Studies On BN Thin Films Grown By RF Magnetron Sputtering And Its Contact Characteristics

Power intergerated circuits can unify power electronic devices with theinformation circuits such as logic, control, protection, sensing, detection andself-diagnosis circuits on the same chip, and realize the integration of the electricalpower and information. Thus power intergerated circuits are used as the idealinterface of mechatronics. Because of the large output power, the requirements for thematerial of power intergerated circuits are very strict. Boron Nitride (BN) has verywide bandgap (Eg>6.3eV), very good thermal conductivity（~13W/cm·K，secondonly to diamond), and excellent thermal and chemical stability, so it perfectlysatisfies the power integrated circuits. However, the artificial preparation of BNcrystals often needs the conditions of high temperature (>1000℃) and high pressure(several GPa), therefore, it is very hard to obtain the large-size and high-quality cubicboron nitride (cBN) crystals, which is bad for the integration and application ofmodern electronic circuits. So people aim to synthesize large-area and high-qualityBN thin films for the power integrated circuits.BN thin films are also ideal substrates of graphene devices. Moreover, as for oneof the third generation semiconductors, BN thin films have potential applications inthe optical surface coating, deep ultraviolet photodetectors and light emitting devices,and high-temperature and high-power electriconic devices.Silicon is widely used for manufacturing integrated circuits, and has the meritssuch as low price, mature technology, and easy integration, so silicon is also selectedas the substrate of BN thin films which is synthesized by RF magnetron sputtering inthis paper. The main research results are listed as follow:1. BN thin films were successfully fabricated on N-type Si wafer by using RFmagnetron sputtering. The RF power was150W, the background vacuum was5×10-4Pa, the working gas was Ar, and the working pressure was1pa. The effects ofdeposition time, substrate temperature and annealing on BN thin films were studied.The infrared spectra of BN thin film samples which were grown for1h,2h and3h respectively were analyzed. Not only the vibration peaks of TO modes of both sp2bonds in hBN and sp3bonds in cBN and wBN are observed in these samples, but alsothe vibration peaks of eBN, which contains equal amount sp3and sp2covalent bonds,are detected. In addition, the absorption peaks of B-N-O vibration (about1280cm-1)were also found. The XPS results also proved the existence of B-N-O in BN thin films.The binding energy of B and N shifts to the high energy due to the higherelectronegativity of O. Thus, the BN thin films have complex components, mainlycontain cBN, hBN and BNxOycompounds. The infrared spectra of BN thin filmsamples grown at the substrate temperature of200℃,300℃and400℃were alsocompared. It was found that increasing substrate temperature was good for the growthof hBN, but the content of BNxOywas still not negligible, which indictaed that theincrease of substrate temperature was also benefical to the formation of the B-N-O.After annealing the BN thin film samples within the quartz tube filled with N2under650℃for1.5h, the inner stress of BN thin films was effectively decreased, and thecrystallization of BN thin films was also improved. Especially for thicker BN films,the effect of annealing was more obvious.2. The electrical property of BN/Si heterojunction and the ultraviolet (UV)absorption characteristics of BN thin films were researched. The I-V Curves showedthat BN/Si heterojunctions had very good rectification characteristics, BN thin filmsare p-type, and Si substrates are N-type, The higheset rectification ratio of p-BN/n-Siis larger than103. BN thin films have strong UV absorption. Based on the UVabsorption spectra, the energy band of BN thin films was analyzed. The results showthat the BN thin films fabricated at300℃have5.23eV optical bandgap, and accordwith the absorption rule of the direct-bandgap materials. That is because the contentof hBN in the BN thin films fabricated at300℃is higher than that in BN thin filmsgrown at200℃and400℃, and the content of hBN determines the UV absorptionand the optical bandgap of BN thin films.3. The preparation of metal electrodes on BN crystals and thin films and thecontact properties between metal electrodes and cBN were studied. Cr and Ti filmelectrodes were succefully fabricated on cBN single crystals by the RF magnetron sputtering. Four probe methode was used to measure the resistivity of the metal films.The results show that the resistivities of these metal films are all about10-3·cm. I-Vcharacteristics indicate that Cr and Ti form schottky contacts with cBN, and thecontact resistances are very large, and I-V curves are nonlinear. In order to improvethe quality of electrode contact with cBN, a layer of Au film was deposited on the Crelectrode in a vaccum chamber, and the Cr/Au electrode was annealed at450℃and900℃respectively for20minutes. After annealing, I-V characteristics show thecontact quality of the electrode and cBN is improved, and Cr/Au electrode annealed at900℃has a non-rectifying contact with cBN.