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Transcript of Plasma Technology_2014
SNT5039 Nano Processing (Plasma Technology) 1
Part II: Plasma Technology
1. PLASMA PROPERTIES- PLASMA PROPERTIES- COLLISIONAL PROCESSES IN PLASMAS- FORMATION OF SPACE CHARGE REGION
2. DC AND RF DISCHARGES- DC DISCHARGES AND SPUTTERING- PARALLEL PLATE RF DISCHARGE- MATCHING NETWORK- HIGH DENSITY PLASMAS
3. PLASMA DIAGNOSTICS- OPTICAL EMISSION SPECTROSCOPY- OTHER DIAGNOSTIC TECHNIQUES
SNT5039 Nano Processing (Plasma Technology) 2
A quasi-neutral gas of charged and neutral particles exhibiting collective behavior. “Quasi-neutral” means that, except for localized regions in space, overall charge density in the plasma is zero. On average, the densities of positively and negatively charged particles
compensate each other. Weakly ionized plasma is formed by a voltage source that drives current
through a low pressure gas between two electrodes. The “collective behavior” comes about because the charged particles
interact with each other via long-range Coulomb forces.
PLASMA PROPERTIES
SNT5039 Nano Processing (Plasma Technology) 3
With the increase of temperature, solid state changes to liquidstate and liquid state changes to gas state. At a sufficiently hightemperature, the gas decomposes to atoms and further to freelymoving charged particles. This substance is defined as theplasma state
Equilibrium plasma (ne = ni = n and Te = Ti = T) Non-equilibrium plasma (ne = ni << n and Te >> Ti )
Non-equilibrium and low temperature plasma can be used forsemiconductor processing, because substrate can be processedat low temperature, while significant amount of radicals and/orhigh energy ions can be obtained
PLASMA PROPERTIES
SNT5039 Nano Processing (Plasma Technology) 4
Log10 Te(V)
HighPressure
arcs
Shocktubes
LaserPlasma
ThetaPinches
Focus
Fusionreactor
Fusionexperiments
LowPressure
GlowDischarges
AlkaliMetal
plasma
Flames
Earth’sIonos-phere
0 1 2 3 4 510-110-2
Log 1
0n
(cm
-3)
5
15
20
10
25
1De cm
34 13 Den cm
Solid Si at room temperature
PLASMA PROPERTIES
SNT5039 Nano Processing (Plasma Technology) 5
(1) Etching (Reactive ion etching)
(2) Photo-resist Stripping (Ashing)
(3) Sputter Deposition
(4) Plasma Enhanced Chemical Vapor Deposition (PECVD)
(6) Surface Modification
Application of Plasmas to Semiconductor Processes
SNT5039 Nano Processing (Plasma Technology) 6
Basic Plasma Equations (Maxwell’s equations)
Equations RelationsGauss’s law for electricity
Net electric flux vs net enclosed electric charge
Gauss’s law for magnetism
Net magnetic flux vs net enclosed magnetic charge
Faraday’s law Induced electric field vs changing magnetic flux
Ampere-Maxwell law
Induced magnetic field vs changing electric flux and current
0
ˆˆqAdE
0ˆˆ AdB
dtdsdE B
ˆˆ
idtdsdB E
000ˆˆ
SNT5039 Nano Processing (Plasma Technology) 7
Basic Plasma Equations (Other equations)
Equations Related equationsConservation(Boltzman Equation)
Particle Conservation
Momentum Conservation
Isothermal relation
Diffusion and mobility
Einstein relation:
Lorentz force law
Elecric and magnetic fields exert forces on charged particles
EnnDJ ˆˆ qkTD
)ˆˆˆ(ˆ BvEqF
LGuntn
)ˆ(0ˆˆ
fafvtf
vr
0ˆˆ umnpEqn m
nkTp
SNT5039 Nano Processing (Plasma Technology) 8
Particle density (using ideal equation)
N is a molar number, N0 is 6x1023mol-1, and R and kB are theBoltzmann constants as R=8.314J/mol K and kB=1.38x10-23J/K.
The gas density (n) in the low pressure processing plasmas of1mTorr to 1Torr is estimated to be in the range of about 3.5x1013 to3.5x1016 cm-3
Rule of thumb on gas densityng (cm-3) = 3.25 x 1013 p (mTorr)
TkP
VNN
nandTkNNNRTPVB
B 00
PLASMA PROPERTIES
SNT5039 Nano Processing (Plasma Technology) 9
Ionization ratio = ni / ng
Plasma density = Particle density x Ionization ratio
Ionization ratio is normally in the range of 10-5 to 10-2 in lowpressure processing plasmas of 1mTorr to 1Torr
The densities of ions (ni) and electrons (ne), sometimes calledplasma density, are typically in the range of 109 to 1012 cm-3
If the plasma density is higher than 1011 cm-3, in themicroelectronics processes we call it “high density plasma”
PLASMA PROPERTIES
SNT5039 Nano Processing (Plasma Technology) 10
Electron and Ion Temperatures
The average energy ischaracterized by thetemperature term (kT) inelectron volt (eV)
The average kinetic energy ofelectrons becomes very high onthe order of 1eV (1-5eV)
The average energy of the ionsis generally close to but slightlyhigher than that of the neutralsin the range of 0.03eV to0.1eV
Q) Compare plasma density and electrontemperature between conventional plasmaand high density plasma
PLASMA PROPERTIES
+
ELECTRONWork Done
Acceleration
Acceleration
ION
Work Done
FtpmeEt
mp
ee
,22
22
ee meE
mF
im
eEt2
2
imeE
E
SNT5039 Nano Processing (Plasma Technology) 11
The average speed of particles in a Maxwell-Boltzmann gas
dnc
ncor
mkTc 18 2/1
sec/107sec/105 52 mxcandmxcc ein
Electrons move much faster and also respond more quickly to an electrical disturbance than ions f = Ee/m, the lighter a particle is, the more it is accelerated and the greater velocity (current) is acquired
PLASMA PROPERTIES
Overall kinetic energy of each gas molecule (root mean square speed)2/1
22 323
21
mkTcandkTcm
SNT5039 Nano Processing (Plasma Technology) 12
Collision Cross Sections N(x): Number of electrons having made no collision, along the path x
N(x+dx) = N(x)(probability that an electron does not collide between x and x+dx)
That is, N(x+dx) = N(x)(1-ndx)
nxNdxxdN )()(
N(x) = N0 exp (- n x)
dxdxdN
Ndxxp
0
1)( Introducing dimensionless parameterp(x)dx as a probability for collision tooccur between x and x + dx )exp()( nxnxp
COLLISIONAL PROCESSES IN PLASMAS
SNT5039 Nano Processing (Plasma Technology) 13
Mean free path
The average distance an electron traveled before collision
0
)( dxxxp
Integrating the above using
1)( n
)exp()( nxnxp
** Estimate mean free path of the electrons in the plasma of 10mtorr that is considered as an ideal gas!! ( = r2 where r is the atomic radius about 0.3nm)
COLLISIONAL PROCESSES IN PLASMAS
SNT5039 Nano Processing (Plasma Technology) 14
Elastic collision
Total kinetic energy of the particles is conserved
Elastic scattering: e + Ar e + Ar
Inelastic collision
Part of the kinetic energy is converted into potential energy
Ionization (conversely, recombination) : e + Ar 2e + Ar+
Excitation (conversely, relaxation) : e + Ar e + Ar*
COLLISIONAL PROCESSES IN PLASMAS
orbit.Bohr first in theelocity electron v theas m/s,2.19x104π
e ve wher
n
v vis velocity Here,
radius)(Bohr m5.29x10me
4πa
),anafor 1(n levellowest For thenmva
momentumangular theof multiples theremomentumsatheir way thatain orbits thelimitsn descriptio quantumA
amv
a4πe
is,That force. lcentrifuga outward theand force ticelectrosta inward thebetween balance by the orbitscircular ain move electons n,descriptio classical aIn
6
0
2
at
atn
112
20
0
02
n
2
20
2
Inelastic Collision
Inelastic Collision
1)n when atom H of potentialn (Ionizatio 13.6V4π
e2emE
nEE and (V),eE(J) WapplyingBy
a4πemv
21W
energy, potential and kinetic theof sum theisenergy electron The
s2.42x10va
w1t
is timescalesticcharacteri The
2
0
2
at
atnnn
n0
22nn
17
at
0at
SNT5039 Nano Processing (Plasma Technology) 17
Scattering cross section
An area that scattering takes placewhen the electron passes through anatom
An effective total cross sectionalarea for scattering between anelectron and an atom, includingcontributions from collisionalprocesses such as elastic scattering,ionization, excitation
The cross section is a strong function of electron energy
COLLISIONAL PROCESSES IN PLASMAS
electrons
atoms
SNT5039 Nano Processing (Plasma Technology) 18
Q) Explain why cross sections decrease with increasing electron energyQ) Explain why threshold energy for excitation is lower than that of ionization
COLLISIONAL PROCESSES IN PLASMAS
1 10 100
(c
m2 )
Electron Energy (eV)
E + Ar
Elastic
Ionization
Excitation
10-15
10-16
10-17
SNT5039 Nano Processing (Plasma Technology) 19
(1) Ion-Atom Collisions with energy exchange: Ar++Ar Ar++Ar or Ar+Ar+
(2) Radiative relaxation: An excited atom returns to the ground state, or to the lower energy-level excited state by emitting a photon:
Ar* Ar + photon In the etching plasma, various radiative relaxation processes occur and
this generates optically visible glow that can be used for monitoring processes
(3) Recombination: e- + Ar+ ArThis process hardly occurs due to energy conservation. But, if the third body participates in the collision, this process can take place in the following ways
e- + Ar++ Ar Ar + Ar ore- + Ar++ wall Ar + Ar
The second process has higher probability and occurs on the reactorwalls. This is the main path the ions are lost in processing plasmas ofsputtering, CVD, and Reactive Ion Etching
COLLISIONAL PROCESSES IN PLASMAS (Collisional Processes Involving Atoms)
SNT5039 Nano Processing (Plasma Technology) 20
Density of various particles in the low pressure processing plasma
SNT5039 Nano Processing (Plasma Technology) 21
PLASMA PROPERTIES
In the low pressure processing plasma, densities ofpositively and negatively charged particles are aboutthe same, but electrons are much more mobile thanpositive ions (ni = ne, ci < ce),resulting in disturbance in charge neutrality (je >> ji)
14
14
e e e
i i i
j en c
j en c
+
+--
+
+--
+
+--
+--
+
+-- 23
4
6.6 1020 293 1/ 404.0 10 / sec
m gT C k eVc cm
Neutrals
23
4
6.6 10500 0.04
5.2 10 / sec
i
i
i
m gT k eVc cm
Ions28
7
9.1 1023200 2
9.5 10 / sec
e
e
e
m gT k eVc cm
Electrons1/ 28( )kTc
m
SNT5039 Nano Processing (Plasma Technology) 22
iiieee cenjcenj41,
41
To maintain the chargeneutrality, electron flux shouldbe equal to ion flux in theplasma, resulting in potentialdifference near the electrode
Plasma potential (Space potential)Potential obtained in the bulk of the plasma when the densities of ionsand electrons are equal, and therefore electric potential is constant.
Floating potentialPotential obtained when satisfying condition that electron flux is equalto ion flux. It is negative with respect to the plasma potential,
PLASMA PROPERTIES
+
+--
+
+--
+-
-
+
+
-
-
4
4
4
e e
i i
n c
nc
n c
SNT5039 Nano Processing (Plasma Technology) 23
ie
eiefp Tm
Tme
kTVV ln
2
• Calculate Vp-Vf for an Ar plasma with electron and ion temperatures of kTe=2eV and kTi=0.1eV !
Sheath (Dark space)- The region that has an excess of ions and,
there charge neutrality does not hold.- The positive space charge shields the
floated body from the bulk of the plasma.- Ions are accelerated towards the
electrode due to the electric field,bombarding the surface.
FORMATION OF SPACE CHARGE REGION
SNT5039 Nano Processing (Plasma Technology) 24
Debye Length:
• A characteristic thickness of the space charge sheath around the grid.
)exp()( 0D
xx
a way to quantify sheath thickness
• Expressed as a function of electron density and electron temperature
FORMATION OF SPACE CHARGE REGION
21
20
enkT
i
eD
SNT5039 Nano Processing (Plasma Technology) 25
Debye length
as a function of electron density and electron temperature
Q) Fill in the Debye length under conditions given in the table.
2/1
20
enkT
i
eD
)( 3cmne )(eVkTe1 3 10
1 x 1010 75mm 130mm
1 x 1011 24mm
1 x 1012
Q) Compare the Debye length between cases of conventional plasma and high density plasma.
FORMATION OF SPACE CHARGE REGION
SNT5039 Nano Processing (Plasma Technology) 26
(1) Two parallel electrodes are grounded at the both ends: V(x) = 0 at x = 0 and x = l.(2) Ion density is constant at ni across the plasma: ni(x) = ni for 0 ≤ x ≤ l. (3) Electron density is 0 across the plasma: ne(x) =0 for 0 ≤ x ≤ l.
(Q1) Using the Poisson equation,
find expressions on the potential V(x), and the electric field, in the plasma.
(Q2) Plot V(x) and E(x) for 0 ≤ x ≤ l.
(Q3) Using the result in Q1, estimate potential at the center, V(x=l/2), assuming that the distance between the parallel electrodes is 10 cm and ion density is 1010 cm-3.
(Q4) According to the electrical measurement results using a Langmuir probe on usual processing plasmas having a reactor size of l ~ 10 cmand an ion density of ni ~ 1010 cm-3, plasma potential is in the range of 10 – 50V. Determine whether the result in Q3 is reasonable or not. If it is unreasonable, explain the reason why the unreasonable result was obtained.
Poisson Equation in Plasmas
02
2 )(
ei nnedxVd
dxdVxE )(
SNT5039 Nano Processing (Plasma Technology) 27
Plasma Technology
1. PLASMA PROPERTIES- PLASMA PROPERTIES- COLLISIONAL PROCESSES IN PLASMAS- FORMATION OF SPACE CHARGE REGION
2. DC AND RF DISCHARGES- DC DISCHARGES AND SPUTTERING- PARALLEL PLATE RF DISCHARGE- MATCHING NETWORK- HIGH DENSITY PLASMAS
3. PLASMA DIAGNOSTICS- OPTICAL EMISSION SPECTROSCOPY- OTHER DIAGNOSTIC TECHNIQUES
SNT5039 Nano Processing (Plasma Technology) 28
The most common reactor geometry in the DC and RF dischargesis a parallel electrode type where the plasma is mostly confinedbetween two planar electrodes
After studying a parallel plate DC discharge which is widely usedfor sputter deposition, we review RF discharges that are used formost of the plasma etching applications as well as PEVCD
In the DC discharges, the voltage applied between the electrodesis constant in time, whereas in the RF discharges the appliedvoltage varies with time.
The time-dependent behavior of an RF discharge needs to bediscussed, although its time-averaged behavior resembles that ofthe DC discharge
PARALLEL PLATE DC DISCHARGES (DC AND RF PLASMAS)
SNT5039 Nano Processing (Plasma Technology) 29
The plasma is generated by
applying a high E to a gas so as to
result in electrical breakdown
Once a steady state is reached,
the externally applied power gives
rise to an electrical current
flowing through the plasma
PARALLEL PLATE DC DISCHARGES (DC PLASMA)
Argon Gas
Target
Substrate
Vacuum Chamber
DCPower Supply
+
_
Argon Gas
Target
Substrate
Vacuum Chamber
DCPower Supply
+
_
SNT5039 Nano Processing (Plasma Technology) 30
Assume that the bulk of the plasma between two electrodes is uniform,
By using the equation about ion flux,
The ion current density at the cathode sheath edge is estimated to be 0.15mA/cm2.
By using to the equation about electron flux,
The thermal electron current density is 28mA/cm2 and it is much larger than 0.15mA/cm2 (je >> ji)
The positive current density at the cathode must be compensated by thenegative current density at the anode. It follows that there must be smallsheath at the anode to reduce the electron current, where the sheathpotential will be equal to the plasma potential, Vp, for grounded anode
eVkTandcmnnn eie 110 3100
2/10 )/( iei mkTenj
2/100 )2/(
41
eee mkTencenj
PARALLEL PLATE DC DISCHARGES
SNT5039 Nano Processing (Plasma Technology) 31
Vtj
dAC o
For continuous plasma, RF frequency higher than about 100kHz is required.
(Ex)-1 mm thick SiO2-1000V DC Bias, 1 mA/cm2 ion current
This requires 130kHz RF for continuous plasma
At low frequency, plasma is short-lived (ON and OFF).
PARALLEL PLATE RF DISCHARGES
SNT5039 Nano Processing (Plasma Technology) 32
RF generator voltage (Va)At low frequency, targetvoltage (Vb) changes withion bombardment andelectron current
>> Steady state with zeronet current
PARALLEL PLATE RF DISCHARGES
SNT5039 Nano Processing (Plasma Technology) 33
Development of Self DC Bias (VDC)PARALLEL PLATE RF DISCHARGES
SNT5039 Nano Processing (Plasma Technology) 34
Development of Self DC Bias (VDC) and Space Charge RegionPARALLEL PLATE RF DISCHARGES
SNT5039 Nano Processing (Plasma Technology) 35
The I-V characteristic of the electrode is determined by the large difference inmobility of electrons and ions
In the negative potential regime, electrons are repelled from but ions areattracted to the electrode, resulting in small net positive current. As the positivepotential increases, electrons become attracted but ions become repelled fromthe electrode, resulting in large net negative current. This is due to high mobilityof the electrons compared to the ions
Apply this to the time-dependent RF discharge where the average currentshould be zero. Net current for one RF cycle becomes largely negative and thismust be corrected for the net current to be zero
If the average value of the RF oscillation is shifted to some negative value, VDC,the net current can be zero. Here, VDC, is called DC self bias, and it has veryimportant implications in determining various characteristics of ion bombardmentin the sputtering and reactive ion etching processes
As a result of negative DC self bias, the sheath of the positive space charge isformed, as we have seen in the DC discharges
PARALLEL PLATE RF DISCHARGES: Development of Self DC Bias (VDC)
SNT5039 Nano Processing (Plasma Technology) 36
MATCHING NETWORK
Purpose of RF matching network
To increase the power dissipation in the discharge and to protect the RF
generator.
(1) Analysis using DC power source
Maximum power is obtained at dP/dR = 0, i.e , R=r.
Therefore, we need to match the resistance of the load to the resistance
of the power supply.
Power dissipated in the variable resistor R,
2
2
)( RrREP
SNT5039 Nano Processing (Plasma Technology) 37
MATCHING NETWORK
(2) Analysis using RF power source• Most common L-type matching network
(shown) consists of a shunt capacitor having susceptance of BM=ωCM and a series inductor having a reactance XM=ωLM.
• Time averaged power flowing into discharge,
22
2
)(~
21
DDT
DT XRR
RVP
0
DXP 0
DRP• Maximum power transferred to the load can be obtained when and .
Therefore, XD=0 , RD=RT and T
T
R
VP
2
max
~
41
• By further circuit analysis, the inductance and capacitance in the matching network for
maximum power transfer can be determined.
SNT5039 Nano Processing (Plasma Technology) 38
Why High Density Plasma?- High utilization of power for high ionization efficiency
(Capacitively coupled plasma (CCP): 1-3%, partially for ionization. Most power is spent in sheaths for CCP, but it is spent in the bulk of the plasma for HDP.)
- Low bias (low damage to devices, high selectivity)- High processing rates (High density of ions and radicals)
High Density Plasma
Table Range of Parameters for Rf Diode and High-Density DischargesParameter Rf Diode High-Density Source
Pressure p(mTorr) 10-1000 0.5-50
Power p (W) 50-2000 100-5000
Frequency f (MHz) 0.05-13.56 0-2450
Volume V (L) 1-10 2-50
Cross-sectional area A (cm2) 300-2000 300-500
Magnetic field B (kG) 0 0-1
Plasma density n (cm-3) 109-1011 1010-1012
Electron temperature Te (V) 1-5 2-7
Ion acceleration energy εi (V) 200-1000 20-500
Fractional ionization Xiz 10-6-10-3 10-4-10-1
SNT5039 Nano Processing (Plasma Technology) 39
How to Generation HDP?- Magnetic enhancement (ME)- Inductive coil- etc
High Density Plasma (Supplementary slide)
B
e
RF power RF power
N NS
Be
E × B
RF power
BERF
RF power
B
MERIE ICPEF = q · r × B E plasma = -dΦB/dt
SNT5039 Nano Processing (Plasma Technology) 40
PARALLEL PLATE RF DISCHARGES (High Density Plasma)
Generation of HDP:
- Magnetic enhancement (ME)- Inductive coil (ICP)- Electron Cyclotron Resonance (ECR)
SNT5039 Nano Processing (Plasma Technology) 41
Faraday’s law:“A changing magnetic field produces an electric field. E = - dFB/dt”In the ICP system, RF power source using coils generates a magnetic field that induces an electric field in the plasma reactor. The efficient power transfer by the inductive coil produces a high density plasma. Schematics on the generation of electric fields from two RF coils are shown below.
Induction of Electric Field in Inductively Coupled Plasma
SNT5039 Nano Processing (Plasma Technology) 42
Density of ICP:
- 1011 to 1012 cm-3,- CCP < ICP < helicon, ECR
In ICP, power is transferred from the electric fields to theplasma electrons within “skin depth” near the surface bycollisional (ohmic) dissipation and by collisionless heatingprocess in which bulk plasma electrons collide with theoscillating inductive electric fields within the layer.
In the collisionless heating process, electrons are acceleratedand subsequently thermalized like the heating process incapacitive RF sheaths.
Inductively Coupled Plasma
SNT5039 Nano Processing (Plasma Technology) 43
(1) In low pressure and high density plasmas, the common feature isthat “RF power is coupled to the plasma across the dielectricwindow or wall” rather than by direct connection to an electrode, asfor the capacitive discharge
(2) That is, non-capacitive power transfer is the key to achieve lowvoltage, normally 20-40V, across the sheath at the dielectric or thewall
(3) To control the ion energy, the substrate can be independently drivenby capacitively coupled RF source. Hence, independent control ofthe ion flux and ion energy is possible
(4) RF coil results inCCP at low plasma density and ICP at high plasma density
Inductively Coupled Plasma
SNT5039 Nano Processing (Plasma Technology) 44
Plasma Technology
1. PLASMA PROPERTIES- PLASMA PROPERTIES- COLLISIONAL PROCESSES IN PLASMAS- FORMATION OF SPACE CHARGE REGION
2. DC AND RF DISCHARGES- DC DISCHARGES AND SPUTTERING- PARALLEL PLATE RF DISCHARGE- MATCHING NETWORK- HIGH DENSITY PLASMAS
3. PLASMA DIAGNOSTICS- OPTICAL EMISSION SPECTROSCOPY- OTHER DIAGNOSTIC TECHNIQUES
SNT5039 Nano Processing (Plasma Technology) 45
Radiative relaxation: An excited atom returns to the ground state, orto the lower energy-level excited state by emitting a photon:
Ar* Ar + photon
* In the etching plasma, various radiative relaxation processesoccur and this generates an optically visible glow that can be usedfor plasma monitoring and end point detection.
OPTICAL EMISSION SPECTROSCOPY (OES)
SNT5039 Nano Processing (Plasma Technology) 46
An excited atom returns to the ground state, or to the lower energy-levelexcited state by emitting a photon: Ar* Ar + photon (Optical Emission)* In the etching plasma, various radiative relaxation processes occur and thisgenerates optically visible glow that can be used for monitoring processes
OXYGEN NITROGEN CHLORINE0
20
40
60
80
100 4p' 2F
4s' 2D2p2 3s 4P
2p2 3p 4Do
3s 3S
3p 3p
3p5 2Po2p3 4So
904nm869nm845nm
210nm211nm
ENER
GY
(cm
-1)
226nm
2p 3p
OPTICAL EMISSION SPECTROSCOPY (OES)
SNT5039 Nano Processing (Plasma Technology) 47
1. Detection of plasma species- used to estimate etching rate and determine the amount of over etching
2. Endpoint detection- the shape of optical emission curve can be used to detect endpoint
OPTICAL EMISSION SPECTROSCOPY (OES)
200 300 400 500 600 700 8000
2000
4000
6000
8000
10000
12000
SiGe etching by products
Si264.5nm
Inte
nsity
Wavelength (nm)
Ge264.5nm
0 20 40 60 80 100 1200
500
1000
1500
2000
2500
3000
Inte
nsity
Time (s)
HBr Main Etching
Substrateetching
HfO2
Si etchingbyproducts: 405 nm
Cl2breakthrough
Si-substrate
HfO2
Poly Si
Mask
SNT5039 Nano Processing (Plasma Technology) 48
For determination of ion density (ni) and electron temperature (Te)
OTHER PLASMA DIAGNOSTICSELECTRICAL PROBES (LANGMUIR PROBES)
SNT5039 Nano Processing (Plasma Technology) 49
e
ppreeee kT
VVemkTAenI
)(exp)2/( 2/1
iieii imkTAenI 2/1)2/( 2/1)
)((15.1
e
ppri kT
VVei
OTHER PLASMA DIAGNOSTICS (LANGMUIR PROBES)
SNT5039 Nano Processing (Plasma Technology) 50
OTHER PLASMA DIAGNOSTICS (LANGMUIR PROBES)
SNT5039 Nano Processing (Plasma Technology) 51
OTHER PLASMA DIAGNOSTICS Mass Spectroscopy
SNT5039 Nano Processing (Plasma Technology) 52
(1) The species in the ionizer should represent the species in the plasmas orspecies near the substrate wafer. Ionization rates can be much different in QMSdue to pressure difference from plasma
(2) Ambiguous identification, for example, both N2 and CO have m=28amu.(3) QMS is more useful for qualitative analysis than for quantitative analysis.
OTHER PLASMA DIAGNOSTICS :Mass Spectroscopy