84. Chapter 84 I’ll show you now!
Chapter 84 I’ll show you now!
As the most critical link in the chip manufacturing process, the basic principle of photolithography is actually very simple, which is to use light to complete the engraving of silicon wafers.
The silicon wafer in photolithography is like a projection cloth hanging on the wall, and the photolithography machine is the projector. If the surface of the projection cloth is not flat and has ups and downs, the projected image will naturally be distorted.
In photolithography, surface defects of silicon wafers will cause the projected circuit design to deform, resulting in reduced yield and even the scrapping of the entire wafer.
So if you want to get a silicon wafer that can be used to make chips, you need to polish and grind the cut single-crystal silicon wafer until its surface flatness is less than 1.5nm RMS.
This is equivalent to hanging a large curtain in a movie theater. Its surface ups and downs cannot exceed the size of a hair, which is infinitely close to a perfect mirror.
Therefore, the requirements for the polishing process of silicon wafer manufacturing are naturally extremely important.
From the small steel ball on the tip of the ballpoint pen, to the raw material silicon wafer of the chip, to the lens on the lithography machine, and finally even the water droplets with flawless surface in the science fiction novel The Three-Body Problem…
In fact, the test of the industrial level of a civilization is to see how finely you can make an object.
And to make fine things, you naturally need a clean room with clean air, otherwise the air is full of dust and bacteria, and no matter how much you polish, you can’t make qualified silicon wafers.
”In fact, in recent years, we have been able to achieve a flatness of 2.6nm RMS by imitating the equipment of the island country, but no matter how much we check, even if every part has met the standard, we still can’t continue to break through…”
Yan Hui introduced their research progress to Kang Chi while wearing protective clothing.
“What polishing liquid was used to polish to 2.6nm RMS?”
”Based on SiO2, add 0-70wt% hydrogen peroxide, and finally adjust the pH to 8.5 with KOH.”
Kang Chi nodded: “Let’s see first.”
After the two put on their protective clothing, they quickly came to the polishing laboratory, and then Yan Hui presided over and demonstrated a polishing experiment to Kang Chi.
In traditional silicon wafer polishing, a mechanical polisher is usually used to perform preliminary polishing on the silicon wafer, then clean it, and finally perform chemical mechanical polishing, also known as fine grinding.
Fine grinding is a process that uses the chemical corrosion function of the polishing liquid and the mechanical polishing of the mechanical turntable to achieve the process standard of the silicon wafer.
The result of the experiment was 3.1nm RMS, which is far worse than the limit they can do.
Kang Chi pondered for a moment, then said: “Change to 30wt% Al2O3 base liquid, add 65wt% potassium permanganate as chemical polishing liquid, and adjust the pH value to 8.0 with 5wt% HNO3 and try again.”
Yan Hui nodded, led the researchers to mix the polishing liquid, and then repeated the experiment.
”Flatness 5.9nm RMS.”
Seeing this result, Yan Hui, who was originally a little bit expectant, couldn’t help showing a look of disappointment.
But Kang Chi remained unmoved, and reported another set of polishing liquid ratios, asking them to repeat the third experiment.
”Flatness 5.9nm RMS.”
5.9?
Still 5.9? ! Is it a coincidence?
Although 5.9 is obviously far from the standard, Yan Hui seemed to realize something and turned to look at Kang Chi in surprise.
“You… calculated it?”
”I guess so.”
Kang Chi nodded.
Yan Hui was completely stunned. You know, the technical difficulty of chemical mechanical polishing is that in addition to the hardware of the polishing equipment meeting the standards, the chemical polishing liquid must be prepared according to the equipment performance and silicon wafer parameters to achieve the perfect combination of chemical polishing and mechanical polishing.
To debug well, first of all, you need to know the equipment well, and secondly, you need to have rich experience in preparing polishing liquid.
But Kang Chi can easily report two sets of polishing liquids with different compositions through just one experimental demonstration, and achieve the same flatness value in subsequent experiments…
Isn’t this a bit incredible? Even Yan Hui, who has participated in countless tests, can never achieve such precise control without computer simulation.
The estimated error is at least 0.3nmRMS.
He asked in disbelief: “How did you do it?” ”Well, I can’t tell… maybe it’s some kind of intuition. I’m quite sensitive to mechanical things.”
Kang Chi thought for a moment and continued,
”I estimate that the normal level that your polishing machine can stably perform is about 3.0nm RMS. 2.6nm RMS is just an accidental achievement by you. It will definitely not exceed three times.”
Yan Hui was stunned again, obviously guessed by Kang Chi.
”Indeed, only once…”
Kang Chi wanted to say something, but his stomach was already growling with hunger. Looking at the time, he found that after three rounds of experiments, it was already eight o’clock in the evening without him noticing.
“Sorry, it’s so late without me noticing… Let’s pack up and have dinner first. You’ve worked hard today.”
”Okay.” Yan Hui nodded, “Then after dinner, come back at nine to continue.”
”Come back to continue?” Kang Chi couldn’t help showing a strange expression, “Continue for what?”
”Do an experiment.”
”It’s useless. This is not a problem with the proportion of the polishing liquid. You are doing useless work.” Kang Chi shook his head and said, “Go home early after dinner, take a shower and go to bed. We will come back tomorrow to dismantle the polishing machine. If I’m not mistaken, there is a problem with your equipment installation.”
Hearing that Kang Chi had guessed the problem, Yan Hui was suddenly a little excited: “No need to wait until tomorrow, we can take it out and dismantle it for you to see now!”
Kang Chi rolled his eyes at Yan Hui: “I’m hungry and tired.”
”…”
Yan Hui couldn’t help but be embarrassed.
“Ahem… Sorry, I forgot that you just came from Gangcheng today.”
”Even if you didn’t come from Gangcheng, it’s time to eat and rest at this time. You too, don’t work overtime if you can. Although time is tight, we should also pay attention to efficiency in our work, rather than just piling up time. You’ve made people dizzy, what kind of research are you still doing?”
”…”
After cleaning up the laboratory, taking off the protective clothing and coming to the company cafeteria, it was already nine o’clock in the evening.
Because the silicon wafer production department is working 24 hours a day, and the scientific researchers in the R&D and manufacturing center often work overtime all night, the company’s cafeteria is also the kind that provides 24-hour supply, and you can eat at any time.
When the auntie serving food in the cafeteria saw Yan Hui, her attitude was quite enthusiastic, and she served more dishes to his plate.
Kang Chi couldn’t help but look at the auntie more, Hmm…
Although she is a little older, she can still be considered charming.
“Ahem, don’t think too much.” Seeing Kang Chi’s complicated expression, Yan Hui quickly coughed and said, “If she knew you were the big boss, she would probably fight more…”
”I didn’t say anything, why are you so nervous?”
Yan Hui: “…”
…
After dinner, Kang Chi contacted the company’s administrative director by phone, and then, under his leadership, he and Chen Hai came to the house that the company had prepared for him in advance.
This is a two-story villa with five bedrooms and two living rooms, which is quite unique.
It’s just that I live alone, so it seems a bit empty and deserted.
Well, after Chen Hai sent Kang Chi home, he didn’t know where he went. I guess he was in the next building?
Kang Chi didn’t invite him to live with him,
Otherwise, two grown men living under the same roof,
How can it be! ? (End of this chapter)