Developing FIB GAE Recipes: Practical Application of “Unfinished Theory”

1. PBS&T Developing FIB GAE Recipes: Practical Application of “Unfinished Theory” Valery Ray vray@partbeamsystech.com 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC

2. Outline • Yield Enhancement and Milling Rate criteria for characterizing beam GAE processes • Choosing beam raster parameters to maximize Milling Rate • Numerical and image examples • Conclusion 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 2

3. GAE Recipe Development:Dose Enhancement vs. Milling Rate • Established GAE theory (K. Edinger, JVST B 18(6) 2000 and Microelectron. Eng. 57–58, 2001, also I. Utke et. al. JVST B 26(4) 2008) is developed with emphasis on yield enhancement criteria • Miling rate is better suitable for practical applications: • Recipes with maximized milling rates are required for etching High Aspect Ratio vias • Recipes with minimized milling rates are required for uniform deprocessing of Cu with minimal dielectric over-etch • Recipes with highest ratio of chemical milling rate to physical sputtering rate are required for high material selectivity 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 3

4. GAE Recipe Development:Yield Equation Removed Atoms AR + AS Yield = ------- = ---------- JtD Incident Ions AR (Atoms Reacted) – FAST, parameter-sensitive, not limited by aspect ratio. AS (Atoms Sputtered) – SLOW, limited by aspect ratio J - Ion Beam Current Density tD – Time of beam dwell within the pixel 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 4

5. Parameter and Limit Pixel Dwell 50 nSec Pixel Overlap ~ 0 Pixel Refresh 1~ 10mSec Effect on AR (Reactive Yield) GAE Recipe Development:Reactive Yield vs. Mill Parameters 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 5

6. GAE Recipe Development:Phases of GAE Within Dwell Point Chemical reactions occur on pico-second scale FIB dwell times are 10s or 100s of nanoseconds tD = tAR + tAS High-Rate GAE within dwell point requires shortest practically possible dwell time tD→ tAR , and tAS→ 0 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 6

7. GAE Recipe Development:View from the Dwell Point • GAE process is happening within dwell point • Replenishment of gas begins when primary particle beam moves away from the dwell point • Therefore refresh time of each dwell point (not the “raster”) is critical for gas replenishment 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 7

8. tRaster = tRefresh = ΣtDi n i=0 GAE Recipe Development:Optimal Raster Time Raster time equivalent to optimal refresh time provides most efficient GAE 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 8

9. tRefresh NDP = ----------------- tD(Min.) GAE Recipe Development:Refresh Time and Number of Dwell Points Practical t D(Min.) for modern FIBs is in the range of 200nSec to 50nSec 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 9

10. L dX = dY = -------------------- (Sqrt (N) - 1) GAE Recipe Development:Via Size Defines Dwell Point Distance Dwell points are desirable on the edges of the via 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 10

11. GAE Recipe Development:Dwell Point Distance = Beam Size For uniform orthogonal raster: • Beam diameter equivalent to pixel distance ensures high reactive yield • Corresponding beam current value is controlled by ion optics; diffused beam is desirable DBeam = dX = dY 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 11

12. GAE Recipe Development:Numerical Example of HAR Recipe 2μm x 2μm via in Si milled with Cl2 (tRefresh = 1 mSec) on system with minimal dwell 0.2 μSec: N = 1000μSec / 0.2μSec = 5000 pixels / raster Beam Diamter = dX = dY = 2μm / (Sqrt(5000) – 1) = ~ 30 nm Corresponding beam current depends on FIB system, but typically will be around 20pA to 10pA or even lower Beam current can be increased for low (less then 5:1) aspect ratio work (surface micromachining) 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 12

13. GAE Recipe Development:10:1 HAR Via Etching Example Needle gas injector Trifluoroacetic Acid Precursor SiO2 substrate ~10min. etching time ~0.6um/min etching rate for 10:1 aspect ratio 6.2μm 0.68μm 0.67μm 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 13

14. GAE Recipe Development:10:1 to 25:1 HAR Via Etching Example Dose nC Time min. All vias are 5μm deep XeF2 precursor on SiO2 substrate Flat ~0.7um/min milling rate with gas concentrator for aspect ratios 10:1 to 25:1 “Proof of Concept” test, milling small HAR vias with Beehive concentrator on FEI Vectra 986+ system Contact, μm 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 14

15. GAE Recipe Development:Cu deprocessing Examples 100nm Cu line cut over 100nm dielectric Flat deprocessing through four layers of “Dummy” Cu 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 15

16. Conclusions • Milling rate criteria is better suitable for characterizing practical GAE processes • Reviewing GAE process from the perspective of beam dwell point allows converting yield-based theory to rate-based practical applications • Rate-optimized GAE process establishes direct relationship between size of repair and beam diameter 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC 16

17. www.partbeamsystech.com 02/24/2012 5th FIB/SEM User Group Meeting, Washington DC