Chapter 32.1.2 - Automated Material Handling System - Drivers Behind AMHS

There are several drivers behind the move to the fab-wide automation of material transfer. These drivers
include personnel utilization, ergonomic considerations, risk reduction, improved tool utilization,
and reduced manufacturing cycle time.

Personnel Utilization.   It is often not practical to provide the necessary number of employees or
aisle space needed to support the manual movement of material between bays in fabs. For example,
consider a 40,000 wafer start per month (WSPM) factory manufacturing a chip that requires 450
process steps. For such a factory, one can calculate the number of moves per hour = 450 process steps ×
40,000 WSPM × (1/25 wafers per lot) × (12 months/year/365 days/year/24 hours/day) × (safety factor
= 2) = ~2000 moves per hour. If one assumes that an employee can move on average six moves
per hour, 200 employees would be required per shift just to move material. Minimizing the number
of employees dedicated to menial tasks such as material movement is one of the drivers of AMHS.

Ergonomic Considerations. A 200-mm wafer carrier weighs approximately 10 lb and a 300-mm
wafer carrier weighs approximately 20 lb. While an individual can easily lift these weights infrequently,
experience in 200-mm fabs has shown that repetitive stress injuries result when individuals
carry and frequently place 200-mm carriers to and from process tools. Therefore, with the conversion
to 300 mm, most companies determined that it would be ergonomically unsuitable to have manual
transport of carriers.

Risk Reduction.   In 2005, the value of a carrier of wafers can vary from $10,000 to $1,000,000. The
risk of human error causing a carrier to be dropped is another of the key concerns leading fabs to
implement AMHS systems.

Tool Utilization.   Ten to twenty percent of a semiconductor fab’s output is often lost due to tools
sitting idle waiting for material to be delivered. Manufacturers view automation as a means of eliminating
variability in delivery times and improving tool utilization. Improved tool utilization through
the use of automation can result hundreds of millions of dollars of savings over the life of a factory.

Manufacturing Cycle Time.   By improving tool-to-tool delivery time and providing a method for
automatically and predictably scheduling workflow, AMHS offers the potential of reducing the manufacturing
cycle time. Cycle time is an important metric for semiconductor fabs because faster time
to market or faster delivery time of product to customers has a significant impact on the value of that
product and simultaneously enables the fab to achieve faster cycles of learning when trying to raise
the yield of a particular product or technology.

There are several drivers behind the move to the fab-wide automation of material transfer. These drivers
include personnel utilization, ergonomic considerations, risk reduction, improved tool utilization,
and reduced manufacturing cycle time.

Personnel Utilization.   It is often not practical to provide the necessary number of employees or
aisle space needed to support the manual movement of material between bays in fabs. For example,
consider a 40,000 wafer start per month (WSPM) factory manufacturing a chip that requires 450
process steps. For such a factory, one can calculate the number of moves per hour = 450 process steps ×
40,000 WSPM × (1/25 wafers per lot) × (12 months/year/365 days/year/24 hours/day) × (safety factor
= 2) = ~2000 moves per hour. If one assumes that an employee can move on average six moves
per hour, 200 employees would be required per shift just to move material. Minimizing the number
of employees dedicated to menial tasks such as material movement is one of the drivers of AMHS.

Ergonomic Considerations. A 200-mm wafer carrier weighs approximately 10 lb and a 300-mm