Fabricating a Trench Isolation with Rounded Corners
Original Publication Date: 2003-Apr-07
Included in the Prior Art Database: 2003-Apr-07
For a system-on-a-chip solution, both logic and non-volatile memory devices have to be fabricated on the same chip. Though both circuits require large device densities, their isolation requirements differ. Non-volatile memory (NVM) devices require trenches with rounded corners while logic devices need the narrowest possible isolation with less corner rounding. The NVM bitcell requires rounded trench corners to avoid electrical field enhancement at trench corners during program and erase. These enhanced fields at non-rounded trench corners could reduce bitcell endurance and reliability. One technique to produce rounded trench corners is to grow a thick trench liner oxide at high temperature. However, thick liner results in excessive active width loss and poor fill of narrow trenches. The latter results in trench voids. As long as the spacing between the active regions is large enough, as it is in NVM arrays, trench liner thickness does not degrade the trench fill process. However, with increasing circuit densities in logic circuits, as the active spaces become smaller, it becomes harder to fill the narrow trenches with thick trench liners used in embedded NVM circuits.