Comparative film thickness determination by atomic force microscopy and ellipsometry for ultrathin polymer films

Abstract

Ellipsometry and atomic force microscopy (AFM) were used to study the film thickness of continuous and discontinuous polymer films in the 1-20 nm thickness range on smooth silicon wafers and on structured aluminium substrates. The methods of exploiting AFM for thickness measurements with a high spatial resolution are described.For continuous films, the AFM method is a direct one, i.e. it does not rely on any model. There is excellent agreement between AFM and ellipsometry in the 1-10 nm thickness range. Very small systematic deviations occur in this range but big deviations occur above 10 nm, and are discussed. The film preparation method, spin coating, was characterized to result in prepolymer films with a very homogeneous thickness.Discontinuous films of 2-9 nm thick were also evaluated by both methods of thickness determination. In tbis case, for one of the AFM approaches a model has to be used too. The agreement between both methods ranged from very good to poor, depending on the kind of sample and on the kind of AFM determination method.

Comparative characterisation by atomic force microscopy and ellipsometry of soft and solid thin films

“…At least two methods have been presented in the literature for creating measurable features in polymer films, from which the thickness can be obtained: (i) gently scratching off a part of the polymer film with a sharp tool 15 and (ii) producing a hole using an AFM tip in the contact mode. 20,42 To investigate whether there was any difference in the thickness values obtained from these methods, we applied both of them to one sample having a thickness of approximately 80 nm (PS spin-coated at 8000 rpm). The results for the hole and the scratch showed reasonable agreement within experimental error (Fig.…”

“…Fang et al 28 studied the relationship between the AFM roughness and the ellipsometric parameters for a chemically treated rough Si surface and showed that AFM roughness without the roughness spectral density information does not determine the ellipsometry parameters unambiguously. However, to our knowledge, all papers published to date deal with either soft organic films 3,20,27,29 or solid semiconductor/dielectric surfaces, 28,30,31 but not both together.…”

“…Morota et al 17 found an 'excellent agreement' between the roughness thickness estimated from ellipsometry and AFM root mean square (rms) values for chemically treated GaP surfaces. The second set can be characterised as showing fair but not perfect agreement between the data obtained from both techniques; 8,10,18,19 usually good agreement has been achieved in a particular interval of film thickness only 20 or results from a special surface treatment. 21,22 The thickness of the top rough layer was identical to the roughness obtained by AFM for untreated polysilicon thin film, but a discrepancy between AFM and ellipsometry was observed after etching in a fluorocarbon plasma, which was attributed to the thin, carbon-rich fluorocarbon layer present on the surface.…”

Structure of self-assembled layers on silicon: Combined use of spectroscopic variable angle ellipsometry, neutron reflection, and atomic force microscopy

“…AFM has the advantage of direct observation of surface morphology and, in particular, can provide information about the surface coverage. 17 A combination of either ellipsometry and AFM 18 or ellipsometry and neutron reflectivity 19 is often used as a means of better characterization of the system under study. This study uses simultaneously three techniques-a rare combination, which results in a more accurate description of the OTS structure at the solid surface.…”

Paradigm change in hydrogel sensor manufacturing: from recipe-driven to specification-driven process optimization

“…This direct measurement procedure allows the determination of the mechanical film thickness at a single position d(x, y). Gesang et al (1995) have shown that for polymer films thicker than 10 nm, ellipsometrically measured thickness values d ellips are significantly larger than the corresponding values d mech obtained by AFM measurements. With respect to the mechanical (acoustic) transducer principle, d mech seems more suitable as a quality-determining film parameter than d ellips .…”