Boron out-diffusion mechanism in oxide and nitride CMOS sidewall spacer: Impact of the materials properties

The interactions occurring between the pMOSFET sidewall spacers and the shallow junctions underneath can be detrimental for the transistor performance. In fact, a significant part of the p-type LDD boron may out-diffuse into the spacer oxide layer during the doping activation annealing, resulting in a deep modification of the junction. This effect was emphasized with the introduction of low thermal budget spacer oxide and nitride dielectrics in recent CMOS technology nodes. This study compares the impact of oxide/nitride spacer bilayers obtained at low temperature either by low pressure chemical vapor deposition (LPCVD) or by plasma enhanced chemical vapor deposition (PECVD). One observes a minimized interaction between the junction and the dielectrics within the PECVD samples. In addition, the boron diffusion activation energies calculated for both stacks are consistent with the models of boron diffusion within oxide films described in the literature.