02/24/2012 5th FIB/SEM User Group Meeting, Washington DC

Valery Ray

vray@partbeamsystech.com

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

PBS&T

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OutlineOutline

Yield Enhancement and Milling Rate criteria for Yield Enhancement and Milling Rate criteria for characterizing beam GAE processescharacterizing beam GAE processes

Choosing beam raster parameters to maximize Choosing beam raster parameters to maximize Milling RateMilling Rate

Numerical and image examplesNumerical and image examples

ConclusionConclusion

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GAE Recipe Development:GAE Recipe Development:Dose Enhancement vs. Milling RateDose Enhancement vs. Milling Rate

Established GAE theory Established GAE theory (K. Edinger, JVST B 18(6) 2000 and (K. Edinger, JVST B 18(6) 2000 and

Microelectron. Eng. 57–58, 2001, also I. Utke et. al. JVST B 26(4) 2008)Microelectron. Eng. 57–58, 2001, also I. Utke et. al. JVST B 26(4) 2008) is is developed with emphasis on yield enhancement criteriadeveloped with emphasis on yield enhancement criteria

Miling rate is better suitable for practical applications:Miling rate is better suitable for practical applications:

» Recipes with maximized milling rates are required for etching Recipes with maximized milling rates are required for etching High Aspect Ratio viasHigh Aspect Ratio vias

» Recipes with minimized milling rates are required for uniform Recipes with minimized milling rates are required for uniform deprocessing of Cu with minimal dielectric over-etchdeprocessing of Cu with minimal dielectric over-etch

» Recipes with highest ratio of chemical milling rate to physical Recipes with highest ratio of chemical milling rate to physical sputtering rate are required for high material selectivitysputtering rate are required for high material selectivity

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GAE Recipe Development:GAE Recipe Development:Yield EquationYield Equation

YieldYield = = -------------- = = --------------------AR + AS

Removed Atoms

Incident Ions

JtD

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

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GAE Recipe Development:GAE Recipe Development:Reactive Yield vs. Mill ParametersReactive Yield vs. Mill Parameters

Effect on Effect on

ARAR(Reactive Yield)(Reactive Yield)

Pixel Pixel RefreshRefresh

1~ 101~ 10mSecmSec

Pixel Pixel OverlapOverlap

~ 0~ 0

Pixel Pixel

DwellDwell

50 n50 nSecSec

ParameterParameter

and Limitand Limit

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GAE Recipe Development:GAE Recipe Development:Phases of GAE Within Dwell PointPhases of GAE Within Dwell Point

ttDD = t = tARAR + t + tASAS

ttDD →→ t tARAR , and t , and tASAS → 0→ 0

High-Rate GAE within dwell point requires shortest practically possible dwell time

Chemical reactions occur on pico-second scaleChemical reactions occur on pico-second scaleFIB dwell times are 10s or 100s of nanosecondsFIB dwell times are 10s or 100s of nanoseconds

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GAE Recipe Development:GAE Recipe Development:View from the Dwell Point View from the Dwell Point

GAE process is happening within dwell pointGAE process is happening within dwell point

Replenishment of gas begins when primary Replenishment of gas begins when primary particle beam moves away from the dwell pointparticle beam moves away from the dwell point

Therefore refresh time of each dwell point (not Therefore refresh time of each dwell point (not the “raster”) is critical for gas replenishmentthe “raster”) is critical for gas replenishment

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GAE Recipe Development:GAE Recipe Development:Optimal Raster TimeOptimal Raster Time

tRaster = tRefresh = ΣtDii=0

n

Raster time equivalent to optimal refresh time provides most efficient GAE

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GAE Recipe Development:GAE Recipe Development:Refresh Time and Number of Dwell PointsRefresh Time and Number of Dwell Points

NDP = -----------------tRefresh

tD(Min.)

Practical Practical t D(Min.) for modern FIBs is in the range of 200nSec to 50nSec

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GAE Recipe Development:GAE Recipe Development:Via Size Defines Dwell Point DistanceVia Size Defines Dwell Point Distance

dX = dY = --------------------L

(Sqrt (N) - 1)

Dwell points are desirable on the edges of the via

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GAE Recipe Development:GAE Recipe Development:Dwell Point Distance = Beam SizeDwell Point Distance = Beam Size

Beam diameter equivalent to pixel distance Beam diameter equivalent to pixel distance ensures high reactive yieldensures high reactive yield

Corresponding beam current value is controlled Corresponding beam current value is controlled by ion optics; diffused beam is desirableby ion optics; diffused beam is desirable

DBeam = dX = dY

For uniform orthogonal raster:

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GAE Recipe Development:GAE Recipe Development:Numerical Example of HAR RecipeNumerical Example of HAR Recipe

22μμm x m x 22μμm via in Si milled with Clm via in Si milled with Cl22 (t (tRefreshRefresh = 1 mSec) on = 1 mSec) on system with minimal dwell 0.2 system with minimal dwell 0.2 μμSec:Sec:

N = 1000N = 1000μμSec / 0.2Sec / 0.2μμSec = 5000 pixels / rasterSec = 5000 pixels / raster

Beam Diamter = dX = dY = 2Beam Diamter = dX = dY = 2μμm / (Sqrt(5000) – 1) = ~ 30 nmm / (Sqrt(5000) – 1) = ~ 30 nm

Corresponding beam current depends on FIB system, but Corresponding beam current depends on FIB system, but typically will be around 20pA to 10pA or even lowertypically will be around 20pA to 10pA or even lower

Beam current can be increased for low (less then 5:1) Beam current can be increased for low (less then 5:1) aspect ratio work (surface micromachining) aspect ratio work (surface micromachining)

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GAE Recipe Development:GAE Recipe Development:10:1 HAR Via Etching Example10:1 HAR Via Etching Example

6.2μm

0.68μm

0.67μm

Needle gas injector Needle gas injector

Trifluoroacetic Acid Trifluoroacetic Acid PrecursorPrecursor

SiO2 substrateSiO2 substrate

~10min. etching time~10min. etching time

~0.6um/min etching rate ~0.6um/min etching rate

for 10:1 aspect ratiofor 10:1 aspect ratio

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0

1

2

3

4

5

6

7

8

0.5 0.4 0.3 0.2

0:00

2:24

4:48

7:12

9:36

12:00

14:24

16:48

19:12

21:36

Penta Dose Beehive DosePenta Time Beehive Time

Dose Dose nCnC

Time Time min.min.

Contact, Contact, μμmm

All vias are 5μm deep

XeF2 precursor on SiO2 substrate

““Proof of Concept” test, milling small HAR vias with Proof of Concept” test, milling small HAR vias with Beehive concentrator on FEI Vectra 986+ systemBeehive concentrator on FEI Vectra 986+ system

GAE Recipe Development:GAE Recipe Development:10:1 to 25:1 HAR Via Etching Example10:1 to 25:1 HAR Via Etching Example

Flat ~0.7um/min milling rate with gas concentrator for aspect

ratios 10:1 to 25:1

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GAE Recipe Development:GAE Recipe Development:Cu deprocessing ExamplesCu deprocessing Examples

100nm Cu line cut 100nm Cu line cut over 100nm dielectricover 100nm dielectric

Flat deprocessing through Flat deprocessing through four layers of “Dummy” Cufour layers of “Dummy” Cu

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ConclusionsConclusions

Milling rate criteria is better suitable for characterizing Milling rate criteria is better suitable for characterizing practical GAE processespractical GAE processes

Reviewing GAE process from the perspective of beam Reviewing GAE process from the perspective of beam dwell point allows converting yield-based theory to rate-dwell point allows converting yield-based theory to rate-based practical applicationsbased practical applications

Rate-optimized GAE process establishes Rate-optimized GAE process establishes direct relationship between size of repair direct relationship between size of repair and beam diameterand beam diameter

02/24/2012 5th FIB/SEM User Group Meeting, Washington DC

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