Non-destructive metrology for IC fabrication

Transcription

1 Non-destructive metrology for IC fabrication Planarisation Technology Workshop UCD, 17 Aug Patrick J. McNally Nanomaterials & Processing Laboratory School of EE, DCU 1

2 Co-Workers Lu Xu, Dr. Donnacha Lowney, Dr. Lisa O Reilly, Dr. Jarujit Kanatharana, (DCU). Prof. Turkka Tuomi, Helsinki University of Technology. Dr. A. Danilewsky, University of Freiburg. Dr. Gabriela Dilliway, University of Southampton. Prof. Nick Cowern, University of Newcastle. Acknowledgements: Science Foundation Ireland, Enterprise Ireland; R. Simon (ANKA), C. Paulmann (HASYLAB); EU FP6 Research Infrastructure Action. 2

3 Metrology Challenges Length scales Lateral (X-Y) Vertical (Z). Focus on Cu/low-k. Requirements: Non-destructive. In situ. In line. Nano sensitivities: small volumes, areas (nm-scale); impurity sensitivites (e.g cm -3 ); nano-void and nano-pore detection; etc. 3

4 Low-k metrology challenges New low-k dielectrics have different mechanical/physical properties compared to SiO 2. Pores in the material. Fragile delamination; stress-induced fracture. BEOL: problems with assembly and packaging. No convenient and competent metrology tools. Source: ITRS

5 Cu metallisation metrology challenges Source: ITRS 2005 Measuring barrier layer(s) under seed copper. Detection of voids in copper lines after CMP and anneal processes. Thick Cu lines mask this voiding. Detection through multi-layer structures e.g. individual layer thicknesses. Delamination of Cu from e.g. low-k layers before and after CMP. Local stress vs. wafer stress. Adhesion strength measurements are still done using destructive methods. Detection of killer pores and voids is not yet possible. 5

6 DCU s Four-Way Approach Gas Cell Photoacoustic Microscopy Micro-Raman Spectroscopy Synchrotron X-Ray Topography Finite Element Strain Modelling 6

7 Photoacoustic Microscopy (PAM) (incl. sample) Source: N. George, Cochin Univ. Sci. & Tech., India. 7

8 Automated PAM system for Si wafer analysis 8

9 Analysis of multi-layer structures on Si wafers SiO 2 Si Cu, SiO 2 layer thicknesses = 500nm Si Cu Si Cu SiO 2 Si 9

10 IC Chip Cracking & Delamination PA Phase [Deg.] Optical Micrograph Delamination Photoacoustic Phase Image 10

11 Wafer bonding defects (Phase Contrast) L. Xu, P McNally, DRIP XII, 9-13 September 2007 Berlin (Germany). Position [mm] Inhomogeneous bonding interference interface effects?? 0 Wafer Bonding defects confirmed by OM Position [mm] Wafer bonding defects confirmed by IR and Optical Microscopy Wafer edge effects Phase [Deg.] ICPAM Phase image ( f =216 Hz). 10,000 pixel image shown is obtained in 8 minutes. The bonding defects acted as extra thermal barrier, shown as extra time delay in phase images. Doppler interference effect at bonded 11

12 Ongoing PAM Developments Upgrade to 200 mm & 300 mm wafer capability (end-2007 Enterprise Ireland Proof of Concept Fund) Porous dielectric measurements early results promising. Wafer edge sub-surface cracks. Measure nm-scale delamination. Technology licensing underway. 12

13 Micro-Raman Spectroscopy (µrs) Incident light excites vibrational modes in the sample. Subsequently scatter the light. Some light is scattered at a different energy (wavelength). Raman light intensity is very weak. Typically about one photon out of Energy exchange between incident photons and semiconductor phonons (internal vibrational modes). The energy difference between the incident light (E i ) and the Raman scattered light (E s ) is equal to the energy involved in changing the phonon vibrational state E ph = E i - E s. 13

14 µrs (contd.) Laser source Mirror Confocal hole CCD detector Lens and mirror Mirror Sample Notch filter Microscope XY stage holding sample Strained/deformed crystal. Vibrations of crystal lattice altered. Spring constant(s) between atoms changed. Shifts frequency of inelastically scattered Raman photons. A plot this shifted light ouput intensity vs. frequency is a Raman spectrum. Strain in regions ~ 1µm diam. measured. 325nm laser penetration depth ~ 9nm true nanometric scale 14 metrology.

15 What is Synchrotron Radiation? Synchrotron radiation arises when energetic electrons or positrons are accelerated. E.g. being forced to travel in a curved path by bending magnets. Relativistic electrodynamics: particle speeds close to c!! Electrons lose energy through the emission of intense x-rays. 15

16 ANKA, Institute for Synchrotron Radiation, Karlsruhe, Germany. E=2.5GeV 16

17 Synchrotron X-Ray Topography White beam, i.e. a continuous spectrum of wavelengths (λ) available. Bragg s Law: Many diffraction directions!!! 2d hkl sinθ B = λ no. of lattice planes White beam: continuous distribution 17

18 SXRT Film 180 o -2θ Β1 X-Rays in Sample 180 o -2θ Β2 Back Reflection (Bragg) Geometry 18

19 Imaging Defects & Strain Low divergence synchrotron beam. Magnify each Bragg/Laue spot X-RAY TOPOGRAPH - a real space image of the energy flow of x-rays through the sample. Strain fields in the crystal modify this flow of energy. Observed as changes in recorded intensity. Sources of strain/defects: dislocations strain due to metallic/dielectric overlayers stacking faults precipitates magnetic domains grain boundaries, etc. 19

20 Electroless Cu deposition for Si IC interconnect Cu metallization Cu seed Ti Device speed limited by e -t/rc for interlayer connections. Reduce C use low-k dielectrics. Reduce R use Cu 20

21 µrs & SRST µrs BRST 21

22 Correlation of Strain Data Stress (MPa) FEM MRS Eq.6-32 Eq Cu line widths P. J. McNally et al., J. Appl. Phys., 96 (12), pp (2004), Semicond. Sci. Technol., 19, pp (2004). 22

23 Summary Photoacoustic Microscopy. Synchrotron X-Ray Topography. Micro-Raman Spectroscopy. FEM Modelling. Combined suite of technologies will provide versatile methodologies for advanced IC metrology. PAM can see through opaque (metallic) layers. Multi-layer characterisation : thicknesses, delamination, porosity. µrs Strain, chemical and dopant analysis from top few nm to >100 µm depths. True vertical nano-metrology. SXRT: Strain, defect, precipitate visualisation from top 10 Å to >100 µm into substrate. Virgin wafer through to completed circuit. Nanometre to mm probe depths. Virtually any materials combination!!! 23

24 Other SXRT Capabilities Packaged Si chip Sapphire substrates Disloc n A g.b = 0 b =

25 Other semiconductors and semiconductor devices examined Oxygen precipitates in Si 1mm Strain in Light Emitting Diodes 25

26 Confocal µrs microscope Allows rejection of radiation originating away from the focal point conjugate to the confocal aperture. This radiation from the blue and red planes does not pass through the aperture, because they are not focussed in the confocal plane. Raman radiation originating away from the sample depth of interest never reaches the entrance to the spectrograph Acquired spectrum is specific to the depth of the sample in focus. 26