Degradation Caused by Excessive Cycle Times During Bosch Process

Degradation Caused by Excessive Cycle Times During Bosch Process

Material Name: Silicon
Record No.: 94
Primary Chemical Element in Material: Si
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: The image on the left shows pillars which were masked with circular disks of resist, at the base of the pillars it is possible to see the individual layers associated with each cycle of etch and passivation layer. At the top of the pillars is a more interesting pattern. There has been significant under etch beneath the mask. This is shown more clearly in the second image (different area on the wafer) in which the etch can clearly be seen to undercut the mask. This is likely to be an artefact of the increasing of the times of the two cycles, specifically the etch cycle. As discussed previously it is possible that this under-etch is occurring in the time indicated on the spectral graph where all of the passivation material appears to have been removed. By a slight adjustment of the proportion of etch time to deposition time it may be possible to reduce this under-etch and achieve more uniform side walls.
Reference: Christopher James Pugh, End Point Detection in Reactive Ion Etching, PhD Thesis, UNIVERSITY COLLEGE LONDON, 2013, p. 129.

Figure 1: Scanning electron microscope images showing two separate areas on a patterned wafer after etching. The degradation caused by excessive cycle times during Bosch process is shown on both areas.