| Popis: |
Wafer charging in barrel etchers, reactive ion etching (RIE) etchers, magnetron RIE (MRIE) etchers and electron cyclotron resonance (ECR) etchers are characterized. The charging voltages were measured by using electrically programmable non-volatile memories. The charging profile for the barrel etchers and the RIE etcher depends critically on the electrode arrangements and wafer locations, while that in the MRIE etchers and the ECR etchers depends on the structure of the magnetic field. Even in the case of a non-divergent magnetic field ECR etcher, wafer charging is built-up when an RF bias is applied to the wafer stage. By analyzing these results, two charging mechanisms are distinguished. One is the plasma nonuniformity around the wafer, which depends on the RF electrode and the wafer location. The other is the anisotropy of the magnetized plasma, which depends on the structure of the magnetic field. Some of the charging profiles due to the former effect is reproduced by using an equivalent circuit model. It is found from the model that even in the uniform density plasma, wafer charging is induced by the RF current which causes a plasma potential variation across the wafer surface. |
