Advanced plasma and advanced gate dielectric - a charging damage prospective

Abstract

Modern advanced processing plasmas tend to have high-density and extremely well engineered uniformity. From the plasma charging damage prospective, high-density suggests the potential for more severe damage once the voltage across the thin gate oxide condition is satisfied. In principle, good uniformity means that the gross non-uniform plasma potential induced damage is not likely to exist. Unfortunately, advanced ultra thin gate oxide greatly reduces the voltage needed to induce significant tunneling. Thus plasma charging due to non-uniform plasma potential continues to exist. Furthermore, charging mechanisms that do not require a non-uniform plasma potential, such as the electron shading effect, become largely unavoidable (pulse modulated plasmas can help in this regard, but they have not found their way into main stream production yet). The consequence is that plasma charging is a fact of life in advanced silicon integrated circuit manufacturing. Strangely, it is precisely when people dismiss the impact of stress current (due to plasma charging) on ultra thin gate oxide that the concern of the gate oxide breakdown reliability heightened. To the experts in the area of gate oxide reliability, there is little margin exist for the ultra thin gate oxide to absorb unexpected electrical stress during fabrication. Indeed, even in the perfectly pristine state, the lifetime of the ultra thin gate oxide in the state of the art technology may not satisfy the long established specification. Any premature electrical stress such as plasma charging damage is definitely a serious problem. Thus, our knowledge about plasma charging and ultra thin gate oxide reliability is in conflict with the common perception in the industry about plasma charging damage. The source of this conflict appears to be the difficulties in measurement. The determination of ultra thin gate oxide reliability has become so difficult that only specialists with substantial resources can handle it. The determination of how much plasma charging damage has degraded the reliability of ultra thin gate oxide is even more daunting