I Have a Research Support System

Chapter 21 Vacuum Coating (Part 2)

There was a loud bang from the air pump, followed by a bang bang bang.

Xu Qiu was startled and shrank back a little.

After waiting for a while, he felt that there was no danger, so he stepped forward to check the air pump.

"It doesn't look like a problem." He said to the senior sister.

"It's really no problem, this is normal. Now the engine is driving the piston to pump air into the air storage tank through the crankshaft. When the air storage is full, it will automatically stop."

Chen Wanqing tried to hold back the smile on her face, but failed, she still laughed.

"Senior sister, you did it on purpose." Xu Qiu made an indignant look.

"How could it be? I'm that kind of person." Chen Wanqing said with a smile.

Xu Qiu shook his head, returned to the main console, and continued the experiment.

He turned on the master control switch, and the digital display screen of the film thickness gauge lit up.

Xu Qiu first checked whether the parameters of the film thickness meter were set correctly, including target name, density and Z factor, etc.

The principle of the film thickness meter is not to directly measure the film thickness, but to calculate it by indirect method.

During the evaporation process, when the target molecules reach 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 film thickness can be obtained by multiplying the rate and time.

After adjusting the film thickness gauge, 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 are you installing 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 minus sixth power to 1 Pa." Chen Wanqing said, and then added:

"The preparations are all done, let's start vacuuming."

Xu Qiu nodded, pressed the start button of the mechanical pump, and opened the ultra-vacuum damper valve at the same time, and there was another roar.

"The noise of the evaporation operation is a bit loud." Xu Qiu, who was used to the quiet experimental environment before, couldn't help complaining.

"Yes, but you will get used to it gradually." Chen Wanqing said.

After the mechanical pump is started, the reading on the barometer decreases rapidly.

From 1.0E5, it quickly changed to 3.2E4, then 8.9E3, until it was around 1E3 Pa, and the descent speed began to slow down.

After about two minutes, the pressure finally dropped below 20 Pa. Xu Qiu closed the ultra-vacuum damper valve and turned on the molecular pump.

The speed of the molecular pump must 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 baffle of the beam source furnace, and then activated the temperature rise control device of the beam source furnace.

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 settings interface.

This screen uses the "day" display method on the calculator, which is mainly used for digital display, so the displayed letters are very abstract.

Fortunately, they are all commonly used words. After Xu Qiu took some time to figure out the meaning of each parameter, he manually set the heating program:

SP1 30

RATE 30

TIME 60

SP2 400

RATE 30

TIME 3

SP3 520

RATE 20

TIME 100

In the first stage, rise to 30 degrees Celsius at a rate of 30 degrees Celsius per minute, and wait for 60 minutes;

In the second stage, rise to 400 degrees Celsius at a rate of 30 degrees Celsius per minute, and wait for 3 minutes;

In the third stage, rise to 520 degrees Celsius at a rate of 20 degrees Celsius per minute, and wait for 100 minutes.

After confirming that it was correct, he long pressed the start button to start the program.

The heating program needs to run for more than an hour.

During this period, Xu Qiu asked the senior sister about the working principle of the vacuum system.

Chen Wanqing explained: "The mechanical pump can only reduce the pressure in the cabin to a few tenths of Pa at most, and the molecular pump must be used to reduce the pressure to the order of ten minus five Pa, so as to achieve the minimum vacuum required for the evaporation experiment. degree requirements.

Molecular pumps can only be used at low pressures. Therefore, when the pressure is higher than 20 Pa, the ultra-vacuum baffle valve is used to block the connection between the molecular pump and the evaporation chamber; when the pressure is lower than 20 Pa, it is closed, and then the molecular pump and the evaporation chamber are connected.

After the molecular pump is started, it will take a long time to make the pressure in the evaporation chamber reach the 1E-5 level.

This time is between half an hour and one and a half hours.

If this degree of vacuum cannot be reached after an hour and a half, there are usually two situations.

One is that the airtightness of the system is not good, for example, when closing the hatch, a plastic bag is caught between the door;

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.

The main reason is that two people stand together, and it's quite embarrassing if they don't interact all the time.

...

After one hour.

The vacuum gauge reached 5.2E-5 Pa, and the heating program entered the second stage, and everything was normal.

Twelve minutes later.

The temperature display 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 reading continued to increase until around 480°C, and the deposition 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, and after waiting for about ten seconds, opened the sample baffle at the same time and reset the film thickness counter of the film thickness meter to zero.

Calcium should be evaporated to a thickness of 10 nanometers, that is, 100 Angstroms.

...

When the film thickness gauge reached 100 angstroms, Xu Qiu quickly closed the sample baffle.

Then, he turned off the numerical control device for heating the beam source furnace, allowing the beam source furnace to cool down naturally.

Finally, change the parameters of the film thickness meter to the parameters of aluminum.

...

half an hour later.

The temperature of the beam source furnace was lowered 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. It is to connect a power supply, a tungsten basket, a potentiometer (similar to a sliding rheostat), a fuse, and an ammeter. By adjusting the potentiometer, the current in the circuit can be changed.

Xu Qiu slowly turned the knob of 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 meter begins to show.

After the current reached 18 amps, Xu Qiu waited for a few seconds, then simultaneously opened the sample shutter 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 fell back to 1.8, and then slowly dropped to 1.7, 1.6 Angstroms per second...

The indication of the galvanometer will also change with time, up and down.

Whenever its deviation from 18 exceeds 1, Xu Qiu adjusts it to 18.

The thickness requirement of aluminum is 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 return the current to zero.

Then close the ultra-vacuum damper valve and stop the molecular pump.

After waiting for ten minutes, the molecular pump speed drops from 27000r.p.m. to 0, and its switch is turned off.

Finally, turn off the mechanical pump and turn off the master console.

…………

"It's finally over!" Xu Qiu sighed with emotion.

"With so many operations, there are actually zero mistakes, amazing!" Chen Wanqing exclaimed.

"This is all taught by senior sister." Xu Qiu said.

"Okay, don't be humble, I know your scientific talent well.

Think about it when I first learned evaporation, but it caused Mr. Wei a lot of headaches. Either I forgot to turn on the air pump, or I forgot to turn on the baffle, and even once I forgot to put the substrate. "Chen Wanqing said.

Hearing the last sentence, Xu Qiu couldn't help laughing.

Seeing his senior staring at him, he quickly suppressed his smile and walked towards the glove box with a serious expression.

After entering the glove box, Xu Qiu turned the upper and lower knobs of the hatch and began to pull the hatch.

Hey, why can't the hatch be pulled down?

After pondering for a while, Xu Qiu understood, because after the vapor deposition is over, the interior of the cabin is still in a vacuum state.

So he turned to look at the senior, but she didn't seem to take the initiative to answer.

So vengeful.

He had no choice but 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 over there that connects to the nitrogen cylinder, which can be used to fill the evaporation chamber with nitrogen."

Xu Qiu walked over, gently opened the valve, and the sound of "hissing" air flow came.

10 seconds later.