BALD Engineering - Born in Finland, Born to ALD: Strem

Friday, April 17, 2020

Volatile ALD & CVD Magnesium precursors for non-volitile memory and flexible display applications

The escalating struggle with further scaling of integrated circuit chips, on account of certain feature sizes in advanced chips gradually hitting atomic dimensions, has compelled the semiconductor industry to become more welcoming to new materials as a possible solution to continued PPAC (Power-Performance-Area-Cost) improvement. Traditionally not so popular in the semiconductor industry, Magnesium (Mg) is being explored for use in various related applications due to the fact that it forms semiconductor compounds with oxygen, sulfur, selenium, and tellurium.

For example, Magnesium Oxide (MgO) is a semiconductor with a wide band-gap and semi-insulating properties. A very thin semi-insulating MgO layer between two metallic ferromagnetic layers is used as a “magnetic tunnel junction”. Magnetic tunneling junctions (MTJs) based on the CoFeB/MgO/CoFeB layer have received great attention as a promising candidate for future spin logic devices. Among various applications of MTJs, spin-transfer-torque magnetic random access memory (STT-MRAM) is emerging as a strong candidate as a next-generation nonvolatile memory due to its simple integration scheme, low voltage operation, and high speed. To fulfill certain critical requirements of 3D MTJ based sub-20 nm, high-density STT-MRAM, Samsung Advanced Institute of Technology (SAIT), Korea, has recently investigated both thermal and plasma-enhanced ALD for depositing a MgO tunnel barrier using bis(cyclopentadienyl)magnesium precursor under the scope of the Industrial Strategic Technology Development Program (10041926, Development of high-density plasma technologies for the thin-film deposition of nanoscale semiconductors and flexible-display processing) funded by the Ministry of Knowledge Economy (MKE, Korea). (Link)

Figure 1. TEM images of (a) Thermal ALD MgO, (b) PE-ALD MgO grown at 300 °C on a CoFeB layer

Recently, Panasonic Corporation, Japan, together with the National Institute of Material Science, Japan, reported ALD based Magnesium Phosphate (MgPO) thin-films as magnesium-ion conducting solid-state electrolytes that are considered to be promising candidates for future energy storage and conversion devices. The deposition was carried out at lower deposition temperatures, ranging from 125 to 300 °C, using bis(ethylcyclopentadienyl)magnesium. (Link)

Apart from semiconductor and energy storage applications, Mg is also an interesting candidate for astronomical and optical applications. For example, recent NASA missions that make observations in the ultraviolet, such as the Hubble Space Telescope and the Galaxy Evolution Explorer, employed primary mirrors coated with aluminum and further protected by thin films of Magnesium Fluoride (MgF₂). Therefore, the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA, reported ALD of MgF₂ using bis(ethylcyclopentadienyl)magnesium supplied by Strem Chemicals, Inc. (Link)

Figure 2. Photograph of a concave mirror and convex diffraction grating for a next-generation UV instrument prototype coated with electron beam evaporated aluminum and a protective coating of 10 nm ALD MgF₂ deposited at 150 °C.

Strem Chemicals, Inc., a leading fine chemicals supplier, headquartered in Newburyport, Massachusetts, USA, offers the most preferred precursors worldwide for ALD of Mg-based compounds, i.e, bis(ethylcyclopentadienyl)magnesium [Mg(CpEt)₂] (catalog number 12-0510). The colorless to pale yellow liquid phase precursor with a density of 0.95 g/cm³ at 20 °C and vapor pressure of 0.0315 Torr is also sold by Strem Chemicals as pre-packed in cylinders:

§ 98-4006: Bis(ethylcyclopentadienyl)magnesium, min. 98%, 12-0510, contained in 50 ml Swagelok® cylinder (96-1070) for CVD/ALD

§ 98-4010: Bis(ethylcyclopentadienyl)magnesium, min. 98%, 12-0510, contained in high-temp 50 ml Swagelok® cylinder (96-1071) for CVD/ALD

About Strem Chemicals: Strem is an employee-owned fine chemicals supplier, manufacturing and marketing high-quality specialty chemicals for more than half-a-century. They provide custom synthesis and FDA inspected current good manufacturing practice (cGMP) services to its clients from academia as well as industry and also to government R&D labs. What distinguishes Strem from the other chemical suppliers are its ISO 9001 Quality Management System (QMS) standard and documenting procedures including for example “Color and Form” for every product as listed in the product details as a quality indicator for researchers. This helps Strem deliver precursors with a minimum metals purity of 99%, with some some metal precursors attaining as high as 99.9999% metal’s purity. Strem offers over 5,000 specialty products in the area of metals, inorganics, organometallics, and nanomaterials. Strem’s product range includes: