Dopant concentration after a Lightly Doped Drain (LDD) implantation into a MOS structure simulated with a three dimensional Analytical-Ion-Implantation module.

 

Ion Implantation has been the dominant doping technique for silicon ICs for the last 40 years. In this process, dopant ions are accelerated to an energy of 100 eV to some MeV and shot onto the wafer. Because of interaction and collisions of the ions with atoms, the ions will be distracted and stopped. Thereby the ions are distributed within the wafer and form doping profiles with the device structures present on the wafer.

The big advantage of this process is its high controlability, since the ion energy, the dose and the direction of the ion beam can be set very accurately. Moreover it is a low temperature process which is beneficial for the effort to keep the thermal budget of single process steps low, since a lot of process steps have to be performed to setup a semiconductor device.

The major drawback of the ion implantation process is that the introduced dopant atoms are not electrically active why a thermal activation has to be performed afterwards.

Within the ion implantation simulation tool MCIMPL-II an analytical module as well as a Monte Carlo module are integrated to calculate the ion implantation induced doping distribution.

 

 

 

 

 

 

 

Schematic picture of the calculation of a dopant profile by convoluting a point response.

Analytical Ion Implantation

 

The analytical method is a purely empirical method. The distribution of the implanted particles is calculated by applying an analytical distribution function (point response function) to the simulation domain. This distribution function can be described by several mathematical probability density functions, e.g. Gaussian or Pearson functions. The Analytical module of MCIMPL-II calculates the distribution of dopants with analytical distribution profiles, which can be delivered either from so-called moment databases or from experimental data or MONTE CARLO data. The result of this are a very short calculation time and a small amount of computer resources.

 

 

 

 

 

Schematic picture of the interaction of an ion with the target material.

Monte Carlo Ion Implantation

 

By the Monte Carlo module of MCIMPL-II the pathes of a lot of ions through the target material are evaluated by calculating the collisions with the nuclei of the target material and the energy dissipation to the electrons of the target material. The final positions of the ions are registered and form the doping distribution. Beside, the material damage generated by the implanted ions is also determined, stored and accumulated. Thereby local (point defects) and global (amorphization) material damage can be accounted which immediately effects the ions pathes and the behaviour of the dopants during a subsequent thermal process.