Method and system for non-contact measurement of microwave capacitance of miniature structures of integrated circuits
In the method and system for non-contact measurements of microwave capacitance of test structures patterned on wafers used for production of modern integrated circuits, a near-field balanced two-conductor probe is brought into close proximity to a test structure, and the resonant frequency of the probe for the test structure is measured. The probe is then positioned at the same distance from the uniform metallic pad, and the resonance frequency of the probe for the uniform metallic pad is measured. A shear force distance control mechanism maintains the distance between the tip of the probe and the metallic pad equal to the distance between the tip of the probe and the test structure. The microwave capacitance of the test structure is then calculated in accordance with a predefined formula. The obtained microwave capacitance may be further used for determining possible defects of the test structure.
1. A method for non-contact measurement of microwave capacitance of miniature structures of integrated circuits, comprising the steps of:
positioning a near-field microwave probe at a predetermined distance from a miniature structure under the test;
measuring a resonant frequency f s of said near-field microwave probe for said miniature structure under the test;
positioning said near-field microwave probe said predetermined distance from a uniform metallic structure;
measuring a resonant frequency f c of said near-field microwave probe for said uniform metallic structure; and,
calculating the microwave capacitance C s of said miniature structure under the test as
C
s
=
(
f
e
-
f
c
)
(
f
e
-
f
c
)
(
f
s
-
f
c
)
4
f
e
2
Z
0
wherein f e is the resonant frequency of said near-field microwave probe in air, and Z 0 is the characteristic impedance of said near-field microwave probe.
2. The method of claim 1 , wherein said near-field microwave probe includes a balanced two-conductor transmission line resonator.
3. The method of claim 1 , wherein the measurements are conducted at microwave frequencies.
4. The method of claim 1 , wherein said near-field microwave probe includes at least a pair of conductors extending in spaced relationship therebetween and separated by a dielectric medium.
5. The method of claim 1 , further comprising the steps of:
maintaining said distance between said near-field microwave probe and said uniform metallic structure equal to said predetermined distance between said near-field microwave probe and said miniature structure under the test by a closed-loop distance control mechanism.
6. The method of claim 5 , wherein said closed-loop distance control mechanism includes a shear force-based distance control mechanism.
7. The method of claim 1 , wherein said near-field microwave probe includes a tip, wherein an area of said uniform metallic structure is at least the size of a cross-section of said tip of said near-field microwave probe.
8. The method of claim 1 , wherein said predetermined distance is maintained below 50-100 nm.
9. The method of claim 1 , further comprising the steps of:
measuring the absolute value of the first derivative of a power reflected from or transmitted through said near-field microwave probe as a function of a frequency of a signal applied thereto, and determining said resonant frequencies f s and f c by a numerical technique chosen from the group of numerical techniques, consisting of:
(a) determining the resonant frequency f s and f c as the frequency at the point on said measured curve where said measured curve has a minimum;
(b) determining the resonant frequency f s and f c as the frequency at the point of said measured curve where the first derivative of the measured power with respect to frequency equals zero and second derivative of the measured power is positive; and
(c) fitting the obtained measured curve to an even order polynomial, and finding the frequency where the first derivative of said polynomial equals to zero.
10. The method of claim 1 , wherein said uniform metallic structure is a contact pad.
11. The method of claim 1 , wherein said miniature structure includes an inter-digital capacitor.
12. The method of claim 1 , wherein said miniature structure includes a single metal wire or a trench in a dielectric.
13. The method of claim 1 , wherein said miniature structure includes an array of metal/dielectric trenches.
14. The method of claim 1 , wherein said miniature structure includes an array of interconnect lines.
15. The method of claim 1 , wherein said miniature structure includes a multi-layered structure.
16. The method of claim 1 , further comprising the steps of:
comparing said calculated microwave capacitance C s with a predetermined capacitance value, and judging whether said miniature structure is defective based on a deviation of said C s from said predetermined capacitance value.
17. A system for non-contact measurement of microwave capacitance of miniature structures of integrated circuits, comprising:
a miniature structure under the test,
a near-field microwave probe having a tip thereof,
a uniform metallic pad of the size approximately equal to the cross-section of said tip of said near-field microwave probe,
a shear force-based distance control unit operatively coupled to said near-field microwave probe to control tip-to-miniature structure separation and tip-to-uniform metallic pad separation,
acquisition means for acquiring resonant frequency f s of said near-field microwave probe for said miniature structure and resonant frequency f c of said near-field microwave probe for said uniform metallic pad, and
processing means for calculating the microwave capacitance C s of said miniature structure under the test as
C
s
=
(
f
e
-
f
c
)
(
f
e
-
f
c
)
(
f
s
-
f
c
)
4
f
e
2
Z
0
wherein f e is the resonant frequency of said near-field microwave probe in air, and Z 0 is the characteristic impedance of said near-field microwave probe.
18. The system of claim 17 , wherein said near-field microwave probe includes a balanced two-conductor transmission line resonator.
19. The system of claim 17 , wherein said near-field microwave probe includes at least a pair of conductors extending in spaced relationship therebetween and separated by a dielectric media.
20. The system of claim 17 , further comprising means for comparing said calculated microwave capacitance C s of said miniature structure under the test with a predetermined capacitance value, and for judging whether said miniature structure is defective based on deviation of said C s from said predetermined capacitance value.