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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