SC12 Product Description

The SC12 was introduced in 1996 to replace the original Spicer Consulting SC07 System. Hundreds of SC12 systems are in use, world-wide, protecting electron and focussed ion beam tools against magnetic fields. It is now being withdrawn in favour of the new SC22 cancelling system.

Typical SEM room installation

The picture on the left shows a scanning electron microscope (SEM) with a cancelling system fitted. The magnetic field sensor is located at the base of the electron beam column. The field cancelling cables are mounted on the walls and above the ceiling in this typical installation. The cables are shown in red, green and blue to identify the axes. The actual cables are grey.

This basic AC cancelling installation comprises the Magnetic Field Control Unit, the X,Y and Z multicore cables and the magnetic field sensor. The system works by superimposing a cancelling field of the correct amplitude, phase and direction to null out the problem field. The SC12 magnetic field control unit contains amplifiers which drive currents through the cables to generate the cancelling field. The magnetic field sensor measures the field on X,Y & Z orthogonal axes in real time, then the measured signals are amplified and fed back in anti-phase to the power amplifiers. Hence the system is closed loop and the negative feedback nulls the field at the sensor location.

The SC12 includes an accurate magnetic field measuring capability with a 3.5 digit panel meter for display. The real time measured fields are also available as analog voltage levels for oscilloscope or chart recorder display. The basic SC12 can measure the true RMS amplitude of AC fields. When a DC sensor is added, the system can also measure incremental DC fields. The panel meter can be switched to display any of the axes.

The Front Panel of the Control Unit
Move the mouse over the image to see the features highlighted.

"Field OK" indication
The user definable field "trip levels" provide rapid "GO/NO GO" monitoring of the field. Green LED indicators on the Control Unit and the Sensor are lit when the field is "OK". Any field value which exceeds the defined trip level will turn off the "Field OK" LED. The field component which caused the trip is displayed on a multi segment red LED indicator on the Control Unit.

With the security of the "Field OK" indicator, the system operates automatically with complete simplicity. For many users, the ability to install the SC12 Magnetic Field Cancelling System, then forget about it, is one of the system's greatest benefits.

DC Field Cancelling
Using the SC12 there are two options for DC field cancelling.

1. The AC sensor can be retained and an SC20 wideband DC sensor plugged into the DC sensor input on the control unit back panel (a plug adapter is required). The SC12 cross-over frequency between the two sensors is at 5Hz.
2. The AC sensor can be discarded and the SC20 wideband DC sensor used alone for AC and DC cancelling (again a plug adapter is required).

Multiple magnetic field sensors
Multiple magnetic field sensors can be used when it is not possible to locate a single sensor at the point where the field needs to be cancelled (which happens often on CDSEMs and large TEMs). External mixers are available for the SC12 which combine the outputs from two AC or two DC sensors. The mixer controls enable the resulting "virtual sensor" position to be adjusted between the centres of the two sensors and tuning for minimal image disturbance on the electron beam tool.