TAGUHI YEGHOYAN, Ph.D., Technology & Market Analyst, Semiconductor Manufacturing at Yole Développement (Yole)
Atomic Layer Deposition (ALD) is a thin film deposition technique derived from Chemical Vapor Deposition (CVD) in 1965. Since the dawn of ALD adoption in semiconductor device production, ALD has been used in two disparate semiconductor chip industry streams.
One stream is related to specialty applications, otherwise called More-than-Moore (MtM) devices, including MEMS and Sensors, Power Devices, RF devices, CMOS Image Sensors, and Photonic devices. Moreover, specialty applications can also refer to the display industry with optical applications such as electroluminescent displays, with which ALD debuted in High Volume Production (HVM) already in the 1980s in MtM devices.
The other stream is related to advanced logic and memory, otherwise called More Moore (MM) devices, where ALD debuted in the 1990s and was used for high-k dielectric coatings inside high aspect ratio trench DRAM capacitors. From that time on, ALD enabled subsequent generations of logic and memory MM devices in terms of node miniaturization and device architecture. Currently, ALD is used to manufacture most logic and memory devices, used, for example, for ALD-deposited thin films in Micron’s 176-layer NAND memory channel, as shown in FIGURE 1.
The principal reasons for CVD replacement were ALD’s unique characteristics, mainly conformal deposition at low temperatures and excellent nanometric thin film quality from the deposition interface. As a drawback, the ALD deposition technique has a much lower throughput, necessitates precise process optimization, and has a higher Cost of Ownership, primarily due to the high prices of ALD metalorganic precursors. The reasons for the high ALD precursor price are the requirements of stability and a long shelf life, but at the same time, reactivity in the ALD reactor chamber at temperatures as low as 50-75 °C.
Besides the semiconductor chip industry, ALD is used in other fast-growing electronic applications, such as batteries for Electric Vehicles, Medtech and biochip production, optical element coating, and energy applications. Moreover, ALD is an enabler for quantum computing devices.
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