Modeling SiH₄/O₂/Ar Inductively Coupled Plasmas Used for Filling of Microtrenches in Shallow Trench Isolation (STI)

Abstract

Modeling results are presented to gain a better insight in the properties of a SiH4/O2/Ar inductively coupled plasma (ICP) and how it interacts with a silicon substrate (wafer), as applied in the microelectronics industry for the fabrication of electronic devices. The SiH4/O2/Ar ICP is used for the filling of microtrenches with isolating material (SiO2), as applied in shallow trench isolation (STI). In this article, a detailed reaction set that describes the plasma chemistry of SiH4/O2/Ar discharges as well as surface processes, such as sputtering, oxidation, and deposition, is presented. Results are presented on the plasma properties during the plasma enhanced chemical vapor deposition process (PECVD) for different gas ratios, as well as on the shape of the filled trenches and the surface compositions of the deposited layers. For the operating conditions under study it is found that the most important species accounting for deposition are SiH2, SiH3O, SiH3 and SiH2O, while ${\rm SiH}_{{\rm 2}}^{{\rm + }} $, ${\rm SiH}_{{\rm 3}}^{{\rm + }} $, ${\rm O}_{2}^{ + } $ and Ar+ are the dominant species for sputtering of the surface. By diluting the precursor gas (SiH4) in the mixture, the deposition rate versus sputtering rate can be controlled for a desired trench filling process. From the calculation results it is clear that a high deposition rate will result in undesired void formation during the trench filling, while a small deposition rate will result in undesired trench bottom and mask damage by sputtering. By varying the SiH4/O2 ratio, the chemical composition of the deposited layer will be influenced. However, even at the highest SiH4/O2 ratio investigated (i.e., 3.2:1; low oxygen content), the bulk deposited layer consists mainly of SiO2, suggesting that low‐volatile silane species deposit first and subsequently become oxidized instead of being oxidized first in the plasma before deposition. Finally, it was found that the top surface of the deposited layer contained less oxygen due to preferential sputtering of O atoms, making the top layer more Si‐rich. However, this effect is negligible at a SiH4/O2 ratio of 2:1 or lower.

Radicals and ions controlling by adjusting the antenna-substrate distance in a-Si:H deposition using a planar ICP for c-Si surface passivation

“…Ions have very short lifetimes (<0.3 μs) due to the ultra-high reaction rate constant (~10 -7 cm/s) and thus a very small diffusion length (three orders of magnitude smaller than the corresponding radicals) [30]. Therefore, the ion effect can be removed in the deposition zone in the case of remote-plasma.…”

Control of higher-silane generation by dilution gases in SiH4 plasmas

“…The positive ions for SiH 4 are limited to SiH + 3 , SiH + 2 , and SiH + . It is mentioning that Si + ion is not taken into consideration, because its density is small, about one or two orders of magnitude lower than the density of SiH + 3 and SiH + 2 [30]. Beyond that, Si 2 H + 4 , generated from ionization of Si 2 H 6 , is an abundant ion in silane plasmas [31].…”

“…Although elastic impact reactions are taken into account, they are not displayed in the tables. Rates for electron impact reactions are determined by electron energy dependent cross-section data and analytical rate coefficients, which can be found in the corresponding references, respectively [25,26,[30][31][32][33][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58].…”

Modeling and experimental investigation of the plasma uniformity in CF4/O2 capacitively coupled plasmas, operating in single frequency and dual frequency regime

“…Therefore, O 2 includes the ground state molecule and two electronic excited levels with thresholds of 8.40 and 10.0 eV; for these three states, one rotational excitation and two vibrational excitations are included. [45][46][47] The electron impact reactions considered in the model for the CF 4 /O 2 plasma are presented in Table II. This table includes the electron collisions with various molecules, radicals, excited species, and ions, i.e., excitation, ionization, recombination, detachment, de-excitation, dissociation, as well as dissociative attachment, excitation, ionization, and recombination.…”