AI Lessons Series 001:  MicroX3™ NanoX3™

Process Steps:

• ALE typically involves two key steps: adsorption and desorption. During the adsorption step, a precursor is introduced, which selectively binds to the surface of the material to be etched. This is followed by an energetic input, such as plasma or heat, that drives the desorption of the adsorbed layer, effectively removing material at the atomic level.

Equation (Surface Reaction): Asurface+Breactant→Aremoved+byproductsA_{\text{surface}} + B_{\text{reactant}} \rightarrow A_{\text{removed}} + \text{byproducts}Asurface​+Breactant​→Aremoved​+byproducts

• Explanation:

  • AsurfaceA_{\text{surface}}Asurface​ represents the surface atoms or molecules of the material to be etched.

  • BreactantB_{\text{reactant}}Breactant​ is the reactive species that interacts with the surface.

  • AremovedA_{\text{removed}}Aremoved​ is the material that is etched away, often forming volatile byproducts that are removed from the chamber.

Visualization:

• Imagine the ALE process as a stepwise removal of material, where each cycle precisely removes a thin layer of atoms, ensuring uniform and controlled etching.

Types of ALE Reactors:

• Plasma-Based Reactors: These reactors utilize plasma to enhance the reactivity of the precursors, enabling etching at lower temperatures and with greater precision. Plasma provides the energetic input needed to drive the desorption step, making it a critical component in many ALE processes.

• Thermal ALE: In contrast to plasma-based ALE, thermal ALE relies solely on heat to drive the etching reactions. This method is particularly useful for substrates that are sensitive to plasma but can tolerate elevated temperatures.

Visualization:

• A typical ALE reactor schematic would highlight the flow of gases, the plasma generation area (if applicable), and the chamber design that ensures uniform exposure of the substrate to the reactive species.

Oxides:

• Silicon Dioxide (SiO2): A commonly etched material in semiconductor manufacturing, silicon dioxide requires precise control during etching to avoid damaging underlying layers.

• Aluminum Oxide (Al2O3\text{Al}_2\text{O}_3Al2​O3​): Etching aluminum oxide can be challenging due to its chemical stability, often requiring specialized precursors and careful process control.

Nitrides:

• Silicon Nitride (Si3N4): Used as a hard mask in many semiconductor processes, etching silicon nitride requires a careful balance between etch rate and selectivity to ensure that underlying materials are not affected.

Metals:

• Tungsten (W): Tungsten is a refractory metal often used in semiconductor manufacturing. Plasma-based ALE is typically required to etch tungsten due to its high melting point and chemical resistance.

Equation (Etching of Silicon Dioxide): SiO2+CF4+O2→SiF4+CO2+byproducts\text{SiO}_2 + \text{CF}_4 + \text{O}_2 \rightarrow \text{SiF}_4 + \text{CO}_2 + \text{byproducts}SiO2​+CF4​+O2​→SiF4​+CO2​+byproducts

• Explanation:

  • Silicon dioxide reacts with a fluorocarbon gas (CF4\text{CF}_4CF4​) and oxygen to form silicon tetrafluoride (SiF4\text{SiF}_4SiF4​) and carbon dioxide (CO2\text{CO}_2CO2​), both of which are volatile and can be removed from the etching chamber.

Overview:

• Plasma-Enhanced ALE (PEALE) incorporates plasma into the ALE process to enhance the reactivity of the precursors, allowing for more precise and controlled etching. The use of plasma enables etching at lower temperatures and can improve the selectivity and uniformity of the etch.

Equation (Plasma Reaction): Surface Layer+Plasma→Volatile Species+Etch Products\text{Surface Layer} + \text{Plasma} \rightarrow \text{Volatile Species} + \text{Etch Products}Surface Layer+Plasma→Volatile Species+Etch Products

• Explanation:

  • The plasma generates reactive species that interact with the surface layer, converting it into volatile products that can be removed from the etching chamber.

Applications:

• PEALE is particularly useful for etching materials that are temperature-sensitive or that require high selectivity. It is also employed in processes where achieving high precision is critical.

Summary:

• Atomic Layer Etching (ALE) is a vital technique in modern semiconductor manufacturing, offering atomic-level precision and high selectivity. Its ability to provide conformal, uniform etching across complex 3D structures makes it indispensable for advanced device fabrication.

Future Trends:

• As semiconductor devices continue to shrink in size and increase in complexity, ALE will play an increasingly important role in enabling next-generation electronics. Future developments may include new precursors and plasma technologies that further enhance the precision, selectivity, and efficiency of the ALE process.