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Center of MicroNanoTechnology CMi

Resists for Lift Off

Table of content

  1. Vistec EBPG5000 overview
  2. What is an electron beam (ebeam) lithography system?
  3. Electrons, resists and substrates
  4. Process Flow for Ebeam Lithography
  5. Data conversion
  6. Running the ebeam

III.2.a. ZEP basics

ZEP is a Styrene Methyl Acrylate based positive ebeam resist and is used in ebeam mostly as a dry etch mask because its better than PMMA (most things are). It has good resolution and is more sensitive than PMMA. Because it's prime use is for dry etch it's used in a standard single layer configuration because you want the sidewalls as verical as possible.

III.2.b. ZEP data

Polarity

Positive

Doses

Higher sensitivity means lower dose. Typical doses for ZEP are between 190 and 400µC/cm2.

Resolution

Resolution should be below 30nm for isolated features.

Chemical capabilities

For Si ZEP has very good dry etch selectivity with the Si-Opto process on the AMS. For large features you can expect ≈16:1 Si:ZEP. For SiO2 the selectivity is ≈4:1 with the SiO2 5:1 process. At the moment I don’t have any information about ZEP’s wet etch selectivity, but I suspect it’s similar to PMMA.

WARNING: Long aggresive dry etch processes cause ZEP to crack and burn. Once this happens it is impossible to remove ZEP even in oxygen plasma.