A Microprocessor-Based Architecture for E-Beam Wafer Transfer System

Moving wafers from atmosphere into a high vacuum chamber and onto an X-Y stage in a system whose primary objective is high throughput can be a challenging undertaking. Position sensing of mechanisms, tolerance to transients and switching noise, flexibility to modify operating modes, extensive diagnostic capability, and a user-friendly set of controls are but a few of the considerations to be made in such a transfer system. Since this is a production tool, reliability and serviceability must be carefully designed into the system from the start. Fail-safe operation is also a necessity and is accomplished through built in interlocks and software routines, however, the inclusion of a failsafe operating system does not preclude the need for failure recovery capability. Although the ultimate objective is to maintain continuous system operation through automatic failure recovery procedures, the control system must provide an unambiguous status of the operation when it cannot recover and requires manual intervention. This is particularly true with an internal wafer transfer, since the operation is invisible and fairly inaccessible to an operator. The architecture to be described accommodates these needs using distributed microprocessor control. The major functions under processor control include vacuum and wafer transfer control, elevator, and transfer arm motor control. Access to this system is via an IBM PC. A larger function done by a single 16-bit microprocess is that of interfacing with an IBM Series 1 computer, which controls an entire E-Beam system. The objectives of this architecture are the following: · separate control functions for greatest efficiency · provide operational flexibility · maximize diagnostic capability by enhancing the operator interface · automate failure recovery using more extensive data evaluations · reduce sensor requirements through quick evaluation of more input data · enhance noise immunity · increase reliability by using standard functional circuitry and microprocessor control.