A NOTE ON CONTROLLING THE HOMOGENEITY OF OXIDE LAYERS

摘要

The paper deals with the problem of the control of the homogeneity of oxide layers. In a first step, a precise definition of what is to be understood by the term homogeneity will be given. It is then shown that the use "Standard-SPC", i.e. the use of a "Shewart-Charts" for the arithmetic mean and the sample standard deviation, is not an appropriate approach for the control of homogeneity, as it does not take into account the three (technically unavoidable) violations to the i.i.d.-presumption that have to be dealt with when one considers random variables on a wafer: these will generally differ in their mean and in their variance; moreover, they will not be independent. A formula will be presented to point out the effects that these violations will have on the expectation of thed sample standard deviation, which is generally considered to be a measure for homogeneity. Finally, a modified approach for the control of homogeneity in a more efficient way will be presented.