Advanced Photoresist TechnologyAdvanced Photoresist Technology

Jie Sun

EE 518

Instructor: Dr. Jerzy Ruzyllo

Apr. 4 2006

Presentation outlinePresentation outline

Introduction of Photoresists

Roadmap of Photoresist Technology

Photoresists Solution for Submicron

lithography

Summary

Introduction of Photoresists

Photoresists Type: Positive: exposed regions dissolve (best resolution) Negative: Unexposed regions dissolve ( Swelling)

Photoresists Structure:

Resin: a binder that provides mechanical properties (adhesion, chemical resistance) Solvent: used to dissolve the resin, allowing the resin to be applied in a liquid state Photoactive Compound (PAC): Act to inhibit or promote the dissolution of the

resin in the developer. PAC inhibits dissolution in positive resists before light

exposure. After exposure the PAC promotes dissolution of the resin.

* George Tech, “Photoresists and Non-optical Lithography”

Photoresists Chemistry (1) Positive Photoresist

Two-component DQN resists:

DQN, corresponding to the photo-active compound, diazoquinone (DQ) and resin,

novolac (N) Dominant for G-line (436nm) and I- line (365nm) exposure and not suitable for very

short wavelength exposures Novolac (N): a polymer whose monomer is an aromatic ring with two methyl groups

and an OH group. dissolves in an aqueous solution easily

Diazoquinone(DQ)

20-50 % weight Photosensitive DQ

UV Carboxylic acid ( dissolution enhancer)

*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.

Photoresists Chemistry (2)

Positive Photoresist

1. DQ molecule will not dissolve in a base developer solution (pH >7).

2. UV light breaks the nitrogen molecule off forming an unstable molecule

3. To “stabilize” itself, one of the 6 carbon atoms in the ring pops out of the ring (leaving 5)

4. Once exposed to water (a developer /water mixture), an OH group attaches to the carbon atom, forming an acid.

5. The acid can then react and dissolve with the basic developer solution.

Advantage:

Unexposed areas unchanged by the presence of the developer, line width and shape of a

pattern precisely retained.

Novolac fairly resistant chemical attack, a good mask for the subsequent plasma etching

Resolution (um) - linearity/ minimum

Sensitivity (mJ/cm2)

Focus margin (um)

Exposure margin (%)

Dry etch resistance(X)

Heat resistance

Adhesion

Standing wave effect (and bulk effect)(um)

BARC (bottom anti-reflective coating) compatibility

Process margin/stability

Shelf-life

Performance of Photoresists

Photoresists Profile

* Han Ku Cho, Samsung Electronics Co., Ltd, “Lithography technology review of what it is and what to be”, March 2003

Roadmap of Photoresists Technology

* Han Ku Cho, Samsung Electronics Co., Ltd, “Lithography technology review of what it is and what to be”, March 2003

Deep UV Photoresist

 

Limitation of Novolac based Photoresist

Strongly absorb below 250nm, KrF (248nm) marginally acceptable but not ArF (193nm)

Photoresist Solution for Submicron Features

PMMA

PAGs ( Photoacid generator) replace PAC

Contrast enhancement layers (CELs)

Inorganic resist (Ag-doped Ge-Se)

Silicon-containing resists (dry developable)

Multi-layer photoresist

PMMA (Ploymethyl methacrylate)

 

Short-wavelength lithography: deep UV, extreme UV, electron-beam lithography

Resin itself is photosensitive

Advantage: high resolution

Disadvantage:

Plasma etch tolerance is very low and thick PMMA to protect the thin film

Dissociation changes chemistry of the plasma etch and polymeric deposits on the

surface of the substrate.

Low sensitivity: Add PAG (chemically reactive dissociating) or elevate exposure

temperature

*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.

Contrast enhance layers (CELs)

 

CEM photo-bleachable

Spun onto the DQN PR after softbake

Formed in-situ “conformal contact mask”

Enhanced contrast

Important for DUV resists with less optical intense and PR radiation absorbtion

* http://www.microsi.com/photolithography/data_sheets/CEM%20365iS%20Data%20Sheet%

Inorganic Resist

 

Advantage:

High contrast γ ≈ 7

Produce fine line

Process: Ag-doped Ge-Se

Ag plated on sputtered Ge-Se

Photodoping create Ag2Se after exposure

Dissolved in alkaline solution

Disadvantage:

Require thick planarizing underlayer due to

thin film nature

Pineholes and defects from Ge-Se

*Stephen A. Campbell, “ The Science and Engineering of Microelectronic Fabrication”.

Dry developable: Polysilynes

 

Bi-layer process

Silicon-containing resists on top of novolac based resist

Highly resistant to plasma process

Bleaching under DUV exposure due to cross-linked siloxane network

Etch silicon selectively to silicon dioxide in HBr plasma

* Roderick R. Kunz, et al, “193 nm Resists and Lithography”, Polymers for Advanced Technologies, Volume 5, p p.12-21

Multi-layer Resists and Hard mask

 

Tri-layer process

Thin layer PR + SiO2 +

thicker planarizing

Oxide layer act as hard mask

Oxide layer: Dry etching

resistant layer

*E.Ong and E.L.Hu, “Multilayer Resists for Fine Line Optical Lithography,” Solid State Technol.

Process Comparison for SLR, BLR and MLR

* Han Ku Cho, Samsung Electronics Co., Ltd, “Lithography technology review of what it is and what to be”, March 2003

Summary

Photoresists technology: Basic and key technology in lithography

PR chemistry structure changed with wavelength of light source

Several PR solutions for DUV application

Multi-layer PR replace the single layer for Sub-100nm features