METHOD AND APPARATUS FOR NON-INVASIVE SEMICONDUCTOR TECHNIQUE FOR MEASURING DIELECTRIC/SEMICONDUCTOR INTERFACE TRAP DENSITY USING SCANNING ELECTRON MICROSCOPE CHARGING
A non-invasive semiconductor technique for measuring dielectric/semiconductor interface trap density can be performed by charging the dielectric by creating charges on the top surface of the dielectric layer over the wafer using Scanning Electron Microscope (SEM) charging. This charging can induce an accumulated, a depleted and/or an inverted semiconductor surface. The states of the semiconductor surface can subsequently be measured, identified, and/or quantified using Electric Field Induced Second Harmonic generation (EFISH). From the measured/acquired EFISH versus SEM charge curve, the interface state density (D it ) can be extracted. A large working distance provides the ability to create charge and measure the Second Harmonic Generation (SHG) at the same semiconductor surface spot without the needing to move the wafer.
1 . A system for optically interrogating a sample accompanied by the application of electric charge to said sample, said system comprising:
an electron beam generation and scanning system comprising an electron gun, an anode, at least one electron lens, and an electron beam deflector disposed with respect to the sample to direct electrons to the sample to place charge on the sample;
a vacuum system comprising a vacuum chamber and a vacuum pump, said electron gun, said anode, said at least one electron lens, said electron beam deflector and said sample included in said vacuum chamber;
a probe optical source configured to emit probing light, said probe optical source disposed so as to direct said probing light onto said sample; and
an optical detector configured to detect second harmonic generated (SHG) light from the sample in response to said probing light directed thereon.
2 . The system of claim 1 , wherein said at least one electron lens comprises an objective.
3 . The system of claim 1 , further comprising an electron detector in said vacuum chamber.
4 . The system of claim 1 , wherein said probe optical source comprises a pulse laser and said optical detector comprise a photovoltaic, a photoconductor, or a photomultiplier tube.
5 . The system of claim 1 , wherein said vacuum chamber has a window or fiber feedthrough for transmission of said probing light into said vacuum chamber.
6 . The system of claim 1 , further comprising a chuck for supporting said sample.
7 . The system of claim 6 , further comprising an ammeter electrically connected to said chuck to measure charge flow from said chuck.
8 . The system of claim 6 , further comprising a high voltage source electrically connected to said chuck to apply a voltage to said sample.
9 . The system of claim 1 , wherein said electron beam generation and scanning system comprises a scanning electron microscope (SEM).
10 . The system of claim 9 , wherein said scanning electron microscope has a work distance of no less than 5 millimeters (mm).
11 . The system of claim 1 , further comprising electronics configured to receive an electronic signal from said optical detector.
12 . The system of claim 11 , wherein said electronics are configured to determine a characteristic of the sample based on a variation in the detected SHG light with different amount of electrical charge deposited on or in the sample and/or the charging of the sample.
13 . The system of claim 11 , wherein said electronics are configured to receive an electronic signal from said optical detector to determine a characteristic based on said SHG light.
14 . The system of claim 11 , wherein said electronics are configured to monitor the SHG signal for varying amounts of charge deposited on or in the sample by the electron beam generation and scanning system and/or for varying amounts of charging of the sample by the electron beam generation and scanning system.
15 . The system of claim 11 , wherein said electronics are configured to estimate a density of states based on said SHG signal.