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PHOTOLITHOGRAPHY GLOSSARY

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.
 

Image Reversal Resist – A photoresist that can be processed both positively and negatively and are therefore also suitable for users who want to process one resist in both tones.

 

PMMA Resist - Poly (methyl methacrylate) (PMMA) is the classical e-beam resist and offers the advantage of extremely high resolution, ease of handling, excellent film-forming characteristics, wide processing latitude, and ready availability. PMMA resist is PMMA polymer in a solvent.
 

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

g-line - Photolithography using 436 nm wavelength UV radiation for exposure.
 

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

Wafer Fabrication - Semiconductor processing facility which turns wafers into integrated circuits. A typical wafer fab employs a series of complex steps to define conductors, transistors, resistors, and other electronic components on the the semiconductor wafer. Imaging steps define what areas will be affected by subsequent physical and chemical processes.
 

Spin Coating - Spin coating is one of the most common techniques for applying thin films to substrates. It is used in a wide variety of industries and technology sectors. The advantage of spin coating is its ability to quickly and easily produce very uniform films, ranging from a few nanometres to a few microns in thickness.
 

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 – Process of pattern transfer; when light is utilized. It is 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
 

Critical Dimensions (CDs) – The widths of the lines and spaces of critical circuit patterns as well as the area of contacts.
 

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.
 

Aligner (align and expose) – A process tool used to align wafers and masks or reticles and exposure the photoresist with a UV or other radiation source.
 

Electron beam lithography (e-beam) – An exposure source which allows direct image formation without a mask. An e-beam can be deflected by electrostatic plates and therefore directed to precise locations, resulting in the generation of submicron-size patterns. Advantages: maskless, diffraction limit of light not a problem - Disadvantages: long exposure time, not good for high-volume production
 

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

 

Source: Glossary terms are abstracted from Beverly Griggs, Anne Miller, and Peter Van Zant, Semiconductor Terminology – Graphic Glossary of Terms, Semiconductor Services, Redwood City, Calif., 1989.