Soft Error Rate Reduction in Trench Technology

Soft Error Rate Reduction in Trench Technology

       Soft Error Rate (SER) is becoming an increasing problem
as dimensions of devices are reduced further and further, so that it
takes less charge to trigger a soft error.  This article describes
one possible process solution to this problem when trenches are
included in the technology in question.  Basically, an N+ region is
added near the trench bottom; the depletion region from this N+ area
acts to collect the charge generated from an alpha-particle or cosmic
ray hit.

      In the structure shown in Fig. 1, the presence of the N+ region
surrounding the bottom portion of trench results in a depletion
region that spreads laterally across the opening beneath the device
region.  If the spacing from trench to trench is small enough, the
depletion regions from the trenches will almost close off the device
regions above; in this case, most of charge from an alpha-particle
hit will be collected in these depletion regions, rather than travel
upward to be collected by a sensitive device node.

      One method for making this structure is as follows:
      a.   Use a conventional trench process to etch the trench
region, grow an oxide liner, line it with nitride and RIE open the
bottom.
      b.   PSG is then deposited by CVD or PECVD methods into the
open bottom trench.  This material will act as a source of phosphorus
for the formation of the N+ trench bottom when a drive-in cycle is
added as shown...