System and method for device performance characterization in physical and logical domains with AC SCAN testing
View Patent ↗A method for data logging from inside a semiconductor device, yielding timing performance information about the logic behind each and every flip-flop in the scan chain and displaying the sensitivity of certain flipflops to speed related manufacturing defects. The method comprises steps for testing, measuring, storing, and analyzing records for frequency characterization of complex digital semiconductors.
1. A method comprising:
applying a series of test patterns to a scan chain while sweeping a frequency defined by a timing between a launch clock pulse and a capture clock pulse for the scan chain; and
recording a timing measurement for each scan cell in the scan chain, the timing measurement being recorded for a particular scan cell by i) as each test pattern is unloaded from the scan chain, comprising successive bits unloaded for the particular scan cell, to identify transitions from pass to fail, and ii) recording a frequency corresponding to each transition as a timing measurement for the particular scan cell, whereby data on continuing failures or passes is compressed.
2. The method of claim 1 wherein said recording comprises indicating a timing performance for each scan cell in the scan chain.
3. The method of claim 2 further comprising retrieving all failures in an AC-Scan test pattern unloaded from the scan chain from automated test equipment.
4. A method comprising:
collecting a plurality of test pattern failures in response to applying a series of test patterns to a scan chain while sweeping a frequency defined by a timing between a launch clock pulse and a capture clock pulse;
associating at least one of said plurality of test pattern failures to a scan cell;
responsive to a first failure of the scan cell at a first testpoint, the first testpoint corresponding to one of the frequencies defined by a timing between a launch clock pulse and a capture clock pulse for the scan chain, setting a scan cell value in a results record to a frequency of a previous testpoint in the series of test patterns applied to the scan chain, the frequency providing a timing measurement for the scan cell.
5. An apparatus comprising:
a tester configured to apply a series of test patterns to a scan chain while sweeping a frequency defined by a timing between a launch clock pulse and a capture clock pulse for the scan chain; and
a non-transitory computer readable media comprising a data structure, wherein said data structure comprises a representation of a timing measurement for each of a plurality of scan cells in the scan chain, wherein the timing measurement for a particular scan cell corresponds to the timing between the launch clock pulse and the capture clock pulse at which successive bits unloaded for the particular scan cell transition from pass to fail.
6. The apparatus of claim 5 wherein said plurality comprises every scan cell of the scan chain.
7. A method for improving manufacturing yield of semiconductor devices at higher speeds, comprising the steps of:
testing a logic device with an AC-Scan pattern at a plurality of testpoints, wherein different testpoints correspond to different frequencies of applying a launch-capture pair of clock pulses, and wherein the AC-Scan pattern is synthesized to exercise flipflops in critical paths which are most vulnerable to delay defects;
storing failure data generated in response to the testing, the failure data including a timing measurement for each scan cell in the logic device associated with a test pattern failure, wherein the timing measurement for a particular scan cell identifies at least one of i) a testpoint representing a lowest frequency at which the AC-Scan pattern causes the particular scan cell to fail, or ii) a testpoint representing a highest frequency at which the AC-Scan pattern causes the particular scan cell to pass; and
displaying at least some of the failure data.
8. The method of claim 7 wherein storing failure data for the particular scan cell comprises:
storing at least three of the following
the testpoint representing the lowest frequency at which the AC-Scan pattern causes the particular scan cell to fail,
the testpoint representing the highest frequency at which the AC-Scan pattern causes the particular scan cell to pass,
an identifier of the AC-Scan pattern which causes the scan cell to fail,
an identifier of the position of the particular scan cell in a scan chain,
an identifier of the scan chain in a unique die,
an identifier of the unique the in a wafer,
an identifier of the wafer,
a hierarchical design name for the particular scan cell consistent with a design database,
a physical coordinate of the position of the particular scan cell in the unique die, and
a physical coordinate of the position of the unique die in the wafer.
9. The method of claim 7 wherein displaying at east some of the failure data comprises:
displaying on a graphical computer display at least three of:
a movable graphical icon by mouse or keyboard selecting a testpoint on a continuum of frequencies at which AC-Scan patterns have been applied to the logic device;
a failing scan cell in a scan chain in an array of scan cells in scan chains, said failing scan cell presenting test values inconsistent with expected test values for an AC-Scan pattern and at least one frequency corresponding to a testpoint;
a failing scan cell in a hierarchical list of flip-flops described in a design description language, said failing scan cell presented as one of a block diagram, a net list and an electrical schematic;
a failing scan cell in a physical map of the logic device, said failing scan cell presented in the context of other scan cells located in the same region of the logic device;
a failing scan cell in a physical map of a wafer including the logic device, said failing scan cell presented in the context of other scan cells located in the same region of the wafer.
10. The method of claim 9 wherein said displaying at least some of the failure data further comprises displaying a logic hierarchy of the logic device, wherein the timing for each logic sub-circuit in the logic hierarchy can be analyzed.
11. The method of claim 10 wherein said displaying at least some of the failure data further comprises displaying a physical layout of the logic device, wherein the timing for each logic sub-circuit in the physical layout can be analyzed.
12. The method of claim 7 , further comprising the step of:
for each scan cell of the logic device not associated with a test pattern failure, storing a notation that the scan cell never failed the AC-Scan pattern at any of the testpoints.