CMOS integrated devices in seeded islands

DETAILED DESCRIPTION The low power consumption of integrated circuits fabricated in CMOS has made such structures the norm for future designs.
Unfortunately, the conventional use of wells or tubs to locate the transistors which have the same source/drain impurity type as a substrate introduces a susceptibility to latching, a phenomenon caused by parasitic bipolar transistors inherent in such composite structures.
Although impurity gradients in substrates have mitigated the liklihood of latching by such parasitic bipolar devices, their catastrophic effects have not been completely eliminated.
Accordingly, new designs have sought to form selective field effect transistors in regions completely isolated by dielectric from the substrate silicon, while retaining the low leakage current and stable threshold voltage characteristics of field effect transistors formed in a monocrystalline silicon.
In the pursue of such desirable objectives, significant recent work has involved the use of laser beam recrystallization to convert polycrystalline or amorphous silicon regions to monocrystalline form by initiating a melt of the polycrystalline or amorphous silicon at a seed point on a monocrystalline silicon substrate, and then extending that seed onto a dielectric region.
The fundamentals of this concept are described in U.
S.
Pat.
No.
4,323,417.
The effects of varying the shape of the initial polycrystalline or amorphous silicon structures and the beams are considered in U.
S.
Pat.
No.
4,330,363, in a context where no seeding is used during the conversion to monocrystalline form.
Further refinements in recrystallization from monocrystalline silicon seed regions are described in U.
S.
Pat.
Nos.
4,592,799 and 4,599,133.
The former relates to the orientation of seeding locations with respect to the scan direction of the laser beam as well as the shape of the beam, a central teaching being that the direction of movement of a beam be transversed to the elongated direction of the beam and the seed region pattern