A layer of 2µm thick silicon dioxide is deposited on <100> silicon wafer. SiO2 layer is patterned using lithography and dipped in BOE to etch the layer. While etching oxide layer, 10nm of silicon is also etched. What is the selectivity of BOE to etch SiO2, when Si is etch stop layer?
200:1
20:1
50:1
100:1
To find the selectivity of BOE (Buffered Oxide Etch) to etch SiO2 when Si is the etch stop layer, we need to calculate the ratio of the SiO2 etch rate to the Si etch rate.
In this case, the SiO2 layer is 2µm thick, and we know that 10nm (0.01µm) of Si is also etched. The selectivity can be calculated as:
Selectivity = SiO2 etch rate / Si etch rate
First, we need to calculate the etch rates for both SiO2 and Si.
The etch rate of SiO2 can be found by dividing the thickness of the SiO2 layer by the etch time:
SiO2 etch rate = SiO2 layer thickness / etch time
Since the SiO2 layer is 2µm (or 2000nm) thick, we cannot find the etch rate with the given information because the etch time is not provided.
On the other hand, the etch rate of Si can be found by dividing the thickness of the Si that is etched by the etch time:
Si etch rate = Si etch depth / etch time
Since 10nm (0.01µm) of Si is etched, we cannot find the etch rate of Si with the given information because the etch time is not provided.
Without knowing the etch rates of SiO2 and Si, we cannot directly calculate the selectivity.
It is important to note that selectivity is often determined experimentally since it can vary depending on various process conditions, including the concentration of the etchant and the temperature.
Therefore, based on the given information, we cannot accurately determine the selectivity of BOE to etch SiO2 when Si is the etch stop layer.