Lateral and Vertical Quantification of Spin-Coated Polymer Films on Silicon by TOF-SIMS, XPS, and AFM

Abstract

PMMA and PVC were spin coated on silicon wafers using a range of polymer concentrations. This resulted in a corresponding range of film thicknesses and, for ultrathin film layers, various degrees of surface coverage. The thickness was determined by AFM profilometry and was used to correlate the time scale of a dynamic TOF-SIMS depth profile analysis to a depth scale. The degree of surface coverage was determined from AFM imaging and was used to correlate polymer secondary-ion yields of a static TOF-SIMS analysis to the degree of surface coverage. TOF-SIMS imaging was found to be inferior to AFM imaging with regard to determining the degree of surface coverage of polymers on silicon surfaces. PVC and PMMA both form separated domains on silicon when using spin-coating solutions with a polymer concentration below a materialdependent threshold. In the intermediate concentration range between domain formation and complete surface coverage, networks form. At low concentrations, the deposited polymer material was heterogeneously distributed in the plane of the film as well as vertically to the substrate, resulting in relatively thick hillocks distributed over a limited surface area. At higher concentrations, where network formation is observed, the polymer is heterogeneously distributed in the plane of the film with a large degree of surface coverage, and the average small thickness of the polymer network is fairly constant. A linear correlation was observed between the secondary-ion yield and the degree of surface coverage for both PVC and PMMA, which constitutes the calibration curves for the lateral quantification.

Influence of the organic layer thickness in (Metal-Assisted) secondary ion mass spectrometry using Ga+ and C60+ projectiles

“…The characterization of polystyrene oligomers (PS) on etched silver by 10 keV monoatomic Ar ϩ projectiles showed that the maximum yields were obtained when PS was prepared as a monolayer [11]. Other experiments performed with PMMA and PVC polymers led to similar conclusions [12]. The common factors for the aforementioned experiments were the use of coatings on specific substrates, in combination with an atomic projectile for analysis.…”

“…The concentration of the spin-coated PS solution was 1 mg/mL and ellipsometric measurements indicate that the layer thickness is in the range 3-4 nm for those samples ( Table 1). The thickness values indicate that for 1 mg/mL, PS forms a monolayer coverage [11,12]. The mass spectra represent the intensity variation of the Au-cationized molecular ion, (M ϩ Au) ϩ , for PS spin-coated on Si and metallized with 0.5 nm Au (a), PS metallized with 6 nm Au (b), and PS spin coated on Au substrate (c).…”

“…Without metallization, the effect of the PS sample concentration on the characteristic secondary ion yields is dramatic and strongly dependent on the chosen projectile type (Figure 2). For atomic projectile bombardment, maximums in the yield versus concentration curves have been already reported for polymers such as PS [11], PMMA [12,26], PVC [12], and for biological films [13]. Norrman et al [12] spin-coated PMMA and PVC on Si wafers using a range of polymer concentrations.…”

“…For atomic projectile bombardment, maximums in the yield versus concentration curves have been already reported for polymers such as PS [11], PMMA [12,26], PVC [12], and for biological films [13]. Norrman et al [12] spin-coated PMMA and PVC on Si wafers using a range of polymer concentrations. They found that the maximum ion yield is observed at 1 mg/mL for both polymers suggesting similar concentrations for what corresponds to 100% surface coverage.…”

An XPS and ToF-SIMS investigation of the outermost nanometres of a poly(vinylidene difluoride) coating

“…The use of a SF 5 + cluster ion as a depth profiling etch tool for use on polymeric samples has been demonstrated by Fuoco et al employing PMMA thin film on silicon [13], Norrman et al also used PMMA and poly(vinyl chloride) films spin coated onto Si wafer [14] and by Mahoney et al who investigated poly(L-lactic acid) (PLLA) doped with 4-acetaminodophenol [15] and PLLA blended with a triblock co-polymer [16]. Most recently, with the introduction of the Buckminsterfullerene (C 60 ) cluster ion source as an etch tool, the depth profiling of polymeric (or organic) materials has taken great strides forward.…”