a process has been developed in which seamless tungsten plugs are used to fill deep , narrow contact holes . the process features initially forming a tungsten plug in a contact hole , via tungsten lpcvd processing , followed by an rie etch back , and recessing process . a second tungsten lpcvd procedure is then used to fill seams or defects in the underlying tungsten plug . another rie etch back procedure is then employed to create a seamless , composite tungsten plug structure , in the deep , narrow contact hole .