Semiconductor Manufacturing Tour
Table of Contents
Slide 5 of 22
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Photography is the best analogy to describe the photolithography process. The stepper is like a photographic enlarger where a light source projects an image through a lens system onto photographic paper.
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In the semiconductor case, the "light bulb" used to be a mercury arc lamp, but for DUV lithography has been replaced by excimer laser light sources. The image comes from our reticle, and this is then projected through a very complex quartz glass lens system on to the wafer which has been coated (spun-on) with an ultra-thin layer of photoresist material. The reticle image is either printed 1:1 in size or reduced by 4:1 or 10:1, depending on the particular stepper. Clearly, for a 4:1 reduction, the features on the reticle need only be one-fourth of those required on the wafer. The exposure time is dependant on many variable including the sensitivity of the resist, lens aperture, etc.
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The machine used to do all of this is called a "stepper" because it literally does one die or a few die at a time, then steps to the next die or set of die until it has exposed the entire wafer.
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