Work in progress: aims to identify the purpose of various wafer test patterns, process control monitors (PCM), alignment markers, etc.

====== Alignment ====== 

{{gallery>image:test_patterns.jpg}}

Pass condition: concentric

Used to align mask/reticle from layer to layer.

====== Continuity ====== 

Pass condition: low resistance.

A long wire that should maintain a good electrical signal.

====== Isolation ====== 

Pass condition: high resistance

Two wires placed close to each other that should not short.

====== Chain (contact, via) ====== 

{{gallery>image:john_mcmaster_ibm_043641wkaa_pattern_regular_64.jpg}}

{{gallery>image:john_mcmaster_ibm_043641wkaa_pattern_regular_68.jpg}}

{{gallery>image:john_mcmaster_ibm_043641wkaa_pattern_regular_61.jpg}}

{{gallery>image:john_mcmaster_ibm_043641wkaa_pattern_regular_18_0.jpg}}

Pass condition: low resistance

====== Contact resistance ====== 

Four point probe. Two

====== References ====== 
  * [[http://www.patentgenius.com/patent/6841890.html]]
  * [[https://cleanroom.byu.edu/sites/cleanroom.byu.edu/files/pdf/Alignment_Tutorial.pdf]]
  * http://www.stanford.edu/class/ee410/TestStructures.pdf