by courtesy of UMS Ulm

The in-situ Plasma Metrology System Hercules® for etch and CVD processes measurements
the plasma parameters as electron density and electron collision rate.

The Hercules® SAPC Server is a stand-alone, easy-to-use Statistical Process Control (SPC)

  Why Spare Parts Management for Plasma Processes ?

  • Any part in contact with the plasma impacts the process.
  • Spare parts are a major cost driver.
  • So often second-source parts are used
    – with sometimes different properties !
  • The process stability depends in particular on large-area parts:
    • Surface temperature if not well controlled (ceramics)
    • Chemical surface conditions, in particular in case of memory effects
    • In particular if regularly cleaning during PM causes seasoning
Critical spare parts of an ICP etcher - Ceramic wall

  Spare parts management

  • Scheduling
  • Qualification and characterization of second source parts
  • Tracking and monitoring of age and cleaning cycles of spare parts.
  • Control:
    • Product wafers → Message comes usually too late.
    • Test wafers → Necessary but not sufficient, not very sensitive.
    • Tool parameters →     ?
    • Plasma parameters →     ?

  Low Pressure Process Example

  • Anisotropic etching of dielectric with low damage

    • CF4, Ar 
    • Low pressure 0.7 Pa (5 mTorr)
  • Medium bias power, due to low pressure no collision in sheath 

  • → Low but well defined ion energy keeps etch rate high but minimizes risk of wafer damage.
  • Critical impact: Ceramic chamber wall changes during PM
  • The most sensitive tool parameters - RF peak voltages at  and does not respond to spare part changes and process adaptation.
  • Collision rate is in this low pressure regime only sensitive to process adaptation – due to stochastic heating of electrons.
Low pressure: Tool parameters - RF peak voltage
  • Three different ceramic parts – same level in plasma current !

  • One Second source ceramic - lower level.
  • Plasma density is also but less affected fits to products parameters still in spec.
Low pressure: Plasma current and density

  High Pressure Process Example

  • Isotropic etching with low damage, surface preparation and descum
    • O2
    • Low pressure 11 Pa (80 mTorr)
  • Very low bias power
    → Mainly chemical (O) etching with very low ion energy.
  • Vp from coil shows only a slight RF power adjustment, please compare RF  power in diagram below.
  • In both RF peak voltages no response to spare part change.
High pressure: Tool parameters - RF peak voltage
  • Plasma current still shows the known, 'ceramic' pattern clearly.
  • Only weak pattern in plasma density.
  • RF Power adjustment not seen here.
  • But ...
High pressure: Plasma current and density
  • …  electron collision rate indicates impact of gas temperature – due to ohmic heating of electrons.
  • Accommodation coefficient and so gas cooling at chamber wall depends strongly on surface conditions.

  • Process pressure adaption shown only through collision rate.
High pressure: Plasma current and collision rate
  • Process adaptation for etch rate and selectivity is best reflected in plasma parameters.
  • The effects of ceramic chamber wall as spare part
    • is well pronounced in plasma parameters and
    • depends on process, mainly the pressure.
  • Potential reasons for impact of ceramic chamber wall:
    • Variations in heat flow from gas to chamber wall → Gas temperature.
    • Different permittivity of the ceramics.
  • Smart spare part management can be controlled by plasma parameters provided by model-based sensors.
  • You are also welcome to contact our Services Team to get additional information.

Reference: to be publish in
H.P. Maucher1, G. Boedege1, and M. Klick2
1 United Monolithic Semiconductors GmbH, Ulm, Germany
2 Plasmetrex GmbH, Berlin, Germany
Smart spare part management and chamber matching in III-V plasma etching
AEC/APC Symposium XXIV, October 31 - November 3, 2010, Austin, TX, USA