Focused ion beam endpoint detection using charge pulse detection electronics

1. A semiconductor milling endpoint detection system comprising:

a focused ion beam (FIB) apparatus for directing a focused ion beam at an integrated circuit sample, wherein a charge pulse is generated each time an ion from the beam strikes the sample;

a plurality of charge pulse detection electronics (CPDE) components, wherein the CPDE components are coupled to the sample; and

a histogram display.

2. The endpoint detection system of claim 1 , wherein the CPDE components comprise:

a charge preamplifier directly coupled to a layer of interest within the sample and configured to amplify and integrate the charge pulse to produce a voltage pulse indicative of the size of the charge pulse;

a pulse amplifier directly coupled to the charge preamplifier and configured to amplify the voltage pulse;

a pulse shaper directly coupled to the pulse amplifier and configured to optimize the shape of the voltage pulse to a height proportional to the charge pulse; and

a multi-channel analyzer (MCA) directly coupled to the pulse shaper and configured to detect the height of the shaped pulse and sort the shaped pulse into one of a plurality of channels, wherein each channel is associated with a range of shaped pulse heights.

3. The endpoint detection system of claim 1 , wherein the histogram display comprises:

an X-axis divided into a plurality of channels;

a Y-axis representing an event count, wherein the event count is generated each time an ion strikes the sample;

a distribution curve, wherein the curve is formed by plotting the event count into an appropriate channel based on a height of each shaped pulse.

4. The endpoint detection system of claim 3 , wherein the system is calibrated by milling a reference sample similar in construction to the integrated circuit sample and obtaining a reference curve for each layer within the reference sample.

5. The endpoint detection system of claim 4 , wherein a noticeable shift in the distribution curve indicates that milling has completed on a layer within the integrated circuit sample.

6. The endpoint detection system of claim 5 , wherein a milling endpoint is detected by comparing the distribution curve formed immediately prior to the shift with the reference curves.

7. The endpoint detection system of claim 3 , wherein the histogram display is refreshed on command.

8. The endpoint detection system of claim 1 , wherein the CPDE components comprise:

a charge preamplifier, wherein the charge preamplifier is directly coupled to a layer of interest within the sample;

a pulse shaper directly coupled to the charge preamplifier;

a pulse amplifier directly coupled to the pulse shaper; and

a multi-channel analyzer (MCA) directly coupled to the pulse amplifier.

9. The endpoint detection system of claim 1 , wherein the CPDE components comprise:

a charge preamplifier is directly coupled to a layer of interest within the sample;

a spectroscopy amplifier directly coupled to the charge preamplifier; and

a multi-channel analyzer (MCA) directly coupled to the spectroscopy amplifier.

10. A method for detecting a focused ion beam milling endpoint on a semiconductor comprising:

striking an integrated circuit sample with an ion beam generated by a focused ion beam (FIB) apparatus;

utilizing a plurality of charge pulse detection electronics (CPDE) components to detect and configure a charge pulse generated each time an ion from the beam strikes the integrated circuit sample; and

creating a distribution curve on a histogram display based on output of the CPDE components.

11. The method of claim 10 , wherein the CPDE components comprise:

a charge preamplifier directly coupled to a layer of interest within the sample and configured to amplify and integrate the charge pulse to produce a voltage pulse indicative of the size of the charge pulse;

a pulse amplifier directly coupled to the charge preamplifier and configured to amplify the voltage pulse;

a pulse shaper directly coupled to the pulse amplifier and configured to optimize the shape of the voltage pulse to a height proportional to the charge pulse; and

a multi-channel analyzer (MCA) directly coupled to the pulse shaper and configured to detect the height of the shaped pulse and sort the shaped pulse into one of a plurality of channels, wherein each channel is associated with a range of shaped pulse heights.

12. The method of claim 10 , wherein the histogram display comprises:

an X-axis divided into a plurality of channels;

a Y-axis representing an event count, wherein the event count is generated each time an ion strikes the sample;

a distribution curve, wherein the curve is formed by plotting the event count into an appropriate channel based on a height of each shaped pulse.

13. The method of claim 12 , wherein the histogram display is calibrated by milling a reference sample similar in construction to the integrated circuit sample and obtaining a reference curve for each layer within the reference sample.

14. The method of claim 13 , wherein a noticeable shift in the distribution curve indicates that milling has completed on a layer within the integrated circuit sample.

15. The method of claim 14 , wherein a milling endpoint is detected by comparing the distribution curve formed immediately prior to the shift with the reference curves.

16. The method of claim 12 , wherein the histogram display is refreshed on command.

17. The method of claim 10 , wherein the CPDE components comprise:

a charge preamplifier, wherein the charge preamplifier is directly coupled to a layer of interest within the sample;

a pulse shaper directly coupled to the charge preamplifier;

a pulse amplifier directly coupled to the pulse shaper; and

a multi-channel analyzer (MCA) directly coupled to the pulse amplifier.

18. The method of claim 10 , wherein the CPDE components comprise:

a charge preamplifier is directly coupled to a layer of interest within the sample;

a spectroscopy amplifier directly coupled to the charge preamplifier; and

a multi-channel analyzer (MCA) directly coupled to the spectroscopy amplifier.

19. An integrated circuit sample milled according to a process comprising the steps of:

striking the sample with an ion beam generated by a focused ion beam (FIB) apparatus;

detecting and configuring a charge pulse generated each time an ion from the beam strikes the sample with a plurality of charge pulse detection electronics (CPDE) components; and

generating a distribution curve on a histogram display based on output of the CPDE components.

20. The sample of claim 19 , wherein the CPDE components comprise:

a charge preamplifier directly coupled to a layer of interest within the sample and configured to amplify and integrate the charge pulse to produce a voltage pulse indicative of the size of the charge pulse;

a pulse amplifier directly coupled to the charge preamplifier and configured to amplify the voltage pulse;

a pulse shaper directly coupled to the pulse amplifier and configured to optimize the shape of the voltage pulse to a height proportional to the charge pulse; and

a multi-channel analyzer (MCA) directly coupled to the pulse shaper and configured to detect the height of the shaped pulse and sort the shaped pulse into one of a plurality of channels, wherein each channel is associated with a range of shaped pulse heights.

21. The sample of claim 19 , wherein the histogram display comprises:

an X-axis divided into a plurality of channels;

a Y-axis representing an event count, wherein the event count is generated each time an ion strikes the sample;

a distribution curve, wherein the curve is formed by plotting the event count into an appropriate channel based on a height of each shaped pulse.

22. The sample of claim 21 , wherein a noticeable shift in the distribution curve indicates that milling has completed on a layer within the sample.

23. The sample of claim 22 , wherein a milling endpoint is detected by comparing the distribution curve formed immediately prior to the shift with the reference curves.