Strain Relaxation in Heteroepitaxial Si 1-x Ge x Films via Surface Roughening Processes
- PDF / 3,259,987 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 51 Downloads / 198 Views
407
Mat. Res. Soc. Symp. Proc. Vol. 399 * 1996 Materials Research Society
decomposition of silane and germane at 15 Torr total pressure where hydrogen was used as a carrier gas. Film deposition was followed by annealing in the reactor for the required temperature and time in a hydrogen evironment. Atomic force microscopy was used to study the surface morphology of the films using a Park Scientific CP system. Plan view and cross sectional transmission electron microscopy was done using a Philips EM 430 operating at 300 KeV to study the morphology and microstructure of surface ridges or islands and to investigate any defects formed. Thin foils for XTEM were fabricated using a standard procedure of stack construction, slicing, thinning, disc cutting, dimpling and ion milling [7]. X-ray diffaction studies were conducted on a Philips 1710 Diffractometer operating at 40 KeV and 30 mA in order to determine the amount of relaxation in these films. Auger electron spectroscopy and Auger mapping were conducted to study the Ge distribution using a Philips 590 AES system operating at 10 kV with a probe size of 5 microns and 1000 A respectively. RESULTS AND DISCUSSION Figures l(a) to l(d) show slope sensitive AFM images (5x5 gim 2 ) of a 100 A thick SilxGex film containing 18% Ge both in the as grown state and subjected to annealing at 850 'C for 5, 20 and 120 minutes respectively. In all of our AFM images,
(a)
(b)
(c)
(d) .
°
Figure 1
408
the features are magnified 20 to 30 times in the height direction. These films are subcritical with respect to dislocation formation. Figure l(a) shows that in the as grown state, the film is virtually flat where only a noise pattern from the surface is obtained. Figures l(b)-l(d) show a sequence of change in morphology at the surface through a series of controlled annealing experiments. In all of these figures, the ridges are aligned along directions. After 5 minutes of annealing (figure l(b) , the average wavelength and the amplitude of the features is around 4400 and 264 A respectively. After 20 minutes, these values reach 1.17 micron and 626 A respectively where the mode of roughening changes from 2-D into 3-D roughening or islanding. In figure l(d), roughening has progressed to a stage where the substrate was exposed between large islands, with an average wavelength and amplitude of 1.64 microns and 628 A respectively. In other experiments with 22% Ge and supercritical films, we have observed ridges aligned along directions, which are related to misfit dislocation networks.
tooo
too0 IS
IIK
II
0.
1 ,
|
04
t, 4 4Ie/m ,m
ao
o
-
-46O
-2O
I1SS90..ne1 -
21411.001
b t90Io10
'g0*0 0,1/Th
.
-
11..... DoI
(a)
.
*.. .O
.
S..ot
ad.0
I
].
(b)
Figure 2 Figures 2(a) and 2(b) show (004) x-ray rocking curves for 100 A thick Si]_xGex films containing 18% Ge which were annealed at 700 °C and 850 'C. The peak position for a fully strained and a fully relaxed 18% Ge film should be located around 1889 and 1068 arc sec. away from the main Si peak (substrate) respectiv
Data Loading...
