Surface induced latch-up in VLSI CMOS circuits

Experimental and simulated results of the gate influence on latch-up in CMOS with and without epitaxy are presented. While in CMOS without epitaxy latch-up is bulk initiated, in structures with an epitaxial layer latch-up is essentially surface controlled. The critical latch-up current in this case is two orders of magnitude higher. The strong surface effect observed is a consequence of the gate influence on avalanche breakdown, on surface conduction of the field oxide MOSFET's and on current gains of the bipolar transistors. In reducing the lateral dimensions, short channel effects of the field oxide transistors imply the most severe limitations for latch-up immunity.