End point detecting method for semiconductor plasma processing

An end point detection method in a semiconductor plasma process, comprising the steps of:

• determining first to fourth specified periods set before an ideal end point of the plasma process is reached;
• subjecting a target object to the plasma process;
• obtaining, during the plasma process, a first approximate expression which approximates a characteristic curve representing a change over time in emission intensity of a first gas in the plasma within the first specified period, and a second approximate expression which approximates a characteristic curve representing a change over time in emission intensity of a second gas in the plasma within the second specified period;
• obtaining, during the plasma process, a first deviation corresponding to a deviation of the emission intensity of the first gas in the plasma with respect to a value of the first approximate expression within the third specified period, and a second deviation corresponding to a deviation of the emission intensity of the second gas in the plasma with respect to a value of the second approximate expression within the fourth specified period;
• obtaining, during the plasma process, first and second intermediate expressions representing ratios or differences between the emission intensities of the first and second gases in the plasma and the values of the first and second approximate expressions after the first to fourth specified periods elapse;
• correcting the first and second intermediate expressions with the first and second deviations, and obtaining a criterion expression representing a ratio of the first intermediate expression to the second intermediate expression;
• and
• determining an end point of the plasma process on the basis of the criterion expression.