Introduction

Ion implantation is a process in which, energetic, charged atoms or molecules are directly introduced into a substrate. Acceleration energies range between 10-200 keV for most implanters. In VLSI fabrication, ion implantation is primarily used to add dopant ions into the surface of silicon wafers.

Advantages

• Ability to accurately control the number of implanted dopant atoms into substrate, by measuring beam current I (in amperes), beam area A (in cm²) and implantation duration, t (in sec).

• It is also reproducible.

• It is anisotropic and directional, so there is less lateral diffusion that leads to fabrication of smaller devices.

• A single implanter can be used for a variety of implant species, with little cross contamination by other species. Any element that can be ionized can be easily introduced into the wafer using implantation.

• Ion implantation is a low-temperature process, so there is lower thermal budget.

• It is possible to get desirable junction depth by controlling the acceleration energy of the ions.

• It is used to make very shallow junctions.

• It can also make retrograde junctions.

• Another advantage of ion implantation is that selected areas can be implanted by using masks that leave well-defined areas of the semiconductor exposed to the beam and other areas masked from the beam.

Disadvantages

• Diffusion is non-destructive to the structure of the target material but ion implantation causes damage to the material structure of the target resulting in crystal defects and amorphous layer. This adds another high temperature annealing step to the process.

• Throughput is typically lower than thermal diffusion process because ion implantation does not lend itself to batch process.

• It is more expensive as the cost of the equipment can exceed $2 million for a production machine.[2] [5]