Common failures and maintenance of CVD equipment
(L) the vacuum is on the high side, the vacuum gauge has indication (that is <133Pa), but the limit vacuum pressure can not draw the original set pressure. This situation may have three kinds of phenomena: the first is the vacuum system, there is a slow leak, the system leak through.
Reason and solution: the O seal ring of each interface is not clean or the joint nut is not tightened. We are familiar with the big furnace door, O type sealing ring is not installed or used for some time, O type sealing ring aging deformation affect sealing, at this time for a O type sealing ring can be solved;
(2) the second cases are abnormal vacuum indication, but the system leak detection is acceptable, the leakage velocity is less than 0.3Pa/min.
Causes and solutions: it is possible for the pressure sensing part is blocked, you can wash out, of course, also can not rule out the possibility of mechanical pumping rate decreased
(3) the third phenomenon is that the vacuum can not be pumped out after the cleaning of the tube,
Reasons and solutions: it may be a cold trap (particle trap), the bellows did not completely dry after cleaning, open the mechanical pump vacuum after the remaining water slowly gasification. Therefore, after cleaning, the bellows and the cold trap can be dried in the oven, and the oven temperature should be kept at 80 and 100.
B, mechanical pump vacuum, vacuum gauge no indication (ie pressure <133Pa).
Causes and solutions: for the import may not completely shut the door when the boat, at this time in the mouth can be heard "squeak" sound. When the door is closed, the phenomenon can be ruled out.
C, deposition rate slows down. Under normal circumstances, when the furnace temperature, gas flow and pressure, the reaction rate remained stable, but the actual work, we found that the deposition rate is sometimes slower, check the gas flow, temperature and working pressure were normal. This phenomenon is particularly common in the SiH2C12+NH3 system.
Reason and resolution: the SiH2C12 flow in the incoming reaction system is reduced, because of the excessive NH3, it is sometimes difficult to see from the work pressure. Apart from the SiH2C12 flow control valve (electromagnetic valve) or sensing part, from the small hole can see the phenomenon of local congestion, after cleaning rate can be restored.
D, not deposited. This phenomenon can appear in the deposition process of polycrystalline silicon thin films, because when the temperature of polysilicon deposition is 550 to 620 DEG C, sometimes due to overcurrent caused by the heating furnace heating power switch off when the temperature jump, the actual deposition has decreased to below 500 DEG C, the gas flow rate of abnormal deposition, not on the phenomenon.
In order to make the CVD equipment normally operate for a long time, in addition to the requirements of the operator, using the correct operation of equipment, adopt some effective methods to maintain good equipment, is the key to protect the normal operation of the CVD device, we can take the following measures:
(L) vacuum the CVD device as vacuum as possible. CVD equipment, according to the deposition process requirements, the process gas and reaction to produce by-products, generally have a strong corrosive. If
When the Si3N4 film is deposited, the residual gas will not be exhausted in time. It is likely to corrode the gas circuit interface, bellows, vacuum gauge, vacuum pump and so on. Therefore, after the Si3N4 film has been deposited, the pumping time of the vacuum pump is extended as far as possible to remove the residual gas as far as possible. If you don't use it for several days, turn on the vacuum pump once, so as to improve the use rate of the equipment.
(2) filling nitrogen in time. After the process has been completed, the quartz vessel in the furnace tube is provided with a deposited silicon wafer. It must be stored in a nitrogen rich environment to prevent oxidation and corrosion, so that it can be better preserved.
(3) regular replacement of vacuum pump oil. Although the vacuum system is equipped with a vacuum pump oil filter, it can keep the pump oil clean for a long time. But for the reaction system such as SiH2C12+NH3, the reaction by-products NH4CI white powder generated in the furnace mouth and tail ends of NH4CI in the reaction tube at the rear part of the corrugated tube, vacuum tube wall deposition is quite serious, and HCI and other harmful impurities at risk of being pumped to vacuum pump. The particles are continuously pumped into the vacuum pump, thickening the pump oil, blocking the pump oil filtration system, and affecting the normal operation of the equipment. Therefore, regular vacuum pump oil must be replaced.
(4) regular maintenance of electromagnetic valve. In order to prevent the vacuum pump oil return vacuum pipe, the electromagnetic valve is installed in the vacuum pump, the electromagnetic valve is a common fault, the solenoid valve due to the presence of a small amount of NH4CI powder, the O type electromagnetic valve seal sealing performance is reduced, resulting in the vacuum system there is a slow leak, the vacuum system the equipment can not keep the vacuum after the shutdown, only regular maintenance of solenoid valves, solenoid valve replacement after cleaning type O sealing rings in the vacuum system, can make the CVD equipment
in the film after deposition in a vacuum.