Buried oxide inhomogeneity in low-dose SIMOX structures

In this work, we will show that the incorporation of Si islands in the SIMOX BOX at doses above optimum correlates with the formation of oxide inclusions with a reduced HF etching rate. The orientation of some of these inclusions is found in registry with the Si crystal substrate. It is suggested that they originate from oxygen precipitation, not only in the form of amorphous SiO/sub 2/ but, also, as coesite-like ribbons which may lock Si islands inside the BOX.