Abstract: As features shrink beyond 32 nm, conventional pulsed nucleation layer (PNL) will not provide the necessary resistivity performance. Tungsten nucleation and CVD fill developments can extend ALD tungsten to 2X nm features and provide needed resistivity.

Abstract: Low pressure chemical vapor deposition has been used to fill carbon nanotube (CNT) forests with inorganic materials (polysilicon and silicon nitride). Forest filling proceeds by deposition around individual CNTs. As the coating thickness around each CNT increases, the free volume between adjacent nanotubes is filled and finally results in a contiguous composite film. The process maintains the forest height and alignment; however, the coating thickness around the CNTs is in general smaller at the base of the forest than it is at the top. This can cause a contiguous solid film to form at the top of the forest while the forest is only partially filled at the base. Once the top of the forest becomes filled, it prevents growth from occurring at the base. Consequently, the growth process can cap the top of the forest and leave voids between thinly coated CNTs at the base. Such composites have reduced hardness (4 GPa or less). Depositing at reduced temperatures and/or decreased precursor gas flow rates reduces the void fraction through improving the step coverage modulus. This allows one to produce thick (> 50 μm) polysilicon-CNT composite films having hardness approximately equal to that of polysilicon thin films (12.4 GPa).

Abstract: This presentation examines aspects of the growth and filling of carbon nanotube forests. Composites containing CNTs are predicted to inherit the best properties of the CNTs (strength, toughness, resistivity, thermal conductivity). However, good dispersion of the CNTs is vitally important in fabricating composites with features approaching those theoretically predicted. Significant deterioration of the composite properties has been shown to occur when the CNTs agglomerate rather than being uniformly dispersed. Filling as-grown CNT forests with various materials can result in a composite with excellent CNT dispersion. Furthermore, the growth of forests is becoming very popular for both single-wall and multi-wall CNTs of high quality. LPCVD is a very good technique to fill the CNT forests with a wide variety of materials, so we have studied the filling process on various forests. Filling begins by coating the individual CNTs with the (inorganic) material. Large coating thicknesses bridge the gap between adjacent CNTs and result in a continuous composite layer. Polysilicon / CNT composites fabricated under conditions that yield good step coverage were found to exhibit hardness similar to that of bulk polysilicon and high fracture toughness but also high sheet resistance. Voids deep inside films over 25 microns thick remain a significant issue.