Characterize Mechanical Properties of Thin Films for Microelectronics

Nanoindentation of low-k thin films for microelectronics

Mechanical characterization of low-k thin films for microelectronics requires nanoindentation

The most common application for nanoindentation is the mechanical characterization of low dielectric constant (low-κ) films for microelectronics. For optimal electrical separation, the dielectric constant (κ) should be as low as possible.  However, processes which tend to lower the dielectric constant, such as increasing porosity in the film, also tend to lower the strength of the material.  An important optimization in microelectronic design is to lower the dielectric constant as much as possible while maintaining sufficient mechanical strength.  

Nanoindentation is the primary means for evaluating the mechanical strength of low-κ materials.  Using the Hay-Crawford model to design an automatic correction for substrate influence, the measured Young’s modulus is the true value for the low-κ film, independent of the substrate upon which it is deposited. This correction is shown graphically in the data for thin low-κ films.

Young's modulus as a function of indentation depth, normalized by film thickness

Young's modulus as a function of indentation depth, normalized by film thickness

The pink and light blue traces are substrate-influenced modulus curves, using the Oliver-Pharr method for dynamic stiffness measurements. At greater indentation depths, the measured Young's modulus increases due to the increasing influence of the silicon substrate. The red and blue traces use the Hay-Crawford model to compensate for substrate modulus. In reporting values for Young's modulus, data from each corrected trace are averaged between the limits of 29% and 31%, as indicated by the parallel black lines.  The Hay-Crawford model allows substrate-independent measurements to be made using indentation depths as large as 40% of the film thickness.

Using this thin film nanoindentation method, the model works well not only with a compliant film on a stiff substrate but also for a stiff film on a compliant substrate. No other existing analytic models have achieved such accurate measurements as the Hay-Crawford model for nanoindentation. This method is incorporated into the Thin Film Indentation Package for the iNano and iMicro systems. 

For a copy of the "Young's Modulus and Hardness of Thin Low-κ Films Using Nanoindentation" Application Note with complete details and experimental method, please fill out the contact form, indicating an interest in nanoindentation for low-κ films.


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