Area-selective atomic layer deposition of dielectrics for semiconductor manufacturing

Xu, Wanxing

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Area-selective atomic layer deposition of dielectrics for semiconductor manufacturing

Xu, Wanxing

Advisor

Agarwal, Sumit

Date Issued

2021

Embargo Expires

2023-04-14

Abstract

As feature dimensions of state-of-the-art semiconductor devices approach the sub-5 nm node, device fabrication based on conventional top-down patterning technique is becoming ever more challenging. Area-selective atomic layer deposition (ALD) offers the advantage of eliminating lithographic patterning through selective growth, allowing for bottom-up fabrication of advanced nanopatterning of features with atomic-scale accuracy. In this work, we have primarily focused on developing area-selective ALD processes for dielectrics guided by optical diagnostic tools including in situ attenuated total reflection Fourier transform infrared spectroscopy and ellipsometry. We first tested a published claim that inherently area-selective ALD of ZrO2 on SiO2 versus Cu could be enabled using C2H5OH as the reducing agent for the Cu, the nongrowth surface, and as the oxygen source for ALD. Surprisingly, and contrary to the previous reports in the literature, no ZrO2 film growth was obtained using Zr[N(CH3)(C2H5)]4 and C2H5OH. However, we showed that using the H2O-C2H5OH mixture as the oxygen source led to ZrO2 film growth, but did not provide selective growth of ZrO2 on SiO2 versus Cu, which was again contrary to the literature. Also, so far, only a few claims of inherently area-selective ALD were published in the literature: this study shows that inherently area-selective ALD is not practical, suggesting that we need a more robust approach, such as site blocking. Secondly, in area-selective ALD based on site blocking, the first part of study focuses on understanding the site blocking ability of aminosilanes on SiO2 during area-selective ALD of ZrO2 and Al2O3. We developed strategies to effectively functionalize the SiO2 through the vapor phase, which was more compatible with the current semiconductor manufacturing than solution-based functionalization method. We showed that ALD of ZrO2 was blocked on aminosilane-functionalized SiO2 for only a few ALD cycles, and identified that the loss of selectivity was due to the strong coordination interaction between the Zr atom in Zr precursors and O atom in Si–O–Si present on aminosilane-functionalized SiO2. This strong interaction led to residual physisorbed molecules on the nongrowth surface, which contributed to the initiation of growth. Our focus then shifted to ALD of Al2O3, which was also technologically relevant. Using a lower reactivity, heteroleptic Al precursor, (CH3)2AlOCH(CH3)2 (DMAI), ALD of Al2O3 was delayed on vapor-functionalized SiO2 with small-molecule aminosilanes for up to ~30 ALD cycles, or ~3.5 nm with a selectivity of ~0.9, which was similar to solution-based functionalization. Furthermore, an effective approach was demonstrated to significantly extend the growth inhibition by lowering the DMAI precursor dose. In this part of study, we find that ideal ALD precursors, which are designed for high reactivity and high GPC, may not be ideal for area-selective ALD. This implies that we need precursor selection and design, such as replacing Al(CH3)3 with DMAI in this study. Finally, area-selective ALD of dielectric on chemically similar growth and nongrowth surfaces is much more challenging than that on chemically dissimilar growth and nongrowth surfaces. We demonstrated that ~2.7 nm of Al2O3 was selectively grown on plasma-deposited SiNx versus SiO2 at a selectivity of ~0.9 using the same functionalization method that was developed in the last part of this study. We showed that plasma-deposited SiNx surface was not fully saturated with aminosilanes, which provided a sufficient number of reactive surface sites for ALD of Al2O3. However, after exposure to ambient, a longer nucleation delay on SiNx surface during the ALD of Al2O3 was observed due to the higher surface coverage of aminosilanes, indicating the need to remove the oxynitride prior to functionalization with inhibitors. In this study, we find that fully passivating the nongrowth surface is necessary for achieving growth inhibition, but ALD can initiate on a partially passivated growth surface.

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Area-selective atomic layer deposition of dielectrics for semiconductor manufacturing

Xu, Wanxing

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