Plasma-Surface Interactions in Patterning High-k k Dielectric Materials

Transcription

1 Plasma-Surface Interactions in Patterning High-k k Dielectric Materials October 11, 4 Feature Level Compensation and Control Seminar Jane P. Chang Department of Chemical Engineering University of California, Los Angeles, CA 995

2 Scaling of the Gate Dielectrics S V G Gate High-k Dielectrics n L n eff p-si D V D I D Gate Electrode (Metal/Poly) Upper Interface Gate Dielectric Lower Interface Channel Layer Si sat I D W (V = µc G -V T ) inv L eff C = κ ε o A t High-k material is needed!! (Or an alternative transistor design) But, what else is going on??

3 Integration Challenges S V G Poly MO n n p-si g m = 1 R g s mo D g g V D mo Low transconductance: S Interfacial layer causes source and drain resistances: A of ZrSiO 4 (Resistivity of zirconium oxide is µω-cm) Plasma etching is needed to pattern high-k materials I D do ( R R ) s d Mobility (cm /V-s) Universal curve 1 3 E (MV/cm)

4 Roadmap for Etching First Year of IC Production High density plasma ECR ICP Helicon New Material Main Etch High k dielectrics К ~ 5-1 К ~ 1 - К > International Technology Roadmap for Semiconductors (1) Reasons and challenges for high-κ dielectric materials: Etchable

5 Plasma Etching of ZrO and HfO Plasma Cl e Cl e Cl e Cl e MCl 4 e MCl Cl e E bulk plasma e - e- e- e- e - e - e _ Cl Cl Cl MCl x sheath ClO mask MCl 4 Surface reactions lead to directional profile and low substrate damage Ion MO 6Cl MCl ClO 4 Silicon MO

6 Plasma Diagnostics Quadruple Mass Spectroscopy (QMS) Quartz Bell Jar Microwave ECR Source Optical Emission Spectroscopy (OES) Langmuir Probe Cl QMS Intensity QMS Intensity Cl Cl ZrCl 3 x 1 4 HfCl 3 ZrCl 4 HfCl 4 OES Intensity OES Intensity Cl Si Si Wavelength (nm) Cl Mass m/z (amu) Wavelength (nm) Quantify chemical species in the plasma through OES and QMS

7 Effect of T e T e Power = 5 W E ion ~ 8 ev Etchrate (Å/min) I I Cl Cl Cl e _ Cl Cl e _ Cl e _ Cl e _ Cl e _ Cl Cl e _ Cl e _ Cl e _ Pressure (mtorr) Etching rate decreases with increased chamber pressure

8 Effect of Ion Energy (in Cl ) ZrO HfO 1 Etchrate in Cl (Å/min) mtorr, 5 W Etchrate in Cl (Å/min) mtorr, 5 W 5 mtorr, 3 W E ion ZrO and HfO etching rate increases with increased ion energy E ion

9 Etching Products in Cl ZrCl ZrO HfO ZrCl HfCl 3 HfCl 3 ZrCl 4 4 Normalized QMS Intensity m/z mtorr and 5 W, surface chlorination confirmed by XPS ZrCl 3 and HfCl 3 are the primary etching products at low ion energies ZrO and HfO etch products are different m/z

10 Etching Products in Cl ZrO HfO QMS Intensity.x x1 5 1.x1 5 ZrCl x ZrCl ZrCl3 ZrCl E ion ZrCl 4 ZrCl 3 ZrCl ZrCl 3 ZrCl 4 QMS intensity HfCl x HfCl 3 HfCl E ion HfCl 3 HfCl 4 HfCl 3 5.x1 4 ZrCl HfCl E ion E ion 3 mtorr and 5 W, surface chlorination confirmed by XPS ZrCl 3 and HfCl 3 are the primary etching products at low ion energies ZrO and HfO etch products are different

11 Surface Composition (Cl ) ZrO HfO Normalized XPS intensities Binding energy (ev) Cl etched ZrO Zr-O Zr-Zr XPS intensities XPS intensities Hf 4d Cl etched HfO as-deposited HfO Hf 4d satellite Cl etched HfO as-deposited HfO Cl p ev 198. ev Binding energy (ev) Hf-O Hf metal As_deposited ZrO Ar sputtered HfO Ar etched ZrO Binding Energy (ev) Binding energy (ev) Chlorine was found on plasma etched surface

12 Etching Mechanism Analysis Cl ClO O M Breaking M-O bond is the critical step Physical sputtering O Chemical etching ClO Cl radicals react with M to form volatile MCl x

13 Etching Selectivity to Si E bulk plasma e - e- e- e - e - e - e _ Cl Cl Cl MCl x Bond strength ( ev) Hf-O 8.3 Hf-Cl 5.16 Zr-O 8.6 Zr-Cl 5.11 Si-O 8.3 Si-Cl 4. Si-Si 3.39 Si-B.99 B-O 8.4 B-Cl 5.31 ZrO BCl3 ZrCl4 BClO Si B BSi HfO BCl HfCl BClO 3 4 Silicon MO Boron could enhance the oxygen removal by forming volatile species Boron would passivate the silicon surface by forming B-Si bonds

14 BCl 3 /Cl Plasma Characterization QMS Intensity QMS Intensity 6x1 6 6x1 6 Cl 5x1 6 4x x1 6 x1 6 x1 6 1x1 6 QMS Measurement BCl B OCl 3 Cl BCl B Cl BCl 3 (%) 3 (%) mtorr, 3 W, -7 V; Ar flow rate was fixed at 5% BCl is the dominant ionic species 5x1 5 4x1 5 3x1 5 x1 5 1x1 5 Langmuir probe Measurement BCl 3 (%) Ion density was maximized at 4% of BCl 3 and reduced at higher BCl 3 flow rate Ion density (cm -3 ) 6x1 1 4x1 1 x1 1 Cl BCl BCl B OCl 3 B Cl 3

15 Selectivity Improvement ZrO Etch Rate HfO Etch Rate Etching Selectivity ER ZrO ER Si = ZrO Etch Rate (Å/min) HfO Etch rate (Å/min) Selectivity Si Etch Rate (Å/min) BCl 3 (%) BCl 3 (%) BCl 3 (%) BCl 3 (%) Pressure = 5 mtorr, Power = 3W, E ion = 78 ev Maximum ZrO and HfO etch rate corresponds to the highest ion density Selectivity is increased at higher BCl 3 flow rate

16 Identification of Etch Products (BCl 3 ) 4x1 6 QMS Intensity 3x1 6 x1 6 1x1 6 ZrO etching background m/z m/z Reactions ZrB Cl 7 After background subtraction ZrB OCl m/z 5 mtorr, 1) MO 3 BCl W, 3( g) 15 MCleV 4( g) 3ion ( BClO) energy 3( g) The etching ) MO 4 products BCl are 3( g ) MCl4( g) different BOCl4( g) to 79. those in Cl plasma, suggesting 3) MOdifferent 3 BCl3( ) MCl Zr 4( ) removal B3OCl 5( ) mechanisms g g g QMS Intensities M = Zr r H (KJ/mol) M = Hf

17 Surface Composition (BCl 3 ) XPS intensity Cl p Binding energy (ev) B-O/B-Cl Zr 3d XPS Intensitiy etched Si Cl p B-Si Binding energy (ev) etched ZrO unetched Si as-deposited ZrO Binding energy (ev) Binding energy (ev) Chlorine was found on BCl 3 plasma etched surface B-Si layer was determined on BCl 3 plasma etched Si film

18 Etching Selectivity (in BCl 3 ) ZrO HfO Selectivity Selectivity ZrO Si Etch rate (Å/min) Selectivity Selectivity Si HfO Etch rate in BCl 3 (Å/min) E ion E ion Higher threshold energy was obtained for etching Si in BCl 3 plasma Low ion energy is preferred toward the end of the etching

19 A Two-Step Etching Process Selectivity Selectivity ZrO Si Etch rate (Å/min) E bulk plasma e - e - e- e - e - e - e _ Cl Cl Cl sheath mask ZrCl x E ion Silicon Higher threshold energy was obtained for etching Si in BCl 3 plasma Low ion energy is preferred toward the end of the etching ZrO

20 Effect of T e on Etching Selectivity BCl 3 Plasma, E ion ~ 75 ev 16 4 Higher n i, T e Higher T e ZrO ZrO 1 Etch rate (Å/min) HfO Si Etch rate (Å/min) 8 4 Si HfO Power (W) Pressure (mtorr) ZrO and HfO have similar responses to T e and n i Si is less sensitive to the plasma variations High power and low pressure is preferred for higher selectivity

21 Formulation of Reaction Model ER MO = α n iβ n γ δ Θ Cl E M-O E ion ε E M-O ER MO : etch rate of MO in BCl 3 (Å/min) n i : ion density (QMS BCl ) n Cl : neutral density (OES I Cl /I Ar ) E ion : ion energy (ev) E M-O : bond strength (ev) Parameters Fitting values Assumptions: α Constant β (n ion density at all E ion i ).63 Identical crystal structure (MO ) γ (n Similar Cl ) 1.11 molar volume (MO ) Similar δ (E M-O ) etching mechanism ε (E th ) θ (E M-O ) 6.71 ER ZrO E E th ε E θ M O Zr O = = ε and θ 1 1 θ ( Eion ( ε EZr O ) ) 1 1 θ ion ( ε Hf O ) ( ) ER HfO E Hf O E E ER MO 1 1 θ ( ( ε ) ) E E E δ M O ion M O δ = α n n β i γ Cl δ α, β, and γ

22 Validation with Experiments (BCl 3 ) 16 Baseline conditions: Pressure = 5 mtorr, Power = 3W, E ion = 78 ev 4 16 Etch rate (Å/min) ZrO HfO Etch rate (Å/min) ZrO HfO Etch rate (Å/min) HfO ZrO E ion 4 6 Power (W) Pressure (mtorr) Model predicts well the experimental results, with some deviation at high power and low pressure (high T e ), probably due to the inaccurate Cl density measurement and neutral temperature change

23 NMOSFET Device S sub D G D G S sub 1x1-8x1-3 L/W = µm/µm A = 4x1-4 cm, t = 9A Vg = 3V C/A (F/cm ) 4x1-6 3x1-6 x1-6 1x1-6 L/W=µm/µm A = 4x1-4 cm t = 9A I D (A) 6x1-3 4x1-3 x1-3 Vg = V Vg = 1V V (V) Vg = V V D (V) Plasma etching of HfO Electron mobility is ~ cm /V-s (much higher mobility compared to NMOSFET made with ZrO HF etch)

24 Conclusion High density and low ion energy plasmas are effective in patterning ZrO and HfO MCl x are the major etching products in Cl MB x Cl y are the major etching products in BCl 3 Etching rates dominated by Surface composition validated by XPS Selectivity to Si increased at lower ion energy and higher T e A generalized model predicts the etching of transition metal oxides n i, n Cl, E ion, E M-O Slight deviation at high T e conditions more accurate Cl flux measurement Plasma etching process successfully integrated in MOSFET device fabrication, yielding high electron mobility E ion

25 FLCC Proposed Research Develop feature-scale models for next-generation, dual frequency dielectric etch reactors Couple feature-profile simulations with tool-scale models and global/pic models of FLCC collaborators Apply simulation to features etched in CenturaTM tool

26 Monte Carlo Simulation Source plane ion radical Simulation domain: o -5 A grid size (~ mixing length) Transport of species in grid-length steps Surface Reaction: Reaction probability based on model Elemental balance Multiple interaction possible PR Surface advancement Grid cells removal and/or addition Thin film Substrate Rigorous incorporation of all the physics and chemistry Computationally robust and straightforward

27 Non-ideality in Plasma Etching Cl Cl e Cl e e Cl e bulk plasma e - e- e- e - e - e - e _ Cl Cl Cl MCl x E sheath Ions are not uni-directional! Profile evolution affected by etching and deposition! ClO MCl 4 Ion MO 6Cl MCl ClO 4 Silicon mask MO

28 Effect of Ion Scattering oxide poly-si oxide Non-directional ion distribution (1 o FWHM) Trenching formation due to ion scattering

29 Effect of Deposition/Redeposition photoresist C SiCl poly-si oxide Non-directional ion distribution (1 o FWHM) Trenching formation reduced due to deposition/redeposition of etching products