In order for semiconductor process equipment to operate efficiently, very precise leveling standards are needed for all wafer process and transfer locations. However, when asked about the leveling standard at their fab, most process or equipment maintenance engineers responded, “We have no leveling standards.” It is inherently difficult to measure the inclination of semiconductor process equipment as access to the equipment may be limited and traditional leveling methods, including eyeballing and bubble levels, do not have the precision or repeatability required to establish leveling standards.

The risks of insufficient inclination measurement and nonconformity acrossthe wafer production process include:

• Wafer damage — as a resultof vibration, slippage, or scratching
• Particle contamination
• Increased equipment downtime
• Increased maintenance burden
• Wafer non-uniformity
• Process nonconformity
• Increased defects and reduced yield

This paper describes case studies illuminating the challenges and limitations of current leveling methods and the experience of one maintenance team in a Korean fab using a new inclination measurement technique, a wireless, leveling wafer that can be handled by the automation and moved anywhere throughout the equipment.

CASE STUDIES: THE LIMITATIONS OF TRADITIONAL LEVELING TECHNIQUES
The following case studies describe some of the limitations presented by thetraditional leveling devices and techniques as introduced above.

Case Study 1: Many important wafer transfer and process locations are not leveled due to inaccessibility

General purpose in nature, bubble levels are typically not easily accommodated by wafer handling equipment, making their use time consuming or sometimes impossible. Figure 1 provides a front side view of a robot arm with multiple paddles that is impossible to level with most bubble levels.

In cases where bubble levels were used to level semiconductor process equipment, fab maintenance teams still reported their use to be time consuming; uniformity issues were hard to troubleshoot because of the lack of objective data collected.

In these applications, a routine check of equipment inclination was either not performed or required multiple engineers the better part of a shift to complete and still did not provide an accurate, numeric output from which process uniformity standards could be established. Wafer process uniformity and leveling standards can only be established based on accurate, repeatable, and objective leveling data. Since traditional leveling devices, including bubble levels, do not provide numeric output that can be recorded on a station-by-station, tool-by-tool, and PM-by-PM (preventative maintenance) basis, wafer uniformityperformance tracking does not exist. Electronic levels output real data, but recording and tracking this information is an intensive additional manual procedure, which accordingly, is often omitted in the push to get the tool back in productionas soon as possible.