This effort focuses on the atomic layer deposition of graphene films on insulating substrates in a manner compatible with CMOS/low-k integration. This requires growth at moderate temperatures on insulating or semiconducting substrates, in order to fabricate metal-insulator (semiconductor) - graphene structures (e.g., Fig. 1). We have chosen as a substrate hexagonal BN(111), an interesting direct-band gap (5.97 eV) material, with applications in optoelectronics and as an interlayer dielectric (k = 2.2.) in back-end CMOS processing.
Studies are carried out in an STM/AFM/LEED/AES/EELS system integrated with an ALD deposition chamber. This system permits single or multiple cycles of BCl3/NH3 cycles. Growth temperatures of 550 K and pressures of > 1 Torr result in growth rates of ~ 1Å/sec. followed by transport under UHV conditions into the introduction chamber, where STM, AFM, AES, EELS, or LEED analyses can be performed.
Recent results are summarized in Figures 2 and 3. Figure 2 shows LEED results for a multilayer (~ 10 Å thick) BN film grown on Ru(0001) at 550 K, and subsequently annealed to 1000 K in UHV.
STM results (Fig. 3) demonstrate that the ordered film exhibits broad terraces (>4000 angstroms in width in some cases) with step heights of 3.2 Å, in excellent agreement with the 3.3 Å step height determined by XRD for the hexagonal phase. The STM and LEED results demonstrate the formation of hexagonal BN(111) on Ru(0001) by ALD. The examination of growth chemistry on other substrates is also in progress. The growth of graphene on BN(111) will be studied in the near future.
