YoHan Kim

 Thin Film  Layer of material ranging from fractions of nanometer to several micro meters in thickness  Thin Film Process  Process to make thin film on a substrate

 Thermal oxidation  Physical Vapor Deposition  Vaporized material bombards onto substrate, i.e. Si wafer.  Chemical Vapor Deposition  Gaseous material reacts on substrate to form thin film

 Vacuum deposition  Evaporation of material required  More expensive, but high quality  Sputtering is widely used  Aluminum, Titanium, Titanium nitrate, Tungsten silicide

 Gas form of material goes under chemical reaction with substrate to form thin film  Remnant gas remains after reaction  Fast, cheap, but poor quality  Forms variety of thin film

 Process to make patterns on a wafer  Removes unwanted area of thin film deposited in previous stage

 Key of Photolithography, called PR  Type of organic material  Very sensitive to UV

 Two types of photoresist  Positive: Exposed PR is removed  Negative: Exposed PR remains

 Wet Etching uses chemicals  Dry Etching uses plasma

 Photoresist is organic material  Must be stripped off after etching

 Sometimes the surface has to be flattened after removing PR  Mechanically polished

 Fabricating nanoscale device is repetition of thin film process and photolithography  Up to 20~30 cycles are repeated  Each layer of semiconductor requires at least 2 photolithography masks

 Extreme UV lithography  X-Ray Lithography  LIGA(x-ray lithographie galvanoformung abformtechnik), German acronym which means “x-ray lithography electro- deposition moding  LIGA is good in 3D fabrication  Photolithography will not be abandoned