Temperature of experimental tube CVD electric furnace

The temperature control of the experimental tubular CVD electric furnace is a core factor affecting the quality of material deposition, film properties, and equipment safety. The temperature range, control accuracy, and stability need to be optimized according to specific process requirements. The following is a detailed explanation:

1. Typical temperature range
The temperature range of the experimental tubular CVD electric furnace is usually from room temperature to 1200 ℃, and some high-end equipment can be extended to 1500 ℃ or even higher, depending on the heating element material and furnace design:

Low temperature CVD (<400 ℃): Suitable for depositing organic thin films, polymers, or certain metal oxides (such as zinc oxide), commonly used in fields such as flexible electronics and optical coatings. Medium temperature CVD (400-800 ℃): widely used in the preparation of semiconductor materials (such as silicon and germanium) and ceramic coatings (such as silicon carbide and silicon nitride), it is a key process for integrated circuits and MEMS devices. High temperature CVD (>800 ℃): Used for synthesizing high melting point materials (such as carbon nanotubes, diamond films) or high-temperature superconducting materials, high-purity inert gas protection is required to prevent oxidation.

2. Key parameters for temperature control
heating rate
Typical value: 5-20 ℃/min (adjusted according to material thermal stability).
Impact: Excessive heating may lead to sample cracking or excessive film stress; If it is too slow, the experimental period will be extended.
Optimization: Segmented heating (such as quickly raising to medium temperature first, and then slowly raising to target temperature).
Holding time
Typical value: 10 minutes to several hours (depending on film thickness requirements).
Impact: Insufficient insulation can lead to uneven film or poor adhesion; If it is too long, it will increase energy consumption and equipment loss.
Cooling method
Natural cooling: suitable for materials that are insensitive to temperature gradients, such as metal films.
Forced air/water cooling: used for rapid cooling after high-temperature processes to reduce thermal stress (such as in the preparation of silicon carbide coatings).
Control cooling rate: Key materials (such as semiconductors) need to be cooled at a rate of ≤ 10 ℃/min to avoid defect formation.

3. Temperature uniformity control
Furnace design
Single temperature zone furnace tube: temperature uniformity ± 5 ℃ (suitable for simple processes).
Multi temperature zone furnace tube: gradient heating is achieved through independent temperature control (such as high in the front and low in the back), optimizing the gas reaction path, and achieving temperature uniformity of ± 1 ℃.
Airflow distribution
Air intake method: Adopt porous air intake or circular gas distribution to ensure uniform diffusion of gas to the surface of the sample.
Exhaust design: Reasonably arrange exhaust ports to avoid temperature differences caused by local airflow stagnation.
Sample placement
Location: The sample should be placed in the center area of the furnace tube (with optimal temperature uniformity).
Spacing: Maintain a spacing of ≥ 10mm between multiple samples to prevent thermal radiation interference.

4. Temperature calibration and maintenance
periodic calibration
Method: Use standard thermocouples (such as K-type, S-type) or infrared thermometers to compare the temperature inside the furnace and calibrate the temperature controller.
Frequency: Calibrate every 3 months or after replacing the heating element.
Thermocouple maintenance
Check: Confirm that the thermocouple is not oxidized, broken, or displaced.
Replacement: Replace the thermocouple every 500 hours of use or when the temperature display is abnormal.
Heating element inspection
Appearance: Regularly inspect the resistance wire for uneven redness, breakage, or deformation.
Lifespan: The molybdenum wire heating element has a lifespan of approximately 2000 hours and requires spare parts in advance.

5. Temperature related faults and solutions
Abnormal temperature display
Phenomenon: The actual temperature deviates from the set value by more than ± 5 ℃.
Reason: Damage to thermocouple, malfunction of temperature controller, aging of heating element.
Solution: Replace thermocouples, calibrate temperature controllers or heating elements.
Large temperature fluctuations
Phenomenon: Temperature fluctuates above ± 3 ℃.
Reason: Improper PID parameter setting, wind circulation system failure, unstable power supply.
Solution: Adjust PID parameters, check the air circulation motor, or install a voltage regulator.
local overheating
Phenomenon: The temperature in a certain area of the furnace tube is significantly higher than in other areas.
Reason: Local short circuit of heating element, overly dense sample placement, or poor airflow.
Solution: Replace heating elements, adjust sample spacing, or optimize intake design.

6. Safety operation standards
over temperature protection
Configure an independent over temperature alarm, set the upper temperature limit (such as 50 ℃ higher than the target temperature), and automatically cut off the power when triggered.
Emergency Cool
Equipped with a backup cooling system (such as nitrogen purging) to quickly cool down in case of temperature loss.
Personnel protection
Wear insulated gloves when operating high-temperature furnace tubes to avoid direct contact with the furnace body; Before opening the furnace door, it is necessary to confirm that the temperature has dropped to a safe range (<50 ℃).