Charge decay measurement systems and methods

Abstract

Various approaches to 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.

That being said, we claim:  
     
         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 beam comprising a plurality of optical pulses, two consecutive pulses of the interrogating 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 two sample times occurring after charging the sample at a sample site by optically pumping;   a controllable optical delay system configured to introduce a variable time delay (Δ) between at least one pulse from the interrogating beam and a reference time with respect to said charging the sample, the variable time delay Δ being shorter than the period (T) of the pulses from the interrogating beam, said controllable optical delay system configured to vary and control the duration of the time delay; 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 , further comprising a first optical shutter disposed in the first optical path, the first optical shutter configured to block one or more pulses from the interrogating optical beam. 
     
     
         3 . The system of  claim 2 , wherein the first optical shutter comprises at least one of a mechanical shutter, an electro-optic shutter, a Kerr cell and a Pockels cell. 
     
     
         4 . The system of  claim 2 , wherein the processing and control module is configured to control the first optical shutter. 
     
     
         5 . The system of  claim 1 , further comprising a second optical path configured to propagate pump radiation that provides said optical pumping. 
     
     
         6 . The system of  claim 5 , further comprising a second optical shutter disposed in the second optical path, the second optical shutter configured to block the pump radiation. 
     
     
         7 .- 48 . (canceled) 
     
     
         49 . A method of optical interrogation of a sample material, the method comprising:
 charging the material at a sample site with radiation to a first charging level;   obtaining charge state decay measurements at the sample site in less than one second by directing an interrogating optical beam at the sample site at multiple time points to provide decay curve data; and   determining a characteristic of the decay curve data to determine a parameter of the sample material.   
     
     
         50 . The method of  claim 49 , wherein determining a characteristic of the decay curve data includes determining a shape of the decay curve data. 
     
     
         51 . The method of  claim 49 , wherein the parameter is selected from at least one of: a charge carrier density, a trap charge density, an occupied trap density, a carrier injection threshold energy, a charge carrier lifetime, a charge accumulation time, and trapping cross-section. 
     
     
         52 . The method of  claim 49 , further comprising obtaining charge state decay measurements at another sample site at multiple time points to provide the decay curve data. 
     
     
         53 . The method of  claim 52 , further comprising charging the material at another sample site with radiation to a second charging level. 
     
     
         54 . The method of  claim 53 , wherein the first and the second charging level are same. 
     
     
         55 . The method of  claim 53 , wherein the first and the second charging level are different. 
     
     
         56 .- 98 . (canceled) 
     
     
         99 . A system for optical interrogation of a sample material, the system comprising:
 an optical source capable of charging the material at a sample site with radiation to a first charging level;   a detection system capable of obtaining charge state decay measurements at the sample site at multiple time points temporally separated by less than 1 second to provide a decay curve data; and   a processor capable of determining a characteristic of the decay curve data to determine a parameter of the sample material.   
     
     
         100 . The system of  claim 99 , wherein the detection system is capable of obtaining charge state decay measurements at the sample site at multiple time points temporally separated by less than 50 milliseconds to provide a decay curve data. 
     
     
         101 . The system of  claim 99 , wherein the detection system is capable of obtaining charge state decay measurements at the sample site at multiple time points temporally separated by less than 1 millisecond to provide a decay curve data. 
     
     
         102 . The system of  claim 99 , wherein the detection system is capable of obtaining charge state decay measurements at the sample site at multiple time points temporally separated by less than 500 microseconds to provide a decay curve data. 
     
     
         103 . The system of  claim 99 , wherein the optical source comprises at least one of: a UV flash lamp, a laser and a pulsed laser. 
     
     
         104 . The system of  claim 99 , wherein the detection system comprises a probe beam; and a detector capable of detecting a second harmonic generation (SHG) signal associated with the probe beam. 
     
     
         105 . The system of  claim 104 , wherein the probe beam is emitted by a pulsed laser. 
     
     
         106 .- 120 . (canceled)