Photolithography Terms and Definitions Page

Description and Purpose

Definitions for different lithography terms and other cleanroom jargon.

Definitions

Photoresist - A light sensitive material that can be used to form a patterned coating on a surface.

Positive Resist - A photoresist that becomes soluble to developer after exposure. Unexposed portions remain insoluble.

Negative Resist - A photoresist that becomes insoluble to developer after exposure. The unexposed portions are soluble.

Dry Film Photoresist - A photoresist that comes as a uniform thickness, semi-solid film on a polyester substrate and is applied through lamination, instead of being in a liquid form.

Exposure Process - of subjecting photoresist to intense light, or something else such as an electron beam, to create a desired pattern by chemically altering portions of it.

Development - After photoresist is exposed a chemical known as a developer is used to remove portions of the photoresist from the substrate.

Etching - The use of a liquid (wet) or plasma (dry) chemical agent to remove the uppermost layer(s) of the substrate in areas not protected by photoresist.

Photolithography - Pattern definition method which uses UV radiation to expose the resist; the most common lithography technique in semiconductor manufacturing. Advantages: exposes entire surface simultaneously, exact control over shape and size - Disadvantages: requires flat substrate, requires a mask

Contact Lithography - Form of photolithography in which the image to be developed is obtained by illumination of a photomask in direct contact with the photoresist coated substrate; Achieves higher resolution, but can damage both the mask and substrate.

Proximity Lithograpy - Similar to contact lithography, but a small gap is introduced between the mask and the substrate; Has lower resolution due to this gap and diffraction, but used more than contact lithography because it is not as damaging to mask and substrate.

Projection Lithography - Achieves higher resolution by projecting the pattern to be developed onto the substrate through a lens system. Highly used for IC production.

Stepper - A machine that uses projection lithography and a 'step-and-repeat' method to expose one small grid area of a wafer at a time and then moves on to the next until the entire wafer has been exposed.

Electron beam lithography (e-beam) - A beam of electrons scans across the surface of the resist exposing some areas and not others in a patterned fashion. Advantages: maskless, diffraction limit of light not a problem - Disadvantages: long exposure time, not good for high-volume production

I-line - Photolithography using 365 nm wavelength UV radiation for exposure.

H-line - Photolighography using 405 nm wavelength UV radiation for exposure. G-line Photolithography using 436 nm wavelength UV radiation for exposure.

Absorption Coefficient - Defines depth of penetration of a given medium with the light of a given wavelength; decreases as the wavelength shortens.

HMDS - A chemical compound often used as an adhesion promoter for photoresist. Full name is hexamethyldisilazane.

MEMS - Acronym for Microelectromechanical Systems. They are very small mechanical devices driven by electricity.