Simple description about the Photo-lithography process.

1. PHOTOLITHOGRAPHY

2. CONTENTS
 INTRODUCTION
 DEFINITION
 STEPS INCLUDED
 EXPLAINING THE PROCESS
 APPLICATIONS

3. INTRODUCTION
 Photolithography, also termed optical lithography
or UV lithography, is a process used in micro
fabrication
 It uses light to transfer a geometric pattern.

4. DEFINITION
 Photolithography is the process of transferring
the geometrical patterns from a mask to the
semiconductor material (silicon wafer) using the
UV Radiation.

5. STEPS INCLUDED...
 Spin coating with Photoresist.
 Exposure to the Radiation.
 Developing
 Etching
 Stripping

6. STEPS

7. PHOTORESIST
 Photoresist is an organic polymer which
changes its chemical structure when
exposed to the sensitive radiation.
 Example: Poly(methyl glutarimide)
(PMGI)

8. SPIN COATING
 The Si wafer is placed on the rotating
platform or chuck and held via vacuum
suction
 Resist is poured onto the wafer, the wafer
spins at a high speed (more than thousand
rpm’s)
 The speed determines the thickness of the
coated resist

9. SPINNING

10. EXPOSURE TO THE
RADIATION
 Exposure to the UV Radiation through a
mask, changes the property of the
photoresist. i.e., exposed region of resist
get softened or hardened, depending on
the type of the resist.

11. EXPOSURE ARRANGEMENT

12. DEVELOPING
 After exposure, the wafer or the substrate is
soaked in a developer solution
 This helps in removal of the softened regions
of the photoresist
 After developing we are left with the
photoresist of the same pattern as its on the
mask

13. AFTER DEVELOPING

14. ETCHING
 After developing, the wafer or the substrate
is soaked in a chemical bath or etchant
 This removes the oxide parts of the
substrate, from where the Photoresist was
removed previously
 Now we are left with the needed pattern,
etched on the substrate

15. AFTER ETCHING

16. STRIPPING
 Now, remove all the photoresist by
soaking the etched Si wafer in a
photoresist removal solution.

17. AFTER STRIPPING

18. APPLICATIONS
 IC patterning process
For transistors
For Op-Amps
For Logic Gates
 Patterning Printed electronic boards

19. REFERENCES
 Lecture - 23 Lithography - I - YouTube [Online] // Dr. Nandita
Dasgupta , Department of Electrical Engineering, IIT Madras. -
https://www.youtube.com/watch?v=v9eGO5OjC8A.
 Linear Integrated Circuits [Book] / auth. D. Roy Chaudhury and
Shail B. Jain : New Age International (P) Limited, 2003.
 Physics of Semiconductor Devices [Book] / auth. Colinge J-P &
Colinge C A. - London : KLUWER ACADEMIC PUBLISHERS.