This dissertation describes the improvement of signal analysis in ultrasonic microscopy for nondestructive testing. Specimens with many thin layers, like modern electronic components, pose a particular challenge for identifying and localizing defects. In this thesis, new evaluation algorithms have been developed which enable analysis of highly complex layer-stacks. This is achieved by a specific evaluation of multiple reflections, a newly developed iterative reconstruction and deconvolution algorithm, and the use of classification algorithms with a highly optimized simulation algorithm. Deep delaminations inside a 19-layer component can now not only be detected, but also localized. The new analysis methods also enable precise determination of elastic material parameters, sound velocities, thicknesses, and densities of multiple layers. The highly improved precision of determined reflections parameters with deconvolution also provides better and more conclusive results with common analysis methods.:Kurzfassung......................................................................................................................II
Abstract.............................................................................................................................V
List ob abbreviations........................................................................................................X
1 Introduction.......................................................................................................................1
1.1 Motivation.....................................................................................................................2
1.2 System theoretical description.....................................................................................3
1.3 Structure of the thesis..................................................................................................6
2 Sound field.........................................................................................................................8
2.1 Sound field measurement............................................................................................8
2.2 Sound field modeling..................................................................................................11
2.2.1 Reflection and transmission coefficients.........................................................11
2.2.2 Sound field modeling with plane waves..........................................................13
2.2.3 Generalized sound field position.....................................................................19
2.3 Receiving transducer signal.......................................................................................20
2.3.1 Calculation of the transducer signal from the sound field...............................20
2.3.2 Received signal amplitude..............................................................................21
2.3.3 Measurement of reference signals..................................................................24
3 Ultrasonic Simulation......................................................................................................27
3.1 State of the art............................................................................................................27
3.2 Simulation approach..................................................................................................28
3.2.1 Sound field measurement based simulation...................................................28
3.2.2 Reference signal based simulation.................................................................30
3.3 Determination of the impulse response.....................................................................31
3.3.1 1D ray-trace algorithm....................................................................................31
3.3.2 2D ray-trace algorithm....................................................................................33
3.3.3 Complexity reduction – optimizations.............................................................35
4 Deconvolution – Determination of reflection parameters............................................38
4.1 State of the art............................................................................................................39
4.1.1 Decomposition techniques..............................................................................39
4.1.2 Deconvolution.................................................................................................41
4.2 Analytic signal investigations for deconvolution.........................................................42
4.3 Single reference pulse deconvolution........................................................................44
4.4 Multi-pulse deconvolution..........................................................................................47
4.4.1 Homogeneous multi-pulse deconvolution.......................................................48
4.4.2 Multi-pulse deconvolution with simulated GSP profile....................................49
5 Reconstruction.................................................................................................................50
5.1 State of the art............................................................................................................50
5.2 Reconstruction approach...........................................................................................51
5.3 Direct material parameter estimation.........................................................................52
5.3.1 Sound velocities and layer thickness..............................................................52
5.3.2 Density, elastic modules and acoustic attenuation.........................................54
5.4 Iterative material parameter determination of a single layer......................................56
5.5 Reconstruction of complex specimens......................................................................60
5.5.1 Material characterization of multiple layers ....................................................60
5.5.2 Iterative simulation parameter optimization with correlation...........................62
5.5.3 Pattern recognition reconstruction of specimens with known base structure. 66
6 Applications and results.................................................................................................71
6.1 Analysis of stacked components................................................................................71
6.2 Time-of-flight and material analysis...........................................................................74
7 Conclusions and perspectives.......................................................................................78
References.......................................................................................................................82
Figures.............................................................................................................................86
Tables...............................................................................................................................88
Appendix..........................................................................................................................89
Acknowledgments.........................................................................................................100
Danksagung...................................................................................................................101Die vorgelegte Dissertation befasst sich mit der Verbesserung der Signalauswertung für die Ultraschallmikroskopie in der zerstörungsfreien Prüfung. Insbesondere bei Proben mit vielen dünnen Schichten, wie bei modernen Halbleiterbauelementen, ist das Auffinden und die Bestimmung der Lage von Fehlstellen eine große Herausforderung. In dieser Arbeit wurden neue Auswertealgorithmen entwickelt, die eine Analyse hochkomplexer Schichtabfolgen ermöglichen. Erreicht wird dies durch die gezielte Auswertung von Mehrfachreflexionen, einen neu entwickelten iterativen Rekonstruktions- und Entfaltungsalgorithmus und die Nutzung von Klassifikationsalgorithmen im Zusammenspiel mit einem hoch optimierten neu entwickelten Simulationsalgorithmus. Dadurch ist es erstmals möglich, tief liegende Delaminationen in einem 19-schichtigem Halbleiterbauelement nicht nur zu detektieren, sondern auch zu lokalisieren. Die neuen Analysemethoden ermöglichen des Weiteren eine genaue Bestimmung von elastischen Materialparametern, Schallgeschwindigkeiten, Dicken und Dichten mehrschichtiger Proben. Durch die stark verbesserte Genauigkeit der Reflexionsparameterbestimmung mittels Signalentfaltung lassen sich auch mit klassischen Analysemethoden deutlich bessere und aussagekräftigere Ergebnisse erzielen. Aus den Erkenntnissen dieser Dissertation wurde ein Ultraschall-Analyseprogramm entwickelt, das diese komplexen Funktionen auf einer gut bedienbaren Oberfläche bereitstellt und bereits praktisch genutzt wird.:Kurzfassung......................................................................................................................II
Abstract.............................................................................................................................V
List ob abbreviations........................................................................................................X
1 Introduction.......................................................................................................................1
1.1 Motivation.....................................................................................................................2
1.2 System theoretical description.....................................................................................3
1.3 Structure of the thesis..................................................................................................6
2 Sound field.........................................................................................................................8
2.1 Sound field measurement............................................................................................8
2.2 Sound field modeling..................................................................................................11
2.2.1 Reflection and transmission coefficients.........................................................11
2.2.2 Sound field modeling with plane waves..........................................................13
2.2.3 Generalized sound field position.....................................................................19
2.3 Receiving transducer signal.......................................................................................20
2.3.1 Calculation of the transducer signal from the sound field...............................20
2.3.2 Received signal amplitude..............................................................................21
2.3.3 Measurement of reference signals..................................................................24
3 Ultrasonic Simulation......................................................................................................27
3.1 State of the art............................................................................................................27
3.2 Simulation approach..................................................................................................28
3.2.1 Sound field measurement based simulation...................................................28
3.2.2 Reference signal based simulation.................................................................30
3.3 Determination of the impulse response.....................................................................31
3.3.1 1D ray-trace algorithm....................................................................................31
3.3.2 2D ray-trace algorithm....................................................................................33
3.3.3 Complexity reduction – optimizations.............................................................35
4 Deconvolution – Determination of reflection parameters............................................38
4.1 State of the art............................................................................................................39
4.1.1 Decomposition techniques..............................................................................39
4.1.2 Deconvolution.................................................................................................41
4.2 Analytic signal investigations for deconvolution.........................................................42
4.3 Single reference pulse deconvolution........................................................................44
4.4 Multi-pulse deconvolution..........................................................................................47
4.4.1 Homogeneous multi-pulse deconvolution.......................................................48
4.4.2 Multi-pulse deconvolution with simulated GSP profile....................................49
5 Reconstruction.................................................................................................................50
5.1 State of the art............................................................................................................50
5.2 Reconstruction approach...........................................................................................51
5.3 Direct material parameter estimation.........................................................................52
5.3.1 Sound velocities and layer thickness..............................................................52
5.3.2 Density, elastic modules and acoustic attenuation.........................................54
5.4 Iterative material parameter determination of a single layer......................................56
5.5 Reconstruction of complex specimens......................................................................60
5.5.1 Material characterization of multiple layers ....................................................60
5.5.2 Iterative simulation parameter optimization with correlation...........................62
5.5.3 Pattern recognition reconstruction of specimens with known base structure. 66
6 Applications and results.................................................................................................71
6.1 Analysis of stacked components................................................................................71
6.2 Time-of-flight and material analysis...........................................................................74
7 Conclusions and perspectives.......................................................................................78
References.......................................................................................................................82
Figures.............................................................................................................................86
Tables...............................................................................................................................88
Appendix..........................................................................................................................89
Acknowledgments.........................................................................................................100
Danksagung...................................................................................................................10
