Circuits and methods for testing through-silicon vias

[0001] Stacked multi-level or “3D” integrated circuits offer several advantages over conventional 2D integrated circuits, such as lower power consumption, faster performance, reduced physical area consumption and package size. Typically, a 3D integrated circuit includes through-silicon vias (TSVs) that facilitate transferring data from one die to another die stacked against the first. Thus, testing of TSVs for electrical integrity should be done before and after stacking the dies to ensure the proper functionality and high manufacturing quality of the 3D integrated circuit.

[0002] Desirable in the art is an improved circuit and method for testing through-silicon vias (TSVs) that would improve upon the conventional circuit and method as to these and other aspects.

[0010] Systems having aspects and objects disclosed herein are discussed with reference to figures demonstrating examples of such systems. Although the exemplary systems are described in detail, they are provided for purposes of illustration only and various modifications are feasible within the scope of this disclosure. In addition to the exemplary systems that are described, examples of methods for testing through-silicon vias (TSVs) are provided to explain the manner in which testing circuits can be used advantageously to detect defects of the TSVs.

[0011] FIG. 1 is a block diagram that illustrates an embodiment of a system having a testing circuit 105 configured to detect defects of TSVs 130. In this example, the testing circuit 105 is electrically connected to a 3D integrated circuit 110 having the TSVs 130. The 3D integrated circuit 110 includes a top die 115 and a bottom die 120 coupled together via an electrical coupling 125 and the TSVs 130. Signals that for purposes of illustration can be deemed input signals 135 are applied to the top die 115 and pass through to the bottom die 120, and vice versa with respect to deemed output signals 140. Which of the oppositely passing signals are to be deemed inputs and which are to be deemed outputs is simply a matter of perspective; however the distinction of input versus output is made in this disclosure for ease of explanation when distinguishing between the opposite signals. The testing circuit 105 is further described in connection with FIGS. 2-7.

[0012] FIG. 2 is a block diagram that illustrates an embodiment of a testing circuit 200, such as that shown in FIG. 1. The testing circuit 200 can be used to detect for defects of the TSV 130 by applying input signals 230 to the 3D integrated circuit 110. The testing circuit 200 includes a first buffer 220A and second buffer 215A, each having a respective input and output coupled as shown to the input and output of a storage element 205 (latch or similar flip-flop device).

[0013] The output of the first buffer 220A is designed to be electrically coupled to the TSV 130 and to the input of the second buffer 215A. The two buffers 220A and 215A can be enabled only one at a time, according to the state of an enable signal En. In a launch scenario, the flip-flop device 205 stores one bit of information and has an output Q that is electrically coupled to the input of the first buffer 220A and also to output signal path 225. Alternatively or additionally, in a launch last-shift scenario the value stored in the flip-flop device 205 can be applied to the TSV 130 via the first buffer 220A, when enabled due to a negative (e.g., low-true) state of the enable signal En. The flip-flop device 205 shifts the value stored in the flip-flop device 205 and inputs the shifted value into the TSV 130 via the first buffer 220.

[0014] The output of the second buffer 215A is coupled to an output 235 and to the input D of the flip-flop 205. It should be noted that the output 235 can be coupled to a functional logic 405 (FIG. 4) of the 3D integrated circuit 110 that receives the signals from the output of the second buffer 215A. The input of second buffer 215A is coupled to the TSV 130 and the output of first buffer 220A. Buffer 215A is enabled by a high-true state of the enable signal En (namely the opposite state from the state that enables buffer 220A. In a functional/capture scenario, the value represented by the level at TSV 130 can be inputted into the flip-flop device 205 via the second buffer 215A.

[0015] According to the foregoing scenarios, the value at TSV 130 is either applied to the input of flip-flop 205 or the value at the output of flip-flop 205 is applied to TSV 130, depending on the state of the enable signal En. The value at the input to the flip-flop 205 is loaded or shifted to the output of flip-flop 205 upon the occurrence of a clock edge. In a silent shift scenario, the flip-flop device 205 shifts in the value stored in the flip-flop device 205 without inputting the value from the flip-flop device 205 into the TSV 130 via the first buffer 220 nor inputting the value from the TSV 130 into the flip-flop device 205 via the second buffer 215A. It should be noted that multiple TSVs 130 can coupled with multiple respective first and second buffers 220A, 215A which are coupled to multiple respective flip-flop devices 205.

[0016] The first and second buffers 220A, 215A can be switched on and off via the En enable signal. For example, if En signal is “0”, the first buffer 220A is switched on and the second buffer 215A is switched off during the operation of inputting the value from the flip-flop device 205 into the TSV 130 via the first buffer 220A. Additionally or alternatively, if En signal is “1”, the second buffer 215A is switched on and the first buffer 220A is switched off during the operation of inputting the value from the TSV 130 into the flip-flop device 205 via the second buffer 215A. The storage element is a scannable flip flop. SI stands for scan-input, D stands for functional input, SE stands for scan_enable. When SE=0, the flip flop is in normal functional mode and Q is driven by D. When SE=1, flip flop is in the shift mode and Q is driven by SI.

[0017] FIG. 3 is a block diagram that illustrates another embodiment of a testing circuit 300, with aspects in addition to those shown in FIG. 1. In this example, the architecture of the testing circuit 300 of FIG. 3 is similar to the architecture of the testing circuit 200 as described in FIG. 2. Like features are labeled with the same reference numbers, such as the first and second buffers 220B, 215B (which in this figure are exchanged left-for-right compared to FIG. 2) and the flip-flop device 205. Further, the testing circuit 300 can be used to detect for defects of the TSV 130 by applying output signals 225 to the TSV 130 via multiplexer 305 and buffer 220B or capturing the value at TSV 130 in the storage element 205 via buffer 215B. The multiplexer 305 includes an input and an output. The input of the multiplexer 305 is coupled to the output 225 of the flip-flop device 205 and a functional input signal 310. The output of the multiplexer 305 is electrically coupled to the input of the first buffer 220B. In the functional operation mode, a value from the functional input signal 310 can be inputted into the TSV 130 via the multiplexer 305 and the first buffer 220B. It should be noted that the functional input signal 310 can be generated by the functional logic 405 (FIG. 4) of the 3D integrated circuit 110.

[0018] By using the various enabled and/or disabled connections and by employing the flip-flop 205 as a register to store the level applied to input D or SI at the time of a clock edge, binary logic values can be applied to the TSV 130 or read from the TSV 130. This enables the operation of the TSV 130 and circuits coupled thereto to be tested for various conditions including open circuits, shorts, coupling of signal lines or coupling of signal lines to power supply levels, etc. By controlling the circuit including the enable/disable signals, clock timing and logic values associated with the flip-flop device 205, a 1149.1 test access port (TAP) 410 (shown in FIG. 4) having a controller (not shown) can be operated to read or apply levels and to monitor for expected nominal operation. Where the operation is found to be nominal and as expected, or to vary from nominal, the 1149.1 TAP 410 thereby can determine whether the TSV 130 is operating correctly and can detect and localize problems such as electrical shorts and electrical opens.

[0019] FIG. 4 is a top-level architecture diagram that illustrates an embodiment of a testing circuit 400 that is electrically coupled to a 3D integrated circuit 110, such as that shown in FIG. 1. Multiple TSVs 130 that are embedded into a die 120 are electrically coupled to multiple TSV input/output (I/O) wraps 105A-C. The TSV input/output (I/O) wraps 105A-C are electrically coupled to multiple boundary scan sections 415 via boundary scan rings 425. The boundary scan sections 415 are electrically coupled to the 1149.1 test access port (TAP) 410 and a functional logic 405. As mentioned above the 11.49.1 TAP 410 can include a controller that can control the testing procedure to detect short or open defects of the TSVs 130. By observing the values at TDO 225 (FIGS. 2 and 3) and comparing the values at TDO 225 with expected value, the 1149.1 TAP 410 can determine if the TSV(s) 130 is working correctly or not. The TSV input/output (I/O) wraps 105A-C can include testing circuits 200, 300 and can cooperate with the 1149.1 TAP 410 to test the TSVs 130 for defects.

[0020] The functional logic 405 is the normal die logic that is a core function of the die. The TSVs 130 are connected to its inputs and outputs. The functional logic 405 can send and receive signals to the TSVs 130 as part of the operation and functionality of integrated circuit 110 via the boundary scans 415, boundary scan rings 425, and TSV I/O wraps 420. Additionally or alternatively, the boundary scan sections 415 can include a flip-flop device 205 (FIG. 2), for example one per coupled signal line or bit position.

[0021] FIG. 5 show diagrams of 3D integrated circuits 505, 510, 515 that are used to illustrate pre-bond testing methods in accordance with an embodiment of the present disclosure. The 3D integrated circuit 505 includes TSVs 130 that are embedded in a substrate 525. One end 530 of each TSV 130 is located adjacent to the bottom portion 535 of the substrate 525 and is coupled to the circuits therein. The bottom portion 535 can include a logic layer 520 and added circuitry 540 that electrically couples the TSVs 130 to probe pads 545. To test for electrical shorts between the TSVs 130, multiple first and second buffers 220, 215 (such as described above) can be electrically coupled to the ends 530 of the TSVs 130 via probe pads 545.

[0022] In the upper part of FIG. 5, the TSVs 130 terminate within the substrate 525. Additionally or alternatively, and as shown in the middle and lower parts of FIG. 5, pre-bond testing can be implemented on the 3D integrated circuit 510 where a portion of the substrate 525 is removed such that an end 555 of each TSV 130, opposite from end 530, is exposed at the surface or protrudes out of the substrate 525. Defects are not necessarily linked to removal of substrate; even during manufacturing of TSVs shorts can happen, therefore it is best not to mention the cause of shorts. In order to test for electrical shorts, multiple first and second buffers 220, 215 can be electrically coupled to the exposed proximal ends 555 of each TSV 130 via the probe pads 545 and the added circuitry 540. Additionally or alternatively and as shown in the middle part of FIG. 5, a layer 550 can be added to the substrate 525 at the exposed proximal end 555 of the TSV 130. The layer 550 deliberately electrically connects the TSVs 130 together. To test for electrical opens, the multiple first and second buffers 220, 215 are electrically coupled to the exposed proximal ends 555 of the TSVs 130. The layer 550 can include an active (conductive) glue, a metal layer, a read distribution layer, or a combination thereof.

[0023] Additionally or alternatively, the pre-bond testing can be implemented on the 3D integrated circuit 515 where the added layer 550 is removed from the substrate 525, shown at the bottom part of FIG. 5. To test for electrical shorts between the TSVs 130 that can be caused by the added layer 550, the first and second buffers 220, 215 are electrically coupled to the exposed proximal ends 555 of the TSVs 130. The pre-bond testing methods can further be described in connection with FIGS. 6 and 7.

[0024] FIGS. 6 and 7 are schematic diagrams that illustrate a configuration of testing circuit 105 for checking the electrical integrity of TSVs 130 in accordance with an embodiment of the present disclosure. In the examples, the testing circuit 105 includes three sets of first and second buffers 220B1-B3, 215B1-B3, multiplexers 305A-C, and flip-flop devices 205A-C arranged along distinct TSV lines including a given line TSV0 and adjacent lines TSV1 and TSV-1. Although it would be possible to arrange any configuration of lines in a coupled arrangement as shown, defects such as shorts are likely to involve lines in proximity and defects such as opens may extend over two or more adjacent lines. The testing circuit 105 in FIG. 6 can be electrically coupled to TSVs 130A-C. In FIG. 6, resistors 605A, B are shown to model the defect (resistance) between the TSVs 130A-C for detecting shorts or low resistance paths between the TSVs 130A-C. Accordingly, the resistors 605A, B are not physically connected between the TSVs 130A-C but are shown figuratively. A slow signal test can detect hard shorts between the TSVs 130A-C.

[0025] In FIG. 7, resistors 705A-C are shown to model the serial resistance of the TSVs 130A-C for detecting resistive opens on the TSVs 130A-C. The slow signal test can detect hard opens between the TSVs 130A-C. Accordingly, the resistors 705A-C and electrical connections 710A, B are not physically part of or connected between the TSVs 130A-C, respectively, but are shown figuratively.

[0026] In testing for both electrical shorts and opens shown in FIGS. 6 and 7, the testing circuit 105 can apply binary logic values can be shifted in the flip flop devices 205A-C. The stored values in the flip-flop devices 205A-C are then applied to TSVs 130A-C. Next, the logic values present at the TSVs 130A-C are captured back in storage elements 205A-C. The captured values are then shifted out of the storage elements via TDO 225 and compared with the expected values. Based on the difference between expected and observed values, possible electrical shorts or opens in the associated TSVs are identified.

[0027] For example, responsive to receiving the test result values from the flip-flop devices 205A-C and the test result values having the values of all zeros (e.g., 000) or all ones (e.g., 111) (or alternating values or other predetermined combinations of zeros and ones), the 1149.1 TAP 410 can determine that whether electrical shorts or opens exist between the TSVs 130A-C based on correspondence of the applied input values (e.g., 001, 100, 110, 011, 111) to the test result values. Additionally or alternatively, responsive to receiving the test result values (e.g., 101, 011, 110) that have the same values as the applied binary values (e.g., 101, 011, 110) from the flip-flop device 205A-C, the 1149.1 TAP 410 can determine whether electrical opens or shorts exist between the TSVs 130A-C.

[0028] As described herein, an improved circuit and method for detecting defects related to the TSVs 130, such as electrical shorts and opens, are presented utilizing the testing circuits 200, 300, 400 and testing methods in FIG. 5 This approach allows for an accurate testing and diagnosis for defects of the TSV 130. Testing for both electrical shorts and opens can be achieved as well as testing for hard and resistive shorts/opens. The testing circuits 200, 300, 400 can be controlled by an existing the 1149.1 TAP 410 and does not include additional chip pins.

[0029] Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly to include other variants and embodiments of the invention that may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.