The overall effect is higher etch rates at the electrode edges, with a gradual reduction in the etch rate as it approaches the center of the electrode. This can be viewed as a target or bull's eye effect, which results in severe process non-uniformity. If unchecked, this non-uniformity will cause parts positioned at the periphery of the electrode to etch more severely than those positioned at the center of the electrode. To obtain uniform etch rates the high energy edge effects must be minimized or eliminated. These electrostatic shields are a patented feature, unique to the Plasma Etch product line.
Results are controllable and repeatable.
Surface treatment of individual parts is independent of location and orientation on the electrodes. Some plasma equipment manufacturers attempt to minimize the bull's eye effect by distancing the electrodes from the vacuum chamber walls. This somewhat improves the uniformity of etch, but does not eliminate the problem. It has the added negative effect of increasing the internal volume of the vacuum chamber and thereby increases the pumpdown time of the vacuum chamber. The use of high frequency R.F. power is instrumental in creating a high efficiency plasma.