Vacuum Technology and Photolithography Concepts

Vacuum Pumps

• Cryo pumps, Diffusion pumps, Turbo-molecular pumps, and Rotary vane pumps all can be used to create a vacuum environment.
• Diffusion pumps can cause oil contamination, while turbo-molecular pumps and rotary vane pumps can also cause oil contamination.
• Moving turbine blades in a turbo-molecular pump add velocity to gas molecules pushing them towards the pump exhaust, this helps reduce pressure in the vacuum chamber.

Pumping Speed and Pressure

• Pumping speed measures the ability of a pump to remove gas from a vacuum chamber.
• Pumping speed is determined by the momentum transfer of gas molecules colliding with the chamber walls during pumping.
• The higher the vacuum, the lower the pressure and the longer the mean free path in the chamber.

Photolithography Resolution

• Higher resolution in photolithography can be achieved by using shorter wavelengths, larger numerical aperture lenses, and phase-shifting masks.
• Resolution is limited by the diffraction of light used for exposure.
• Thick photoresist does not improve photolithography resolution.

E-Beam Lithography

• E-beam lithography has a smaller beam spot size and a higher flexibility compared to photolithography.
• E-beam lithography can have raster and vector modes for exposing the desired pattern.
• E-beam lithography has a limited fabrication throughput, but this can be overcome by using newer technologies.

Thin Film Deposition

• Sputtering and evaporation are common methods for thin film deposition.
• Atoms deposited by evaporation typically have lower kinetic energy than sputtered atoms.
• Sputtered atoms undergo more collisions before landing on the substrate compared to evaporated atoms.
• Sputtering has better step coverage than evaporation, but fewer grain orientations compared to evaporation.
• Sputter yield depends on the energy of incident ions and the crystallographic orientation of the target.
• In evaporation deposition, a shutter is often used to control the deposition process and ensure homogeneity of the film.

Diffusion

• Diffusion is a process where particles move from areas of high concentration to areas of low concentration.
• The particle flux is directly proportional to the concentration gradient.
• The main parameters for a simplified atomistic model of diffusion are jump frequency, jump distance, and activation energy.

Debye Length

• The Debye length is a measure of the size of the mobile electron cloud that forms around a positive ion when it is pushed into charge-neutral plasma.
• It can also be seen as the average distance between charged particles in the plasma.

Crystallography

• Miller indices are used to describe plane orientations in a crystal lattice.

Photoresist Adhesion

• Photoresist adhesion is affected by the wetting characteristics of the resist, surface smoothness, and the alignment of the resist during processing.
• Postbake is not needed for wet etching, lift-off, and Ar-ion etching processes.

Le Chatelier's Principle

• When a system in equilibrium is subjected to a change in conditions, the system will shift in a direction to minimize the change.
• The new state of the system will be the new equilibrium.

Thin Film Thickness

• Thin-film thickness can be affected by many factors, which may leads to a gradient in film thickness across the wafer.
• In cases where a wafer is not perfectly level the film thickness will be greater in the center of the wafer and lesser at its edges.

Explore the principles behind various types of vacuum pumps and their applications in creating optimal vacuum conditions. This quiz also covers the essentials of pumping speed, pressure, and resolution techniques in photolithography, crucial for manufacturing processes. Test your knowledge on these integral topics in vacuum technology and imaging systems.