New precursors for selective atomic layer deposition of metal oxides with small molecule inhibitors

Abstract

Improved selective atomic layer deposition of metal oxides is provided that has large-ligand (i.e., molecular weight >20) metal precursors. A small molecule inhibitor on non-growth surfaces is used to distinguish growth surfaces from non-growth surfaces. This approach does not rely on formation of a self-assembled monolayer on the non-growth surfaces.

Claims

1. A method of performing selective atomic layer deposition (ALD) of a metal oxide, the method comprising: preparing a substrate having one or more first regions and one or more second regions; passivating the one or more second regions with a small molecule inhibitor (SMI) to provide a passivation-patterned surface, wherein the SMI has a maximum molecular dimension of 1 nanometer, wherein the SMI has a vapor pressure of at least 5 Torr at 20 degrees Celsius, wherein the SMI includes a functional group that reacts with the substrate to form a surface adsorbed species and a hydrocarbon group, and wherein hydrocarbon groups in the surface adsorbed species are independent of each other; performing atomic layer deposition of the metal oxide on the passivation-patterned surface such that the metal oxide is deposited on the one or more first regions but not deposited on the one or more second regions; wherein a precursor for the atomic layer deposition of the metal oxide has a molecular structure having a metal species bound to organic ligands, wherein the metal species corresponds to the metal oxide, and wherein the organic ligands all have a molecular weight greater than 20.

2. The method of claim 1, wherein the metal species is selected from the group consisting of: Al, Zn, Ga, In, Zr, Ti and Hf.

3. The method of claim 1, wherein the SMI is an organosilicon compound.

4. The method of claim 1, wherein the first and second regions have dissimilar compositions.

5. The method of claim 4, wherein exposure of the entire substrate to the SMI leads to selective adsorption of the SMI on the second regions.

6. The method of claim 1, wherein the organic ligands are linear chain alkyl groups having a formula given by —C.sub.nH.sub.2n+1 for n≥2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 schematically shows selective atomic layer deposition according to embodiments of the invention.

[0014] FIG. 2 is a table showing small molecule inhibitors considered in the experimental work of section B.

[0015] FIGS. 3A-B show the dependence of water contact angle on dose time and temperature for one of the SMIs of the experimental work of section B.

[0016] FIG. 4 shows the change of water contact angle as ALD growth pulses are performed for a control and two different Al precursors.

[0017] FIGS. 5A-B shows molecular spectroscopy results for an SMI coated substrate in the presence of TMA and TEA precursors.

[0018] FIGS. 6A-B show selectivity results for TMA and TEA precursors.

[0019] FIG. 7A is an image of a bare substrate.

[0020] FIG. 7B is an image of the substrate of FIG. 7A after selective ALD of Al.sub.2O.sub.3.

[0021] FIG. 7C is an elemental line scan corresponding to the image of FIG. 7B.

DETAILED DESCRIPTION

[0022] Section A is a discussion of general principles relating to embodiments of the invention, and section B is a description of a specific example.

A) General Principles

[0023] An exemplary embodiment of the invention is shown on FIG. 1. This example is a method of performing selective atomic layer deposition of a metal oxide. A substrate includes one of more first regions 102 and one or more second regions 104. Step 110 is passivating the one or more second regions 104 with a small molecule inhibitor (SMI) to provide a passivation-patterned surface 106. Step 112 is performing atomic layer deposition of the metal oxide 108 on the passivation-patterned surface 106 such that the metal oxide 108 is deposited on the one or more first regions 102 but not deposited on the one or more second regions 104.

[0024] The precursor for the atomic layer deposition of the metal oxide has a molecular structure having a metal species bound to organic ligands, where the metal species corresponds to the metal oxide, and wherein the organic ligands all have a molecular weight greater than 20. For example, the organic ligands can be linear chain alkyl groups having a formula given by —C.sub.nH.sub.2n+1 for n≥2. The case n=2 for aluminum is considered below in section B, where the precursor is Al(C.sub.2H.sub.5).sub.3. Other representative precursors include: tetrakis(diethylamido)hafnium Hf(N(C.sub.2H.sub.5).sub.2).sub.4 and aluminum-tri-sec-butoxide-Al(OCH(CH.sub.3)C.sub.2H.sub.5).sub.3.

[0025] Without being bound by theory, it is believed that the relatively large-ligand precursors defined above are less able to penetrate an adsorbed layer of SMI on a substrate than small-ligand precursors, thereby improving ALD selectivity. Section B below shows a specific example consistent with this hypothesis, where an Al(C.sub.2H.sub.5).sub.3 precursor (large ligand) provides selective ALD with an SMI inhibitor, but an Al(CH.sub.3).sub.3 precursor (small ligand) does not provide selective ALD with an SMI inhibitor.

[0026] Therefore, it is expected that the present approach will be applicable to growth of a wide variety of metal oxides, since the apparent advantage of large-ligand precursors should be independent of the metal in the precursor. In the example described below, Al is the metal species. However, as indicated here, it is expected that the present approach is also applicable to selective ALD of other metal oxides. Accordingly, suitable metal species include, but are not limited to: Al, Zn, Ga, In, Zr, Ti and Hf.

[0027] The SMI has a maximum molecular dimension of 1 nanometer, and has a vapor pressure of at least 5 Torr at 20 degrees Celsius. The SMI also includes a functional group that reacts with the substrate to form a surface adsorbed species and a hydrocarbon group. Hydrocarbon groups in the surface adsorbed species are independent of each other. Here this independence is understood to refer to the hydrocarbon groups on one SMI molecule being independent of the hydrocarbon groups on any other SMI molecule in the surface adsorbed species. The net result of this independence is that a self-assembled monolayer is not formed in the SMI surface adsorbed species. In other words, these hydrocarbon groups do not contribute to self-assembly by stabilizing surface adsorption of the SMI through interactions with hydrocarbon groups on neighboring surface-adsorbed SMI molecules.

[0028] The SMI can be an organosilicon compound, where an organosilicon compound is an organic compound with one or more silicon-carbon bonds.

[0029] Preferably, the first and second regions have dissimilar compositions. In such cases, it is preferred for these compositions and the SMI to be chosen such that exposure of the entire substrate to the SMI leads to selective adsorption of the SMI only on the second regions. In this way, no masking step is needed to define the pattern for the selective ALD growth.

[0030] Practice of the invention does not depend critically on the compositions of the first and second regions.

[0031] Exemplary materials for the second regions (non-growth surfaces) include SiO.sub.2; metal oxides such as HfO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, Cr.sub.2O.sub.3, MnO.sub.2, CuO, SnO.sub.2, and TiO.sub.2; and nitrides such as SiN, TiN, and TaN. Materials chemically similar to silicon oxide can be used as the materials where deposition of the metal oxide is blocked by the SMIs. Here the most relevant parameter for chemical similarity appears to be surface —OH density. Surface acidity (SA) is also relevant, more for deposition time than for deposition selectivity.

[0032] Exemplary materials for the first regions (growth surfaces) include Cu, Pt, Au, Ag, Co, and Ru. Materials chemically similar to copper can be used as the material on which the metal oxide is deposited. Here also the most relevant parameter for chemical similarity appears to be surface —OH density. Surface acidity is also relevant, more for deposition time than for deposition selectivity.

B) Example

[0033] FIG. 1 is a schematic for the selective growth studied in this work. Organosilicon small molecule inhibitors (SMIs) were used as inhibitors for metal-dielectric patterned substrates. These substrates were first exposed to the SMI before subsequent exposure to a standard ALD (atomic layer deposition) process, without breaking vacuum. ALD processes using trimethylaluminum (TMA) and triethylaluminum (TEA) as the aluminum precursors and water as a co-reactant were done to prepare Al.sub.2O.sub.3 thin films under N.sub.2 purge gas.

[0034] FIG. 2 is a table listing the SMIs that were used in this work. Exposures for each inhibitor were standardized to 45 Torr-min for each experiment, with bubbler temperatures between 20-50° C. required for sufficient vaporization of each SMI. These SMIs are methoxytrimethylsilane (MTMS), dimethoxydimethylsilane (DMDMS), trimethoxymethylsilane (TMMS), trimethoxyethylsilane (TMES), and trimethoxypropylsilane (IMPS).

[0035] FIGS. 3A-B show changes in water contact angle (WCA) for DMDMS on SiO.sub.2, copper oxide, and copper (oxide etched away) with variations in (FIG. 3A) dose time and (FIG. 3B) substrate temperature. Process conditions are displayed as dose time-soak time-purge time.

[0036] FIGS. 3A-B show the results of adsorption of one of the SMIs, DMDMS, on three substrates: SiO.sub.2, copper oxide, and copper (with the oxide etched away by an acetic acid bath). Total uptake of the SMI on the substrate is reflected in the difference between the original WCA and the new WCA upon adsorption, thus the figures plot changes in WCA as a function of either dose time or adsorption temperature. As shown in FIGS. 3A-B, the WCA depends strongly on the substrate, dose time, and reaction temperature. For the copper oxide and SiO.sub.2 surfaces, the WCA generally increases with DMDMS dose as well as with substrate temperature, indicating increasing adsorption of the DMDMS molecule at the surface since the methyl-terminated surface is more hydrophobic (higher WCA) than the hydroxyl-terminated surface. Based on the WCA curves, surface reaction rates between DMDMS and the native oxides of copper and silicon appear similar, with both surfaces showing quick uptake of the SMI with 10 s of dosing (FIG. 3A). However, the two oxidic surfaces differ in the saturation times, with DMDMS saturating the SiO.sub.2 substrate after 30 s of DMDMS dosing, while more than 60 s is required for saturation on the copper oxide. On the other hand, the bare (etched) copper surface reveals a different saturation profile: across all dose times studied, the WCA and hence DMDMS surface coverage remains low. Moreover, the WCA remains low on etched copper even at higher substrate temperatures up to 200° C., suggesting that there is no facile reaction pathway for DMDMS to adsorb on bare copper (FIG. 3B).

[0037] In FIG. 4, the change in WCA relative to that of TMPS-passivated SiO.sub.2 is plotted following increased exposure to H.sub.2O, TMA, or TEA. Water did not induce significant changes in the surface energy at the optimized temperature of 150° C., suggesting that the passivated surface is reasonably inert to this precursor. The aluminum precursors show a more divergent effect at the surface. After just one pulse, TMA quickly induces the development of a more hydrophilic interface and continues to degrade the hydrophobic surface with subsequent pulses. On the other hand, TEA does not significantly impact the WCA of the TMPS passivation layer across 10 pulses of this precursor, similar to the water.

[0038] FIGS. 5A-B show integrated peak areas for alkyl and hydroxyl stretching modes taken from in-situ FTIR (Fourier Transform Infrared) spectra comparing the effects of (FIG. 5A) TMA and (FIG. 5B) TEA pulses on TMPS-passivated SiO.sub.2 gel. The relative inertness of TMPS-passivated SiO.sub.2 to TEA compared to TMA was probed further with in situ FTIR spectroscopy. Spectra were collected for as prepared TMPS-exposed SiO.sub.2 as well as after successive pulses of either TMA or TEA. Chemisorption of both the SMI and Al precursor can be followed by the appearance of C—H symmetric and antisymmetric vibrational stretching modes (2900-3000 cm.sup.−1), and by the relative disappearance of similar excitations from surface-bound hydroxyl groups (3650-3750 cm.sup.−1) present on the SiO.sub.2 substrate. The integrated C—H stretching modes and OH stretches are plotted in FIGS. 5A-B as a function of SMI and TMA or TEA exposure. In both experiments, pulses of the SMI resulted in an initial increase of the C—H vibrational modes and reduction of the O—H excitation modes, as expected upon adsorption of TMPS due to the presence of the terminating methyl group on TMPS, as well as the ligand exchange reaction between surface hydroxyls and TMPS that reduces the density of O—H reactive sites. Subsequent Al precursor pulses led to different spectral behavior depending on whether TEA or TMA was used. The integrated intensity of both the alkyl and hydroxyl stretches remains unchanged with consecutive TEA pulses, consistent with the lack of reaction between this precursor and the TMPS-passivated SiO.sub.2 gel (FIG. 5B). Conversely, successive TMA pulses increase the integrated intensity of the C—H modes and decrease that of the O—H modes (FIG. 5A), suggesting chemisorption of the TMA precursors and removal of some hydroxyl groups. The result indicates that even in the presence of the inhibitive TMPS-passivation layer, TMA can react at the surface.

[0039] FIGS. 6A-B show the atomic fraction of aluminum on various TMPS-treated and untreated substrates as a function of ALD cycles for a TMA-based Al.sub.2O.sub.3ALD process (FIG. 6A) as well as TEA-based Al.sub.2O.sub.3ALD process (FIG. 6B). Growth on reference unpassivated SiO.sub.2 substrates is also shown. Plotted in each figure is Al atomic fraction determined by XPS as a function of ALD cycle number as well as selectivity on TMPS-exposed copper over TMPS-exposed SiO.sub.2, defined in Eq. 1 below.

[0040] For both precursors, with increasing number of Al.sub.2O.sub.3ALD cycles, the Al atomic fraction on copper substrates exposed to TMPS is nearly indistinguishable from that on blanket SiO.sub.2 substrates, further supporting our earlier observation with WCA goniometry that TMPS has limited adsorption on etched copper substrates. For TMA-based Al.sub.2O.sub.3ALD, the nucleation delay caused by TMPS passivation on SiO.sub.2 was slight yet distinct compared to blanket SiO.sub.2, with nucleation beyond 5 cycles of ALD leading to reliable growth. On the other hand, TEA-based Al.sub.2O.sub.3ALD on TMPS-passivated SiO.sub.2 had a nucleation delay that extended beyond 30 cycles of Al.sub.2O.sub.3ALD, compared to Al.sub.2O.sub.3 growth on blanket SiO.sub.2 substrates like that of TMA-supported Al.sub.2O.sub.3ALD.

[0041] To quantify the selectivity, we compared relative amounts of Al.sub.2O.sub.3 deposition on nongrowth (NGS) and growth (GS) surfaces, as shown in the following equation.

[00001]$\begin{array}{cc}{S}_x=\frac{R_{\mathrm{GS}}-R_{\mathrm{NGS}}}{R_{\mathrm{GS}}+R_{\mathrm{NGS}}}& \left(1\right)\end{array}$

[0042] An SEM image was produced to show the structure of the patterned substrate before Al.sub.2O.sub.3 deposition, where 50 μm-wide SiO.sub.2 features were produced between 200 μm-wide Cu lines (FIG. 7A). This patterned substrate was then subjected to the same TEA process as performed on the blanket Cu and SiO.sub.2 substrates, where TMPS was first pulsed, followed by 30 cycles of Al.sub.2O.sub.3ALD with TEA and water. As shown from the elemental mapping produced from AES (FIG. 7B), Al.sub.2O.sub.3 growth is abundant in the copper region, while remaining well-inhibited in the silicon region, clearly demonstrating the facility of this process to produce selective growth. An elemental line scan performed with AES further verified this selective growth (FIG. 7C), where selective growth of Al.sub.2O.sub.3 on copper is inferred from the aluminum signal only increasing in tandem with the copper signal. Aluminum intensities from this line scan in the GS (copper) and NGS (SiO.sub.2) regions can be compiled and ratioed against their respective substrate intensities to produce a cumulative value for selectivity using the method described above (Eq. 1). The selectivity of the process in FIGS. 7A-C, 93.7%, describes highly selective growth, with Al.sub.2O.sub.3 limited to growing in preferred copper regions.