Thickness measured with ellipsometry

The thickness dependence of the InAs deposits as a function of the As deposition potential is shown in Figure 28. At positive potentials, above —0.6 V, little deposit is formed, as would be expected. Below —0.6 V, a relative plateau is observed, which gradually increases between —0.625 and —0.775 V. Below about —0.7 V, the deposits correspond to over 1 ML/cycle, and some roughening is evident with optical microscopy. Below —0.775 V, the coverages measured with ellipsometry drop to a level expected for about 1 ML/cycle, but microscopy shows the deposits to be greatly roughened, sandy. Coverage measurements with EPMA also indicate the deposits at... 

Ellipsometry at noble metal electrode/solution interfaces has been used to test theoretically predicted microscopic parameters of the interface [937]. Investigated systems include numerous oxide layer systems [934-943], metal deposition processes [934], adsorption processes [934, 944] and polymer films on electrodes [945-947]. Submonolayer sensitivity has been claimed. Expansion and contraction of polyaniline films was monitored with ellipsometry by Kim et al. [948]. Film thickness as a function of the state of oxidation of redox active polyelectrolyte layers has been measured with ellipsometry [949]. The deposition and electroreduction of Mn02 films has been studied [950] below a thickness of 150 nm, the anodically formed film behaved like an isotropic single layer with optical constants independent of thickness. Beyond this limit, anisotropic film properties had to be assumed. Reduction was accompanied by an increase in thickness, which started at the ox-ide/solution interface. 

Since an additional ellipsometric measurement would be needed to determine the carbon-overcoat thickness, the ellipsometric measurement of PFOM thickness directly on non-carbon-overcoated silicon is more straightforward. Silicon strips and wafers were dip coated with PFOM. The PFOM thickness measnred by ellipsometry and the dIX from XPS are listed in table 4.8. The thickness measured by ellipsometry was divided by the dIX from XPS for each sample (last two columns in table 4.8). The experimentally determined average electron mean free path for PFOM film is X = 2.66 nm. Sliders were dip coated with PFOM at the same conditions as the silicon wafers and strips, and dIX was measured on the air bearing surface of each slider by XPS. These dIX were multiplied by A, = 2.66 nm, as determined above, to estimate the PFOM thickness on the air bearing surface. These results are listed in table 4.9. The concentration of the PFOM solution was 650 ppm, and the withdrawal rate was 1.6 mm/s. 

The d-PS-g-MA with an MA content of 0.3 wt% can only give rise to structurally very simple graft copolymers compared to the complex graft copol)miers resulting from high functional SMA types. This also means that the low interfacial thickness of the bi-layer PA-6I/d-PS-g-MA (NR data) does not a priori exclude the large interfacial thickness of the bilayers PA12/SMA [102] (measured with ellipsometry). 

Gas barrier properties of polymeric membranes are strongly dependent on thickness, making it critical to verify thickness measurement with multiple methods. Several techniques for obtaining film thickness were reviewed here to demonstrate the benefits and challenges associated with each. Although ellipsometry is a common technique for non-contact and non-destructive thin film characterization, the other methods are necessary to confirm the measured thickness. 

In recent years, high-resolution x-ray diffraction has become a powerful method for studying layered strnctnres, films, interfaces, and surfaces. X-ray reflectivity involves the measurement of the angnlar dependence of the intensity of the x-ray beam reflected by planar interfaces. If there are multiple interfaces, interference between the reflected x-rays at the interfaces prodnces a series of minima and maxima, which allow determination of the thickness of the film. More detailed information about the film can be obtained by fitting the reflectivity curve to a model of the electron density profile. Usually, x-ray reflectivity scans are performed with a synchrotron light source. As with ellipsometry, x-ray reflectivity provides good vertical resolution [14,20] but poor lateral resolution, which is limited by the size of the probing beam, usually several tens of micrometers. 

Optical Exposure. Multicomponent LB films were prepared from solutions of novolac/PAC varying in concentration from 5-50 wt% PAC, and transferred at 2.5 -10 dyn/cm. The films were composed of 15 - 20 monolayers, with an average film thickness of 30 nm, as measured by ellipsometry. Exposures were performed with a Canon FP-141 4 1 stepper (primarily g-line exposure) at an exposure setting of 5.2 and with a fine line test reticle that contains line/space patterns from 20 to 1 pm (40 to 2 pm pitch). They then were then developed in 0.1 - 0.2 M KOH, depending on the PAC content The wafers received a 20 min 120°C post development bake to improve adhesion to the Cr. Finally, the Cr was etched in Cyantek CR-14 chromium etchant, and the resist and Cr images were examined by SEM. 

Fig. 5.10 Voltage-time curve (solid line) for an n -type silicon electrode (3 mficm) anodized with a constant current density of 6.25 mA crrf2 for t> 0 (sample at OCP for t<0) in 0.3 mol kg- NH4F (pH = 3.5). The thickness of the anodic oxide was measured by ellipsometry (open circles, broken line fitted as a guide to the eye). The etch rate of the anodic oxide in the electrolyte was measured (values above arrows) at different...

No carbon was recorded for the D-treated film. The O/Si composition ratio was found to be 2.08 and is attributed to the extent of condensation as the organic phase has been removed completely. Based on the amount of Si for sample D and assuming a density of 2.3 g cm3 for amorphous SiC>2, the top layer would correspond to a thickness of 154 nm, if a dense layer is assumed. As the actual layer thickness is 458 nm, this would imply a porosity of 66%. Here a considerable discrepancy with the porosity obtained from ellipsometry is evident. In this respect it should be noted that the RBS measurement was done more to the edge of the sample than ellisometry, where the thickness is smaller than in the centre. Further, the refractive index determined with ellipsometry is very accurate. However, the relation of porosity with refractive index depends on the model used. 

Ellipsometry is suitable for the measurement of films whose thickness is much less than the wavelength of light. The thickness measurement of films having hundreds of molecular layers is best carried out using a stylus device such as the Talystep. Here a groove is scribed in the film and the stylus measures the depth of this groove. In the case of very soft materials, the film can be coated with a metallic layer having a thickness of about 20 nm which is deposited in vacuo after the line has been scribed. 

Measurement of such small thicknesses is difficult. Ellipsometry [3] and angle-dependent XPS [5] may be used with care to avoid complications caused by surface roughness. 

Peyser and Stromberg63 used the ATR method to measure the thickness of a polystyrene layer adsorbed on a quartz surface from cyclohexane solution at 35 °C and compared it with the thickness obtained by ellipsometry. Good agreement was observed although the ellipsometric measurements were made for the chrome plate. 

Takahashi et al.67) prepared ionene-tetrahydrofuran-ionene (ITI) triblock copolymers and investigated their surface activities. Surface tension-concentration curves for salt-free aqueous solutions of ITI showed that the critical micelle concentration (CMC) decreased with increasing mole fraction of tetrahydrofuran units in the copolymer. This behavior is due to an increase in hydrophobicity. The adsorbance and the thickness of the adsorbed layer for various ITI at the air-water interface were measured by ellipsometry. The adsorbance was also estimated from the Gibbs adsorption equation extended to aqueous polyelectrolyte solutions. The measured and calculated adsorbances were of the same order of magnitude. The thickness of the adsorbed layer was almost equal to the contour length of the ionene blocks. The intramolecular electrostatic repulsion between charged groups in the ionene blocks is probably responsible for the full extension of the... 

Polyimide surface modification by a wet chemical process is described. Poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA) and poly(bisphenyl dianhydride-para-phenylenediamine) (BPDA-PDA) polyimide film surfaces are initially modified with KOH aqueous solution. These modified surfaces are further treated with aqueous HC1 solution to protonate the ionic molecules. Modified surfaces are identified with X-ray photoelectron spectroscopy (XPS), external reflectance infrared (ER IR) spectroscopy, gravimetric analysis, contact angle and thickness measurement. Initial reaction with KOH transforms the polyimide surface to a potassium polyamate surface. The reaction of the polyamate surface with HC1 yields a polyamic acid surface. Upon curing the modified surface, the starting polyimide surface is produced. The depth of modification, which is measured by a method using an absorbance-thickness relationship established with ellipsometry and ER IR, is controlled by the KOH reaction temperature and the reaction time. Surface topography and film thickness can be maintained while a strong polyimide-polyimide adhesion is achieved. Relationship between surface structure and adhesion is discussed. 

Polyimide surface modification with KOH or NaOH aqueous solution is well defined. The reaction initially gives potassium or sodium polyamate which is then protonated with acid to yield polyamic acid. The outermost layer (5 A) of PMDA-ODA can be completely modified within a minute of reaction in KOH solution. The depth of modification can be measured by a method using an absorbance-thickness relationship established with ellipsometry and external reflectance IR. The modification depth of PMDA-ODA treated with 1 M KOH aqueous solution at 22 °C for 10 min is approximately 230 A. Surface topography and film thickness can be maintained while a strong... 

Deposition of a monolayer film of 3S at 20 mN/m surface pressure on a silicon wafer was achieved by z-type with transfer efficiency consistently in the range of about 0.5-0.6 (Figure 2). Such low transfer may imply that the hyperbranched polymer can be squeezed under compression, through either conformational change or intercalation. The overcompression could be relieved by transfer onto a solid substrate where the molecule occupies an area larger than on the water/air interface. The thickness of the deposited monolayer measured by ellipsometry was about 32A for the first few layers, but this number declined slowly as the number of depositions increased. The homogeneity of the film, judged from the standard deviation of the film thickness, also deteriorated. The... 

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