Thin films are formed by formed by 
atomic layer deposition, whereby the composition of the film can be varied from 
monolayer to 
monolayer during cycles including alternating pulses of self-limiting chemistries. In the illustrated embodiments, varying amounts of 
impurity sources are introduced during the cyclical process. A graded 
gate dielectric is thereby provided, even for extremely thin 
layers. The 
gate dielectric as thin as 2 nm can be varied from pure 
silicon oxide to oxynitride to 
silicon nitride. Similarly, the 
gate dielectric can be varied from aluminum 
oxide to mixtures of aluminum 
oxide and a higher 
dielectric material (e.g., ZrO2) to pure high k material and back to aluminum oxide. In another embodiment, 
metal nitride (e.g., WN) is first formed as a barrier for lining dual damascene trenches and vias. During the alternating 
deposition process, 
copper can be introduced, e.g., in separate pulses, and the 
copper source pulses can gradually increase in frequency, forming a transition region, until pure 
copper is formed at the upper surface. Advantageously, graded compositions in these and a variety of other contexts help to avoid such problems as etch 
rate control, 
electromigration and non-ohmic electrical contact that can occur at sharp material interfaces. In some embodiments additional seed 
layers or additional transition 
layers are provided.