Chapter 1608 Second-hand preparation

After the tour, the group came to a dedicated meeting room on the top floor of the base with a very high security level.

The heavy soundproof door closed, leaving only a few core members.

After a brief silence, Chang Haonan picked up the teacup, took a sip, put it down, and looked directly at Wu Minghan.

"Academician Wu, aside from continuing to optimize multiple exposure and resolution enhancement technology, is there a more direct technical path to improve the resolution of a single exposure under the existing 193nm ArF light source conditions?"

With negative refractive materials as a trump card in hand, the most fundamental solution is of course to move towards surface plasma lithography, replacing low-frequency transmission wave imaging with evanescent waves carrying high-frequency information, which directly digs up the ancestral grave of the current semiconductor production system.

But this is like building a tall building from scratch, and even the theoretical basis has to be started from scratch. It is obviously not something that can be accomplished overnight.

Therefore, in order to cope with the crisis that may occur at any time, it is better to come up with some quick and easy upgrade methods based on the existing ones.

Wu Minghan has been thinking about Chang Haonan's real purpose, but this question is too common to find out anything.

I had to answer as usual:

"Under the same wavelength of light source, the core indicators of performance differences between different types of lithography machines, such as the NXT:1950i we are using now and ASML's more advanced NXT:2000i, are still numerical aperture (NA) and process coefficient."

He picked up the laser pointer and projected a simple optical path diagram on the table:

"The NA value, in simple terms, determines the ability of an optical system to collect and focus light. The higher this term is, the smaller the theoretically achievable resolution limit is."

The laser pointer's light spot stays at the position of the lens group symbolizing the objective lens:

"Specifically, NA is equal to the product of the refractive indices (n) of the bottom mirror, immersion fluid, and photoresist, multiplied by the sine of the half-angle of the aperture angle. Of course, the design freedom of the photoresist and the aperture angle is limited, so the materials of the other two items are mainly important."

"The NXT:1950i we are currently using has a calcium fluoride bottom lens. With the 2G series immersion fluid, the NA can reach up to about 1.35. The more advanced NXT:2000i has a lithium barium fluoride bottom lens with better performance and the immersion fluid is also the optimized 3G series, which can push the NA up to about 1.45."

Wu Minghan put down the laser pen and looked at Chang Haonan:

"However, this is basically the limit of the traditional technology route."

Chang Haonan had been listening attentively, and now frowned slightly: "I'm not familiar with immersion fluid, but...why can't the bottom mirror be made of a material with a higher refractive index?"

Then he added a more detailed number: "I remember... the refractive index of lutetium aluminum garnet is close to 1.9?"

This was used in previous experiments.

As soon as this question was asked, everyone in the conference room, including Zhou Xue and Huang Wei, became excited almost at the same time.

It’s not that the problem itself is very profound.

But be specific enough.

This is not a question that a layman can ask casually.

No matter what the answer is, it strongly confirms one thing: Academician Chang came here with a clear technical purpose and solution!

Wu Minghan responded immediately: "Lutetium aluminum garnet is indeed the transparent material with the highest refractive index in the deep ultraviolet band known so far... In theory, if it can be successfully applied to the objective lens bottom lens, combined with the current top-end third-generation immersion fluid, it is indeed possible to increase the NA value to 1.70... or even higher."

He first boasted about it, and then changed the subject:

"However, the high NA value brought by the high refractive index also has disadvantages." He picked up the laser pen again and emphasized the position of the bottom mirror on the previous schematic diagram: "An excellent lithography objective lens group requires that the light path in the system is as smooth as possible, and the large refraction angle propagation of light will inevitably bring greater aberration and dispersion difference to the system."

"In the process of designing the objective lens group, on the one hand, we must prevent the multiple reflectors in the system from blocking the imaging beam, and on the other hand, we must minimize the aberration and dispersion caused by the ultra-high refractive index. This is extremely difficult... Even if the design can be realized, it will require the introduction of more lens elements and more complex surface designs..."

"..."

Wu Minghan is not from the field of optical systems, but this part of his knowledge is not particularly cutting-edge in the field of semiconductor production, so he can explain it quickly:

"In short, it's not possible at the moment."

However, this result did not discourage Chang Haonan.

Especially when he heard the other party talking about aberration and chromatic aberration——

Regardless of whether the conjecture of "breaking the diffraction limit" can be realized, the inherent negative dispersion characteristics of negative refractive index materials are certain to exist.

Its disruptive ability in chromatic aberration compensation alone is enough to become the key to solving the pain points in the design of ultra-high NA objective lens groups.

He quickly calculated in his mind:

If the NA value of the existing DUV lithography machine can be significantly increased from 1.35 to above 1.70, it is equivalent to compressing the equivalent resolution wavelength from 142.2nm to 112.9nm.

This will greatly expand the practical capabilities of existing DUV equipment, and may directly solve the 40nm or even 28nm patterning problem, significantly reducing dependence on multiple exposure technology, thereby bypassing the quagmire of yield and cost!

After a moment's thought, Chang Haonan had a preliminary plan in his mind.

He still did not directly point out the existence of negative refractive index materials, but decided to take it a step further.

“To be honest, the Torch Lab is currently exploring a new optical system design concept that involves some…unconventional paths,” he said carefully. “In order to better evaluate the potential of this new concept, we urgently need some key design input parameters.”

Wu Minghan thought to himself that it had finally arrived.

The requirements put forward by the other party were extremely specific and professional, and the target was clearly the objective system.

Combining the previously mentioned "new design concept" and the focus on the characteristics of lutetium aluminum garnet, a vague but exciting outline gradually emerged in Wu Minghan's mind -

Academician Chang may have a disruptive technology in his hands that can solve the problem of high NA values!

Thinking of this, he took out the paper and pen he had prepared long ago at a speed that was difficult to discern with the naked eye:

"You say"

Chang Haonan was also stunned when he saw the well-prepared appearance in front of him, and then began to list the requirements:

"First, we need to clearly define the optical design specifications required by the actual lithography process under the target NA value. These include, but are not limited to, the size of the effective imaging field of view, the maximum allowable wave aberration, the distortion tolerance, and the working distance of the system and other hard indicators."

"The second is the overall structural layout of the lens group..."

"..."

He spoke eloquently and it took him more than ten minutes to finish.

Wu Minghan browsed through it from beginning to end.

I don’t know if Chang Haonan did it on purpose, but in any case, it hardly involves the core technology of Huaxin International.

He can make decisions at this level directly without even asking the board of directors for advice.

So he nodded towards Zhou Xue.

The latter immediately took over the conversation:

“Although the research and development project of the all-refractive objective lens has been terminated, all technical documents and experimental data are archived and preserved. I can directly authorize access. Although the original design was far from reaching the 1.7NA indicator, the design logic, material selection considerations, and records of aberration problems encountered at the time should be very valuable.”

"Don't worry, it's enough to check it." Chang Haonan nodded, "It's all in the same system. I know there will be some confidentiality requirements internally, so it won't be copied."

After hearing this, Zhou Xue breathed a sigh of relief:

If the other party really wants to make a copy and take it away, he will be the only one who will have a hard time.

"Thank you for your understanding, Academician Chang."

Zhou Xue rubbed his hands, but then his tone changed:

"However, Academician Chang, regarding the catadioptric objective system... we at Huaxin only have some basic understanding of the principles and superficial information that can be collected from public literature. We have very little detailed design data, material application, and aberration control experience."

"The first domestic company that is truly proficient in this area should be Changguang Group. They are the absolute main force in the country's research and development of high-end lithography optical systems, and are also responsible for the task of tackling key problems in objective lens systems..."

Wu Minghan had already put away the notebook and spoke again:

"Academician Chang, if necessary, I can contact Changguang immediately, and we at Huaxin will coordinate to see if we can get the necessary specification information or design references for you... Changguang's Zhang Runing research team is a real authority in this area."

really.

Chang Haonan thought.

This saves a lot of effort.

He stood up and took the initiative to shake hands with Wu Minghan:

"Then I'll trouble Academician Wu."