VERIFICATION OF ESD ENVIRONMENT IN PRODUCTION Credence Technologies PHILOSOPHY, METHODOLOGY AND TOOLS Vladimir Kraz Credence Technologies, Inc. 1
Company Overview Credence Technologies designs and manufactures products for measurement of electromagnetic fields and other parameters Two main product lines: Electromagnetic compliance (EMC) FCC, CE, VCCI ESD and EMI measurements Semiconductors, Disk Drives, FPD Both lines share common technology of state-of-the-art electromagnetics Products sold and supported worldwide through local distribution Credence Technologies is located in Santa Cruz, California
Practical Approach to Safe ESD Environment "The greatest obstacle to discovery is not ignorance - it is the illusion of knowledge." Daniel J. Boorstin "Where facts are few, experts are many. Donald R. Gannon
Your Company Has Spent Millions on ESD Protection Your ionizers are within their specification Your wrist-straps are OK Your equipment is grounded You do not see voltage build-up Your workers wear proper garments Your floors are static-dissipative You passed ESD Audit By now you shouldn t have an ESD problem Then why we are all here?
Assumption vs. Verification All ESD-protective measures are designed to PREVENT ESD Occurrences By utilizing them you How do you ASSUME that your ESD problems are solved VERIFY it?
What Defines Safe ESD Environment? The ultimate goal of any ESD program is to minimize ESD exposure to components and its influence on the process. Without closed-loop control, the success of ESD program is always uncertain. Most of current ESD controls are centered on performance of individual components of ESD protection, such as grounding, ionizers, materials, etc. If there are ESD occurrences in your environment, it is not ESD-safe regardless of performance of individual protection components What matters is the END RESULT of the entire ESD program, not just performance of its individual components
ESD Monitoring as ESD Management Tool ESD monitors can tell you the status of current ESD environment this will help you with determining the needs for ESD protection Once you have implemented ESD protection, ESD monitors will inform you whether it works and to what degree in real time Because ESD environment changes all the time, ESD monitors provide continuous supervision and warn you before ESD becomes a big problem Continuous ESD monitoring provides you with the closedloop control of a critical parameter in your process
Need to Monitor ESD Events ESD Events is the ultimate measure of ESD safety of your environment No matter how good your ground is or how well your ionizer works, if you still have ESD Events, something is not working By providing real-time feedback on ESD Events in your environment, ESD monitoring gives you factual, not assumptive information about the state of your ESD environment
Important Properties of ESD Events ESD Events produce damage to electronic devices Specific parameters that affect the degree of damage are: Rise edge Magnitude of the pulse Duration of the pulse Combination of these parameters is representative of the power of the discharge which is harmful to the devices Judging the danger of ESD Event by any one parameter alone is misleading
Can Electrostatic Voltmeter Be an ESD Event Monitor? ESD Events last nanoseconds (10-9 seconds) too fast for a static voltmeter ESD Event may not always completely discharge accumulated static voltage Knowing voltage alone doesn t tell you how strong a discharge would be Charged object may never cause ESD Event A static voltage or charge meter cannot serve as a tool for ESD Event monitoring
ESD Event Happened: Now What? ESD Event Happened: What Does it Mean? Presence of ESD Events means that something in your environment causes it. It also means that your ESD-protective measures are not fully working. In essence, your ESD environment is not safe. If an ESD Event Already Happened, isn t it too Late? It is for that particular component that was exposed to ESD, but it is not to late for many components that will follow it if only you act upon this information and improve your ESD environment Isn t knowledge of static voltage enough to determine whether the environment is ESD-safe? Static voltage is generated extremely quickly and discharges may happen before any voltage is detected. The voltage of concern is very low making monitoring of only static voltage an unreliable criteria. If it is an ESD Event that damages components, then it only makes sense to monitor the ESD Events.
Need to Monitor Static Voltage Presence of electrostatic charge in your environment indicates potential for ESD Events Charged objects are subject to particle contamination Induced static voltage creates discharges in reticles, components and electronic circuits Static charge is created instantly on separation of dissimilar materials Static voltage measured once in a while during an audit is not an assurance of its absence at all times
Need for Ionizer Monitoring Ionizer adjustment is performed right under the ionizer at specified distance Your work may be performed in a different place Air flow irregularities and blockage may prevent even a perfectlyadjusted ionizer from having optimal performance in a place where it matters Without maintenance in a few month an ionizer turns into a fan Monitoring of ionizer balance and decay at the place of operation assures proper ionizer performance at all times Area of good decay and zero balance CPM Area where components are handled. Decay is poor Balance may not be zero
Ionizer Monitoring Two main parameters: Decay Balance Decay is the most fundamental property of an ionizer Zero balance readings may mean dead ionizer ionizer turned away air flow blocked air flows into grounded metal surface ionizer is in perfect health
Example of a Need for Ionization Monitoring Die-attach operation in a back-end facility in Asia ESD Events occur when die is separated from the wafer die is placed onto a lead frame Ionizer is placed in such way that there is no airflow to the critical areas. Air flows directly into grounded metal surface Ionizer itself is functioning perfectly
Need for Ground Monitoring Good common grounding is assurance of zero voltage difference across your facility and in your tools Static charges have way of dissipating via properly-done grounding Grounding of equipment and personnel can change at any time Ground wires can break Grounding can be disconnected during maintenance Operators may not use wrist straps properly or not wear them Continuous monitoring of ground connections assures that everything is properly grounded at all times
ESD Safety Basics Think through your process from ESD point of view Do a baseline assessment of the actual ESD environment Identify problematic areas and steps in the process Apply necessary protective measurements Verify their effectiveness Continuously monitor your ESD environment Do not ignore warning signs Keep records Never assume always verify
EM Aware ESD Monitors ESD Events Electrostatic Voltage Ionizer Balance Ionizer Decay All parameters are monitored using the same antenna All outputs are provided via single interface Zero Balance Ionizer Feedback
How Does EM Aware Measure ESD Events EM Aware is a miniature calibrated patent-pending microwave receiver with broad dynamic range EM Aware takes into account the following parameters: Rise edge Magnitude of the pulse Duration of the pulse Combination of these parameters is representative of the power of the discharge which is harmful to the devices EM Aware is fully characterized for all discharge models: HBM, MM, CDM EM Aware Output, V DC EM Aware Response to MM Discharges 4.50 4.00 3.50 3.00 2.50 2.00 1.50 2 3 4 5 6 7 8 9 10 Distance from the Discharge, In. 5V 10V 30V 50V 100V 200V 500V
EM Aware in Ionization Control Monitors both ionizer balance and decay Capable of directly controlling balance of certain types of ionizers, i.e. Ion s 5810 Uses miniature remote antenna to monitor parameters in the immediate proximity to work area No high voltage exposure to components unlike conventional CPM Individual data outputs for balance and decay and ESD Events Connects to major facility monitoring systems for data collection
ESD Trends for Semiconductors Geometry is getting smaller (0.10µ) higher sensitivity to ESD Conventional ESD protection measures do not handle well high-speed signals due to high capacitance Lower operating voltages (i.e. 1.8V) push the limits on protective clamping devices Increased number of I/O pins statistically increases probability of IC failure Larger die size in ICs make losses expensive Automated equipment increases ESD exposure due to high speed and metal-to-metal contact ICs exposed to ESD may not fail right away -- latent damage causes losses and alienates customers
ESD and Reticles Reticle damage happens mostly due to induced static voltage during handling If damage does unnoticed, the consequences won t be: high cost of repair or replacement of reticle high cost of defective ICs produced with the damaged reticle high cost of lost fab time high cost of damage control and lost customers
Reticle Damage: Action Plan Monitor ESD Events at every step of reticle handling Know which station generates ESD Events so that it can be improved Know the exposure of each reticle to ESD and re-route exposed reticles to inspection rather than to production Have an ESD passport for each reticle -- know its true exposure to ESD Manage reticles in a non-emergency way Construct and verify your ESD-preventive measures based on factual information
ESD Monitoring on the Back End ESD damage on back end is the most expensive place in the process to have it Back-end ESD exposure leads to possible shipment of defective ICs ESD issues are here to stay. Incorporation of ESD monitoring in the process makes it controllable Proper monitoring of ESD exposure can: isolate ESD occurrences identify exposed parts alert personnel of ESD problems verify improvements provide valuable statistics be a part of SPC
ESD Monitoring Examples in the Back End Applications IC Handlers Die Attach Manual Operations
ESD Issues in IC Handlers Observed ESD Events in IC Handlers: IC is picked up from the input tray IC is placed in the input shuttle IC is placed in the test socket IC is lifted from the test socket IC is placed in the exit shuttle IC is placed in the output tray After IC has been tested. No means of detecting failures at this point
Integrated Operation of ESD Monitors in IC Handlers ESD Events are continuously monitored If an ESD Event is detected, IC handler automatically separates ICs exposed to ESD If too many high-energy discharges occurs within short period of time, an alarm sounds, indicating problem in the handler. ESD Event has Occurred Above Damage Threshold? No Above Latent Threshold? No Yes Yes Place of Disharge Re-Test IC Pass After Test No Statistics on ESD exposure is collected and analyzed. End Yes Place IC into Separate Tray
ESD Audit Is your ESD Audit made to test just your preventive measures or your actual ESD environment? Regular ESD Audit checks for everything except the for very phenomenon it supposed to prevent: ESD Events
ESD Audit: Going by the Facts ESD Audit Report (Assumption) Wrist straps Ground Ionizers Dissipative floors Dissipative garments Static voltage levels Gloves Tweezers Packaging Shelving ESD Audit Report (Facts) 12 ESD Events stronger than 200V HBM were observed at workstation # 5 during the shift Maximum strength of ESD Event was 350V HBM ESD Events were correlated with new materials arrival and handling Correction and verification to follow immediately
ESD Audit Tool: EM Aware Starter Kit EM Aware starter kits provide factual data on all ESD parameters in process Includes everything needed for ESD Audit and Diagnostics (except computer)
Why EMI? ElectroMagnetic Interference is electromagnetic emission that causes equipment malfunction EMI causes: Outright equipment lock-up Software errors Tools do things they weren t supposed to do Erratic response Parametric errors Sensor misreading EMI is becoming a serious problem in manufacturing
EMI Audit: Basics Conduct baseline EMI survey. Measure both average and peak values of EMI Create EMI map of your facilities Determine your EMI hot spots Similar equipment should have similar EMI signature. Deviations may mean trouble Do not let problems just sit there -- devise plan of action and follow-up Do EMI audit on scheduled basis. Monitor progress. Find where the problems appear Field Strength,mV/m 200 180 160 140 120 100 80 60 40 20 0 Sub Fab Ground EMI
EMI Audit: Grounds Voltage causes electric field. High-frequency EMI can be easily measured with broadband EMI meter (not static field meter!) If there is a rise in electromagnetic emission near grounded surface, there is a high frequency voltage present indicating poor EMI ground Measure field strength near each ground plate, grounded tool cover, grounding wires Recommended distance from the grounded surface: 10mm Data log the readings and make them part of EMI Audit Report
Tools for EMI Audit Field Strength Meter Broadband Sensitive Average and Peak Detectors Data Logging EMI Monitors Broadband Sensitive Average and Peak Detectors Data Logging Spectrum Analyzer Broadband Antenna High-Speed Oscilloscope 500MHz min. 5GS/Sec. Min.
Contact Information Vladimir Kraz Credence Technologies, Inc. 3601-A Caldwell Dr. Soquel, CA USA Tel. 831-459-7488 FAX 831-427-3513 E-mail vladimir@credencetech.com Web site http://www.credencetech.com Contact Information: Vladimir Kraz vkraz@bestesd.com www.bestesd.com +1-408-202-9454