Nanotechnology at Zyvex - faq

By: Zyvex  09-12-2011
Keywords: Transistor

All four systems share similar aspects of Zyvex’s core technology for nanomanipulation. The nProber is the top of the line nanoprobing system specifically designed for semiconductor characterization. The system is designed for customers working at small geometries who want to have the most user friendly and efficient system on the market. The system is semi-automated and has 8 positioners for a variety of advanced applications. The dProber is a lower cost solution to a dedicated system. The system has 6 positioners and an XYZ stage for higher throughput but does not have all of the automation that comes with the nProber. The system replaces the door of a repurposed SEM at the customer site or can be coupled with a new SEM as the dProber+. The sProber is a 4 positioner system that includes everything needed for semiconductor level probing. The system is designed for FA and yield labs that have an SEM being used for multiple purposes. The sProber is installed quickly by the user when probing is only needed ‘sometimes.’ The S200 is the most basic system with 4 positioners and targeted for research and education customers only. The system is meant to be used in a lab with multiple users and on an imaging platform that is used for many different purposes. The S200 can be outfitted with multiple upgrades, end effectors and application packages to achieve exactly what the customer wants.

The sProber, dProber, and nProber are all used extensively for non-visual fault localization. They can also be used for device characterization, metal-line resistance measurements, butterfly probing, and bitcell characterization. They can be further upgraded to perform hot/cold measurements, CV characterization, Pulsing measurements, and Electron Beam Induced/Absorbed Current characterization. The tools are used at all metal layers and at the contact level to characterize and find faults.

The Zyvex SEM nanoprober product line is integral in locating non-visual fails. Most commonly, a failing bit is identified using some larger scale method. The sample is then deprocessed to contact level (if it hasn’t been already) and put in the Zyvex system. The user probes six transistors in a reference bit and then six transistors in the failing bit. The data is analyzed and a problem is found that points to a pair of contacts in a specific transistor. The transistor is cross sectioned and then put in a TEM. The image of the fail is then used to solve the root problem. In many cases, customers stop after nanoprobing when the electrical signature corresponds to previously seen fails. This greatly improves throughput and cycle time. The system can also be used at higher levels when fails are suspected in the metal levels or when other tools are unable to resolve a single bit fail. This can keep a user from deprocessing past a unique fail.

The S200 can be used as an all purpose nanomanipulator platform. The system can be upgraded to provide for electrical measurements, force characterization, pick-and-place, surface adhesion and stiction testing, and a numerous types of sample preparation. Some examples include electrical characterization of a nanolithography built device on a sample, force characterization of a nanowire, and removal of a specific nanotube for further analysis. The system is perfect for a lab atmosphere with multiple project ideas.

The system will mount directly on the SEM stage. Depending on the SEM there may be some loss of tilt, rotation, or Z movement while the head is installed but the majority of the SEM stages will not be affected by the Zyvex system. With the head removed, full functionality of the SEM is restored.

In most cases, the system can be installed and removed in under five minutes. No system design will require longer than ten minutes to install or remove.

This varies with the SEM model and the amount of application packages purchased with the Zyvex system. This can range from one to five ports but the average user will only need two to three open ports. Zyvex is able to customize all of the flanges and design around different SEM models as well.

The system will replace the entire door and stage of the SEM. The dProber has its own sample stage and when not probing you can image and move around a sample approximately 25 mm2 in size.

All of the Zyvex systems come with a Windows-based software platform to control the manipulators. The motion itself is controlled by the user through a high-precision joystick. The sProber, dProber, and nProber all come with integrated software to control the parametric analyzer and Optimizer. This is an optional upgrade on the S200.

The Optimizer is a downstream ashing tool that uses a plasma outside of the chamber to inject free radical oxygen into the vacuum system. This free radical oxygen scrubs the chamber of hydrocarbons that lead to Electron Beam Induced Deposition (a fancy term for contamination). The Optimizer is vital if the user wants to make ohmic contact with the sample for electrical characterization.

The Optimizer should be run every time the chamber is exposed to air, every time a sample is exchanged, once in the morning, and once at night. If contamination begins to build up after a long probing session then the Optimizer should be run as well.

The key difference between these two techniques is how the sample is imaged. SEM based Nanoprobing uses the SEM as the imaging tool and the probe tips as the contact points. With Atomic Force Probing (AFP) the sample is imaged using the AFM probe tips which are also used to probe the device. This leads to slower image acquisition times and possible mechanical damage to the device. The image quality is also affected by the tip quality and so image quality degrades as the tips are used to probe the devices. As the image quality degrades it becomes harder to probe and thus more force is needed and the tip quality further degrades. There is also no real time image for user feedback so the user can not quickly reposition tips to achieve the best possible contact. Zyvex Instruments prefers the decoupled nature of SEM based Nanoprobing.

Probe Related Questions

Probe lifetime can vary widely based on the user’s experience, the sample under study, the application being performed, the Zyvex system being used, and the environment where the system is installed. Usages can range from one day of measurements on carbon nanotube electrical characterization to more than three weeks of SRAM transistor fault localization.

Again this can vary widely depending on the application and user. In general, a semiconductor customer will use around 1000 probes a year and a university customer will use around 200 probes a year.

Zyvex considers the probes to be consumable items and will not rework or warranty probe tips after they are used. However, during system training Zyvex will train users on how to use the manipulator to quickly rework a slightly bent probe tip. This is one of the advantages of using a SEM-based nanomanipulator as your nanoprobing solution.

These are removable holders that plug into the fine positioner assembly. There are various types of end effectors that are used depending on the application. The most common end effector holds a single probe.

All of Zyvex’s systems are compatible with industry standard probe tips with a 0.5 mil shank diameter. However, Zyvex does not guarantee tool performance as specified if third party products are used.

SEM Related Questions

EBID is short for Electron Induced Beam Deposition; sometimes referred to as SEM burn or raster burn. This effect is seen in all electron beam imaging systems. A user can usually see a dark box on the sample after imaging the same area for longer than 10 minutes. The presence of this box is sometimes not seen because of the beam energy or detector used but it is always present. Diffuse hydrocarbons cover the sample, stage, and chamber walls of the SEM. As the E beam rasters across the sample the hydrogen atoms are knocked off leaving sp3 hybridized carbon on the sample. This is a diamond-like film that is completely insulating. More diffuse hydrocarbons move into the area and the process continues. A very thick layer can be built in the time it takes to probe the device. Zyvex has a tool called the Optimizer to clean the chamber and sample of these diffuse hydrocarbons before probing and imaging begins. This insures a clean environment for long probing sessions.

Zyvex is constantly working with SEM partners to evaluate and integrate the best suited SEMs available for the nProber platform. There are multiple platforms in use today and more platforms will be added as materials change and technologies continue to shrink.

Measurement Related Questions

Yes. The standard procedure utilizes two outer probes as the voltage source and drain. Two inner probes are set to source zero current and act like high impedance voltage measurement probes. The contact resistance of the system can then be removed and the true resistance of the nanostructure is measured.

Fortunately, all of the probing done with Zyvex systems is in vacuum and thus there is not a continuous stream of contamination agents. There are three factors that Zyvex manages to achieve low ohmic contact. First, Zyvex uses the Optimizer to insure a carbon free environment on the sample. Secondly, Zyvex has a unique in situ probe cleaning method to insure pure tungsten ohmic contact with the probes. Thirdly, Zyvex has a recommended procedure to clean the sample prior to probing. Zyvex also has a contact optimization feedback loop so the user can monitor the quality of the contact in real time.

Nanoprobing is non-destructive to the transistor. However, if the voltage or current levels are applied beyond the transistor’s normal operating conditions then the transistor can be stressed and possibly damaged. However, the voltage/current can be set / controlled thru the Zyvex system to ensure that they are well below the range that would damage the transistor.
There are other techniques like Scanning Capacitance Measurement, Reactive Ion Etching, and Focused Ion Beam Milling that may weaken devices and result in damage prior to nanoprobing. Since these are not part of SEM nanoprobing, they should not be used in conjunction with SEM nanoprobing.

All of Zyvex’s systems are outfitted with multiple connection paths to the probe tips. Almost all third party measurement equipment can be connected to the system. However, Zyvex does not guarantee tool performance as specified if third party products are used.

Zyvex positioners can handle up to 100V and 200mA. Prober cables can handle up to 200 mA of current and voltages as high as 250 volts. The probes can take in excess of 4mA and will act like a fuse in the circuit. If a probe burns out at the point of breakdown during tests, a resistor can be placed in series with the probe. If the probes touch while they are at high voltage, the instantaneous current can be much higher than 200 mA. In this situation the sharp probe tips will vaporize similar to a fuse and this will keep such large currents from damaging any wiring on the device.

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Keywords: Transistor

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