photolithography steps, masking, printing techniques, photo resists (positive and negative), methods of application.

1. PHOTOLITHOGRAPHY
Neha Sharma
Assistant Professor
Department of Electronics and Communication Engineering
Engineering College Jhalawar (Rajasthan)

2. SYLLABUS
■ INTRODUCTION TO IC TECHNOLOGY- Semiconductor Substrate- Crystal defects, Electronic Grade
Silicon, Czochralski Growth, Float Zone Growth, Characterization & evaluation of Crystals; Wafer
Preparation- Silicon Shaping, Etching and Polishing, Chemical cleaning.
■ DIFFUSION & OXIDATION - Ficks diffusion Equation in One Dimension, Atomic model, Analytic
Solution of Ficks Law, correction to simple theory, Diffusion in SiO2. Ion Implantation and Ion
Implantation Systems. Oxidation Growth mechanism and Deal-Grove Model of oxidation, Linear and
Parabolic Rate co-efficient, Structure of SiO2, Oxidation techniques and system, Oxide properties.
■ CHEMICAL VAPOUR DEPOSITION AND EPITAXIAL LAYER GROWTH- CVD for deposition of
dielectric and polysilicon thick Layer – a simple CVD system, Chemical equilibrium and the law of mass
action, Introduction to atmospheric CVD of dielectric, low pressure CVD of dielectric and semiconductor.
Epitaxy-Vapour Phase Expitaxy, Defects in Epitaxial growth, Metal Organic Chemical Vapor Deposition,
Molecular beam epitaxy.
■ PATTERN TRANSFER & ETCHING - Introduction to photo/optical lithography, Contact/ proximity
printers Projection printers, Mask generation, photo resists. Dry & Wet etching, methods for anisotropic
etching, Plasma etching, Reaction ion etching (RIE).
■ VLSI PROCESS INTEGRATION- Junction and Oxide Isolation, LOCOS methods, Trench Isolation,
SOI; Metallization, Planarization. Fundamental consideration for IC Processing, NMOS IC Technology,
CMOS IC Technology, Bipolar IC Technology. Fault diagnosis and characterization techniques.

3. SYLLABUS
■ INTRODUCTION TO IC TECHNOLOGY- Semiconductor Substrate- Crystal defects, Electronic Grade
Silicon, Czochralski Growth, Float Zone Growth, Characterization & evaluation of Crystals; Wafer
Preparation- Silicon Shaping, Etching and Polishing, Chemical cleaning.
■ DIFFUSION & OXIDATION - Ficks diffusion Equation in One Dimension, Atomic model, Analytic
Solution of Ficks Law, correction to simple theory, Diffusion in SiO2. Ion Implantation and Ion
Implantation Systems. Oxidation Growth mechanism and Deal-Grove Model of oxidation, Linear and
Parabolic Rate co-efficient, Structure of SiO2, Oxidation techniques and system, Oxide properties.
■ CHEMICAL VAPOUR DEPOSITION AND EPITAXIAL LAYER GROWTH- CVD for deposition of
dielectric and polysilicon thick Layer – a simple CVD system, Chemical equilibrium and the law of mass
action, Introduction to atmospheric CVD of dielectric, low pressure CVD of dielectric and semiconductor.
Epitaxy-Vapour Phase Expitaxy, Defects in Epitaxial growth, Metal Organic Chemical Vapor Deposition,
Molecular beam epitaxy.
■ PATTERN TRANSFER & ETCHING - Introduction to photo/optical lithography, Contact/ proximity
printers Projection printers, Mask generation, photo resists. Dry & Wet etching, methods for anisotropic
etching, Plasma etching, Reaction ion etching (RIE).
■ VLSI PROCESS INTEGRATION- Junction and Oxide Isolation, LOCOS methods, Trench Isolation,
SOI; Metallization, Planarization. Fundamental consideration for IC Processing, NMOS IC Technology,
CMOS IC Technology, Bipolar IC Technology. Fault diagnosis and characterization techniques.

6. Lithographic Transfer Process

7. Lithographic Transfer Process

8. Lithographic processing

10. Photomask
■ Masks are made from glass emulsion
plates like the Kodak high-resolution
plate (HRP). or glass covered with a hard
surface material. Emulsion masks are
the least expensive, but they are usually
only used with feature sizes in the 5 μm
region.
■ All e-beam generated masks are made
with hard-surface materials such as
chromium, chromium oxide, iron oxide,
or silicon. These masks are more
expensive than emulsion but features in
the 1 μm region can be defined on them.

11. Glass IC photomask

12. Photo resist
■ Photoresist is an organic polymer which becomes
soluble/insoluble when exposed to ultraviolet light. It contains a
light-sensitive substance whose properties allow image transfer
onto a substrate. Using photoresist prevents etching or plating of
the area it covers (this is also known as resist).
■ Types : Positive and Negative
■ Composition:
o Polymers
o Solvents
o Sensitizers
o Additives

13. Positive and Negative Resist
■ Positive PR : After exposure to the proper light energy, the
polymers are converted into a more soluble state. Ex.
diazonaphthaquinone (DNQ)
■ Negative PR: After exposure to proper light energy, the
polymers are converted into a less soluble state. Ex. Methyl
methacrylate.

16. Application of Photo resist
Spin
coating
Soft baking
convection Oven
 Vaccum Oven
 Hot Plate
 Microwave and
IR lamps
Exposure

17. OPTICAL PHOTOLITHOGRAPHY
Contact printing Proximity Printing Projection Printing

18. Contact Printing Proximity Printing Projection Printing

19. Developers
 Negative developer
• xylene • Rinser: n-butyl •
 Positive developer
• NaOH, KOH, TMAH • Rinser: DI water •
 Problems – Incomplete development (leave a thin resist
layer) – Over development (too much edge removed)
 Immersion development
 Spray Development
 Check for pattern, misalignment and surface issues.

21. Photoresist Removal
■ Want to remove the photoresist and any of its residues
■ Positive PR: • Acetone, • solvents
■ Negative PR: • CH3COC2H5 (MEK), • CH4COC4H9 (MIBK)

22. Advanced Lithography
■ To get very high resolution (minimum feature size)
■ Electron Beam Lithography ( feature size 0.25-0.1 )
■ Ion Beam Lithography ( feature size 0.05-0.1 )
■ X Ray Lithography ( feature size <0.1 )

23. E-Beam Lithography
• PR :PMMA Polymethylmethacrylate,
PBS poly(butene-l sulfone),
• Developer : Methyl-isobutyl-ketone
(MIBK)
Advantages
Print complex patterns directly on
wafers
Eliminates the diffraction problem
High resolution up to 20
nm(photolithography ~50nm)
Disadvantages
Slower than optical lithography.
Expensive and complicated Forward
scattering Backscattering
Secondary electrons

24. Ion Beam Techniques
■ Less scattering
■ Secondary electrons produced
have less energy
■ More fast than EBL.
■ RF ion Source is used
Disadvantages:
• Large size apparatus
• Prone to vibrations
• Fine focusing required
• Applications limited to
mask repairs and making
small cuts and vias.