Title: FABRICATION OF SILICON
1FABRICATION OF SILICON ON INSULATOR (SOI)
DONE BY, A.POOJA SHUKLA ECE B
(190912066) SAVEETHA UNIVERSITY
2AIM
- To fabricate PHOTONIC CRYSTAL in SOI.
- To use 248-nm deep UV Lithography for
fabrication. - To use metal-oxide-semiconductor process.
3ABSTRACT
- Demonstration of wavelength-scale photonic
nanostructures, including PHOTONIC CRYSTALS. - Fabrication of silicon on insulator using deep UV
Lithography. - Comparing UV lithography with E-BEAM lithography.
4INTRODUCTION
- Overview of photonic crystals, using deep UV
Lithography. - Use in optical waveguides.
- Current Lithography techniques for fabrication of
PICs.
5PROCESS INVOLVED
- PHOTONIC CRYSTALS
- SOI FOR INTEGRATED OPTICS
- LITHOGRAPHY FOR PHOTONIC CRYSTALS
- FABRICATION
- LITHOGRAPHY ISSUES
61. PHOTONIC CRYSTALS
- PHOTONIC CRYSTALS are periodic optical
nanostructures that are designed to affect the
motion of photons in a similar way that
periodicity of a semiconductor crystal affects
the motion of electrons. - They have separate high dielectric and low
dielectric regions. - Periodic spacing for relevant light frequency.
7ADVANTAGE OF PHOTONIC CRYSTAL
- Reduce Band Gap
- Reduce defects
- example if there is a LINE DEFECT in
structure, it will act as a waveguide - Avoids Propagation of a Material
8CONSTRUCTION STRATEGIES
- The fabrication method depends upon the number of
dimensions that the photonic band gap must exist
in. - 1-D Photonic Crystals
- 2-D Photonic Crystals
- 3-D Photonic Crystals
9PHOTONIC CRYSTAL SLAB
- Any type of dimension can be used.
- High refractive index contrast gives high
diffractive property. - PBG bounds defects in crystal.
- Completely lossless and allows short bends
without radiation loss.
102. SOI FOR INTEGRATED OPTICS
- SOI was first used in CMOS application to reduce
the parasitary capacitance to the silicon
substrate. - The top layer of SI acts as an optical waveguide
due to high vertical index contrast. - SOI uses large cores i.e., top SI layers of upto
10um thick but we use 205nm. - SOI wafer bonding of a buried oxide is 400nm.
- Due to leakage slab waveguide remains single
mode for a silicon thickness upto 268nm. - The minimum loss of 6 db/mm.
11SILICON LAYER THICKNESS CHART
123. LITHOGRAPHY FOR PHOTONIC CRYSTALS
- Photolithography (or "optical lithography") is a
process used in microfabrication to selectively
remove parts of a thin film or the bulk of a
substrate. - It uses light to transfer a geometric pattern
from a photomask to a light-sensitive chemical
"photoresist", or simply "resist," on the
substrate. - For example, in complex integrated circuits, a
modern CMOS wafer will go through the
photolithographic cycle up to 50 times
13GENERAL COMPARISON
- Size within 10nm.
- Most used for research purpose.
- Structure is not defined.
- Defines extremely small features.
- Not suitable for large volume because the process
is very slow.
- Size of any illuminated wavelength.
- Widely used for CMOS fabrication.
- Mostly used for structure defining.
- Reduced wavelength become fuzzy.
- High end deep lithography
144. FABRICATION
- Steps involved in the fabrication of the PHOTONIC
CRYSTALS are given below, - FABRICATION PROCESS
- 1. Lithography
- 2. Etching
- DENSE SQUARE LATTICES
- SUPERDENSE TRIANGULAR LATTICES
15FABRICATION PROCESS
1. LITHOGRAPHY
16- The deep uv lithography facilities we use
5500/300 deep uv stepper with an illumination
wavelength of 248 nm. - The stepper uses 200 nm wafers.
- It is used in resist coating, baking, and
development. - Steps for lithography,
- 1. Wafer illuminated in stepper
- 2. Post exposure bake resist
impurity is removed - 3. Development
-
172. ETCHING
The etching of the SOI wafer is done using a
double etch, in different chambers
18TOP AND BOTTOM VEIW OF SILICON ETCHING
- No air is exposed when two chambers are etched.
- The top layer of silicon is etched using LOW
PRESSURE and HIGH DENSITY. - The top layer of silicon can be replaced by
AMORPHOUS SILICON.
19 DENSE SQUARE LATTICES
20- The first lithography test were carried out
using a CMOS process evaluation mask with dense
contact holes. - For perfect crystal we expose LARGER HOLES but
SAME PITCH (400 to 600 nm), ratio is (0.25 to
0.35). - Vertical sidewalls show roughness in square
lattices so we prefer SUPERDENSE TRIANGULAR
LATTICES
21 SUPERDENSE TRIANGULAR LATTICES
22- The triangular lattice provides various pitch
and hole size, both in top-down and cross-section
view. - Holes are very uniform through out the lattice.
- There is an strong effect of side lobes from the
crystal wall.
235. LITHOGRAPHY ISSUES
- A common problem in dense structures are,
- The size and shape of a structure is changed
with the presence of a neighboring structures. - The various structures on photonic Ics each
require different lithography conditions. - The effects are,
- (a) Optical Proximity
Effects - (b) Line Hole Bias
24 OPTICAL PROXIMITY EFFECTS
BASIC PRINCIPLE
- Photonic crystals are superdense periodic
structures with feature sizes close to the
illumination wavelength. - During lithography, neighboring holes interfere
with eachother. - Due to this the holes get larger or smaller
during the print. - This phenomenon is called as OPTICAL PROXIMITY
EFFECTS (OPE).
25EFFECT IN SUPERDENSE LATTICE
- The denser the structures and the smaller the
pitch, the stronger the OPE becomes
26- The border holes are smaller than the holes in
the bulks. - The hole in the inner corner prints more smaller
than the border holes. - EXAMPLE
- When the OPE of the
lattice with a relatively large pitch of 530 nm,
but with holes targeted at 420 nm.
27 LINE HOLE BIAS
- Different geometrics are on the same level of
the chip, and preferably printed together. - Small holes needs a much higher illumination
than the larger holes i.e, a few hundreds of nm
in width.
28RESULTS
- The new mask structures should be included to
study the effect of OPE in photonic crystals. - The lithography should target the features with
the highest exposure. - The bias should be applied on the mask to the
features that need less energy to print on target.
29CONCLUSION
- Deep uv lithography has potential for the mass
fabrication of ultra compact photonic Ics based
on photonic crystal. - SOI shows well defined holes with very little
edge roughness. - The neighboring of the holes can be avoided by
using OPTICAL PROXIMITY CORRECTION (OPC) method. - Thus, deep uv lithography is suitable for
providing mass-manufacturing capabilities to the
ultracompact photonic Ics.
30REFERENCES
- Fabrication of photonic crystals in SOI using
248 nm deep uv lithography, IEEE. - SOI Photonic Crystal Fabrication Using Deep UV
Lithography, IEEE. - www.google.com
- www.wikipedia.com
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