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Many semiconductor equipments require high vacuum, such as magnetron sputtering table, electron beam evaporation table, ICP, PECVD and other equipments. In a high vacuum environment, cleanliness is high and water vapor is rare. Some semiconductor equipment to be used in toxic or corrosive special gases, in the low leakage rate vacuum conditions, these gases are not easy to leak, the equipment can be timely pumped away from the unresponsive gases and gaseous reaction products, to ensure the safety of process personnel. However, with the increase in the number of production equipment, as well as new processes on the improvement of equipment requirements, vacuum failure increases.
1 vacuum pump
Semiconductor equipment commonly used vacuum pumps are rotary vane vacuum pumps,semiconductor testing Roots pumps, dry pumps, molecular pumps and cold pumps. Diffusion pump has been rarely used.
The rotary vane vacuum pump can be connected to N2 gas town to prevent the pumped gas from condensing in the pump oil; connected to the filter to filter the impurities in the pump oil; connected to the oil mist filter and automatic oil return device to reduce the oil loss. The rotary vane vacuum pump is divided into common type and anti-corrosion type. The oil used is also divided into common vacuum pump oil and anticorrosive vacuum pump oil, and these two kinds of oils can not be mixed.
The main function of Roots pump is to increase the pumping speed under low vacuum. Dry pumps are used more and more, which use a small amount of anticorrosive vacuum pump oil, but the pumping part does not contain oil.
Molecular pumps rely on high speed rotating vanes together with stationary vanes to pump away gases to produce a high vacuum. Cold pumps generate a high vacuum by generating a very low temperature of about 11 K in the cold head of the pump and adsorbing the gas in an adsorption trap. The cold pump consists of a cold pump and a high-efficiency He compressor.
2 Vacuum gauges and vacuum components
Common vacuum gauges are resistance vacuum gauge (Pirani vacuum gauge), thermocouple vacuum gauge,semiconductor failure analysis capacitance vacuum gauge, ionization vacuum gauge, cold cathode ionization vacuum gauge and full scale vacuum gauge. Among them, cold cathode ionization vacuum gauge is divided into three kinds: Penning gauge, magnetron gauge and anti-magnetron gauge.
Full-range vacuum gauge is a combination of low vacuum gauge and high vacuum gauge; resistance vacuum gauge range is wide, more commonly used; thermocouple vacuum gauge range is narrow, simple structure, not easy to be damaged; capacitance vacuum gauge measurement value is not affected by the type of gas; ionization vacuum gauge belongs to the high-vacuum gauge, it will be heated; cold cathode ionization vacuum gauge belongs to the high-vacuum gauge, not heated, easy to maintain; full-range vacuum gauge automatic range switching, easy to use.
Nowadays, most of the vacuum gauges have the probe head and signal processing circuits made together, which can improve the anti-interference ability and promote its miniaturization. Most probes are made of metal rather than glass, which makes them stronger and smaller. Vacuum gauge display controller is also required to miniaturize, some do the volume of 105 mm × 110 mm × 250 mm, the quality of 1.3 kg, with three connectors, each connector can be connected to the resistance vacuum gauge or cold cathode ionization vacuum gauge, etc., this intelligent vacuum gauge controller is very convenient to carry and use.
The sealing methods of vacuum valves are: retractable bellows, retractable laminated bellows, PTFE or PFA gaskets, rotary shaft seals, O-rings, etc. The sealing methods of vacuum valves are as follows Bellows seals have a relatively long life, but once a problem occurs it is very troublesome to repair and requires the use of a special laser welding machine, rotary actuators often use magnetic fluid seals. Vacuum chambers are connected with many fittings, common fittings are ISO-KF fittings, ISO fittings, CF fittings, VCR fittings, VCO fittings and ferrule fittings, etc. The leakage rate of each fitting is required to be 5%. The leakage rate of each joint is required to be 5×10-10 Pa-m3/s.
3 He mass spectrometer leak detector use
Semiconductor equipment vacuum system failure is generally divided into two categories: one is the failure of the vacuum pumping unit and measurement system, and the other is the vacuum system leakage. For the first type of failure,aotomatic prober testing the vacuum pump limit vacuum or replace the good vacuum gauge can be confirmed. For the second type of failure, leak testing is required. In the semiconductor equipment leak detection often use two methods: hydrostatic leak detection method and He mass spectrometry leak detection method. Hydrostatic leak detection method is to use the valve to separate the vacuum chamber and vacuum pumping unit, measuring the internal pressure changes. He mass spectrometry leak detection method is a little more complicated.
He mass spectrometry leak detector generally need to be taken to the site, the leak detector has a molecular pump, so the handling should be light. Often choose the leak detector high sensitivity way to leak detection, which is conducive to the protection of the molecular pump. The pumping capacity of the leak detector is limited, so it is often necessary for the equipment to pump a good vacuum. Vacuum pumping to 0.5~10Pa can be. Wait until the leakage rate shows stability or turns to decrease from stability before starting the leakage detection.
If it is necessary to operate the door valve, rough pumping valve, bleeder valve, etc. in the process of leakage detection, it is necessary to let the leakage detector stop leakage detection and select the leakage port without bleeder, so as to avoid damage to the leakage detector caused by the sudden entry of a large amount of gas into the vacuum chamber. The door valve and roughing valve should be closed after the vacuum is pumped to avoid the shunt leading to the measured value of the leakage rate being smaller than the actual value. It is better to stop the molecular and mechanical pumps on the equipment so as to avoid their interference; the equipment with cold pumps should stop the cold pumps in order to detect the leakage thoroughly.
With the vacuum method to detect the leakage rate of double seal structure products, there is often a slow increase in the leakage rate of the phenomenon occurs, so in the leakage detection process should pay attention to this point. In addition, the requirement of He bag does not leak, generally require the spray He flow is small, which is conducive to confirm the location of the leakage point. However, there are special cases, need to spray more He in some He is not easy to reach the place, in order to avoid leakage detection. Leak detection when the addition of the bellows can not detect leaks, leaks are found after the second confirmation, leak repair should be carried out again after the leak detection confirmation.
4 Physical deposition equipment leak detection
Physical deposition equipment has magnetron sputtering stage and electron beam evaporation stage and other equipment. Now take the magnetron sputtering table as an example to illustrate. As shown in the figure below, when the equipment is normal, the vacuum can be pumped to 8×10-5Pa in 2h, and the pressure of the vacuum chamber rises to 5Pa after closing the door valve and not pumping the vacuum chamber for 14h. After the failure, the vacuum can only be pumped to 3×10-4Pa in 2h, and the pressure of the vacuum chamber rises to 1.4×102Pa after closing the door valve and not pumping the vacuum chamber for 14h and the quality of the products is affected.
First of all, hydrostatic leakage detection was carried out on the equipment. After the vacuum chamber is pumped to 9×10-4Pa, 3min hydrostatic leakage check is carried out, the pressure of the vacuum chamber rises to 7.3×10-3Pa/min, and the volume of the vacuum chamber is about 0.3m3. The deviation of the readings of the capacitance vacuum gauge and the full-range vacuum gauge of this equipment is not large, and the probability of the two gauges failing at the same time is very small. Therefore, equipment leakage is considered first. Leak detection with He leak detector, found that the film thickness crystal connector leakage rate of 4 × 10-9 Pa-m3 / s, extend the time of spraying He, the leakage rate of 1 × 10-8 Pa-m3 / s. Then stopped the cold pump, testing the rough pumping valve, bleeder valve, the main gas valve. Then the cold pump was allowed to start the regeneration program to warm up to room temperature and then stop the regeneration. Opened the N2 charging valve of the cold pump and sprayed He to test the gate valve, and found that the leakage rate was 1.3×10-8Pa-m3/s.
Finally, the leak detector was connected to the cold pump, and the piping valves on the cold pump were leak detected. Next, remove the crystal connector, found that it has a dirty seal, cleaned and coated with a thin layer of vacuum grease. After installing back and then check, still leaking, so remove the crystal connector to replace a plug, and then leak test to confirm normal. Remove the valve plate, found that the valve plate on the sealing ring and the valve body sealing surface has a lot of metal debris, cleaned up and installed back, the leakage test is normal. Restart the equipment and the cold pump to confirm that the equipment vacuum has returned to normal. Now wait for the vacuum chamber pumped to 9 × 10-4Pa, and then do 3min hydrostatic leakage test, the vacuum chamber pressure rise rate of 4.3 × 10-3Pa / min. Magnetron sputtering table common vacuum faults are dirty seals, valve bellows leakage and vacuum gauge is not allowed. Electron beam evaporation stage in addition to the above failures, there are crucible water-cooled seals leakage and high-pressure electrode leakage and other failures.
5 chemical deposition and etching equipment leakage detection
This kind of equipment has PECVD, RIE, ICP and so on. Often involved in special gases and special reactants, the vacuum chamber is relatively small, often using molecular pumps to pump high vacuum. Now take an ICP as an example to illustrate.
After the failure, after 3min hydrostatic leakage check, the pressure rise rate of the vacuum chamber exceeded the permissible value of 1.3×10-1Pa/min, and reached 10Pa/min. Leakage check was carried out by He leakage tester, and it was found that the stacked piece of retractable bellows under the thimble of the vacuum chamber was leaking, so the bellows was removed, and was installed back after repairing, and leakage check found that the place had been restored to normal. However, when starting the equipment for hydrostatic leakage testing, it was found that the pressure rise rate of the vacuum chamber was 1Pa/min, which was still greater than the permissible value. Continuing the leakage check, the molecular pump was stopped without stopping the dry pump, and the leakage rate of the door seal was found to be 1.4×10-8Pa-m3/s. After stopping the dry pump, the pressure in the vacuum chamber rose from 6.5Pa to 30Pa very quickly, and it was obvious that there was a leakage of gas into the vacuum chamber through the vacuum pipeline.
Opened the rough pumping valve connected to the dry pump for leakage checking, the leakage rate was 2×10-8 Pa-m3/s, so the valve was repaired, but then the leakage checking did not pass, and the valve could only be replaced. The cleaning valve connected to the molecular pump was removed, and spray He checked valve 1, and found that the leakage rate of valve 1 was 5×10-8 Pa-m3/s. The cleaning valve was put back in place, and the valve was repaired by removing the valve and putting it back in place, and the valve was restored to normal. Then pump the vacuum chamber and molecular pump chamber with a dry pump in the repair mode, open the door valve 1 under the condition of ensuring the pressure difference between the two sides of the door valve <1×103Pa, so that the vacuum chamber and the molecular pump chamber are connected, test the pipelines and valves on the molecular pump, and no new problems were found.
Finally repair the leak at the door seal. Replace the door seal seal, the leakage rate did not improve. Carefully check the structure at the door seal, found that the upper cover has a screw protruding downward, resulting in a bad seal. However, it was difficult to remove the screw as it required loosening the top cover. The top cover is connected to the water-cooling pipe, which limits the range of movement of the top cover; the right side of the top cover is connected to the upper plane of the vacuum chamber through a rotating shaft, and at the same time the top cover and the lower part of the vacuum chamber are held together by an elastic rod with high elasticity, which makes it difficult to dismantle and install the door seal, as shown in the figure below. Later it was found that when the top cover was opened, the elastic force of the elastic rod became very small, which made it easy to disassemble and install the elastic rod; two screws were exposed after loosening the two gear plates, and loosening them loosened the rotor shaft. In this way, loosen the upper cover, tighten the downward screws upward, and then install the upper cover, the door seal back to normal. Start the unit to confirm that the fault has been repaired.
Semiconductor equipment vacuum part has many parts, if a part of the leakage rate is large, it is easy to lead to high vacuum pumping does not go up. Most of the difficult vacuum failures of semiconductor equipment are caused by micro-leakage, resulting in high vacuum pumping. The difficulty of vacuum leakage detection is to pay attention to the detailed part of operation and be patient. In addition, it is necessary to leave a margin when choosing a domestic high vacuum gauge, otherwise it will not be able to show the desired high vacuum.
