Wafer metrology technologies
Various approaches can be used to interrogate a surface such as a surface of a layered semiconductor structure on a semiconductor wafer. Certain approaches employ Second Harmonic Generation and in some cases may utilize pump and probe radiation. Other approaches involve determining current flow from a sample illuminated with radiation. Decay constants can be measured to provide information regarding the sample. Additionally, electric and/or magnetic field biases can be applied to the sample to provide additional information.
1. A system for characterizing a sample, the system comprising:
a first optical path configured to propagate an interrogating optical beam to the sample, the interrogating optical beam comprising a plurality of optical pulses, two consecutive pulses of the interrogating optical beam being spaced apart by a period (T), the period (T) corresponding to a repetition rate of the interrogating optical beam, said interrogating optical beam generating second harmonic generated light from the sample;
an optical pump source outputting pump radiation;
a detector configured to sample intensities of the generated second harmonic light at at least two temporally separated sample times, the at two temporally separated sample times occurring after charging the sample at a sample site by optically pumping;
a gating system configured to block pump radiation for a plurality of varied blocking periods;
a controllable optical delay system configured to introduce a variable time delay (A) between at least one pulse from the interrogating optical beam and a reference time with respect to said charging the sample such that the variable time delay causes the interrogating optical beam to interrogate the sample after a blocking period of the plurality of varied blocking periods; and
a processing and control module configured to obtain a characteristic of the sample based on intensities of said second harmonic generated light at the at least two sample times.
2. The system of claim 1 , wherein the processing and control module is configured to obtain a characteristic of the sample based on the second harmonic generated light intensity measured at no more than four different sample times.
3. The system of claim 1 , wherein the processing and control module is configured to obtain a characteristic of the sample based on the second harmonic generated light intensity measured at no more than three different sample times.
4. The system of claim 1 , wherein the processing and control module is configured to generate a decay curve based on the sampled intensities of the second harmonic generated light at the at least two sample times.
5. The system of claim 4 , wherein the processing and control module is configured to obtain a characteristic of the sample based on the second harmonic generated light intensity at three different sample times.
6. The system of claim 4 , wherein the processing and control module is configured to obtain a characteristic of the sample based on the second harmonic generated light intensity at four different sample times.
7. The system of claim 1 , wherein the processing and control module is configured to determine a time constant of a charge decay process from the sampled intensities of the second harmonic generated light at the at least two sample times.
8. The system of claim 7 , wherein the processing and control module is configured to charge the sample site by optical pumping between the at least two sample times.
9. The system of claim 7 , wherein the processing and control module is configured to cause sampling of the intensities of the second harmonic generated light without the sample site being charged between the at least two sample times.
10. The system of claim 1 , wherein the processing and control module is configured to control the controllable optical delay system.
11. The system of claim 1 , wherein said system is configured to obtain measurements at multiple sites on the sample.
12. The system of claim 1 configured to be integrated in a semiconductor fabrication line, wherein the system includes an automated wafer handling module.
13. The system of claim 1 configured to be part of an assembly line.
14. The system of claim 1 configured to detect impurities in the sample.