Depositing and Patterning a Robust and Dense Low-k Polymer by icvd

Transcription

1 SRC/SEMATECH ERC for Environmentally Benign Semiconductor Manufacturing Depositing and Patterning a Robust and Dense Low-k Polymer by icvd December 11, 2008 Nathan J. Trujillo Karen K. Gleason

2 Anatomy of an integrated circuit Low-k Dielectric (ILD) Cu Interconnects Increasing ILD feature size Features are getting closer together! 2

3 Why low-k? Metal Dielectric L m A W m A cs REDUCE: T m T d RC Delay τ~ RC ~κε 0 ρl m 2 /T m T d either metal or dielectric Power Consumption P~ CV 2 f Cross Talk Noise N ~ C line-to-line /C total } dielectric only 3

4 Acquired electric dipole moment per unit volume: Polarization electronic polarization (induced dipole moment) P = Zqd P = polarization Z = number of charge centers per unit volume q = electronic charge } d = displacement qd = induced dipole moment relationship of dielectric constant & polarization k = 1+4πP/E 4

5 k: How low can you go? Composition Fully dense k SiO Si:O:F (FSG) Air k =1.0 Si:O:C:H (OSG) C:F

6 Air to get us there Although k scales with porosity, mechanical properties of porous low-k typically scale as (1-P) 3 Advantageous to start from a dense film with a lower k Refractive Index Our Starting Point! Dielectric Constant Annealing Temperature ( C) Annealing Temperature ( C) D.D. Burkey, K.K. Gleason, J. Vac. Sci. Technol. A, (2004) 22 (1) 6

7 Need for environmentally friendly low-k To Summarize: Need k = 2.1 by 2012 and 90% raw chemical utilization by 2011! 7

8 Attractive ILDs have Electrical Chemical low κ low dissipation low leakage low charge trap high breakdown high resistivity Mechanical film uniformity adhesion low stress high tensile modulus low shrinkage high hardness elasticity Environmentally Friendly Processing low moisture absorption high etch selectivity high chemical resistance high purity no metal corrosion low gas permeability Thermal high thermal stability high glass transition high thermal conductivity low thermal shrinkage low thermal expansion 8

9 icvd Process chemistry preserves functionality T filament = 250ºC I+M Initiator 2I*+M tert-butyl peroxide Thermally Labile Initiator Distribution Baffle Hot Filament Array Proposed Polymerization Mechanisms icvd (novel low energy process) Exhaust to Pump Heated Monomer PECVD (conventional process) Chilled Substrate 9

10 Low-k icvd precursor: V4D4 Free volume of siloxane ring for low-k Commercial PECVD Precursors for Low-k Chemical structure analogous to commercially used low k organosilicate glass (OSG) precursors such as TOMCATS Four vinyl groups make ideal for free radical polymerization via icvd Vinyl Group for icvd No need for cross linker 3-D network from puckered ring 1,3,5,7-TETRAVINYLTETRAMETHYLCYCLOTETRASILOXANE Novel icvd Precursor 10

11 Si-O-Si region deconvolution Network Suboxide Cage Increasing T anneal from 50 C to 500 C Wavenumber (cm-1) 11

12 Annealing increases cage-like structure Dielectric Constant FTIR Si-O cage/total Si-O *Plasma Deposited DMCPSO with Cyclohexane porogen Annealing Temperature (C) Open structure analogous to MSQ Increasing cage structures associated with decreasing k As-deposited structure primarily dominated by ring structure. S. Lee et al. Jpn. J. Appl. Phys., Vol. 46, No. 2 (2007) icvd p(v4d4) 12

13 Reduced film density with anneal Refractive Index icvd Deposited pv4d4 with no porogen *Plasma Deposited pv3d3 with pmma porogen k = 2.3 Dielectric Constant Annealing Temperature (C) Refractive Index *D.D. Burkey, K.K. Gleason, J. Vac. Sci. Technol. A, (2004) 22 (1) A. Grill, J. Appl. Phys., Vol. 93, No. 3, 1 February 2003 icvd p(v4d4) 13

14 Increased crosslinking with CH3 removal O O Si O O Q Group Fully Networked CN = 2.67 O Si O C O T Group Crosslinking CN = 2.4 C O Si C D Group Chain Propagating CN = 2.0 O Increasing T anneal from 50 C to 500 C Wavenumber (cm -1 )

15 Remaining methyl groups indicate an open film structure Dielectric Constant FTIR Si-CH 3 /Si-O Area *Plasma Deposited pomcts with CHx porogen Loss of CH3 improves mechanical properties, yet sufficient groups remain to help keep k low Annealing Temperature (C) 0.02 S.M. Gates, A. Grill et al. J. Appl. Phys. 101, icvd p(v4d4) 15

16 High connectivity at higher temperatures 2.55 Connectivity Number A. Ross, K.K. Gleason, J. Appl. Phys. 97, (2005) icvd p(v4d4) Annealing Temperature (C) Percolation threshold at CN = 2.4. Above threshold, film is amorphous and rigid! 16

17 Mechanical enhancement Enhanced mechanical properties 200 C suggests bond rearrangement Greater than 0.5 GPa hardness above percolation threshold Hardest film associated with lowest dielectric constant. No trade-off between k and H. Hardness (GPa) k = 2.7 k = 2.15 Burkey(2004):H 0.54GPa, M 3.5 GPa, k 2.4 Grill (2003):H 0.21GPa, M 3.3 GPa, k Annealing Temperature (C) Modulus (GPa) icvd p(v4d4) 17

18 Atomic composition by X-ray Photoelectron Spectroscopy (XPS) Oxygen Silicon Carbon Ratio C:O Anneal Temperature ( C) Ratio C:Si As Dep 100ºC 200ºC 300ºC 400ºC 500ºC Constant composition 200 C suggests bond rearrangement Increased Q groups from oxygen injection at high temperatures responsible for improved H and M Between 200 C to 400 C, constant Si:O with decreased Si:C indicates Si-Si bond formation Ratio O:Si Anneal Temperature ( C) Anneal Temperature ( C) 18

19 Thermo Gravimetric Analysis (TGA): decomposition and reaction in several stages 100 % Mass Remaining V4D4 annealed in dry air V4D4 annealed in helium Anneal Temperature ( C) Staged decomposition, compared to porous-msq Enhanced reactivity in air, not just thermal dissociation Stable mass retention is larger, suggests oxygen incorporation Spin-On MSQ precursor with 38% porogen loading A. Zenasni et al. Thin Solid Films 516 (2008)

20 Several chemistries indicated by Residual Gas Analyzer (RGA) 0.35 Major decomposition events occur at lower temperatures for films annealed in air Over 60 potential species tracked by TGA/RGA system % Mass/ C V4D4 annealed in dry air V4D4 annealed in helium No water detected in asdeposited film Most species evolve during first two events. The third event mainly represents -CH3 decomposition Log( Ion Current (A)) 1.00E E E E Anneal Temperature ( C) Corresponding Anneal Temperature 120 C 475 C 200 C Mass 39 Mass 73 Mass 30 Mass 18 Mass 91 Mass 44 Mass 56 Mass 27 Mass 26 Mass 15 Mass E Time (minutes) 20

21 Reduced polarizability results in lower k 3.6 Dielectric Constant Anneal Temperature ( C) C=O, High Electronic Polarizability T anneal = 300 C T anneal = 400 C T anneal = AD, 100 C, 200 C, 500 C Wavenumber (cm -1 )

22 Curing behavior for annealed films Annealed films would be most attractive for application In subsequent thermal cycles, annealed films, > 400 C, stable thickness within 1% No water uptake in cured film, as evidenced by FTIR Film loss in curing process comparable to literature %Shrinkage k = 2.05 k = 2.16 k = Annealing Temperature (C) S. Lee et al. Jpn. J. Appl. Phys., Vol. 46, No. 2 (2007) S.M. Gates, A. Grill et al. J. Appl. Phys. 101, *D.D. Burkey, K.K. Gleason, J. Vac. Sci. Technol. A, (2004) 22 (1) icvd p(v4d4) 22

23 Additive polymer patterning using self-assembled mask (no traditional lithography) Non-Conventional lithography offers: Cost-saving alternative to conventional photolithography. No need for expensive steppers Solvent Substitution IPA vs. TMAH Non-hazardous Hazardous Biodegradable Toxic Non-toxic Colloidal SAM monolayer (a) (b) (c) Si Si (d) Grafted icvd Polymer Si Patterned/Grafted icvd Polymer Si 23

24 Low-k icvd p(v4d4) Patterns: 25 nm features & no traditional lithography a 1 µm Template 200 nm Template 25 nm Template b c 2 µm 75 nm 25 nm 1900 (i) (j) 1600 V4D * * * Utility: Low dielectric constant Decreasing monomer polymer for integrated circuits Template Diameter * polymer Si O O Si Si O O Si k ~ 2.7 T g = > 400ºC Eliminates need for etching of low-k, a problematic step wavenumber (cm -1 )

25 Multi-scale patterned low-k by template assisted assembly Top Down helps bottom-up : Capillary Force Lithography Template (a) (b) T,P (c) PDMS Mold PS Melt Substrate Solidify Polymer, Remove Mold Deposit Colloidal SAM a b (Side View) (TopView) Multi-scale low-k features that are spatially addressable. No Conventional Lithography! 25 µm 25 µm c d 25 µm 1 µm 25

26 In summary icvd is a low-energy process for depositing a novel low-k precursor V4D4 The high degree of organic content in the as-deposited films affords the ability to systematically tune the film properties by annealing. The incorporation of atmospheric oxygen, at high temperatures, enhances the mechanical and electrical properties of the films. These dense annealed films provide favorable mechanical and electrical properties for incorporating thermally sensitive porogen molecules Multi-scale features were patterned for the dielectric constant polymer, down to 25 nm, without the need for environmentally harmful solvents or expensive lithography tools 26