Vladimír Čudek

Optical characterization of non-uniform thin films using imaging spectrophotometry

In this paper the method of imaging spectrophotometry enabling us to characterize non-absorbing thin films non-uniform in the optical parameters is described. This method is based on interpreting the spectral dependences of the local absolute reflectances measured at the normal incidence of light. It is shown how to determine the area distribution of thickness and refractive index of the non-absorbing non-uniform thin films by treating these reflectances. Moreover, the generalization of the method for the optical characterization of slightly absorbing non-uniform thin films is also indicated. Furthermore, the two-channel imaging spectrophotometer enabling us to apply the method of imaging reflectometry is described. The procedure for determining the spectral dependences of the local absolute reflectance in the points aligned in a matrix situated on the illuminated area of the non-uniform thin film by means of the spectrophotometer is also presented. The practical advantages of the method are specified. The method is illustrated by means of the optical characterization of a selected epitaxial ZnSe thin film prepared using molecular beam epitaxy onto gallium arsenide single-crystal substrate.

Mapping of properties of thin plasma jet films using imaging spectroscopic reflectometry

The construction of a normal-incidence imaging spectrophotometer for mapping of thin film properties is described. It is based on an on-axis reflective imaging system, utilising a telescope-like arrangement. A charge-coupled device camera is used as the detector, permitting measurements in the spectral range of 275-1100 nm with resolution of 37 mu m. The performance of the instrument is demonstrated by optical characterisation of highly non-uniform thin films deposited from hexamethyldisiloxane on silicon substrates by a single capillary plasma jet at atmospheric pressure. The imaging spectrophotometry is used as a self-sufficient technique for the determination of both the film optical constants and maps of local thickness. The thickness maps are compared with the results of conventional thickness profile characterisation methods, profilometry and atomic force microscopy and the differences and errors are discussed.

Measurement of thickness distribution, optical constants, and roughness parameters of rough nonuniform ZnSe thin films

Epitaxial ZnSe thin films exhibiting two important defects, i.e., boundary roughness and thickness nonuniformity, prepared on GaAs substrates, are optically characterized using a combination of variable-angle spectroscopic ellipsometry, spectroscopic near-normal reflectometry, and imaging spectroscopic reflectometry (ISR). The influence of boundary roughness is incorporated into optical quantity formulas by the Rayleigh-Rice theory. Thickness nonuniformity is included using averaging of the unnormalized Mueller matrices. The dispersion model of the optical constants of the ZnSe films is based on parametrization of the joint density of electronic states. Very thin overlayers represented by thin films with identically rough boundaries are taken into account on the upper boundaries of the ZnSe films. Standard optical techniques are used to determine the spectral dependencies of the optical constants of the ZnSe films, together with the parameters of roughness and thickness nonuniformity. ISR is then used to find the maps of the local thickness and local rms value of height irregularities. The values of roughness parameters, determined using the standard techniques and ISR, are verified by a comparison with results obtained by atomic force microscopy.

New Method for the Complete Optical Analysis of Thin Films Nonuniform in Optical Parameters

In this paper, a new optical method for characterizing thin films exhibiting area nonuniformity in optical parameters is described. This method is based on interpreting the spectral dependences of the reflectance measured using the special experimental arrangement described in detail. Using this method, the distribution of both the optical parameters, i.e. the local thickness and local refractive index, describing the thin film studied can be determined along a large area of the substrate. It is shown that the method presented can be employed for determining strong nonuniformities in the optical parameters of the films studied. The method is illustrated through the optical analysis of strongly nonuniform thin films formed by a mixture of CNx and SiOy deposited onto silicon single-crystal substrates.

Characterization of thin films nonuniform in optical parameters by spectroscopic digital reflectometry

In this paper, a new optical method for characterizing nonuniform thin films is employed. For applying this method the special experimental arrangement containing CCD camera as a detector is used. Using this experimental arrangement the spectral dependencies of the local reflectances are obtained. After treating these experimental data of the distributions of the values of the local thicknesses and local refractive index along a large areas of the substrates of the nonuniform films are found. Moreover, it is shown that this method can be used to determine strong nonuniformities in both the optical parameters. The method is illustrated through the optical characterization of a nonuniform ZnSe epitaxial thin film deposited onto gallium arsenide single-crystal substrate and nonuniform film formed by the mixture of CNx and SiOy deposited onto silicon single-crystal substrate.

Optical measurement of mechanical stresses in diamond-like carbon films

In this paper the mechanical stresses taking place in diamond like thin films prepared by the plasma enhanced chemical vapor deposition onto silicon single crystal substrates are studied. For determination of the stress values the Stoneys formula is used. The values of the film thicknesses are determined using the combined method of variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry. The values of the curvature radii of the deformed silicon substrates in consequence of the film stresses are evaluated using interferometric method based on two-beam interferometry and chromatic aberration method. The dependence of the mechanical stress inside these films on their thickness values is determined. It is found that this dependence can be approximate by the straight-line. The results achieved for the mechanical stresses obtained by both the optical methods, i.e. by the interferometric and chromatic aberration method, are compared. It is shown that within the experimental accuracy the stress values determined using both these method are identical. Thus, it is shown that the chromatic aberration method is suitable for measuring the mechanical stresses inside the thin solid films and it is the competitive method for the other optical methods utilized for this purpose so far.

Mechanical stresses studied by optical methods in diamond-like carbon films containing Si and O

In this paper the quantitative dependence of the mechanical stress inside diamond-like carbon films containing Si and O atoms on a flow rate ratio of methane CH4 and hexamethyldisiloxane C6H18Si2O in the deposition mixture is determined. For this purpose the modified Stoneys formula is employed. The important quantities taking place in this formula, i.e. the radius of curvature of the spherical surface of a deformed silicon substrate because of the film stress and the film thickness, are determined using the combined optical method based on two-beam interferometry, variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry. It is shown that the influence of the flow rate ratio on the values of the mechanical stresses taking place inside these films is negligible within the experimental accuracy achieved for determining these stresses if the total flow rate of gases used to be constant in the deposition mixture. A discussion of this fact is also performed. The film studied were prepared using the plasma enhanced chemical vapor deposition.

Measurement of optical parameters of thin films non-uniform in thickness

A multi-pixel modification of the data fitting procedure for imaging spectroscopic reflectometry is used for the optical characterisation of thin films non-uniform in thickness. It is shown that this procedure allows a more precise and reliable determination of the optical parameters compared to the standard application of the imaging spectroscopic reflectometry. This modification is applied to SiOxCyHz and carbon nitride thin films. The optical constants of these films are verified by standard variable-angle spectroscopic ellipsometry.