Lithography in the semiconductor technology

Semiconductor Equipment
Crystec Technology Trading GmbH

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Lithographie   Mask Aligner   MEMS


Photolithography is a technology for transferring patterns from a mask or reticle onto an substrate. Critical parameters are linewidth control, overlay, and defects. This methode is used for the manufacturing of integrated circuits ICs, but also for the production of LEDs, OLEDs and in the MEMS technology.
The first step is the deposition of photosensitive photo resist on the substrate, which is then dryed and cured. Using a mask or reticle the areas of the substrate are covered, which should not be illuminated. In order to do that it is necessary to position the substrate very accurately with automatic pattern recognition systems and marks on the substrate and using a high precision stage, who can approch the requested position precisely.

Lithographie Strahlengang

A lens system is projecting the short wave UV-light on the mask / reticle. The shorter the wave length, the more precise it the optic, the higher is the possible resolution, that can be achieved with this technology and the smaller are the structures, that can be reproduced exactly. Usually marcury lamps are used as a light source. They emit light with a wavelenght between 280nm and 450nm. The frequency range can be selected by using filters. For deep UV usage and a wavelength of 220nm to 280nm, eximer laser are used. Equipment for the exposure and of the complete substrate is called mask aligner. Two types of mask aligners are available: contact / proximity aligner, where the photomask is in direct contact with or close to the substrate and projection aligners which show a larger distance to the mask. Only this technology can expose thick resist layers or deep structures, as it is required for micromechanical of microfluidic applications. Also this is a reliable technology which can work faster and cheaper than so called stepper, which exposes the substrate in parts step by step. Stepper are used, when extremly high resolution is requested and they use reticles instead of masks. A mask is always same size as the substrate, while a reticle has a factor 4, 5 or 10 larger image of the pattern. For many applications which do not need so high resolutions like manufacturing of MEMS or LEDs, cheaper mask aligners with mirror projection technology can be used.
After the exposure, the photo resist will be developed, meaning that either illuminated or non-illuminated parts of the resist are resolved. The main process is then following, e.g. the depostion of oxide or nitride or plasma etching of some layers. Finally the remaining photo resist is removed in an asher. Usually, many of such steps are necessary for the production of integrated circuits and illumination equipment like mask aligners belong therefore to the most important pieces of equipment in the semiconductor industry.

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