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CPD 408

Critical point dryer

Overview

Critical Point Dryer for MEMS

The CPD408 Critical Point Dryer has been developed for critical point drying of large, flat specimens e.g. wafers for MEMS. The unique double chamber system ensures a minimum consumption of CO2. The handling is very simple and the fully automatic process is computer controlled.

Key Features

  • Safe and easy operation
  • Gentle substate treatment
  • Clean room compatible
  • Compact bench unit
  • Economical operation
  • Excellent visual access

The critical point drying method

Drying micro electro mechanical systems (MEMS) in air or under vacuum can drastically alter their structures or even destroy them completely. They must therefore be dried by a gentlier method. One well-known method is "Critical Point Drying".

The surface tension of the water, isopropanol or acetone in a micro device at the point at which it changes from the liquid phase to the gaseous phase can destroy the device through capillary forces (e.g. membrane). By increasing the pressure and temperature of the substrate it is possible to dry it without crossing a phase boundary. This is possible because once the critical point has been passed, the density of the "liquid" and the density of the "gas" are the same.

The critical point for water is 228.5bar and 374°C. However, this high pressure and extreme temperature would normally destroy a substrate. For this reason the substrate must be treated in a suitable transitional fluid such as CO2 whose critical point of 73.8bar and 31°C is considerably more advantageous.

Safe and easy operation

The solenoid high pressure valves, the heating and cooling are operated fully automated from the touchpad keyboard (no difficult-to-use manual valves). Start – Stop operation is programmed.

Gentle substrate treatment

Damaging turbulences caused by admitting and draining fluids too fast are reduced to a minimum through the use of apertures

Compact bench unit

Space saving design with separate cooling/heating unit

Economical operation

Minimum consumption of the CO2 transitional fluid because of integrated refrigerator (no cooling agent required) and unique double chamber system.

Excellent visual access

Digital temperature and pressure displays and a mimic diagram to indicate the momentary operational status of the unit.