etching ( part 1) - ntnufolk.ntnu.no/jonathrg/fag/tfe4180/slides/ch16 etching (part 1).pdf ·...
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TFE4180 Semiconductor Manufacturing Technology
Etching ( Part 1)Chapter 16: Semiconductor Manufacturing Technology by M. Quirk & J. Serda
Saroj Kumar PatraTFE4180 Semiconductor Manufacturing Technology
Norwegian University of Science and Technology ( NTNU )
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Etching
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Introduction
Photoresist mask Film
to be etched
(a) Photoresist-patterned substrate (b) Substrate after etch
Photoresist mask Protected
film
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Objectives1. List and discuss nine important etch parameters.2. Explain dry etch, including its advantages and how etching
action takes place.3. List and describe the equipment systems for seven dry plasma
etch reactors.4. Explain the benefits of high-density plasma (HDP) etch and the
discuss the four types of HDP reactors.5. Give an application example for dielectric, silicon and metal
dry etch.6. Discuss wet etch and its applications.7. Explain how photoresist is removed.8. Discuss etch inspection and important quality measures.
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Etch Processes• Dry etch
– Wafer exposed to a plasma– Primary method for submicron geometries
• Wet etch– Liquid chemicals
• Material to be etched:– Metal etch– Dielectric etch– Silicon etch
• Patterned or unpatterned
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Etch parameters• Etch rate• Etch profile• Etch bias• Selectivity• Uniformity• Residues• Polymer formation• Plasma-induces damage• Particle contamination and
defects
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Etch rate• The speed at which material is removed from the wafer surface
during etching.
T
Start of etch End of etch
t = elapsed time during etch
T = change in thickness
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Etch profile• Isotropic and anisotropic etching
Isotropic etch - etches in all directions at the same rate
Substrate
Film
Resist
Isotropic etch - etches in all directions at the same rate
Substrate
Film
Resist
Anisotropic etch - etches in only one direction
Resist
Substrate
Film
Anisotropic etch - etches in only one direction
Resist
Substrate
Film
Resist
Substrate
Film
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Etch profile – Wet Etch vs. Dry Etch
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Etch bias
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Etch bias
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Etch selectivity
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Selectivity
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Measure etch rate at 5 to 9 locations on each wafer, then calculate etch uniformity for each wafer and compare wafer-to-wafer.
Randomly select 3 to 5 wafers in a lot (lot = 24 wafers)
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Uniformity
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• Unwanted material remaining after etch
• Caused by impurities in film, contaminants, bad choice of etchant etc.
• Can cause undesirable electrical connections
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Residues
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Plasma ions
Resist
Oxide
Polymer formationSilicon
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Polymer Sidewall Passivation for Increased Anistropy
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• Ions, electrons and excited molecules• Can cause damage to sensitive devices• I.e. trapped charges on the gate electrode of transistor
due to nonuniform plasma• Caused by poor design- or operation of equipment• Removed by annealing or chemical wet etch
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Plasma-induced Damage
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• Particle contamination from etchant by-products• Optimized tool design, tool operation and
appropriate gas chemistry
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Particle Contamination
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• Dry etch techniques• Potential Distribution• Advantages of Dry Etch over Wet Etch
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Dry etch
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8) By-product removal
1) Etchant gases enter chamber
Substrate
Etch process chamber
2) Dissociation of reactants by electric fields
5) Adsorption of reactive ions on surface
4) Reactive +ions bombard surface 6) Surface reactions of
radicals and surface film
Exhaust
Gas delivery
RF generator
By-products3) Recombination of
electrons with atoms creates plasma
7) Desorption of by-products
Cathode
AnodeElectric field
Anisotropic etch Isotropic etch
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Plasma Etch Process of a Silicon Wafer
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Chemical and Physical Dry Etch Mechanisms
Reactive +ions bombard surface Surface reactions of
radicals + surface film
Desorption of by-products
Anisotropic etch Isotropic etch
Sputtered surface material
Chemical EtchingPhysical Etching
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Chemical Versus Physical Dry Plasma Etching
Etch Parameter
Physical Etch (RF field
perpendicular to wafer surface)
Physical Etch (RF field
parallel to wafer surface)
(chemical)
Chemical Etch(wet etching)
Combined Physical and
Chemical
Etch Mechanism
Physical ion sputtering Radicals in
plasma reacting with wafer surface*
Radicals in liquid reacting with wafer surface
In dry etch, etching includes ion sputtering and radicals reacting with wafer surface
Sidewall Profile Anisotropic Isotropic Isotropic Isotropic to Anisotropic
Selectivity Poor/difficult to increase (1:1)
Fair/good (5:1 to 100:1)
Good/excellent (up to 500:1)
Fair/good (5:1 to 100:1)
Etch Rate High Moderate Low Moderate
CD Control Fair/good Poor Poor to non-existent Good/excellent
* Used primarily for stripping and etchback operations.
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Schematic View of Reactor Glow Discharge with Potential Distribution
Plasma (+Vp)Ion
sheath
RF
Powered electrode (Vt)
Grounded electrode
-V 0 +V
Vp
Vt
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Effects of Changing Plasma Etch Parameters
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Advantages of Dry Etch over Wet Etch
1. Etch profile is anisotropic with excellent control ofsidewall profiles.
2. Good CD control.
3. Minimal resist lifting or adhesion problems.
4. Good etch uniformity within wafer, wafer-to-waferand lot-to-lot.
5. Lower chemical costs for usage and disposal.
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