Chapter 21: Vacuum coating (below)

　　 There was a loud noise from the air pump, followed by a "boom boom" noise.
　　 Xu Qiu was shocked and shrank back.
　　 After waiting for a while, he felt that there was no danger, so he went to check the air pump.
　　 "It looks like there is no problem." He said to the senior sister.
　　 "It is indeed okay, this is normal. Now the engine is passing the crankshaft, driving the piston to pump air into the air cylinder, and when it is full, it will automatically stop."
　　 Chen Wanqing tried to stretch the smile on her face, but she didn't succeed and smiled.
　　 "Senior sister, you did it on purpose." Xu Qiu looked indignant.
　　 "Why, I am such a person." Chen Wanqing smiled.
　　 Xu Qiu shook his head and returned to the main console to continue the experiment.
　　 He turned on the master control switch, and the digital display screen of the film thickness meter lights up.
　　 Xu Qiu first checks whether the parameters of the film thickness meter are set correctly, including the target name, density and Z factor.
The principle of the 　　 film thickness meter is not to directly measure the film thickness, but to calculate it through an indirect method.
　　In the evaporation process, when the target molecule reaches the crystal oscillator, an electrical signal will be generated. After fitting calculation, the electrical signal can be converted into the evaporation rate, and finally the rate and time are multiplied to obtain the film thickness.
　　 After adjusting the film thickness meter, the digital display screen displays:
　　The evaporation material is calcium, the rate is 0.00 angstroms per second, and the film thickness is 0.00 angstroms.
　　 At the same time, Xu Qiu observed that there are two barometers on the main console, which can monitor the pressure in the evaporation chamber in real time.
　　 One of the indications is an atmospheric pressure, that is, 1.0E5 Pa, and the other is in a non-working state.
　　 "Why do you want to install two barometers?" Xu Qiu wondered.
　　 "The pressure measurement ranges of the two are different, the former is about 0.1 to 10,000 Pa, and the latter is about ten to the negative sixth power to 1 Pa." Chen Wanqing said, and then added:
　　 "The preparations are ready, let's start vacuuming."
　　 Xu Qiu nodded, pressed the start button of the mechanical pump, and at the same time opened the ultra-vacuum flapper valve, another roar came.
　　 "The noise of the evaporation operation is a bit loud." Xu Qiu, who was used to the quiet experimental environment before, couldn't help but complain.
　　 "Yes, but you will get used to it gradually." Chen Wanqing said.
　　 After the mechanical pump is started, the barometer's indication decreases rapidly.
"From 1.0E5, it quickly changed to 3.2E4, then 8.9E3, until about 1E3 Pa, the descending speed began to slow down.
　　 After about two minutes, the pressure finally dropped below 20 Pa. Xu Qiu closed the ultra-vacuum baffle valve and turned on the molecular pump.
　　 The rotational speed of the molecular pump has to be gradually accelerated from 0 to 27000r.p.m. before it can work normally, which takes about 10 minutes.
　　 After the molecular pump was running smoothly, Xu Qiu opened the beam source furnace baffle, and then activated the beam source furnace's heating control device.
The screen of the 　　 device displays the current temperature and set temperature of the beam source furnace, which are 27 and 30 degrees Celsius respectively.
　　 He opened the setting interface.
　　 This screen uses the "day" font display method on the calculator, which is mainly used for digital display, so the displayed letters are very abstract.
Fortunately, 　　 is a commonly used word. After Xu Qiu spent some time figuring out the meaning of each parameter, he set the heating program manually:
　　SP130
　　RATE30
　　TIME60
　　SP2400
　　RATE30
　　TIME3
　　SP3520
　　RATE20
　　TIME100
　　In the first stage, the temperature rises to 30 degrees Celsius at a rate of 30 degrees Celsius per minute and waits for 60 minutes;
　　 In the second stage, it will rise to 400 degrees Celsius at a rate of 30 degrees Celsius per minute, and wait for 3 minutes;
　　 In the third stage, the temperature rises to 520 degrees Celsius at a rate of 20 degrees Celsius per minute and waits for 100 minutes.
　　 After confirming that it is correct, he long presses the start button to start the program.
　　 The temperature program needs more than an hour to run.
　　 During this period, Xu Qiu asked her senior sister about the working principle of the vacuum system.
Chen Wanqing explained: "Mechanical pumps can only reduce the pressure in the cabin to a few tenths of a pascal at most, and molecular pumps must be used to reduce the pressure to the order of ten minus five square pascals, so as to achieve the lowest vacuum required for the evaporation experiment. Degree requirements.
　　 Molecular pump can only be used under low pressure. Therefore, when the pressure is higher than 20 Pa, an ultra-vacuum baffle valve is used to block the connection between the molecular pump and the vapor deposition chamber; when the pressure is lower than 20 Pa, it is closed, and the molecular pump is connected to the vapor deposition chamber.
After the 　　 molecular pump is started, it will take a long time to make the pressure in the evaporation chamber reach 1E-5 level.
　　 This time is between half an hour and one and a half hours.
　　 If the vacuum cannot be reached after one and a half hours, there are usually two situations.
　　 One is that the airtightness of the system is not good, for example, when the door is closed, a plastic bag is clamped in the door gap;
　　 Another situation is that there are too many evaporation residues in the cabin and need to be cleaned. "
　　 Although there are video materials in the system for Xu Qiu to study, he thinks it is better to listen to the senior sister's explanation.
　　 is mainly two people standing together, it is quite embarrassing to not interact all the time.
　　……
after an hour.
　　The vacuum gauge indicates 5.2E-5 Pa, and the heating program has entered the second stage, everything is normal.
　　 Twelve minutes later.
　　The temperature reading reaches 400 degrees Celsius, the real-time evaporation rate displayed by the film thickness meter fluctuates between -0.01 and 0.01 angstroms per second, and the film thickness display is still 0.00 angstroms.
　　 Three minutes later.
　　The temperature indication continued to increase until around 480 degrees Celsius, and the evaporation rate began to fluctuate between 0.00 and 0.03 angstroms per second.
　　 When the temperature reaches 520 degrees Celsius, the evaporation rate is maintained at 0.20 to 0.30 angstroms per second.
　　 Xu Qiu first turned on the sample stage to rotate. After waiting for about ten seconds, he opened the sample baffle and reset the film thickness counter of the film thickness meter to zero.
　　 Calcium is deposited to a thickness of 10 nanometers, which is 100 angstroms.
　　……
　　 When the film thickness gauge reached 100 angstroms, Xu Qiu quickly closed the sample baffle.
　　 Then, he turned off the Shuyuan Furnace's heating numerical control device and let the Shuyuan Furnace cool down naturally.
　　 Finally, change the parameters of the film thickness meter to that of aluminum.
　　……
　　 half an hour later.
　　The temperature of the beam source furnace was reduced to 77 degrees Celsius.
　　 Xu Qiu closed the baffle of the calcium beam source furnace and turned on the current heating device.
　　This heating device is very simple, that is, connect the power supply, tungsten basket, potentiometer (similar to a sliding rheostat), fuse, and ammeter together. By adjusting the potentiometer, the current in the circuit can be changed.
　　 Xu Qiu slowly twisted the potentiometer to gradually increase the ammeter reading from 0 to 18 amperes.
　　 When the current reaches 16 amps, the evaporation rate on the film thickness gauge begins to show an indication.
　　 After the current reached 18 amps, Xu Qiu waited for a few seconds, then opened the sample baffle at the same time and cleared the film thickness counter of the film thickness meter.
　　 The evaporation rate first increased rapidly from 0.2, 0.3 to 3.0, then quickly dropped to 1.8, and then slowly decreased to 1.7, 1.6 angstroms per second...
　　The reading of the ammeter will also change over time, up and down.
　　 Whenever its deviation from 18 exceeds 1, Xu Qiu adjusts it to 18.
　　The thickness of aluminum is required to be 100 nanometers, which is 1000 angstroms.
　　……
　　 When the film thickness gauge reached 1000 angstroms, Xu Qiu quickly pressed the sample baffle.
　　 Then slowly twist the potentiometer to reset the current to zero.
　　 Then close the ultra-vacuum flapper valve and stop the molecular pump.
　　 After waiting for ten minutes, the molecular pump speed dropped from 27000r.p.m. to 0, and the switch was turned off.
　　 Finally, turn off the mechanical pump and turn off the main console.
　　…………
　　 "It's finally over!" Xu Qiu sighed with emotion ~EbookFREE.me~.
　　 "With so many operations, there are no mistakes, it's amazing!" Chen Wanqing exclaimed.
　　 "This is all taught by my senior sister." Xu Qiu said.
　　 "Okay, don't be humble, I know your talent for scientific research.
　　Think about how I learned vapor deposition at the beginning, but it caused Teacher Wei to have a headache. He either forgot to turn on the air pump or the baffle, and even forgot to put the substrate once. "Chen Wanqing said.
　　 Xu Qiu couldn't hold back a smile when he heard the last sentence.
　　 Seeing the senior sister staring at him, he quickly suppressed his smile and walked towards the glove box with a serious expression.
　　 Entering the glove box, Xu Qiu unscrewed the knobs on the upper and lower hatch and started to pull the hatch.
　　咦, why can't the hatch be pulled down?
　　After pondering for a while, Xu Qiu understood, because after the evaporation, the inside of the cabin was still in a vacuum state.
　　 So he turned to look at the senior sister, but she didn't seem to have the intention to answer.
　　 Such a grudge.
　　 He had to ask: "Senior sister, how do you do this?"
　　 Chen Wanqing pointed to the side of the glove box and said:
　　 "There is a valve connected to the nitrogen cylinder over there, and the vapor deposition chamber can be filled with nitrogen."
　　 Xu Qiu walked over and gently opened the valve, and the sound of "hissing" airflow came.
　　 10 seconds later.
　　 20 seconds later.
　　 30 seconds later.
　　 Nothing happened.
　　 "Senior sister, when should I stop?" Xu Qiu couldn't help asking.
　　 "Continue to deflate." Chen Wanqing said blankly.
"Oh."
　　 40 seconds later.
　　50 seconds later.
　　 60 seconds later, just when Xu Qiu was about to ask another question.
"boom!"