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it possible to measure the thickness of wafers from 0.05 mm to around 1 mm. As transparency decreases with doping, the maximum measurable thickness is reduced to around 0.8 mm for highly doped wafers.
The white light interferometers each consist of a compact sensor and a controller, which is housed in a robust, industrial-grade housing. The active temperature control included in the controller ensures high measurement stability. Micro-Epsilon offers two different device types for use in the thickness measurement of wafers. A high degree of protection is required for integra- tion in lapping machines so that the sensors are not affected by the mixture of liquid and cutting grains used. With this type, both the sensor and the controller unit comply with protection class IP67. However, thickness measurement can also be used in other stages of semiconductor produc- tion, for example, quality control. The conditions here are completely different: work is carried out in a cleanroom and, if necessary, in a vacuum.
Instrumentation Monthly January 2025
Micro-Epsilon offers a device with a vacuum-com- patible sensor. Connection to the controller, which can be installed in a control cabinet, is made via a fibre optic cable.
SUCCESSFUL PRODUCT LAUNCH The new range of interferometers from Micro-Ep- silon for measuring the thickness of wafers have already been extensively tested in reference projects in the semiconductor industry. Even challenging applications were mastered: in the lapping machines, the devices measure reliably even when there is liquid with the cutting grains on the wafer surface. The cleanroom variant uses Micro-Epsilon’s own cleanroom technology, which enables cleanroom-compatible packaging of the components, for example.
The IMS5420-TH white light interferometer opens up new perspectives in industrial thickness meas- urement of monocrystalline silicon wafers. Due to its broadband superluminescent diode (SLED), the IMS5420-TH can be used for undoped, doped and
highly doped SI wafers. In wafer thickness measure- ments, the IMS5420-TH impresses with an excellent price/performance ratio.
The white light interferometer achieves a signal stability in the sub-micrometer range. The thickness can be measured from a distance of 24 mm. The measuring system is therefore ideally suited for inline measurements.
The measuring system is available as a thick- ness measuring system or as a multi-peak thickness measuring system. The multi-peak system measures thicknesses of up to five layers, for example, wafer thickness, air gap, films and coatings. In addition to silicon wafers, the IMS5420 also precisely detects the thickness of silicon carbide wafers. For thickness measurements in harsh environmental conditions, the IMS5420/IP67 controller is available with IP67 protection and stainless steel housing.
Micro-Epsilon
www.micro-epsilon.co.uk 17
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