End point detection method for plasma etching of semiconductor wafers with low exposed area
First Claim
1. A method for controlling a plasma processing chamber, wherein the plasma processing chamber includes an RF generator, the RF generator providing a drive signal to an electrode to generate a gas plasma, and an RF sensor for sensing operating characteristics of the drive signal, wherein the plasma processing chamber processes a single semiconductor wafer at a time, the method consisting of:
- (1) selecting a mathematical model equation of the form X(ti)=A+Be(exp (−
λ
*ti)), wherein X(ti) is an instant electrical reactance of the plasma processing chamber;
(2) commanding the plasma processing chamber to begin processing the wafer according to a predetermined plasma etching recipe;
(3) receiving a plurality of data sets from the RF sensor, each data set comprising a representation of RMS voltage, RMS current, and phase angle between the RMS voltage and RMS current during a first time period, wherein each data set corresponds to a unique time point;
(4) saving the data sets received from the RF sensor and their corresponding time points;
(5) calculating the variable parameters A, B, and λ
using the data set values;
(6) receiving an additional data set from the RF sensor during a second time period;
(7) saving the additional data set received from the RF sensor and its corresponding time point;
(8) using the values of the variable parameters A, B, and λ
from the first time period, calculating a value of the mathematical model for a time point corresponding to the same time point of the additional data set;
(9) calculating a residual between the additional data set and the value of the mathematical model for the time point corresponding to the time point of the additional data set;
(10) if and the residual is greater than a predetermined threshold, commanding the plasma processing chamber to stop processing; and
(11) if the residual is not greater than the threshold, repeating the process steps beginning with the operation (6) above, thereby extending the second time period.
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Abstract
A method for controlling the plasma etching of semiconductor wafers determines the impedance of a plasma chamber using values representing voltage, current, and the phase angle between them, as provided by a sensor. All or less than all of the data during a first time period may be used to calculate a model. During a second time period, real time data is used to calculate a version of the instant impedance of the chamber. This version of impendence is compared to a time-projected version of the model. The method determines that etching should be stopped when the received data deviates from the extrapolated model by a certain amount. In some embodiments a rolling average is used in the second time period, the rolling average compared to the model to determine the end point condition.
29 Citations
10 Claims
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1. A method for controlling a plasma processing chamber, wherein the plasma processing chamber includes an RF generator, the RF generator providing a drive signal to an electrode to generate a gas plasma, and an RF sensor for sensing operating characteristics of the drive signal, wherein the plasma processing chamber processes a single semiconductor wafer at a time, the method consisting of:
-
(1) selecting a mathematical model equation of the form X(ti)=A+Be(exp (−
λ
*ti)), wherein X(ti) is an instant electrical reactance of the plasma processing chamber;(2) commanding the plasma processing chamber to begin processing the wafer according to a predetermined plasma etching recipe; (3) receiving a plurality of data sets from the RF sensor, each data set comprising a representation of RMS voltage, RMS current, and phase angle between the RMS voltage and RMS current during a first time period, wherein each data set corresponds to a unique time point; (4) saving the data sets received from the RF sensor and their corresponding time points; (5) calculating the variable parameters A, B, and λ
using the data set values;(6) receiving an additional data set from the RF sensor during a second time period; (7) saving the additional data set received from the RF sensor and its corresponding time point; (8) using the values of the variable parameters A, B, and λ
from the first time period, calculating a value of the mathematical model for a time point corresponding to the same time point of the additional data set;(9) calculating a residual between the additional data set and the value of the mathematical model for the time point corresponding to the time point of the additional data set; (10) if and the residual is greater than a predetermined threshold, commanding the plasma processing chamber to stop processing; and (11) if the residual is not greater than the threshold, repeating the process steps beginning with the operation (6) above, thereby extending the second time period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification