Toroidal Plasma  Deposition  of  Diamond

NDNC-­‐2015

William  HolberPlasmability,  LLC

Co-­‐Workers:Robert  Basnett PlasmabilityAndrew  Basnett PlasmabilityRobert  Krchnavek Rowan  University

Some  Historical  PerspectiveSteady  Progress  in  Dep.  Rates

0

10

20

30

40

50

60

70

80

1990 1995 2000 2005 2010 2015

Dep.  Rateum/hr

AsmussenMortetTaillaireHorinoZuBresnehanGuGicquel

SCD

PCD

Some  Historical  Perspective

Gicquel,  et.al.  2014

Atomic  Hydrogen  is  the  Key• higher  pressure• higher  microwave  power• higher  gas  temperature

What  This  Means• To  grow  high  quality  diamond  material  at  high  rates  the  

following  are  needed:– high  gas  temperature  to  generate  lot  of  atomic  H

• for  microwave  systems  this  means  high  pressure  and    high  microwave  powers

– high  quality  vacuum  practice• avoid  nitrogen  leaks  and  other  impurities

– materials  of  construction  that  will  not  erode  and  cause  contamination– careful  temperature  control  of  the  sample

• Our  program  is  to  develop  a  reactor  technology  that  will  accomplish  these  goals  at  significantly  lower  cost  and  complexity.

Our  Program• Develop  an  rf-­‐based  alternative  to  microwave  plasma  

diamond  deposition  reactors• Don't  try  to  reinvent  the  physics  -­‐ aim  for  same  power  

densities,  operating  conditions,  etc• Why  might  this  be  attractive  ?

– rf power  is  much  more  energy  efficient  to  product  relative  to  microwave

– rf is  more  reliable  and  does  not  need  maintenance  (magnetron  tube  replacement  for  microwave)

– rf is  much  less  bulky  and  more  flexible  to  integrate– use  may  reduce  overall  costs  significantly– rf is  highly  scalable  in  power  

Goals  of  Initial  Activity

• Investigate  toroidal plasma  as  alternative  to  microwave  • Assess  how  toroidal plasma  operates  in  process  range  of  

interest• Identify  possible  materials  compatibility  issues• Identify  scaling  possibilities• Understand  capital  cost  components• Understand  cost  of  ownership  (dollars  per  carat)• Identify  key  application  space

Toroidal Plasmas  -­‐ Background• Toroidal plasmas  are  used  in  semiconductor  manufacturing  

for  generating  large  fluxes  of  atomic  species– O,  N,  H,  F,  etc– CVD  chamber  clean– photoresist  removal– surface  oxide  removal

• Power  densities  in  the  plasma      50+ W cm-­‐3

• Gas  temperatures  >3000  C  • Typical  pressures  2-­‐20  Torr• 400  kHz  power  – inexpensive,  compact  and  highly  reliable• 5  kW  – 25  kW  used  today  • scalable  to  higher  powers

Toroidal Plasma  Commercial  Examples

MKS  Instruments

Advanced  Energy New  Power  Plasma

Semiconductor  Manufacturing(over  40,000  installed)

Lighting

Sylvania

Why  Toroidal Plasmas  ?• It  is  very  difficult  to  obtain  the  desired  plasma  conditions  

using  a  simple  rf discharge– 100+  W  cm-­‐3  volumetric  power  density  desirable– 40-­‐200  Torr gas  pressure– 3000+  C  gas  temperature  in  discharge  region

• Capacitively coupled  systems  will  not  have  the  the  power  density  or  gas  temperature

• Inductively  coupled  systems  may  generate  the  power  density,  but  typically  only  in  a  localized  region  near  walls  or  antennas

• DC  or  rf plasma  torches  will  have  the  requisite  plasma  conditions,  but  with  difficulties  related  to  contamination  and  wear

Toroidal PlasmasICP  with  a  Ferromagnetic  Core  

Conventional  ICP's:• typically  several  kV  on  the  antenna• large  and  variable  power  losses  in  antenna  and  

matching  network• capacitive  coupling  hard  to  eliminate  – erosion  

and  contamination• power  supplies  and  matching  networks  costly• resonant  matching

Toroidal Plasma  Sources  (ICP  with  a  ferromagnetic  core)• strong  coupling  between  input  power  and  plasma• magnetic  core  closes  the  flux  loop• high  current,  low  voltage  operation  • lower  frequency  power  without  capacitive  coupling• non-­‐resonant  matching

Valery  Godyak2005  GEC  

Toroidal Plasma  -­‐ Principal  of  Operation• Plasma  runs  in  a  closed  loop  and  acts  as  

the  secondary  of  a  transformer  circuit.• The  primary  of  the  transformer  circuit  is  

a  400  kHz  power  source• The  primary  turns  ratio  helps  to  match  

the  load  impedance  to  the  source.• No  active  matching  circuit  necessary.  

Power  automatically  increased  until  desired  plasma  impedance  is  achieved.

• At  400  kHz  almost  no  capacitive  coupling.

Gas In

Gas Out

Plasma

Magnetic Core

Primary Winding

RF source

Experimental  Apparatus

process  chambermagnetic  cores

Polysilicon Results  -­‐ Raman

Ar:   1325  sccmH2:   250  sccmCH4:  10  sccmO2:   3.5  sccm30    Torr9.5  kW1030  C15  um/hr

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800

Intensity

cm-­‐1

2/8/15

Initial  Results  in  SCD

Process  conditions:2000  sccmAr240  sccmH24  sccm CH40.75  sccm O250  Torrtemp  990  C  Dep rate:  5  um/hr

What  Have  We  Learned  ?• Toroidal plasma  design  can  generate  plasma  conditions  similar  

to  that  for  microwave  systems• Shape  of  plasma  lends  itself  to  unique  process  opportunities

– In  principal  can  capture  nearly  100%  of  the  available  reactant– For  example,  can  coat  inside  and  outside  of  tubular  structures

• Highly  scalable  in  power• Very  compact  source• Applications  such  as  coating  large  silicon  wafer  maybe  not  

best  choice  for  this  technology• Initial  deposition  rates  comparable  to  or  greater  than  for  

microwave  reactors• Presence  of  argon  does  not  seem  to  damage  growing  surface

Next  Steps

• Further  process  development  for  both  polycrystalline  and  single-­‐crystal  material

• Characterize  high-­‐capture  sample  holder

THANK  YOU