JULINE_AVS10_V03 - Mark Kushner Group
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Transcript JULINE_AVS10_V03 - Mark Kushner Group
REACTION MECHANISM AND PROFILE
EVOLUTION FOR CLEANING AND SEALING
POROUS LOW-k DIELECTRICS USING He/H2 AND
Ar/NH3 PLASMAS
Juline Shoeba) and Mark J. Kushnerb)
a)
b)
Department of Electrical and Computer Engineering
Iowa State University, Ames, IA 50011
[email protected]
Department of Electrical Engineering and Computer Science
University of Michigan Ann Arbor, Ann Arbor, MI 48109
[email protected]
http://uigelz.eecs.umich.edu
October 2010
AVS10_01
*Work supported by Semiconductor Research Corporation
AGENDA
Sealing of Low-k Dielectrics
Modeling Platforms
Generation of Hot H
Polymer Removal and PR Stripping In He/H2 Mixtures
Sealing Mechanism Using Ar/NH3 Plasma Treatment
Sealing Efficiency
Pore Radius and Aspect Ratio
Pulsing Effect On Etch Rate
AVS10_02
University of Michigan
Institute for Plasma Science & Engr.
POROUS LOW-k DIELECTRICS
The capacitance of the
insulator contributes to RC
delays in interconnect
wiring.
Low-k porous oxides, such
as C doped SiO2 (CHn lining
pores) reduce the RC delay.
Porosity 0.5,
Interconnectivity 0.5.
Ref: http://www.necel.com/process/en/images/porous_low-k_e.gif
Inter-connected pores open
to plasma may degrade kvalue by reactions with
plasma species.
Desire to seal pores to
prevent diffusion into
porous network.
AVS10_03
University of Michigan
Institute for Plasma Science & Engr.
LOW-k
PROCESS INTEGRATION
Typical porous SiO2 has CH3
lineing pores with Si-C bonding –
referred to as SiOCH.
Ave pore radius: 0.8-1.1 nm
Mask
Porosity: up to 50%
Etching and sealing SiOCH is an
integrated, multistep process
Porous
Low-k
SiCOH
Si
AVS10_04
Etch
Ar/C4F8/O2 CCP
Clean
Activate
Ar/O2 or He/H2 ICP
He/H2 ICP
Seal
Ar/NH3 ICP
University of Michigan
Institute for Plasma Science & Engr.
PORE SEALING
PROCESS INTEGRATION
Step 1: Ar/C4F8/O2 CCP
Etch trench leaving PR
mask and CFn polymer
Step 2: Ar/O2 ICP
Remove PR and CFn
polymer with O radicals
O atoms diffuse into
pore network to etch
CH3 groups.
Degrades low-k
material.
AVS10_05
University of Michigan
Institute for Plasma Science & Engr.
PORE PLASMA
SEALING MECHANISM
Step 3: He ICP
Activate surface by
sputtering and photodetachment to create
dangling bonds.
Step 4: Ar/NH3 ICP
Seal pores with NHn
radicals by forming C-N
and Si-N bonds which
bridges opening.
AVS10_06
University of Michigan
Institute for Plasma Science & Engr.
He/H2 CLEAN-ACTIVATE
Highly motivated to eliminate
Ar/O2 step as degradation of
SiOCH occurs.
Possible alternative is He/H2
ICP plasma cleaning.
Hot H atoms (> 1 eV) are
produced by dissociative
excitation and charge
exchange.
e H2 H H * e
H * Si : CFn Si HF, CHFn , H * Si CH3 Si CH n Hn
H* remove PR and CFn while activating surface sites.
Low mass of H reduces likelihood for sputter of CHn.
Must optimize H* production
AVS10_07
University of Michigan
Institute for Plasma Science & Engr.
MODELING : LOW-k PORE SEALING
He/H2
PLASMA
Coils
Plasma
Metal
Wafer
Porous Low-k
Substrate
Hybrid Plasma
Equipment Model
(HPEM)
AVS10_08
Energy and
angular
distributions
for ions and
neutrals
Ar/NH3
PLASMAS
Plasma Chemistry
Monte Carlo Module
(PCMCM)
Monte Carlo
Feature Profile
Model (MCFPM)
University of Michigan
Institute for Plasma Science & Engr.
MONTE CARLO FEATURE PROFILE MODEL (MCFPM)
HPEM
PCMCM
Energy and angular
distributions for ions
and neutrals
MCFPM
Provides etch rate
And predicts etch
profile
AVS10_09
The MCFPM resolves the surface
topology on a 2D Cartesian mesh to
predict etch profiles.
Each cell in the mesh has a material
identity. (Cells are 4 x 4 A ).
Gas phase species are represented by
Monte Carlo pseuodoparticles.
Pseuodoparticles are launched towards
the wafer with energies and angles
sampled from the distributions obtained
from the PCMCM.
Cells identities changed, removed, added
for reactions, etching, and deposition.
University of Michigan
Institute for Plasma Science & Engr.
TYPICAL PLASMA PROPERTIES: H2/He ICP
Total ion density (cm-3):
1.5 x 1011
Neutral densities (cm-3):
H
H2
H2(v=1,5)
9 x 1012
7 x 1013
1.5 x 1012
Major fluxes to the
substrate (cm-2 s-1):
H
H2
H2(v=1,3)
H+
AVS10_10
6 x 1017
3 x 1018
6 x 1016
2 x 1015
Conditions: H2/He = 25/75,
10 mTorr, 300 W ICP
University of Michigan
Institute for Plasma Science & Engr.
Ar/C4F8/O2 CCP TRENCH ETCH
Photo-Resist
CCP for trench etch.
Ar/C4F8/O2 = 80/15/5
40 mTorr, 300 sccm
10 MHz
5 kW
CFx polymer deposited on the sidewalls efficiently seal the open
pores. CFx polymers are harmful to
diffusion barrier metals such as Ti
and Ta.
Porous
Low-k
SiCOH
Polymer layers can be removed by:
He/H2 plasmas without surface
damage.
O2 plasmas that etch the CH3
groups.
AVS10_11
Animation Slide-GIF
Si
University of Michigan
Institute for Plasma Science & Engr.
HOT H GENERATION: He/H2 ICP
Vibrational Excitation
e + H2(v=0) H2(v=1)
+e
e + H2(v=n) H2(v=n+1) + e
Hot H Generation
e + H2(v=n) H** + H** + e
Charge Exchange Reactions
H2(v=n) + H2+ H2(v=n)** + H2+
H2(v=n) + H2+ H**
H
+ H2+ H2(v=0)** + H+
H2(v=n) + H+ H**
H
AVS10_12
+ H 3+
+ H+ H**
**Translationally
+ H 2+
+ H+
hot
Conditions: H2/He =
25/75, 10 mTorr, 300 W
ICP
University of Michigan
Institute for Plasma Science & Engr.
POLYMER REMOVAL AND PR STRIPPING
He/H2 plasma used for both polymer (P)
removal and photoresist (PR) stripping.
PR
Hot H, H2, H+ and H2+ remove polymer
and masking PR layers as CH4, HF, and
CxHyFz
H** + P(s)
CF + HF
H** + P(s)
CHF2
H2** + P(s)
CH2F2
Porous
Low-k
SiCOH
H** + PR(s) CH4
H2** + PR(s) CH4.
CHn groups are also activated by H
removal
Si
H** + CHn(s) CHn-1 + H2.
Animation Slide-GIF
AVS10_13
**Translationally
hot
University of Michigan
Institute for Plasma Science & Engr.
POLYMER REMOVAL, CH3 DEPLETION
Ar/O2 plasma efficiently
removes polymer.
Also removes CH3 groups
in pores as O atoms
diffuse into the porous
network.
Low-k
SiCOH
Net result is increase in
pore size.
Pore openings can get too
large to easily seal.
He/H2 plasma removes
polymer without
significantly depleting
CH3.
AVS10_14
Si
University of Michigan
Institute for Plasma Science & Engr.
SEALING MECHANISM IN Ar/NH3 PLASMA
N/NHx species are adsorbed by activated sites forming Si-N and C-N
bonds to seal pores.
Further Bond Breaking
N/NHx Adsorption
M+ + SiO2(s)
SiO(s) + O(s) + M
M+ + SiO(s)
Si(s)
NHx + SiOn(s)
SiOnNHx(s)
NHx + Si(s)
SiNHx(s)
NHx + CHn-1 (s)
CHn-1NHx(s)
NHx + P*(s)
P(s) + NHx(s)
+ O(s) + M
SiNHx-NHy/CNHx-NHy compounds seal the pores where end N are
bonded to Si or C by C-N/Si-N
NHy + SiNHx(s)
SiNHx-NHy(s)
NHy + CHn-1NHx(s) CHn-1NHx-NHy(s)
AVS10_15
University of Michigan
Institute for Plasma Science & Engr.
PORE-SEALING BY SUCCESSIVE He/H2 AND NH3/Ar
TREATMENT
·Initial Surface Pores
·He/H2 Plasma
Site Activation
·Ar/NH3 Plasma
Pore Sealing
Surface pore sites are activated by 610s He/H2 plasma treatment.
Ar/NH3 plasma treatment seals the pores by forming bridging Si-N,
N-N and Si-N bonds.
Animation Slide-GIF
AVS10_16
University of Michigan
Institute for Plasma Science & Engr.
SEALING: WITH POLYMER REMOVAL AND PR STRIP
He/H2 Activation
Sealing
Ar/O2 Clean: additional
He treatment is
required for surface
activation, followed by
NH3 plasma sealing.
He/H2 Clean: Performs
both activation and
cleaning in a single
step. Can seal with NH3
just after the clean.
He/H2
Activation
Si
AVS10_17
Animation Slide-GIF
Sealing
Si
University of Michigan
Institute for Plasma Science & Engr.
SEALING EFFICIENCY: PORE RADIUS
Ar/O2 Clean: Sealing efficiency
decreases with increasing pore
size.
Ar/O2
Clean
He/H2
Clean
H2/He Clean: Sealing is less
sensitive to pore radius.
Good
Sealing
Poor
Sealing
Animation Slide-GIF
AVS10_18
University of Michigan
Institute for Plasma Science & Engr.
SEALING EFFICIENCY: ASPECT RATIO
O2 Clean: sealing
efficiency on
sidewalls decreases
with increasing
aspect ratio.
He/H2 Clean: sealing
does not degrade with
higher aspect ratio.
Hot H activates all of
the surface sites due
to its broad angular
distribution.
AVS10_19
University of Michigan
Institute for Plasma Science & Engr.
PULSING EFFECT ON PR REMOVAL: He/H2 ICP
PR
SiCOH
Duty cycle reduction increases ion to
neutral flux ratios.
AVS10_20
Conditions: H2/He = 25/75, A low duty cycle can increase PR
removal rate.
10mTorr, 300 W ICP
CONCLUDING REMARKS
Integrated porous low-k material sealing was investigated
Ar/C4F8/O2 Etch
H2/He Clean, PR Strip, and Surface Activation
Ar/NH3 Sealing
He/H2 plasmas clean polymer, strips off PR and activates
surface sites in a single step. Higher activation and lower
damage seal the surface better.
Pulsing can enhance the PR removal rate.
Si-N and C-N bonds formed by adsorption on active sites
followed by one N-N bond linking C or Si atoms from opposite
pore walls.
For Ar/O2 clean, sealing efficiency degrades when pore radius
is >1 nm and aspect ratio >10. He/H2 clean enables sealing of
larger pores and higher aspect ratio trenches.
AVS10_21
University of Michigan
Institute for Plasma Science & Engr.