The history of thin film semiconductor manufacturing has been one of constant process improvement. The key to cost effective production has been through implementation of automated metrology systems. Traditionally, metrology refers to measurement of any type of physical dimensions. In the film manufacturing industry automated metrology systems measure parameters such as thickness, refractive index, resistivity and stress of the thin films. However, these systems are not only used to track the physical properties of the material, but also to feed this information back into the manufacturing process.
Since many of the thin film properties require temperature stability, thermal management plays an important role. To constantly receive accurate measurements over a longer period, temperature control of the stages and other critical components is critical.
The need for higher throughput and packaging density in combination with high speed optical or electrical measurement system places ever increasing demands on the thermal management system. Each metrology tool may also have different thermal needs which makes it even more complicated. Furthermore, lacking temperature control would lead to bad data, incorrect decisions conclusions and significant yield loss.
In the stage where semiconductor wafers are used for measurement, a Thermoelectric Assembly (TEA) could provide precise temperature control. This is because they can manage to change the heat pumping direction through the device under test by reversing the current flow through the device. Under steady state conditions, temperature stability to within ±0.01°C is achievable. For this type of cooling application TEA’s from tens of watts to more than 300 Watts of cooling capacity are required.
The water-cooled stainless-steel measurement stage can also be cooled using a water-glycol mixture. The channeled cold plate is directly attached to the measurement stage and a chiller provides a cooling fluid to maintain precise temperature control. Usually highly reliable thermoelectric based chillers with 150W and 300W capacity are used to provide this capacity. Units such as these are designed for bench-top or rack mount configurations.
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Laird Thermal Systems was entrusted to provide a liquid cooling system for a semiconductor tool manufacturer in Silicon Valley. The key requirement was to create a reliable system with minimal down time under 24/7 operation and stability of temperature control to as tight a tolerance as possible. In the end, Laird Thermal Systems could develop a robust thermoelectric recirculating chiller with 300 Watts of cooling capacity. Read more about the case in our application note Thermal Management for Semiconductor Metrology Equipment