be formed by depositing and etching an intermediate
layer either on etch stop layer 805 (e.g., retardation layer 810)
or on the previously deposited cap layer (e.g., retardation layers
820, 830, and 840), and then depositing materials to fill the
etched trenches and form the cap layers.
[0106] In some embodiments, additional etch stop layers can be
deposited onto a cap layer prior to forming a subsequent
retardation layer. Of course, other layers may also be included,
such as antireflection films, for example.
[0107] In general, the thickness of retardation layers 810, 820,
830, and 840 along the z-direction, the width of their portions
(along the x-direction), and the materials used to form them may
vary as desired. In some embodiments, retardation layers 810, 820,
830, and 840 are identical, while in other embodiments, one or more
of the retardation layers can be different (e.g., composed of one
or more different materials to the other retardation layers, have a
different thickness, and/or have a different birefringence).
[0108] Moreover, while optical retarder 800 has four retardation
layers, in general, embodiments can include more than or less than
four retardation layers. Optical retarders can include two
retardation layers, three retardation layers, or five or more
retardation layers (e.g., about 10 or more retardation layers,
about 20 or more retardation layers, about 30 or more retardation
layers, about 100 or more retardation layers, about 1000 or more
retardation layers).
[0109] The total phase retardation for light of wavelength .lambda.
propagating through an optical retarder having more than one
retardation layer can be relatively large. For example, an optical
retarder can have a phase retardation of about 2.pi. or more at
.lambda. (e.g., about 3.pi. or more, about 4.pi. or more, about
5.pi. or more, about 8.pi. or more, about 10.pi. or more, about
12.pi. or more, about 15.pi. or more, about 20.pi. or more, about
30.pi. or more.
[0110] The total thickness (along the z-direction) of optical
retarders than include more than one retardation layer can be about
200 .mu.m or more (e.g., about 500 .mu.m or more, about 800 .mu.m
or more, about 1,000 .mu.m or more, about 1,500 .mu.m or more,
about 2,000 .mu.m or more, about 5,000 .mu.m or more).
[0111] In certain embodiments, optical retarders can be used as an
optical walk-off crystal, which splits non-normally incident light
(i.e., light not propagating along the z-direction) into an
ordinary and an extraordinary ray, which exit the retarder along
different paths. Such optical walk-off crystals can be re-cut and
polished into a wedge. Walk-off crystals can be used in numerous
applications, such as in telecom isolators, circulators, or
interleavers, and/or in consumer applications, such as optical low
pass filters, for example.
[0112] Although embodiments of optical retarders have been
described that include form birefringent layers that have a
rectangular grating profile, other embodiments are also possible.
For example, in some embodiments, the grating profile of a form
birefringent layer can be curved, such as having a sinusoidal
shape. In another example, the grating can have a triangular or
sawtooth profile.
[0113] Furthermore, while the grating period in the form
birefringent layers of optical retarders has been described as
constant, in certain embodiments the grating period may vary. In
some embodiments, portions of form birefringent layers can be
non-periodically arranged.
[0114] Optical retarders such as those described herein can be
incorporated into optical devices, including passive optical
devices (e.g., polarizers) and active optical devices (e.g., liquid
crystal displays). Optical retarders can be integrated into the
device, providing a monolithic device, or can be arranged
separately from other components of the device.
[0115] Referring to FIG. 7, an example of a passive optical device
incorporating an optical retarder is a polarizer 660. Polarizer 660
includes a polarizing film 670 and an optical retarder 680.
Polarizing film 670 can be a sheet polarizer (e.g., iodine-stained
polyvinyl alcohol) or a nano-structured polarizer, such as is
disclosed in U.S. patent application Ser. No. 10/644,643, entitled
"MULTILAYER STRUCTURES FOR POLARIZATION AND BEAM CONTROL," and PCT
Patent Application Serial No. PCT/US03/26024, entitled "METHOD AND
SYSTEM FOR PROVIDING BEAM FOR POLARIZATION," the contents both of
which are hereby incorporated by reference in their entirety.
[0116] Polarizing film 670 linearly polarizes light incident on
polarizer 660 propagating along axis 661. Optical retarder 680 then
retards the linearly polarized light, providing polarized light
with a desired ellipticity exiting polarizer 660. The ellipticity
of the exiting light can vary as desired by choosing the parameters
associated with the retardation layer of optical retarder 680 to
provide a desired amount of retardation. For example, the exiting
light can be circularly polarized or elliptically polarized.
[0117] Referring to FIG. 8, an example of an active optical device
incorporating an optical retarder is a liquid crystal display 700,
which includes a substrate 710 (e.g., a silicon substrate), a
reflective electrode 720, a layer 730 of a liquid crystal (e.g., a
nematic or ferroelectric liquid crystal), a transparent electrode
740 (e.g., formed from indium tin oxide), an optical retarder 750,
and a polarizing film 760. Optical retarder 750 retards polarized
light transmitted through polarizing film 760. This light reflects
from electrode 720, propagating through liquid crystal layer 730
twice. The reflected light is again retarded by optical retarder
760 before impinging on polarizing film 760 a second time.
Depending on the voltage applied across electrodes 720 and 740, the
reflected light is either absorbed or transmitted by polarizing
film 760, corresponding to a dark or bright pixel, respectively.
Optionally, LCD 700 includes color filters that absorb certain
wavelengths in the visible spectrum providing a colored image.
While LCD 700 is a reflective display, the optical retarders
disclosed herein can be used in other types of display, such as
transmissive displays or transflective displays.
[0118] The following examples are illustrative and not intended as
limiting.
EXAMPLES
[0119] Optical retarders were prepared as follows. A 0.5 mm thick
BK7 wafer (four inches in diameter), obtained from Abrisa
Corporation (Santa Paula, Calif.), was cleaned by removing
insoluble organic contaminants with a
H.sub.2O:H.sub.2O.sub.2:NH.sub.4OH solution, and removing ionic and
heavy metal atomic contaminants using a H.sub.2O:H.sub.2O.sub.2:HCl
solution. Thereafter, the wafer was rinsed with isopropyl alcohol
and deionized water, and spin dried.
[0120] A sub-wavelength grating was etched into the BK7 wafer as
follows. The BK7 wafer was spin coated with a thin layer
(.about.180 nm) of PMMA (molecular weight of 15 K purchased from
Sigma-Aldrich, St. Louis, Mo.), which was baked on a hot plate at
about 115.degree. C. for about one hour. After baking, the resist
was imprinted with a grating mold having a period of 200 nm and
depth of about 110 nm, and a grating linewidth of about 100 nm. The
mold included a patterned SiO.sub.2 layer (about 200 nm thick) on a
0.5 mm thick silicon substrate. The mold was prepared using methods
disclosed by J. Wang, Z. Yu, and S. Y. Chou, in J. Vac. Sci.
Technol., B17, 2957 (1999). After imprinting, the deformed UV
curable resist was fully cured by exposing to UV light through the
BK7 substrate side. The mold was then separated from the resist,
leaving a mask with a negative pattern of the mold profile. The
mask was etched by O.sub.2 RIE until the BK7 wafer was exposed in
the recessed portions of the mask. This etch was performed using a
plasma-therm 790 (available from Unaxis, Inc., St. Petersburg,
Fla.). The pressure during etching was 4 mtorr. The power was set
to 70 W and the oxygen flow rate during the etching was 10 sccm.
The total thickness of resist etched to expose the BK7 wafer was
about 120 nm.
[0121] After etching the mask, about 50 nm of Cr was deposited on
the remaining resist/exposed BK7 wafer by e-beam evaporation at
high vacuum (i.e., less than about 5.times.10.sup.-6 torr) at an
oblique angle from the wafer normal. The oblique angle was about 65
degrees. Cr was deposited on the top and sidewall of the remaining
mask lines, providing a hard mask for etching of BK7. After Cr
deposition, O.sub.2 RIE was used again to etch any exposed resist
that was not covered by the Cr. CHF.sub.3 RIE was then used to etch
exposed portions of the BK7 wafer surface to form a subwavelength
grating in the wafer. The BK7 was etched using a plasma-term 720.
The chamber pressure was about 5 mtorr, the power was about 100 W,
and flow rate of 10 sccm and 1 sccm of CHF.sub.3 and O.sub.2 were
used, respectively. 100 nm wide trenches having a depth of about
630 m were etched into the BK7 wafer. After etching the BK7, the Cr
was removed by immersing the wafer into CR-7 Cr etchant (obtained
from Cyantek, Fremont, Calif.) for about 30 minutes. Residual
resist was subsequently removed by O.sub.2 RIE.
[0122] The trenches were filled with a nanolaminate material
composed of TiO.sub.2 and SiO.sub.2. The nanolaminate material was
deposited by ALD, which was performed using a P-400A ALD apparatus,
obtained from Planar Systems, Inc. (Beaverton, Oreg.). Prior to
depositing the nanolaminate, the etched wafer was heated to
300.degree. C. inside the ALD chamber for about three hours. The
chamber was flushed with nitrogen gas, flowed at about 2 SLM,
maintaining the chamber pressure at about 0.75 Torr. The TiO.sub.2
precursor was Ti-ethaoxide, which was heated to about 140.degree.
C. The SiO.sub.2 precursor was silanol, heated to about 110.degree.
C. For both precursors, the reagent used was water, which was
maintained at about 13.degree. C. The Ti-ethaoxide and silanol were
99.999% grade purity, obtained from Sigma-Aldrich (St. Louis, Mo.).
The nanolaminate was formed by repeating a cycle in which 10
monolayers of TiO.sub.2 were deposited, followed by a single
monolayer of SiO.sub.2. To deposit a TiO.sub.2 monolayer, water was
introduced to the chamber for two seconds, followed by a two second
nitrogen purge. Then Ti-ethaoxide was introduced to the chamber,
followed by another two second nitrogen purge. SiO.sub.2 monolayers
were deposited by introducing water to the ALD chamber for one
second, followed by a two second nitrogen purge. Silanol was then
introduced for one second. The chamber was then purged for three
seconds with nitrogen before the next pulse of reagent. The
refractive index of the nanolaminate was estimated to be
approximately 1.88 at 632 nm, as determined from measurements of a
nanolaminate film similarly prepared on a flat glass substrate.
[0123] The retardation of an optical retarder was measured using an
M-2000V.RTM. Spectroscopic Ellipsometer (commercially available
from J.A. Woollam Co., Inc., Lincoln, Nebr.) to be 23.85 nm at a
wavelength of 551 nm.
[0124] Unfilled and filled gratings were studied using scanning
electron microscopy, which was performed using a LEO
thermo-emission scanning electron microscope. To perform this
study, a sample was cleaved and coated with a thin layer of Au. The
cross section of the cleaved interface was then viewed. FIGS. 9A
and 9B show SEM micrographs of a grating prior to and after trench
filling, respectively.
[0125] Other embodiments are in the following claims.
* * * * *