AVS 61st International Symposium & Exhibition
    Materials Characterization in the Semiconductor Industry Focus Topic Tuesday Sessions
       Session MC-TuP

Paper MC-TuP3
SIMS Measurements of Impurities and Alloying Elements in Cu Films used for BEOL Processes

Tuesday, November 11, 2014, 6:30 pm, Room Hall D

Session: Poster Session for all areas of Materials Characterization in the Semiconductor Industry
Presenter: Steven Novak, SUNY College of Nanoscale Science and Engineering
Authors: S.W. Novak, SUNY College of Nanoscale Science and Engineering
T. Laursen, SUNY College of Nanoscale Science and Engineering
M. Rizzolo, IBM Albany Nanotech Center
B. O'brien, SUNY College of Nanoscale Science and Engineering
Correspondent: Click to Email
Significant recent work has concentrated on the impurity contents of electroplated copper and how they affect the crystallization of copper interconnects. Plating bath additives cause elevated impurity contents in electroplated Cu films that have been thought to pin grain boundaries and strongly affect the recrystallized grain structure of the Cu. SIMS is among the most utilized technique to measure impurity contents in electrochemically deposited Cu however SIMS data is typically only given as relative comparative data. We present quantitative measurements for C, O, S and Cl contents in ECD Cu using both TOF-SIMS (IonTof V) and quadrupole (Phi 6650) SIMS instruments. Using ion-implanted standards we have found that detection limits for impurity elements are typically well below the required limit for ECD Cu. Detection limits are typically one order of magnitude lower using dynamic SIMS compared to TOF-SIMS. The high mass resolution available for TOF-SIMS allows unambiguous quantitative measurement of impurities like S, which experiences mass interference from the O2 molecular ion. Quantitative SIMS analyses show linear increases in impurity contents within plated Cu films as the additive content increases in the plating bath. Although impurity elements are commonly cited as a major effect on the grain size of recrystallized Cu films, recent experiments with intentionally layered Cu samples, having impurity content differences of 2-3X, show that the impurity content has little effect on ultimate crystallite size. Impurity measurements in Cu trenches have been a goal for SIMS for some time. Ion imaging of Cu trenches 450-35nm wide has been carried out using the Bi LMIG gun of the IonTOF V instrument. This instrument is capable of 200nm image resolution. Depth profile analysis of Cu trenches show higher impurity contents within clearly-resolved 450nm wide trenches and suggest even higher contents within smaller trenches, when compared to the Cu overburden. Detection limits in image mode are at least one order of magnitude higher than standard depth profile mode. Alloying Cu with other metals has been proposed as a means of minimizing electromigration within plated Cu lines. Presently Mn is used as an alloy element in seed Cu layers. In addition to Mn, we have studied ion implants of Ag, Co and Ni in Cu as standards for quantifying these elements in seed Cu layers. The alloying element will be present below 1 at percent, less than can be reliably measure with other surface analytical techniques. SIMS analytical methodology and detection limits will be presented for each of these elements in Cu.