Characterization of Films with Thickness Less than 10 nm by Sensitivity-Enhanced Atomic Force Acoustic Microscopy

We present a method for characterizing ultrathin films using sensitivity-enhanced atomic force acoustic microscopy, where a concentrated-mass cantilever having a flat tip was used as a sensitive oscillator. Evaluation was aimed at 6-nm-thick and 10-nm-thick diamond-like carbon (DLC) films deposited, using different methods, on a hard disk for the effective Young's modulus defined as E/(1 - ν2), where E is the Young's modulus, and ν is the Poisson's ratio. The resonant frequency of the cantilever was affected not only by the film's elasticity but also by the substrate even at an indentation depth of about 0.6 nm. The substrate effect was removed by employing a theoretical formula on the indentation of a layered half-space, together with a hard disk without DLC coating. The moduli of the 6-nm-thick and 10-nm-thick DLC films were 392 and 345 GPa, respectively. The error analysis showed the standard deviation less than 5% in the moduli

Characterization of nano-thin films and membranes by use of atomic force acoustic microscopy methods

The atomic force acoustic microscopy (AFAM) technique combines the principle of atomic force microscopy (AFM) for nanoscale imaging with the ability to detect changes in elastic modulus on a tested sample. Depending on the mode of operation, AFAM provides qualitative and quantitative information on the effective stiffness of the probed sample either in the form of images or point measurements. AFAM is a contact based method and as such provides information on the sample indentation modulus from a volume that is compressed under the AFM tip. The size of the compressed volume depends on the static load applied to the tip, tip radius, and the elastic properties of the tip and the probed sample and thus it can be controlled. The AFAM technique can be a powerful tool for characterization of thinfilm systems and detection of defects that are buried at a depth of about 30 nm - 150 nm. We used the AFAM method to study various nano-thin systems. A set of nine square membranes 3.7 µm x 3.7 µm large, with thickness increasing in 30 nm steps from 30 nm to 270 nm was dry etched in silicon. AFAM qualitative images obtained on the surface of this sample showed all the membranes allowing for their localization. In addition, we used AFAM to determine indentation modulus of silicon oxide films Mf with the thickness varying from 7 nm to 28 nm. The values obtained for Mf varied from 80 GPa to 90 GPa and were in good agreement with the literature values

Nanometer deformation of elastically anisotropic materials studied by nanoindentation

The reduced modulus, E-R, of elastically anisotropic materials (Si, CaF2 and MgF2) was determined for sub-10 nm, several-10 nm and several-100 nm indentation depths, applying the Hertzian and Oliver-Pharr approaches. The E-R values determined for Si(100), Si(111), CaF2(100) and MgF2(100) deforming at sub-10 nm indentations (i.e. 135 GPa, 177 GPa, 142 GPa and 168 GPa) are in good agreement with the theoretical unidirectional E-R values (i.e. 125 GPa, 173 GPa, 135 GPa, 160 GPa). With increasing penetration depth up to several-10 nm, the E-R values gradually deviate from the unidirectional values to the weighted averaged values. E-R remains constant for sub-10 nm and several-10 nm penetration depths, performing the same indentation tests on amorphous organosilicate glass. The results of this study indicate that the modulus determined by nanoindentation depends on the size of indentation (ratio between contact radius and tip radius, a/R), especially in the case of elastically anisotropic materials. It is demonstrated for several-10 nm and several-100 nm penetration depth that the phase transformations in Si during the indentation tests strongly affect the E-R values