Lithography Glossary

Written by Chris Mack
Brought to you by the creators of PROLITH

E-beam Lithography
see Electron Beam Lithography

EBR
see Edge Bead Removal

Edge Bead
A build-up of resist along the outer edge of a wafer caused by resist surface tension during the spin coat process.

Example: If not removed, the edge bead causes contamination during subsequent wafer processing.

Edge Bead Removal (EBR)
A process by which resist is removed from the outer edge of a resist coated wafer in order to remove the thick "bead" of resist that is usually formed along this edge during the spin coat process.

Example: The spin coat module included both front and backside edge bead removal systems.

Electron Beam Lithography
Lithography performed by exposing resist with a beam of electrons. Also called e-beam lithography.

Example: Electron beam lithography remains the most popular technique for producing high resolution masks.

Embedded PSM (EPSM)
see Attenuated PSM

Entrance Pupil, Lens
The image of the pupil (also called the aperture stop) of an imaging lens when viewed from the entrance side of the lens.

Example: The distance from the object to the entrance pupil of the lens is exactly equal to the distance from the exit pupil to the image times the reduction ratio of the lens.

EPSM
see Attenuated PSM

EUV
see Extreme Ultraviolet

EUV Lithography
Lithography using light of a wavelength in the range of about 5nm to 50nm, with about 13nm being the most common. Also called soft x-ray lithography.

Example: Although many problems remain, EUV lithography could potentially have both high resolution and large depth of focus.

Excimer Laser
Laser using a gas or gases to create an excited dimer (e.g., KrF), usually resulting in pulsed deep-UV radiation.

Example: Excimer lasers are used extensively in deep-UV lithography due to their extremely high output power.

Exit Pupil, Lens
The image of the pupil (also called the aperture stop) of an imaging lens when viewed from the exit side of the lens.

Example: The effective focal length of a lens is defined as the distance from the exit pupil to the image plane.

Exposure
The process of subjecting a resist to light energy (or electron energy in the case of electron beam lithography) for the purpose of causing chemical change in the resist.

Example: The chemically amplified resist was very sensitive to any delay between exposure and post-exposure bake.

Exposure Dose
see Exposure Energy

Exposure Energy
The amount of energy (per unit area) that the photoresist is subjected to upon exposure by a lithographic exposure system. For optical lithography it is equal to the light intensity times the exposure time. Also called the exposure dose, or simply dose.

Example: Accurate control of the exposure energy delivered to the resist is an important function of any lithographic exposure tool.

Exposure Field
see Field, Exposure

Exposure Latitude
The range of exposure energies (usually expressed as a percent variation from the nominal) that keeps the linewidth within specified limits.

Example: A minimum exposure latitude of 10% is needed for this process in order to get adequate CD control.

Exposure Margin
The ratio of the dose to size to the dose to clear.

Example: In most cases, increasing exposure margin results in an increase in process latitude.

Extinction Coefficient
Another name for the absorption coefficient of a material, often using a base 10 definition.

Example: The effectiveness of the dye was determined by measuring the extinction coefficient of the resist.

Extreme Ultraviolet (EUV)
A common though vague term used to describe light of a wavelength in the range of about 5nm to 50nm. Also called soft x-ray.

Example: The historical progress of optical lithography towards ever smaller wavelengths has convinced some that extreme ultraviolet radiation will be the next logical step.