Chapter 182 How to make a single crystal (3k)
Duan Gong took the phone again and smiled at Gao Zhendong: "Director Gao, I won't say anything else. I'm bothering you again. Don't worry. I promise that whenever you have a list of graphite components, I will personally keep an eye on it every time.”
This is a good thing, as it can ensure the source quality of single crystal furnace graphite components to the greatest extent.
Confidential communication resources are still very precious. After finishing the matter and wishing each other new year again, we hung up the call.
As for other issues in the production of graphite materials, the Carbon Research Institute did not ask, and Gao Zhendong could not take the initiative to say. Firstly, maybe their choice is better, and secondly, there is a confidentiality rule. Well, even technical consultants cannot casually ask about topics other than the information provided by the other party.
Look at the calendar, New Year's Eve is just two days away.
Gao Zhendong came out of the confidential room and did not go back to the office. Instead, he went to the single crystal furnace laboratory.
Yu Yuncheng is in charge of the specific affairs here.
Having this person with a professional background, Gao Zhendong is also relieved. He is ahead in ideas and principles, and the specific details are not necessarily better than Yu Yuncheng.
Yu Yuncheng is responsible for the specific landing process and is more suitable than him.
Seeing Gao Zhendong coming, Yu Yuncheng also came over. He happened to have some questions he had accumulated and wanted to ask: "Director Gao, are you here?"
Gao Zhendong smiled and said: "Well, Yu Gong, what's going on now?" How's it going?"
Yu Yuncheng is also in a good mood: "It's going relatively smoothly. I'm pretending one by one and adjusting one by one."
At this point, he followed the trend. He raised the questions in his mind.
"Director Gao, from a principle analysis, the material purity of the zone melting method is higher than that of the Czochralski method. Why don't we directly use the zone melting method."
He was not very comfortable asking this question at first. It involved a principle and route issue. Seeing how complete the design of Gao Zhendong's single crystal furnace was, asking this question at first felt like a complete overthrow.
Gao Zhendong smiled and said: “In addition to the Czochralski method and zone melting method we are doing now, there are many ways to make silicon single crystal, such as the pedestal method, flake single crystal growth, and vapor phase growth. , ingot casting method, liquid phase epitaxy, etc.”
Hearing Gao Zhendong’s words, Yu Yuncheng, who is already a professional in silicon single crystal production, opened his mouth. What Director Gao said is quite remarkable. Some of them have never heard of it at all. Just this sentence is enough for him to ponder for several years.
“There are so many ways?” He looked a little silly.
Gao Zhendong nodded: "Yes, but these methods have problems of one kind or another. In general, the semiconductor materials used in electronic technology, in my opinion, are the most suitable for quite some time. It’s also the Czochralski method we’re working on and the zone melting method you mentioned.”
In fact, even decades later, the production methods of silicon single crystals for semiconductors are still dominated by these two methods, of which the Czochralski method accounts for about 75% of the output.
Hearing Gao Zhendong confirm his idea, Yu Yuncheng felt a little happy.
Then Gao Zhendong told him why he did not do the zone melting method at the beginning: "But from the two methods, the one with the widest adaptability, the easiest way to make the crystal diameter larger, and the simpler technology is "Czochralski method."
Yu Yuncheng knows something about the zone melting method, but he does not understand the principle and specific implementation method of the zone melting method. He is probably famous but has never met.
"Director Gao, what is the specific area melting method?"
Gao Zhendong simply introduced the principles of the zone melting method to Yu Yuncheng.
To put it simply, the Czochralski method is to burn silicon in a pot and then pull the crystal upward.
The zone melting method is to lift the silicon rod, burn the lower end, and then pull the crystal downward.
Yu Yuncheng was a little surprised when he heard this: "Ah, that's it. It seems to be more difficult to control."
As expected of someone who did this, he understood it as soon as he heard it. Gao Zhendong smiled and said: "Yes. , the molten silicon liquid in this method is mainly maintained by surface tension, so it is more difficult to make the diameter larger than the Czochralski method. At the same time, the controllability of the entire crystal pulling process is poor, which can easily lead to crystal structure defects.”
Yu Yuncheng understood: "Well, it seems that the selection of technical routes cannot rely on a single indicator, but must be comprehensively considered."
Gao Zhendong smiled and said: "That's right, for now, Czochralski method Its shortcomings can be compensated or weakened through design means, such as adding a quartz inner crucible, but its benefits are real. We are not engaged in theoretical research. Theoretical research can only focus on the high point, we are engaged in application. For research, you still need to look around. "
Yu Yuncheng understood more: "Ah, I was wondering why I put a layer of quartz crucible in the graphite crucible. It turns out that I didn't think it through. " Gao Zhendong said: "For our current needs, the advantages of the zone melting method are actually not used very much, but the disadvantages are real. The Czochralski method has high production efficiency and low difficulty in automated production technology. , it is easier to control the doping concentration, and it is easier to prepare large-diameter single crystals, which are what we urgently need now.”
Single crystals used in semiconductor devices are inherently doped. One of the commonly used processes, at this point, Czochralski is much more convenient than zone melting.
After finishing speaking, he added: "Wait until Zhila has something to look at before doing district melting. After all, district melting also has its benefits."
Yu Yuncheng was convinced by Gao Zhendong's class and came here. Sure enough, I came to the right place. Not only did I learn technology, I also learned the ideas of scientific research.
So he was not embarrassed at all to learn from Gao Zhendong. If he didn't take advantage of Director Gao's free time to pick up more things, Director Gao's visit would not have been in vain.
"Director Gao, in my opinion, as long as the heating temperature of the crucible is stable, the thermal field is stable. The heating temperature of the crucible can be controlled by the power supply, and the pulling rotation and height of the crystal can be controlled by Why do we need to add complex lifting and rotation controls to the seed crystal side? Doesn’t this greatly increase the complexity of the system?"
Gao Zhendong heard this and understood that he was serious. After thinking deeply about the functions and roles of each subsystem he mentioned in the system, I still mainly rely on experience to think about problems and lack certain theoretical support.
It is not easy for some people to clearly distinguish the functions and roles of subsystems.
To put it simply, function refers to what this subsystem can do.
The function refers to the function of this subsystem and what benefits or impact it can bring to the entire system.
The former is the cause and the latter is the effect.
Sometimes some people tend to fall into the worship of functions. The more functions, the better, and the more complex the functions, the better. As for what role it can play, is it beneficial to the system, or is it necessary to pay for this benefit? I have never thought about or thought about whether such a high price is worth it.
Gao Zhendong's mentor in his previous life gave an example. In a certain project, in order to transmit less than 1k bytes of data every few minutes between two places 500 meters apart, the design unit decided to pull a single-mode optical fiber between the two places.
Then count how much consideration they have made for this optical fiber, such as the ground wire composite optical cable to prevent lightning, the optical cable armor to prevent physical damage, and the deep digging and deep burial to prevent pressure
Gao Zhendong’s mentor I was reviewing the project, so I asked a question: "Don't you know how to use a VHF digital radio? The reliability is guaranteed at low speeds, the installation is simple, and no maintenance is required. The data arrival rate can be guaranteed very well through protocol control. The price is cheap, you can get a very good pair for a thousand yuan.”
The other party was speechless, but maybe it was not the design unit that was stupid, but Gao Zhendong’s mentor.
So Gao Zhendong was very happy to hear Yu Yuncheng ask this question and explained it to him carefully.
"I added this system not for crystal pulling and rotation control, but for thermal field control."
"The rotation of the graphite crucible is partly for uniform heating. After all, no matter how good the control system is, it cannot To ensure that the temperature is uniform throughout the heating furnace, one thing to note is that during the crystal pulling process, the formation of the crystal is greatly affected by the temperature gradient of the thermal field. ”
“Temperature gradient? ”
< br>"Yes, the change of temperature in a certain direction. It is divided into radial temperature gradient and longitudinal temperature gradient. The former can be regarded as the temperature gradient on the circular cross section of the crystal, and the latter is the temperature in the height direction. Gradient.”
Now, Yu Yuncheng understood a little bit.
Gao Zhendong took the pen and paper and drew the temperature gradient curve during the crystal pulling process for Yu Yuncheng, explaining in detail the source and influence of the temperature gradient.
Yu Yuncheng and the surrounding scientific research team members who were watching and learning felt that a door to a new world had been opened. Many previous relevant experiences could be explained in this.
Finally, Gao Zhendong concluded: "In principle, the radial temperature gradient should be as uniform as possible. This is part of the reason why I just said to rotate the crucible."
"The lifting and lowering of the crucible is similar. You have all seen the influence of the radial temperature gradient just now. It should be higher, so that the latent heat of crystallization of the growth of single crystal silicon can be dissipated in time and the interface temperature can be kept stable. But it cannot be too high. If it is too high, polycrystalline or a large number of structural defects may occur.”
Seeing that everyone understands this principle, Gao Zhendong explained the reason for adding a crucible lifting system: “One of the simplest ways to increase the temperature gradient is to That is to increase the height of the crucible. In other words, the simplest way to adjust the longitudinal temperature gradient is to lift the crucible."
Before Gao Zhendong finished speaking, Yu Yuncheng had already learned to answer: "Also, can it work with other control systems to adjust the furnace temperature, improve the crystallization conditions and environment, and adjust the crystallization state?"
Gao Zhendong He smiled and said: "Yes!"
After these words, the core control conditions of single crystal crystallization have been explained clearly. Everyone here, don't talk about making a single crystal furnace in the future. But there may still be ideas for repairing a single crystal furnace.
As for people like Yu Yuncheng who are already great, they have benefited a lot.
(End of this chapter)