SEALING OF POROUS LOW- k DIELECTRIC WITH H 2 /He PLASMA CLEANING

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

[email protected]

b) Department of Electrical Engineering and Computer ScienceUniversity of Michigan Ann Arbor, Ann Arbor, MI 48109

[email protected]

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


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.


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


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


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)


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


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


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


**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


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.


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.


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.


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.


ICOPS10_18

PoorSealing

GoodSealing

He/H2

Clean

Ar/O2

Clean

Animation Slide-GIF

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.

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.


SEALING OF POROUS LOW- k DIELECTRIC WITH H 2 /He PLASMA CLEANING

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