Question

During ion-implantation, the impurity atoms entering the crystal, gives up their energy to the lattice via collisions. These impurity atoms come to rest at certain average penetration depth known as :

• A. Straggle
• B. Diffusion Range
• C. Epitaxial Range
• D. Projected Range

Hint:

In any Gaussian profile $N(x) = N_{max} \exp[-(x - R_p)^2 / (2\Delta R_p^2)]$, the center peak $R_p$ is the Projected Range, and the width factor $\Delta R_p$ is the Straggle.

Answer 1

The Correct Option is D

Step 1: Concept:
The question asks for the technical term used in semiconductor manufacturing to describe the average depth at which high-energy ions settle into a target substrate during the ion implantation process.

Step 2: Key Terminology:
- Ion Implantation: A process where ions are accelerated in an electrical field and smashed into a solid.
- Projected Range ($R_p$): The average distance an implanted ion travels into the target material perpendicular to the surface before losing all its kinetic energy and coming to a halt.
- Straggle ($\Delta R_p$): The statistical variation or standard deviation of the depth distribution around the projected range.

Step 3: Step-by-step Explanation:

• When highly energetic ions bombard a crystal lattice, they undergo a series of nuclear and electronic collisions, losing energy at each step.

• Because these collisions are random, not every ion stops at the exact same depth. They form a Gaussian distribution profile beneath the surface.

• The mean (average) penetration depth, which marks the peak concentration of the implanted ions, is officially termed the Projected Range.

• "Straggle" refers to the spread of the profile, not the average depth itself. "Diffusion range" and "Epitaxial range" are entirely different concepts relating to thermal diffusion and crystal growth, respectively.

Step 4: Final Answer:
The average penetration depth is known as the Projected Range. This corresponds to option (D).