Noncontact Thickness Measurement of Cu Film on Silicon Wafer Using Magnetic Resonance Coupling for Stress Free Polishing Application

A novel noncontact measurement method based on double-coil sensor is proposed for determining the thickness of copper (Cu) film on the silicon wafer in the process of stress free polishing (SFP). The double-coil sensor consists of two identical coaxial eddy current coils and corresponding auxiliary circuits, where the two coils are excited with the same sinusoidal signal and interact through the magnetic resonance coupling. The induced currents are produced in the Cu film through the electromagnetic coupling between double coils. The interaction equivalent circuit model of Cu film and two coils of double-coil sensor is discussed and the coil design and its lumped parameter extraction are analyzed. The linear relationship between the inductance difference of two coils and lift-off distance change (LODC) is formed and analyzed. By simulating the Cu film with different thicknesses sandwiched between two coils, the distribution and intensity of the magnetic field are presented. The slope of the relationship line between the inductance difference and the LODC is termed as SOR. Dependent on the LODC, the relationship between SOR and thickness of Cu film is extracted. Finally, the double-coil sensor is fabricated and the experiment is implemented. Different specimens with the thickness ranges from 100 to 500 nm are prepared and measured, where the measured maximum relative error is 4.7% and standard errors are between 2 and 13 nm. The experimental results demonstrate that the proposed measurement method is feasible and can confirm the thickness of Cu film on the silicon wafer. It is not only insensitive to the LODC but also can measure the thickness of less than $1~\mu \text{m}$ for Cu film on the silicon wafer.

[1]  Gui Yun Tian,et al.  An approach to reduce lift-off noise in pulsed eddy current nondestructive technology , 2014 .

[2]  Wei Li,et al.  A Thickness Measurement System for Metal Films Based on Eddy-Current Method With Phase Detection , 2017, IEEE Transactions on Industrial Electronics.

[3]  Karen Maex,et al.  Low-k dielectric materials , 2004 .

[4]  W. Barth,et al.  An overview of stress free polishing of Cu with ultra low-k(k<2.0) films , 2003, Proceedings of the IEEE 2003 International Interconnect Technology Conference (Cat. No.03TH8695).

[5]  Kai Xu,et al.  A Novel Triple-Coil Electromagnetic Sensor for Thickness Measurement Immune to Lift-Off Variations , 2016, IEEE Transactions on Instrumentation and Measurement.

[6]  Gui Yun Tian,et al.  Thickness measurement using liftoff point of intersection in pulsed eddy current responses for elimination of liftoff effect , 2016 .

[7]  Yi Wang,et al.  Design and experiment of wireless power transfer systems via electromagnetic field near-zone region , 2016 .

[8]  Brandt,et al.  Screening effect of Ohmic and superconducting planar thin films. , 1996, Physical review. B, Condensed matter.

[9]  Toh-Ming Lu,et al.  Development of an in-line X-ray reflectivity technique for metal film thickness measurement , 2001 .

[10]  T. Kojima,et al.  Application of CMP process monitor to Cu polishing , 2000 .

[12]  Karey Holland,et al.  Endpoint detection for CMP , 1998 .

[13]  C. Mulligan,et al.  Characterizing tantalum sputtered coatings on steel by using eddy currents , 2004, IEEE Transactions on Magnetics.

[14]  Bomson Lee,et al.  Alternative Expressions for Mutual Inductance and Coupling Coefficient Applied in Wireless Power Transfer , 2016 .

[15]  Zhihua Feng,et al.  Non-contact online thickness measurement system for metal films based on eddy current sensing with distance tracking technique. , 2016, The Review of scientific instruments.

[16]  Wuliang Yin,et al.  Thickness measurement of non-magnetic plates using multi-frequency eddy current sensors , 2007 .

[17]  Arun K. Sikder,et al.  Chemical mechanical planarization for microelectronics applications , 2004 .

[18]  Wuliang Yin,et al.  Thickness Measurement of Metallic Plates With an Electromagnetic Sensor Using Phase Signature Analysis , 2008, IEEE Transactions on Instrumentation and Measurement.

[19]  C. Mandache,et al.  Study of Lift-Off Invariance for Pulsed Eddy-Current Signals , 2009, IEEE Transactions on Magnetics.

[20]  Wei Li,et al.  Noncontact Thickness Measurement of Metal Films Using Eddy-Current Sensors Immune to Distance Variation , 2015, IEEE Transactions on Instrumentation and Measurement.

[21]  Nicola Bowler,et al.  Electrical conductivity measurement of metal plates using broadband eddy-current and four-point methods , 2005 .

[22]  Gui Yun Tian,et al.  Reduction of lift-off effects for pulsed eddy current NDT , 2005 .

[23]  Xinchun Lu,et al.  In-situ measurement of Cu film thickness during the CMP process by using eddy current method alone , 2013 .

[24]  H. Hocheng,et al.  A comprehensive review of endpoint detection in chemical mechanical planarisation for deep-submicron integrated circuits manufacturing , 2003 .

[25]  Yonggang Meng,et al.  Improvement of sensitivity of eddy current sensors for nano-scale thickness measurement of Cu films , 2014 .

[26]  Wuliang Yin,et al.  Simultaneous measurement of distance and thickness of a thin metal plate with an electromagnetic sensor using a simplified model , 2003, IEEE Transactions on Instrumentation and Measurement.

[27]  Gottlieb S. Oehrlein,et al.  Chemical Mechanical Planarization of Copper Damascene Structures , 2000 .

[28]  Cheng-Ching Yu,et al.  Application of soft landing to the process control of chemical mechanical polishing , 2003 .

[29]  D. Davidov,et al.  High-frequency eddy-current technique for thickness measurement of micron-thick conducting layers , 2001 .