A fully recessed field isolation technology using photo - CVD oxide

We have developed a new isolation technique that employs a low temperature (100°C) photo-CVD oxide (photox^TM) in conjunction with a photoresist lift-off. The resulting isoplanar structure is bird´s beak free, which is ideal for VLSI circuits. Moreover, the new process eliminates the narrow channel effect on threshold voltage down to 1.2 µm(the smallest channel width fabricated). Also, the transconductance of narrow FETs made with the new process is ∼70% larger than obtained with devices of the same size, but isolated by etching the channel areas in the field oxide. Two-dimensional modelling explains these observations by showing that the electron concentration across the channel of the new devices is substantially more uniform than in the non-isoplanar ones.