Chapter 525 Resolution 10μm
Porcelain Flying Factory has made up its mind. Mr. Xiao went to the capital, but things on Gao Zhendong’s side are far from over.
At this time, he was taking the information about the bomber, another fifth master, sent by the National Defense Work Committee, calculating and considering it carefully.
What he wanted to leverage was not just the attack-5 radar.
Just when he was lost in thought, there was a knock on the door.
Gao Zhendong stood up and opened the door. At the door were Yi Zhonghai and Ma Juan, a junior sister assigned to Wudaokou. Although Ma Juan has a relatively straight personality and some heroic spirit of a man, she has a very careful heart. She is suitable to represent the electronic laboratory of the branch factory to follow up. Lithography machine assembly matters.
"Senior Brother Gao, good news, good news!" Ma Juan was not as strict as Wu Shengyuan, and she was also called Senior Brother Gao in the work unit, which Gao Zhendong was quite pleased with.
"Is the photolithography machine assembled?" She came over with Yi Zhonghai. There couldn't be anything else but this.
"Yes, yes, yes, it's installed. Let's try it out first. All the indicators are completely up to standard."
"Great, let's go and have a look." Gao Zhendong put on his hand the As soon as he put away his things, he stood up and walked to the photolithography machine trial production workshop.
Yi Zhonghai and Ma Juan followed, and Ma Juan smiled and said: "The reason we are here is to ask you to preside over the final overlay accuracy test."
Gao Zhendong nodded repeatedly: "Well, yes, yes Try, have to try. Go! Go!”
It can be said that Yi Zhonghai and the masters have basically completed it with the cooperation of Ma Juan. This overlay accuracy is considered the ultimate. Comprehensive inspection.
Walking into the photolithography machine trial production workshop and looking into the clean room through the glass, what appeared in front of Gao Zhendong was something like a ventilation test cabinet in a chemical laboratory, or something like a biological laboratory. It’s a microscopic device with biological protection. You can’t tell what it does. It’s just the microscope that stands out.
This microscope is used for manual alignment and inspection. It mainly solves the alignment problem during overlay engraving. Gao Zhendong designed alignment marks on the mask, but the alignment operation is manual on this photolithography machine, and the microscope is used to do these things.
Ordinarily, Gao Zhendong has seen this machine come and go many times, and he can be considered an old friend, but when he saw it this time, he still felt excited.
It can be regarded as a result. In Gao Zhendong's heart, this thing is no longer a piece of equipment, but a breath.
In Gao Zhendong’s previous life, he had been competing online for many years. From being able to spray whatever his opponents caught, he could only spray whatever he caught, and gradually evolved into saying whatever he could spray.
In the end, I simply became a deadlock, squatting in those few areas and not moving away, no matter how strong the wind was, I stood still and said, "Yes, yes!"... ...Do you know how many kinds of light sources there are in lithography machines?" Gao Zhendong became more and more impatient and walked away with the keyboard.
Going far, far away, these things were indeed not completely acquired until he traveled through time, at least not the high-end ones, and the lithography machine was one of them.
Damn it, I will build one myself for fun in this life. I don’t know how many light sources there are, but I know this one can be used, and it’s pretty good!
Gao Zhendong himself also put on protective clothing and walked into the clean room with several testers.
The test staff had already prepared the test. After walking in, they turned on a few switches and signaled to Gao Zhendong: "Mr. Gao, it's ready."
Gao Zhendong picked up the The special clamp carefully picked up a single crystal silicon wafer from the silicon wafer rack with desiccant, placed it on the workpiece table, and then flipped the switch to adsorb and fix the silicon wafer.
These single crystal silicon wafers have been cleaned, dried, etc., and their adhesion to the photoresist is greatest at this time.
Then Gao Zhendong took a step back and handed over the next test to Ma Juan.
What is important is the refreshing feeling at the beginning. As for the specific operation, these testers are much more agile than him. Professional things should be left to professionals.
To say that Gao Zhendong's lithography machine is primitive, it is really primitive. After fixing the silicon wafer, Ma Juan turned on the switch and the silicon wafer began to rotate.
This is Gao Zhendong’s design. He did it in one step. He directly applied the spin coating method for photoresist coating. He didn’t know what coating method our earliest photolithography machine used in his previous life, but he I know that the spin coating method is definitely the best in overall performance.
The spin coating method is used to coat a flat and simple surface such as a single crystal silicon wafer. It has strong flattening ability, easy to control the thickness, high coating density and uniform thickness. It is not without defects, but it can be accepted and processed.
The rotation quickly reaches the preset rotation speed. When the coating is determined, the coating thickness and other coating result parameters are highly related to the rotation speed. While rotating, the workpiece table is also heating the silicon wafer in order to further remove the surface. Reattachment of moisture vapor.
These small details were all brought over by Gao Zhendong from his previous life. They are inconspicuous, but very important.
After the heating time met the preset requirements and the rotation had stabilized, Ma Juan picked up the dropper. Yes, it's the kind of dropper used in chemical experiments. It's not fancy at all, but it's enough for a photolithography machine like Gao Zhendong.
A dropper is born with an imprecise measuring function. For example, one milliliter of water is about 15 drops. In short, when the viscosity of the liquid is determined, it will drip from the dropper. The volume of each drop of liquid is basically the same, and the same is true for changing the dropper, as long as it is a normal dropper.
The excess photoresist will be thrown out by the rotating silicon wafer, which is also the advantage of spin coating.
Ma Juan dropped some photoresist into the center of the rotating silicon wafer. The photoresist quickly followed the rotation and spread evenly along the surface of the silicon wafer, very evenly, as if it did not exist.
This is also a blessing because the adhesion between the photoresist and the silicon wafer is very good. Otherwise, the substrate must be coated before applying the photoresist to strengthen the adhesion of the photoresist.
The silicon wafer slowly stops rotating. At this time, the workpiece table begins to heat the silicon wafer again, which is curing the photoresist.
After the curing was completed, Ma Juan began to press the button, adjust the workpiece table, and place the silicon wafer in the appropriate position under the optical system.
Although Gao Zhendong asked the comrades of the Northeast Optics Institute to develop a projection range of 160mm diameter, considering the yield of crystal pulling and the reason that the maximum distortion of the optical system appears at the edge, the specifications of the silicon wafer are still set at 130mm, which is about 5 inches, but this is our native process, so naturally we do not use inches as the unit of measurement for silicon wafers.
As the earliest and most primitive photolithography machine, Gao Zhendong does not use the most primitive contact photolithography. In this method, the silicon wafer and the mask are in direct contact, and the resolution is higher than the proximity method.
However, in contact photolithography, the photoresist or individual dust on the silicon wafer will contaminate and damage the mask. It can be used for research, but not for mass production.
He jumped over contact lithography and used proximity lithography. During actual lithography, there is a very small distance between the silicon wafer and the mask, on the order of 10μm, so that the mask can be avoided. The mold is damaged.
The disadvantage is that the resolution of proximity lithography is worse than that of contact lithography. In the best case, it is about 2μm, which is enough for Gao Zhendong now.
Using proximity lithography, the mask and the workpiece are separated, which is beneficial to automated lithography. This is why Gao Zhendong puts the mask into the optical system. The mask basically does not move in the optical system and moves. It's the workpiece table.
After leveling, the workpiece stage controls the silicon wafer to approach the mask, eventually reaching the distance set in the design - 20μm.
There is no need to align too carefully this time, because it is the first time to engrave. Strict alignment is a matter of overlay engraving. If it is overlay engraving, you also need to align the overlay engraving marks.
The next step is exposure and development, which sounds similar to film camera photography, but in fact the principles are basically the same.
After the development was completed, Ma Juan began to use a microscope to check the image quality. It took a long time and her eyes were probably blurred. Finally, she raised her head and nodded to Gao Zhendong with a happy face.
The mask this time is a standard mask for process testing. Looking at it like this, at least a resolution of 10μm is no problem.
"Brother Gao, it is the same as what we tested before. There is no problem with the line width of 10μm, it is very stable."
If there is a problem with the imaging quality, then the silicon wafer must be taken out and washed away Photoresist, prepare to start all over again.
These days, silicon wafers are very expensive and cannot be wasted. Even if silicon wafers are not so expensive in a few decades, they still have to be washed. If the problem lies in the photolithography process in the middle and later stages of the process, Secondly, the previous craftsmanship is also expensive!
Gao Zhendong was excited and nodded to her to continue.
Next, according to the normal integrated circuit process, it should be sent to other processes, such as etching, doping, ion implantation, metal removal, etc., depending on the purpose of photolithography. However, this is to test the resolution and set-up of the photolithography machine. If the engraving accuracy is not high, this process does not need to be done, and it cannot be done. We don’t have those things here.
For example, etching seems simple and just corrosion is enough, but in fact there is a whole special safety management line behind it. If you also build a line here, it will cause trouble, and it is not used often. arrive.
Not to mention doping, which requires equipment, is impossible to do.
Considering that after development, only the required part of the photoresist is left, the experimenter's idea is to apply photoresist again to see the degree of overlap between the two photolithography and development results.
This is also a stupid method. If in this case, the residue of the old photolithography process affects the new photoresist adhesion, resulting in poor test results, then consider photolithography - send 1274 etching - the experimental process of photolithography.
The line width alone is 10μm. In fact, the photolithography machine process cannot reach 10μm, because there are other parameters that determine the photolithography machine process. One of the most important ones is the overlay accuracy, which is what Gao Zhendong will finally test today. something.
When making integrated circuits, even if the process is as simple as PMOS, overlaying is required, because even transistors cannot be made with one photolithography, let alone a complete circuit.
(End of this chapter)