AVS 51st International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS-MoP

Paper PS-MoP14
Anomalous Ionization of Copper Atoms in Argon-Based Sputtering Plasmas

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: H. Kadota, Chubu University, Japan
Authors: H. Kadota, Chubu University, Japan
K. Nakamura, Chubu University, Japan
N. Nafarizal, Nagoya University, Japan
K. Sasaki, Nagoya University, Japan
M. Kobayashi, ANELVA, Japan
Correspondent: Click to Email
Plasma-enhanced metal sputter deposition has been widely used for formation of seed and/or barrier layers of high aspect ratio contact holes in ULSI semiconductor devices. In this process, sputtered metal atoms are ionized during flight in Ar plasma, and the metal ions can arrive at the bottom of the hole since the metal ions are accelerated in the sheath around the wafer in the direction perpendicular to the substrate. This paper reports on ionization characteristics of sputtered copper atoms in Ar plasmas, especially for ionization fraction of the copper atoms as well as ion density ratio of copper to argon. An inductively-coupled argon plasma is produced in a stainless steel vessel by supplying 13.56 MHz RF powers with a loop bare copper antenna. A blocking capacitor is inserted in series at each end of the antenna conductor, consequently a negative self-bias voltage appears during the operation at the antenna. Therefore, copper atoms are injected into the plasma because of physical antenna sputtering. The ion density ratio [Cu@super +@]/[Ar@super +@] is obtained by combining mass spectroscopic measurements and Langmuir probe measurements, whereas the copper ionization fraction is measured with a biased crystal micro balance. The ion density ratio increases with the Ar pressure, and reaches ~30 at ~100 mTorr. The ionization fraction also increases with the Ar pressure and approximately reaches ~100% at the same pressure. This means that copper plasma is likely to be produced even in the argon discharge. These characteristics are independent to the discharge power, suggesting an ionization mechanism of the copper atoms except for electron impact.