AT&T's MOS V Qualified Manufacturing Line
(Manufacturing Strategy / Examples)
AT&T Microelectronics' manufacturing facility in Allentown, PA, demonstrated its ASIC (Application Specific Integrated Circuit) design/MOS V (metal oxide semiconductor V) Wafer Fabrication/JIT Assembly and Test lines capability to the government and was the first company to obtain qualified manufacturers list (QML) certification in December 1989. When AT&T demonstrated process stability and predictability on its products, its 1.25 micron CMOS technology was qualified in March 1990. The following provides an overview of the process AT&T went through to obtain QML qualification. (Personal communications with W. Vesperman and D. Kane, AT&T Microelectronics, Allentown, PA.)
When the DoD used components from vendors without checking for reliability, systems started to fail because of component defects. The failures were due to component failures. This prompted the DoD to require checking every component. As more and more systems used low volume, complex (ASIC, etc.) components, this approach, based on extensive destructive testing of components became too costly. In addition, rigid requirements in the traditional military procurement documents made it difficult for manufacturers to offer their latest innovations/technologies to the military markets. So the DoD changed the rules for component suppliers. The new DoD components specifications impose statistical process control, and in many cases, maximum failure rates on products.
The Defense Electronics Supply Center (DESC), the DoD agency, began to watch over vendor parts. Rome Laboratory (formerly RADC) and DESC stressed statistical process control and initiated the qualified manufacturer's list (QML) specification for microcircuit production. DoD has created a structured method to certify a manufacturer's facility and thereby validate the reliability of microelectronic components.
QML specification is only the beginning of a larger DESC thrust, that by 1992, could affect 60,000 electronic components in 56 categories. (Keller, John. "Defense Electronics Supply Center: Lending the QML Approach to All Electronic Spare Parts." Military & Aerospace Electronics. vol. 1 (7), July 1990, p. 49.)
In 1986, Rome Air Development Center (RADC) contracted AT&T, GE, and Honeywell to develop generic qualification procedures for VHSIC/VLSI devices. The preliminary draft of a specification for QML was issued in 1988.
In 1989, MIL-I-38535, General Specification for Integrated-Circuit [Microcircuit] Manufacturing, based on the qualified manufacturing line concept, was issued.
Objectives of QML
Obtaining QML status is a generic way to qualify a manufacturer without extensive end-of-manufacturing qualification testing on each device design. It reduces and replaces the end-of-manufacturing testing with in-line monitoring and testing using SPC. It shifts the focus from device-level to process-level.
The foundation for this approach is a TQM approach within the manufacturing environment. It enables a manufacturer to apply for the Malcolm Baldridge National Quality Award within five years of the initial request for the QML status. (Spurgeon, Susan P., Marcinko, Frank, Mengele, Martin J., Lyman, Richard C. "QPL or QML - A Quality Trilogy Approach." 1990 - ASQC Quality Congress Transactions - San Francisco. 1990, pp. 189-193.) QML approach certifies processes rather than individual parts.
The key objectives of the QML are:
Certification Requirements. The certification requirements are:
self-audit with quality enhancement
technical-review board (TRB) acting as corporate conscience
verified reliability of process
Qualification Requirements. The qualification requirements are:
demonstration of the stability and predictability of the manufacturing line (for example, two actual microcircuits and the standard evaluation circuit [a line-monitoring vehicle] must be run on the QML-certified line).
comparison of qualification, yield, reliability, and failure-mode analysis to data on those two products
demonstration of a good correlation and satisfactory
QML as a Business Strategy
AT&T found the QML concept to be a good business practice because it ensures cost-effective programs and operations. AT&T believed that obtaining QML qualification is consistent with various quality initiatives in practice in- house. In addition, AT&T was a part of the team that drafted the generic qualification procedures for integrated circuits.
AT&T decided to follow the QML concept to develop a single manufacturing process for both commercial and military systems. AT&T realized the following benefits of QML qualification and incorporated QML in its business strategy:
improved efficiency of operations
long-term cost reductions
improved customer satisfaction
The associated graph shows AT&T's conversion of customer requirements
Planning for QML Qualification
AT&T started QML planning by:
identifying and translating customer and quality-assurance requirements given in MIL-I-38535, General Specification for Integrated Circuit
Manufacturing, into internal systems and documents
doing a self audit against MIL-I-38535 specifications to ensure that all needs were met
identifying the metrics to evaluate the process
understanding the role of SPC, process
AT&T developed a Total Quality Management (TQM) plan to include the key aspects of QML: Technology-Review Board, process flow, design process, line-monitoring program, reliability-monitoring program, quality-improvement plan, yield-improvement program, change-control program, device-qualification plan, field-monitoring program, self-audit program, and failure-mode-analysis program.
AT&T formed a technology-review board (TRB) which is a technical management organization to oversee the technical, quality, and reliability issues for QML products. The TRB has representatives from design, wafer fab, assembly, test, product engineering, quality control, qualification, reliability, and marketing organizations. A quality manager chairs the TRB and has absolute veto power.
The TRB is actively involved in all aspects of certification, qualification, and manufacturing. The TRB generates reports on its activities to the government.
AT&T defined the total process flow for its MOS QML line (integrated-circuit- line) to include: design centers, mask manufacturing, wafer fabrication line, assembly line, and test center. AT&T ensured that all elements of the process flow and interfaces among those elements met QML requirements.
AT&T's ASIC Design Center complied with QML requirements and concepts by ensuring and documenting the necessary controls of the basic elements of the design process:
the technology database (models and design rules)
an integrated CAD/CAE system
standardized design practices and procedures
all interfaces between the customer and
To monitor the processes in-line and maintain a controlled line during production, AT&T used a line-monitoring program that included:
a statistical process control plan
a standard evaluation circuit
a technology-characterization vehicle
process zone monitors
Statistical Process Control Plan. AT&T developed an SPC plan to monitor the process for unwanted changes and to maintain stability. The plan included capability to:
identify critical nodes and establish control charts
do process-capability studies on all critical nodes
calculate process-capability-index values for all critical nodes
continuously cause improvement at all critical
Standard Evaluation Circuit (SEC). AT&T designed a functional microcircuit called SEC to monitor and control the manufacturing process. SEC serves as a well-characterized, easily diagnosable standard product. It is used to exercise the existing design documentation, software tools, and performance simulations. It is also used to demonstrate design and manufacturing reliability.
Technology Characterization Vehicle (TCV). The TCV is used to characterize a technology's susceptibility to intrinsic reliability failure mechanisms. AT&T dedicated the majority of the Tester Reliability Yield Component (TRYC) area to yield testers, which monitor the defect densities of various process zones after the full process sequence.
Process (Parametric) Monitors. AT&T uses a family of test structures called process monitors to measure electrical characteristics of each wafer type containing the product chips. The process monitors are positioned to determine the uniformity across the wafer. The use of process monitors enables manufacturing to select an individual wafer or a wafer lot based on whether it met the pass or fail criteria.
Process Zone Monitors. AT&T implemented process zone monitors to monitor defect density for particular processing segments of the wafer fabrication. The process zone monitors are used to:
AT&T set up a reliability-monitoring program to define inspection procedures to ensure that the device and lot quality requirements are met. The reliability monitoring program addresses all aspects of MIL-STD-883C Method 5005, Qualification and Quality Conformance Procedures. Data were generated at an increased frequency with increased sample sizes under this program. SEC data are correlated to data from other products in the same technology. The program replaces some end-of-line tests with in-line rigorous process controls when appropriate.
AT&T set up a reliability-review board (RRB) consisting of experts. The RRB reports to the TRB. The RRB evaluates the reliability data, and corrective actions and decided the product disposition procedures.
AT&T implemented a quality-improvement plan with a strong focus on quality and customer satisfaction. The quality-improvement plan included setting up quality-improvement teams who defined the yield and quality requirements. The plan also included training and sensitization of all employees to various aspects of quality.
AT&T developed a yield-improvement plan to remove yield-limiting defects. The objective of this plan is to improve quality, reliability, and customer satisfaction. This plan included use of SPC, SEC, TCV, parametric and zone monitors to drive yields. The plan also included a yield model to identify defect-density structures and predict yields.
AT&T set up a qualification-review board (QRB) comprising reliability experts from all areas of the process flow. The QRB developed the change-control program which required all changes to be fully documented and approved by quality, manufacturing, and R&D managers. The QRB assesses all changes for their possible impact on product reliability. The QRB defines the following test requirements to prove-in changes:
All changes should be reported to the TRB.
All major changes require TRB approval prior to implementation.
Major changes require customer approval prior to implementation.
The QRB developed the device-qualification plan using MIL-STD-883C, Method 5005. Documented guidelines helped the QRB to group devices into processing and packaging families whose reliability characteristics are likely to be identical. The QRB performs tests for all known failure mechanisms and stores all reliability data (from qualification, monitoring, etc.) in a database.
AT&T Customer Technical Support Center manages a highly active field-monitor program that:
receives and acknowledges complaint/query
coordinates and tracks timely solution
documents results of failure-mode analysis (FMA) for the customer
maintains database of all device issues
disseminates customer concerns to management and TRB
advises customers of quality concerns and product changes
recalls devices for upgrading and screening
coordinates visits to customer locations and hosting
AT&T has a very active self-audit program to verify the adequacy and implementation of total-quality program. This program included self-audit that:
documents findings (deficiency notices)
tracks deficiency notices to resolution
verifies corrective actions
reports monthly to TRB and higher
The following summarizes the valuable lessons the AT&T team learned during QML certification and qualification:
Management support is a must for the success of the program.
Educating and sensitizing all employees to quality makes the transition smooth.
Up-front involvement of the manufacturer, DESC/RADC, and validation teams simplifies the process.
QML makes good business sense and can be used for
commercial applications also.
AT&T is using QML concepts and disciplines to develop the manufacturing practice for both commercial and military applications. The goal is to economically improve manufacturability, quality, and reliability. AT&T plans to have a uniform manufacturing process for all commercial and military products.