KPFM and XPS Metrology of Self-Assembled Monolayer Barrier for Copper Metallization

Abstract

Silane based Self assembled monolayer (SAM) has been demonstrated as a diffusion barrier layer on lowK dielectrics for sub 10 nm Cu interconnects for Integrated Circuit (IC) applications. A key problem in developing barrier layer is its monitoring capability, especially its thickness, uniformity, its coverage and defect density. The aim of this work is to develop surface analysis methods for characterizing those variables providing in line monitoring techniques that can predict barrier quality and reliability. The approach presented in this paper was to examine the defect density and coverage properties of the SAM on LowK dielectric using physical methods for the characterization of monolayer thick films, i.e. Variable Angle X-Ray Photoelectron Spectroscopy (VA -XPS) and Kelvin Probe scanning Force Microscopy (KPFM). The SAMs were deposited on three different substrates: bare-Si wafers, thermal oxide/Si and Low-k dielectrics on silicon wafers. The silanization was performed by chemical deposition from various solvents, both polar and non-polar, containing 1-2% silane in ethanol as a solvent at temperature range between 60oC to 120oC. The deposited films where characterized as follows: Variable Angle XPS measurement of High Resolution Multiplex . Next, the XPS data was analyzed as follows: a plot of ln [\U0001d475\U0001d494\U0001d496\U0001d483 \U0001d740\U0001d494\U0001d496\U0001d483 \U0001d470\U0001d490)/(\U0001d475\U0001d490 \U0001d740\U0001d490 \U0001d470\U0001d494\U0001d496\U0001d483+1] Versus 1/sin(α) was drawn , where Nsub is the atomic number density for the substrate , No is the atomic number density for the overlayer, \U0001d740\U0001d494\U0001d496\U0001d483 is the substrate Inelastic Mean free Path, \U0001d740o is the overlayer Inelastic Mean free Path, Isub is the signal intensity of electrons coming from the substrate, Io is the signal intensity of electrons coming from the overlayer and α is the take of angle from the sample surface. The Thickness of the overlayer was calculated from the slope of the graph. Using that data thickness of the SAM was obtained. The method and results will be shown and compared to other methods such as TEM. The XPS data yielded average values on large areal spots (> 10-4 cm2). To achieve high resolution analysis a Kelvin probe force microscopy (KPFM) were performed on SAM. KPFM gives a good image of SAM on low K material. We can learn a lot about Homogeneity and Coverage properties. A study of the nucleation and growth of the SAM, dependent on temperature and time was conducted. It seems that after 60 minutes, the SAM had the best homogeneity and surface coverage. (Figure 1). After mastering the use of the two methods for SAM, the results are compared in order to find the most suitable method for SAM metrology and monitoring that can be employed by the Semiconductor industry. Figure 1