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Polymers Used in Microelectronics and MEMs. An Introduction to Lithography. Integrated Circuits. Micro-electro-mechanical Devices (MEMS). Moore’s Law. Year Processor Transistor Minimum Name Count Feature size 1971 4004 2300 10 micron 1972 8008 3500 10 micron

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polymers used in microelectronics and mems

Polymers Used in Microelectronicsand MEMs

An Introduction to

Lithography

moore s law
Moore’s Law

Year Processor Transistor Minimum

Name Count Feature size

1971 4004 2300 10 micron

1972 8008 3500 10 micron

1974 8080 6000 6 micron

1976 8085 6500 3 micron

1978 8086 29000 3 micron

1982 80286 134,000 1.5 micron

1985 80386 275,000 1.5 micron

1989 Intel486 1.2 million 1 micron

1993 Pentium 3.1 million 800 nanometer

1997 Pentium II 7.5 million 350 nanometer

1999 (Feb.) Pentium III 9.5 million 250 nanometer

1999 (Oct.) Pentium III 28 million 180 nanometer

2000 Pentium IV 42 million 130 nanometer

Source: Intel

the drivers in microelectronics
The Drivers in Microelectronics
  • Cost: more for less!
    • $1000 bought:16MB in 1993

1000MB in 2000

    • A single transistor costs about the same as a single 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 microelectronics1
The Drivers in Microelectronics
  • Size
    • Wafer processing time independent of feature 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
slide8

The Chip-making Process

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

Up to 20X

1 Time

photolithographic process
Photolithographic Process
  • Spin Coat
  • Expose
  • Bake
  • Develop

Silicon Substrate

  • Etch
  • Strip

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

imaging process
Imaging Process

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

photolithographic process1
Photolithographic Process

Photoresist

Substrate

Coat

Mask

h

Exposure

Negative

Positive

Develop

Etch

Strip

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

important properties of a photoresist
Important Properties of a Photoresist
  • Resist Thickness (etch resistance)
  • Solubility for deposition/development
  • Wettability
  • Lithographic performance
    • Sensitivity, contrast
  • Transparency(more important for 193 nm and beyond)
optics of imaging
Optics of Imaging

Wavelength 365 nm 248 nm 193 nm 157 nm

Notation i-line DUV 193 nm 157 nm

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

Feature Size 365+ nm 500 - 100 nm130 - 70 nm* 90 - 45 nm*

R = resolution = smallest feature size

R   / NA

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

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

g and i line resists
G- and I-line Resists
  • Novolac resin
    • Base-soluble positive resist (TMAH)
    • Variety of structures and MW’s
  • Diazonapthaquinone (DNQ)
    • Photoactive compound (Wolfe Rearrangement)
    • Inhibits base-dissolution of novolac

h

-N2

g and i line resists1
G- and I-line Resists

novolacresin &

photocatalysis products

novolacresin &

DNQ

1,000 —

100 —

10 —

1 —

0.1 —

Dissolution Rate

(nm/sec)

novolacresin

slide18

G- and I-line Resists

  • An “engineer’s approach”
  • Fast N2 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)
evolution from i and g line to 248 nm duv
Evolution from I- and G-Line to 248 nm (DUV)
  • Demand increases for smaller features:R   / NA
  • Diazoquinone novolac photoresists lacked sensitivity at 248 nm
  • Introduced at 0.365 micron (365 nm)
motivation for chemical amplification
Motivation for Chemical Amplification
  • Challenges Encountered:
    • First exposure tools for 248 nm had low output intensity
    • Need increased sensitivity to avoid use of extremely bright sources, which are expensive
  • Chemical amplification invented (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
Chemical Amplification
  • DUV exposure generates catalytic amount of acid from a photoacid generator (PAG)
  • 1-2 min PEB to trigger deprotection
  • Catalytic chain length is extremely long
    • About 500 - 1000 carbonate cleavages per proton

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

Acc. Chem Res.1994, 27, 150.

slide23

Photoacid Generators (PAG)

2,6-Dinitrobenzyl tosylate

New fluorinated PAGs

slide24

Ionic PAG Mechanism

Photolysis of diaryliodonium salts

slide25

2-Nitrobenzyl Ester PAG Mechanism

o-Nitrobenzyl Rearrangement

duv resists
DUV Resists

Extremely high contrast

Initial resistance inmanufacturing setting

Applicable at i-line with sensitizers

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

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