Oven and chamber furnace options for modified atmospheres

Modified atmosphere options for ovens up to 700°C

For temperatures up to 700°C, Carbolite Gero manufactures the HTMA range of modified atmosphere ovens. These ovens are specifically designed to achieve excellent control of an inert atmosphere with the primary aim of reducing the concentration of oxygen to very low levels.

Separate flow controls for purge and process gases mean that once the chamber has been purged of atmospheric air process gas can be used with lower flow rates. Switching between purge and process gases can either be done manually or by adding the option of an automatic programmable control system. Oxygen levels down to 50 ppm are achievable.

A105 NiCr alloy (Inconel) retort

The A105 NiCr alloy (Inconel) retort is sealed by a removable front opening insulated door fitted with a silicone rubber seal. Gas inlet and outlet connections are easily accessible at the front. Oxygen levels down to 30 ppm are achievable when purging with an appropriate inert gas.

A105 retorts for CWF laboratory furnaces are fitted with a 3 mm thermocouple  gland through the centre of the door. The retort and furnace must be ordered together as the furnace is modified to allow it to be used with, and without, the retort. The A105 retort can be used in combination with the laboratory gas safety system for safe use with hydrogen.

Cylindrical GLO retort

The GLO annealing furnace features a vacuum tight retort with highly symmetric positioning of the heating elements. The front door of the cylindrical retort can be heated if required as well as air cooled from the outside or purged with cold, inert gas with the optional fast cooling system.

1. opened door
2. radiation shields
3. ceramic fiber insulation and heating elements
4. charging rack
5. thin metallic sourrounding
6. afterburner
7. frame

Modified atmosphere options for vacuum furnaces up to 3000°C

For temperatures higher than achievable in a chamber furnace, a vacuum furnace can be used to create modified atmospheres up to a temperature of 3000°C.

Náš rozsiahly sortiment vákuových pecí zahŕňa vákuové komorové pece, vákuové zvonové pece, pece so spodným plnením, laboratórne vákuové pece a vákuové rúrkové pece. Každá pec môže byť použitá buď s reaktívnym plynom alebo s inertným plynom. Väčšina výrobkov v sortimente vákuovej pece je k dispozícii buď s kovovou, grafitovou alebo keramickú izoláciou. Na želanie môžu byť grafitové modely konfigurované tak, aby bezpečne fungovali až do 3000 °C.

Custom example: HTMA 6/220 for semi-conductor wafers

This modified HTMA 6/220 was modified for the heat treatment of large numbers of semi-conductor wafers. The process involved alloying 330 nanometres (nm) of gold on 8-inch silicon wafers, 50-200 micrometres (µm) thick. The wafers are thinned and have different thicknesses:

• Two wafers 52 µm thick, with a 700µm thick “Taiko” ring along the edge
• One wafer 200 µm thick
• One wafer 120 µm thick

The customer also required the ability to process materials under a modified atmosphere to ensure a low oxygen concentration. This can be achieved by creating a nitrogen within the oven chamber. The ability to maintain uniformity at low temperatures was vital, as rapid cooling of the wafers was a requirement of the customer’s process.

Riešenie

The oven has been fitted with the fast-cooling option to rapidly cool the oven from 420°C to 200°C in 20 minutes. Two cooling fans are located at the rear of the oven.

Cool air is blown around the outside the chamber through ducts located between the insulation and chamber wall. To prevent any excess airflow when cooling is not required, an automatic butterfly valve is also located in the outlet pipe.

The temperature controller is programmed to use the status of the door interlock to automatically start or stop a process cycle, thus enabling a continuous cycle. Heating is triggered when the lambda sensor detects that the level of oxygen within the chamber has dropped below a certain threshold; for example, when the oxygen drops to 50 parts per million (ppm), the temperature program starts.

Other modifications include custom shelf positions within the chamber to allow space for racks of wafers on each shelf, additional flowmeters to accommodate the use of alternative gases, such as argon, and an optional floor stand to raise the oven up to a workable position for the operators. The temperature controller is also configured to automatically switch between purge and process gas flow rates.

Performance

In order to maintain a continuous processing cycle, it was important that when the door was opened at 200°C for unloading and reloading, the HTMA quickly returned to prime operating conditions, both in terms of temperature and oxygen concentration within the chamber.

Example process cycle

• Heat up the oven to 200°C.
• Open the door and load in the wafer trays.
• Purge with nitrogen until the oxygen level is below 50ppm.
• The controller automatically starts heating to 420°C and lowers the nitrogen flow.  The heating rate is set to a maximum of 10°C per minute.
• Dwell at 420°C for 10 minutes.
• Cool down as fast as possible to 200°C (waiting temperature).
• Open the door and remove the wafers.
• The maximum program cycle time is less than 2 hours.

Custom example: Furnace for calcining (thermal decomposition) of catalyst materials

This furnace is designed for the calcining (thermal decomposition) of catalyst materials, for use in production chemistry.  The processing of such materials can create a corrosive environment within the furnace, hence the requirement to construct the retort from Hastelloy C-2000®, an alloy composed of nickel, chromium, molybdenum, iron and copper. This combination offers greater resistance to corrosion.

Riešenie

This custom retort chamber furnace is capable of reaching temperatures of up to 1200°C, however due to the thermal resistance properties of the retort material, the furnace is limited to a maximum working temperature of 1000°C. Typical working temperatures are up to 700°C.

The retort has a volume of 1000 litres and is designed to accept up to 12 of the customer’s own sample trays supported on a carrier also constructed from Hastelloy C-2000®. A gas inlet pipe enables the customer to modify the atmosphere within the retort by introducing a non-flammable gas, such as nitrogen or argon, to suit the requirements of their process. The retort door is held closed by industrial over-centre clamps and is securely interlocked by two pneumatic cylinders.

The furnace is divided into three heated zones, one in the hearth and two situated vertically up either side of the chamber. Temperature control is provided by three Eurotherm 3508 controllers linked via digital communications, allowing for the retransmission of setpoint from the centre zone controller to the other two controllers. Each heated zone is linked to a separate 3216CC over-temperature controller.

All instrumentation is housed within a separate control cabinet, which also features a kilowatt hour meter to allow the customer to monitor their power consumption.

The unit includes a forced cooling system designed to blow ambient air into the cavity between the retort and the furnace insulation. The fan is capable of delivering 600m³ of air per hour at a pressure of 9” water, reducing the overall cooling period down to approximately 3 hours.