Why Spare Parts Management for Plasma
Processes ?
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- 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
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Spare parts management
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- 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.
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Low Pressure Process Example
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-
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.
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- 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.
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High
Pressure
Process Example
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- Isotropic etching with low damage, surface
preparation and descum
- 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.
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- Plasma
current
still shows the known, 'ceramic' pattern
clearly.
- Only weak pattern in plasma density.
- RF Power adjustment not seen here.
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- … 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.
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- 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.
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- You are also welcome to contact our Services
Team to get additional information.
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