Koichi Sakata, control system designer
Since joining Nikon in 2011, Dr. Koichi Sakata has worked on the development of general control systems for FPD lithography systems and the improvement of existing devices. He has written several research papers on motion control, for which he has received various excellence awards from groups like the Institute of Electrical Engineers of Japan (IEEJ). He is contributing to the development of cutting-edge technologies.
Addressing difficult requirements for precise motion control.
Please tell us about your work.
I am in charge of control system design for FPD lithography systems. More particularly, I work on design of the high-speed and precise positioning of the mask stage, plate stage, multi-lens system and vibration isolation tables. These control technologies are the most difficult to design of our lithography systems. Mainly I create algorithms and address the task of solving problems using a combination of our knowledge and new theories based on mathematic formulae from a control technology perspective.
What are FPD lithography systems?
FPD lithography systems are applied to manufacture LCD panels and organic LED panels. The systems have become ever larger to process larger glass plates for increased productivity. What's more, recent systems need to be able to produce high-resolution panels corresponding to smartphone and high-definition TV displays with increasingly higher resolution.
What is machine control of FPD lithography systems?
To put it simply, the control technology for these systems means achieving ideal numbers of certain target values, which comprise many parameters.
An FPD lithography system exposes the photomask and copies its circuit pattern onto the glass plate. The position controllability is crucial because many layers of the circuit patterns are exposed on a glass plate. Also, in this process, it is necessary to control the synchronization between the mask stage and the plate stage during exposure. Because the plate area is several square meters and the stage's weight is several tons, accurate controllability is absolutely essential below the 1-micrometer level during high-speed movement.
For the vibration isolation system, there is not only the role of supporting the several tens of tons of the machine's weight, but also that of isolating the machine from the vibration of the floor. In order to support the machine, this vibration isolation system must be solid, but if too solid, this allows more vibration to travel from the floor to the machine. To address this contradiction, we design an active system that varies its solidity depending on the frequency of vibration from the floor. When sensing a vibration in a particular frequency band, springs and actuators flex the vibration isolation system and suppress the vibration. They harden the system when detecting a lower frequency to support the machine. Inventing technology based on frequency as a principle is part of the enjoyment of control system design.
Researching with Nikon in college and beyond.
When did you decide to major in science, and why?
My favorite subjects were math and physics, so I was already thinking of focusing on science when I was in junior high, so I entered the engineering department in college. For the first three years there, though, I spent too much time playing billiards (laughs). I became hooked on it partly because the game has something in common with physics, I think. But when considering which laboratory to belong to in my senior year, I decided to mend my ways. Following my interest in robotics, I chose the control engineering laboratory, run by Prof. Hiroshi Fujimoto*, who still collaborates with Nikon in research today. Then I became more interested in research than I was in billiards, and advanced to graduate school.
- *Currently the Associate Professor at the University of Tokyo Graduate School (Department of Advanced Energy as well as Department of Electrical Engineering). Specializes in control engineering and conducts research in motion control, nano-scale servo systems and electric vehicle control.
You joined a research project in collaboration with Nikon in your first year in the masters program. How did this happen?
Back then, Nikon was about to begin producing FPD lithography systems designed for the 6th-generation glass plates. The company needed a breakthrough because conventional control technologies could not achieve the required specifications. The leader of the control design team attended a lecture by Prof. Fujimoto and decided to collaborate with him. Together, we researched a perfect tracking control method, a digital control technology that accurately tracks positions and contributes to increasing the productivity of FPD lithography systems.
Then you advanced to the doctoral program?
Yes. I was progressing with R&D of an experimental device while attending masters. I wanted to complete it, which motivated me to go to the doctoral program. It gave me many opportunities to present at academic meetings both in Japan and overseas. I also got the chance to exchange with researchers in universities abroad. Looking back, such experiences gained me the knowledge and courage to interact equally with specialists and overseas researchers.
Do you have any fond memories of the research with Nikon?
It was very exciting, conducting experiments on actual machines and inventing new ideas and technologies through meetings. The Nikon staff was a small but smart group of people with flexible and open minds, implementing new ideas one after another. I was impressed with the way they stayed positive while constantly exploring innovation.
Did you join Nikon because of the research collaboration?
Yes. Initially I couldn't decide if I should stay in college or join a company. But I decided to enter Nikon because I wanted to continue research while observing developed machines actually in use. I found it quite entertaining that we could treat a huge machine like a toy during research (laughs).
