Chapter 7. Step Structures on Semiconductor Surfaces
Chapter 7. Step Structures on Semiconductor
Surfaces: Thermodynamics, Kinetics and Influence on
Heteroepitaxy
Sponsor
Joint Services Electronics Program (Contract DAAL03-89-C-0001)
Academic and Research Staff
Professor Simon G.J. Mochrie
Graduate Students
Douglas A. Abernathy
In this program high resolution x-ray reflectivity and diffraction experiments are employed to
study the structure and phase behavior of semiconductor surfaces and thin films.
Project Goals
Miscut Si[100] Q=(4+q,0,0)
Our project goals are to study:
1.75
1. The thermodynamic stability of semiconductor surfaces.
We have been employing the MIT-IBM x-ray
beamlines at the National Synchrotron Light
Source at Brookhaven National Laboratory to
achieve these goals. In addition, we have
had access to a rotating anode source at
MIT. During the past year, we completed
construction of a similar facility here that has
a vacuum chamber suitable for studying
semiconductor surfaces.
Our in-house
facility is now operational.
10
°-
1.25
0
2. The growth of insulators and semiconductors on semiconductor substrates.
3. The kinetics of steps on semiconductor
surfaces.
=-0.036
.
I 0I
0
.=
0
E
.
... ,-
4 -
q--O.O
0
8
2 -
0
I
0.2
0
0
0.1
00
0
0
-.....
0
q=0.012
0
.....
4
2.00 1.25
I
,0
04
29.25
29.50
29.75
,
30.00
0-
q=0.036
o
,
x10-4
29.00
In addition, we have demonstrated the applicability of x-ray techniques to these surface
problems through experimentation. Figure 1
shows a series of diffraction profiles obtained
from a wafer of silicon in air with a surface
misaligned from the (100) direction by 4
degrees. The shift of the peak position for
data further from the Bragg peak (which corresponds to the center profile) is a direct
This
consequence of this misalignment.
I
q=-0.012
oO
0.005 -
0
s
6
30.25
30.50
0 (degrees)
Figure 1. Scans through the reflectivity of a silicon
surface misaligned from the (100) direction by 4
degrees in the neighborhood of the (400) Bragg peak
(center profile).
shows that we are able to probe details associated with the surface with a relatively
In fact, the
straightforward measurement.
113
Chapter 7. Step Structures on Semiconductor Surfaces
Au Si3N4 Si Reflectivity
6
105
10
Rx10 4 = si,-s
RxlO = A.- N4-Si unannealed
2
Rxl
= Au-S!N 4-Si onnealed 1-
RxO = Au-SiNSi onealed 12
13
10
10
*4
10
10-
7
"41
L (Si r..u.'s)
Figure 2. X-ray reflectivity of Si-SiN-Au wafers. Different profiles correspond to different annealing times.
114
RLE Progress Report Number 131
dependence of the shift as a function of the
displacement from the Bragg condition
reveals details of the step structures on the
Si(100) surface required by the misalignment.
Figure 2 shows the results of experiments
conducted in collaboration with Professor
Carl V. Thompson. These profiles show the
x-ray reflectivity of gold films grown on a
silicon-nitrate substrate. The rapid oscillation
corresponds to the silicon nitride film, which
is 1000 A thick. The much longer period of
oscillation corresponds to the thickness of
the gold film. The different profiles shown
were annealed at high temperatures for differing periods of time and, as a result, the
initially uniform gold film becomes discontinuous with larger crystals growing at the
expense of smaller ones. The change in the
period of the long period oscillation corresponds to this change in morphology. Currently, we are attempting to describe these
profiles quantitatively with simple models of
the morphology of the gold.