Methods of forming boron-containing films are provided. The methods include introducing a boron-containing precursor into a chamber and depositing a network comprising boron-boron bonds on a substrate by thermal decomposition or a plasma process. The network may be post-treated to remove hydrogen from the network and increase the stress of the resulting boron-containing film. The boron-containing films have a stress between about −10 GPa and 10 GPa and may be used as boron source layers or as strain-inducing layers.