Detection of Water in Low-k Dielectric Films - eufanet

Monitoring the change of the amount of water in the dielectric over time. Sample stack – Using the infrared reflection-absorption method. (IRRA spectroscopy).
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Fakultät Elektrotechnik und Informationstechnik, Institut für Halbleiter- und Mikrosystemtechnik

Smart Failure Analysis for New Materials in Electronic Devices

Detection of Water in Low-k Dielectric Films Christoph Kubasch, Johann W. Bartha

Dresden, 17.09.2012

Outline Introduction of low-k dielectrics Investigation of the water absorption Measurement equipment Contact angle measurements Gravimetrical measurements Electrical measurements Optical measurements Summary

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1 Introduction of low-k Dielectrics

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1 Introduction of low-k Dielectrics

W. Volksen et al., Chem. Rev. 110 (1) (2010) 56–110.

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1 Introduction of low-k Dielectrics Damaging of the dielectrics Defect free ideal case

RIE process

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CMP process

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1 Introduction of low-k Dielectrics Damaging of the dielectrics

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2 Investigation of the water absorption in low-k dielectric films Questions:

Do the low-k material absorb water from the atmosphere and how much is it? How fast is the water diffusion in the dielectrics? What kind of interaction between water and the dielectric occurs?

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Measurement Equipment Electrical and gravimetrical measurement setup

Measurement equipment

Keithley 4200-SCS • 3 SMU (max. 200 V) • CV-Unit • Pulse generator and oscillator Keithley SMU 237 (max. 1100 V) Rel. humidity between 0 and 90 % Dresden, 17.09.2012

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Quartz crystal microbalance Slide 8 of 19

Measurement Equipment Optical measurement setup Bruker Vertex v80 Spectrometer FTIR Spectrometer Measurement in vacuum • Reflection • Transmission • ATR 300-mm-Wafer-Mapper • Reflection • Transmission

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2.1 Contact Angle Measurements How is the wettability of a ULK dielectric with water?

The contact angle is depending on: • Sample conditions (roughness, contaminations) • Dispense conditions (liquid temperature, density, drop volume, time between dispense and measurement) • Laboratory conditions (humidity, temperature)   Water drop on a ULK surface Dresden, 17.09.2012

The contact angle measurement is a qualitative method to characterize the wettability It is not possible to estimate the water absorption of the dielectric by measuring the contact angle TUD / C. Kubasch

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2.2 Gravimetrical Measurements How much water is in the low-k dielectric?  Quartz Crystal Microbalance (QCM) • •

Direct relationship between change of mass and measurement signal High accuracy in the range of nanogram Δf f0 Δm m0

Sample stack

Frequency shift Resonance frequency Change in mass Mass of quartz crystal

Challenges • Deposition and structuring of the low-k dielectric on top of the quartz crystal • Determination of the “sensitivity factor” for the QCM system • Considering of the surface coverage with water Dresden, 17.09.2012

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2.2 Gravimetrical Measurements Quartz Crystal Microbalance (QCM) (Benzocyclobutene - BCB)

 Water uptake of BCB is about 0.14 wt% [1] [1] C. Kubasch and J. Bartha, IITC/MAM 2011 Dresden, 17.09.2012

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2.3 Electrical Measurement How fast is the water diffusion in the low-k dielectric?  Capacitance-Time-Measurement (C-t) • •

Contact pad used as water diffusion barrier Monitoring the change of the permittivity C ε0 εr A/d

Capacitance Permittivity of vacuum Absolute permittivity Area/Thickness

Sample stack – MIM structure

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2.3 Electrical Measurement Capacitance Time Measurement (ULK)

´

 Diffusion constant D0 of water in the shown ULK ≈ 1.1 × 10−11 m2/s [2] D0(SiLKTM) ≈ 10−10 m2/s [3] and D0(Polyimide) ≈ 10−12 m2/s [4] [2] C. Kubasch et al., IEEE Trans. Electron Devices, 57 (8) (2010) 1865–1872. [3] T. M. Shaw et al., Proc. Mater. Res. Soc.—AMC (2003) 77–84. [4] P. Bhargava et al., J. Appl. Polym. Sci. , 102 (2006) 3471–3479. Dresden, 17.09.2012

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2.3 Electrical Measurement Relationship between C-t and QCM measurements  Debye equation

εr N k T µ a

Absolute permittivity Numbers of molecules per m³ Boltzmann constant Temperature Permanente dipole moment Polarizability

Calculation of the water amount in the dielectric with the Debye equation

εr,dry Nw µw

Absolute permittivity in dry state εr,sat Numbers of water molecules per m³ aw Permanente dipole moment of water vapor

Absolute permittivity in saturation state Polarizability of water vapor

 The calculated amount of water are in very good agreement with the measured results of the QCM measurement [1] C. Kubasch and J. Bartha, IITC/MAM 2011 Dresden, 17.09.2012

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2.4 Optical Measurement Is there an interaction between water and the dielectric?  Fourier Transform Infrared (FTIR) Spectroscopy • • •

Investigation of structural changes in the dielectric Investigation of the bonding types Monitoring the change of the amount of water in the dielectric over time

Sample stack – Using the infrared reflection-absorption method (IRRA spectroscopy)

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2.4 Optical Measurement FTIR spectroscopy – Overview of two ULK spectra Lambert-Beer Law Relationship between light absorption, concentration and film thickness But! The relationship is valid for film thicknesses larger than the wave length of the used light Handbook of Spectroscopy, G. Gauglitz and T. Vo-Dinh, 2006

Comparison of Spectra Comparison of films with about the same thickness Calculation of the ratio between a peak and the main characteristic peak of the material (Si−O−Si) Water absorption Water absorption will change the spectra in the range between 3000 cm-1 and 3700 cm-1 The amount of silanol (Si−OH) is a critical factor for the water absorption [5] C. Kubasch et al., Trans. Electron Devices 58 (9) (2011) 2888–2894. Dresden, 17.09.2012

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2.4 Optical Measurement FTIR spectroscopy (ULK)

Water difference spectra at different times in respect to the outgased state

Area of the difference spectra at different times

A change in the silanol bonding state can be noticed. The results of the investigation of the outgasing process with the help of the FTIR is comparable to the results of the C-t measurements. Dresden, 17.09.2012

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3 Summary Contact Angle Measurement • •

Characterization of the wettability No conclusions about the water absorption possible

Quartz Crystal Microbalance • •

Precise determination of the water amount Sample preparation is challenging

Capacitance Time Measurements • •

Monitoring the change in the permittivity over time  Diffusion behavior Calculation of the water amount by using the Debye equation

FTIR Spectroscopy • Investigating structural changes of the material matrix • Detection of changes in the chemical bonds • Monitoring of the diffusion behavior Dresden, 17.09.2012

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Acknowledgment

Dresden University of Technology Institute for Semiconductors and Microsystems GLOBALFOUNDRIES Dresden Module One, Limited Liability Company & Co. KG, Dresden, Germany Hartmut Ruelke and Ulrich Mayer Unterstützt durch die Sächsische Aufbaubank

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References C. Kubasch and J. Bartha, "Fundamental relationship between capacitance-time measurements and gravimetric measurements for water absorption in a low-k dielectric," in Interconnect Technology Conference and 2011 Materials for Advanced Metallization (IITC/MAM), 2011 IEEE International, pp.1–3. C. Kubasch, C. Klaus, H. Ruelke, U. Mayer, and J. W. Bartha, "Investigation of Moisture Uptake in Low-k Dielectric Materials," IEEE Transaction on Electron Devices, vol. 57, no. 8, pp. 1865–1872, 2010. C. Kubasch, H. Schumacher, H. Ruelke, U. Mayer, and J. Bartha, "Fourier Transform Infrared Spectroscopy of Moisturized Low-k Dielectric Materials," IEEE Transaction on Electron Devices, vol. 58, no. 9, pp. 2888 -2894, 2011. T. M. Shaw, D. Jimerson, D. Haders, C. E. Murray, A. Grill, and D. C. Edelstein, "Investigation of delay, crosstalk and crosstalk delay in sub 90 nm CMOS interconnects," Advanced Metallization Conference 2003 (AMC 2003): Proceedings, 20th International Conference, vol. -, no. 1, pp. 77-84, 2003. W. Volksen, R. Miller, and G. Dubois, "Low Dielectric Constant Materials," Chemical Reviews, vol. 110, no. 1, pp. 56– 110, 2010. P. Bhargava, K. C. Chuang, K. Chen, and A. T. Zehnder, "Moisture diffusion properties of polyimide HFPE-II-52 resin," Journal of Applied Polymer Science, vol. 102, pp. 3471–3479, 2006. G. Gauglitz and T. Vo-Dinh, "Handbook of Spectroscopy," 2006.

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