AVS 46th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS2-ThA

Invited Paper PS2-ThA5
Characterization of Process-Induced Charging Damage in Scaled-Down Devices and Reliability Improvement using Time-Modulated Plasma

Thursday, October 28, 1999, 3:20 pm, Room 609

Session: Pulsed Plasmas
Presenter: K. Noguchi, NEC Corporation, Japan
Authors: K. Noguchi, NEC Corporation, Japan
S. Samukawa, NEC Corporation, Japan
H. Ohtake, NEC Corporation, Japan
T. Mukai, NEC Corporation, Japan
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The charging damage from metal etching and dielectric etching was studied using MOS devices with gate oxide thickness of 1.9-6.0nm, and the impact of the plasma charging on reliability of scaled-down devices, as well as damage monitor methods appropriate for each plasma process and oxide thickness were investigated. Obtained results are as follows. For metal etching, in which electron shading effect is a major cause of charging, hot carrier effect dominated device degradation for oxide of 3.5-6.0nm. For thinner oxide ( < 3.0nm), however, a gate leakage failure dominated but the failure rate decreased with gate oxide thinning below 3.0nm and became negligibly small below 2.2nm. For dielectric etching, the gate leakage current was an effective damage monitor, though high oxide electric field of >10 MV/cm was required to detect the latent damage effectively. Charge-to-breakdown or hot carrier degradation was less sensitive to the dielectric etching damage. Similar to the metal etching, the failure rate was lower for thinner oxide. Although the oxide damage seemed to decrease with device scaling, the problem may remain as latent damage or reduced reliability. To realize plasma process with low damage, time-modulated (TM) plasma technology was applied to the ECR metal etcher, the ultrahigh frequency (UHF) dielectric etcher, and the ICP polysilicon etcher. These etchers all showed reduction in charging damage compared to the conventional continuous-wave plasma. For example, the estimated amount of the charging current from the plasma was reduced to 1/4 in the metal etcher. The oxide yield improved by about 2 times in the dielectric etcher. The density of oxide traps created by the plasma process decreased in the polysilicon etcher. Thus, the use of the TM plasma is an effective and practical method to realize scaled-down MOS devices with better yield and reliability.