ICMCTF1998 Session D2: Synthesis and Characterization of Diamond and Related Materials

Tuesday, April 28, 1998 8:50 AM in Room Forum/Senate/Committee
Tuesday Morning

Time Period TuM Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF1998 Schedule

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8:50 AM D2-2 A Technique for Large Area Deposition of Diamond via Comubstion Flame Synthesis
R.T. Rozbicki, V.K. Sarin (Boston University)
The nucleation and growth of diamond on silicon nitride (Si3N4) based substrates deposited via the oxy-acetylene combustion flame technique were studied. The fundamental process parameters of the combustion flame technique are widely considered to be the ratio of input gases (Rf), substrate position in the flame (Ps), and substrate temperature (Ts). These parameters were systematically varied and the resulting diamond coatings are discussed with regard to nucleation density, crystal growth rate, and diamond quality. Within the range of process parameters investigated, the nucleation density for all experiments was of the order of 105 nuclei/cm2 and no experiment produced a continuous diamond coating. An Arrhenius plot of growth rate vs. substrate temperature yielded an activation energy for diamond growth of 11.4 and 5.9 kcal/mol at the center and outside annulus of the deposit, respectively. Using the Volmer model for heterogeneous nucleation, the activation energy for diamond nucleation on Si3N4 was calculated to be 37-46 kcal/mol. These results suggest that the heterogeneous nucleation of diamond is a highly energetic process and once initiated, growth proceeds easily. Factors influencing the activation energy barrier for nucleation of diamond on Si3N4 are discussed.
9:10 AM D2-3 Microwave Plasma Chemical Vapor Deposition of Diamond Films with Low Residual Stress on Large Area Porous Silicon Substrates
H.A. Naseem, M.A. Khan, M.S. Haque, A.P. Malshe, W.D. Brown (University of Arkansas)
Diamond films were deposited on 3 inch diameter p-type <100> oriented porous silicon substrates using the wavemat microwave plasma disc reactor (MPDR). Thin porous silicon layers were obtained on silicon wafers by anodizing the top surface of the silicon wafers in H2O : HF :C2H5OH solution as well as by simple chemical etching in HF : HNO3 solution. Process parameters were varied to obtain best quality uniform porous silicon films. Diamond films were deposited on these substrates with and without a dry seeding technique utilizing 0.004 - 0.005 ¨ diamond particles. Pressure and power were varied in the range of 2800 - 3300 watts and 50 - 60 torr, respectively, while the methane concentration was kept constant at 1%. These films were characterized using SEM, AFM, and XRD. The stress in the films was measured by XRD by d-sin2 Ψ method. Diamond films deposited without pre-treatment were not uniform, where as films deposited with pre-treatment were continuos and uniform. Optimization of the porous silicon layer thickness and its properties is under progress that will enhance the nucleation density without any seeding and give cluster free diamond films. films deposited on porous silicon substrates showed considerably low intrinsic stress compared to those on regular silicon substrates.
9:30 AM D2-4 Effects of D.C. Bias Voltage on the Formation of Interfacial Layer of Diamond on Silicon by MPECVD Synthesis
X.J. Guo, S.L. Sung (National Tsing Hua University, ROC); K.P. Huang, F.R. Chen (Naitonal Chung Hsing University, ROC); H.C. Shih (National Tsing Hua University, ROC)

To grow highly oriented diamond film, the d.c. bias pre-treatment is crucial, since the initial orientation of the diamond nuclei controls the subsequent growth of the diamond film. It is well-known that an amorphous interlayer with silicon carbide particles imbedded predominantly formed between the substrate Si and the diamond nuclei during the bias stage. Thus the control and elimination of these interfacial layers are essential to the achievement of direct epitaxy of diamond on Si.

Samples prepared by MPECVD with various bias voltages and CH4/H2 ratios were investigated by HRTEM and SEM as well as Raman spectroscopy.

Experimental results show that colored rings, which were formed during bias stage on the Si substrate, correspond to amorphous layers of different thickness. Diamonds nucleate subsequently on these amorphous layers. The nucleation density is found to be a function of bias voltage with fixed bias time. Also, the amounts of interfacial silicon carbide show similar results. For higer CH4/H2 ratios and more negative bias voltage, the spatial distributions of the nuclei are more even and uniform morphologically. All Raman spectra show similar trends, but with broadened diamond and graphite peaks.

Detailed analysis of HRTEM results and microstructural evolution, etc. will be discussed in this paper.

9:50 AM D2-5 DC Electrical Conductivity of Chemical Vapour Deposited Diamond Sheets: A Correlation with Hydrogen Content and Paramagnetic Defects
A.K. Sikder, A.P. Jacob, T. Sharda, D.S. Misra (Indian Institute of Technology, India); M. Pandey (Bhabha Atomic Research Centre, India); D. Kabiraj, D.K. Avasthi (Nuclear Science Centre, India)
Electrical properties of the chemical vapor deposited (CVD) polycrystalline diamond films often differ remarkably from those of the single cyrstal bulk diamond because of grain boundary effects and the impurities intrinsic to CVD process. It is, however, essential to understand the origin of the difference in the properties to exploit the potential of CVD diamond fully. In this paper we report a systematic variation in the dc electrical conductivity of the films grown with controlled amount of hydrogen (H) and non-diamond carbon impurities. The diamond films were grown on p-type Si (100) substrates at 20, 40, 60 and 80 Torr with 0.8% methane in balance H2 at 890 ° C by hot filament CVD process. The thickness of the films varied from 22 to 50 micron. The non-diamond carbon content in the films were estimated by performing Raman spectroscopy. The H concentration of the films was determined using elastic recoil detection analysis. A consistent increase in the non-diamond content in the films results in increasing H concentration with the growth pressure. A window of diameter 6-7 mm was cut on the Si substrates by chemical etching with proper masking. Electrical contacts of Cr-Au were deposited on both sides of self standing diamond sheet to perform dc electrical conductivity measurements in sandwich configuration. The conductivity of the films varies systematically from 10-6 S. cm-1 in the films grown at 20 Torr to about 10-11 S.cm-1 in the films grown at 80 Torr. Such a large variation in the values of electrical conductivity can not be easily understood. It is interesting to note that the films with least amount of non-diamond carbon and H have highest conductivity values. At the same time the spin concentration in the films as estimated by electron paramagnetic resonance decreases with the growth pressure. Our results strongly indicate that the electrical conductivity of CVD diamond films is defect controlled
10:10 AM D2-6 Break

10:30 AM D2-7 Hard Materials Rivals to Cubic Boron Nitride
A. Badzian, T. Badzian, W. Drawl, R. Roy (The Pennsylvania State University)

It is common to divide hard materials into two groups: ultrahard with diamond, boron nitride and hard materials listed as SiC, TiC, ect. Between these two groups a few ternary phases have hardness overlapping this of cBN. They can also be attractive because of their wide band gap characteristics as well as protective coatings.

One material, B-C-Si has atomic structure of boron carbide with silicon atoms located in the carbon chains linking the boron icosahedra. Synthesis has been conducted by Rf plasma CVD and by melting the elements. The Vickers hardness was measured as 6340 kg mm -2 which compares with 5000 kg mm -2 usually assigned to cBN.

The second material composed of Si-N-C is an analog of Si3N4 structure. In the crystalline form it was synthesized in the nitrogen microwave plasma by etching both graphite and silicon. An amorphous form of silicon carbonitride exhibits Vickers microhardness of 6500 kg mm -2 and oxydation resistance up to 1600C in air. SiNC crystals were also created on Si substrate instead of a hypothetical C3N4.

The third material composed of Si-O-C is an analog to SiO 2 and is known in the amorphous form. It can be formed during nucleation of CVD diamond on SiO 2. We have discovered the formation of a new crystalline phase during attempts at the hydrothermal synthesis of diamond by hydrolysis of SiC.

We will report on synthesis of ternary phases which has been conducted by a microwave plasma ignited in the mixture of gases N 2, O 2, CH 4, B 2H 6. Chemical etching of substrates or solids immersed in the plasma contributes to the synthesis of ternaries.

10:50 AM D2-8 Correlation Between the OES Plasma Composition and the Diamond Film Properties During Microwave PA-CVD with Nitrogen Addition
T.C.S. Vandevelde, M. Nesladek, C. Quaeyhaegens, J. Vlekken, T.-D. Wu, M. D'Olieslaeger, L.M. Stals (Limburgs Universitair Centrum, Belgium); I. Gouzman (Limburgs Universitair Centrum, Beligum); A. Hoffman (Technion-Israel Institute of Technology, Israel)

The mechanisms of nitrogen incorporation in diamond are still an unsolved riddle. This is mainly due to the complexity of the processes involved as they not only depend on empirical parameters (e.g. vessel pressure, substrate temperature, type and concentration of the N-containing compound, ) but also on the plasma chemistry and the surface chemical reactions.

In this study, small quantities (ppm range) of two nitrogen containing compounds (nitrogen and vaporised nitromethane) are added to a conventional hydrogen-methane feed gas mixture to study nitrogen incorporation in diamond films prepared by Microwave Plasma Assisted Chemical Vapour Deposition. Optical Emission Spectroscopy (OES) is used to survey the plasma composition during depositions. The intensities of the CN and C2 emitting radicals and the Balmer atomic hydrogen lines are correlated to the Raman film quality and to the nitrogen content in the film studied by SIMS.

11:10 AM D2-9 Effect of Nitrogen on the Structure and Properties of Highly Tetrahedral Amorphous Carbon Films
A. Wei (Zhongshan University, China); D. Chen, N. Ke (The Chinese University of Hong Kong); S. Peng (Zhongshang University, China); S.P. Wong (The Chinese University of Hong Kong)
The containing-nitrogen tetrahedral amorphous carbon (ta-C) films have been prepared at nitrogen partial pressure PN varying from 0 to 100% using a magnetic field filtered plasma stream deposition method. The optical and electrical properties of samples were studied using UV-Visible optical absorption spectroscopy, Fourier transform infrared absorption spectroscopy, X-ray photoelectron spectroscopy and electrical conductivity measurement in a temperature range from 300 K to 500 K. The films deposited at low PN contain more sp2 C than the pure ta-C films deposited at PN=0, resulting in slightly drop of band gap and increase of room temperature electrical conductivity. At PN≥50%, nitrogenation of films is very pronounced and the new CNx films are formed, leading to a wide band gap 4.0 eV and extremely low conductivity 10-15 (Ωcm)-1. The structure characteristics of CNx films were also discussed.
11:30 AM D2-10 Nucleation and Growth of Amorphous Carbon Films
B. Wei, J. Ying, B. Zhang (Hyundai Electronics America)
It becomes extremely important to understand early growth stages of carbon films as the thickness requirement for magnetic recording hard disk overcoat approaching to 10nm and less. This paper focuses on the characterization of carbon nucleation and growth processes. The samples with thickness 1nm to 50nm were sputtered on smooth NiP substrate (0.5nm roughness) under different deposition temperature and nitrogen partial pressure. Angle resolve XPS analysis suggests a critical film thickness, ~4nm, below which the carbon film is not continuous. This critical thickness varies with deposition conditions. The AFM study of surface roughness indicates an increase of roughness from 0.5nm to 1.2nm as the films grow from 1nm to 50nm. The initial roughness change of the surfaces has be attributed to the carbon nucleation and formation of the islands. A structure function has been constructed based on the AFM image data to analyze the effects of carbon nucleation on surface nano- topography. The structure function of the surfaces has been found to exhibit a power law scale dependence in two distinct regimes, corresponding to the inter- and intra- grain roughness of the carbon materials. The structure function has be related to the fractal geometry which can be used to describe randomly nucleated thin films. The fractal dimension of the carbon films calculated based on the structure function has been found to be changed only in inter- grain roughness regime.
Time Period TuM Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF1998 Schedule