Characterization of Cl2/Ar high density plasmas for semiconductor etching

Abstract

Chlorine-based high density plasmas, commonly used in the etching of elemental and compound semiconductors, are characterized using mass spectrometry, optical emission spectroscopy, and electrostatic probes. Plasma fluxes are characterized by three-dimensional Langmuir probe measurements and optical emission spectroscopy. The flux is further characterized at the substrate platen by mass spectrometry to determine its makeup in terms of charged or neutral species and atomic or molecular species. Langmuir probe investigations show variations in electron temperature (2–6 eV), plasma density (1×1010 to 1×1012 cm−3), and plasma potential (5–25 V) as process conditions (microwave power, total pressure, and fraction of Cl2 in Ar) and measurement location are varied. Concurrent optical emission spectroscopy measurements of ionized species are in general agreement with Langmuir probe results. Further, optical emission spectroscopy of neutral and ionized species provides global insight into the variation of atomic/molecular fractions in the plasma as it is transported to the substrate processing region. At the substrate, mass spectrometric characterizations show Cl+ and Ar+ dominating the flux for low pressure and high powers, while Cl2 and Ar dominate at high pressure and low power. For Cl2 fractions greater than 25% molecular chlorine begins to dominate the flux to the substrate. These observations of processing space are discussed with respect to implications on semiconductor etching and regions most suitable to high rate, anisotropic processing conditions are identified.

Characterization of the CH4/H2/Ar high density plasma etching process for HgCdTe

“…However, Cd(CH 3 ) and Te(CH 3 ) 2 show a slight decrease with increasing microwave power. When combined with flux characterization results, 22 these observations imply that neutral methyl radicals are preferred over ionized methyl radicals for Cd and Te removal. Further, microwave powers ≤300 W are sufficient to maximize etch product formation.…”

“…This choice will certainly enhance polymer deposition at the surface by having more of the incident CH x in the form of x = 1,2, but flux characterization shows the predominant form remains CH 3 . 22 The effect of variations in coupled microwave power to the plasma source on the mass peak intensities of etch products is presented in Fig. 4.…”

“…The metal alkyl etch products start to saturate for pressures greater than 2 mTorr. Flux characterizations 22 show that for pressures greater than 2 mTorr, the fraction of dissociated CH 4 in the flux is severely reduced due to gas phase recombination. These results imply that a sufficient flux of CH x is required to promote surface etching and, thus, pressures ≤2mTorr are more desirable.…”

“…The coupled microwave power controls two factors in determining the plasma flux to the surface, degree of dissociation and degree of ionization. Mass spectral flux characterization 22 shows that the degree of ionization is most affected over the 200-400 W range. Over this range CH 3 + and Ar + dominate the spectrum for 300-400 W (or higher powers) and CH 3 and Ar dominate for 200-300 W. Atomic and molecular hydrogen were not monitored in these studies, but can be assumed to follow similar trends since H-H and CH 3 -H bond strengths are similar (4.48 and 4.51 eV, respectively) and H + and CH 3 + ionization potentials are similar (13.6 and 9.8 eV, respectively).…”

Etch Processing of III-V Nitrides

“…These studies have involved the use of mass spectrometric sampling through the substrate platen with and without the substrate present. Studies without the substrate were performed to evaluate the make-up of the incident plasma flux as a function of process conditions (pressure and microwave power) [33]. Studies with unpatterned GaN films (grown by MOCVD on sapphire) were performed to evaluate the rate of etch product formation as a function of variations in the plasma flux and the incident ion energy.…”