Patent Application
20080018356
a is a logic diagram of an SPI control circuit for selecting pFET structures during test.
b is a logic diagram of an SPI control circuit for selecting nFET structures during test.
Logic control 110 enables each DUT 170 or 180 to be activated individually for test. Decoder 210 is shown in
In operation, input I to DLT 120a comes from decoder 210. When the output signal D3 from decoder 210, which is connected to the I pin of DLT 120a, is high, the P and N outputs of DLT 120a are active (i.e. N=1, and P=0), which turns on the associated DUT 170 gates, as well as the associated DUT 180 gates. The supply voltage inputs to DLT 120a are shown in Table 1 below.
In Table 1, “single” supply represents DUT 170 and DUT 180 input from a single voltage source (S0P, S0N) which will drive simple logic 1's and 0's to DUT 170 and DUT 180 respectively.
In Table 1, “dual” represents input from two distinct voltage supplies where HN on nFET level translator 320 receives the signal S1 and LP on pFET level translator 310 also receives the signal S1.
In dual supply mode, S1 is sent to the gates of DUT 170 and 180 from outputs P and N respectively. S1 can be swept to determine the switching voltage (Vth) and FET current (ION) of DUT 170 and DUT 180.
In general, DLT 120 enables logic control 110 to control DUTs 170 and 180 residing in different voltage realms. DLT 120 provides a means for communication between two voltage domains including Vdd, supplied to control logic 110, and SPM “Supply/VDD/GND” used to generate S0 for DLT 120. The purpose of DLT 120 is to provide accurate logic levels and/or analog gate voltages to DUT 170 and DUT 180 in order to perform device level testing. In the case of BEOL characterization, either nFET level translator 320 or pFET level translator 310 will be used, depending on the FET type used to control DUT 120. Equalizing DUT experiments (equal n and p experiments) optimize use of the SPM.
HP and LP are driven according to the type of test, as shown in Table 1. The output P is sent to DUT 170.
The input to pFET level translator 310 is inverted by the first inverter to achieve an opposite output state when enabled, which is required by pFETs associated with DUT 170. In a single supply application, e.g. applying S0P to HP, the output of pFET level translator 310 has the opposite logic level with respect to the input.
In a dual supply application, S1 is applied to LP. GND is replaced by S1 to allow voltage sweeping through a pass-gate, shown in
nFET level translator 320 has an input which is non-inverting. The power supply for nFET level translator 320 may originate from a derivative of the entire SPM power supply (S0N), or from a separate power supply (S1). S1 controls analog gate voltages for DUT 180.
Isolation circuit 630 further includes level translator 640 having a supply/VDD/GND power supply, an enable input I, and an output P, which is coupled to a pFET of supply circuit 620. A detailed schematic diagram of isolation circuit 630 is shown in
Level translator 640 of
Since the SPM separates nFET and pFET DUTs, it supplies each with a dedicated SPI structure. Only one of SPI circuits 140 or 150 is activated at a time. This is accomplished by selecting the appropriate SPI circuit 140 or 150 to activate using either SPI control circuit 130 or SPI control circuit 160 respectively. Although
a shows a logic diagram of SPI control circuit 130 and
The supply voltage is sourced through supply circuit 620. Supply circuit 620 includes a large supply pFET which sends an output signal to DUT 170.
The gate of the supply pFET is coupled to the output of isolation circuit 630, the source is connected to Supply/VDD/GND, and the drain is connected to the output of protect circuit 610. The supply pFET is sufficiently large to ensure it will have a minimum voltage drop during SPM measurements (<50 mV), but robust enough to handle high voltages, which may be at or above 3.0V.
SPI protect circuit 610 protects the supply pFET of supply circuit 620 from excessive source to drain, and gate to drain potential differences when high voltages are applied to Supply/VDD/GND (fatwire I/O). During high voltage applications, Supply=3.0 v and the SPM is inactive (off), i.e. all DUTs 170 and 180 are turned off. When Enable=0 and Efuse_prog=1, VDD is forced through protect circuit 610 and onto the drain of the supply pFET of supply circuit 620. The largest potential difference across the supply pFET is guaranteed to never be larger than Supply minus VDD. Simulation was completed to verify this voltage level is not damaging to the supply pFET.
In the single supply mode of operation either during wafer or module final test (WFT, MFT), a tester (not shown) calculates the current by measuring the background current (IBG) and DUT current (IMEAS) for each of DUT 170 and DUT 180. ION is equal to the difference between IMEAS and IBG (i.e. ION=IMEAS−IBG). The tester records the ION data for both DUT 170 and DUT 180. Table 2 shows a truth table for the Single Mode of operation used for controlling the SPM DUTs.
The SPM is also configurable to separately control the DUT 170 and 180 gate voltages. Dual supply mode testing enables threshold voltage, Vt, measurement capability, in addition to ION measurement capability. In dual supply mode, effective current (Ieff) can be calculated. Ieff is a better indicator of device performance than ION alone. To implement dual supply mode a dedicated pad, S1, must be wired out. S1 is shown in
Table 3 shows an example truth table for dual supply mode.
The SPM may be placed in various locations within an ASIC design to test different areas of the same chip. Alternative DUT structures may also be incorporated into the design such that each SPM is able to test a particular DUT structure in proximity to it. A single SPM may also be designed to test multiple varieties of DUT structures, such as wires, resistors, capacitors, inductors, etc., within a specific chip location.
The above description and drawings are only to be considered illustrative of exemplary embodiments, which achieve the features and advantages of the invention. It should be appreciated by one of ordinary skill in the art that modification and substitutions to specific layout designs, systems for performing the tests and analysis, and the devices themselves can be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be considered as being limited by the foregoing description and drawings.
