Introduction:

Some advanced technologies require tight specifications around thickness and total thickness variation without compromising other critical tolerances such as surface finish, subsurface damage and contamination


Challenge:

Achieving next generation accuracy and thickness control requirements is extremely difficult using conventional manufacturing processes

 

Proposed solution

MRF can be used to target a desired thickness and meet tight total thickness variation specifications for: 

  • SOI wafers
  • Coatings
  • MEMS applications

 



 

Objective:

Correct thickness uniformity of top Si layer

 

SOI (Silicon-on-Insulator) Wafer

  • Size: 200 mm Φ
  • Material: Silicon

 

The MRF System Configuration

  • Rotational polishing mode
  • 150 mm wheel
  • Large spot to minimize cycle time
  • D20 MRF fluid
  • Low roughness

 


  


 

Measuring Thickness

Uniformity

  • Measure thickness of top Si coating layer
  • Wafer flatness does not have to be perfect
  • Measurement is extremely accurate and repeatablemrfApp4 fig3

 

 


 


 

Thin film 200mm SOI Wafer

  • PV < 2 nm achieved!
  • Shows MRF capable of polishing to metrology limit

 

mrfApp4 fig4

 

 

 


   


 

 Conclusion

  • Total thickness variation of <2nm was achieved
  • MRF routinely polishes glass and crystalline materials to a surface roughness of <5Å RMS
  • MRF uses sheering forces to removal material so no subsurface damage is introduced