In a 300mm fab, wafers are transported from tool to tool via a material handling system.The wafers themselves are carried in special sealed, clean environment enclosures called FOUP's, which stands for Front Opening Universal Pod. A FOUP is the size of a breadbox and has a handle that allows a robot to pick it up and move it around. When the factory control system tells the material handling system to deliver wafers to a specific tool--such as a lithography or deposition tool--the robot brings it to a Pod Door Opener or PDO. The job of the PDO is to accept a FOUP from the material handling system and then open up the FOUP and present the wafers to the tool to which the PDO is attached. We don't say "drop the FOUP off" because the value of the contents of a single FOUP can be staggering. If a FOUP contains 25 300mm wafers, each with 1,000 microprocessors--and this is conservative--the value of the FOUP can be several million dollars. So, the material handling system will "handshake" with the PDO to make sure that it is ready to accept a FOUP. Before the material handling system releases it, the PDO will confirm that it has a grip on the FOUP.

Once the PDO has the FOUP clamped to its base, the PDO will slide the FOUP up against a sealed pocket. Grippers will then unlock the FOUP's front door, and the door will be removed. The wafers are now exposed to the extremely clean environment inside of the semiconductor tool. Wafers are then removed and processed. Eventually wafers--perhaps the same wafers--are then reloaded into the FOUP. The door is then placed back on the FOUP and the door is latched up tight. The PDO then awaits a command from the material handling system to begin the careful undock and handoff of the FOUP back to the factory for further processing.

This silly little PDO is quite a complex machine. One of the most popular ones is pneumatically driven and does not contain its own controller. That's where Soft-I/O comes in.

The Brooks Load Port Module

This Pod Door Opener contains pneumatic actuators--either cylinders or rotary actuators--to handle motion in the following axes:

1. The Clamp/Unclamp cylinder causes small levers to grip the bottom of the FOUP and hold it firmly to the base of the PDO.
2. The Slide In/Out cylinder causes the FOUP to dock with the window that will allow access into the tool.
3. The Paddle cylinder swings in and out and brings the door latch grippers into contact with the FOUP door to position it for removal.
4. The Latch rotary actuators turn the two door latches to unlock the door.
5. The slide cylinder lowers the door to put it out of the way so that the tool robot can access wafers from the FOUP.

Sensors and Actuators

In order to make a pneumatic motion control system work well, it is necessary to employ sensors that detect the end of travel of all the movements. Thus, the FOUP is clamped by actuating the clamp cylinder and then monitoring the end-of-clamp sensor. This is just what Soft-I/O is made for. Brooks provided the PDO interface in a convenient 50-pin connector on the back of the unit. The company integrating the Brooks PDO simply split the 50-pin connector into two 25-pin cables and attached one Soft-I/O module to each connector. One Soft-I/O module handled the pneumatic actuators and sensors. The second Soft-I/O module handled the buttons, lights and interface to the material handling system.

The use of two Soft-I/O modules allowed a division of effort on the PDO. One module handled the operator interface and material handling system state machines while the other module handled the pneumatic motion control.

Soft-I/O sequences were developed in minutes that caused the PDO to clamp and then open the FOUP. Another sequence did the reverse. The "pause" and "resume" buttons triggered--using Soft-I/O event triggering--other sequences that paused the load and unload sequences. When the Soft-I/O sequences were run, the PDO performed extremely quickly because the time from end-of-travel actuation to next step was measured in a few milliseconds.

How did the integrator couple the two Soft-I/O modules? Soft-Link. When the operator pressed the "Load" button, Soft-Link communicated this button press to the second Soft-I/O module and the sequences ran quickly thereafter.

One other nice addition was to couple the air compressor into the system such that any PDO needing air resources could use Soft-Link to request air, and the air compressor would provide air. The completed PDO system has been applied to modern 300mm fabs. Soft-I/O provided small, inexpensive and high performance control that has been very reliable.