Historically, the semiconductor industry was driven by physics and chemistry, essentially perfecting the processes that have allowed remarkable advances in microelectronic technology. The focus was the process — what happens in deposition and etching chambers. What happened outside was far less important. The industry existed with low levels of automation: wafers were manually transported between tools. But as wafers became larger with smaller widths, issues like productivity, throughput, reliability, and automation have gained a much larger share of mind.

Focusing on throughput, not processing time

Moving wafers into and out of a fabrication tool, positioning and repositioning them within the tool, and changing setups and job parameters all have a significant influence on the overall productivity of the tool. As tools process wafers faster and more accurately, material handling productivity bottlenecks become more apparent. The more time the tool spends waiting for a wafer to be delivered for processing, the less efficient the overall production. Efficient wafer handling between tools becomes increasingly critical to improving productivity.

Automation is one aspect to consider in the process. Semiconductor fabs are increasing automation levels significantly, replacing manual transport with automated material handling systems and turning more attention to the flow of materials throughout the fab. As a result, there is also a need for more sophisticated process integration, such as enabling in-line metrology to detect errors faster and earlier, and thereby increasing yields.

A renewed interest in the quality, reliability, and performance of automation components must also be considered. Automation components must meet the challenge of delivering product to the processing area more efficiently. For example, simply increasing the speed of motion in transferring wafers is not sufficient. The mechatronic handling systems must be optimized to meet cycle time requirements, yet still protect delicate, high-value wafers.

Focusing on differentials

Tool-makers in the semiconductor industry are starting to outsource non-core engineering, concentrating internal resources on the strategic differentials they bring to market. This inside vs. outside attitude is a mark of a maturing industry where vertical design is replaced by collaborative design. For example, one wafer-processing equipment manufacturer tapped our expertise in precision motion control to design a high-performance wafer lift subassembly.

The company had been purchasing about 30 separate components from a handful of vendors and was building the lift assembly in-house. While the existing design worked well, the OEM wanted to reduce engineering expenses in designing a new lift, lower the cost of the assembly, and streamline the supply chain by obtaining the item as a single part number. In short, they were receptive to outsourcing the design and manufacturing to Bosch Rexroth. The result: Rexroth supplies each assembled and tested lift mechanism ready for installation — while meeting the cost-saving objectives over the previous design. And the OEM has only one part to purchase.

Just a few years ago, such a move was virtually unthinkable. Beyond obtaining a reliable product, such outsourcing also streamlines the supply chain, simplifies purchasing and inventory, and helps moderate risk in the cyclical semiconductor market.

Focusing on reliability

Because throughput is becoming increasingly important as a measure of productivity, downtime anywhere in the flow is disastrously expensive. Tool-makers and fab designers place increasing emphasis on reliability, which includes extensive qualification of components. Engineers evaluate not only basic performance criteria, but also maintainability, durability, environmental characteristics, mean time to failure, cycle life, and similar metrics that will give some measure of reliability.

It is also important that various components integrate with each other easily. It's not unthinkable that you would find multiple motion control devices — servo controls, pneumatics, and linear motion — within just a few feet of each other throughout the fabrication process. Making sure those devices work well together is a major concern.

On the supplier side, the types of products designed for use in fabs and tools are growing rapidly. From cleanroom-certified products to controls designed specifically for wafer-processing equipment, OEMs can select more off-the-shelf components or subassemblies. Rexroth's growing line of cleanroom-certified products, for example, includes pneumatic cylinders and valves, linear actuators, lean manufacturing components, and aluminum structural framing.

Reliability, however, is not the only benefit semiconductor tools can gain from embracing smarter systems.

Focusing on intelligent systems

Today's most sophisticated controls use distributed intelligence to increase capabilities of servo drives and motors and eliminate processing bottlenecks that occur in centralized control systems. The sophisticated monitoring and predictive diagnostics can be a disadvantage of distributed intelligence, however.

Integrated intelligence monitors drive characteristics such as angle, speed, position, current, bus voltage, winding temperature, rotor position, and speed. These characteristics are compared to "ideal" conditions measured at commissioning. Deviations can be measured, allowing the drive to diagnose faults. It can detect conditions like motor bearing damage; friction, binding, and skewing in linear actuators; play, stiffness, and slippage in gearing and couplings; loose belts; dirt in the linear measuring system; and varying load conditions.

The drive not only can warn of deviations, it can also pinpoint the cause and degree of deviation — telling the user, in the extreme case, that the need for maintenance is critical and a shutdown, planned or otherwise, is imminent. Or it can advise that maintenance will be needed soon, providing ample opportunity to complete the required maintenance during the next scheduled downtime rather then closing down the entire line for emergency service.

Advanced diagnostic and predictive maintenance functions are also available on Rexroth pneumatic systems. The Rexroth Drive and Diagnostic Link (DDL), for example, is a bus communication module that provides diagnostics down to the valve/solenoid level in pneumatic systems. The intelligence of electropneumatic systems also offers new capabilities to ensure reliability and productivity.

Total cost of ownership

As they focus more on throughput and efficient material handling, fabs are beginning to evaluate their purchase of new equipment on the total cost of ownership principle (TCO). Investing to buy superior equipment can save in the long run through:

• Reduced downtime. If a fab produces 50,000 wafers a month, downtime costs almost $250,000 an hour. So, there's a huge incentive to keep operations running smoothly, whether by preventing failures or reducing unscheduled or even scheduled maintenance. Clearly, saving a few dollars here and there on less reliable equipment is pennywise and pound foolish.
• Time savings. Everything from engineering the system to tool startup and commissioning, restarts, and maintenance should go faster and easier with proven equipment from a well-established supplier.
• Supply chain considerations. Establishing solid purchasing relationships with experienced, sophisticated suppliers can pay significant benefits, not just in filling orders, but also in helping solve any number of production problems as they arise. And a supplier who knows the industry can even be a partner in helping anticipate future needs.

Focusing on the inside and outside

The leaders of the semiconductor industry will continue to improve their technical superiority by advancing their internal, inside-the-tool processes. If they focus their attention on the throughput, reliability, and cost improvements that can be achieved outside the tool, they can reach surprising levels of profitability as well.

For more information, visit Bosch Rexroth.