9.2.2 Large Angle Tilt Implant Optimization

To compensate the influence of the source/drain regions on the channel below the gate edges, it is possible to artificially raise the p doping level below the gate edges by local boron implants into the transition region between the source/drain regions and the channel. One way of realization is to use a large-angle tilt (LAT) implant of boron ions into the NMOS device after the formation of the LDD structure [HKS91].

A frequently encountered process engineering task deals with determining the optimum parameter settings for the LAT implant. The procedure for establishing these values consists of several tasks:

1. For the nominal device, screen the influence of the three LAT parameters to determine ranges for the optimization.
2. Select nominal parameter settings from the results of the screening analysis.
3. Create a response surface model for the dependence of the device behavior on the LAT parameters in the vicinity of the nominal point.
4. Use the RSM model to optimize the LAT parameter values.

The creation of the response surface model - or any other analytical model the can be evaluated sufficiently fast - is not a necessity, as the optimization process could also be carried out on the process and device simulations directly.