On the primary process in the plasma-chemical and photochemical vapor deposition from silane. III. Mechanism of the radiative species Si*(1P ) formation

Abstract

Surface hydrogen content and passivation of silicon deposited by plasma induced chemical vapor deposition from silane and the implications for the reaction mechanismThe mechanism of the radiative species Si * ( I pO) formation from SiH 4 was investigated with ab initio molecular orbital-configuration interaction calculations on two reaction routes: (a) the simplest one-step reaction mechanism SiH 4 --+ Si + 2H z and (b) the second simplest twostep reaction mechanism SiH 4 --+ SiH z + Hz --+ Si + 2H z . The conclusions obtained are as follows: (i) the one-step mechanism (a) operates effectively in the generation of the radiative species Si*epo), (ii) no effective path was found for the formation ofSi*epo) in the two-step mechanism, (iii) the radiative species Si*epo) originates from the fifth lowest excited singlet state 11TI ofSiH 4 at the Td structure in the one-step mechanism (a), whereas the nonradiative species SiC ID) is produced spontaneously from the fourth lowest excited singlet state lIE in both reaction mechanisms of (a) and (b), (iv) the nonradiative species SiH z (1IB I ) is spontaneously generated from the lowest excited singlet state II T z of SiH 4 , (v) the electronic state ofthe radiative Si*epo) has Rydberg character and the emission ofSi*epo) at 288.2 nm is approximately expressed by 3p4s( IpO) --+ 3p2( ID) where 4s is a Rydberg atomic orbital (AO). It was also concluded that the contributions of 3d AOs are important for making a description of the quantitative energy separations among the lower lying singlet states, 1 D, IS, and IpO ofSi atoms.

Microcrystalline silicon.

“…Electronic excited states of complicated molecules like SiH 4 are usually dissociating states, from which dissociation occurs spontaneously to SiH 3 , SiH 2 , SiH, Si, H 2 and H as shown in Fig. 1 depending on the stereochemical structure of excited states without emitting photons to return back to their ground state [8]. Hydrogen molecule is also decomposed to atomic hydrogen.…”

Thin-Film Silicon –Growth Process and Solar Cell Application–

“…1, depending on the stereochemical structure of the electronic excited states, without emitting photons to return to their ground state. 8) Hydrogen molecules are also decomposed to atomic hydrogen. As a matter of course, excitation of ground-state electrons to the vacuum state gives rise to ionization events that produce new electrons and ions to maintain the plasma.…”

Calculations of the chemical composition of helium–silane plasma

“…From Table 1 it follows that the main products of the reaction of silane molecules with long-living excited states of helium atoms are SiH + ions that will not penetrate to the film surface [3]. At the same time, this process differs for the excited argon atoms.…”

“…Thus, in modeling of plasma chemical processes during deposition, we can reduce significantly both the number of components and chemical reactions. As a result of an electron impact, silane in HF-discharge plasma dissociates through two most important channels: 4 2 SiH SiH 2H e e + → + + , (R1) 3 SiH H e → + + , (R2) 2 SiH H H e → + + + , (R3) 2 2 SiH H e → + + .…”

“…Nevertheless, collisions of electronically excited inert gas atoms with silane molecules in the immediate proximity of the substrate lead exactly to the formation of the active molecules whose contact with the substrate is undesirable. Moreover, SiH and SiH 2 are formed from the second excited silane state with excitation energy of 9.47 eV [3]. In turn, the excited silane state is formed as a result of collision with a metastable inert gas atom having energy above 9.47 eV.…”