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To: graphicsguru who wrote (253016)	6/8/2008 8:25:50 AM
From: misen	Read Replies (1) \| Respond to of 275872

Forgive the ignorance (I know very little about lithography), but how do you etch multiple layers at once? I naively assumed that each layer had to be separately etched before the next layer was applied. And how do you put different patterns on different layers if they're etched in a single patterning? To etch multiple layers at once, you need to have an etch chemistry/chemistries that can etch the materials in each layer. Back when Aluminum metallization was used, the metal etch process typically needed to be able to etch both aluminum and titanium since some type of titanium was often used on top of metal as an anti-reflective coating to make the lithography better. The key requirement is that you want the same pattern for the multiple layers. This is true in both the metallization example as well as the VCSEL example Pete provided in his link. If you look at the photos in the link, you can see that all the "multiple layers" in the VCSEL have the same pattern. So you can etch them at the same time with a single patterning. In fact, in Pete's link, it would be more difficult to use a separate patterning step for each layer, because you would have some misalignment between each patterning step where the patterns don't line up exactly with the previous step. Think of stacking a bunch of the same coins -- you don't always get each coin to be exactly congruent with the previous or subsequent coin. Etching in one patterning step actually avoids this problem. If you need different patterns for the different layers, you would generally need multiple patterning steps. Misen