Scanning electron microscope and methods of inspecting and reviewing samples
A scanning electron microscope incorporates a multi-pixel solid-state electron detector. The multi-pixel solid-state detector may detect back-scattered and/or secondary electrons. The multi-pixel solid-state detector may incorporate analog-to-digital converters and other circuits. The multi-pixel solid state detector may be capable of approximately determining the energy of incident electrons and/or may contain circuits for processing or analyzing the electron signals. The multi-pixel solid state detector is suitable for high-speed operation such as at a speed of about 100 MHz or higher. The scanning electron microscope may be used for reviewing, inspecting or measuring a sample such as unpatterned semiconductor wafer, a patterned semiconductor wafer, a reticle or a photomask. A method of reviewing or inspecting a sample is also described.
1. A method of inspecting a sample comprising:
generating a master clock signal;
generating a beam-deflection scan synchronized with the master clock signal;
generating a first pixel clock signal synchronized with the master clock signal;
generating a primary electron beam and focusing the primary electron beam on a sample;
using the beam-deflection scan to scan the primary electron beam over an area of the sample;
collecting back-scattered electrons from the sample in a first multi-pixel solid state detector;
generating first digitized signals by digitizing a first output signal generated by each pixel of the first multi-pixel solid state detector in each period of the first pixel clock signal; and
using the first digitized signals to determine the presence or absence of a defect in the area of the sample,
wherein collecting back-scattered electrons comprises causing the back-scattered electrons to pass through a pure boron layer on an electron-sensitive surface of said first multi-pixel solid state detector, and
wherein each said pixel of said first multi-pixel solid state detector comprises a p-type electron-sensitive layer, an n-type buried channel layer disposed on the electron-sensitive layer, an n+ floating diffusion disposed in the buried channel layer, and an amplifier coupled to the floating diffusion.
2. The method of claim 1 , further comprising:
generating a second pixel clock signal synchronized with the master clock signal;
collecting secondary electrons from the sample in a second multi-pixel solid state detector;
generating second digitized signals by digitizing a second output signal generated by each pixel of the second multi-pixel solid state detector in each period of the second pixel clock signal; and
using the first digitized signals and the second digitized signals to determine the presence or absence of a defect in the area of the sample.
3. The method of claim 2 , wherein collecting secondary electrons comprises causing the secondary electrons to pass through a second pure boron layer formed on an electron-sensitive surface of the second multi-pixel solid state detector.
4. The method of claim 3 , wherein the first pixel clock signal and the second pixel clock signal are generated with the same frequency.
5. The method of claim 1 , further comprising determining an approximate energy of a backscattered electron from the first digitized signals.
6. The method of claim 5 , further comprising determining a type or a material of the defect in the area of the sample.
7. The method of claim 1 , wherein generating and focusing the primary electron beam comprises directing the primary electron beam onto one of an unpatterned semiconductor wafer, a patterned semiconductor wafer, a reticle and a photomask.
8. A method of inspecting a sample comprising:
generating a primary electron beam and focusing the primary electron beam on a sample;
collecting back-scattered electrons from the sample in a first multi-pixel solid state detector;
generating first digitized signals by digitizing an output signal generated by each pixel of the first multi-pixel solid state detector; and
using the first digitized signals to determine the presence or absence of a defect in the area of the sample,
wherein each said pixel of said first multi-pixel solid state detector comprises:
a p-type electron-sensitive layer configured to generate multiple electrons in response to each said incident electron that enters said electron-sensitive layer through a first surface of said electron-sensitive layer;
an n-type buried channel layer disposed on a second surface of the electron-sensitive layer and configured to collect at least some of the multiple electrons generated by the electron-sensitive layer;
an n+ floating diffusion disposed in the buried channel layer and configured to accumulate at least some of the electrons collected by the buried channel layer such that a voltage of the floating diffusion changes in proportion to a number of said electrons accumulated on the floating diffusion; and
an amplifier configured to generate said output signal in accordance with the voltage of the floating diffusion.
9. The method of claim 8 , wherein collecting back-scattered electrons comprises causing the back-scattered electrons to pass through a pure boron layer on an electron-sensitive surface of said first multi-pixel solid state detector.
10. The method of claim 8 , further comprising:
collecting secondary electrons from the sample using a second multi-pixel solid state detector;
generating second digitized signals by digitizing a second output signal generated by each pixel of the second multi-pixel solid state detector; and
using the first digitized signals and the second digitized signals to determine the presence or absence of a defect in the sample.
11. The method of claim 10 , wherein collecting secondary electrons comprises causing the secondary electrons to pass through a second pure boron layer formed on an electron-sensitive surface of the second multi-pixel solid state detector.
12. The method of claim 8 , further comprising determining an approximate energy of a backscattered electron from the first digitized signals.
13. The method of claim 12 , further comprising determining a type or a material of the defect in the sample.
14. The method of claim 8 , wherein generating said first digitized signals comprises utilizing a plurality of analog-to-digital converters, wherein each of the multiple analog-to-digital converters is operably coupled to receive an associated said output signal generated by an associated pixel of said first multi-pixel solid state detector.