Post on 31-Dec-2015
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SEALING OF POROUS LOW-k DIELECTRIC WITH H2/He PLASMA
CLEANING
Juline Shoeba) and Mark J. Kushnerb)
a) Department of Electrical and Computer EngineeringIowa State University, Ames, IA 50011
jshoeb@eecs.umich.edu
b) Department of Electrical Engineering and Computer ScienceUniversity of Michigan Ann Arbor, Ann Arbor, MI 48109
mjkush@umich.edu
http://uigelz.eecs.umich.edu
June 2010
*Work supported by Semiconductor Research Corporation ICOPS10_01
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
Concluding Remarks
AGENDA
University of MichiganInstitute for Plasma Science & Engr.ICOPS10_02
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.
Inter-connected pores open to plasma may degrade k-value by reactions with plasma species.
Desire to seal pores.
Ref: http://www.necel.com/process/en/images/porous_low-k_e.gif
University of MichiganInstitute for Plasma Science & Engr.ICOPS10_03
PORE PLASMA SEALING MECHANISM
Investigated 2-step process:
He/H2 plasma
He+ and photons break Si-O bonds
Hot H, He+ remove H from pore lining CHn groups, thereby activating sites.
Hot H strips off photo-resist.
Ref: A. M. Urbanowicz, M. R. Baklanov, J. Heijlen, Y. Travaly, and A. Cockburn, Electrochem. Solid-State Lett. 10, G76 (2007).
Plasma Treatment
Time (s)
Function
He/H2 610 Polymer Clean, PR
Strip, Surface Activation
Ar/NH3 35
( Post-He/H2)
Sealing
NH3 plasma: Seals pores by forming C-N and Si-N bonds which bridges opening.
Reaction mechanisms and scaling laws for He/H2 and NH3 plasma sealing of porous SiCOH have been developed based on results from a computational investigation.
University of MichiganInstitute for Plasma Science & Engr.ICOPS10_04
MODELING : LOW-k PORE SEALING
Hybrid Plasma Equipment Model (HPEM)
Plasma Chemistry Monte Carlo Module (PCMCM)
Monte Carlo Feature Profile Model (MCFPM)
Energy and angular
distributions for ions and
neutrals
He/H2 PLASMA
Porous Low-k
Coils
WaferSubstrate
Metal
Plasma
Ar/NH3 PLASMAS
University of MichiganInstitute for Plasma Science & Engr.ICOPS10_05
MONTE CARLO FEATURE PROFILE MODEL (MCFPM)
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 ).
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.
PCMCM
Energy and angular distributions for ions
and neutrals
HPEM
MCFPM
Provides etch rateAnd predicts etch
profile
University of MichiganInstitute for Plasma Science & Engr.ICOPS10_06
80 nm thick porous SiCOH.
CH3 lines pores with Si-C bonding.
Ave pore radius: 0.8-1.1 nm
Process integration steps:
1. Ar/C4F8/O2 CCP: Etch 10:1 Trench
2. He/H2 ICP: Remove CFx polymer, PR; activate surface sites.
3. NH3 ICP: Seal Pores
INITIAL LOW-kPROCESS INTEGRATION
University of MichiganInstitute for Plasma Science & Engr.
ICOPS10_07
Hard Mask
Si
Porous Low-kSiCOH
SiOCH ETCHING IN Ar/C4F8/O2 PLASMAS
SiO2 Etching M+ + SiO2(s) SiO2*(s) + M
CxFy + SiO2*(s) SiO2CxFy(s)
M+ + SiO2CxFy(s) SiFm + COn + M
CHn Group Etching M+ + CHn(s) CHn-1(s) + H + M
O + CHn(s) CO + Hn
Polymer Deposition M+ + SiO2CxFy(s) SiO2CxFy*(s) + M
CxFy + SiO2CxFy*(s) SiO2CxFy(s) + POLY(s)
CxFy + CHn-1 CHn-1(s) + CxFy(s)
M+ + CxFy(s) CxFy*(s) + M
CxFy* + CxFy (g) CxFy(s) + POLY(s)
University of MichiganInstitute for Plasma Science & Engr.ICOPS10_08
He/H2 PLASMAS: POLYMER/PR ASHING AND SURFACE ACTIVATION
Polymer Removal M+ + POLY(s) CF2 + M
H** + POLY(s) CHF2
H** + POLY(s) CF + HF
H2** + POLY(s) CH2F2
PR Etching M+ + PR(s) PR + M
H** + PR(s) CH4
H2** + PR(s) CH4
SiO2/CHn Activation M+ + CHn(s) CHn-1(s) + H + M
H** + CHn(s) CHn-1(s) + H2
M+ + SiO2(s) SiO(s) + O(s) + M
hν + SiO2(s) SiO(s) + O(s)University of MichiganInstitute for Plasma Science & Engr.ICOPS10_09 **Translationally hot
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 M+ + SiO2(s) SiO(s) + O(s) + M
M+ + SiO(s) Si(s) + O(s) + M
N/NHx Adsorption NHx + SiOn(s) SiOnNHx(s)
NHx + Si(s) SiNHx(s)
NHx + CHn-1 (s) CHn-1NHx(s)
NHx + P*(s) P(s) + NHx(s)
SiNHx-NHy/CNHx-NHy compounds seal the pores where end N are bonded to Si or C by Si-C/Si-N
NHy + SiNHx(s) SiNHx-NHy(s)
NHy + CHn-1NHx(s) CHn-1NHx-NHy(s)University of Michigan
Institute for Plasma Science & Engr.ICOPS10_10
PORE-SEALING BY SUCCESSIVE He/H2 AND NH3/Ar TREATMENT
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-C bonds.
Initial Surface Pores
University of MichiganInstitute for Plasma Science & Engr.
Animation Slide-GIF
He/H2 Plasma Site Activation
Ar/NH3 Plasma Pore Sealing
ICOPS10_11
TYPICAL PLASMA PROPERTIES: H2/He ICP Total ion density (cm-3):
1.50 x 1011
Neutral densities (cm-3): H
9.0 x 1012 H2 7.0 x 1013 H2(v=1) 3.0 x 1011 H2(v=2) 3.0 x 1011
H2(v=3) 3.0 x 1011 H2(v=4)
3.0 x 1011 H2(v=5) 3.0 x 1011
Major fluxes to the substrate (cm-2 s-1): H
6.0 x 1017
H2 3.0 x 1018
H2(v=1) 2.0 x 1016 H2(v=2)
2.0 x 1016 H2(v=2) 2.0 x 1016 H+
2.0 x 1015
H2+
8.0 x 1013
Conditions: H2/He = 25/75, 10 mTorr, 300 W ICP
University of MichiganInstitute for Plasma Science & Engr.
ICOPS10_12
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** + H3
+
H + H2+ H2(v=0)** + H+
H2(v=n) + H+ H** + H2+
H + H+ H** + H+
Conditions: H2/He = 25/75, 10 mTorr, 300 W ICP
University of MichiganInstitute for Plasma Science & Engr.ICOPS10_13
**Translationally hot
CCP for trench etch.
Ar/C4F8/O2 = 80/15/5 40 mTorr, 300 sccm 10 MHz 5 kW
CFx polymer deposited on the side-walls efficiently seal the open pores. CFx polymers are harmful to diffusion barrier metals such as Ti and Ta.
Polymer layers can be removed by one of the following:
He/H2 plasmas without surface damage.
O2 plasmas that etch the CH3 groups.
Ar/C4F8/O2 CCP TRENCH ETCH
Animation Slide-GIF
University of MichiganInstitute for Plasma Science & Engr.
ICOPS10_14
Photo-Resist
Si
Porous Low-kSiCOH
POLYMER REMOVAL AND PR STRIPPING
He/H2 plasma used for both polymer (P) removal and photoresist (PR) stripping.
Hot H, H2, H+ and H2+ remove polymers and
masking PR layers as CH4, HF, and CxHyFz
H** + POLY(s) CF + HF
H** + POLY(s) CHF2
H2** + POLY(s) CH2F2
H** + PR(s) CH4
H2** + PR(s) CH4.
CHn groups are also activated by H removal
H** + CHn(s) CHn-1 + H2.
University of MichiganInstitute for Plasma Science & Engr.
Animation Slide-GIF
Si
ICOPS10_15
PR
Porous Low-kSiCOH
**Translationally hot
POLYMER REMOVAL, CH3 DEPLETION
Ar/O2 plasma efficiently removes polymer.
Also removes CH3 groups in pores as O atoms diffuse into the porous network.
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.
University of MichiganInstitute for Plasma Science & Engr.
Si
ICOPS10_16
Low-kSiCOH
SEALING: WITH POLYMER REMOVAL AND PR STRIP
Ar/O2 Clean: additional He treatment is required for surface activation, followed by NH3 plasma sealing.
He/H2 Clean: can do both activation and cleaning in a single step.
Successive NH3 plasma exposure seals the surface pores forming Si-N and C-N bonds.
University of MichiganInstitute for Plasma Science & Engr.
Si
Animation Slide-GIFICOPS10_17
He/H2 Activation
Sealing
He/H2
ActivationSealing
Si
SEALING EFFICIENCY: PORE RADIUS Ar/O2 Clean: sealing efficiency
decreases with increasing pore size.
H2/He Clean: selective cleaning does not enlarge openings. Broad angular distribution of H improves surface activation and sealing.
University of MichiganInstitute for Plasma Science & Engr.
ICOPS10_18
PoorSealing
GoodSealing
He/H2
Clean
Ar/O2
Clean
Animation Slide-GIF
SEALING EFFICIENCY: ASPECT RATIO
University of MichiganInstitute for Plasma Science & Engr.
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.
ICOPS10_19
CONCLUDING REMARKS
Integrated porous low-k material sealing was computationally 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.
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.
University of MichiganInstitute for Plasma Science & Engr.ICOPS10_20