Data processing: measuring – calibrating – or testing – Calibration or correction system – Error due to component compatibility
Reexamination Certificate
2003-03-21
2004-10-12
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Error due to component compatibility
C324S763010
Reexamination Certificate
active
06804620
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a semiconductor test system for testing semiconductor devices such as integrated circuits (ICs), and more particularly, to calibrating individual tester pins in a semiconductor test system without the need for external test equipment.
BACKGROUND OF THE INVENTION
In testing semiconductor devices such as ICs using a test system such as an IC tester, test systems such as automatic test equipment (ATE) provide the device under test (DUT) with test signals or test patterns at specific functional test pins. The test signals are transmitted to the DUT using drivers which may generate the test signals at a selectable amplitude, impedance, current, slew rate, and the like. The test system receives output signals from the DUT in response to the test signals, and the output signals are strobed or sampled by analog comparators upon receipt of strobe signals generated at predetermined time intervals. The captured output data is compared with expected output data to determine whether the DUT is functioning correctly.
FIG. 1
illustrates an exemplary test system environment
100
. Test vectors from pin unit
102
on pincard
104
may need to pass through a driver
106
, cabling
108
, functional “pogo pins”
110
, traces
112
on loadboard
114
, socket
116
, and finally into DUT
118
. Output signals must return to the pincard
104
through a similar path, except that the output signals would pass through one or more comparators
120
rather than a driver
106
. The driver
106
and comparator
120
are typically assembled in blocks known as pin units or pin electronics
122
.
As supplied from pincard vendors, each pincard
104
installed into the test system
100
is identical in design. However, the installed pincards
104
reside in different slots within the test system
100
and therefore have unique physical signal paths. Lengthy signal paths may contain parasitic resistances and capacitances (RCs) which can slow down the propagation of the signals and rise and fall times. Moreover, although the signal paths through each pin unit
102
on each pincard
104
utilize the same circuit designs and part types, part-to-part variations may also introduce differences in propagation delays, voltage and current levels, and rise and fall times. Because testing of the DUT can require precise control of the alternating current (AC) and direct current (DC) characteristics of input test signals and precise measurement of output signal timing and parametrics, test signals and output signals in the pin units
102
need to be calibrated to account for measurement error and signal degradation, thereby ensuring accurate measurements.
Calibration data can be thought of as compensation data used to adjust the measurement or stimulus of a device to provide the most accurate results. Calibration data can be used in several ways. For example, it can be a hardware correction register parameter or an adjustment parameter used to correct a measured result. Calibration data may be needed in a test system on a per-pin basis to compensate for reference driving voltages, reference comparison voltages, driving current loads, parametric measurement circuits connected to the test pins, timing strobes used to trigger comparisons, timing triggers used to drive test pin stimulus, and the like.
Traditionally, calibration of functional test pins has been performed using test equipment external to the test system such as oscilloscopes, voltmeters, current meters, and the like. These traditional methods can be very time consuming. The compensation data is obtained when each tester pin is measured for all DC and AC characteristics. For DC measurements, the test equipment needs to have Voltage Source, Current Measure (VSIM) and Current Source, Voltage Measure (ISVM) capabilities. This method provides DC measurements with an error factor associated with the error of the measuring equipment. For AC measurements (i.e., timing related characteristics such as edge placement, waveform rise time, and waveform fall time), a high-speed oscilloscope may be used. For these measurements as well, the error factor is the error of the measuring instrument. One limitation of external measuring instruments is that they are typically controlled by General Purpose Interface Bus (GPIB) protocols that have a slow response time. Because all measurements are taken by external test equipment via a GPIB, the large number of tester pins on current ATE systems results in a very time consuming process to obtain all measurement data and to compute compensation values whenever and wherever compensation is needed.
Therefore, a need exists for an ATE calibration method that does not require external test equipment to calibrate individual tester pins, and provides balanced timing skews among the pincards.
SUMMARY OF THE INVENTION
Embodiments of the present invention are directed to an ATE calibration method and system that does not require external test equipment to calibrate individual functional pins and provides balanced timing skews among the functional pins and pincards.
A test system environment generally applicable to embodiments of the present invention includes multiple pincards, each pincard coupled to a DUT interface such as a loadboard via cabling. The pincards are also connected to test system components common to the pincards such as a tester controller through a tester bus on a backplane. Each pincard may have multiple functional pins and one or more precision measurement units (PMUs). PMUs may be shared between two or more functional pins, or dedicated to a single functional pin. The PMUs on all pincards in a test system together comprise a universal DC unit (UDC) (a.k.a. central measurement unit or central DC reference unit). In embodiments of the present invention, the UDC can also function as a distributed measurement circuit capable of making DC measurements on tester pins themselves and thus can act as a substitute for external test equipment. The UDC is connected to functional pins for measuring a DUT when the test system is in a normal test (not calibration) mode.
Embodiments of the present invention assign at least one functional pin in the test system as a reference or “golden” pin specifically for calibration purposes. In addition, one PMU is assigned as the reference PMU. In one implementation, the reference PMU is located on the same pincard as the reference pin. Alternatively, it can be located on the backplane or on another pincard. Because reference pin is selected from among the functional test pins, the reference pin has the same characteristics as any other functional test pin. However, once a functional pin is designated as a reference pin, in preferred embodiments that pin is prohibited from being used as a functional pin. However, in alternative embodiments, the reference pin may be used as a functional pin.
Once the reference pin and reference PMU have been designated, external test equipment is used to measure the AC and DC characteristics of the reference pin. The reference PMU is also used to measure the AC and DC characteristics of the reference pin. Note that it is possible to measure and store data on the reference pin for two different operational modes. Because the test equipment reference pin measurements become the standard against which all functional pins and PMUs are measured, the tester controller compares the reference PMU reference pin measurements to the test equipment reference pin measurements. Any deviation represents an error in the reference PMU that is taken into account when measuring and calibrating functional pins using the reference PMU. Once the parameters and characteristics of the reference pin and reference PMU are determined, all other functional pins in the test system can be connected to and measured against the reference pin using the reference PMU, without the need for external test equipment.
Each functional pin and reference pin contains driver and comparator circuitry. To measure the output driver characteristics of a functional pin,
Larson Douglas
Le Anthony
Rajsuman Rochit
Tong Carol Qiao
Advantest Corporation
Morrison & Foerster / LLP
Walling Meagan S
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