Advances in Radio Frequency Plasma Power Delivery Systems

Transcription

1 Advances in Radio Frequency Plasma Delivery Systems D. Carter & D. M. Shaw Advanced Energy Industries, Inc. 1

2 Outline Introduction RF Delivery Systems: Overview Impedance Matching Techniques Fixed f, P del Regulation w/fixed Match Fixed f, P del Regulation w/variable Match Variable f, P del Regulation w/variable Match Variable Frequency Process Example RF Pulsing Summary / Conclusion 2

3 RF Delivery System: Overview Forward Delivered RF Generator Coaxial Cable Match Network Reflected Impedance (VSWR) Plasma Chamber Purpose Enable reliable and consistent plasma ignition Accurately deliver RF power to changing plasma conditions Components RF generator Coaxial cable Matching network Plasma chamber 3

4 Impedance Matching Techniques Fixed f, P del Regulation w/fixed Match Fixed f, P del Regulation w/variable Match Variable f, P del Regulation w/variable Match 4

5 Fixed f, P del Regulation, Fixed Match Tune match for central impedance point Tool may have several different central impedance points depending on range of recipes Forward Fixed match Delivered Fixed frequency RF Generator Coaxial Cable Reflected Match Network Impedance (VSWR) Plasma Chamber 5

6 Fixed f, P del Regulation, Fixed Match Very fast relies on generator s fast electronics rather than slow mechanical match No moving parts (no variable capacitors) minimizes component wear-out Generator s ability to handle reflected power is critical typically requires oversized generator Limited range depending on magnitude of impedance change for each process 6

7 Impedance Matching Techniques Fixed f, P del Regulation w/fixed Match Fixed f, P del Regulation w/variable Match Variable f, P del Regulation w/variable Match 7

8 Fixed f, P del Regulation, Variable Match Forward Variable match gives very wide process range No need to define known impedance points variable match automatically tunes Preset match points can minimize time to achieve 50 Ω tune Variable match Delivered 8 Fixed frequency RF Generator Coaxial Cable Reflected Match Network Impedance (VSWR) Plasma Chamber

9 Fixed f, P del Regulation, Variable Match Very fast relies on generator s fast electronics rather than slow mechanical match Autotuning match allows very wide process range Variable capacitors subject to wear-out in highly cyclical processes Generator s ability to handle reflected power is critical typically requires oversized generator 9

10 Impedance Matching Techniques Fixed f, P del Regulation w/fixed Match Fixed f, P del Regulation w/variable Match Variable f, P del Regulation w/fixed Match 10

11 Variable f, P del Regulation, Fixed Match Forward Fixed match Generator varies frequency to obtain best match combined with delivered power regulation allows wide operating Often, fixed match may be used to cover all required process ranges Variable match may be added for added range if necessary Delivered 11 Variable frequency RF Generator Coaxial Cable Reflected Match Network Impedance (VSWR) Plasma Chamber

12 Variable f, P del Regulation, Fixed Match Requires frequency agile generator (ability to frequency tune) VERY fast tunes typically in 10 s of msec Minimizes need for oversized generator (reduced reflected power) Allows development of process recipes requiring extremely precise power delivery 12

13 Variable f, P del Regulation, Fixed Match Example of frequency tuning into a plasma power change Match network is fixed Tune with minimum reflected power achieved in less than 150 µsec 13

14 Plasma Ignition Using Three Different Techniques Variable match Tuned in ~2.3 sec Variable match w/presets Tuned in ~1.1 sec Frequency tune w/fixed match Tuned in ~ 10 ms Faster tune results in more repeatable processes, especially for short steps 14

15 Process Example Pulsed flow, electronegative ti and electropositive gases Could represent deep silicon etch process or complex gate stack etch recipe 15

16 Process Example: Fixed Frequency Traditional variable match network Fixed frequency generator Match continuously moves plasma condition never reaches stable operating point 16

17 Variable Frequency Process Example Fixed match network Variable frequency, auto-tuning generator Match never moves plasma always receives desired d power 17

18 Summary Option Advantage Disadvantage Load Regulation Variable Match with autotune Frequency tuning Fast, accurate delivery to into 50 and non-50 Ω loads Widest impedance matching range available. Adjustable pre-sets for minimizing time to achieve match. Fast, broader impedance range for load regulation Limited range depending on required power or changes in plasma impedance Slow mechanical components in match. Subject to wear in highly cyclical processes. Operating range smaller than variable match Load power regulation, frequency tuning & variable match Broadest operating range, fastest performance available None 18

19 Conclusions Modern RF delivery systems offer several different methods Choice depends d on specific process requirements Step times Impedance range delivery accuracy requirements Some systems are available that are fast enough to tune even during pulsed RF power delivery 19