Chapter 10 Etching
1. Introduction to etching.
2. Wet chemical etching: isotropic.
3. Anisotropic etching of crystalline Si.
4. Dry etching overview.
5. Plasma etching mechanism.
6. Types of plasma etch system.
7. Dry etching issues.
8. Dry etching method for various films.
9. Deep Si etching (can etch through a wafer).
1
NE 343: Microfabrication and thin film technology
Instructor: Bo Cui, ECE, University of Waterloo; http://ece.uwaterloo.ca/~bcui/
Textbook: Silicon VLSI Technology by Plummer, Deal and Griffin
Dry etching advantages
Eliminates handling of dangerous acids and solvents
Uses small amounts of chemicals
Isotropic or anisotropic/vertical etch profiles
Directional etching without using the crystal orientation of Si
Faithful pattern transfer into underlying layers (little feature size loss)
High resolution and cleanliness
Less undercutting
Better process control
Types of dry etching:
Non-plasma based - uses spontaneous reaction of appropriate reactive gas mixture.
Plasma based - uses radio frequency (RF) power to drive chemical reaction.
Why dry etching?
Dry etching disadvantages:
Some gases are quite toxic and corrosive.
Re-deposition of non-volatile compound on wafers.
Expensive equipment ($200-500K for R&D, few million for industrial tools ).
2
Non-plasma based dry etching
4Si(s) + 2Cl
2
(g) ---> 4SiCl
4
(g) + 130 kcal/mole
This is very rare. For example,
Although there is a large gain in free energy, the large activation energy does
not allow low temperature processes - reaction is only effective above 800C.
In order to succeed with gas etching, one has to go out of equilibrium.
The solution is plasma etching.
One exception is room temperature XeF
2
etching of Si. (same for BrF
3
& ClF
3
)
XeF
2
is a white powder, with vapor pressure
3.8 Torr at 25
o
C.
Isotropic etching, non-polish etching (rough)
High selectivity for Al, SiO
2
, Si
3
N
4
, photoresist,
and PSG (phospho-silicate glass).
Typical etch rate 1m/min
Heat is generated during exothermic reaction
XeF
2
reacts with water (or vapor) to form HF
2XeF
2
+ Si 2Xe (g) + SiF
4
(g)
Gas phase etching, no stiction between
freed structure and substrate (no liquid
involved like KOH etch, so no need of
drying that collapses pattern due to
capillary force).
Popular for MEMS application.
Xenon di-fluoride (XeF
2
) etching of Si:
MEMS: micro electro mechanical systems
3
Plasma-based etching
Directional etching due to presence of ionic species in plasma and (self-) biased
electric field. (The self-bias electric field is not applied externally, but is created
spontaneously in RF plasma)
Two components exist in plasma
o Ionic species result in directional etching.
o Chemical reactive species result in high etch selectivity.
Control of the ratio of ionic/reactive components in plasma can modulate the dry
etching rate and etching profile.
Neutrals (etchant gas)
Ions
Free radicals
adsorb
react
surface
Gaseous products
Plasma
) ( ) ( 4 ) (
4
g SiF g F s Si
4
RF plasma chemistry
RF plasma is more widely used for dry etching than DC plasma is there DC plasma dry
etching?
CF
4
plasma
Figure 10-9
5
As seen in previous slide, in a plasma, unstable particles are continuously generated.
The concentrations of ions, radicals, active atoms, & electrons increase until their loss
rate is equal to the generation rate, forming a steady-state plasma.
Recombination of ions and electrons: they attract each other and are annihilated.
Drift, diffusion to walls: electrons are lost at conductive surfaces, chamber walls or
electrodes. Ions are lost (converted to neutral particles) by contact with conductive
surfaces, especially positive electrode.
Recombination of radicals: e.g. 2O O
2
.
Chemical reaction (what we want): e.g. 4F + Si SiF
4
(fluorine radical combines with
silicon wafer to produce silicon tetra-fluoride gas. This is a typical dry etching process.)
Loss mechanisms
Plasma TV
In a plasma TV, the recombination of ion-
electron or radical, or de-excitation of atom or
molecule, generates the colorful light we see.
In equilibrium, degree of ionization typically 10
-3
-
10
-6
, very low, meaning majority gas not ionized.
(plasma density = number of ions/cm
3
typically 10
9
10
13
/cm
3
.)
6
Chapter 10 Etching
NE 343: Microfabrication and Thin Film Technology
Instructor: Bo Cui, ECE, University of Waterloo, bcui@uwaterloo.ca
Textbook: Silicon VLSI Technology by Plummer, Deal, Griffin
1. Introduction to etching.
2. Wet chemical etching: isotropic.
3. Anisotropic etching of crystalline Si.
4. Dry etching overview.
5. Plasma etching mechanism.
6. Types of plasma etch system.
7. Dry etching issues.
8. Dry etching method for various films.
9. Deep Si etching (can etch through a wafer).
7
Plasma etching mechanism overview
In a plasma, reactive neutral chemical species (free radicals, e.g. F atoms or molecular
species CF
3
) are mainly responsible for the chemical reaction due to their much greater
numbers compared to ions (e.g. CF
3
+
is also reactive, but with low concentration in a
plasma. But Ar
+
is not reactive, and etches/sputters much slower than chemical etching,
even when ion energy is high -- generally chemical etching is much faster than physical).
Those free radicals and molecules also serve as primary deposition species in PECVD.
Those free radicals are more abundant than ions because: 1) they are generated at lower
threshold energy (e.g. < 8eV; in comparison, Ar is ionized at 15.7eV); and 2) they
(uncharged radicals) have longer lifetime in the plasma.
The neutral radicals arrive at cathode surface by diffusion (thus non-directional).
Figure 10-10
8
Charged ions are accelerated to the
cathode due to self-bias.
(Unless with very high energy of >100eV
as in ion beam/sputter etching), ion itself
doesnt contribute significantly to the
chemical reaction mostly due to its very
low concentration, but ion
bombardment can greatly enhance the
chemical reaction in ion-enhanced
etching.
Chemical etch: highly selective, but isotropic
Due to their incomplete bonding (incomplete outer shells), free radicals (neutral,
e.g. CF
3
and F from CF
4
plasma) are highly reactive chemical species.
Free radicals react with film to be etched and form volatile by-products.
Pure chemical etch is isotropic or nearly isotropic,
and the etching profile depends on arrival angle
and sticking coefficients of free radicals.
Free radicals (un-charged) in plasma systems have
isotropic arrival angles.
The sticking coefficient S is very low, typically only
S0.01 (i.e. most free radicals adsorb then just
bounce back without reaction).
This leads to isotropic character of etch, as free
radicals can etch area beneath the mask due to
bouncing, as seen in the figure. The resulted
profile has large undercut.
Adsorption rate onto surface
9
Sticking coefficient S
Reaction, here momentum transfer by physical
bombardment, takes place at every shot, usually
sputter off a few atoms, so S1.
Most adsorbed species just left
the adsorption site without doing
anything, so S<<1.
Figure 10-11
10
Si etching with F radicals
Isotropic etching
11
Etch byproducts should have low boiling point
Boiling points of typical etch products
Low boiling point means very volatile, so it can be pumped away.
This is not necessary for physical etching/sputtering, where etch product is
sputtered off that ideally doesnt fall on the other part of the wafer (re-deposition).
12
Physical etch component in a plasma etch system
(much less important than chemical etch)
Ionic species are accelerated toward each electrode by built-in self-bias.
The ionic species such as Cl
2
+
, CF
4
+
, CF
3
+
(or Ar
+
in a purely physical sputter
etch) strike wafer surface and remove the material to be etched.
Directional, non-selective - similar sputter yield for different materials.
(But CF
3
+
can also etch Si chemically, then with high selectivity)
It may result in significant re-deposition.
Ar plasma
Pure physical etch: sputter etching system
Self-bias few 100V, but low ion energy
(order 10V) due to collision energy loss.
Thus very low milling rate in a sputter
system, often for surface cleaning only.
Here is the case for sputter etching system
with gas pressure order 10mTorr.
For a dedicated ion milling system (no
plasma, see later slides), the pressure is
10
-4
Torr or even lower (cannot sustain a
plasma), leading to large mean free path,
high ion energy and high milling rate.
13
Ion enhanced etching (IEE):
chemical etch assisted by physical bombardment
IEE is an anisotropic (due to directional ion bombardment) and highly selective (due to
chemical reaction) etching process.
Reactive ion etch (RIE) is the most popular form of IEE.
Ion bombardment can enhance one of the following steps during chemical etch: surface
adsorption, etching reaction (by physically damaging/weakening the chemical bond of
the material to be etched), by-product (inhibitor layer) removal, and removal of un-
reacted etchants.
Inhibitor layer: e.g. fluorocarbon
polymer formed from CHF
3
during
etching of SiO
2
.
When removal rate << deposition
rate, net deposition will occur,
then the process becomes similar
to PECVD!!
Indeed, the RIE and PECVD are
pretty similar tools, except PECVD
is typically heated.
Chemical etch enhanced
by ion bombardment
Inhibitor removed by
ion bombardment
Figure 10-13
14
IEE: first proof of etching mechanism
15
Gas phase etch, with or without
the aid of Ar ion beam.
NO plasma.
Very slow etch when pure
chemical or physical etch alone
The ion enhancement could be due to the damage/weakening of silicon lattice by
ion bombardment, which makes the etching by XeF
2
easier.
The resulted profile will be anisotropic since the horizontal surfaces are much more
bombarded than vertical ones.
This is one example of CAIBE (chemically assisted ion beam etching), see later slides
Ion enhanced etching
is highly anisotropic
Sidewall reactions can lead to an isotropic etch
component.
To prevent sidewall etching, one can build up a
passivation (inhibitor inhibit chemical
reaction) layer that protects it.
Then there is a competition between passivating
and etching reaction.
For the feature base/horizontal surfaces, etch
rates tend to be temperature independent
because of ion energy input (i.e. inhibitor
sputtered away by ions).
On sidewall, substrate temperature can play an
important role as sidewall passivation depends
on the volatility of the inhibitor that is
controlled by temperature (cryo-etcher at below
-100
o
C is available recently, then the sidewall
passivation layer is not volatile).
Even without sidewall passivation, lower
temperature still increases anisotropy since
chemical attack of sidewall is suppressed at low
temperature. (Attack of horizontal surfaces are
assisted by ion bombardment)
16
High inhibitor
deposition rate
Low inhibitor
deposition rate
Example:
etching profile of Si or SiO
2
Fluoropolymer (like Teflon) in CHF
3
or CF
4
+H
2
RIE of Si
or SiO
2
is the inhibitor.
If Ar gas is added, inhibitor is mainly removed by ion
bombardment. So less attack of inhibitor on sidewall.
If O
2
gas is added, inhibitor on sidewall is removed at
faster rate than Ar ion, but the etch of inhibitor at
horizontal surface is even faster.
Yet at very low temperature, inhibitor SiO
x
F
y
(not act
as inhibitor at higher temperature when it is volatile)
forms when O
2
is added, which is the mechanism for
fast anisotropic etching of Si using cryo-etcher. (deep
Si etcher, popular for MEMS micro electro
mechanical systems)
Teflon
Figure 10-14
17
Anisotropy due to ion bombardment: summary
Due to its extremely low density, ions dont contribute much to etching; neutral radicals do.
So even with directional ion bombardment, the overall etching can still be pretty isotropic.
For instance, SF
6
etch of Si is very isotropic with large undercut like wet etch.
To achieve anisotropy, there are two mechanisms:
o Energy-driven anisotropy: bombardment by ion disrupts an un-reactive substrate and
causes damages such as dangling bonds and dislocations, resulting in a substrate more
reactive towards etchant species (electron or photon can also induce surface activation).
o Inhibitor-driven anisotropy: ion bombardment removes the inhibitor layer from horizontal
surface (sidewall remain passivated), and reaction with neutrals proceed on these un-
passivated surfaces only.
One may think that ions wont help much due to its much lower density than radicals. But ion
has sticking coefficient S1 (every ion bombardment counts), whereas radicals S0.01 (most
radicals hit the surface and left without doing anything).
Energy-driven
anisotropy
Inhibitor-driven
anisotropy
18
Chapter 10 Etching
NE 343: Microfabrication and Thin Film Technology
Instructor: Bo Cui, ECE, University of Waterloo, bcui@uwaterloo.ca
Textbook: Silicon VLSI Technology by Plummer, Deal, Griffin
1. Introduction to etching.
2. Wet chemical etching: isotropic.
3. Anisotropic etching of crystalline Si.
4. Dry etching overview.
5. Plasma etching mechanism.
6. Types of plasma etch system.
7. Dry etching issues.
8. Dry etching method for various films.
9. Deep Si etching (can etch through a wafer).
19
Plasma etching in barrel etchers
Barrel etcher:
Chemical etching only, isotropic and selective
like pure wet etch.
Use plasma shield to keep ion bombardment
from wafers, thus very little damage.
Poor uniformity edge to center.
Used in non-critical steps such as photoresist
removal by O
2
plasma (Barrel asher
Polymer + O CO
2
+ H
2
O).
Quartz tube
Figure 10-15
20
Downstream etchers
Plasma is formed in a cavity which is
separated from the etching chamber.
Wafers are shielded from bombardment.
Only neutral free radicals reach wafers.
Etching is completely chemical and
isotropic.
High selectivity achievable - Si:SiO2 = 50:1
Plasma may be generated by RF
(13.56MHz) or by microwave (2.45GHz).
21
Parallel plate = capacitively coupled plasma (CCP)
You will see later on ICP : inductively coupled plasma
Plasma etching in parallel plate systems plasma mode
Similar to PECVD except that etch gas is used instead of precursor gas.
Equal or larger (grounded to chamber) wafer electrode (which defines plasma mode)
gives weaker ion bombardment of wafers (smaller DC voltage drop near larger electrode).
The etch is more uniform than barrel, but typically etches only one or a few wafers (cassette
for barrel etcher) at a time.
Both chemical and physical etch occur (wafer in contact with plasma), though the later is
weak, particularly at higher pressure when DC voltage drop near wafer is smaller.
Etching is fairly isotropic and selective due to the strong chemical component.
Figure 10-7
22
Very often, plasma mode etching is
considered as just a kind of reactive
ion etching (RIE), but done at
higher pressure.
Of course, both plasma mode
etching and RIE is plasma etching.
Parallel plate etchers (regular RIE, low density plasma)
Absolutely the most important form of dry
etching, though recently ICP (see later slides) is
becoming more and more popular.
Compared to plasma mode: smaller wafer
electrode (counter electrode grounded to
chamber wall), lower pressure (<100mTorr), more
physical bombardment (voltage drop many 100V).
Ion enhanced etching mechanism, (usually)
directional/anisotropic and selective.
RIE using parallel plate setup is low
density plasma system (ions 10
8
10
10
/cm
3
), thus low etch rate.
Here low (ion) density plasma also
implies low density of free radicals.
Thus low etching rate.
VERY roughly, one can say that plasma consists of order
1% radicals (reactive neutral species) and 0.01% ions.
23
Due to its simultaneous anisotropy and
selectivity, RIE is intensively used.
Works for most semiconductors and
dielectrics.
OK for few metals that form volatile etch
products: Al (form AlCl
3
), Cu (CuCl
2
) (not
really), Ti (TiF
4
, TiCl
4
), W (WF
6
), Cr (CrO
2
Cl
2
).
Reactive ion etch (RIE)
Etching mask
Schematic RIE process
a) Ion sputtering, b) reactive ion etching, c)
radical formation (?), d) radical etching
(most important)
In RIE, ion energy is low (several 10s eV, << voltage drop near wafer surface, due to collision
energy loss), and its number density is very low, thus negligible etching by ion bombardment.
The name reactive ion etching is very misleading since ions dont contribute directly to
etching it just helps chemical etching.
24
Ion energy vs. pressure for a plasma
Lower pressure (<10mTorr) increases mean free
path as well as voltage drop near wafer electrode,
both of which leads to more energetic and
directional ion bombardment, thus more
anisotropic, but less selective and slower etching
rate due to low ion/free radicals density.
High pressure (>100mTorr), short mean free path,
low voltage drop, isotropic chemical etching.
Thus it is desirable to have a low pressure plasma
with high ion density.
Plasma mode: >100mTorr
RIE mode: 10-100mTorr
Sputter etching: pressure as low as possible, as long as
plasma can be sustained, but still very slow etching rate.
RIE with tilted wafer, will etch vertically or not?
25
Etching in high density plasma (HDP) systems
Ion flux and ion bombarding energy can be independently controlled. For regular RIE,
they are tightly coupled (e.g. higher power increases both).
High plasma (ion) density (> 10
11
) enhances etch rate.
Since ionization is much more efficient, can operate at lower pressure, which leads to less
ion collision, so more directional/anisotropic, thus enhances profile control.
As ion energy is independently controlled, it can be kept low if desirable.
Then the extent and amount of damage will be reduced, without sacrificing etching rate
that is still high for high density plasma.
Currently HDP represents an optimum compromise in high etch rates, good selectivity,
good directionality, while low ion energy and damage (??).
(What I think) For sidewall profile control and selectivity, hard to say which one (regular
RIE vs. HDP) is better. But if wanted one can always turn off the HDP power, then the
machine operates like a regular RIE.
The bottom line: for deep etching (>>1m) that needs very high etching rate, HDP is the
only choice.
26
ECR was introduced in 1985.
ICP was introduced much later (1991- 1995).
Electron cyclotron resonance (ECR)
and inductively coupled plasma (ICP)
Dual plasma source:
Top one (ECR or ICP RF power) generates HDP,
determines ion density/current.
Bottom one (CCP RF power) generates bias voltage like
regular RIE, determines ion energy.
CCP: capacitively coupled plasma, parallel plate, used for conventional regular RIE.
Typical parameters for HDP and conventional plasma etcher
ions/cm
3
should be lower
27
High magnetic field in the coil, so electrons move in circles with long path, leading to
higher collision and ionization probability, and much less electron loss to chamber wall
and the bottom plate where sit the wafer. Moreover,
For ICP, AC magnetic field induces circular electrical field, which accelerates electrons.
For ECR, DC magnetic field, electron cyclotron =qB/m; electrons accelerated if this
frequency matches the microwave frequency.
Inductively coupled plasma (ICP)
(four systems at Waterloo)
ICP RF power
(for dense plasma)
RF bias power
(similar to RIE, parallel plate)
plasma
Electron cyclotron resonance plasma
(less common nowadays)
ECR and ICP
28
Microwave source 2.45 MHz
Wave guide
Diffuser
Quartz window
Electrostatic chuck
Cyclotron magnet
Plasma chamber
Wafer
Additional magnet
13.56 MHz
Vacuum system
Schematic of ECR etcher
30
Electromagnet
Dielectric
window
Inductive coil
Biased wafer chuck
RF generator
Bias RF generator
Plasma
chamber
Schematic of ICP etcher
As you see, there is practically no top plate as in parallel plate regular RIE.
The wafer sees the ICP power the two power sources are not physically separated.
Otherwise, even though the plasma density in the upper part is high, it will get lost due
to re-combination and de-excitation when it travels through the bottom part.
31
Electromagnet
(1 of 4)
13.56 MHz
Biased wafer chuck
Wafer
Magnetically enhanced reactive ion etch (MERIE)
Like regular parallel plate RIE, but magnetic field forces electron to go circles, increasing
collision with gas molecules and decreasing loss to chamber walls or top/bottom plates.
However, now that electrons dont loss to bottom plate, no or little bias voltage need to
apply an external bias to accelerate ions.
I havent seen any MERIE, so
it is not popular.
On the contrary, magnetron
sputtering is very popular.
This is probably because
there are many ways to
increase etching rate; but
sputter without magnetron
is always very slow:
few nm/min, vs. 10s to 100s
nm/min RIE etching rate.
32
Sputter etching and ion milling
Sputter etching: (etch inside plasma)
The etch mechanism is purely physical and ion
energies are greater than 500 eV.
Very similar in principle to sputter deposition, but
now the target becomes substrate to etch.
Poor selectivity (2:1 or 1:1), very anisotropic.
Sputtering rate depends on sputter yields which can
be a function of incident angle.
Problems include faceting (sputter yield is a
function of incident angle), trenching, re-deposition,
charging and ion path distortion, radiation damage.
Not popular, etches too slow, though reactive gas
(CF
4
, CCl
4
, O
2
) can be added to slightly improve
selectivity and etching rate.
Figure 10-8 Problems associated with
sputter etching (or any etching that has
a high degree of physical/ionic
etching): a) trenching at bottom of
sidewalls; b) redeposition of
photoresist and other materials; c)
charging and ion path distortion.
33
Physical milling when using heavy inert gases (Ar).
Plasma is used to generate ion beam (Ar
+
), which is extracted and accelerated to etch
the sample. (i.e. sample outside of plasma)
Thus the ion density (determined by plasma source) and ion energy (determined by
DC acceleration voltage bias by applied DC voltage, not by RF bias as in high density
plasma etching system), can be controlled independently.
Low pressure 10
-4
Torr (>1 order lower than RIE), so large mean free path and less
energy loss due to collision. (such low pressure cannot sustain a plasma, so ion
milling is not plasma etching)
High acceleration voltage (>1kV), leading to mill rate 10-30nm/min.
Despite the high voltage and low pressure, such a rate is still < typical RIE rate where
chemical etching dominates.
Used whenever RIE is not possible (due to the lack of volatile species formation).
Usually employed to etch Cu, Ni, Au, superconducting materials containing metals
Ion milling or ion beam etching (IBE)
Used to call ion milling, seems now more called as ion beam etching.
34
RF plasma ion beam source
(here reactive gas added, so it is
actually a CAIBE, see next slide)
Ion beam etching system:
triode configuration
DC plasma ion beam source
Electrons sprayed to sample to
neutralize ions.
Tilted sample to greatly increase
milling rate.
But then shadowing may become
a problem when milling high
aspect ratio structures.
Electron beam is first generated
by hot filament.
Ions are generated by electron
bombardment, then accelerated
to bombard the substrate.
35
CAIBE: chemically assisted ion beam etching,
inert Ar ion, neutral reactive gas is introduced
into lower chamber, so not ionized, though
some may be ionized due to backflow into
plasma region or bombardment by Ar ion.
RIBE: reactive IBE, reactive gases are
introduced into plasma region together with
Ar gas, so they are ionized. RIEB is virtually
the only example where the same ion has
both a physical (ion impact) and chemical
(reactive etching) component.
Chemically assisted ion beam etching system
Adding reactive gases (CF
4
, CCl
4
, O
2
, Cl
2
) to increase etching rate and selectivity.
Usually physical etching still dominates, no need of volatile etch product.
But for some special situations, like gas phase (no plasma) XeF
2
etching of Si assisted by
ion bombardment, chemical etching dominates with very high etching rate. But there the
etch product SiF
4
is volatile.
Here it is chemically assisted physical etching, different from RIE that is a kind of physically
assisted chemical etching.
36
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Selectivity
Energy (power)
Anisotropicity
Summary: plasma etching mechanism
Chemical etching: free radicals react with material to be removed. E.g. plasma etching at high
pressure close to 1Torr.
Physical etching or sputtering: ionic species, accelerated by the built-in electric field (self-bias),
bombard the materials to be removed. E.g. sputter cleaning using Ar gas in sputter deposition
system.
Ion enhanced etching: combined chemical and physical process, higher material removal rate
than each process alone. E.g. reactive ion etching (RIE), which is the most widely used dry
etching technique.
37
Figure 10-19
Dry etching techniques: summary
38
Three etch process
(e.g. XeF
2
gas etch Si even without plasma)
(e.g. ion beam etching/milling using Ar
+
)
Here strip
and PR
(photoresist)
etch refers to
barrel or
downstream
etch.
Etch rate and selectivity
conflict in RIE
39
Modes of plasma etching
40
Dry etching techniques: summary
41
Configurations Activity
Pressure
(Torr)
Arrangement
High
Density
Plasma
Biasing
Bias
Source
Profile
Barrel Reactive 10
-1
to 1
Coil or electrodes outside
vessel
No In cassette (bulk) RF Isotropic
Parallel Plate (Plasma) Reactive 10
-1
to 1 Planar diode (two electrodes) No
On powered
electrode (anode)
RF Anisotropic
Downstream Plasma Reactive 10
-1
to 1
Coil or electrodes outside
vessel
No
In cassette (bulk)
downstream of
plasma
RF or
Microwave
Isotropic
Triode Planar Reactive 10
-3
Triode (three electrodes) No
On platform
electrode
Anisotropic
Ion Beam Milling Inert 10
-4
Planar triode No
On powered
electrode (anode)
Anisotropic
Reactive Ion Etch
(RIE)
Reactive < 0.1 Planar or cylindrical diode No On cathode Anisotropic
Electron Cyclotron
Resonance (ECR)
Reactive
10
-4
to 10
-
3
(low)
Magnetic field in parallel with
plasma flow
Yes On cathode RF or DC Anisotropic
Distributed ECR Reactive (low)
Magnets distributed around
central plasma
Yes On cathode RF or DC Anisotropic
Inductively Coupled
Plasma (ICP)
Reactive (low)
Spiral coil separated from
plasma by dielectric plate
Yes On cathode RF or DC Anisotropic
Helicon Wave Reactive (low)
Plasma generated by
electromagnets and plasma
density maintained at wafer by
magnetic field
Yes On cathode RF or DC Anisotropic
Dual Plasma Source Reactive (low)
Independent plasma and wafer
biasing
Yes On cathode RF or DC Anisotropic
Magnetically
Enhanced RIE
(MERIE)
Reactive (low)
Planar diode with magnetic
field confining plasma
Yes On cathode RF or DC Anisotropic
Dry etcher configurations
42
