In this work, for the purpose of contact-hole process control, new metrics for contact-hole edge roughness (CER) are being proposed. The metrics are correlated to lithographic process variation which result in increased electric fields; a primary driver of time-dependent dielectric breakdown (TDDB). Electric field strength at the tip of spokeshaped CER has been simulated; and new hole-feature metrics have been introduced. An algorithm for defining critical features like spoke angle, spoke length, etc has been defined. In addition, a method for identifying at-risk holes has been demonstrated. The number of spike holes can determine slight defocus conditions that are not detected though the conventional CER metrics. The newly proposed metrics can identify contact holes with a propensity for increased electric field concentration and are expected to improve contact-hole reliability in the sub-40-nm contact-hole process.
INTRODUCTIONLSI devices continue to shrink in size and increase in fabrication complexity. As the number of process variables increase, yield has become an ever challenging criteria to meet. One of the contributing factors that have been of an increasing focus is edge roughness (ER). With typical post develop CD's ranging from 40-60 nm in the 22 nm node and even smaller in the 16 nm node, ER on the order of 10% can drastically impact final device performance or reliability and is not a negligible [1,2]. Most of the recent work in studying how ER is related to performance or reliability has focused on looking at the impact of line edge roughness (LER) in the gate and interconnect levels [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].With such intense scrutiny on LER, some have also begun studying contact edge roughness (CER) and its impact on the contact and via levels [1,2]. Both LER and CER are caused by process variation by intrinsic imaging properties of the resist coupled with image contrast [18], and although both can be minimized, CER tends to be more random in occurrence then LER. An additional complication with CER is in the definition the edge roughness itself. There are two common definitions of this ER mechanism. The first is the deviation of the processed structure from that of a perfect circle, or its ellipticity. The second definition is related to the first in that it is a metric of circularity, but more focuses on the presence of a concave or convex protrusions in the hole structure. It is this second definition that is critical to device reliability as it can cause either enhancements in the electric field or shorting in a device; and not only a degradation in the time dependant dielectric breakdown (TDDB) but a loss of yield [2].In light of the above-described circumstances, new CER metrics are proposed to identify the number of these spoked holes for process control and optimization. Since the problem of electric field concentration is the same as discussed for the interconnect layer [13-17], we initially wanted to look at the best method for identifying the areas on a spoke...