Evidence for anti-synergism between ion-assisted etching and in-plasma photoassisted etching of silicon in a high-density chlorine plasma

Hirsch, Emilia W.; Du, Linfeng; Economou, Demetre J.; Donnelly, Vincent M.

doi:10.1116/1.5138189

Title: Evidence for anti-synergism between ion-assisted etching and in-plasma photoassisted etching of silicon in a high-density chlorine plasma

Journal Article · Thu Jan 30 00:00:00 EST 2020 · Journal of Vacuum Science and Technology A

DOI:https://doi.org/10.1116/1.5138189· OSTI ID:1801521

Hirsch, Emilia W. ^[1]; Du, Linfeng ^[1]; Economou, Demetre J. ^[1]; Donnelly, Vincent M. ^[1]

Univ. of Houston, TX (United States)

Etching of p-Si in 60 mTorr 10%Cl2/90%Ar Faraday-shielded inductively coupled high density plasmas was investigated under both ionassisted etching (IAE) and photoassisted etching (PAE) conditions. Real-time etching rates and after-etching Si surface chemical compositions were obtained by laser interferometry and vacuum-transfer x-ray photoelectron spectroscopy (XPS), respectively. Precisely controlled ion energy distributions (IEDs) were generated by applying pulsed negative DC bias on the conductive sample stage. Above a 36 eV threshold at a total flow rate of 250 SCCM, the IAE rate increased with the square root of the ion energy. In contrast to the DC bias, etching under RF bias did not exhibit a threshold ion energy because of the wide IED. XPS spectra revealed that the surface layer under PAE conditions had a significantly lower chlorine content, composed of only SiCl. Under IAE conditions, however, silicon dangling bonds (Si•), SiCl₂, and SiCl₃ were found on the surface, in addition to SiCl, with a relative abundance of SiCl > SiCl₂, and SiCl₃. The absence of higher chlorides and Si• under PAE conditions suggested that vacuum ultraviolet photons and above threshold-energy ions interact with the surface very differently. By varying the duty cycle of the pulsed DC bias, it was found that the IAE rate scaled with the energetic ion dose, but only for low duty cycles. For higher duty cycles, the apparent IAE yield fell off with an increasing Cl coverage on the surface, as the duty cycle went up, which pointed to a negative synergy (antisynergism) between PAE and IAE as the explanation. This antisynergism was further supported by the observed decrease of the total etching rate with an increasing period of the pulsed DC bias. A plausible mechanism is that increasing the pulsing period causes more near-surface damage, creating more recombination centers that lead to a higher loss rate of electron-hole pairs through recombination, thereby reducing the PAE rate.

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Research Organization:: Univ. of Michigan, Ann Arbor, MI (United States)

Sponsoring Organization:: USDOE Office of Science (SC)

Grant/Contract Number:: SC0001939

OSTI ID:: 1801521

Alternate ID(s):: OSTI ID: 1596175

Journal Information:: Journal of Vacuum Science and Technology A, Vol. 38, Issue 2; ISSN 0734-2101

Publisher:: American Vacuum Society / AIPCopyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 6 works

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