Page 1 NSF STC Polymers Used in Microelectronics and MEMs An Introduction to Lithography

Page 1 NSF STC

Polymers Used in Microelectronics

and MEMs

An Introduction to An Introduction to

LithographyLithography

Polymer SynthesisCHEM 421

Integrated Circuits


Micro-electro-mechanical Devices (MEMS)


Moore’s Law

Year Processor Transistor MinimumName Count Feature size

1971 4004 2300 10 micron1972 8008 3500 10 micron1974 8080 6000 6 micron1976 8085 6500 3 micron1978 8086 29000 3 micron1982 80286 134,000 1.5 micron1985 80386 275,000 1.5 micron1989 Intel486 1.2 million 1 micron1993 Pentium 3.1 million 800 nanometer1997 Pentium II 7.5 million 350 nanometer1999 (Feb.) Pentium III 9.5 million 250 nanometer1999 (Oct.) Pentium III 28 million 180 nanometer2000 Pentium IV 42 million 130 nanometerSource: Intel


Industry Road Map


The Drivers in Microelectronics

• Cost: more for less!

–$1000 bought:$1000 bought: 16MB in 199316MB in 1993

1000MB in 20001000MB in 2000

–A single transistor costs about the same as a A single transistor costs about the same as a single printed word in a local newspapersingle printed word in a local newspaper

AMD Athlon chip Local Newspaper

22 million transistors 80 pages x 1600 words per page

$200 $0.50

J. Phys. Org. Chem. 2000, 13, 767.


The Drivers in Microelectronics

• Size– Wafer processing time independent of Wafer processing time independent of

feature dimensionfeature dimension

»Printing smaller features or larger wafers allows a greater number of devices to be made in the same amount of time, improving manufacturing yields

• Speed

–Smaller feature sizes also improve computing speeds by decreasing the travel distance of electrical signals


Example – A State-of-the-Art $5 Billion Fab Line

The Chip-making Process

Up to 20X

1 Time

Polymer SynthesisCHEM 421Semiconductor Manufacturing


Silicon Substrate

• Expose

• Strip

• Etch

• Develop

• Bake

• Spin Coat

Process can be repeated up to 30 times: Solvent Intensive!

Photolithographic Process


Imaging Process

Handbook of Microlithography, Micromachining and Microfabrication v. 1, P. Rai-Choudhury, ed. SPIE Optical Engineering Press, 1997.


Photolithographic Process

J. Phys. Org. Chem. 2000, 13, 767.

Coat

Exposure

Develop

Strip

Etch

Photoresist

Substrate

Maskh

PositiveNegative


Important Properties of a Photoresist

• Resist Thickness (etch resistance)Resist Thickness (etch resistance)

• Solubility for deposition/developmentSolubility for deposition/development

• WettabilityWettability

• Lithographic performanceLithographic performance

–Sensitivity, contrastSensitivity, contrast

• TransparencyTransparency(more important for 193 nm and beyond)(more important for 193 nm and beyond)


Optics of Imaging

R = resolution = smallest feature sizeR / NA

• is the wavelength of light• NA is the numerical aperture (a function of the optics)

Magic!!!!! (aka phase shifting masks…)Magic!!!!! (aka phase shifting masks…)

Wavelength Wavelength 365 nm 248 nm 193 nm 157 nm

NotationNotation i-line DUV 193 nm 157 nm

mercury KrF ArF F2 excimer Source Source lamp excimer excimer laser laser laser

Feature Size Feature Size 365+ nm 500 - 100 nm 130 - 70 nm* 90 - 45 nm*

Polymer SynthesisCHEM 421“Transitions” in Optical Lithography

365 nm365 nm


G- and I-line Resists

• Novolac resinNovolac resin– Base-soluble positive resist (TMAH)Base-soluble positive resist (TMAH)– Variety of structures and MW’sVariety of structures and MW’s

• Diazonapthaquinone (DNQ)Diazonapthaquinone (DNQ)– Photoactive compound (Wolfe Rearrangement)Photoactive compound (Wolfe Rearrangement)– Inhibits base-dissolution of novolacInhibits base-dissolution of novolac

OH

CH3

OH

CH3

CH2

O

N2

R

O

R R

C

O

H2O

R

CO2H

h

-N2


G- and I-line ResistsD

isso

luti

on

Ra

te(n

m/s

ec)

1,000 —

100 —

10 —

1 —

0.1 —

novolacresin

novolacresin &

photocatalysis products

novolacresin &

DNQ


• An “engineer’s approach”An “engineer’s approach”

• Fast NFast N22 outgassing can damage the resist film outgassing can damage the resist film

–Controlled by using a less-intense light source or a less sensitive resist

• Wavelength limited resolution (350 nm)

• Low contrast (competitive rates of dissolution)

G- and I-line Resists

Polymer SynthesisCHEM 421“Transitions” in Optical Lithography

365 nm365 nm

248 nm248 nm


Evolution from I- and G-Line to 248 nm (DUV)

• Demand increases for smaller features:Demand increases for smaller features:

R / NA

• Diazoquinone novolac photoresists lacked Diazoquinone novolac photoresists lacked sensitivity at 248 nmsensitivity at 248 nm

• Introduced at 0.365 micron (365 nm)Introduced at 0.365 micron (365 nm)


Motivation for Chemical Amplification

• Challenges Encountered:Challenges Encountered:

– First exposure tools for 248 nm had low First exposure tools for 248 nm had low output intensityoutput intensity

– Need increased sensitivity to avoid use of Need increased sensitivity to avoid use of extremely bright sources, which are extremely bright sources, which are expensiveexpensive

• Chemical amplification invented Chemical amplification invented (Frechet, Willison and Ito)(Frechet, Willison and Ito)

Exposure to photons initiates a chain reaction or promotes a cascade of reactions (500-1000) that changes resist solubility in exposed regions


Chemical Amplification

• DUV exposure generates DUV exposure generates catalytic amount of acid catalytic amount of acid from a photoacid generator from a photoacid generator (PAG)(PAG)

• 1-2 min PEB to trigger 1-2 min PEB to trigger deprotectiondeprotection

• Catalytic chain length is Catalytic chain length is extremely longextremely long

– About 500 - 1000 About 500 - 1000 carbonate cleavages carbonate cleavages per protonper proton

J. Phys. Org. Chem. 2000, 13, 767.Acc. Chem Res. 1994, 27, 150.

CH CH2

O

O

O

H+

CH CH2

O

O

O

CH CH2

O

OH

O

H+

CH CH2

OH

C

O

OH

H+


Photoacid Generators (PAG)

2,6-Dinitrobenzyl tosylate New fluorinated PAGs

NO2

NO2

CH2O S

O

O

CH3

I B

F3C

F3C

F3C CF3

CF3

CF3

CF3F3C


Ionic PAG Mechanism

Photolysis of diaryliodonium salts

Crivello, J. V.; Lam, J. H. W.; M acromolecules. 1977, 10, 1307-1315.

I2

CF3

CF3

B4

Diphenyliodonium tert-(3,5-bis(trif luoromethyl) phenyl boronium

hvI

2

CF3

CF3

B4

*

I + +CF3

CF3

B4

I + S HI SH +I H+S= solvent, polymer, or other compounds


2-Nitrobenzyl Ester PAG Mechanism

o-Nitrobenzyl Rearrangement

N+ O–

O

O Ts

H

OTs

N

OTs

OH

ON

HO

ON

HO S

O

O

h

Reichmanis, E.; Smith, B. C.; Gooden, R.J . Polym. Sci.: Polym. Chem. Ed. 1985, 23, 1

N O

HO

OTs

O

O

CH3+

Sulfonic acid

R R R

RR

R= NO2 or CF3


DUV Resists

Levinson, Harry J. Principles of Lithography. SPIE Press, 2001.

Extremely high contrast

Initial resistance inmanufacturing setting

Applicable at i-line with sensitizers

Documents

Page 1 NSF STC Polymers Used in Microelectronics and MEMs An Introduction to Lithography