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0956-J08-02

Synthesis of Sub-Micron Diamond Films on Si(100) for Thermal Applications by BENMPCVD Samuel Saada1, Jean-Charles Arnault2, Licinio Rocha1, and Philippe Bergonzo1 1 LIST (CEA-Recherche Technologique)/DETECS/SSTM/LTD, CEA, Gif-sur-Yvette, F-91191, France 2 DSM-DRECAM-SPCSI, CEA Saclay, Gif-sur-Yvette, F-91191, France ABSTRACT Diamond is the ultimate candidate for heat-spreading applications because of its extreme thermal management properties. The synthesis of sub-micron diamond films is of great interest for SOD (Silicon On Diamond) wafer technology as well as for specific thermal device applications. The challenge here is the necessity to fabricate ultra-thin layers (down to 100 nm) that are continuous and homogeneous. We studied the Bias Enhanced Nucleation (BEN) pretreatment on microwave plasma reactors in order to have very high nucleation densities (> to 1011 cm-2) and optimised the following growth step of the process to obtain sub-micron covering diamond films. In this study, we focus on the bias step parameters to increase the nucleation rate and to limit the growth rate during the bias step. Then, we performed a growth step to control the morphology of the films. We obtained diamond films with thickness lower than 80 nm and with a 6 nm Root-Mean-Square roughness.

INTRODUCTION Diamond is a very promising material for thermal applications due to its extreme thermal management properties. It has an excellent thermal conductivity (in theory 1000 times that of SiO2) with a high electric resistivity. In order to be compatible with SOI (Silicon-On-Insulator) technology substrates, where they could be used as the buried insulator with high thermal spreading capability [1,2], they have to cope with several requirements imposed by the processing steps. Namely, ultra-thin films are required, but remain a real challenge. To achieve this, the pretreatment of the silicon substrate to promote diamond nucleation is crucial. In order to reduce the thickness of the film and its roughness, it is essential to increase the nucleation density. In this paper, we report a study of the Bias Enhanced Nucleation pretreatment in order to reach very high nucleation density to elaborate ultra-thin films with low roughness.

EXPERIMENTAL SET-UP Diamond films were synthesized on silicon (100) (10x10 mm2) substrates using Chemical Vapour Deposition assisted by Microwave Plasma (MPCVD) at 2.45 GHz. An effort has been made on the cleanliness of the reactor. The base vacuum of the reactor is 3.10-9 hPa and hydrogen gas is purified via a catalytic purifier on line. The samples are introduced via a fast entry lock. The Bias Enhanced Nucleation step is applied by biasing negatively the substrate holder in order to promote diamond nucleation [3]. The temperature of the substrate is regulated with an accuracy of +/- 1 K via an halogen lamp located under the substrate. Samples are

characterized by Field Emission Gun Scanning Electron Microscopy (Hitachi S-4500 FEG-SEM) and Atomic Force Microscopy (Molecular Imaging PicoLE).

RESULTS