Precautions for operating a vacuum tube CVD electric furnace

When operating a vacuum tube CVD furnace in the semiconductor industry, the following precautions must be strictly followed to ensure equipment safety, process stability, and coating quality:

1. Equipment installation and preparation
Environmental and power inspection
Ensure that the equipment is placed on a stable workbench with a carrying capacity exceeding 200kg.
Check the cooling water circulation system and ensure that the water pressure remains stable between 0.3-0.5MPa to avoid equipment overheating and damage.
Component integrity verification
Check whether the furnace tube, sealing ring, thermocouple and other components are intact, whether there are cracks in the quartz tube or corundum tube, and whether the sealing ring is aging.
Confirm that the gas pipeline is connected correctly, the valve is leak free, and the gas purity meets the process requirements (such as SiH ₄, NH ∝, etc., which need to reach 99.999% or above).
Oven treatment
After the first use or long-term disuse, it is necessary to bake at 120 ℃ for 1 hour and 300 ℃ for 2 hours to remove moisture and impurities in the furnace and prevent furnace cracking.

2. Standard operating procedures
Sample installation and sealing
The sample needs to be pre treated (such as sandpaper polishing, ultrasonic cleaning) to ensure that the surface is clean and free of impurities. After being loaded into a quartz boat, it is pushed into the constant temperature zone of the furnace tube, and the sample spacing is uniform without overlap.
Cover the insulated drum lid, seal the furnace lid, and insert insulated furnace plugs at both ends to reduce heat radiation loss.
Vacuum pumping and airtightness testing
Start the vacuum pump and pump until the pressure inside the furnace is below 5Pa. Then, introduce inert gas (such as nitrogen or argon) for three gas washing operations, each lasting for 5 minutes.
After turning off the vacuum pump, let it stand for 1 hour. If the pressure gauge reading remains unchanged, then the airtightness is good; Otherwise, it is necessary to investigate the leakage points (such as the bellows interface and electrode seal).
Heating up and atmosphere control
Heating rate: Set according to the material of the furnace tube, quartz tube ≤ 10 ℃/min, corundum tube ≤ 5 ℃/min, to avoid sudden cooling and heating that may cause furnace tube rupture.
Temperature limit: Silicon molybdenum rod heating elements are prone to low-temperature oxidation at 400-700 ℃, and long-term insulation should be avoided; The maximum operating temperature shall not exceed the rated value (such as 1650 ℃), and the operating time at the maximum temperature shall not exceed 1 hour.
Atmosphere regulation: Inject reaction gases (such as methane and hydrogen) in proportion, control the flow rate within the range of 50-200 sccm, and maintain dynamic equilibrium inside the furnace.
Real time monitoring and recording
Record temperature, pressure, and gas flow data every 15 minutes to ensure process stability.
If the pressure fluctuates abnormally or the temperature deviates from the set value by more than ± 5 ℃, immediately suspend the experiment and investigate for air leakage or heating element failure.

3. Safety and emergency response
Personal Protection
Wear protective clothing, goggles, and heat-resistant gloves during operation to avoid burns or chemical injuries.
Alarm devices must be installed in areas where flammable gases such as hydrogen are used, and open flames are strictly prohibited. Regular calibration is required.
Pressure and temperature control
The pressure inside the furnace tube shall not exceed 0.02MPa to prevent equipment damage; When the furnace temperature exceeds 1000 ℃, the furnace tube needs to maintain a normal pressure state to avoid vacuum causing the quartz tube to lose transparency or rupture.
Do not open the furnace door when the furnace temperature is ≥ 200 ℃ to prevent high temperature burns or furnace tube explosions.
Emergency operation
In case of sudden power outage, immediately close the main valve of the gas cylinder and manually open the pressure relief valve to prevent gas backflow or excessive pressure.
When the furnace tube ruptures, immediately cut off the power supply, evacuate personnel, and wait until the furnace body is completely cooled before disposing of the fragments.

4. Maintenance and upkeep
Daily cleaning
After the experiment, clean the sediment on the inner wall of the furnace tube with a soft bristled brush. Stubborn residues can be soaked in hydrofluoric acid and rinsed.
Check the heating wire for oxidation and fracture every month, and apply vacuum silicone grease to the sealing ring to maintain lubrication.
periodic calibration
Check if the thermocouple is in good contact and measure the resistance with a multimeter, which should be between 10-50 Ω.
When the vacuum degree does not meet the standard, the airtightness should be tested in sections, with a focus on checking the corrugated tube interface and electrode seal.
Long term suspension management
Drain the cooling water to prevent pipeline freezing and cracking; The graphite base is calcined at high temperature once a month to remove surface carbides and improve thermal conductivity.
Establish equipment operation records, including temperature rise curves, gas ratios, deposition rates, and other data, to facilitate problem tracing.