Abstract
IC manufacturing is about process, in particular precision chemical delivery – flow control, temperature control, and pressure control. The chemical delivery system – the integration of mass flow controllers (MFCs) and other components – is the heart of the process. The chemical delivery system provides the required control for the formulated process chemistry recipes. Constant monitoring, constant verification, and timely maintenance are necessary to insure process quality and product yield. Seaware’s Mobius test and verification system service is dedicated to optimizing chemical delivery systems, reducing process maintenance and improving yield.
Introduction
Ever better solutions for process control are needed to meet today’s fab challenges to continually improve yield. Fabs need to find and fix problems before they become yield killers. (1) The in-line chamber solutions for yield improvement provided by
measurement, inspection, and metrology systems can and should be meaningfully supplemented and correlated with test and verification of the chemical delivery system, to collect and translate data into process control parameters and reduce performance variation. This is part of “equipment performance optimization,” one of five continuous improvement technologies comprising APM (advanced precision manufacturing). The other four are APC (advanced process control), yield management systems, product performance targeting, and integrated production scheduling. (2) Ultimately, every factor contributing to yield and fab productivity improvement stands to be enhanced by effective automation technology that is “tuned to processes to keep tools in spec, online and producing revenue…to collect data and automate process optimization to minimize hands-on, process tweaking by process engineers and operators…(with) machine(s)…taken offline for maintenance only when recipes cannot be tuned to keep the machine within specification.” (3) To facilitate interconnectivity of process equipment and automation technologies, SEMI’s Interface A has been developed using SOAP/XML messages to enable APM or equipment engineering systems (EES) applications, which include APC/AEC (advanced equipment control) and e-diagnostics. (4) With the introduction of Seaware’s Mobius system, practical solutions are becoming available to improve yield by finding and even fixing problems in chemical delivery systems before their effects show up in process results. Chemical delivery system manufacturers, OEMs, and rebuilders, as well as fabs themselves need the value of data driven system-level testing and verification.
Test Integrated Flow Devices
To accurately measure and control the flow of gases to the process chambers where the semiconductor wafer is targeted, process tools depend on the mass flow controllers and related components integrated into the chemical delivery system. Whether these components fail completely or marginally, and regardless of the reason for failure, overall process yield is directly affected by the degree to which actual measures of flow, pressure, and temperature deviate from indicated measures on any of the components in the integrated system. Considerable effort downstream of the chemical delivery system is expended to improve process yield, but little has been done at the chemical delivery system itself, due largely to the lack of test and verification tools for chemical delivery systems.
Industry practice is to rely on operator trial and error to isolate and replace “problematic MFCs.” As operating engineers troubleshoot the chemical delivery systems of their process tools, mass flow controllers too often erroneously believed to be faulty or in need of re-configuration are collected and sent out to be serviced. Servicing MFCs outside of the integrated system misses underlying causes of failures within the integrated system. Only servicing the integrated system will insure desired yield improvement.
Find and Fix Marginal Failures in Chemical Delivery Systems
A complete failure amounts to inability to flow or reach set point. Marginal failures are anything less than a complete failure where a difference between indicated and actual measures occurs. These many typically undiagnosed variations between actual and indicated measures of flow, pressure, and temperature, present a sizeable and yet untapped opportunity to improve process yield.
The larger portion of marginally failed MFCs have no defects, but show symptoms manifested by problems elsewhere in the chemical delivery system that are not accurately diagnosed. Without effective system level monitoring and verification, many if not most marginal failures, while potentially having a negative impact on process yield, are not specifically apparent to operators.
Seaware, using it’s proprietary Mobius test system, improves yield by finding the marginal failures before their effects show up in process results. Mobius takes a preemptive (act before failure) approach rather than the reactive (after failure) approach. (5) Mobius checks every device in a chemical delivery system individually and as interrelated parts of the whole system to precisely diagnose, identify the real causes of failures of any kind, complete or marginal.
Since actual measures of flow components integrated into chemical delivery systems are prone to vary from indicated measures, the real-time system-level pinpoint accuracy provided by Mobius is vital to overall product performance of process tools and therefore to achieving the objective of ever improving process yield.
Correlate Metrology and Chemical Delivery System Data Analyses
In monitoring and maintaining the precision required for wafer production, individual component performance parameters are reported to a system controller from which operational status is determined to be acceptable or out of range, providing the basis for any needed process termination. A log of these parameters during process runs is maintained. This log and physical characteristics measured from the wafers are statistically evaluated.
Productivity and yield improvement are limited by three deficiencies in current practice. First, there is a problematic time delay. Process parameters may be adjusted based on metrology analysis long after real time processes have completed, not real time process control.
Second, current methods measure and monitor each performance parameter independently giving no indication of interactive effects.
Third, the information indicated from each individual device about its performance is not always correct. Actual performance often deviates from indicated performance in what may be termed “marginal failures.” Interactive marginal failures result in what may be termed a “system effect,” which is not monitored or measured, but which inhibits
productivity and yield improvement.
Fab operators know performance is not always as indicated, that performance tends to drift. Because “rapid flux” or “excursions” of process parameters being monitored can be detected, fab tool engineers set pass/fail limits so that process runs can be aborted to avoid costly waste. But if actual performance extends beyond acceptable limits while individually indicated performance parameters remain within acceptable limits, the result is significant productivity or yield loss due to marginal failures not picked up until actual physical inspection of the wafers is performed, which is undesirably late.
Scheduled preventative maintenance operations try to address the changing system effect of diminishing drift out of acceptable range.
Summary: Solve the System Problem
The process chemistry distribution and control subsystem is critical to every step comprising the device manufacturing sequence. The complexity and preciseness necessary to produce profitable quality, thus sufficient yield rate, present an ever-growing challenge.
- For process tools to function properly, “indicated measures” of flow, pressure, and temperature must be the same as “actual measures.”
- Within integrated assemblies, “actual measures” may vary from “indicated measures” because of individual device variations, but also because of other system effects stemming from interconnect interactions.
- Testing MFCs outside the system verifies device performance on a standalone basis only.
- When components are integrated into a gas panel system of plumbing and electrical work, a new set of conditions is created that allows actual system variations in pressure, temperature, and flow to affect “actual measures” of specific devices, even though “indicated measures” are within spec.
- “Indicated measures” differing from “actual measures” are inaccuracies or marginal failures, which result in lower yield.
Seaware’s Service Solution
- Seaware has the ability to test and document every component individually and the integrated system to precisely pinpoint defects.
- Seaware’s service uses the Mobius platform for automated test, measurement, and monitoring of process chemistry systems in wafer process tools – individual and interactive component performance and system level operating parameters.
- Seaware can service all device types, device arrangements, communication protocols and application specific operations.
- Innovative software and hardware architecture allow for ever-changing industry requirements.
Sources and Citations
(1) “Enhancing Process Control for Sub-90mm Applications,” Applied Materials, p. 134, FabTech, 25th edition
(2) “AMD Integrates Manufacturing Through APM,” Semiconductor International, Peter Singer, Editor-in-Chief, 9/1/05, www.reed-electronics.com/semiconductor
(3) “How to Improve Fab Productivity,” Semiconductor International, Carl Fiorletta, Adventa Control Technologies Inc., Plano, TX, 7/1/05, www.reed-electronics.com/semiconductor
(4) “The Standard Pieces of SEMI’s Interface A,” Semiconductor International, Brian Rubow, Cimetrix Inc., Salt Lake City, 7/1/05, www.reed-electronics.com/semiconductor
(5) “Four Strategies for the Age of Smart Services,” Harvard Business Review, Glen Allmendinger and Ralph Lombrelia, October 2005, p. 131, Reprint R0510J
