Optical emission spectroscopy study of positive direct current bias enhanced diamond nucleation

Optical Emission from C2– Anions in Microwave-Activated CH4/H2 Plasmas for Chemical Vapor Deposition of Diamond

“…Negative bias enhanced nucleation (BEN) has long been recognized as a route to accelerating diamond film growth on silicon substrates and is generally rationalized in terms of impacting C/H-containing cations yielding an interfacial SiC layer that facilitates subsequent diamond growth. − The present identification of C 2 – * anions in a MW activated C/H plasma typical of those used for diamond CVD, and the deduction that other anions (e.g., C 2 H – , and CN – in the presence of adventitious N 2 ) must also be present in the near substrate region, offer a plausible explanation for the (fewer) previous reports ,, that the application of a positive bias voltage to the substrate can also lead to enhanced nucleation densities and growth rates. Negative BEN exploits the majority ions: as shown above, the cation densities in these plasmas are several orders of magnitude higher than those of the anions.…”

“…Previous analyses of MW-activated C/H/(Ar) containing plasmas 60,61 have assumed that the negatively charged particles partnering the cations (assumed to be mainly C 2 H 2 + and C 2 H 3 + in our previous work 60 ) are exclusively electrons. Lastly, the presence of negatively charged carbon-containing species in diamond CVD plasmas offers a possible rationale for previous findings that nucleation densities and growth rates can be enhanced by applying not just a negative 62 but also a positive 31,40,63 bias voltage to the substrate.…”

“…Optical emission spectroscopy (OES) has found widespread use as a relatively straightforward and easy-to-implement probe of DC arc-jet − and microwave (MW) − plasmas used for the chemical vapor deposition (CVD) of diamond. Species amenable to study in this way in traditional dilute carbon/hydrogen (C/H) plasmas include electronically excited H atoms (via the Balmer emissions), H 2 molecules (typically via lines within the Fulcher system), and CH and C 2 radicals.…”

“…To this list can be added electronically excited Ar atoms (when Ar is added to the process gas mixture), − ,,− ,,,− ,,,,− ,− ,− ,,,,, B and BH (if a B-containing dopant is added), ,, CN and N 2 (when N 2 is present, either by design or as an impurity), ,,,,− ,,,, and OH and CO (when, for example, CO 2 is used as the carbon source). ,,,,,, The emitting species are generally formed by electron impact excitation (EIE) either of the corresponding ground-state species, or of a low-lying excited state in the case of C 2 . Thus, the emission intensities are sensitive not just to the respective lower state populations but also to the electron temperature, T e , and number density, n e , and the variation of all of these quantities with changes in process conditions, e.g., in the gas composition and mixing ratio, total pressure p , applied MW power P , sign and magnitude of any substrate bias voltage, etc., ,,− ,− ,− ,,,− ,,− …”

“…Species amenable to study in this way in traditional dilute carbon/ hydrogen (C/H) plasmas include electronically excited H atoms (via the Balmer emissions), H 2 molecules (typically via lines within the Fulcher system), and CH and C 2 radicals. To this list can be added electronically excited Ar atoms (when Ar i s a d d e d t o t h e p r o c e s s g a s m i xture), [1][2][3]10,[12][13][14]16,18,[21][22][23][24]26,28,31,[33][34][35][36][37][39][40][41][42][44][45][46][47][48]50,54,56,57,60 B and BH (if a B-containing dopant is added), 39,44,58 CN and N 2 (when N 2 is present, either by design or as an impurity), 1,6,15,18,[24][25][26]35,41,54,…”