AVS 45th International Symposium
    Plasma Science and Technology Division Wednesday Sessions
       Session PS-WeM

Paper PS-WeM5
Suppression of Charging Damage Caused by Electron Shading Effect in Gate Etching Technology

Wednesday, November 4, 1998, 9:40 am, Room 318/319/320

Session: Plasma Damage
Presenter: K. Yoshida, NEC Corporation, Japan
Authors: K. Yoshida, NEC Corporation, Japan
K. Tokashiki, NEC Corporation, Japan
H. Miyamoto, NEC Corporation, Japan
Correspondent: Click to Email
Recently, the charging damage caused by electron shading effect has become a serious problem in etching processes using high-density low-pressure plasma. This effect causes profile distortion and/or gate oxide degradation. It is expected that these problems would be enhanced in sub-quarter-micron device fabrication because of their high aspect ratios. We reported in American Vacuum Society 44th National Symposium(PS-MoM8) that the profile distortion was suppressed by applying the high pressure(@>=@20 mTorr) and low source power in HBr gas plasma to over-etching step for 0.18 µmm gate etch process. Furthermore we have studied the correlation between the profile distortion and the gate oxide degradation in order to suppress the charging damage successfully. The impact of gas chemistry (Cl@sub 2@ and HBr) and pressure on charging damage was evaluated in gate etching. Especially we focused on the just and over etch period because the charging damage takes place in this period. Thickness of gate film and that of gate oxide were 200 nm and 4.5 nm, respectively. An initial-electron-trapping-rate (IETR) method was applied to monitor the charging damage. We measured dV/dt slope under 40 mA/cm@super -2@ stress current with antenna ratios ranged from 50 to 66,700. At low pressure (2 mTorr) Cl@sub 2@ and HBr plasmas, dV/dt slope increased significantly as the antenna ratio were over 10,000. The dV/dt reached about 10 mV/sec, which means serious damage took place. However, as increasing in pressure, dV/dt slope or charging damage was effectively suppressed (dV/dt@<=@2 mV/sec at 20 mTorr). It was also found that HBr plasma more effectively suppressed the damage than Cl@sub 2@ plasma. Interestingly, these damage test results corresponded to the dependence of the profile distortion on gas chemistry and pressure. One of reasons for the different damage result between Cl@sub 2@ and HBr correlates with the different plasma characteristics between them. Electron temperature(T@sub e@) and density(N@sub e@) for Cl@sub 2@ plasma were higher than that of HBr plasma at the pressure ranged from 2 to 20 mTorr. T@sub e@ and N@sub e@ decreased with increasing pressure, 4.2 to 2.9 eV of T@sub e@ and 2.5E10 to 9.5E9 cm@super -3@ of Ne for Cl@sub 2@ plasma. In HBr plasma, T@sub e@ and N@sub e@ were lowered to 2.6 eV and 4E9 cm@super -3@ at 20 mTorr. In conclusion, the gate oxide degradation caused by electron shading effect correlates with the profile distortion. And the use of relatively high pressure(@>=@20 mTorr) HBr plasma in just and over etch period is useful to suppress the charging damage caused by electron shading effect.