Electronic – How do they make photo lithography lens so accurate


How are the lenses and other apparatus required for projecting a miniaturized version of the circuit using photo lithographic technique for IC manfuacture made?

Its known that even the tiniest spec of dust can ruin an entire chip so do you make sure the lens is perfectly clean and devoid of any distortions or scratches that may ruin the projection?

Best Answer

Actually, for the most part dust on the lens surface won't produce intolerable results at the wafer. At the lens surface the image being projected is not in focus, so a dust particle will not produce an image of the particle at the wafer.

The everyday example of this used to be called the "screen door effect", although don't bother to Google it - the meaning of the term has changed. It used to refer to the fact that a screen door can be optically opaque from a distance, but transparent up close. Put your nose up against a screen door and you can't see the screen pattern.

What you do see is a slight blurriness. This means that cleanliness is, as the saying goes, next to godliness, particularly in clean rooms. So a resist projector will undergo scrupulous cleaning before it is installed - it's just that a single speck on the lens surface is unlikely to cause significant issues.

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