Kinetics Approach to the Growth of Cubic Boron Nitride
- PDF / 2,327,940 Bytes
- 9 Pages / 414.72 x 648 pts Page_size
- 79 Downloads / 270 Views
•"
i
i
i
o.6s m4/cmi 20 i Ibn F•ux O l ' " ' i" ' " i . .. . i . . . . i . . . . i , , , , I -100
-110
-120
•
2 •
-130
0
......
-35
Substrate Bias (V)
•, ! i'i• ! F,'i
i J
.......... i• /c •....... ,,I .... l.... i.... i.... l.... i,, 45
-55
-65
.
Substrate Bias (V
Figure 1. Percent of sp3-bonding (cubic BN) calculated from the FTIR absorptance spectra of two series of BN films grown with different nitrogen ion currents. The solid line is a polynomial fit to the data. In each case, formation of the cubic phase is achieved in a narrow (-30 eV) window of ion-energy and optimization occurs in an even narrower range - only several eV in width.
266
Electron diffraction and high resolution imaging have revealed that the well crystallized BN films grow with a layered morphology; a thin amorphous layer (-50A) at the substrate interface, followed by a region of hexagonal/turbostratic BN oriented with the (0002) planes perpendicular to the substrate, upon which a polycrystalline cubic BN layer forms. This has been well documented for BN films grown by ion-assisted processes on silicon[9-1 1] as well as other[4,12] substrates. An example of the film morphology can be seen in the high resolution cross-sectional TEM micrograph shown in Figure 2. The film is near the initial nucleation stage of the cubic BN layer and shows a cubic crystallite, - 500 A in length, on top of perpendicularly oriented hexagonal planes. The amorphous and hexagonal layer thicknesses are - 50 and 300 A, respectively.
Figure 2. High resolution cross-sectional TEM micrograph of a BN film near the initial nucleation stage of the cubic BN layer. The micrograph depicts the layered film morphology; an amorphous layer (-50 A) at the substrate interface, followed by a region of hexagonal/turbostratic BN oriented with the (0002) planes perpendicular to the substrate, upon which a polycrystalline cubic BN layer forms.
267
Although the interface between the hexagonal and cubic layers is quite rough, once a continuous layer of cubic BN is formed, further deposition leads to essentially single phase cubic material. This is supported by the IR absorptance spectra shown in Figure 3. The sp2 -bonding features associated with the amorphous and hexagonal interface layers remain of similar intensity, while the sp 3 -bonding feature of the cubic BN TO phonon increases with film thickness. This demonstrates that for well crystallized films, the cubic BN fraction (or sp 3 -bonding percentage) is simply a function of film thickness.
1 .2 0
, ,
, ,
i
, , t
,
1,, J, , I1
' '0 1
1.20
1.00
cubic BN TO/
4000 A
1078 cm 1
C 0.80
"
0.60
isooA
0
c
0.40
/o70
S0.20
-
0.00 2000 1800 1600 1400 1200 1000
800
600
Wavenumber (cm 1) Figure 3. Infrared absorptance spectra from a series of cubic BN films of different thickness. The cubic TO phonon absorptance at 1078 cm- 1 increases with film thickness while the hexagonal BN features, near 770 cm- 1 and 1380 cm- 1 , are of similar intensity in each film. This supports TEM diffraction data
Data Loading...
