Optical: systems and elements – Optical modulator – Having particular chemical composition or structure
Reexamination Certificate
2003-08-05
2004-09-21
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Having particular chemical composition or structure
Reexamination Certificate
active
06795231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming photonic crystals and, more particularly, to a method of forming photonic crystals using a semiconductor-based fabrication process.
2. Description of the Related Art
A photonic crystal is a spatially-periodic dielectric structure that reflects electromagnetic radiation that falls within a range of frequencies, and passes radiation that falls outside the range of frequencies. The range of frequencies, in turn, is defined by a number of factors, including the center-to-center spacing of the structure and the dielectric constants of the materials used to form the structure.
FIG. 1
shows a perspective view that illustrates a first example of a prior-art photonic crystal
100
. As shown in
FIG. 1
, crystal
100
includes a block
110
that has a first side
112
, an opposing second side
114
, and a number of first openings
116
formed through block
110
that extend from first side
112
to second side
114
.
Block
110
also has a third side
120
, an opposing fourth side
122
, and a number of second openings
124
formed through block
110
that extend from third side
120
to fourth side
122
. In addition, openings
116
and
124
, which are perpendicular to each other, are formed in alternating layers. Further, block
110
has a fifth side
126
and an opposing sixth side
128
.
In the example shown in
FIG. 1
, block
110
is a dielectric material and therefore has the dielectric constant of the material, while openings
116
and
124
are air filled and therefore have the dielectric constant of air (openings
116
and
124
can also be filled with other materials). Further, openings
116
and
124
have a center-to-center spacing
130
.
In operation, when electromagnetic radiation is incident on fifth side
126
, crystal
100
allows frequencies outside of a range to propagate through crystal
100
and exit from sixth side
128
, while at the same time stopping frequencies within the range from propagating through crystal
100
.
FIG. 2
shows a perspective view that illustrates a second example of a prior-art photonic crystal
200
. As shown in
FIG. 2
, crystal
200
includes a block
210
that has a first side
212
, an opposing second side
214
, and a number of first rods
216
formed through block
210
that extend from first side
212
to second side
214
.
Block
210
also has a third side
220
, an opposing fourth side
222
, and a number of second rods
224
formed through block
210
that extend from third side
220
to fourth side
222
. In addition, rods
216
and
224
, which are perpendicular to each other, are formed in alternating layers. Further, block
210
has a fifth side
226
and an opposing sixth side
228
.
In the example shown in
FIG. 2
, rods
216
and
224
are formed from a first dielectric material and therefore have the dielectric constant of the first material. The space between rods
216
and
224
, however, is filled with a second dielectric material and therefore has the dielectric constant of the second material. Further, rods
216
and
224
have a center-to-center spacing
230
. Crystal
200
operates the same as crystal
100
.
One of the difficulties with photonic crystals is that photonic crystals are difficult and/or expensive to manufacture. For example, crystal
100
is formed by drilling openings
116
and
124
through block
110
. Drilling, however, has inherent size limitations with regard to the maximum thickness of block
110
, the minimum diameter of openings
116
and
124
, and the minimum spacing between openings
116
and
124
.
On the other hand, crystal
200
requires a number of layers and a large number of processing steps for each layer. For example, the first layer of crystal
200
can be formed by depositing a layer of first material, and masking and etching the first layer to form first rods
216
. After this, the second material is deposited to fill up the gaps between first rods
216
, and is then planarized to form the first layer. These steps must then be repeated for each layer in crystal
200
.
Thus, there is a need for a method of forming photonic crystals that is not subject to the size limitations of drilling and requires substantially fewer processing steps.
SUMMARY OF THE INVENTION
The present invention provides a method for forming a photonic crystal using a semiconductor-based fabrication process. Current-generation semiconductor fabrication processes are capable of producing deep sub-micron device sizes. As a result, the photonic crystal of the present invention can be formed down to sub-micron sizes. In addition, the present invention requires relatively few processing steps, and can be formed as part of an integrated circuit that includes circuitry which responds to the electromagnetic radiation received by the crystal.
In accordance with the present invention, the method begins by forming a first layer of material over a substrate. The first layer of material has a first dielectric constant. Next, a second layer of material is formed on the first layer of material. The second layer of material has a second dielectric constant.
Following this, the forming the first layer step and the forming the second layer step are repeated a predetermined number of times to form a multi-layered structure with alternating layers. The multi-layered structure has a top layer and a plurality of underlying layers. The top layer has a top surface.
Next, the top layer and the underlying layers are etched to form a plurality of photonic stacks and a space between the photonic stacks. The plurality of photonic stacks have a plurality of top surfaces. After this, a layer of interstack material is formed over the substrate to fill up the space between the photonic stacks.
The present invention also includes a photonic crystal that is formed on a semiconductor substrate. The photonic crystal includes a plurality of spaced-apart photonic stacks that are formed over the receiving region of the substrate. The photonic stacks have top surfaces.
Each photonic stack has a plurality of layers of material that alternate between a first layer of material and a second layer of material. The first layer of material has a first dielectric constant, while the second layer of material has a second dielectric constant. The photonic crystal also includes an interstack material that is formed over the substrate between and adjoining the plurality of photonic stacks.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description and accompanying drawings that set forth an illustrative embodiment in which the principles of the invention are utilized.
REFERENCES:
patent: 5335240 (1994-08-01), Ho et al.
patent: 5739796 (1998-04-01), Jasper et al.
patent: 5990850 (1999-11-01), Brown et al.
patent: 5998298 (1999-12-01), Fleming et al.
patent: 5999308 (1999-12-01), Nelson et al.
patent: 6064511 (2000-05-01), Fortmann et al.
patent: 6521136 (2003-02-01), Sfez et al.
Dang Hung Xuan
National Semiconductor Corporation
Pickering Mark C.
Tra Tuyen
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