In-line Hybrid Metrology Solutions Brad Lawrence Regional Sales & Product Marketing Manager, XwinSys
ED-XRF Based Metrology with Hybrid Sensor Technology
Hybrid Sensor In-Line Metrology Process feedback of several parameters in one wafer pass ED-XRF, 3D Confocal, High resolution 2D Higher Footprint Value Holistic approach - The Whole is greater than its Parts
XwinSys Equipment Configuration
XwinSys ONYX Configuration XRF/3D/2D/He Purge XRF Beam Array of XRF Detectors [Film Thickness, Material Composition] 3D [Height, Roughness] 2D [Pattern Recognition, Inspection, Navigation] Helium Purge Sphere [Light Element Detection]
Holistic Recipe Integrates all Sensor Signals
Copper Pillar Height Measurement
Multiple Sensors provide a Hybrid Solution Measuring a bump taller than XRF can accommodate Due to fluorescence saturation Total Height 38um SnAg 12um Nickel 3um Copper 23um
Traditional XRF - Standards Dependency XRF technology is a 2 nd order technology Standards are required in order to convert intensity to thickness or composition Standards should be very accurate and as similar as possible to the application itself
How Does the Standard FP function? There are a few options to calibrate the application using FP algorithm The most popular option is to use one standard from a known structure From this standard we extract the parameters listed in the table The FP Algorithm compensates for: secondary excitation, self absorption Limitations: Beyond the standard values the accuracy drops - as with an excursion Thick Layer (Cu) sensitivity is relatively low due to saturation Ni Intensity Cu Intensity A g Sn Intensity Solder 20 Ni 3 Cu 23
1 st Order (Standard-Less) 3D/EDXRF Solution - UBM case Unique FP algorithm, XRF standards are NOT required Real time solution - fast and clean using internal nominal values only FP algorithm analysis using real-time geometrical parameters Thickness Nominal 1 st Order Step 1 Nominal Values Step 2 CD value from 2D Microscope Step 3 Total height Value from 3D scanner Step 4 XRF measurement Step 5 Accurate 1 st Order solution Au 0.2 0.34 Ni 2.5 2.27 Cu 2.5 2.83 38 µm Au 0.2 Au 0.34 Ni 2.5 Cu 2.5 5.44 µm 5.44 µm Ni 2.27 Cu 2.83
How does the XwinSys Calculate 1 st order XRF? Using the Total Height from the 3D confocal as a standard for the XRF. The constraints are: Constraint 1: TCu + TNi + TSn = Total Height Total Height Solder 20 Ni 3 Cu 23 3 unknowns - 3 constraints Secondary excitation & self absorption are taken into consideration
Advantages & Innovation Using total height as a standard for the EDXRF - clean and fast calibration method Real time - real device - actual site High accuracy and speed of the standard values from the 3D confocal Not necessary to re-measure standards periodically No down time for calibration
Total Height / Cu / Ni / SnAg (3D/XRF vs. FIB/SEM)
PCB Copper Seed Measurement
PCB Electroless Cu Seed Thickness Using Light Element Detection
System XRF Setup Parameter Tube Molybdenum Voltage (kv) 8 Current (µa) 400 Range (kev) 40 Filter Open window Detector Light Element Helium purge On
Methodology Cu Seed Layer thickness is measured by an automated algorithm using two methods - Direct method (0-0.7 µm Cu thickness) by measuring peak and calculating Cu layer thickness using linear regression - Indirect method (0.7-1.4 µm Cu thickness) by measuring Si peak and calculating Cu layer thickness using exponential regression In thicker layers (above 0.7 µm) peak intensity is in saturation due to low energy element (0.93KeV) therefore Cu layer thickness is measured indirectly using the Si from the epoxy layer. Automated recipe Direct Method Indirect Method 0 µm 0.7 µm 1.4 µm Cu Layer thickness
XRF Analysis and were clearly detected by the ED- XRF. Cu seed layer thickness can be monitored by using both peaks independently - or peaks. Acquisition time: 4 sec
Calibration curves Regression curves is presented below. - Linear regression for the direct method - exponential regression for the indirect method
Results Direct Measurement of Cu Indirect Calculation of Cu by measuring Si Nominal [µm] Direct Method [µm] Indirect Method [µm] 0.4 0.398 0.382 0.5 0.496 0.462 0.6 0.613 0.571 0.7 0.689 0.704 0.8-0.788 0.9-0.888 1.0-0.960 1.1-1.083 Direct method has a higher accuracy for Cu layer thickness < 0.7 µm Indirect method have higher Cu thickness range up to 1.4 µm
Bond Pad Al 2 O 3 Thickness Measurement (50Å)
Aluminum Bond Pad - Oxide Thickness (FP Algorithm compensates for pad thickness changes) Aluminum Ground Pad Al O Si Ti Ground Pad Signal Pad Aluminum Signal Pad
Correlations Between XRF & Auger There is correlation between the Auger results and the new thickness values of the Alumina after using the FP to correct the thickness values There is ~40% thickness difference between pad 1 & 3 The secondary excitation improved the accuracy of the Alumina results and the correlation to the auger is better [ Å ]
Aluminum Bond Pads with Underlying Tungsten
Backside Via Plating Thickness
Backside Contact to GaAs Device (Detecting Au) XRF to determine if Au is present on contact vs. TEM After contact etch Magnification X2 Magnification X10 After Au Plating
XRF Cu & Au Thickness
2D & 3D Measurements Cu Au Contact Step: 1µm 89.00 µm Bottom CD (13um/34um) Top CD (67um/78um) 86.93 µm Step: 1µm
Real Time Review / KLARF Review
Real Time Review with Hybrid Metrology (2 passes) (Example) 2D/3D Sampling ED-XRF Missing Metal Layer
Review AOI Results File
Summary
Back End Processing Hybrid Metrology
Holistic Recipe Integrates all Sensor Signals