Tanner B.K., Danilewsky A.N., Wittge J., Garagorri J., Elizalde M.R., Allen D., McNally P., Fossati M.C., Jacques D. and Ryan P.

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1 Intensity (cps) Re fe re nc e [Com pa rison 1] Com pa rison 2 Com pa rison O m e ga (se c ) X-ray Diffraction Imaging for Prediction of the Propagation Probability of Individual Cracks in Brittle Single Crystal Materials Tanner B.K., Danilewsky A.N., Wittge J., Garagorri J., Elizalde M.R., Allen D., McNally P., Fossati M.C., Jacques D. and Ryan P XXXX rev1.xx Jordan Valley

2 Motivation Edge damage is known to break wafers during rapid thermal anneal X-ray topography sees crystalline damage, some of this may result in broken wafers Question was which damage is important? EU Framework 7 program to investigate nature of damage which leads to wafer breakage Jordan Valley 2

3 SIDAM Investigation of Si wafer damage in manufacturing processes EU FP7 collaborative research project University, research lab and industrial partnership Universities of Durham, Freiburg, City University Dublin ANKA synchrotron CEIT Spain Jordan Valley Semiconductors (UK) Industrial Advisory Panel Intel Ireland MEMC (Italy) Siltronic (Germany) AMD (Germany) now Global Foundries Nanotechnology Knowledge Transfer Network (UK) Jordan Valley 3

4 XRDI Digital imaging by X-ray diffraction BedeScan, patented 2004 Jordan Valley 4

5 Transmission mode direct beam stop sample digital camera K b K a 2 K a 1 Mo Microsource b a (220) Geometric resolution = source size * (b/a) Resolution = m possible Jordan Valley 5

6 How is an Image Created? Raw data is a collection of frames collected as the wafer is scanned through the X-ray beam These frames are stitched to make stripes The tiling software assembles the stripes to make a complete image Scanning can be completely customized! Jordan Valley 6

7 Example XRDI Image Edge scan of wafer with edge damage thermal slip dopant striations resolution: 10 µm sample courtesy Dr D.K. Lee, LG Siltron, Korea Probable microcracks Jordan Valley 7

8 Which defects are critical? XRDI shows all defects above a critical strain field size 300mm wafer broke here! Which of these will cause process failure? What processes will induce failure? Jordan Valley 8

9 The Programme: Quantitation Wafers were deliberately damaged using nano-indenter to introduce repeatable defects Physical measurements of defects in damaged wafers using XRDI and other techniques Fracture mechanics modelling (prediction of crack severity) Edge cracks Dislocation propagation and slip bands Use fracture mechanics and XRDI images to predict which wafers will break Verification: RTA on wafers with quantified defects Dissemination: Industrial advisory panel helped with advice Intel, Global Foundries, MEMC, Siltronic Jordan Valley 9

10 Deliberate Damage XRDI of perfect sample Each wafer was checked before indentation for damage Damage induced using different loads in 12 locations on each wafer Damage was checked with SEM / Raman to measure stress Damage locations SEM of damaged area Jordan Valley 10

11 Topography and RTA XRDI of damaged area before anneal Thermal modelling of crack and projected path XRDI of damage before anneal Image used to predict crack path RTA used to validate model τtensile τcompressive r compressive τ τ r tensile cm r Tangential stress component r Radial stress component Wafer after anneal Jordan Valley 11

12 Theory Using crack propagation theory and fracture mechanics the probability of failure is r A B CT hold ( F T max Dt E T / t) A, B, C, D, E and F are parameters which need to be determined from linear regression from specific RTA chamber is a parameter determined from the XRDI images T max is the maximum anneal temperature t hold is the time held at maximum temperature T max is the maximum temperature gradient within wafer on cooling max Jordan Valley 12

13 Actual Breakage (1 = break, 0 = no break) f Validation of Model 1.4 Model Adequacy y = 1.021x R 2 = Many samples were measured All wafers with <50% probability of failure did not break in anneal All wafers with >50% probability of failure DID break Not Break Break r Predicted probability of Breakage Jordan Valley 13

14 JV Solution: QC-TT Specification developed from FP7 project Detects crystalline defects through the wafer body: Cracks, Slip, Dislocations, Micro-Pipes, Micro-Cracks FULL wafer scan OR Selective Region mode Measurements of a wide range of material High resolution topography down to 2.7µm Up to 300mm wafers or multiple smaller wafers Roadmap to 450mm tool Open cassette robot (2 200mm) available The essential choice of topography system for: Wafer Manufacturing R&D laboratories Jordan Valley 14

15 Defects imaged Surface, near-surface damage and defects Reflection mode R bulk and buried defects (even single dislocations) T Transmission mode edge exclusion zone monitoring T Transmission mode cross sectional defect depth (section) wafer frontside wafer backside T Transmission mode Jordan Valley 15

16 Challenges Near-term challenges in the area of Metrology for c-si photovoltaics Control of edge damage of c-si wafers Monitoring and evaluating the influence of slip and other defects on the efficiency Top long-term challenge(s) in the area of Metrology for c- Si photovoltaics As wafer sizes increase, probability of wafer breaking due to damage also increases Control of defects as wafer sizes increase Jordan Valley 16

17 Summary Edge damage is known to break wafers during rapid thermal anneal X-ray topography sees crystalline damage, some of this may result in broken wafers Question was which damage is important? Jordan Valley have developed a method to predict wafer breakage based on Edge damage characteristics Thermal properties of anneal cycle Transmission scanning can enable prediction QC-TT system now available Jordan Valley 17