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Figure 1. Microstructure type diagram illustrating the influence of sputtering conditions on relief of epitaxial BST/(OO1)MgO films: region I

-

region 3

-

0- 140-

L

oriented facet

blocK growth (o). The surface relief of thin films sputtered at conditions corresponded to the boundaries between the regions (f). [1] was intermediate

4,

•4-,-

0 a- 120-

semi-spherical

blocKs formation (o), mirror-smooth region 2 epitaxy (o),

4 .o

0

:1

-

3•

100-

4- -

V)

i2

LJJ

80-

o0

it

z LU 600

X 0

o:

40-

---ra I

-00

0

600

I

700

I

800

.

.

1.

900

.

. .

.

. .

. .

SUBSTRATE TEMPERATURE Ts (TC)

411 Mat. Res. Soc. Symp. Proc. Vol. 388 01995 Materials Research Society

I

1000

the T values varied from 500 to 1000 0 C. Three regions on the microstructure type diagram with the increase of P and/or T were observed: at the lowest P and/or T values the semi-spherical blocKs were formed (region 1 on P-T diagram); the increase of P and/or T resulted In the mirror-smooth epitaxy (region 2); the further increase of P and/or T led to the oriented facet blocK growth (region 3). The diffused boundaries between these regions corresPonded to the intermediate surface relief. The Present Paper is aimed at understanding the growth mechanisms of epitaxial (Ba,Sr)TiO3/(00i)MgO (DST) films. EXPERIMENTAL PROCEDURE BST films were rf sputtered onto (001) cleavage faces of MgO crystals from the stoichiometric targets in an 02 atmosphere. The fact of epitaxial growth, blocK misorientations and orientation relations between the film and the substrate were established by XRD method. The surface and cross-section reliefs (before and after chemical etching) of thin film - substrate sandwiches were studied by usage of the electron microscope (Pt/C unfolded replica technique). To reveal the dislocations both in the M9O

substrate and on the film surface the aqueous HH03 solution with the addition of HF was used as an etchant.

RESULTS AND DISCUSSION Different types of surface reliefs of the epitaxial BST films deposited in the regions t, 2, and 3 of the above mentioned P-T diagram were due to the gradual change in the following mecha-

Figure 2. Surface relief of epitaxial BST/(0O1)MgO films deposited at the growth conditions corresponding to the regions 1, 2, and 3 of the P-T diagram, respectively. C/Pt replica. Bar - 1 um. 412

nisms of nucleation and growth: three-dimensional nucleation, layer-by-layer growth, and three-dimensional nucleation again, respectively (Fig. 2). At the lowest values of P and T (region 1 on the P-T diagram) the three-dimensional growth of the epitaxial films having semispherical grains tooK Place (Fig. 2.1). The increase In P and/or T mirror-smooth films resulted in the growth of (region 2) Spiral steps indicating the presence of screw growth (Flg.,2.2). of these films. surfaces dislocations were observed on the Spiral Patterns were seen more clear after the chemical etching The thicKness of these films at which their of the film surface. continuity may be achieved is not more than the depth re