Advanced Optical Inspection Techniques

Transcription

1 Advanced Optical Inspection Techniques September 9, 2010 Andrei Brunfeld

2 Contents Introduction Current Challenges Areal Density (Tb/in2) Areal Density and Critical Defect Size - Expected Evolution Areal Density - Low Estimate (Tb/in²) Areal Density - High Estimate (Tb/in²) Critical Particle Size (µm) Critical particle size (um) Year 200nm 100nm 50nm Xyratex solution Surface under testdiffracted field Detector U1 (from every cell) U2 Laser beam U 0 Cells region Propagation region Π surf Rz 2 Main defect categories images Summary 2

3 In-Line Testing Challenges Brief Review

4 Areal Density and Bit Dimension Bit aspect ratio continues to decline Required critical defect detectability more stringent Current in-line inspection is limited Detectability vs. Speed Classification Special requirements 4

5 Key Production Concerns: Substrate Media Drive Drive reliability (at fly-height sub 3 nm range) Thermal Asperities & Head damage Embedded particles Buried defect Fly height variations Bumps Shallow defects (slider wavelength based) Raised scratches Soft defects (parametric thresholds) Fly height variations Shallow defects parametric variations Scratches Shallow pass then fail when head changes slightly Grown defects Presputter contamination Yield Requirements vary from Drive Company to Drive Company Defect counts Presputter Scratches Sputter voids Surface roughness Thermal Asperities (see above) Servo failures PES failures most likely due to scratches Drive reliability and yield requirements ARE conflicting! 5

6 Main Defect Categories Shallow defects Area Pits (short, long) Bumps Craters Large waviness slider wavelength related Stains film/coating H= -8nm W= 30000nm Shallow defects Scratches Ridges (raised scratches) Particles/Protrusions Grown defects Voids Handling damages Thermal asperities Particulates Line Point H= -1.3nm W= 50nm 6

7 Drive sensitivity to spacing loss (scratches/shallow defects) 25% signal loss critical for servo, 50% critical for drive error rate Spacing Loss vs. Year A = A πd/λ % Signal Loss 2.50 Depth (nm) % Signal Loss Year Required spacing variation currently at around 2 nm Future challenge heading toward 1nm 7

8 Particle Size Detectability Estimation Areal Density and Critical Defect Size - Expected Evolution Areal Density - Low Estimate (Tb/in²) Areal Density - High Estimate (Tb/in²) Critical Particle Size (µm) Areal Density (Tb/in2) Critical particle size (um) nm 100nm Year 50nm Current production requirements about 100nm PSL equivalent Future requirements toward 50nm PSL equivalent or less 8

9 Main Reasons for/against Optical Testing For Optical But Defect concerns are similar for substrate, media, drive Sensitive, fast and repeatable Possible 100% surface inspection Can be used at any step in process Simple, well-known, traceable Similar optical defects have different effects in singular applications Optical Mechanical Magnetic Only optical information available Thorough classification is required Within limits 9

10 Critical Requirements for Optical Detection Shallow defects: 1 2 nm depths 10,000-50,000nm diameter Up/Down discrimination Scattering Optical Signals Phase/Height/Polarization Scratch sensitivity: 1-2nm depths <100nm width Side discrimination (transparent substrates) Particles: 100nm PSL detection (less in the near future) Potential for separating removable from non removable Side discrimination (transparent substrates) All requirements to match production line throughput, approx 2000pph 10

11 Current optical inspection systems concepts Monolithic: Single inspection head, single spindle High sensitivity Multiple signal channels: dark-field, bright-field, polarization, etc. Small spot size High classification level Limited speed Monolithic: Single inspection head, multiple spindles High speed Dark-field and bright-field Large spot size Limited classification Modular: Multiple inspection heads, multiple spindles Miniature optical head High sensitivity and high speed Dark-field and bright-field Medium spot size High classification versatility Distributed test recipes available for each head+spindle system Special tests (e.g. for glass: side discrimination, cracked disk) 11

12 Xyratex Sensor

13 Concept Mathematical model for actual electromagnetic field propagation Surface roughness considered in the model Accurate evaluation of signal for each detector Good optimization possibilities Proven results consistent with experiments Single source - dual detection Simple and efficient, dark field and bright field channels Scattering and non-scattering defects Correlation between two channels for classification Side discrimination Miniature sensor Complete separation between dark and bright field channels Modular construction Sensor Tester Production cell 13

14 Diffraction and Propagation Surface under test Diffracted field Detector U1 (from every cell) U2 R propagation operator U Complex amplitude Laser beam U 0 Cells region Propagation region Π Phase (height) function Π surf Rz 2 U [ U ] z = R z Πsurface z= 0 ( ) 2iπh x, y 2iπ Π ( x,y) = exp = 1+ h x, y ( ) surface m n λ λ m,n exp(ikz) iπ 2 Rz[ U ]( r2) = exp ( 2 ) U( )d iλz r r r r λz exp(ikz) 2iπ iπ U = U + h exp ( r r) U( r)dr ideal 2 z z mn 2 iλz λ m,n λz r m,n Define surface in optical terms: cells Define cells interaction with the laser beam Introduce defect function as an abnormal cell Propagate through the optical system Calculate the optical amplitude and the signal 14

15 Area Shallow Defects Modeling Results Shallow Defects - Estimated Differential Signal 25µm width 50µm width 100µm width 10 Optical signal for 100% reflectivity (%) Defect depth (nanometers) Note the decrease of the signal with increased defect size 15

16 Particle Defects Detection Modeling Results (PSL) Summary of Expected PSL Sensitivity Various Substrates and Spot Sizes 25 Al 9 x 4.5 Al 13 x 6.5 Glass 9 x 4.5 Glass 13 x 6.5 Expected Gaussian Interraction (um) PSL Size (nm) Note the non-linear relation with the particle diameter 16

17 Main Defect Categories - Images

18 Area Shallow Defect Crater (glass substrate) HRV 2 Amplitude (mv) HRV 2 Amplitude (mv) Microns 18

19 Linear Shallow Defect - Light Scratch (Al substrate) Depth x Width 1.5nm x 50nm 19

20 Particle Sensitivity (glass substrate) 90nm PSL 100nm PSL 20

21 Side Discrimination Glass Substrates Medium Scratch Defect on Side A Defect on Side B Signal (mv) Backside detection <0.2% Distance (um) The current head has less than 0.2% cross talk 21

22 Advanced Algorithm for Side Discrimination Most defects easily detected and side defined Scratch Shallow-Disk 5 Defect On Bottom Ghost Elimination 22

23 Summary Focus on optical testing Bit density vs. defect size Production concerns Optical testing pro and contra Detection requirements/challenges Throughput Xyratex sensor Concept Modularity Maps of main detector categories Contributors Andrei Brunfeld Bryan Clark Gregory Toker Morey Roscrow Peter Goglia Entire Titan project team 23