Dram cell buried strap leakage measurement structure and method

Abstract

A test structure and method for determining DRAM cell leakage. The cell leakage test structure includes a pair of buried strap test structures. Each buried strap test structure includes multiple trench capacitors formed in a silicon body. Each trench capacitor is connected to a trench sidewall diffusion by at least one buried strap. An n-well ring surrounds each buried strap test structure and divides the buried strap test structure into two separate array p-wells, one being a contact area and the other a leakage test area. The contact area includes contacts to the trench capacitor plates for the corresponding buried strap test structure. In one buried strap test structure, a layer of polysilicon, essentially covers the trench capacitors in the leakage test area to block source/drain region formation there. The other of the two buried strap test structures includes polysilicon lines simulating wordlines with source and drain regions form on either side. A buried n-band contacts the n-well rings, essentially forming an isolation tub around each array well. Cell leakage is measured by measuring leakage current in each buried strap test structure, individually, and then extracting individual leakage components from the measured result.