The question asks for the term that describes the average depth at which impurity atoms come to rest after losing energy through collisions during ion implantation into a crystal lattice.

Ion Implantation Process Overview

Ion implantation is a process used to introduce impurity atoms (dopants) into a material, typically a semiconductor crystal. Energetic ions of the impurity are directed towards the crystal surface.

Energy Loss and Stopping Mechanism

As the impurity ions penetrate the crystal lattice, they collide with the atoms of the crystal. During these collisions, the ions transfer their kinetic energy to the lattice atoms, gradually slowing down.

• Collisions cause energy transfer from the implanted ion to the crystal lattice.
• This energy loss leads to the deceleration of the impurity ions.
• The ions eventually come to rest within the crystal.

Defining the Average Penetration Depth

The depth at which these impurity atoms stop varies due to the probabilistic nature of atomic collisions. However, there is an average depth characteristic of the process under specific conditions.

This average depth, measured along the direction of incidence, is referred to as the Projected Range.

Analyzing the Options

• Straggle: This term describes the variation or spread in the depth distribution of the implanted ions, not the average depth.
• Diffusion Range: Diffusion is a different physical process and not the primary term for the stopping depth in ion implantation.
• Epitaxial Range: Epitaxy relates to crystal growth and is unrelated to the stopping depth of implanted ions.
• Projected Range: This precisely defines the average depth where implanted ions come to rest after losing energy.

Therefore, the average penetration depth where impurity atoms come to rest is known as the Projected Range.