FIB Etching and Deposition on Nanoscale Studied by TEM and Numerical Modeling

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1 FIB Etching and Deposition on Nanoscale Studied by TEM and Numerical Modeling V. Ray, E. Chang, Sz.C. Liou, K. Toula, and W.A. Chiou 8 th FIB/SEM Workshop, John Hopkins APL, Laurel MD

2 Outline Motivation Single line etching and deposition experiment Etching and Deposition Profiles Data extraction and processing Beam profile reconstruction Numerical results Conclusions Acknowledgements 3/26/ th FIB/SEM Workshop 2

3 Motivation Understanding nanoscale details of FIB-induced etching and deposition is critical for developing advanced gas-assisted processes for patterning thin films and prototyping microelectronics devices FIB etching and deposition is happening on nano-scale, within the single point of beamsample interaction. Improved understanding of nanoscale details would help with development of macro-scale models for GAE and deposition. 3/26/ th FIB/SEM Workshop 3

4 Single-Line Etch/Depo Experiment No Gas 1 pa Dwell 25nS 24 pa 7.7 pa 1 pa XeF pa 24 pa Overlap -25% FIB etching FIB W deposition FIB Pt E-beam C 24 pa 7.7 pa 1 pa No Gas XeF 2 No Gas XeF 2 No Gas XeF 2 1 pa 7.7 pa 24 pa nc/µm 2 nc/µm 2 nc/µm 2 3/26/ th FIB/SEM Workshop 4

5 Physical Sputtering Profiles 1pA 0.2nC/µm 2 non-gae line 7.7pA 0.6nC/µm 2 non-gae line Al Al Amorphization and rounding of edges on sputtered Al layer on both surface (result of direct ion impact) and substrate (result of reverse recoil of ions during collision) sides. Agglomeration of implanted Ga and formation of distinct zones within the implantation layer. 3/26/ th FIB/SEM Workshop 5

6 Gas Assisted Etching Profiles 7.7pA 0.6nC/µm 2 GAE XeF 2 24pA 1.8nC/µm 2 Reduced Implantation Sensitivity to ion beam current density distribution 7.7pA 0.6nC/µm 2 Physical Sputtering Reference 24pA 1.8nC/µm 2 3/26/ th FIB/SEM Workshop 6

7 W Deposition Profiles 1pA deposition 1.8 nc/µm nc/µm nc/µm 2 7.7pA deposition 1.8 nc/µm nc/µm nc/µm 2 Width of deposited W and depth substrate damage appears to be expanding with dose after W material began depositing 3/26/ th FIB/SEM Workshop 7

8 Data Extraction and Processing Deposition profile extraction 1pA 0.2nC/µm 2 Empirical data and fitted curves 1pA 0.2nC/µm 2 deposition profile Empirical data and fitted curves 7pA 0.7nC/µm 2 physical sputtering 3/26/ th FIB/SEM Workshop 8

9 Ion Beam Profile Reconstruction Assumptions: Ion beam is Bi-Gaussian Width of beam tails is equivalent to width of beam damage visible on no-gas etching profiles. Depth of physical sputtering is linearly proportional to ion dose for holes with aspect ratio 3:1 TRIM-simulated profile of Ga implantation without correction for sputtering Overlay with scale-matched profile of no-gas etched line Ions uniformly distributed along the etched and deposited lines Beam profile with simulated implantation that closely matches experimental would adequately describe current density of FIB used for etching and deposition Ga implantation simulated with sputtering correction 3/26/ th FIB/SEM Workshop 9

10 Numerical Analysis of Etching Profiles 3/26/ th FIB/SEM Workshop 10

11 Nanoscale lightning bolts Deep lightning-like traces 1pA physical sputtering profiles 1pA XeF 2 GAE profiles Deep lightning-like traces observed in TEM on etching profiles are not well understood. Appearance seems to be stronger under lines etched without gas. Long-range ion scattering? Sample preparation artifact? Cracking of due to ESD? Post-sample preparation artifact due to charge embedded into the fused silica during etching? 3/26/ th FIB/SEM Workshop 11

12 Conclusions Presented methodology for studying FIB etching and deposition within single beam profile. Discussed nanoscale details of FIB processes. Developed procedure for estimating FIB current density from line etching profiles. Demonstrated evidence of higher GAE efficiency in the areas of low ion beam current density. 3/26/ th FIB/SEM Workshop 12

13 Acknowledgements Oleg Sidorov of FEI Company contributed by outstanding execution of single-line etching and deposition experiment Research was partially supported by NSF- MRSEC (DMR ) and UMD Shida Tan et. al. credited for the idea of singleline experimental approach JVST B(30) /26/ th FIB/SEM Workshop 13

14 3/26/ th FIB/SEM Workshop 14