Greetings. When I deposit a thin film layer, say a block of metal on top of a mesa structure, and then deposit another layer which covers the original one only partially and extends to the mesa, what is the thickness profile of the second layer over the border of the metal block?
Suppose the metal layer has 100nm of height and I deposit on top of that 100nm of Al oxide. So, on top of the mesa I have a 100nm Al oxide block and on top of the metal I have another 100nm tall Al oxide block (being 200nm tall in total, accounting for the metal block height itself). What is the transition like between both areas? In the attached file I made a picture with an extreme case, but I don't think the transition is so sharp. My concern is that there is a leak current through that sharp transition area.
Thank you very much.
Can you measure the topography after each deposition with a profilometer or AFM?
This looks like a typical "step coverage" issue, which can be experimentally evaluated with cross-sectional SEM or FIB analysis.
The parameters that affect the top layer profile at the edge location are various and all important:
- step height
- step slope or non-linear profile
- ratio between the deposition thickness of the top layer and the step height
- the top layer material, its deposition process, possible post-deposition thermal processes
- the topography of the patterned first layer before the top layer is deposited, specially when the top layer thickness is comparable or larger than the openings in the patterned first layer
Turning to your specific case, the occurrence of a leakage close to the edge location may possibly stem from a negative-angle step coverage of alumina at the metal line edge: the alumina thickness on the vertical metal edge decreases from top to bottom till almost zero-thickness, which statistically may cause local alumina voids at the metal edge basis along your pattern.
Use of SEM analysis (on a statistical sample of cross section at the edge, and on tilted surfaces following the on-top profile of the metal pattern) is mandatory if you want to characterize the step coverage also in view of process/design modification to improve the result.
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