Copper/low k interconnects is needed to replace the aluminum/silicon dioxide metallization beyond the current 130nm device generation. In spite of the extensive effort from the semiconductor industry, the implementation of low k dielectrics has been delayed for about three years. The basic difficulty arises from the weak thermomechanical properties of the low k dielectrics. This will be examined focusing on the correlation of dielectric polarizability and bonding characteristics and the tradeoff between dielectric constant and mechanical properties. The development of porous low k materials is discussed and its challenge is highlighted by recent results obtained on the porosity effect on material properties of porous organosilicate films. The impact of material properties on reliability will be examined and recent results obtained on thermal stresses and electromigration for Cu damascene structures will be discussed.