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Semiconductor analyzer packs integrated CV, IV capability

Posted: 08 Apr 2005 ?? ?Print Version ?Bookmark and Share

Keywords:keithley instruments? wafer tester? agilent technologies? device analyzer? cv?

On the heels of the announcement by Keithley Instruments of its third-generation wafer tester, test-and-measurement giant Agilent Technologies is introducing a Windows-based semiconductor device analyzer that integrates CV (capacitance versus voltage) and iv (current versus voltage) measurements into a single instrument.

This single-box SMU (source-measure unit) approach is expected to appeal to users facing challenges when both IV and CV measurements are required for characterization. Most instruments are designed for only one type of measurement. That means that two different instruments are typically be used for tests, and that demands mastery of two interfaces.

Proper connection of CMU (capacitance measurement unit) cables to a DUT (device under test), and precise cable length compensation, are also necessary to ensure accurate CV measurement results.

The cable conundrum
Most CMUs use BNC coaxial cable connectors, but source-measurement units typically use tri-axial connectors. Switching between these incompatible connectors can be difficult and confusing, especially when using positioners on a wafer prober.

Tri-axial cables have three layers: a center force/sense line, a middle guard, and an outer ground shield. The reason that SMUs use tri-axial cables rather than BNC cables is that ultra-low current measurements (down into the femtoamp range) are not possible using BNC cables. Leakage current between the inner conductor and the outer ground shield of a BNC cable limits these types of cables to measurements of 1nA or greater.

However, tri-axial cables isolate the inner conductor from the outer ground shield via a middle guard shield. Therefore the SMU has an active circuit that always keeps the voltage potential of the driven guard the same as that of the inner conductor. Since there's no voltage difference between the driven guard and the inner conductor, there's no leakage current. Using tri-axial cables, current measurements down to the sub-femtoamp (attoamp) range are possible.

Self-contained and xpandable
Enter Agilent's new B1500A tester. It's a self-contained and expandable system suitable for parametric characterization and analysis of ICs. As a state-of-the-art tester, it can accommodate 65nm lithographies and beyond.

As a modular instrument, the B1500A has a 10-slot configuration. On the software side, it supports Agilent's new EasyEXPERT software, providing an intuitive top-down approach to device characterization. EasyEXPERT's Windows-based graphical user interface is familiar, even to new engineers who are inexperienced with parametric measurement instruments. "The B1500A and EasyEXPERT software can turn every user into a parametric test expert," claims Minoru Ebihara, VP and GM of Agilent's Hachioji Semiconductor Test Division.

Library of device application tests
In use, explains Ebihara, the EasyEXPERT software supplies a library of device application tests that you select based on the type of measurement required. After making a few simple selections, such as identifying the technology by classification and selecting the appropriate device type, the software selects the appropriate settings, makes the measurements, analyzes the data and displays it graphically.

"Using EasyEXPERT software, even a beginner can start making productive measurements within a few minutes of powering up the B1500A," avows Ebihara.

The B1500A's 10-slot configuration also supports three SMU types. You can choose high-resolution SMUs, medium-power SMUs, or high-power SMUs. A multi-frequency capacitance measurement unit is also available, and a 4.2A ground unit is included with all B1500A mainframes.

Besides integrating CV measurement into the device analyzer mainframe, the multi-frequency capacitance measurement unit also possesses measurement capabilities not usually available on comparable external capacitance meters. It can measure capacitance at up to 5MHz and provide 25V of DC bias.

Tightly coupled units
In addition, the combination of the capacitance measuring unit and SMUs within the same instrument enables these measurement resources to be tightly coupled. When joined using a B1500A SMU CMU Unify Unit, or SCUU, the multi-frequency capacitance measurement unit and SMU combination supports capacitance measurement with 100V of DC bias.

Agilent claims its B1500A SCUU provides a convenient and foolproof means to connect two SMUs and the MFCMU together, and to switch between these different measurement resources without using a separate external switching matrix. The B1500A software handles all of the IV-CV switching, compensation and return path issues.

To begin making accurate measurements, you need only to select an IV or CV algorithm and push a button.

Buy only what you need
The flexibility to tailor your measurement approach can also help reduce the cost of test by ensuring that you buy only what you currently need, leaving room to grow as your needs change. Because of its low-current, low-voltage, and compensated capacitance measurement capabilities, Agilent claims its B1500A can also be used for a wider range of characterization for semiconductor devices and emerging materials, including nano-technology devices.

An ASU (atto-sense and switch unit) is also available. It can provide measurement resolution at 0.1-femtoamp (100-attoamps), and 0.5?V. That's typically needed for measurements such as MOSFET Idoff, and memory-cell leakage characterization. The ASU can be connected to the high-resolution SMU and the CMU so you can switch between precision IV and compensated CV measurements, too.

The B1500A semiconductor device analyzer can be ordered now. Pricing starts at about $45,000 for a basic 4-SMU IV measurement system. A basic CV-IV measurement system will cost about $58,000. Product is expected to ship in August of this year.

- Alex Mendelsohn

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