Chapter 20: Vacuum coating (top)

After 　　 spin coating was completed, Xu Qiu approached Chen Wanqing and asked about the next experimental operation.
Sister 　　 took out the experiment notebook and explained the teaching while writing and drawing:
　　 "What we finally want to get is a multi-layer structure solar cell device. For example, the system we are doing now, the positive structure is: PSS/P3HT:PC[60]BM:PC[70]BM/Ca/Al.
　　 has a six-layer structure, separated by "/" between layers, and ":" means that the layer is a blend of two or more substances.
　　 Then, the work you have done these days is:
　　First, clean the glass substrate with ITO pattern to obtain a part;
　　 Then, spin-coating the PEDOT:PSS solution and the effective layer to obtain the PEDOT:PSS/P3HT:PC[60]BM:PC[70]BM part;
　　 The last step, which is the next step, is to use a vacuum coating method to evaporate calcium and aluminum onto the substrate to obtain the Ca/Al part.
　　Vacuum coating method, the principle is to heat the target material to vaporize it under vacuum conditions. The gaseous molecules formed by the target material will move in the chamber, and finally uniformly deposit on the sample surface to form a thin film.
　　 There are two heating methods we use, one is beam source furnace heating, and the other is tungsten wire heating.
The operation of 　　 evaporation is cumbersome and there are many details that need attention, so I will personally guide you. "
　　 "Okay, senior sister." Xu Qiu said.
　　…………
　　 The two of them took precautions and entered the laboratory.
　　 Xu Qiu first took the spin-coated substrate out of the glove box, and then quickly transferred it to the glove box equipped with an evaporation device.
　　 There are three rubber gloves outside the glove box, and only one person can enter at the same time.
　　 So, Xu Qiu entered the box while the senior sister was outside.
　　 There are mainly two large-scale equipments in the box, and the evaporation device on the left.
　　The cabin body of the vapor deposition cabin is made of heavy steel plate, and the cabin doors are connected to the cabin body by rails.
　　 Xu Qiu pushed the hatch door to the right, pushing it quite heavy.
　　 He curiously said: "Senior sister, this equipment is not cheap, right."
　　"The whole set of equipment is about 200,000 yuan, including the evaporation chamber, molecular pump, circulating water system, and main console. It was ordered by a company specializing in vacuum equipment in Shenyang.
　　 Their company is far away from here, so if it breaks, it will be troublesome to repair. Last time the circulating water failed, they came to repair it and the toll cost was 5,000. "Chen Wanqing.
　　 "How did the senior sister know so clearly?" Xu Qiu asked in confusion.
"Because the school wants to count the fixed assets of the laboratory, any price over 1,000 yuan must be reported. Although the laboratory is under the management of Teacher Wei, the ownership belongs to the state, because the scientific research funds applied for are provided by the state. Unless the boss himself If you pay for your pockets or the company pays for it, then you will say otherwise." Chen Wanqing said.
　　 Xu Qiu nodded and began to look inside the cabin.
　　 There are four cylindrical furnaces underneath, which should be beam source furnaces.
　　 There are two metal platforms next to the four beam source furnaces. Each platform has a metal plate, about six centimeters long, three centimeters wide, and one centimeter thick. The metal plates are connected to the platform by hexagonal screws with a certain gap in the middle.
　　 "Sister, what is this for?" Xu Qiu asked, pointing to the platform.
"This is an electric current heating device. Place a basket made of tungsten wire between two platforms, press the two ends of the tungsten basket with a metal plate, and apply current to heat the tungsten basket. It can reach a high temperature and make the inside The target material is vaporized and evaporated." Chen Wanqing said.
　　 Xu Qiu continued to look at the cabin, and there was a probe-shaped object in the middle part, hanging above the beam source furnace and the platform like a chandelier.
　　Senior sister followed Xu Qiu's gaze and took the initiative to introduce:
"This is a crystal oscillator device. The probe is equipped with a crystal oscillator to detect the thickness of the deposited film in real time. Its position must not be changed because the current parameters have been calibrated. If you move its position, the film The test result of the thickness is not standard. In addition, the crystal oscillator has a life span, so it is necessary to replace the crystal oscillator regularly and recalibrate the thickness."
　　 The uppermost part of the cabin is a large circular metal baffle and a rotating sample stage.
　　 "The above one must be the sample stage, why is a metal baffle installed below?" Xu Qiu asked.
"This metal baffle is called the sample baffle. When it is open, it can effectively prevent gas molecules from depositing on the surface of the sample. Therefore, we can use it to control the start and end time of evaporation to obtain a precise thickness." Chen Wanqing said.
　　 After understanding the situation in the cabin, Xu Qiu began to make preparations before evaporation.
　　 The device structures of the two batches of substrates are different, and the vapor deposition needs to be divided into two.
　　 The first batch is of normal structure, that is, evaporation of calcium and aluminum.
　　 Xu Qiu first filled the tungsten basket with 99.995% pure aluminum ingots, and then asked the senior sister to help open the baffle of the calcium beam source furnace.
　　The switch of the baffle is numerically controlled and needs to be operated on the master console outside the glove box.
　　 After opening the baffle, he took out the ceramic crucible inside the beam source furnace, poured out the residue left after the last use, and added two spoons of new 99.995% pure calcium powder.
　　Ceramic crucible is special, can withstand at least 1000 degrees Celsius high temperature, and is very stable, will not react with the target material and produce impurities.
After 　　 was finished, he asked the senior sister to close the baffle of the beam source furnace.
　　 Finally, he placed the substrates face down on the sample holder, and then put the sample holder back on the sample table.
　　 "Sister, UU reading www.uukanshu.com is okay, can you close the hatch." Xu Qiu looked at Chen Wanqing.
　　 "Yeah." Chen Wanqing nodded.
　　 Xu Qiu pushed the hatch back to its original position from right to left, and then turned the two knobs on the top and bottom of the hatch until it could not be turned.
　　……
　　 Xu Qiu left the glove box and came to the main console with the senior, because the rest of the operation was mainly done in the main console.
　　 The main console is nearly two meters high and is composed of more than a dozen modules, with a total of more than 30 control buttons.
　　 "There are operating instructions next to it, just follow the instructions strictly." Chen Wanqing said.
　　 Xu Qiu picked up the "Instructions for Vacuum Coater" and looked through it. There were only two pages of A4 paper, not as many as expected.
　　 On the surface, he was reading the manual, but he was looking at the system in his mind.
　　 The system has copied the senior sister’s skills, and you can see the details of each step of the operation, so the text version of the manual has little meaning.
　　 "I'm finished reading." Xu Qiu said.
　　 "So fast?" Chen Wanqing said: "Okay, then you can do it. I will remind you if there is any problem."
　　 The first step is to turn on the circulating water system and air pump.
　　 The former is used to cool the molecular pump, while the latter is used to push the sample baffle.
　　 Xu Qiu found the circulating water device behind the main console, pressed the green start button, and heard the buzzing sound of the instrument. If you listened carefully, there was still water flowing.
　　 Then, he walked to the air pump.
　　 There is an orange-red bottle cap-sized switch on the air pump, which needs to be pulled up to start the machine.
　　 Xu Qiu tried to pull up, but the switch didn’t move. He didn’t dare to use too much force, so he said:
　　 "Sister, how do you do it."
　　 "Hold it hard."
"boom!"