MICROLOADING EFFECT IN REACTIVE ION ETCHING

The etch rate of silicon, during reactive ion etching (RIE), depends o n the total exposed area. This is called the loading effect. However, local variations in the pattern density will, in a similar way, cause local variations in the etch rate. This effect is caused by a local de pletion of reactive species and is called the microloading effect. Sil icon wafers patterned with silicon dioxide have been etched in order t o study the microloading effect. The pattern consists of a large expos ed area and narrow lines at different distances from the edge of the l arge area. This arrangement makes it possible to study how the distanc e from the large area, which depletes the etchants, influences the etc h rate. The influence of different processing parameters like, e.g., p ressure, gas flow rate, and flow direction on the microloading effect have been investigated. It has been found that the microloading effect is small (<10%) compared to other pattern dependent nonuniformities. It is also shown that the nonuniformities caused by the microloading e ffect can be decreased by, e.g., decreasing the pressure or increasing the gas flow rate.