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CAE (Computer Aided Engineering)

Thermal flow simulation for stepper wafer stage.
Fig. 1: Thermal flow simulation for stepper wafer stage.
Visualization of virtual particle flow.
Figure 2
Fig. 2: Heat analysis of 300 mili-wafer based on a finite element method
While capturing the overall macro view, micro simulation is carried out on focusing areas.

The product development process is changing drastically: as functionality and quality continue to improve, costs must be reduced. The product life cycle is steadily getting shorter, reducing the amount of time that can be spent on product development. The key to winning in this competitive situation is to create high-performance products with excellent cost performance as quickly as possible.

This is where computer-aided engineering (CAE) comes in. Computers can provide simulation technology, supporting product development through engineering.

Normally in product development, a continual process of prototyping and evaluation confirms function, performance and operation. Problems are fixed, improving reliability and bringing the prototype closer to final product specifications. Repeated prototyping, however, can be an impediment to speed, a key factor in development. Computer simulation is a key to reducing the required number of prototypes.
For example, to manufacture steppers, said to be the most precise pieces of industrial equipment of all time, Nikon applies incredibly precise control, of the nanometer* order, to a process in which performance can be affected by micro vibration and temperature change. In developing new steppers, we make extensive use of CAE for simulation, utilizing our software technology to simulate stepper performance for various structures, mechanisms, heat transfer, thermal fluid, electromagnetic fields and sound fields.

Effective simulation with CAE, however, requires development of a mathematical model that accurately portrays the phenomena involved.
In analyzing thermal flow in a stepper, using simulation of air currents inside the chamber and accounting for heat generated by the stepper, for example, it is impossible to predict how the air flows will respond to different parameters unless the simulation is based on a mechanism accurately describing how air flows in the chamber.
For steppers, CAE starts with development of a model for this mechanism defined on the nanometer order.

The next premise is about "how to increase calculation efficiency" when using a model of nanometer order.
This condition is important to increase the product development speed.
For example, with regard to the heat deformation analysis on exposure, it is necessary to monitor general heat deformation for a whole wafer and precise points of heat deformation on exposure accurately at a same time. To expect nano-order deformation due to increased temperature caused by exposure, a simulation with a finite element method is carried out. A finite element method divides a target element area (meshing), and constantly find an overall solution from hour to hour by using a physical law that is appropriate for each element. To expect heat deformation with a high degree of accuracy, the traditional analysis method required very fine dividing of elements under real exposure conditions and focusing on each element in all areas. However, such a method required a lot of calculation time and could not reach the necessary product development speed.
Nikon developed a unique simulation technique that sets some focusing areas on a whole wafer and forecasts the focusing areas with a high degree of accuracy. Fig. 2 shows a condition where a circuit pattern is exposed in sequence on a 300mm wafer by using a scanning method, and temperature increases. The area indicated with a white arrow is the focusing area. This method has successfully reduced the analyzing time to a couple of percent of the traditional method while keeping the analysis accuracy at the level of the ordinary method. In the development of steppers, it is important to get the macro picture of the simulation data as well as a micro view of them.

This is not to say that CAE can accurately predict every phenomenon. Various phenomena which cannot be accurately predicted are verifiable through prototyping, with the results fed back to improve the numerical model. This continuous software improvement is important for future simulations.
Research and development clarifying new phenomena is a joint effort between product design and CAE R&D teams, working according to short product design cycles.
As the precision and reliability of CAE software improves, development accelerates, helping new technologies mature to the point of commercialization.
The utilization of CAE to minimize prototyping also greatly helps to reduce environmental impact.

  • *One billionth of a meter (10-9 meters).

Posted May 2006