Precautions for maintenance of experimental tubular CVD electric furnace

The experimental tube CVD electric furnace is a precision experimental equipment, and its performance stability directly affects the reliability of experimental results. To extend the lifespan of the equipment and ensure experimental safety, it is necessary to carry out systematic maintenance in terms of daily cleaning, component maintenance, operating standards, and safety protection.

1. Daily cleaning and maintenance
Furnace cleaning
Frequency: After each experiment or every 24 hours of continuous use.
method:
After the furnace cools to room temperature, use a soft bristled brush or vacuum cleaner to remove residual deposits (such as carbides and metal particles).
Avoid using hard tools to scrape the inner wall of the furnace to prevent damage to refractory materials (such as alumina ceramics).
If the sediment is stubborn, it can be soaked in diluted hydrofluoric acid (HF) or hydrochloric acid (HCl) solution (wearing protective equipment), but it needs to be thoroughly rinsed and dried.
Furnace tube cleaning
Quartz tube:
Use a dust-free cloth dipped in alcohol to wipe the outer wall to avoid scratches.
The sediment on the inner wall needs to be removed by hydrofluoric acid corrosion (professional operation is required to prevent the quartz tube from thinning and breaking).
Stainless steel furnace tube:
Clean with neutral detergent to avoid corrosion from acidic or alkaline solutions.
After cleaning, it needs to be dried to prevent rusting.
Gas pipeline cleaning
Frequency: Every quarter or when changing gas types.
method:
Blow the pipeline with high-purity nitrogen (N ₂) or argon (Ar) to remove impurities.
Check if there is any air leakage at the pipeline connection (which can be detected with soapy water).
Replace aged or clogged filters and valves.

2. Key component maintenance
Heating element (resistance wire/silicon carbide rod)
Inspection cycle: monthly or every 200 hours after use.
Maintenance content:
Observe whether the heating element turns red uniformly, and whether there is any fracture or deformation.
Measure the resistance value and replace it if the deviation from the initial value is greater than 10%.
Avoid frequent start stop and reduce damage to components caused by thermal shock.
thermocouple
Calibration cycle: Every 3 months or when the temperature display is abnormal.
Maintenance content:
Check if the thermocouple wiring is loose and if the oxide layer affects signal transmission.
Calibrate the thermocouple with a standard temperature source (such as a constant temperature bath), and replace it if the deviation is greater than ± 1 ℃.
When replacing, ensure that the thermocouple is inserted to the same depth as the original position (usually 5-10mm from the sample).
temperature controller
Inspection cycle: monthly.
Maintenance content:
Confirm that the PID parameter settings are reasonable (such as P=10-20, I=1-3, D=0.5-1, need to be adjusted according to the process).
Check if the wiring between the temperature controller, heating element, and thermocouple is secure.
Backup the temperature controller program to prevent data loss.
Vacuum system (if equipped)
Maintenance cycle: quarterly.
Maintenance content:
Check the oil level of the vacuum pump and replenish or replace it when it is below the scale line (usually change the oil every 500 hours).
Clean the air inlet filter of the vacuum pump to prevent blockage.
Test the vacuum degree, and if it cannot reach the set value (such as<10 ⁻ ³ Pa), check whether the sealing ring is aging.

3. Operating standards and precautions
Heating and cooling control Heating up: To avoid directly rising from room temperature to high temperature (such as>800 ℃), temperature should be increased in stages (such as 200 ℃ → 500 ℃ → target temperature).
The heating rate should be controlled at 5-15 ℃/min to prevent furnace tube cracking caused by thermal stress.
Cooling:
After high-temperature processing, it is necessary to slowly cool down (such as ≤ 10 ℃/min) to avoid sample cracking or film detachment.
Do not open the furnace door to forcibly cool down, to prevent air from entering and causing oxidation.
Sample placement requirements
The sample should be placed in the central area of the furnace tube (with optimal temperature uniformity), avoiding proximity to the inlet or outlet.
Maintain a spacing of ≥ 10mm between multiple samples to prevent thermal radiation interference.
The sample holder should be made of high-temperature resistant materials (such as quartz and ceramics) to avoid deformation of the metal holder at high temperatures.
Gas flow control
Before the experiment, blow the pipeline with high-purity gas for 10-15 minutes to remove air.
The gas flow rate needs to be adjusted according to the process (for example, CVD deposition of silicon requires an H ₂ flow rate of 50-100 sccm and a SiH ₄ flow rate of 5-20 sccm).
Avoid sudden changes in gas flow rate and prevent pressure shock from damaging the pipeline.

4. Safety protection measures
over temperature protection
Configure an independent over temperature alarm and set the upper temperature limit (such as 50 ℃ higher than the target temperature).
Regularly test the over temperature protection function to ensure that the power is automatically cut off when triggered.
Leakage protection
The grounding resistance of the equipment should be less than 4 Ω, and the grounding wire should be checked regularly for looseness.
Install a leakage protection switch that automatically shuts off when the leakage current exceeds 30mA.
Gas leakage detection
Before the experiment, check if there is any air leakage at the connection of the gas pipeline (soap water or a portable gas detector can be used).
The experimental area needs to be well ventilated and equipped with toxic gas alarms (such as using gases such as H ₂ S and PH ∝).
Personal Protection
Wear insulated gloves and protective face shields when operating high-temperature furnace tubes to prevent burns.
Wear gas masks and chemical protective clothing when handling corrosive gases or liquids.

5. Long term disuse maintenance
Equipment power outage
Turn off the main power switch, unplug the plug, and prevent damage to the equipment from lightning strikes or voltage fluctuations.
Furnace protection
Place desiccants (such as silica gel) in the furnace to prevent damage to refractory materials caused by moisture.
Cover the equipment with a dust cover to prevent dust from entering.
Component maintenance
The heating element needs to be coated with high-temperature lubricating grease (such as molybdenum disulfide) to prevent oxidation.
Vacuum pumps need to empty the liquid inside the pump to prevent rusting.