TABLE OF CONTENTS The main objective of this section is to determine the consequences of reducing the processing temperature on doping activation and the electrical resistivity of p- and n-type silicon germanium thin films. In general, the electrical conductivity of poly SiGe can be controlled by adding donor atoms (phosphorus is commonly used) or acceptor atoms (usually boron) either by ion implantation or from gas phase during deposition (in situ doping). In spite of the fact that ion implantation is not the optimal choice for MEMS post-processing on top of standard prefabricated electronics, it is relevant for applications where different doping levels are required in the active material. Surface micromachined uncooled IR detectors are a good example that clarifies this issue (see Figure 4.9). In this case the active part of the device needs to be lightly doped in order to have high sensitivity for the incident radiation. The supports connecting the detector to the driving electronics, however, which are realized by the same material, need to be highly doped. This can be only achieved by combining ion implantation and in situ doping. Section 4.5.1 provides an overview of the characteristics of ion-implanted Si 1-xGe x under a wide range of thermal treatments and it specifies the minimum activation temperature that can be practically realized. The advantage of in situ doping is presented in Section 4.5.2. It is demonstrated that combining boron in situ doping with a high Ge content (~65%) can reduce the...
