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The secret of self-limiting reaction: Why can ALD precisely control film thickness?
In today's semiconductor and nanotechnology fields, precise control of film thickness is critical to ensuring product performance. Atomic layer deposition (ALD) technology is one of the key methods to meet this demand. The characteristic of ALD is that it uses the principle of self-limiting reaction, which enables the deposition process of thin films to achieve extremely high accuracy and uniformity.
ALD grows films layer by layer on a substrate surface through cyclic exposure to chemical precursors. During the reaction process, the reaction between the precursor and the substrate proceeds in a self-limiting manner, which means that the reaction will automatically stop when all reactive sites are consumed.
The basic working mechanism of ALD relies on this self-limiting reaction. Unlike traditional chemical vapor deposition (CVD), during the ALD process, the precursors do not appear in the reaction chamber at the same time, but are carried out at different times. This design ensures that each reaction is only performed on the exposed substrate surface, thereby accurately controlling the amount of material deposited.
The principle of ALD
In the process of ALD, the sample is first exposed to the first precursor A, and the reaction between the precursor and the substrate is completed in a short time. Subsequently, the residual A is expelled from the reaction chamber, and the second precursor B enters and reacts with the substrate. This alternating exposure process constitutes an ALD cycle.
ALD ensures that the deposition growth of each layer is uniform and predictable, allowing the thickness and composition of the final film to be controlled at the atomic level.
The amount of growth per ALD cycle is determined by the interaction of the precursor with the substrate, so planned reaction and degassing times are critical when designing deposition parameters. The flexibility of this mechanism enables ALD to achieve uniform film deposition on a variety of complex-shaped substrates regardless of geometry.
History of ALD
The development of ALD can be traced back to the 1960s, when it was first proposed and experimentally developed by Russian scientists. With the advancement of technology, ALD was further applied in the 1980s, and with the evolution of microelectronics technology, it gradually became one of the key technologies in semiconductor manufacturing.
Technological evolution
Over the past few decades, ALD has expanded beyond the deposition of metals and oxides, with many variations of the technology now developed, including attachment deposition and light-based ALD. The development of these technologies has enabled ALD to be applied not only to microelectronic components, but also to applications in optoelectronic materials and other nanomaterials.
Application areas of ALD
Currently, ALD technology has been widely used in microelectronics, solar cells, gas isolation materials and other fields. In the field of microelectronics, ALD has extremely high application potential for the deposition of high dielectric constant materials, which can effectively reduce leakage current when scaling down to below 45 nanometer technology.
In the manufacture of products such as dynamic random access memory (DRAM) and metal oxide semiconductor field effect transistors (MOSFET), ALD is also the only deposition method that can meet their design requirements.
In addition, because of its self-limiting reaction properties, ALD will continue to lead the technology in terms of the uniformity and accuracy of deposited films. This feature is particularly suitable for the growing needs of nanotechnology and the development of new materials.
Conclusion
In summary, atomic layer deposition technology relies on its unique self-limiting reaction mechanism to provide precise control methods for thin film deposition, thus playing an indispensable role in many advanced technologies. In the face of the continued advancement of technology in the future, we may be able to think further: What role will ALD technology play in future technological development?
