Photolithography is the process of transferring shapes on a ‘mask’ to a surface made of silicon wafer. There are several steps involved in the process. These are: wafer cleaning, barrier layer formation, photoresist application, soft baking, mast alignment, exposure and development and hard-baking.
Wafer cleaning
Wafer is chemically cleaned to remove foreign matter that would otherwise affect the result of the final image.
Barrier formation
Silicon dioxide is applied on the surface of the wafer which creates a barrier layer.
Photoresist application
Photoresist is then applied to the surface of the wafer via high speed centrifugal whirling (the wafer is spun at high speeds which serves to create an even layer on the surface of the platform)
There are two types of photoresist:
Positive photoresist is exposed with ultra violet light which changes the chemical structure of the resist so it becomes soluble in the developer. Then the exposed resist is washed away leaving the underlying material with an exact copy of the pattern which remains on the wafer.
Negative photoresist behaves in the opposite way. The resist exposed to UV light becomes hard and more difficult to dissolve and thus remains on the surface and only the unexposed portions are washed away. Masks used for negative photoresist contain the negative of the pattern to be transferred.
Soft baking
This step removes completely removes all solvents from the photoresist coating. When soft baked the photoresist becomes photosensitive
Mask alignment and exposure
The mast (a square glass plate with patterned emulsion of metal film) the mask is aligned with the wafer so the pattern can be transferred accurately. Once aligned, the photoresist is exposed through the pattern on the mask with UV light.
Development
The image is developed in a developing solution. The final image result depends on the development time as well as weather the image was of positive or negative photoresist and how long the image was exposed.
Wafer cleaning
Wafer is chemically cleaned to remove foreign matter that would otherwise affect the result of the final image.
Barrier formation
Silicon dioxide is applied on the surface of the wafer which creates a barrier layer.
Photoresist application
Photoresist is then applied to the surface of the wafer via high speed centrifugal whirling (the wafer is spun at high speeds which serves to create an even layer on the surface of the platform)
There are two types of photoresist:
Positive photoresist is exposed with ultra violet light which changes the chemical structure of the resist so it becomes soluble in the developer. Then the exposed resist is washed away leaving the underlying material with an exact copy of the pattern which remains on the wafer.
Negative photoresist behaves in the opposite way. The resist exposed to UV light becomes hard and more difficult to dissolve and thus remains on the surface and only the unexposed portions are washed away. Masks used for negative photoresist contain the negative of the pattern to be transferred.
Soft baking
This step removes completely removes all solvents from the photoresist coating. When soft baked the photoresist becomes photosensitive
Mask alignment and exposure
The mast (a square glass plate with patterned emulsion of metal film) the mask is aligned with the wafer so the pattern can be transferred accurately. Once aligned, the photoresist is exposed through the pattern on the mask with UV light.
Development
The image is developed in a developing solution. The final image result depends on the development time as well as weather the image was of positive or negative photoresist and how long the image was exposed.
http://www.tcd.ie/Physics/Magnetism/images/nanofa32b.jpg
http://www.ece.gatech.edu/research/labs/vc/theory/photolith.html
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