Low Volume Resistivity Chemical Vapor Deposited Boron Doped Polycrystalline Thin Diamond Film Growth on Sapphire

  • PDF / 1,311,856 Bytes
  • 6 Pages / 414.72 x 648 pts Page_size
  • 88 Downloads / 274 Views

DOWNLOAD

REPORT


in-situ doping on sapphire. In this study, 1" diameter (X-A120 3 discs were used as substrates. The HFCVD reactor consisted of straight tungsten filaments placed horizontally over the substrate with a filament-to-filament distance of 7 mm. In order to keep the level of tungsten contamination low, the filaments were pre-treated using a gas mixture of hydrogen and methane of 85 and 15 sccm, respectively. Since the CVD diamond films grown on sapphire are expected to have poor adhesion, the substrate underwent a two-step surface treatment first using 15 I.tm grit diamond paste for 20 minutes followed by a smoothing period of 10 minutes with 0.25 L.tm grit diamond paste. The first abrasion was found necessary to improve the adhesion while the smoothing step was utilized to promote the growth of smaller size crystals for growth of a smooth film surface. Prior to introduction to the CVD system, the substrate was rinsed with DI water and air dried. To further reduce cracking and peeling, the growth process was divided into two to three timed growth periods. The substrate was placed about 7 mm beneath the treated tungsten filaments on a Mo

plate. Its temperature was monitored using a K-type thermocouple placed against the substrate backside through the Mo plate. Reacting gases were H2 and CH 4 with flow rates of 98 and 1.5 sccm, respectively. The dopant source used was trimethyl borate, B(COCH 3)3, in acetone. Flow of the dopant gas was controlled at 0.5 sccm to provide the desired ratio of boron to carbon in the chamber (200 to 1000 ppm). Reacting constituents were introduced into the chamber using a gas feed through with a 1/4" copper tube positioned above the filaments. Chamber pressure was kept at 29-31 Torr with a substrate temperature of 7657750 C. RESULTS Mechanical abrasion using diamond paste and a timed growth process resulted in a significant reduction in cracking and peeling of the films. Extra care was also taken during the cool down period and subsequent sample introduction to atmospheric pressure to further reduce the flaking. To show the area covered by the diamond film, a photograph of sample Sli is given in Fig. 1. Viewing the figure, one can see that the grown diamond film has completely adhered to the substrate. This film has been stable for several months. It must be noted that the non-uniformity present on the picture is due to the residue of the silver thick film conductors that were applied for I-V measurements. In order to characterize the as-grown diamond films on sapphire, SEM, X-ray diffraction, and I-V measurements on the films were obtained. Crystal structure of the films were examined using scanning electron microscope. A micrograph of sample S7 is presented in Fig.2. Well faceted crystals having good crystal structure with preferred (100) orientation normal to the surface of the film is observed in the figure.

590

Fig. 1: Photograph picture of sample Sl, showing area covered by the diamond film

Fig. 2: SEM micrograph of sample S7 The X-ray diffraction pattern of the samples indicated th

Data Loading...