Differential surface charging of the dielectric during plasma etching and surface charge leakage kin

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Differential surface charging of the dielectric
during plasma etching and surface charge leakage
kinetic

• Original Authors MK Abatchev, BJ Howard , DS
  Becker , RL Stocks and J Chapman
• Micron Texhnology, Inc.
• Presented by Venu Krishnardula for EE7730
• Auburn University

2
Outline

• Purpose of the paper
• Some Fundamentals
• Experimental details
• Conclusions

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Purpose of the paper

• The paper reported their investigations of the
  kinetics of charge leakage.
• To know the dependence of the aspect ratio and
  the charge density

4
Fundamentals

• Flux of charged particles on to the surface
  during plasma processing of dielectric materials
  results in surface charging.
• The charge density and its distribution along the
  surface depend on plasma parameters like plasma
  uniformity , energy and angle distribution of
  ions and electrons and Structure geometry
• The differential surface charging can result in
  distortion of the etch profile and it is one of
  the possible sources of etch stop phenomenon
  during dielectric etch process.

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Plasma-Induced Charging in Microstructures
Directionality difference between ions
andelectrons induces local charging and
potentialbarrier (order of sheath voltage) in
micro-pattern. Thin gate-oxide damage and notching
http//kstar.knfp.net/kpsdpp/KPS_Poster/2002_kps/p
df_file/KPS2002spring_H02_kss.pdf
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http//kstar.knfp.net/kpsdpp/KPS_Poster/2002_kps/p
df_file/KPS2002spring_H02_kss.pdf
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http//kstar.knfp.net/kpsdpp/KPS_Poster/2002_kps/p
df_file/KPS2002spring_H02_kss.pdf
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Experimental details

• Two types of samples were used
• 1. 20000A thick film of boron-phosphorous doped
  silicon glass (BPSG)deposited on p-type Si.
• 2. 20000A thick film of BPSG deposited on 2000A
  thick thermal oxide on
• p-type.
• 8300A thick DUV photo resist with a hole
  patterns of 0.19 micron in diameter was used as
  the etching mask.
• To improve the pattern definition 300A thick
  DARC(deposited Anti-Reflective Coating) underlay
  was deposited on BPSG.
• Samples were etched at different etch times
  to produce holes of different aspect ratios in
  BPSG.

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Experimental details contd..

• After ashing of the photoresist in the oxygen
  plasma, wafers have been processed through a wet
  clean to neutralize the surface charge.
• Then they were exposed to Ar plasma for
  recharging the surface. Applied materials P5000
  MRIE etchers were used for generating the AR
  plasma.
• Profile and depth holes were observed under the
  SEM.
• Surface voltage versus time after plasma
  processing has been measured using the CPD
  technique.

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CPD technique

• A new method for on-line monitoring of oxide
  surface charge accumulation has been developed
  using CPD (Contact Potential Difference), a
  material analytical technique. In this work, CPD
  maps of oxide-covered wafers subjected to plasma
  processing were related to capacitor
  breakdown-voltage maps, as well as to the plasma
  parameter profiles2.

• Figure 2. Map of the oxide surface charge on a
  wafer exposed to a 1000 W microwave power, 2
  mTorr, 50 W RF power, non-uniform plasma.
  Different shades reflect different amount of
  charge stored on the wafer surface. The highest
  magnitude of the charge is found on the center of
  the wafer. The displayed dots represent the
  location of the floating potential measurements.

http//cpam.engr.wisc.edu/newsletter/VOL9NUM2/char
ging.html
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Charge leakage
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Conclusions

• Experimental data showed that the magnitude of
  the residual charge accumulated on the surface
  during charging is a function of the aspect
  ratio.
• Surface voltage not a monotonic function of the
  etch depth, but has amaximum at a certain depth.
• Surface voltage reduces considerable versus time
  for deep holes ( thin remained dielectric), while
  it was relatively consistent for shallow holes.
• These results suggested that the charge does leak
  between the bottom of a hole and the Si
  substrate.
• And the charge leaks faster for a thinner
  remained dielectric film.