Identification of halogen containing radicals in silicon etching plasmas and density measurement by UV broad band absorption spectroscopy

Abstract

Silicon etching by-products play a major role in silicon gate etching processes because they are the precursors to SiOClX passivation layer formation on feature sidewalls and on reactor walls. As a result, the understanding and modelling of these processes relies on the knowledge of the absolute value of SiClX (SiBrX) fluxes to the surfaces exposed to the plasma. However, only a few experimental data on the absolute concentration of SiClX etch byproducts are available in the literature. In this work, we show that broad band UV absorption spectroscopy can be used to measure the absolute densities of SiClX (X = 0–2), SiFX (X = 1–2) and SiO species, as well as to detect SiBr molecules. In addition, a new absorption spectrum has been observed and attributed to the SiClF radical. We have used a state of the art silicon gate etching process operating in a low pressure high density HBr/Cl2/O2/CF4 plasma etching a 200 mm diameter silicon wafer to produce the different radicals.The absorption bands of these species are all located in the 200–400 nm spectral region. Absorbances of 10−4 could be detected with a good signal to noise ratio in a few seconds exposure time using a Xe arc light source and a photodiode array detector. Details of the experimental procedure used to measure absorption spectra and to extract absolute concentrations from these spectra are presented, including a discussion concerning the influence of the monochromator spectral resolution on the absolute density determination for atomic species.

Halogenated silanes, radicals, and cations: Theoretical predictions on ionization energies, structures and potential energy surfaces of cations, proton affinities, and enthalpies of formation

“…Previous studies have found this type of structure for cations of fluorinated and chlorinated silanes [29,85] and germanes [23]. The non-classical structures are lower in energy than the classical ones except for [SiH 3 Br] + and [SiH 2 Br 2 ] + . It is again difficult to measure the adiabatic IE a s to the non-classical cations.…”

“…6). Ion complexes SiHF + -H 2 , SiH 2 + -FH, SiHCl + -H 2 , and SiH 2 + -ClH are lower in energy than their classical ones, while the three [SiH 3 Br] + structures are within 7 kJ/mol. Photoelectron spectroscopic studies have obtained vertical IEs of 11.61-11.65 eV and 10.96-11.03 eV for SiH 3 Cl and SiH 3 Br [86][87][88][89].…”

“…Using 3 and SiCl 3 were from the equilibrium study of SiX 2 (g) + SiX 4 (g) → 2SiX 3 (g) and that for SiBr 3 from the averaged Si-Br bond dissociation energy in SiBr 4 . The results (−1085.3 ± 16.7, −390.4 ± 16.7, and −201.7 ± 6.3 kJ/mol) are significantly lower than the G3(CC) predictions.…”

“…The free radicals and cations play important roles and have been detected in these processes, especially in radio frequency (RF) or plasma-enhanced deposition and etching processes where free radicals and cations have been detected [1][2][3][4][5][6][7][8][9][10][11][12][13]. Information on structure and thermodynamics of the silanes, radicals, and cations would provide useful guidelines for selection of processing conditions [9,14].…”

Nickel atom and ion densities in an inductively coupled plasma with an internal coil

“…46,47 In fact, the population transfer between the a 3 D ͑3d 9 4s 1 configuration͒ and a 3 F ͑3d 8 4s 2 configuration͒ manifolds by collision with Ar atoms in the plasma is expected to be very small because rare-gas collisions are very inefficient for transferring an electron from a 3d shell to a 4s shell. For example, in a Cu hollow cathode discharge with ϳ1 Torr Ar carrier gas, the ratio of the Cu 2 D metastable state ͑3d 9 4s 2 ͒ to the ground state 2 S ͑3d 10 4s 1 ͒ was much higher than that measured in a Cu thermal evaporation.…”