Sample Preparation: Use of Vacuum Technology

1. Experimental Techniques for
Interdisciplinary Research Work
(Sample Preparation: Use of Vacuum Technology)
By
Dr. C.L. Saini
(clsaini52@gmail.com, clsaini52@uniraj.ac.in)
(Mobile No. : +91-9413119927)
(Assistant Professor)
Solar and H2 storage Laboratory
Department of Physics
University of Rajasthan, Jaipur
JLN Marg Jaipur, Rajasthan – 302004, India
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2. Sample Preparation by
Different techniques
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3. Purpose of Deposition
• Conductive or insulating layers on a substrate
• It creates locally conductive paths that can be
used to interconnect devices
• Deposition can be used to build up more
complex structures one layer at a time (which
is known as multilayer)
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4. Deposition Types
1) Silicon Dioxide SiO2
– Insulating layers
– Protective coatings
– Gate oxides
2) Silicon Nitrides
– Protective layers
– Isolation
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3) Polysilicon
– Heavily doped silicon
– Conductive
– Used for interconnects and gate
4) Metals
– Aluminum/Aluminum-Copper
– Tungsten
– Titanium Alloys

5. Deposition Processes
• Physical or Chemical (or both?)
– Physical Processes Deposit the material without
chemical reactions
– Chemical processes utilize liquid or vapor forms
of precursors that react with the surface to form
the desired deposition
– To combine the processes and gain the benefits of
each
– Many processes are carried out in reduced
pressure (limited vacuum range) environments
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6. Requirements of Deposition
• Any deposited layer must be compatible in many customs with
the following properties:
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i. Film Stress
ii. Conformality
Good Poor
iii. Uniformity
iv. Step Coverage
v. Thermal compatibility
Source file From
MATEC Module 45

7. • Deposition rate
• Film uniformity:
• Materials that can be deposited: metal, dielectric, polymer.
• Quality of film:
Physical and chemical properties
Electrical property, breakdown voltage
Mechanical properties, stress and adhesion to substrate
Optical properties, transparency, refractive index
Composition, stoichiometry
Film density, defect (pinhole…) density
Texture, grain size, boundary property, and orientation
Impurity level, doping
• Deposition directionality:
Directional - good for lift-off, trench filling
Non-directional - good for step coverage
• Cost of operation.
General characteristics of thin film deposition
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8. Physical Deposition Processes
• Sputtering
– Plasma is created by RF or HV DC source
– Inert gas (such as Ar) is used in a low pressure
environment (~ 10-3 Torr)
– Free electrons strike Ar atoms, causing positive
ions to be formed
– Negatively charged target material attracts ions
– Ions dislodge particles that are deposited on
substrate
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9. Sputtering
(Process and mechanism)
Source: www.wikipedia.com
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10. Sputtering
• Advantages
– Low temperature process
– Good Conformal Coating
– Good Step Coverage
• Disadvantages
– Dielectrics require RF Source
– RF environment may affect other depositions
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11. Evaporative Deposition
• Utilizes the principle of vapor pressure
– Metallic species are melted in a low pressure environment
– Higher vapor pressure metals evaporate first
– Deposition of the vapor on the surface occurs
– A low temperature process on the substrate
– Alternatives include laser ablation (Laser strikes a target, causing local melting)
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Source file: Wikipedia

12. Evaporative Deposition
• Advantages
– Uniformly covers substrate
– Simple process without chemicals or gases
• Disadvantages
– Alloys are difficult to deposit
• Different metals have different vapor pressures
– High aspect ratio features are difficult to cover
• Trajectory of evaporated particles tends to be vertical, which
may not pattern sidewalls evenly
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13. Spin On Coating
• A Physical Deposition Process
– Similar to photoresist spin-on
– Si-based liquid is applied
– Coating is baked on to remove volatile liquid
• Used to planarize or flatten wafer surface
– Can be patterned and etched for contacts
• Adds steps to process
• Alternatives – Chemical Mechanical Polish
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Experimental Set-up
Different size chucks

14. Basic principle and working mechanism
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Device fabrication using Spin Coating
unit
Device architecture
XRD data
Optical properties
I-V Curve

16. Chemical Deposition Processes
• Wet or Dry Method?
– Wet processes use liquids and immersion
Electroplating
Electro-less deposition
Wet growth of SiO2 insulating layer (water vapor)
– Dry processes use chemical vapors
a) Atmospheric Pressure Chemical Vapor Deposition
b) Low Pressure Chemical Vapor Deposition
c) Plasma Enhanced Chemical Vapor Deposition
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17. Types of Chemical Vapour Deposition (CVD)
For Research & Development, PECVD is most popular, followed by LPCVD.
(can be higher)
and epitaxy Si…
(can have high
deposition rate)
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18. Chemical Deposition Processes
• Atmospheric Chemical
Vapor Deposition (CVD)
• Main steps for deposition
considerations:
i. Wafers are heated
ii. Chemical gases are
introduced
iii. A temperature
dependent deposition
rate
iv. Mass transport limited
at higher temperatures
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Source file: Wikipedia

19. Chemical Deposition Processes
• Plasma Enhanced Low
Pressure (CVD)
Steps to be considered:
 Lower Temperature Process
due to Plasma Enhancement
 Dissociation of precursor gas
molecules (Homogeneous
reactions)
 Ions bombard surface making
it more reactive
 Higher rates of deposition are
possible than with LPCVD
Source file: From MATEC Module 54
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20. Chemical Deposition Processes
• Use of chemical deposition process to
deposits Anti-reflective coatings
a) Utilize thin film deposition to create coatings
that have λ/2 thickness at the exposure lamp
wavelength
b) This results in destructive interference
canceling reflection in the photo-resist layer
c) Reflection from glossy layers below photo-resist
causes indistinct features
d) By this method better lithography is possible
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Thank you
very much
Suggestions are invited for improvement in the ppt file.
Send your feedbacks at Email: clsaini52@gmail.com