rca esquemaproceso

8/7/2019 rca esquemaproceso

1/12

Prof. Milo Koretsky

Chemical Engineering Dept .

Cleaning

Cleaning

1.Clean Factories

2.Wafer Cleaning

3.GetteringFrom Intel

75% of Yield loss due

to particles

3-pronged appraoch:

Prof. Milo Koretsky


Cleaning

1. Clean Factories

Class of the clean room

From Middleman

Laminar

Flow


2/12

Prof. Milo Koretsky


Cleaning

2. Wafer Cleaning It is important to have clean wafers at all stages of fabrication. Cleaning is especially important before any high temperature

process.

Improper cleaning can result in yield loss and process variability

Cleaning comprises roughly 1/4 of the IC process steps

Cleaning

solution

Wafers

Prof. Milo Koretsky


Cleaning

Typical Chemicals InvolvedChemical Name

H2O (DI) De-Ionized water

H2SO4 Sulfuric Acid

H2O2 Hydrogen Peroxide

H2O Water

HF Hydrofluoric Acid

NH4OH Ammonium Hydroxide

HCl Hydrochloric Acid

IPA Isopropyl alcohol


3/12

Prof. Milo Koretsky


Cleaning

Si SurfacesThe chemical nature of the Si surface affects reactivity with contaminants

Si Si Si Si

Si Si Si Si

Si Si Si Si

Bare Si

Si Si O

Si Si OO

O Si

Si SiO

O Si

O O O O

Si SiO Si SiO

O O O O

Si Si O

Si Si OO

O Si

Si SiO

O Si

O O O O

Si SiO Si SiO

O O O O O O O OH H H H H H H H

Silicon oxide Silanol on silicon oxide

Prof. Milo Koretsky


Cleaning

Generic Contaminated Si Surface

Silicon Wafer

Silicon Oxide

Water

Air

Absorbed gas

Particles

Nonpolar organics

Polar Organics

Water

Oxide


4/12

Prof. Milo Koretsky


Cleaning

De-ionized (DI) Water Ions are reactive. They can make liquid products from solids. Theycan also bond to the solid.

Normal tap water has many different types of ions.

If we want to clean wafers without causing any reactions, we can notuse tap water. We need special water which is free of ions.

De-ionized waterTap water

Na+

Cl-

Na+

K +

K +

Cl- F-

F-

Ion free water is

called

De-ionized water

orDI water.

Prof. Milo Koretsky


Cleaning

Relative Strength of Binding Forces Important forAqueous Cleaning

Adsorption Type Energy (eV)

Chemical Bonds

Ionic

Covalent

Metallic

Physical Forces

H bonds

dipole-dipole

Despersion

6-11

0.6-7

1-3.5


5/12

Prof. Milo Koretsky


Cleaning

General Scheme - RCA CleanH2SO4H2O2125oC

H2O Rinse

Room Temp

H2O / NH4OH /H2O2(5:1:1)

80oC

H2O Rinse

Room Temp

H2ORinse

H2O / HCl /H2O2(6:1:1)

80oC

H2O Rinse

Room Temp

Alcohol (IPA)

Dry

Room Temp

H2O : HF

(10 : 1)

Room Temp

H2O Rinse

Room Temp

H2O : HF

(100 : 1)

Room Temp

Sulfuric Clean; Organics 10 to 1; Oxide Etch

SC 1; Particles SC 2; Surface Metals

100 to 1; Oxide Etch Wafer dry

W. Kern and D.A. Puotinen, Cleaning solutions based on hydrogen peroxide in

silicon semiconductor technology, RCA Rev. 31, 187-206 (1970).

Prof. Milo Koretsky


Cleaning

Individual Cleaning Processes Lets see the purpose of each

of these steps.

Sulfuric Clean(Piranha)

Recipe: H2SO4 /H2O2 /125oC

Removes: Organics

Hydrogen peroxide (H2O2) provides the chemical action for the

sulfuric clean.

H2O2 has two oxygens.

It easily gives up one of its oxygen atoms.

H2SO4H2O2125oC

H2O Rinse

Room Temp

H2O / NH4OH /H2O2(5:1:1)

80oC

H2O Rinse

Room Temp

H2ORinse

H2O / HCl /H2O2(6:1:1)

80oC

H2O Rinse

Room Temp

Alcohol (IPA)

Dry

Room Temp

H2O : HF

(10 : 1)

Room Temp

H2O Rinse

Room Temp

H2O : HF

(100 : 1)

Room Temp

OHO

H Hydrogenperoxide

(H2O2)

OHO

H

(H2O2)H

O

H(H2O )

product formed byusing other oxygen

from H2O2


6/12

Prof. Milo Koretsky


Cleaning

Sulfuric Clean (Piranha) Action: Organics are mainly carbon (C) and hydrogen (H)

Hydrogen peroxide (H2O2) wants to give up one of its

oxygen atoms. It readily produces CO2( g ) and H2O( l ) on

reacting with organics.

CO2( g )

H2O( l )

OHO

H

O

HO

H

C C C

HHOH

O

H

Hydrogen

peroxide

(H2O2)

Organic Impurity OHO

H

Prof. Milo Koretsky


Cleaning

DI Water Rinse Recipe: H2O* / Room Temperature

Removes: Cleaning chemicals

and reaction products from an

earlier wet clean.

Action:

Dissolves chemicals and reaction products

A DI water rinse may also be used to stop the action of

cleaning chemicals.

H2SO4H2O2125oC

H2O Rinse

Room Temp

H2O / NH4OH /H2O2(5:1:1)

80oC

H2O Rinse

Room Temp

H2ORinse

H2O / HCl /H2O2(6:1:1)

80oC

H2O Rinse

Room Temp

Alcohol (IPA)

Dry

Room Temp

H2O : HF

(10 : 1)

Room Temp

H2O Rinse

Room Temp

H2O : HF

(100 : 1)

Room Temp


7/12

Prof. Milo Koretsky


Cleaning

Oxide Etch Recipe: H2O / HF Removes: Oxide (SiO2)

Action:

HF reacts with SiO2 to

make liquid products.

SiO2( s ) + 6HF( l )-> H2SiF6( l )+ 2H2O( l )

The etch rate (or reaction rate of HF with oxide) can be

slowed by adding more water. The lowers the concentration

of HF.

A DI water rinse is used to stop the action of acid after thiscleaning step.

H2SO4H2O2125oC

H2O Rinse

Room Temp

H2O / NH4OH /H2O2(5:1:1)

80oC

H2O Rinse

Room Temp

H2ORinse

H2O / HCl /H2O2(6:1:1)

80oC

H2O Rinse

Room Temp

Alcohol (IPA)

Dry

Room Temp

H2O : HF

(10 : 1)

Room Temp

H2O Rinse

Room Temp

H2O : HF

(100 : 1)

Room Temp

Prof. Milo Koretsky


Cleaning

P-Si

N-SiN-Si

(10:1) Oxide Etch The wafer goes through many processing steps before gate oxide

can be deposited.

A thick layer of poor quality oxide is grown in these steps to help ion

implant.

Now we need to remove this poor quality oxide before we can grow

high quality gate oxide.

This removal is done in the (10:1) Oxide Etch. A high concentration

of HF is used because we have a lot of oxide.

P-Si

N-SiN-Si


8/12

Prof. Milo Koretsky


Cleaning

(100:1) Oxide Etch: Importance The silicon at the bottom of contact holes reacts with oxygen in theair. It forms a thin layer of oxide. This oxide is called native oxide.

We want to remove the native

oxide. This allows the metal to

make a good contact with the

source and drain.

The trick here is:

To remove the oxide at the bottom (native oxide)

Not to remove much of the oxide from the sides of the contact

holes.

This removal is done in the (100:1) Oxide Etch. A low concentrationof HF is used because we dont want to remove oxide from the sides.

Native oxide

Contact hole

Prof. Milo Koretsky


Cleaning

Particle Removal: SC-1 Particles from processing

steps, machinery or handling

can contaminate wafers.

These particles are removed

by the SC-1 clean.

The name of the solution used in this clean is Standard Clean -1

or SC-1 solution. Also called APM or RCA-1.

The cleaning solution is a mixture of five parts de-ionized

water(H2O*), one part ammonium hydroxide (NH4OH ) and one

part hydrogen peroxide(H2O2 ).

H2SO4H2O2125oC

H2O Rinse

Room Temp

H2O / NH4OH /H2O2(5:1:1)

80oC

H2O Rinse

Room Temp

H2ORinse

H2O / HCl /H2O2(6:1:1)

80oC

H2O Rinse

Room Temp

Alcohol (IPA)

Dry

Room Temp

H2O : HF

(10 : 1)

Room Temp

H2O Rinse

Room Temp

H2O : HF

(100 : 1)

Room Temp


9/12

Prof. Milo Koretsky


Cleaning

SC-1 Clean Recipe: H2O / NH4OH / H2O2 80oC(5:1:1)

Removes: Particulates

Action:

This works in two ways

1) By repulsion of like charges

Both the particle and the wafer get negatively charged when

dipped in the solution. The particle is repelled from the surface.

- - - - - - - - - - - - - - - - - -

- - -

- -

Negativelycharged

surface

Negatively

charged particle

moves away

Prof. Milo Koretsky


Cleaning

SC-1 Clean - Electrochemistry!

Prefers

Re

duced

Form

Prefers

Ox id

ized

Form

Reduction Half reaction E0O 3+ 2H

++2e

-O2 +H2 2.07

H 2O2 + 2H+

+2e-2H2O 1.77

Cu2++ 2e

-Cu 0.34

Fe3++ 3e

-Fe -0.17

Ni2++ 2e

-Ni -0.25

Cr3++ 3e

- Cr -0.71

SiO2 + 4H++ 2e

-Si +2H2O -0.84

Mn2++ 2e

-Mn -1.05

Al3++ 3e

-Al -1.66


10/12

Prof. Milo Koretsky


Cleaning

SC-1 Clean2) By chemical actioni) Hydrogen peroxide gives its extra oxygen to the silicon

substrate and makes a thin oxide film;

Si( s ) + 2 H2O2( l )-> SiO2( s )+ 2 H2O( l ).The oxide film lifts the particles.

ii) Ammonium Hydroxide etches the oxide and loosens theparticles; 2NH4OH( l ) + SiO2( s )-> (NH4)2SiO3( l ) + H2O( l )

iii) The loose particles are removed by shaking.

( i ) ( ii ) ( iii )

Substrate

Particle

Prof. Milo Koretsky


Cleaning

Surface Metal Removal: SC-2 Surface metal contaminants

are first oxidized

They are then removed by

reaction with hydrochloric

acid.

The name of the solution used in this clean is Standard Clean -2

or SC-2 solution. Also called HPM or RCA-2.

The cleaning solution is a mixture of six parts de-ionized

water(H2O*), one part hydrochloric acid (HCl) and one part

hydrogen peroxide(H2O2 ).

H2SO4H2O2125oC

H2O Rinse

Room Temp

H2O / NH4OH /H2O2(5:1:1)

80oC

H2O Rinse

Room Temp

H2ORinse

H2O / HCl /H2O2(6:1:1)

80oC

H2O Rinse

Room Temp

Alcohol (IPA)

Dry

Room Temp

H2O : HF

(10 : 1)

Room Temp

H2O Rinse

Room Temp

H2O : HF

(100 : 1)

Room Temp


11/12

Prof. Milo Koretsky


Cleaning

SC-2 Clean - Electrochemistry!

Prefers

Re

duced

Form

Pr

efers

Ox

idized

Fo

rm

Reduction Half reaction E0

O 3+ 2H+

+2e-O2 +H2 2.07

H 2O2 + 2H+

+2e-2H2O 1.77

Cu2++ 2e

-Cu 0.34

Fe3++ 3e

-Fe -0.17

Ni2++ 2e

-Ni -0.25

Cr3++ 3e

- Cr -0.71

SiO2 + 4H++ 2e

-Si +2H2O -0.84

Mn

2+

+ 2e

-

Mn -1.05

Al3++ 3e

-Al -1.66

Prof. Milo Koretsky


Cleaning

SC-2 Clean Recipe: H2O / HCl / H2O2 80

oC

(6:1:1)

Removes: Surface metal ions

Action:

hydrochloric acid reacts with the ions and removes them.

Al +++Cl -

Cl -

Cl-

Chloride ions from HCl react with

aluminum ion and carry it away


12/12

Prof. Milo Koretsky


Cleaning

Vapor Dry Recipe: Isopropyl Alcohol (IPA)

Removes: water from wafers

Action:

Alcohol vapors displace

water from surface

IPA Vapors

Drop of

water

IPA displaces water IPA evaporates

The alcohol evaporates more easily than water. It leaves a dry surface

H2SO4H2O2125oC

H2O Rinse

Room Temp

H2O / NH4OH /H2O2(5:1:1)

80oC

H2O Rinse

Room Temp

H2ORinse

H2O / HCl /H2O2(6:1:1)

80oC

H2O Rinse

Room Temp

Alcohol (IPA)

Dry

Room Temp

H2O : HF

(10 : 1)

Room Temp

H2O Rinse

Room Temp

H2O : HF

(100 : 1)

Room Temp

Prof. Milo Koretsky


Cleaning

3. Gettering

Metals:

Traps on back

or in bulk

Alkali ions:

Dielectric layer

on topside SiO2 Precipitates

Damage induced

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