Area selective atomic layer deposition of metal oxides on metal-dielectric patterns [electronic resource]
Keywords: Materials Science and Engineering.

The downward scaling of devices in recent years and the trend toward increased 3D functionality have promoted fabrication challenges, as the process required to generate these structures faces progressively more difficult demands. The top-down fabrication of conventional lithographic patterning is becoming more challenging to scale in part because it consists of many steps that may result in misalignments when used for building 3D structures or multi-layer 2D structures. Selective deposition approaches to device fabrication have therefore gained increased interest as a way to provide direct, additive deposition of desired materials with a variety of thicknesses without the need for extra lithography steps. Due to the chemical specificity of atomic layer deposition (ALD) and its precise control over the thickness of the deposited film, ALD processes can be modified to achieve selective patterning over large areas. Selective deposition can be realized by manipulating, prior to deposition, surface functional groups according to a chosen pattern to either block or allow film growth as desired. In addition, ALD provides the benefit of conformality and uniformity, and hence is a widely-used deposition method in the fabrication of today's electronic devices. Nano-patterning using area selective ALD (AS-ALD) can facilitate fabrication of electronic and sensing devices by enabling additive processing. 2D or 3D metal/dielectric patterns found in integrated circuits, such as in FinFET structures and interconnects, could also benefit from AS-ALD. AS-ALD, reported previously by several groups, requires improvements for the process to be compatible with current device fabrication goals. Various studies have achieved AS-ALD using methods such as relying on inherent selectivity differences between different surface materials or using an unreactive polymer film as a blocking layer in the regions where ALD is not desired. However it is more common that the surface of the substrate is chemically modified with self-assembled monolayers (SAMs) in the regions where ALD is not desired. These organic monolayer films form spontaneously on solid surfaces and are important in the fabrication of micro- and nanostructures. SAMs have also been used for studies of interfacial phenomena of thin films, chemical sensing and protection of metals against corrosion. Most previous studies of area selective ALD have achieved deposited thicknesses on the order of only a few nanometers and are focused on selective deposition of materials on dielectric patterns. In this work, we probe the thickness limits of area selective deposition of dielectric-on-dielectric by selectively depositing an organic SAM as the blocking layer on the metal parts of metal/dielectric (Cu/SiO2) patterns. We show that both alkanethiol and alkylphosphonic acid SAMs can prevent subsequent deposition of metal oxide dielectric films via ALD on copper. First we selectively deposit octadecylphosphonic acid (ODPA) SAMs for 48 hours on a Cu/SiO2 pattern and show selective deposition of ZnO on Si while Cu is blocked with ODPA. We show ODPA SAMs can prevent subsequent deposition of metal oxide dielectric films via ALD. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) confirm no growth of the metal oxide on the ODPA-protected Cu for up to 36 nm of metal oxide deposition, while ellipsometry and XPS results show metal oxide growth on the dielectric regions of the samples, i.e. SiO2. Next, we show that after the selectivity is eliminated, dielectric film deposited on Cu can be removed by electrochemical reduction of the Cu surface. In order to decrease the required deposition time for ODPA and improve the selective deposition limit for dielectric materials, we selectively deposit ODPA SAMs on a Cu/SiO2 pattern for a reduced deposition time. Subsequent ALD processes of dielectric material on the substrate results in poor or no selective deposition on the substrates. Then, we use a mild etchant to selectively remove the deposited dielectric film on Cu surface without affecting the film grown on neighboring SiO2. We thus show that using this method, short time deposition of ODPA is sufficient and a more than tenfold increase in selectivity can be achieved for deposition of different high-κ dielectric materials. Next, we demonstrate selective deposition of dielectrics on metal/dielectric patterns by protecting metal surfaces using alkanethiol blocking layers. We examine alkanethiol self-assembled monolayers (SAMs) with two different chain lengths deposited both in vapor and in solution and show that in both systems, thiols have the ability to block surfaces against dielectric deposition. We show that thiol molecules can displace Cu oxide, opening possibilities for easier sample preparation. A vapor deposited alkanethiol SAM is shown to be more effective than a solution deposited SAM in blocking ALD, even after only 30 seconds of exposure. We propose and test a fully integratable vapor approach for selective deposition, and show that it improves the film thickness for which selective deposition can be realized by at least 3 times. DDT SAMs were deposited as the blocking layer against ALD on Cu regions of Cu/SiO2 patterns. The process inserts a regeneration step for the blocking layer via re-dosing of the thiol molecule, allowing for improvement of the selectivity and resultant high quality material patterning.