METHOD AND SYSTEM FOR TESTING AN INTEGRATED CIRCUIT

Abstract

A method for analyzing an integrated circuit includes: applying an electric test pattern to the IC; delivering a stream of primary electrons to a back side of the IC on an active region to a transistor of interest, the active region including active structures such as transistors of the IC; detecting light resulting from cathodoluminescence initiated by secondary electrons in the IC; and analyzing the detected light regarding a correlation with the electric test pattern applied to the IC. A system for analyzing an IC is provided.

Claims

1. A method, comprising: a) applying an electric test pattern to an integrated circuit (IC); b) delivering a beam primary electrons to a side of the IC on an active region comprising active structures of the IC; c) detecting light resulting from cathodoluminescence initiated by secondary electrons in the IC; and d) analyzing the detected light to correlate the detected light with the electric test pattern applied to the IC.

2. The method of claim 1, wherein detecting the light comprises at least one member selected from the group consisting of detecting a number of photons of the light, detecting photon wavelengths of the light, detecting a polarization of the light, and detecting an angle of the light.

3. The method of claim 1, wherein the electron beam has a resolution, the resolution is about a size of the active structure, and the resolution is less than a spacing between active structures of the IC.

4. The method of claim 3, wherein an area of the IC covered by the electron beam is less than a spacing between transistors of the IC, and/or wherein an energy of the electron beam is equal or lower than 500 eV.

5. The method of claim 1, further comprising detecting secondary electrons released from the IC.

6. The method of claim 1, wherein detecting the light comprises using a single mirror or a two mirror objective design.

7. The method of claim 1, wherein applying a test pattern comprises operating the IC so that at least one transistor of the IC is switching.

8. The method of claim 1, further comprising at least partially thinning a semiconductor substrate of the IC, and delivering the electron beam to the thinned portion of the IC.

9. The method claim 5, wherein the thinned portion covers one or more transistors.

10. The method of claim 1, wherein analyzing comprises analyzing a timely variation of photons.

11. The method of claim 1, further comprising scanning an area of interest of the IC.

12. The method of claim 1, further comprising performing a)-c) in a loop to improve the signal to noise ratio by repetition.

13. The method of claim 1, wherein the active structures of the IC comprise transistors.

14. A system, comprising: a) an integrated circuit (IC) holding structure; b) an electron beam source; c) a cathodoluminescence detector; d) an IC testing device; and e) a control device configured to control the electron beam source, the cathodoluminescence detector and the IC testing device so that an electric test pattern applied to the IC is correlatable with a signal of the cathodoluminescence detector.

15. The system of claim 14, wherein the control device is configured to scan the electron beam over a surface portion of the IC and/or to deliver electrons to a specific site of the IC.

16. The system of claim 14, further comprising a secondary electron detector.

17. A method, comprising: analyzing cathodoluminescence light emitted from integrated circuit (IC) due to the delivery of a beam of primary electrons to a side of the IC on an active region comprising active structures of the IC while applying an electric test pattern to the IC, thereby correlating the cathodoluminescence light with the electric test pattern applied to the IC.

18. The method of claim 17, further comprising detecting the cathodoluminescence light by a process which comprises at least one member selected from the group consisting of detecting a number of photons of the light, detecting photon wavelengths of the light, detecting a polarization of the light, and detecting an angle of the light.

19. The method of claim 17, wherein the electron beam has a resolution, the resolution is about a size of the active structure, and the resolution is less than a spacing between active structures of the IC.

20. The method of claim 1, wherein analyzing the cathodoluminescence light comprises analyzing a timely variation of photons.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Various features and advantages of the present disclosure may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0039] FIG. 1 shows a schematic cross sectional view of a system for testing an IC;

[0040] FIG. 2 shows a basic schematic sketch of a cathodoluminescence event in a FinFET device; and

[0041] FIGS. 3 and 4 show lens arrangements for collecting cathodoluminescence light.

DETAILED DESCRIPTION

[0042] FIG. 1 shows a schematic cross sectional view of a system 100 for testing an IC. The actual size of individual components relative to each other is not to scale and may differ in an actual embodiment.

[0043] The system 100 includes an outer housing 102 that is adapted to provide an appropriate high vacuum inside. A vacuum outlet 104 is symbolically provided—the vacuum concept for a real system 100 may be more sophisticated and may include several pressure levels and vacuum pumps.

[0044] A device under test (DUT) 106, which is not part of the system 100 itself, is placed inside the housing 102 on a sample holder 108. The sample holder 108 is adapted to provide a coarse positioning of the DUT 106 as well as to provide for cooling and/or heating, as desired.

[0045] The sample holder 108 also provides for an electric connection of the DUT 106 by appropriate test lines 110. The test lines 110 are fed through the housing 102 and are connected to an automated test equipment (ATE) 112.

[0046] The DUT 106 is flip-chip mounted on the sample holder 108 and has a thinned back side 114.

[0047] The system 100 further includes within the vacuumed inside an electron beam column 115 including an electron source 116 producing an electron beam 118. The electron beam 118 may have an energy of about 200 eV up to 1 keV for the present intended application. The electron beam 118 is focused by one or two condenser lenses 120. The condenser lenses 120 may be magnetic or electrostatic lenses. The system 100 further includes a scanning unit 122 and/or deflector plates for deflecting the electron beam 118 in an x- and y-direction.

[0048] The electron beam 118 impinging on the back side 114 of the DUT 106 releases or generates cathodoluminescence light, symbolized by the light rays 124. The cathodoluminescence light 124 is radiated in all spatial directions and is collected by a catoptric lens 126. The lens 126 is designed to provide a high numerical aperture. The collection aperture of the lens 126 can be up to 40° half angle. The wavelength of the cathodoluminescence light in silicon is in the range of 500 nm to 600 nm and can be collected by the lens 126 inside the electron beam column 115. After the collimating lens 126 in z-direction, a mirror 128 is arranged for diverting the cathodoluminescence light 124 out of the electron beam column 115 to a detector unit 130. The detector unit 130 includes a fast detector 132 such as a fast PIN diode detector allowing to detect signals up to the 10 GHz range.

[0049] The detector unit 130 may additionally include analyzing tools for determining other light properties besides the intensity. These properties may include polarization, wavelength or the like.

[0050] The system 100 further includes a control unit 140. The control unit 140 is connected with the electron beam column 115, see line 142, with the detection unit 130, see line 144 and with the ATE 112, see line 146. The control unit is adapted to control the position of the electron beam 118, any waveform generated by the ATE 112 and submitted to the DUT 106, and to receive a signal correlated with the generated cathodoluminescence light 124, detected in the detection unit 130 by the detector 132.

[0051] The process for testing a DUT 106 like an IC is as follows:

[0052] The DUT 106 is inserted into the vacuum chamber 105 onto the sample holder 108, after its back side 114 has been thinned to the desired depth. The device under test 106 is operated by the ATE 112 through the lines 110. In particular, certain test patterns are run on the device 106 to evaluate the functionality of certain active structures on the device 106 and/or to analyze timing of the active structures of the device 106. The electron beam 118 is generated and focused onto an area of the device 106 of interest. The electron beam 118 impinging on the back side 114 enters the semiconductor material to a depth of about 100 nm in the given energy range. The lateral diameter for excitation is about 5 nm. In this volume, the cathodoluminescence light is generated and leaves the semiconductor material over the back side 114 of the DUT 106. The catoptric collimation lens 126 collects the cathodoluminescence light 124 and directs it to the fast photon detector 132.

[0053] In the control unit 140, the waveform applied by the ATE 112 and the corresponding intensity waveform as provided by the detection unit 130 can be correlated. In combination with the position of the electron beam 118—this information is provided by the electron column 115 to the control unit 140—the operation of an active structure can be closely monitored.

[0054] By the ATE 112, the active structures of interest of the DUT 106 can be addressed by applying the appropriate waveforms. In particular, the operation of the active structure of interest can be monitored in real time, since the detection of cathodoluminescence light is at least as fast as the operation of the active structure.

[0055] The electron beam column 115 allows for a field of view of 1 μm radius as well as the navigation of the beam. Within this area, the electron beam 118 can be directed to different positions and switched between them. The control unit 140 can measure the time delay for the difference of the waveform applied by the ATE 112 to the DUT 106. This allows to analyze the time difference between different active structures, which might be within a specified maximum allowed time difference. This allows to measure whether signals on the DUT 106 (e. g. an IC) are synchronous or whether they deviate so much that the IC is not able to run a specified high frequency. This allows to find out the maximum frequency up to which a device 106 can be operated.

[0056] FIG. 2 shows the DUT 106 in more detail, but still in a very basic and schematic drawing. The DUT 106 is in this case in this embodiment of a FinFET, but any other semiconductor device can be analysed with the present disclosure. The DUT 106 includes as a FinFET 150 a silicon substrate 152. This backside has been thinned in an area of interest 154 to a thickness below 100 nm to allow access of the election beam 118 to relevant areas of the FinFET device 150. The device 150 also includes an oxide layer 154, a gate 156. The gate 156 may be a metal gate controlling the operation of the thin 158. Electrons from the electron beam 118 can penetrate into the thin 158 and create electron hole pairs, which then combine to admit photons 116 as a cathodoluminescence light, which can then be detected. The voltage variations in the fin 158 will enable the local waveform to be traced out. The intensity of the cathodoluminescence light and its wavelength are expected to vary as per the voltage.

[0057] FIG. 3 shows by schematic Cassegrain lens arrangement. The admitted cathodoluminescence light 124 passes through a first stop 160 within a reflective surface 162 and impinges on a second reflective surface 164. The second reflective surface 164 is of a hyperboloid shape and reflects the cathodoluminescence light 124 to the first reflective surface 162, which has a paraboloid shape. The Cassegrain lens arrangement allows a small field of view, a high resolution and a long effective focal length.

[0058] FIG. 4 shows an alternative lens arrangement, namely a Schwarzschild set up. The cathodoluminescence light is reflected on a primary reflective surface 172 and impinges on a secondary reflective surface 174.

[0059] Of course, other suitable lens arrangements may be used with the disclosure.