Origin of Subboundary Formation in Encapsulated Recrystallized Si Films on SiO 2
- PDF / 2,284,541 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 100 Downloads / 194 Views
ORIGIN OF SUBBOUNDARY FORMATION IN ENCAPSULATED RECRYSTALLIZED Si FILMS ON Si0 2
Avid KAMGAR, S. NAKAHARA and R. V. KNOELL AT&T Bell Laboratories, Murray Hill, New Jersey 07974
ABSTRACT We have made extensive microdiffraction studies of the crystallographic orientation of recrystallized (001) Si films, and transmission electron microscopy (TEM) analysis of dislocations at the initiation sites of the subboundaries. The microdiffraction studies reveal a characteristic folding behavior between the subgrains with an increasing tilt angle in the direction away from the initiation sites. The TEM results show straight dislocations along the [1101 direction initiating from the nucleation site, the appearance of curved dislocations, and buckling of the epi film around the nucleation site, all indicative of a strong bending force at the initiation site. These two predominant characterististics of the recrystallized films, i.e., (1) crystallographic orientation of the subgrains, and (2) subboundaries together with their associated defects can be successfully interpreted in terms of the model which we recently proposed for the subboundary formation. I. INTRODUCTION In a separate paper [1, we proposed a model for the formation of subboundaries in recrystallized Si films sandwiched between Si0 2 layers. This model is based on two fundamental physical properties of a thin Si film solidifying between two rigid layers of Si0 2; (1) the large difference between thermal conductivities of Si (KSi) and Si0 2 (Ksio 2), and (2) the expansion of Si upon solidification. Briefly, the model suggests that in an encapsulated Si film because of the higher thermal conductivity of Si (KSi > 10 KSio 2 ) heat is transferred away more effectively in the middle of the Si film as compared with its boundaries with the Si0 2 layers. Hence, solidification proceeds in the middle of the Si film at a faster rate (Fig. 1(a)), as opposed to the current assumption that the solidification front is nearly vertical to the Si0 2 boundaries (Fig. 1(b)). The slight curvature is due to the wetting angle between Si and Si0 2 [2].
sio,
Si02 a)
SOLID
LIQUID
Z
Fig. I
bI
............... .......................... ......................... SOLID
LIQUID
SiO2
Sketches of solid/melt front in a cross-sectional view. (b) the standard assumption.
(a) our model, and
According to this model, the regions near the Si/Si0 2 interfaces should freeze last. It is conceivable that such regions provide convenient sites for impurities to segregate to. The particles observed in the TEM cross sections of recrystallized Si films [3] are examples of this. In Fig. 2, we again illustrate the presence of interfacial particles (P) which have presumably been swept by the solidification front and were deposited near the upper and lower Si0 2 boundaries. Mat. Res. Soc. Symp. Proc. Vol. 74. c 1987 Materials Research Society
572
Fig. 2
Cross-sectional TEM micrograph of a recrystallizeed Si film showing a subboundary (GB) and particles (P) near the Si0 2 boundaries.
The liquid/solid
Data Loading...
