Lithography, the fundamental fabrication process of semiconductor devices, is playing
a critical role in micro- and nano-fabrications and the revolution in high density integrated
circuits. Traditional optical lithography (photolithography) including contact and project
photolithography has contributed significantly to the semiconductor device advancements.
As the resolution requirement increases for fabrication of finer and smaller components and
devices, the technological dependence on photolithography becomes a serious problem
since the photolithography resolution is restricted by the diffraction limitation of optics.
Reducing the light wavelength from blue to near ultraviolet (UV) and to deep UV is
expected to improve the photolithography resolution, but it is far not enough to catch up
with the pace in resolution demand in integrated circuit fabrication.
To overcome the limitation of photolithography, several advanced lithography
techniques have emerged including maskless laser direct write lithography to eliminate the
needs of photo masks, gray-scale lithography to increase the aspect ratio of the lithographic
features, immersion lithography to increase the numerical aperture of the focusing optics
and thus the resolution, and lithographic techniques based on further reducing wavelengths
for better resolution such as extreme ultraviolet (EUV) lithography and X-ray lithography.
The uses of particle waves like electrons and ion beams have resulted in high resolution
electron beam (E-beam) lithography and ion beam lithography. Besides these wave and
beam based lithographic techniques, there are also direct contact lithography such as soft
lithography using soft molding and nanoimprint lithography with extremely high
resolution. The plasmonic lithography is now in the horizon.
This book is the result of inspirations and contributions from many researchers
worldwide. Although the inclusion of the book chapters may not be a complete
representation of all lithographic arts, it does represent a good collection of contributions in
this field. We hope readers will enjoy reading the book as much as we have enjoyed
bringing the book together. We would like to thank all contributors and authors of book
chapters who entrusted us with their best work. We also acknowledge the great effort of
people who had invested their time in reviewing manuscripts and revision updates.
Each lithographic technique has its advantages and limitations. The conventional
photolithography is not discussed here due to its technological maturity. This book begins
with maskless, gray-scale, and immersion lithography since they are most close to the
conventional photolithography in terms of resolution. Laser nonlinear lithography with
capability of non-flat surface fabrication and character projection lithography are also
included in this chapter. Further chapters present discussion on objective lens, resist
materials and processing, and optical proximity correction.
