Transcript Introduction

1
Spatially Resolved Heat Flux Sensor
on a Silicon Wafer
for Plasma Etch Processes
SFR Workshop
May 24, 2001
Mason Freed, Costas Spanos, Kameshwar Poolla
Berkeley, CA
2001 GOAL: Design, build, and test an array of heat flux sensors
on a silicon wafer, with external electronics.
5/24/2001
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Motivation
• Plasma etch processes are highly sensitive to wafer
temperature, in terms of etch rate, selectivity, and anisotropy
• Heat delivered to the wafer has two principle sources: ion flux
bombardment, and exothermic chemical etch reactions
• It is very difficult to measure these two quantities, spatially
resolved, without using wafer-mounted sensors
Plasma
Chemical
heating
Ion flux
heating
Chuck
cooling
Wafer
Chuck
5/24/2001
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Sensor Geometry: Modified Gardon Gauge
Membrane
Top View





T  q D2 ln D
8kw b
T
D
Membrane
thickness=w
Membrane
Side View
 sensitivity depends
on diameter squared
Incident
heat flux
Heat flow within
thin dielectric
membrane
Antenna
b
Incident heat
flux (q )
Heat sink
Heat flow within membrane
T
5/24/2001





Heat sink
Antenna
Base
T
Membrane
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Discrimination of Ionic / Chemical Heating
• Use two heat flux sensors, one with an exposed layer
of etched material (“exposed” in diagram) and the
other without this material (“covered”)
• Place sensors into Wheatstone bridge arrangement:
Router,exposed
V
+ chemical –
Rinner,exposed
Router,covered
+
Vionflux
Rinner,covered2
–
Rinner,covered
Router,covered2
•  Vchemical  qexothermic , Vionflux  qionflux
•  antenna structure keeps this added material from
adversely affecting the sensitivity
5/24/2001
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First Process – High Built-In Stress Gradient
Warped
Antenna
Etch
Holes
Membrane
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First Process – Printability Problems
Open
Circuit
“Gunk”
Polysilicon
central
resistor
Metal
Wires
5/24/2001
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Second Process
• Moved to polysilicon antenna structure, from
previous aluminum/oxide/photoresist stack
• Enlarged wires to allow better printability
• Switched to wet Aluminum etchant, to avoid
aluminum/polysilicon selectivity problem with Clbased plasma etch
• Modified layout to place etch holes closer together,
and more evenly spaced
• Modified layout to allow better matching between the
inner and outer temperature-sense resistors
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Problems Solved
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2002 and 2003 Goals
Demonstrate heat flux sensor in plasma etch environment, with
external electronics, by 9/30/2002.
Design wireless heat flux sensor wafer and demonstrate it in
plasma etch environment, by 9/30/2003.
5/24/2001