Chapter 1607 Multiple Exposure

Three days later, the Future Information Industry Conference came to a successful conclusion.

Chang Haonan declined the subsequent exchange activities and, accompanied by Zhou Xue and two plainclothes guards, took a low-key minibus and went straight to the production and R&D base of Huaxin International in the Haihe New District of Tianjin.

At Chang Haonan’s own request, the base did not hold a grand welcome ceremony.

Only the person in charge Huang Wei, the technical director Wu Minghan who returned to Tianjin a day earlier, and several core technical personnel were waiting quietly.

Seeing Chang Haonan getting off the car, the two leaders immediately stepped forward.

After a brief greeting, Chang Haonan and his group went to the changing area under the guidance of a special person.

The cleanliness requirements for wafer manufacturing are a hundred times stricter than those in an operating room. Therefore, before entering the core area, one must change into a full set of specially made dust-free clothing and undergo a strict air shower dust removal procedure.

After stepping out of the pneumatic gate, the only thing left in the air was the unique smell of a clean room and the faint hum of machines.

Through the observation window, you can see a batch of silicon wafers that have been polished and cleaned and have mirror-smooth surfaces being precisely sent into the deposition area by a robotic arm for thin film growth.

"Academician Chang, this is one of our most basic steps, the preparation and initial processing of silicon wafers." Huang Wei's voice came through the communication system, "After surface treatment, cleaning, and deposition of necessary coating operations, the wafer will enter the subsequent mask production... that is, the photolithography stage."

Huang Wei introduced the process while watching the completion of the automated process.

Coincidentally, a batch of wafers had just completed coating and were taken out by a robotic arm.

He signaled the operator to take out a sample and show it to Chang Haonan through a special window.

The surface of the wafer reflects the cold light from the ceiling lamp, presenting a uniform luster.

Chang Haonan leaned over and stared at the size and edge of the wafers. He stretched out his hand to measure through the glass and asked, "Mr. Huang, is this batch 200mm (8 inches)?"

"Yes, Academician Chang." Huang Wei affirmed, "This is the main size we are currently mass-producing."

Wu Minghan next to him added: "The 12-inch (300mm) production line is still in the preparation stage, mainly because... most of the company's funds and top engineering resources are now concentrated on breakthroughs in the lithography process, especially using existing deep ultraviolet (DUV) equipment to tackle the research and development of more advanced processes."

"However, from the perspective of technological reserves, we are not far behind. Once the funds or key equipment are in place, the speed will be accelerated very quickly."

Chang Haonan nodded slightly, without saying much, and gestured to continue moving forward.

"The photomask production area is at the back." Huang Wei introduced as he led the way. "The IC design is engraved on a quartz wafer with an electron beam to make a photomask. This thing is similar to a photographic film. The wafer just produced is the photographic paper. The basic principle is similar to developing a photo."

Although not completely accurate, it is vivid enough and easy to understand even for laymen.

"This is our main area for providing foundry services to customers." Huang Wei pointed to several lithography machines in operation and said, "In addition to meeting the needs of domestic IC design companies, we also accept some orders from international manufacturers such as Texas Instruments."

Chang Haonan showed a slightly surprised expression, but it couldn't be seen through the mask.

“Are there any foreign orders?”

"Well, our products are mainly for the domestic and Central Asian markets," Wu Minghan explained. "For low- and medium-level processes, our tape-out yield and speed have advantages."

Chang Haonan suddenly realized that the current situation of the semiconductor industry was far more complicated than in his past timeline.

During the introduction, Huang Wei noticed that Chang Haonan's eyes were not fixed on the running mass production equipment, but on an area separated by a transparent fence not far away.

It is also a mask production area, but there are more technicians gathered around, and the atmosphere is more tense and focused.

"Academician Chang, that's our R&D area," Huang Wei explained. "As you can see, production and R&D often share the same line in the lithography process, and the equipment and technology are interoperable."

"They are trying double or even quadruple exposure technology, with the goal of using our existing NXT:1950i DUV lithography machine to impact smaller feature sizes."

Chang Haonan turned his gaze to Wu Minghan: "Is this the link with the lowest yield rate and the highest cost that you mentioned before?"

A complicated expression appeared on Wu Minghan's face.

He did not answer directly, but led Chang Haonan to a special display stand next to the area.

"Academician Chang, please look this way."

On the display stand, there are not gleaming finished chips, but dozens of wafers neatly arranged.

At first glance, they do not appear to be much different from the coated wafers we just saw.

Chang Haonan turned to the other party, waiting for further explanation.

Wu Minghan picked up a wafer near him and pointed to several tiny ghost areas on it that were almost indistinguishable to the naked eye: "This is the scrap caused by 'overlay error'. In multiple exposures, the pattern formed by the first exposure and the second exposure need to be precisely aligned. Even if there is only a deviation of a few nanometers, the entire circuit will fail after superposition."

He put down the piece and picked up another one, pointing to some places on the surface where the thickness of the lines was obviously uneven:

“This is ‘critical dimension deviation’, the cumulative effect of multiple exposures, developments, and etchings, which results in the line widths in different areas not being consistent, exceeding the specification limit.”

He picked up the third piece and said, "This is a 'development defect'... The process window is too narrow. If you are not careful, the pattern will be ruined..."

"..."

He listed the reasons for each type of scrapping in detail, his tone calm, as if he was showing the remains of a miniature battle.

"These are all the tuition fees we paid... However, at a time when EUV lithography equipment is unlikely to be available, this is the only technical path we can see to a more advanced process."

There isn't much complaint in his words, only a sense of helplessness in the face of objective laws.

Chang Haonan's eyes slowly swept across this shocking "scrap display area", lingering for a few seconds on these wafers that carried the high price and mark of failure.

Just as he looked away, his gaze fell on an inconspicuous display frame on the wall next to the display stand.

The frame does not contain a photo or a certificate, but a slightly old-fashioned engineering structure diagram with dense lines.

Or more strictly speaking, a series of structural diagrams.

It looks quite old, so the various optical parameters and lens structures marked on it are a bit blurry.

"This... is the design drawing of the objective lens assembly?" Chang Haonan walked a few steps closer and pointed at the drawing. "You have also done research and development of photolithography equipment?"

The people around were slightly stunned. They didn't expect Chang Haonan to notice this corner.

"Academician Chang has a good eye." Wu Minghan stepped forward and explained, "But this happened... many years ago."

He stood in front of the picture and looked it up and down:

"At the beginning of the century, there was almost no UV lithography machine in China. We did set up a research and development team to try to develop core components, especially the objective lens system... Listed on this picture are a series of results that have been designed one after another."

His tone was filled with nostalgia and emotion:

"However, we have limited resources and cannot divert our attention to equipment research and development... In addition, Changguang Institute and Shanghai Institute of Optics and Electronics also quickly took on the task of tackling the problems of lithography equipment and core components. Therefore, after internal evaluation, we stopped the project in this area and focused our efforts on process optimization and process improvement. The research stopped at these drawings."

He pointed to the complex arrangement of lenses in the diagram:

"You see, this is a typical all-refractive design, which relies on a combination of a large number of high-precision lenses to focus light. The mainstream advanced immersion lithography machines now use more complex, more precise, but also more powerful catadioptric objective lens groups that can combine the advantages of reflective mirrors and refracting mirrors."

When this history was mentioned, the atmosphere in the crowd became a little subtle for a moment.

Zhou Xue, who had been listening quietly, also added:

"Although we didn't build the lithography machine ourselves in the end, the early R&D investment was not in vain...Our understanding of the essence of the lithography process mainly came from this stage, and it also laid the foundation for our rapid absorption and mastery of the equipment and the production process."

Chang Haonan stared at the slightly yellowed drawing, gently running his fingers over the circular outlines representing the lenses and the rays representing the light paths on the glass of the display frame, and nodded thoughtfully.

There were still some issues, and he had originally planned to go to Changguang Institute again to take a look.

But now it seems that it is easier.