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Introduction to Plasma Etching

姜克 2013年2月3日

contents

Intro to plasma? What is plasma?

Examples of plasma.

Plasma in IC.

What is plasma etching?

Plasma Etching Principles.

Summary

Section 1：Intro to Plasma

What is plasma?

plasma is a the forth state of matter. Heating a gas

may ionize its molecules or atoms thus turning it into a

plasma, which contains charged particles: positive ions and

negative electrons. (99.9% of matters in the space)

Examples of plasma

Temperature measurement in the early days

Examples of plasma

Small plasma ball Big plasma ball

Plasma in daily life and IC

Plasma Etching

Plasma-Immersion Ion Implantation (PIII)

Plasma Deposition

Plasma Stripping (Ashing)

Plasma in IC manufacturing

Stress Relief

Section 2：What is Plasma etching

Plasma process that removes material from surface

Selective etch transfers IC design image on the

photoresist to the surface layer on wafer

Other applications: Mask making, 3D integration

What is plasma etching?

Trench etch (0.2 μm wide by 4 μm deep)

Plasma etcher （刻蚀机）

Section 3：Plasma etching Principle

Chemical

Neutral Radical Volatile by-Product

Chemical Reaction

Thermalized neutral radicals chemically combine with

substrate material forming volatile products

- Isotropic

- Purely Chemical Reaction

- High Pressure

- Batch Wafer Type

- Less Electrical Damage

Plasma etching principles

Sputtering

Ion

Sputtered Atom (Molecule)

Physical bombardment

The ion energy mechanically ejects substrate material

- Anisotropic

- Purely Physical Process

- High Directionality

- Low Pressure

- Single Wafer Type

- Low Etch rate

Plasma etching principles

Energetic Ion Enhanced (Chemical + Sputtering)

Neutral Radical

Volatile by-Product

Chemical Reaction

Ion bombardment enhances or promotes the reaction

between an active species and the substrate material

- Physically Enhanced

Chemical Reactivity

- Damage Enhanced

Chemical Reactivity

- Chemically Enhanced

Physical Sputtering

- Ion Reaction

Ion

Plasma etching principles

Etchant Additives Inert Gas

Purpose Primary Etchant Selectivity

Control

Stablize Plasma, Dilute Etchant

Examples See below table O2, N2, H2, etc He, Ar, Xe, etc

Solid Etchant By-Products (Tb) Applications

Si

NF3, SF6, CF4, ..

Cl2, CCl4,

HBr

SiF4 (-86℃)

SiCl4 (58℃)

SiBr4 (154℃)

STI, Gate

SiO2

(Si3N4, SiON)

CF4, C4F8, C4F6, …

CHF3, CH2F2, CH3F, …

SiF4 &

CO(-191℃), CO2 (-57℃),

HCN (26℃)

Contact

Al Cl2, BCl3 AlCl3 (180℃, subl.)

Interconnectio

n Ti, TiN Cl2, CCl4 TiCl3 (136℃)

W NF3, SF6, CF4, Cl2 … WF6 (19℃), WCl6 (337℃)

PR (a-Carbon) O2, N2, … CO, CO2, HCN Mask

Cu, Fe, Ni, Co, Pt, … Difficult to Etch Cu2Cl2 (1490℃), Cu2F2 (1100℃) Metal

Plasma etching recipe.

- Etched thickness x divided by etching time t - ~10um/min (Si) PSX800 from Panasonic

t

xER Etch Rate (ER)

Selectivity

- The ratio of the etch rates of two materials etched simultaneously such as etched layer and PR mask

B

ABA

ER

ERS /

In the same plasma condition = Etch rate of layer A = Etch rate of layer B

AER

BER

Uniformity

-how uniform the etching rate for die to die, wafer to wafer, lot to lot

100/2

][ minmax

NE

EEUniformity

i

ERi : Etch rate at several points ERmax : Maximum etch rate ERmin : Minimum etch rate

x

Plasma etching principles

Section 4：Summary

18

Plasma- 4th state of matter.

Plasma etching + litho are used to do pattern

transfer in nano/micro-electronics

manufacturing.

Energy and Vacuum is needed to maintain

plasma (gas discharge).

poly, oxide and metal (some) can be etched.

Home Taking Message

Q: Wanna homebrew plasma trick?

A: Vaccum+Energy

Thank you