Advances in Radio Frequency Plasma Power Delivery … in Radio Freqqyuency Plasma Power Delivery Systems D. Carter & D. M. Shaw Advanced Energy Industries, Inc. [email protected]

Advances in Radio Frequency q yPlasma Power Delivery Systems

D. Carter & D. M. ShawAdvanced Energy gyIndustries, Inc.

[email protected]

2008-3-26 CSMIC 2008, InterContinental Hotel, Shanghai1

Outline

• Introduction• RF Power Delivery Systems: Overview• Impedance Matching Techniques

– Fixed f, Pdel Regulation w/Fixed Match– Fixed f, Pdel Regulation w/Variable Match– Variable f, Pdel Regulation w/Variable Match

Variable Frequency Process Example• Variable Frequency Process Example• RF Power Pulsing

S / C l i


• Summary / Conclusion

RF Power Delivery System: OverviewDelivered

RF Match

Forward Power

Power

RFGenerator

Match Network

Plasma Chamber

Reflected

Coaxial Cable

Impedance ChamberPower Impedance(VSWR)• Purpose

– Enable reliable and consistent plasma ignition– Accurately deliver RF power to changing plasma conditionsAccurately deliver RF power to changing plasma conditions

• Components– RF generator – Coaxial cable


– Matching network– Plasma chamber

Impedance Matching Techniques

• Fixed f, Pdel Regulation w/Fixed Match• Fixed f, Pdel Regulation w/Variable Match• Variable f, Pdel Regulation w/Variable Match, del g


Fixed f, Pdel Regulation, Fixed Match

•Tune match for “central” impedance point T l h l diff t•Tool may have several different

“central” impedance points depending on range of recipes

Delivered

Fixedmatch

RFGenerator

Match Network

Forward Power

Coaxial Cable

Delivered Power


Plasma Chamber

Reflected Power

Impedance(VSWR)

Fixedfrequency

Fixed f, Pdel Regulation, Fixed Match

•Very fast—relies on generator’s fast electronics rather than slow mechanical matchmechanical match•No moving parts (no variable capacitors)—minimizes component wear-outp•Generator’s ability to handle reflected power is critical—typically requires “oversized”

tgenerator•Limited range depending on magnitude of impedance change for each process


for each process


• Fixed f, Pdel Regulation w/Fixed Match• Fixed f, Pdel Regulation w/Variable Match• Variable f, Pdel Regulation w/Variable Match, del g


Fixed f, Pdel Regulation, Variable Match

•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 Ωminimize time to achieve 50 ΩtuneVariablematch

RFG t

Match N t k

Forward Power

C i l C bl

Delivered Power


Generator Network

Plasma Chamber

Reflected Power

Coaxial Cable

Impedance(VSWR)

Fixedfrequency

Fixed f, Pdel Regulation, Variable Match

•Very fast—relies on generator’s fast electronics rather than slow mechanical matchmechanical match•Autotuning match allows very wide process range•Variable capacitors subject toVariable capacitors subject to wear-out in highly cyclical processes•Generator’s ability to handle yreflected power is critical—typically requires “oversized” generator



• Fixed f, Pdel Regulation w/Fixed Match• Fixed f, Pdel Regulation w/Variable Match• Variable f, Pdel Regulation w/Fixed Match, del g


Variable f, Pdel Regulation, Fixed Match

•Generator varies frequency to obtain best match—combined with delivered power regulation allows wide operatingallows wide operating •Often, fixed match may be used to cover all required process rangesranges•Variable match may be added for added range if necessaryFixed

match

RFG t

Match N t k

Forward Power

C i l C bl

Delivered Power

match


Generator Network

Plasma Chamber

Reflected Power

Coaxial Cable

Impedance(VSWR)

Variablefrequency


•Requires frequency agile generator (ability to frequency tune)tune)•VERY fast—tunes typically in 10’s of msec•Minimizes need for “oversized”Minimizes need for oversized generator (reduced reflected power)•Allows development of process p precipes requiring extremely precise power delivery



•Example of frequency tuning into a plasma power change M t h t k i fi d•Match network is fixed

•Tune with minimum reflected power achieved in less than 150 µsecµsec


Plasma Ignition Using Three Different g gTechniques

Variable match Variable matchw/presets

Frequency tunew/fixed match

•Tuned in ~2.3 secw/presets•Tuned in ~1.1 sec

w/fixed match•Tuned in ~ 10 ms

•Faster tune results in more repeatable processes especially for


•Faster tune results in more repeatable processes, especially for short steps

Process Example

P l d fl l t ti d l t iti•Pulsed flow, electronegative and electropositive gases •Could represent deep silicon etch process or complex gate stack etch recipe


Process Example: Fixed Frequency

•Traditional variable match network•Fixed frequency generator•Match continuously moves—l diti hplasma condition never reaches

stable operating point


Variable Frequency Process Example

•Fixed match network•Variable frequency, auto-tuning generator•Match never moves—plasma l i d i dalways receives desired power


SummaryO ti Ad t Di d tOption Advantage Disadvantage

Load Power Fast, accurate delivery to into 50 and non-50 Ω loads

Limited range depending on required power or

Regulation changes in plasma impedance

Variable Match withWidest impedance matching range available Adjustable

Slow mechanical components in matchVariable Match with

autotunerange available. Adjustable pre-sets for minimizing time to achieve match.

components in match. Subject to wear in highly cyclical processes.

Fast broader impedance Operating range smallerFrequency tuning

Fast, broader impedance range for load regulation

Operating range smaller than variable match

Load power regulation

Broadest operating range, fastest performance

None


regulation, frequency tuning & variable match

fastest performance available

Conclusions

• Modern RF delivery systems offer several different methodsCh i d d ifi i t• Choice depends on specific process requirements– Step times– Impedance rangeImpedance range– Power delivery accuracy requirements

• Some systems are available that are fast enough to tune even during pulsed RF power delivery


Documents

Advances in Radio Frequency Plasma Power Delivery … in Radio Freqqyuency Plasma Power Delivery Systems D. Carter & D. M. Shaw Advanced Energy Industries, Inc. [email protected]