What is Lithography – TroubleinthepeaceS

Is a set of photochemical processes to create details on the surface of silicon wafers (wafers) with the same size and shape as the design. To do this requires masks, UV light source photoresist and developer solution. The mask is usually a sheet of organic glass coated with a chromium film on which details are depicted consistent with the design of the sensor or integrated circuit (IC).

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2.Exposure to UV – Exposure under ultraviolet light• Parts of the wafer are selected for exposure by carefully aligning a mask between an ultraviolet-UV light source and the wafer.• In the transparent areas of the wafer. mask, light passes through and exposes the photoresist layer. There are 2 types of inks. Positive and negative photoresist.• negative – UV rays make negative resist polymerize and more difficult to dissolve.• Positive – UV light changes the chemical structure of resist so that it becomes more soluble in the photoresist. Currently Positive resists is the more dominant type used. If the type is positive, the hidden part will remain. Type negative, the part covered will be erased. In this stage, the only one is photoresist because it contains solvents that cause cancer. After this step, the photoresist will harden or not harden depending on the positive or negative photoresist.

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Masks:The mask is a square sheet of glass with a patterned metallic film emulsion, usually a chromium film, on one side. A wafer needs a lot of masks, from hundreds or more masks with ICs, or a few masks with transistors. Each set of masks usually consists of several tens to several hundred images of a die (1 die will be an IC). The mask is aligned with the wafer, so that the drawing pattern can be transferred onto the wafer surface. Each mask must be aligned with the sheet in front. Photoresist is exposed (captured) through the pattern on the mask to an intense ultraviolet light.• There are three main exposure methods: contact-exposure, proximity-proximity and projection-projection.• The main advantage of the projection method is that the mask can be slightly larger than the final sample and through manipulations optical and mechanical, better precision/resolution can be put on top of photoresist – Direct Wafer Stepping (DWS)

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