SiGe technology has become a major application for dynamic SIMS. Indeed, dynamic SIMS enables fast, efficient monitoring of Ge and B in-depth distribution in multilayer structures.
Optimized sputtering conditions
In SiGe structure, the Ge at% concentration spreads from several at% to tens of at%, which is a concentration range outside of the dilute concentration conditions required for easy SIMS data quantification. However, accurate Ge and B in-depth profiles in Si1-xGex can be obtained provided that matrix effects in such “non-dilute” system are properly addressed with sputtering conditions that ensure a full oxidation of the crater bottom.
Under these conditons, the Ge concentration remains directly proportional to the Ge+ secondary ion intensity over a large concentration range, a prerequisite for easy quantification. On Quadrupole SIMS, these conditions are reached at the best with near normal incidence and low energy O2+ primary ion beam (<1keV).
Optical Conductivity Enhancement
The CAMECA Quadrupole SIMS can be equipped with the Optical Conductivity Enhancement option. This device directs an intense laser beam on the measurement area, thus generating additional charge carriers for surface charging inhibition. With such analytical protocol, the CAMECA Quadrupole SIMS is the tool of choice for SiGe process monitoring. The tool stability and easy data quantification allow to monitor the key parameters which are [Ge] at%, Si1-xGex layer thickness, [B] at/cm3.
Figure 1 (above) presents typical SIMS data for a SiGe structure.
Figures 2 & 3 (below) show results of process stability tests performed on a CAMECA SIMS 4550 equipped with OCE option. The results for [Ge] of the SiGe plateau and the B peak in-depth position show an excellent stability of the CVD process presently tested.
Blue dots represent relative [Ge] at% of eleven different wafers with the same SiGe process. Red dots represent data of repeated measurements for 4 wafers. Agreement between "blue" and "red" data is better than 0.5%.
This data set demonstrates a CVD process stability better than 2.8% (1σ).
Boron peak in-depth position is a key parameter for the electrical properties of SiGe based device.
The CVD process stability ensures a B peak position with a precision better than 0.4% (1σ).