Automation of Chemical Beam Epitaxial Wafer Manufacturing

Author(s):
Shahzad Sarwar - Averna Technologies
Daniel Cox - Averna Technologies, Inc.

Industry:
Semiconductor

Products:
PXI/CompactPCI, Signal Conditioning, LabVIEW, Real-Time Module

The Challenge:
Implementing several enhancements to process control, monitoring, hardware configuration, user interface, and data logging features of control software in modern wafer growth facilities.

The Solution:
Using National Instruments LabVIEW Real-Time with a PXI and SCXI-based system to provide a reliable interface and control of process hardware.

Introduction
Our clients, based on years of experience in chemical beam epitaxial (CBE) growth, needed a highly reliable, extendable, and flexible system capable of configuring, monitoring, and operating nearly 200 transducers and industrial actuators in a networked environment with a very intuitive user interface.We perform the CBE wafer growth in a vacuum chamber maintained at a programmable temperature. With the system hardware, you can switch between 10 different gas lines, injecting the doping material onto the wafer. The hardware elements control and monitor thermocouples, thyristers, vacuum pumps, pressure transducers, check and regulatory gas valves, and relays. With the process controller, you can program and control execution of a time sequence or event-driven state transitions (recipe) of the entire hardware. Recipe programming, its execution, and relevant bookkeeping are the main tasks needed from the control software.

The process controller also provides periodic system monitoring, alarm handling, data logging, and remote access through the Internet. The real-time system interfaces, across the network, to multiple monitoring and user interface modules built with LabVIEW and a process database. We achieved manufacturing process sequencing through innovative use of editing LabVIEW block diagrams (VIs). We maintained a process data and operations log on a remote database using National Instruments SQL Toolkit and ODBC connectivity.
The physical design of our control application consists of a real-time control module running on the PXI platform. Built with LabVIEW Real-Time, it provides the interface and control of process hardware. We implemented the system monitoring and user interface to configure and operate the hardware with LabVIEW. The new system replaces a conventional programmable logic controller (PLC)-based control, while providing both a reliable and user-friendly operation of the manufacturing facility.

Hardware Configuration and Control
The hardware configuration module provides the user interface for configuring the existing hardware, adding new elements and defining their interface type, I/O channel association, and conversion constants. We follow a graphical hardware editing approach where you can interact with the synoptic view of the system and open editing windows for individual hardware elements by clicking your mouse.
The control module, while running in an independent thread on the PXI controller, performs the following continuous tasks:

1. Reads all process variables and displays a complete hardware status
2. Calculates the difference between the set points, reads values for process variable data, and detects alarm conditions
3. Publishes process data across the network
4. Checks for data changes greater than dead bands and logs it to the database
5. Performs PID regulations for gas cells and heaters

You can define the data logging in the software configuration part. After each data logging interval, the system compares the present process data with the previously logged values. If it finds variations greater than the specified tolerance, new data values are pushed into a logging buffer along with the time stamp, and the database interface VI is invoked to update the database.

Recipe Programming and Execution
A process recipe is edited by a LabVIEW VI diagram in a restricted development environment where you can place one or more recipe step VIs while connecting them with a recipe control cluster. A standard procedural logic VI of the LabVIEW functions pallet remains available to you while editing a recipe. Additional functions pallet groups are also available. These pallets provide an organized and hierarchical access to the entire recipe library containing the following salient groups of VIs:

1. Basic action VIs provide instantaneous interaction with the system
2. PID VIs can define set points for PID-controlled elements
3. Ramp VIs establish controlled variations in set points
4. Execution control VIs can programmatically pause or abort recipes
5. Sub-recipe VIs can be customized

The recipe VIs are all connected in a cascaded manner by the recipe control cluster. During the run phase, LabVIEW maintains this cluster as a global variable and provides a means of controlling the recipe progression by the execution control module. You can run a recipe in simulation, diagnose or active run, and report mode. In simulation mode, no hardware actions are invoked, and assuming an ideal performance, the growth and temperature profile are computed and displayed in a report. The diagnose mode verifies that all the functionality programmed in the recipe is handled by the current hardware configuration. The run and report mode actually executes the recipe while interacting with the hardware and generating an execution report.

Distributed Monitoring
The system display and user interaction (SDUI) module interacts with the PXI controller through Ethernet, while using the VI server for remote invocation of VIs and NI DataSocket as a source of process data. Multiple instances SDUI modules can simultaneously run on different remote stations and interact with the real-time system. Whereas data access is provided to all SDUI clients, you can allocate control privileges to only one client at a time.

A graphical synoptic view of system hardware is presented in SDUI. The display refresh-rate is user programmable in units of read-cycle interval. After each refresh-rate, the SDUI module reads the latest system state through DataSocket and updates the display screen. All the hardware is interactively controllable from the SDUI synoptic view window. Pop-up sub-VIs launch from the synoptic view and can define set points and other features of system hardware and also view the past trend for the corresponding process data. As the settings are changed on the hardware, they are time stamped and logged in the database.
The synoptic view window of one of the dedicated SDUI modules, with the current state of system, is published as an HTTP page enabling remote monitoring through Web browsers.

Conclusions
This application improved the reliability and efficiency of semiconductor manufacturing facilities. We innovatively used the LabVIEW block diagrams as a process sequence-programming tool. Our approach is cost effective and flexible, while providing an intuitive, convenient, and network-based manufacturing control system.

For more information, contact:

 Shahzad Sarwar

Averna Technologies, Inc.

19 Le Royer West, Suite 400

Montreal, Quebec, H2Y 1W4 Canada

Tel: (514) 842 7577

E-mail: shahzad.sarwar@averna.ca

Author Information:
For more information on this Case Study, contact:
Daniel Cox
Averna Technologies, Inc.
87 Prince - Suite #140
Montreal H3C 2M7
Canada
Tel: (514) 842-7577
Fax: (514) 842-7573
info@averna.com

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