SEMINAR PRESENTATIONON

IC FABRICATION PROCESS

PREPARED BY: GUIDED BY:

VAIBHAV RAJPUT(12BEC102) Dr. USHA MEHTA

SOURABH JAIN(12BEC098)

CONTENTS

• PROCESS OVERVIEW

• DETAILED EXPLANATION OF EACH STEP

• REFERENCES

PROCESS IN THE “REAL SENSE”

HOW DO THEY DO IT ?

• Si used for crystal growth is purified from SiO2 (sand) through refining, fractional distillation and CVD.

• The raw material contains < 1 ppb impurities. Pulled crystals contain O (» 1018 cm-3) and C (» 1016 cm-3), plus any added dopants placed in the melt.

• Essentially all Si wafers used for ICs today come from Czochralski grown crystals.

• Polysilicon material is melted, held at close to 1417 °C, and a single crystal seed is used to start the growth.

• Pull rate, melt temperature and rotation rate are all important control parameters.

CZOCHRALSKI PROCESS

HERE SIZE DO MATTER !

• <100> p-type is used for IC fabrication

• Wafer: 10 cm to 30 cm (~4 to ~12 inches) and 1 mm thick.

OXIDE GROWTH• Oxidation layering

-> Creates a layer of SiO2 for insulation.

• Wet Oxidation uses water vapour and Dry Oxidation uses high-purity oxygen and hydrogen at ~1000 degrees C.

• SiO2 growth consumes silicon, grows into the substrate.

• SiO2 is twice the volume of Si, projects above the substrate as well.

• Etched Field Oxide Isolation

• First grow field oxide and then create active regions (where transistors will be created) by etching

• LOCOS (Local Oxidation of Silicon)

• First define active regions and then grow the oxide layers in remaining areas

• Fabricate thin SiO2 layer adjacent to THICK SiO2 layers.

• Transition from THICK to thin SiO2 layers fabricated WITHOUT creating sharp vertical transitions.

SPINNING OF ORGANIC COATING

• Photoresist coating : A light-sensitive polymer (latex) is evenly spread (thickness 1 mm) by spinning the wafer.

• Negative photoresist: Unexposed photoresist soluble in organic solvent, light exposure causes cross-linking making exposed regions insoluble.

• Positive photoresist: Originally insoluble, exposure makes it soluble. Positive photoresist has higher resolution compared to negative resolution

n-Type Si

n-Type Si

SiO2

n-Type Si

SiO2 photoresist

n-Type Si

SiO2 photoresist

UV-light

MASK

ETCHING• Wet etching

• Material is selectively removed from areas that are not covered by photoresist using acids, bases and caustic solutions.

• Chemicals used here can be very dangerous to humans and the environment.

• Hydrofluoric acid (HF) is used for SiO2.

• Dry etching or plasma etching

• popular.

• Here, wafer is given a negative charge in a chamber heated to 100 degrees C under vacuum.

• A positively charged plasma is introduced (usually a mix of nitrogen, chlorine and boron trichloride).

• Rapidly moving plasma causes a chemical sandblasting action in the well defined direction of the electric field.

• Clean vertical cuts can be etched using this method.

• Sputtering (a)

• Wet etching: by chemical like HF acid (b)

• Dry etching : by plasma

• Ion enhanced energetic (c)

• Ion-enhanced-inhibitor(d)

n-Type Si

SiO2 photoresist

n-Type Si

SiO2

photoresist

n-Type Si

SiO2

THE NEXT BIG Q

WHAT ARE THE METHODS OF INSERTING IMPURITY ATOMS INTO Si SUBSTARTE ?

THE ANSWER IS-

1)Diffusion (impurity applied at Si surface, high temperature and long time, control of doping concentration not very precise)

2)Ion implantation (impurity applied by scanning a high energy focussed ion beam at Si surface, low temperature, acceleration, precise control of doping concentration)

n-Type Si

SiO2 p-Type BORON

n-Type Si

p-Type BORON

LITHOGRAPHY TECHNIQUES

FUTURE AGENDA

• 3-D IC FABRICATION PROCESS

• 3-D PHOTOLITHOGRAPHY

• CURRENT TRENDS IN FABRICATION

• SOI-THE TECHNOLOGY OF FUTURE

• BLOG ON HOW IT IS MADE?

REFERENCES

• CMOS FABRICATION PROCESS BY Dr. USHA MEHTA

• IC FABRICATION PROCESS- INTEL CORPORATION

• IC FABRICATION PROCESS ANIMATION- www.ewebpal.org

• PHTOLITHOGRAPHY- www.movie.diginfo.tv

• HOW WE MAKE OUR PRODUCTS BY LEXAR

• HOW PROCESSORS ARE MADE FROM MICROCHIPS- www.green-translation-service.de

THANK YOU