Dry Etching
Dry Etching, Introduction
What is Dry Etching?
Gas phase etching
Both etchants and byproducts
are gaseous.
Materials are removed by
both chemical & physical
reactions
Wafers are exposed to
gaseous etchants in plasma
Natural Dry
Etching
Pros vs. Cons of Dry etching
Pros:
• Anisotropic etching
• More directional control
• More control on process conditions such as
pressure, flowrate, temperature & power etc.
• Increased selectivity
• Higher resolution
Cons:
• Cost of equipment
• Chemical gases involved
Types of Dry Etching
Good directional control of dry etching
Physical Etch: physical process,
etches by ion bombardment only,
uses a non-reacting gas, it is
anisotropic and non-selective
Chemical Etch: chemical process,
specially selected gases to react
with materials, ion bombardment
is negligible, it is isotropic and
selective
Combined Etch: ion bombardment
complements chemical etch, varies
from isotropic to anisotropic with
fair selectivity
3 Types of Dry Etching
Plasma
Ionized gas
High mobile electron density
Unique state of matter
Electric fields energize plasma
Natural plasma: air is ionized.
Plasma Generation
As energy increases, nucleus and electrons separate from
each other, allowing electrons to freely move around
Plasma Generation: Magnetic Field
Magnetic field is generated in the chamber. The magnetic field increases
the kinetic energy of electrons and the gas changes to plasma.
Gas is introduced
Ionized by plasma
Diffusion of particles through sheath
Plasma/Chemical
Etch Types
The term plasma etch systems can
refer to any system that uses plasma
generation in order to etch a sample
A sample can be biased to improve
bombardment’s effect on the etching.
This is called Reactive Ion Etching
(RIE)
A sample can be left unbiased which
takes way much of the effects of
bombardment, leaving chemistry as
the dominant etching force. This is
known as Plasma Etch (PE)
Etch Systems
• Horizontal Plate RIE
• Parallel Plate Etch
• Microwave Etch
• Electron Cyclotron Resonance (ECR) Etch
• Hexode RIE
• MERIE
• Inductively Coupled Plasma (ICP) Etch
• Ion Beam Etch
• Advanced Strip and Passivation (ASP)
Horizontal Plate RIE
The substrate is placed on a
powered cathode
The cathode is generally water-
cooled to remove the heat
generated by ion bombardment.
Chamber walls usually function as
the anode and may also be
temperature controlled.
Generic Parallel Plate Plasma Model
Most of the plasma body consists
of etch gas molecules, etch by-
product molecules and radicals.
A typically low-density plasma
consists of less than 1% charged
species.
Positive Ions
Electrons
Neutral Atoms and Molecules
Molecular Fragments
Simple Diagram of a Horizontal Plate RIE
Ion drawn to negatively
charged cathode
-
50 Ω
Impedance
Match
~
Typical Horizontal Plate Reactive Ion Etch System
MFC’s
Vent/Purge
TC1
Cathode
with CF4 O2
Ion Gauge backside
cooling Roughing
Valve N2
Capacitance Manometer Typical Gases
for throttle valve control Throttle
Valve Scrubber
Impedance Match Turbo Pump - C Mechanical Pump - C
Blocking Capacitor TC2
13.56 MHz
RF Power Foreline Valve
Source
Simple Diagram of a Parallel Plate (Planar)
Ion not directed
to substrate
-
50 Ω
Impedance
Match
~
Short around capacitor
Microwave Etch
Plasma is Generated
2.45 GHz “Out of Sight” of the
Power supply substrate.
MFC’s
Tuning Stubs
Vent/Purge
Baffling: blocks
line of sight TC1
He O2
Ion Gauge
IR Substrate Roughing
Heating Lamp Valve N2
Typical Gasses
Throttle
Capacitance Manometer Valve
for throttle valve control Mechanical Pump - C
Turbo Pump - C
TC2
Foreline Valve
Electron Cyclotron Resonance Etch (ECR)
The design provides a high ion
density at low pressure to more
effectively transfer energy to
the free electrons and at the
same time keep them in the
plasma region longer.
Electron Cyclotron Resonance Etch
Additional magnets may surround
the substrate area to aid in plasma
uniformity
Relatively high bombardment
damage and inability to etch
substrates larger than 150mm
generally make this technically
obsolete.
Typical ECR Etch System
2.45 GHz Wave Guide Magnets
MFC’s
Power supply 873 Gauss
Tuning Stubs Wave Guide
Window
Vent/Purge TC1
Cathode CF4 O2
with
Ion Gauge backside
cooling Roughing
Valve N2
Capacitance Manometer
Typical Gasses
for throttle valve control Steering Magnets
Throttle
Valve Scrubber
Impedance Match Turbo Pump - C
Blocking Capacitor Mechanical Pump - C
TC2
Optional
13.56 MHz
RF Power Foreline Valve
Source
Hexode RIE
MFC’s
Anode Typical Gases
Vent/Purge
Hexode
TC1
(Cathode)
He O2
Substrates
Roughing
Valve N2
Blocking Capacitor
Throttle
Impedance Valve
13.56 MHz Throttle
Match
RF Power Valve
Source
Capacitance Manometer
for throttle valve control Turbo Pump - C
TC2
Mechanical Pump - C
Foreline Valve
Typical MERIE System
Magnets
~0-75 Gauss
MFC’s
Vent/Purge
TC1
Cathode CF4 O2
Ion Gauge with
backside
cooling Roughing N2
Valve
Capacitance Manometer
for throttle valve control
Typical Gases
Throttle
Valve
Scrubber
Impedance Match
Turbo Pump - C
Blocking Capacitor Mechanical Pump - C
TC2
13.56 MHz
RF Power
Source Foreline Valve
Magnetically Enhanced RIE (MERIE)
Magnet A
Plasma Body Magnet B
E
Magnet B’ Magnet A’
Sample
Blocking Capacitor
E – Electric Field Vector Impedance Match
B – Magnetic Flux Vector
Rotation of these vectors 13.56 MHz
occurs at low frequencies
The Effect of a Magnetic Field on the Plasma
Plasma
E e- Sheath
B
Cathode
B – Static Field
E – Field Oscillation at 13.56 MHz
Electron Motion in a Magnetic Field
Effect of Magnetic Field on DC Bias
More collisions = more ions
Electrons are not lost to the walls; they are contained in the magnetic
field.
Grand result is more ion population with less individual ion energy
Recall high individual ion energy leads to damage.
High etch rate leads to faster throughput, and reduced
manufacturing cost!
Inductively Coupled Plasma Etch (ICP)
13.56 MHz
RF Power
Source Impedance Match
MFC’s
Coil
Vent/Purge
Dielectric Plate
High Density Plasma TC1
CF4 O2
Roughing N2
Valve
Cathode
Typical Gasses
CM for
throttle Scrubber
Impedance Match valve
Throttle control
Valve
Blocking Capacitor Turbo Pump - C
Mechanical Pump - C
TC2
13.56 MHz RF or
100KHz Power
Source Foreline Valve
Ion Beam Etchers (IBE)
High energy
Gas (Ar) Inlet
electron stream
Neutral Ar atom Cathode Ionized Ar atom
Anode
Highly collimated ion Solenoid Magnetic field
beam extraction grid which increases ionization
Ar Ions with momentum
Neutralization filament
Ar atoms with momentum
Substrate (Wafer)
Tilted rotating substrate holder
ASP Chamber
Gas / RF
Blocking Plate Gas Distribution Shield
Vacuum
Channel
Isolation Sample Vacuum
Plate Channel
Susceptor
Quartz Lamp
Window
Heating Lamps
ASP Strip & Passivation Recipe
Recipe 200 mm Sample 150 mm Sample
Parameters
Step 1 Step 2 Step 1 Step 2
O2 (sccm) 3500 3000
N2 (sccm) 200 200
H2O (sccm) 500 300 500 300
Pressure (T) 2 2 2 2
Power (W) 800 1400 800 1400
Temperature (C) 250 250 220 220
Time (sec) 60 60 60 60
Survey of Dry Etch Equipment, A
Type of Etch Typical Pressure
Descriptions
Tool Range
Slow etch rate, batch loading required for throughput, less
affected by high rate etching damage, asymmetric electrode
Reactive Ion Low
configuration, negative DC Bias on the cathode, no sputtering
Etch (RIE) (10 mT – 150 mT)
of anode, samples are placed on the powered electrode
(cathode).
Usually single wafer, symmetric configuration, No DC Bias, high
rate required for adequate throughout, samples can be placed
either on the grounded electrode (Plasma etch Mode) or the
Parallel Plate Medium
powered electrode (Reaction Ion Etch Mode), sputtering of
Etcher (Planar) (100 mT – 1 T)
both electrodes can occur, less sample – to – sample variability
than in a typical batch system, good individual sample endpoint
detection control possible.
No high energy ion bombardment, reactive species created
Downstream outside of the etching region, then transported to the etching
High
Microwave chamber downstream of the plasma, etching is isotropic
(0.5 – 2 T)
Etch without application of bias to the sample, useful for photoresist
stripping and other “non-critical” applications.
Survey of Dry Etch Equipment, B
Type of Etch Typical Pressure
Descriptions
Tool Range
Batch process RIE tool. Wafers are mounted on a large
six-sided cathode, etch chamber walls acting as the
High
Hexode RIE anode. The large cathode distributes the bias, and with
100’s mT
the high pressure results in low bombardment. Use often
as a photoresist striper.
Magnetic field is responsible for more efficient plasma
Magnetically
generation at lower pressures, higher ion and reactant
Enhanced Low
species production, denser plasma, high etch rates,
Reactive Ion (10 mT – 250 mT)
lower bias for less bombardment “damage”, controlled
Etch (MERIE)
anisotropy.
Electron
Magnetron microwave source, magnetic coils, high
Cyclotron Very Low
density plasma, low ion energy, complicated and
Resonance (< 20 mT)
expensive, technology continues to mature
(ECR Reactor)
Survey of Dry Etch Equipment, C
Type of Etch Typical Pressure
Descriptions
Tool Range
ICP is a high density plasma system that uses a separate power
Inductively
Low supply outside of the etch chamber to control the plasma in the
Coupled
(100’s mT) etch chamber. Separate power supplies for plasma generator
Plasma (ICP)
and sample electrode allow for better control of ion generation.
Physical sputter mechanism, high excitation energy, strongly
Ion Beam Etch Low
directional (anisotropic), ion density and acceleration voltage
(IBE) (< 100 mT)
can be independently controlled, poor selectivity, low etch rates.
Advanced
Strip &
Passivation Two stage process. The first step neutralizes caustic chemicals
(ASP) High on the sample by flowing in stem. The second stage ashes of the
Also known as (0.5 - 2 T) PR with oxygen. High pressure results in shorted mean free path
Resist Strip & and reduced bombardment.
Passivation
(RSP)
Study Activity
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