Atomic Level Deposition (ALD) is a process widely and increasingly used in advanced semiconductor fabrication for memory (3D-NAND and new stacked DRAM) and advanced logic processes (gate all-around, etc.). These processes are characterized by the need to precisely control thin film layers with thicknesses of tens of molecules and tens of angstroms (1Å = 1 × 10-10m).

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ALD can deposit a wide variety of materials, including oxides, nitrides, and metals The ALD process is widely used because it can provide conformal, pinhole-free, controllable, ultra-thin monolayers The ALD market is expected to grow at a CAGR of 16-20% between 2020 and 2025 (source: ASM). The ALD market is projected to grow at a CAGR of 16-20% from 2020 to 2025 (Source: ASM).

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Effective monitoring and control of the ALD process requires a fast, chemically specific quantification and metrology solution that can handle harsh process gases such as hydrochloric and hydrofluoric acid byproducts, as well as condensation particles that form on the chamber surface during processing.

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The metrology solution must quantify the gases present so that it can accurately, quickly, and efficiently transition through the multiple operating stages of precursor gas injection, gas purging, reaction gas injection, and byproduct gas removal. Since each cycle typically takes only a few seconds, the metrology solution must operate in real time with high sample rates and sensitivity.

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However, most ALD processes either have no plasma or use weak remote plasma sources. This means that traditional in-situ measurement techniques such as optical emission spectroscopy (OES) are left in the dark. The lack of a strong plasma source results in a low signal-to-noise ratio and a complete lack of signal to provide the necessary information.

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This is because there must be sufficient margin between steps to ensure that the precursor and reaction gases do not inadvertently mix in the chamber. Also, if the ALD process is run without a measuring instrument, there is a risk of a significant drop in line yield or abnormal process termination if, for example, one of the reaction gas concentrations becomes too high or too low.

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Fast, robust chemistry-specific mass spectrometers such as Atonarp's Aston are a new solution that provides in-situ measurement and control in these non-plasma ("lights-off") processes. fast, chemically specific in-situ quantitative gas analysis down to parts-per-billion levels enables and provides the real-time data needed for effective ALD process control.

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To learn more about Aston and how it supports atomic-level deposition, download the application brief below.