| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS+TF-WeA |
| Session: | Plasma Deposition and Plasma Assisted ALD |
| Presenter: | Erwin Kessels, Eindhoven University of Technology, Netherlands |
| Authors: | H.C.M. Knoops, Oxford Instruments Plasma Technology, UK R.H.E.C. Bosch, Eindhoven University of Technology, Netherlands T. Faraz, Eindhoven University of Technology, Netherlands M. van Drunen, Eindhoven University of Technology, Netherlands L.E. Cornelissen, Eindhoven University of Technology, Netherlands M. Creatore, Eindhoven University of Technology, Netherlands W.M.M. Kessels, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
This contribution highlights insights into atomic layer deposition (ALD) of silicon nitride (SiNx) and shows how considering these results in high material quality at low deposition temperatures. Thermal ALD processes generally require high temperatures for sufficient SiNx quality and therefore plasma ALD has been studied extensively in the last few years. The model system discussed here consists of ALD processes using aminosilane precursors, such as SiH2(NHtBu)2 (BTBAS) and SiH3N(sBu)2 (DSBAS), and N2 plasma as reactant.
Most plasma ALD processes for nitrides utilize NH3 or H2/N2 plasmas, but for SiNx it was found that the presence of H-containing species in the plasma strongly inhibits precursor adsorption.1 DFT calculations demonstrated that groups with H on the surface have low reactivity with aminosilane precursors. Under-coordinated surfaces however, such as those obtained after N2 plasma, have a much higher reactivity. To determine the nature of the surface, surface FT-IR studies were carried out. These indicated that the surface chemistry is rather complex as C and H species typically remain on the surface after the plasma step. Mass spectrometry showed that this can be related to reaction products that are created by the plasma step but which dissociate in the plasma and subsequently redeposit.2 Shorter gas residence times reduce this redeposition effect and provide improved film properties (e.g., wet-etch rate, impurity content, and refractive index). The surface chemistry during the precursor step is relatively straightforward as gas-phase IR measurements and mass spectrometry measurements reveal that amino-groups from the precursor are released from the surface (e.g., in the form of H2NtBu). Note that not all the groups are released during the precursor step, as evidenced by the aforementioned redeposition effect.
Taking these aspects into account, high quality SiNx layers were prepared by ALD at low temperatures. One particular example is that films prepared at 120 °C using BTBAS precursor and Ar/N2 plasma were found to have excellent barrier properties against moisture.3 Intrinsic water-vapor transmission rates in the range of 10−6 g/m2/day were obtained for films as thin as 10 nm.3 When DSBAS is used as precursor the redeposition effect appears to be reduced further, likely due to the fact this is a mono-aminosilane precursor. Precursor saturation, material quality and conformality vary with precursor and plasma employed and these aspects will be discussed in the contribution .
1 Ande et al., J. Phys. Chem. Lett.6, 3610 (2015)
2 Knoops et al., Appl. Phys. Lett.107, 014102 (2015)
3 Andringa et al., ACS Appl. Mat. Inter.7, 22525 (2015)