Quantum cascade laser based monitoring of CF2 radical concentration as a diagnostic tool of dielectric etching plasma processes

Abstract

Dielectric etching plasma processes for modern interlevel dielectrics become more and more complex by the introduction of new ultra low-k dielectrics. One challenge is the minimization of sidewall damage, while etching ultra low-k porous SiCOH by fluorocarbon plasmas. The optimization of this process requires a deeper understanding of the concentration of the CF2 radical, which acts as precursor in the polymerization of the etch sample surfaces. In an industrial dielectric etching plasma reactor, the CF2 radical was measured in situ using a continuous wave quantum cascade laser (cw-QCL) around 1106.2 cm(-1). We measured Doppler-resolved ro-vibrational absorption lines and determined absolute densities using transitions in the nu(3) fundamental band of CF2 with the aid of an improved simulation of the line strengths. We found that the CF2 radical concentration during the etching plasma process directly correlates to the layer structure of the etched wafer. Hence, this correlation can serve as a diagnostic tool of dielectric etching plasma processes. Applying QCL based absorption spectroscopy opens up the way for advanced process monitoring and etching controlling in semiconductor manufacturing

In Situ Monitoring Capabiities of Quantum Cascade Laser Absorption Spectroscopy in Industrial Plasma Processes

“…If instead molecular constants for the species of interest are available, a spectral simulation can be applied to retrieve line strength values S as demonstrated by Gabriel et al [5] and Hübner et al [15] for the CF 2 radical and Hancock et al for the CF 3 radical [16]. (1).…”

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

“…The inset shows a schematic diagram of the lateral cross-section of a structured porous SiCOH wafer. The numbers in the upper curve represent the numbers given as the inset [59], Reproduced from [59], with the permission of AIP Publishing.…”

“…To further improve performance, the next step is a further reduction of parasitic interlevel and intralevel capacitances by using low-k dielectrics, i.e., using a material with a lower dielectric constant than silicon dioxide. Nowadays, this is achieved by using of porous SiCOH, which is an ultra low-k material with a dielectric constant less than 2.5 [59]. The low-k material SiCOH has been of special interest, e.g., in the field of inter-level dielectrics see [58] and references therein.…”

“…Outline of the Oxford Plasmalab System 100 ICP etch chamber equipped with Q-MACS Process fiber system. CF2 radicals were detected using a multipass cell just above the wafer [59], Reproduced from [59], with the permission of AIP Publishing. Figure 27.…”

“…Experiments were carried out in an Oxford Plasmalab System 100 inductively coupled plasma (ICP) etch chamber equipped with a QCL based absorption spectroscopy system (Q-MACS Process fiber, neoplas control GmbH) as schematically depicted in Figure 27 [59]. Figure 27 [59].…”