Epitaxial Tin Films on Sapphire and Silicon-on-Sapphire by Pulsed Laser Deposition
- PDF / 1,842,910 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 40 Downloads / 221 Views
Mat. Res. Soc. Symp. Proc. Vol. 397 ©1996 Materials Research Society
have demonstrated high quality epitaxial TiN films on Si(l00) 1,3,5 and MgO(100) 11 by PLD. The electrical resistivity of single crystal TiN film was 15I.ti-cm, which is comparable to the value of polycrystalline TiSi 2(C-54 phase). This letter describes the formation of epitaxial TiN films on sapphire (0001) and silicon-on-sapphire (SOS) substrates by PLD. The epitaxial films were very smooth, dense, and stable, with low electrical resistivities in the range of 20-22gD.Q-cm and good adhesion characteristics. To our knowledge, this is a first report on epitaxial growth of TiN on sapphire and SOS. The advantages of epitaxy of TiN on SOS are to scale-up the MOS and bipolar devices with high packing density while reducing in the parasitic capacitance, latch up and high crosstalk. In contrast to metals such as Cu, Ag and Au, TiN has a thermal coefficient of expansion (TCE) close to that of sapphire (Table I). Hence, thermal stresses can be reduced in the TiN contact layers. Table I: Physical properties of TiN, silicon and sapphire Parameter
TiN
Crystal structure Face-centered cubic Lattice constant (A) a=4.24 Density (g/cm 3 ) 5.43 Hardness (Mohs) 10 9x10- 6 TCE (/C)
oz-A12 0 3
Si
Rhombohedral a=4.758, c=12.991 3.98 9 8.4x10- 6
Face-centered cubic a=5.43 2.33 7 3x10-6
EXPERIMENTAL Our PLD system has been described previously 1,3 ,5 ,6, 11 . In brief, TiN films were deposited inside a stainless steel vacuum chamber evacuated by a turbomolecular pump to a base pressure of 2-5x10- 7 Torr. A KrF excimer laser was used to ablate the stoichiometric hot-pressed TiN target at an energy density of 2-3 J/cm 2. Commercially available sapphire (0001) and SOS substrates were first degreased with acetone and methanol. The sapphire substrates were thermally annealed at 11000 C in 02 atm for 12hrs. The SOS substrates were dipped into 10%HF solution before deposition. TiN films were characterized by x-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), four point probe electrical resistivity, and adhesion measurements. RESULTS AND DISCUSSION A critical parameter for TiN epitaxy in PLD was found to be the substrate temperature (Ts) during thin-film growth. Figure 1(a) shows XRD 0-20 scan of the 2500A epitaxial TiN film grown on sapphire at 500'C. It clearly shows that TiN film is highly oriented along [1111 direction normal to the (0001) planes of the sapphire crystal. The lattice parameter was determined to be 4.24_+0.005A which is close to that of stoichiometric TiN. We found that (111) orientation 272
Figure 1. XRD patterns of epitaxial TiN films
is predominant for films grown on sapphire (0001) in, the temperature range 20 to 600'C. However, the (111) peak intensity was found to be strong function of the substrate temperature. The TiN(l 11) peak intensity was found to increase significantly with temperature above 300'C. To study the alignment of the TiN lattice planes with that of the sub
Data Loading...
