Steady state method for measuring the thickness and the capacitance of ultra thin dielectric in the presence of substantial leakage current
First Claim
1. A method of determining the thickness of a dielectric layer deposited on a semiconducting wafer, the method comprising:
- depositing an ionic charge onto a surface of the dielectric layer disposed on the semiconducting wafer with an ionic current sufficient to cause a steady state condition;
measuring, via a non-contact probe, a voltage decay on the dielectric surface as a function of time; and
determining the thickness of the dielectric layer based upon the measured voltage decay.
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Abstract
A method is described for non-contact measuring the capacitance and the equivalent oxide thickness of ultra thin dielectric layer on a silicon substrate. The surface of a dielectric layer is electrically charged by a flux on ions from a corona discharge source until a steady state is reached when the corona flux is balanced by the leakage current across a dielectric. The flux is abruptly terminated and the surface potential of a dielectric is measured versus time. The steady state value of the surface potential is obtained by extrapolation of the potential decay curve to the initial moment of ceasing the corona flux. The thickness of a dielectric layer is determined by using the steady state potential or by using the value of the surface potential after a predetermined time. The method produces highly accurate results for oxide thickness below 40 Å with a demonstrated repeatability of a 0.03 Å in a series of 10 measurements. Alternatively, the rate of surface potential decay is calculated at the initial moment providing a measure of the charge dissipation on a dielectric capacitor. The capacitance of a dielectric layer is calculated from this rate.
132 Citations
27 Claims
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1. A method of determining the thickness of a dielectric layer deposited on a semiconducting wafer, the method comprising:
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depositing an ionic charge onto a surface of the dielectric layer disposed on the semiconducting wafer with an ionic current sufficient to cause a steady state condition;
measuring, via a non-contact probe, a voltage decay on the dielectric surface as a function of time; and
determining the thickness of the dielectric layer based upon the measured voltage decay. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A method of determining the thickness of a dielectric layer deposited on a semiconducting wafer, the method comprising:
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illuminating the dielectric surface;
depositing a precharging ionic charge on the dielectric layer;
depositing an ionic charge onto a surface of the dielectric layer with an ionic current sufficient to cause a steady state condition;
ceasing ionic charging after establishing the steady state condition;
measuring, via a non-contact probe, a voltage decay on the semiconducting wafer as a function of time after ceasing the ionic charging;
analyzing the voltage decay to determine a characteristic of the measured voltage decay, the characteristic of the measured voltage decay being selected from the group consisting of an initial surface potential, V0, a surface potential at a time greater than t=0, VD, and an initial rate of voltage decay, dV/dt|t=0; and
determining the thickness of the dielectric layer based upon the characteristic of the measured voltage decay.
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Specification