Patent Description:
Embodiments of the invention relate generally to a method and apparatus for in-tool monitoring and characterization of electrostatic discharge (ESD) events, and/or to a CDMES/MiniPulse apparatus and method, and/or other types of charged device model event simulators (CDMES), detectors, and methods. At least one method and apparatus disclosed herein provide real time ESD events monitoring in, for example, integrated circuits (ICs) production tools and/or different processes and assist to prevent ESD related failures using one or more method(s) of the charged device model (CDM). One method of monitoring ESD events and two methods for calibrating the monitor are disclosed herein.

CDM events represent electrostatic discharges which happen in manual and automated production systems for electronic ICs (integrated circuits). In production tools, the IC (integrated circuit) may acquire electrical charges by many ways, such as, for example, by contact, friction, and/or induction from a nearby electrical field, just to mention a few possible ways. When conductive parts of ICs come into contact with grounded equipment parts or parts with lower electrical potentials, the accumulated IC charges are free to discharge spontaneously. As a result, a relatively high discharge current (ESD event) may destroy or damage the IC (see, e.g., <FIG> and <FIG>).

The design of IC components usually incorporates special means (or particular components) for protection against ESD effects. The semiconductor industry has developed several standard methods for testing IC devices and defined their CDM ESD threshold parameters such as, e.g., withstand voltage and current amplitude. The applicable standards also detail the test apparatus requirements for automated IC CDM tests. These methods and devices are useful during IC design stages, final testing for product certification, and failure analyses of damaged devices.

However, conventional technology suffers from various constraints and/or deficiencies as will be discussed below. A goal in accordance with various embodiments of this invention is to provide a method and apparatus for real time ESD event monitoring and calibration in IC production tools and manufacturing processes.

<FIG> illustrates a typical discharge model <NUM> of a charged (IC) device CDM event in a tool or processing chamber. In <FIG>, the "MiniPulse" (SIMCO-ION) ESD detector <NUM> (or another type of ESD detector <NUM>) intercepts the ESD signal <NUM>, and the Robot Placement Effector <NUM> (or another suitable type of robotic arm <NUM>) places a charged device <NUM> into a test socket <NUM>. The test socket <NUM> is typically placed on a suitable test bed <NUM>, base <NUM>, or another suitable platform <NUM>. As the charged device <NUM> approaches the test socket <NUM>, a discharge (ESD) <NUM> occurs and the antenna <NUM> which is a part of "MiniPulse" Detector (coupled to the MiniPulse Detector <NUM>) intercepts the ESD signal <NUM> of the discharge event. In this example, the ESD event is a discharge <NUM> that takes place in the form of a spark between two conductive parts <NUM> and <NUM> that are both characterized by different voltage potentials. The conductive parts <NUM> and <NUM> and other semiconductor processing equipment may be in a tool or processing chamber <NUM> that may have any suitable size such as, for example, approximately 2x2 feet, 4x4 feet, or other dimensions.

One of current problems with conventional technology and instrumentation is in the difficulty in calibrating an ESD detector. This difficulty is due to, for example, the challenge in providing the repeatability of the electrostatic discharge events themselves. Other difficulties exist due to conditions imposed upon detecting of the radiated electrical field waveform by the materials and configuration of the process point itself Yet another big problem and/or limitation is the relatively high electromagnetic noise level in the tools and IC production floors. Therefore, the current technology and devices are limited in their capabilities for ESD events detection and suffer from at least the above constraints and deficiencies. Embodiments of the invention provide systems and methods for overcoming the difficulties in calibrating the ESD detectors and reliable detection of the ESD events in production conditions. <CIT> relates to a method and apparatus for simulating electrostatic discharge events in manufacturing and calibrating monitoring equipment. <CIT> relates to an in-tool ESD Events Monitoring Method And Apparatus. <CIT> relates to an electrostatic discharge event and transient signal detection and measurement device and method. <CIT> relates to an electrostatic discharge event detector. <CIT> relates to a process parameter event monitoring system and method for process.

<FIG> shows a screen shot of a typical example voltage/current waveform of a CDM electrostatic event where a discharge takes place in the form of a spark between two conductive parts moving to contact (later named as a "collapsing capacitor"). The top waveform <NUM> is an example output signal (current pulse that is similar to an example output signal that is produced by a CDMES (Charged Device
Model Event Simulator) as will be discussed below in accordance with an embodiment of the invention. The lower waveform <NUM> is the resulting incident waveform captured by the "MicroESD" monopolar antenna <NUM>.

The "MiniPulse" detector <NUM> includes an electronic circuit that is capable of receiving the signal that is intercepted by the antenna <NUM>. The electronic circuit will filter/classify this signal as an ESD event if the electronic circuit determines that this signal is a real ESD event of interest based upon a detecting algorithm and multistage filtering including the radiated ESD energy spectrum, pulse duration and threshold levels as discussed in details below in various embodiments of the invention.

In one embodiment of the invention, there is provided an apparatus for detecting electrostatic discharge ESD events as defined by independent claim <NUM>.

In yet another embodiment of the invention, a method for detecting electrostatic discharge ESD events as defined by independent claim <NUM> is provided.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one (several) embodiment(s) of the invention and together with the description, serve to explain the principles of the invention.

Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals may refer to like parts throughout the various views unless otherwise specified.

In the description herein, numerous specific details are provided, such as examples of components, materials, parts, structures, and/or methods, to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, methods, components, materials, parts, structures, and/or the like. In other instances, well-known components, materials, parts, structures, methods, or operations are not shown or described in detail to avoid obscuring aspects of embodiments of the invention. Additionally, the figures are representative in nature and their shapes are not intended to illustrate the precise shape or precise size of any element and are not intended to limit the scope of the invention.

Those skilled in the art will understand that when an element or part in the drawings is referred to as being "on" (or "connected" to or "coupled" to or "attached" to) another element, it can be directly on (or directly attached to) the other element or intervening elements may also be present. Furthermore, relative terms such as "inner", "outer", "upper", "above", "lower", "beneath", "below", "downward", "upward", "toward", and "away from" and similar terms, may be used herein to describe a relationship of one element relative to another element. It is understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

Although the terms first, second, and the like may be used herein to describe various elements, components, parts, regions, layers, chambers, and/or sections, these elements, components, parts, regions, layers, chambers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, part, region, layer, chamber, or section from another element, component, part, region, layer, chamber, or section. Thus, a first element, component, part, region, layer, chamber, or section discussed below could be termed a second element, component, part, region, layer, chamber, or section without departing from the teachings of the present invention.

Additionally, the elements illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of an element of a device and are not intended to limit the scope of the invention. Furthermore, based on the discussion of the embodiments of the invention as presented herein, those skilled in the art will realize that the positions and/or configurations of the components in the drawings can be varied in different sizes, different shapes, different positions, and/or different configurations. Therefore, various components shown in the drawings can be placed in other positions that differ from the configuration as shown in the drawings. The components in the drawings are illustrated in non-limiting example positions for purposes of explaining the functionalities of the embodiments of the invention, and these components in the drawings can be configured into other example positions.

The charged device model (CDM) testing and ESD event monitoring system (or apparatus), in accordance with an embodiment of the invention, were developed under consideration that, in general, processing chambers (e.g., semiconductor tools) are essentially echoic chambers with a relatively high electrical noise level due to a surrounding metal enclosure. Example elements of noise sources may be electronics, brush DC (Direct Current) motors, robotic actuators, switches, electrical systems, and/or the like.

In practical terms, each tool has unique characteristics (e.g., EMI (electromagnetic interference) landscape) in reflecting internal electromagnetic field radiation caused by electrostatic discharge events. The typical scenario for CDM events is that a charged IC device is discharged when it contacts a tool or process element of a different electric potential. This discharge across a dielectric gap (typically air) causes the dipole formed by the differing electrical potentials to collapse or a capacitor formed between charged IC and tool parts to collapse. An embodiment of the invention also provides an ESD event monitor, which is also referred herein as a "MiniPulse" detector (comprising a MiniPulse/MicroESD antenna and a MiniPulse detector unit) or ESD monitor. The monitor is, for example, a low-cost event monitor for workstations, electronics production tools, processes, and/or mobile applications. The resulting radiated electromagnetic pulse waveform (radiated signal) is detected by, for example, the MiniPulse detector and an antenna that is communicatively coupled to the MiniPulse detector. If the detected field voltage level of this pulse waveform is above the threshold calibrated with the Charged Device Model Event Simulator (CDMES) equipment, then the MiniPulse detector registers a significant CDM/ESD event.

The CDM/ESD events are, for example, characterized by short (typically less than approximately <NUM> nano-seconds) duration changes in the electromagnetic field and generate, in the antenna, an induced voltage (current) rising signal with a high slew rate. Therefore, regarding in tool ESD monitoring, the detection system used should distinguish a CDM signal of interest from a general tool noise in an echoic chamber environment.

According to various embodiments of the invention, calibration methods for ESD detectors are provided. A suitable equipment such as, for example, a CDMES device known in the art, may be used to simulate CDM events, and a calibration method is then performed according to an embodiment of the invention. For example, in situ monitoring of CDM events is facilitated by simulating a group of spark gap discharges in the real tool at the point where IC devices contact conductive tool elements. The collapsing charged capacitor discharge simulates CDM events at a pre-selected voltage/energy threshold value for a given IC device. When this procedure is completed, the tool can be said to be calibrated for IC (integrated circuit) CDM ESD event detection at the specified level.

The CDMES is configured in an example of one embodiment as a device with an open moving electrode in the discharge gap (or the device may be a mercury or RF relay, or high voltage RF relay such as, for example, a reed relay).

The CDM/ESD event simulated discharges generate signals that are intercepted and detected in the receiving antenna of the monitoring device (MiniPulse). The MiniPulse antenna (MicroESD antenna) is coupled to the MiniPulse (see <FIG>) and permits the MiniPulse to receive the waveforms due to an ESD event. The MiniPulse can be calibrated in situ by varying the CDMES discharge voltage/energy and/or the position of the MiniPulse antenna with respect to the expected CDM event source.

Therefore, the CDMES is a charged device simulator that creates a known energy radiated spark that is similar to a discharge occurrence when a charged device (like IC) is approaching or contacting a socket. This CDMES is used to calibrate the MiniPulse. A DC power supply is coupled to the CDMES, and any or various suitable power supply voltage values (e.g., 100V, 200V, 500V, or other values) are driven into the CDMES. When an ESD event is simulated, the antenna detects the waveform from the CDMES-created discharge, and the MiniPulse captures and processes the waveform detected by the antenna. An example of a waveform due to a CDMES-created discharge is observed in the oscilloscope as shown, for example, in <FIG>, as also further discussed below.

Based upon a calibration plot and known product CDM failure thresholds, the ESD threshold voltage level may be set up (or otherwise configured) for the MiniPulse detector. The output alarm signal from the MiniPulse will be generated and may be sent to a tool control system if CDM events exceed the threshold level for real IC discharge events in the tool.

The CDM Event Simulator has been designed to allow ESD monitors (detectors) to be calibrated inside the tools and processes where CDM events occur. This simulation device allows the creation of calibrated CDM events of different voltage amplitudes to be produced at the point where production devices are most vulnerable and where ESD monitoring sensors are located. This approach allows the highest level of handling safety for sensitive devices.

CDMES version/example: "Collapsing capacitor" with a mechanical gap to generate a CDM Event (see <FIG> and <FIG>).

This version or embodiment of the CDM Event Simulator (CDMES) uses a mechanical gap to generate a controlled discharge event and simulate the electrostatic discharge which occurs between a charged IC and either an object (target) at a different electrical potential or a ground reference. This mechanical gap is between two small plates forming a collapsing capacitor, wherein the collapsing capacitor comprises one charged plate with a contact point and one ground plate with second contact point.

Specifically, this embodiment models the Charged Device Model (CDM) discharge type which is characterized by a fast single-peak pulse waveform of transferred current between the device and ground. The CDMES power circuit incorporates high resistance (up to, for example, approximately <NUM> mega Ohms or more) so that the voltage across the mechanical gap is high (approximately 25V-3000V range) and the applied current is less than approximately <NUM> micro amperes across this range.

An electrostatic discharge would occur for an arbitrary charged contact and typical ground contact (see <FIG> and <FIG>). Therefore, when the CDMES <NUM> (<FIG>) is charged with a DC power supply voltage <NUM>, the CDMES <NUM> will simulate an ESD event.

The conducted CDM pulse as reproduced on the oscilloscope is a graph of the current pulse waveform and corresponds to the classical CDM waveform referenced in standards documents (IEC <NUM>-<NUM>-<NUM>, ISO10605, JESD22-C101E). The produced waveform also corresponds to the input CDM pulse waveform which formal device test machines (see standards referenced above as examples) use to evaluate device ESD susceptibility. That is why this type of collapsing capacitor CDMES presents a convenient calibration instrument for use in tools and other processing areas.

<FIG> is a diagram of a general view of a system <NUM> comprising a charged device model event simulator (CDMES) <NUM> with an external HVPS (high voltage power supply) <NUM>, in accordance with an embodiment of the invention. The CDMES <NUM> has a discharge head <NUM>, and the discharge head <NUM> is mounted to a handle and triggering mechanism <NUM>, in accordance with an embodiment of the invention. The EM (electromagnetic) transparent discharge head enclosure (e.g., made from Delrin) accommodates the collapsing capacitor. This collapsing capacitor is electrically coupled to an external DC HVPS (high voltage power supply) <NUM>. The high voltage power cable <NUM> connects power to the discharge head <NUM>. Cable <NUM> connects discharge head <NUM> with common ground <NUM>.

<FIG> is a diagram of a CDMES <NUM> with a collapsing capacitor, in accordance with an embodiment of the invention. The mechanical structure of a CDMES <NUM> with the "collapsing" capacitor comprises the following features.

The basic CDMES <NUM> uses a capacitor, created/arranged by a conductive plate on both of two PCBs (printed circuit boards) in close proximity to each other. The charged PCB <NUM> (in CDMES <NUM>) is movable by pressing the test button <NUM> on the handle <NUM> end, while the other PCB <NUM> (in CDMES <NUM>) is fixed.

The whole assembly (internal to the CDMES <NUM>) is contained within, for example, a Delrin housing to which are mounted the power connector <NUM>, ground connector <NUM> and the handle <NUM>. The voltage plate <NUM> of the movable charged PCB <NUM> is charged to the desired test voltage through a high value resistor <NUM>.

The fixed plate <NUM> (of fixed PCB <NUM>) contains a grounded plane surrounding an isolated "pogo pin" contact <NUM> (or another suitable type of contact <NUM>). This contact <NUM> is connected (via ground connector <NUM>) through a cable <NUM> to ground <NUM>.

When the CDMES button <NUM> is pressed, the charged board <NUM> is physically moved toward the fixed board <NUM>. Just before the PCBs contact, an ESD event will occur to the pogo pin contact <NUM>, thereby discharging the capacitor <NUM> formed by the plates <NUM> and <NUM>. Careful design eliminates contact bounce, ringing, etc., thereby leaving a clean ESD event which may be used to calibrate the "MiniPulse" or other ESD monitor. When the CDMES button <NUM> is released the movable PCB <NUM> returns to its relaxed position and is once again charged and ready for the next ESD event test.

An appropriate power supply <NUM> is used to generate the desired test voltage, from approximately <NUM> volts up to <NUM>,<NUM> volts. The test voltage, current limited by a resistor <NUM> of, for example, approximately <NUM> MΩ, is applied to the input connector <NUM> in order to power the board <NUM> and the electrode <NUM> (on the board <NUM>). The current is further limited by an internal 30MΩ resistor string <NUM> which is connected to the movable Charge Plate PCB <NUM> plane <NUM> through a flexible wire <NUM>. Another suitable type of resistor <NUM> may be used to limit the current to the PCB board <NUM>.

This board <NUM> which is in close proximity (e.g., approximately <NUM>") to the Target PCB <NUM> creates a capacitor "C" <NUM> which becomes charged to the desired full test voltage. To generate a test pulse, the spring <NUM> loaded Test Button <NUM> is depressed, thereby causing the Charge Plate PCB <NUM> to move toward the ground plane Target PCB <NUM>. As the separation distance decreases, the Source Charge Electrode <NUM> on the board <NUM> approaches the Target Electrode <NUM> until an arc/spark discharge is generated. This arc/spark causes a radiated signal to be emitted and this radiated signal is used to calibrate the MiniPulse ESD monitor (e.g., detector <NUM> or ESD detector <NUM> in <FIG>).

During the process of calibrating the MiniPulse detector, the collapsing capacitor (C) <NUM> allows the user to simulate various supply voltage values (e.g., approximately 20V, 100V, 500V, or other values) that are discharged into the Target Electrode <NUM> on PCB <NUM>. The user can also mechanically control the gap distance between the boards <NUM> and <NUM> by use of the button or actuator <NUM>. The arcing will be dependent on the voltage applied to the board <NUM> and the gap distance at the time of the discharge.

Additionally, the pulse is available through the coaxial wire connection <NUM> with a shield ground connection <NUM>. A coaxial wire <NUM> carries the pulse signal to the SMA output connector <NUM>. When the Test Button <NUM> is released, the spring load <NUM> causes the PCB <NUM> to return to the original position of the PCB <NUM> and the capacitor <NUM> recharges, and the capacitor <NUM> will be ready to perform the next test. Any suitable mechanism (e.g., springs or other mechanisms) may be used for automatically returning the PCB <NUM> to the initial position of the PCB <NUM> away from the PCB <NUM> when the button <NUM> is released.

Typically, the enclosure in <FIG> is a dielectric wall(s) and this enclosure will preferably not provide real attenuation to the electromagnetic fields (waveforms) occurring therein. Additionally, the power supply <NUM> and CDMES discharge head (connector <NUM>) must be tied to the same ground.

The collapsing capacitor <NUM> may have an effective capacitance of approximately <NUM> pF - <NUM> pF or more depending on the desired discharge energy range.

If the second electrode <NUM> is grounded, as in the case shown in <FIG>, the discharge energy W is fully defined as follows:
<MAT>
where C is the collapsing capacitor value, and V<NUM> is the voltage applied to the capacitor (before discharge). For example, if C = <NUM> pF and the applied voltage is 100V, then the discharge energy will be <NUM> x <NUM>-<NUM> J (Joules).

When the CDMES <NUM> activates, both electrodes of the capacitor C come to ground potential (the capacitor C is collapsed) and the electrical discharge of known energy W is generated.

<FIG> is a diagram of a system <NUM> (or apparatus <NUM>) including a charged device model event simulator <NUM> (or CDMES unit <NUM>), and wherein the system <NUM> is configured to also provide/illustrate a calibration method for an ESD event detector <NUM> (detector <NUM> and antenna <NUM> or ESD detector <NUM>), in accordance with an embodiment of the invention. Therefore, <FIG> illustrates a depiction and an example of a mutual position of a CDMES and ESD detector during the calibration of an ESD Event Detector <NUM> coupled to the antenna <NUM>. The ESD simulation performed by the CDMES <NUM>, and a calibration method for the ESD event detector <NUM>, may be done in a real tool or processing chamber <NUM> (in-situ). However, as mentioned above, embodiments of the CDMES <NUM> may also be used in an open work bench, any tabletop, a real environment, or any other suitable environment where a calibrated CDM event is created and detected for purposes of calibrating an ESD detector. More discussion on the ESD detector calibration in tool and processing is also discussed with reference to <FIG>. Additionally, the CDMES unit <NUM> may be embodied as the CDMES <NUM> in <FIG> and/or 2b.

As similarly discussed with reference to <FIG> and <FIG>, the CDMES <NUM> is coupled with (and operates with) the HVPS <NUM> (as shown, e.g., in <FIG> and <FIG>). When the handle's trigger button <NUM> (see <FIG>) is pressed, the CDMES unit <NUM> uses the voltage from the HVPS <NUM> and an ESD event generating mechanism (e.g., the features of the CDMES <NUM> as shown in <FIG>) in order to produce an ESD discharge pulse event.

The discharge head (of CDMES <NUM>) is charged by the preset calibration voltage from the HVPS <NUM> (<FIG> or <FIG>). The antenna <NUM> (coupled to the ESD detector <NUM>) intercepts the radiation <NUM> (or electromagnetic waves <NUM>) of the discharge event generated within the CDMES <NUM>. In an embodiment of the invention, the antenna <NUM> is specifically designed to certain applications to be used with this product ("MicroESD" antenna) and will be discussed below in additional details. The antenna <NUM> (or MicroESD antenna <NUM>) is configured to detect the different discharge energy levels in the radiation <NUM>. As also mentioned above, the simulation of the ESD event, by use of the CDMES <NUM> and corresponding elements (e.g., HVPS <NUM> and ESD detector <NUM> and antenna <NUM>), may be performed in the chamber <NUM> or may be performed outside of the chamber <NUM> (i.e., may be performed in an open work bench, any tabletop, a real environment, or any other suitable environment where a calibrated CDM is created and detected for purposes of calibrating an ESD detector <NUM>).

The drawing of <FIG> shows radiation waves <NUM> in the direction of the propagating electrical field, as the antenna <NUM> is positioned normal/perpendicular to the radiating element (discharge head) of CDMES <NUM>. Any signal will be largely due to reflections. If the CDMES head <NUM> were rotated approximate <NUM> degrees CCW (counterclockwise) the signal produced by antenna <NUM> would be significantly affected.

The CDMES <NUM> is generating a discharge at the point (as close as possible) where normal device handling occurs (e.g., at socket or sockets <NUM>), thereby simulating a device CDM discharge event in-situ. The ESD detector <NUM> (MiniPulse <NUM>) has a relay output to inform a tool control system of ESD events.

An antenna <NUM> (which is part of the ESD detector) is attached to the MiniPulse <NUM> input. The ESD trigger threshold energy level of the "MiniPulse" detector <NUM> is calibrated by an adjustment potentiometer to distinguish ESD events of interest.

The relay output of the ESD detector <NUM> may be used to monitor the MiniPulse Alarm status (of MiniPulse <NUM>). The relay output is, for example, an open collector driver which is pulled to ground concurrently with the audible alarm sounding from the MiniPulse <NUM>.

During the process of calibrating the MiniPulse detector <NUM> (<FIG>), various polarity and values of the supply voltage (e.g., approximately 20V, 100V, 500V, or other values) and the collapsing capacitor of CDMES <NUM> allow the user to simulate the desired ESD event energies/strength.

This apparatus and method of CDMES calibration of the novel ESD detector disclosed herein in an embodiment of the invention have a number of possible benefits that may be one or more of the following.

Additional possible advantages of this version of the pair/tandem CDMES - ESD event detector ("MiniPulse") include one or more of the following in one or more embodiments of the invention:.

Many applications in semiconductor, disk drive, FPD (Flat Panel Display), automated IC handling, and a host of other manufacturing processes operate with ESD sensitive products in locations which are difficult to monitor/control directly. In addition, many of these environments by their nature are saturated with EMI noise sources ranging from HVDC supplies, electrical motors, and actuators to broadband communication (RF) units. Detecting ESD events at specific points related to product handling can be challenging.

The main features of this embodiment of the detector/monitor (i.e., the novel ESD events detector <NUM>) are at least the following:
Controlling ESD detection by a pulse slew rate and duration in the nanosecond range: The "MiniPulse" detector <NUM> (<FIG>) is able to discriminate between different pulse event types. This allows the detector <NUM> to determine and select valid ESD-type events from other EMI (electro-magnetic interference or emission) pulse packet signals (e.g., signal discharges from motors, switching devices, cell phones, TV (television), WiFi, environmental noises, etc.).

Therefore, the "MiniPulse" detector <NUM> (see <FIG>) determines if an ESD pulse event fits within a selected pulse event threshold so that the "MiniPulse" detector <NUM> can determine if that ESD pulse event falls within the CDM charged device model instead of the machine model and human model. As known to those skilled in the art, ESD events in the charged device model (CDM) and the human body model (HBM) will differ in resistance factors, capacitance factors, and signatures. Although an embodiment of the MiniPulse detector <NUM> does not actually indicate the difference between CDM and HBM type ESD events, the MiniPulse detector <NUM> decides trigger validity based upon a signal amplitude (related to discharge energy) over the trigger threshold and whether the pulse event fits within the time buffer (i.e., qualifying as a pulse).

Adjustable discharge energy Threshold Control: Due to electromagnetic field attenuation over distance, many wider-area ESD events can be filtered out by adjusting the sensitivity threshold voltage to match local event amplitudes (e.g., thresholds of approximately <NUM> volt, <NUM> volts, <NUM> volts, or other values) so that the detector <NUM> compares the voltage levels of local event amplitudes with a sensitivity threshold voltage, or maybe present a threshold energy density in Joules with a range of approximately <NUM>. 002W/m2 to 663W/m2 so that the detector <NUM> compares the energy levels of local event amplitudes with a threshold energy level.

A selective ESD detection method is provided in an embodiment of the invention: ESD events produce electromagnetic pulses. This pulse is formally described as an electromagnetic radiation flux density which radiates outward spherically from the source, with radiated energy decreasing as the wave progresses away from the source. The MiniPulse <NUM> (detector <NUM>) samples this expanding field through interaction with an antenna <NUM> through inductive field coupling. The energy of the expanding electric field couples to the antenna <NUM>, thereby producing a signal on the antenna and cable. The MiniPulse detector unit <NUM> demodulates the incoming signal on the cable, thereby decomposing the various frequencies into their power components. The MiniPulse <NUM> measures the combined power of the radiated pulse transient to determine if the measured combined power (i.e., energy level of the radiated pulse transient) is greater than the detection threshold set (i.e., set threshold for detection). If the energy level is below the set threshold for detection, the event is ignored. In addition, the MiniPulse detector <NUM> also samples the incoming signal for pulse duration using a comparator circuit (see comparator <NUM> in <FIG> and comparator <NUM> in <FIG>) to determine if the pulse qualifies as a likely ESD event. If the pulse duration is within the time interval boundaries typical for CDM and HBM ESD events, the pulse triggers the detector <NUM>. This method of selective detection is different from standard time-domain (versus frequency domain) signal analysis. The MiniPulse <NUM> works like a spectrum analyzer which extracts the energy of the ESD event signal. The main advantage of this approach is in significant economy of detection hardware. The radiating pulse power across the signal frequencies gives a very good first order approximation of the signal power, thereby enabling a comparison to be made between different ESD event energy levels.

The "MiniPulse" energy threshold control sensitivity allows fine tuning down to very small signal acquisition areas (ESD source/target within a range of approximately <NUM> - <NUM> of antenna placement). This is an important aspect of limiting detected ESD events to only those of critical importance and/or those of interest to the user.

The antenna configuration in an embodiment of the invention is specifically designed and engineered as an ESD antenna <NUM> (see <FIG> and <FIG>). The antenna <NUM> can be embodied as an antenna assembly <NUM> of <FIG>, <FIG>, and <FIG> and will be discussed below in additional details.

<FIG> is a diagram of a system (or apparatus) <NUM>, in accordance with another embodiment of the invention. The diagram shows an example of an interaction of an ESD detector <NUM> with an in-tool controlling system.

The MiniPulse detector <NUM> has a controlled duty cycle feature which allows On-demand signal processing to aid/enhance in ESD signal separation from general noise (for example, in the form of non-ESD electromagnetic (EM) pulses). This signal filtering method is available for both the standalone and Novx monitor versions (when ESD detector <NUM> is combined with another sensor(s)). This signal filtering method is in addition to antenna and other filter features of this detector <NUM> as described herein.

The MiniPulse ESD detector <NUM> implements a standby mode which allows instantaneous activation and deactivation of signal acquisition. This standby mode feature allows processing tools to control ESD signal capture to the highest reputability of ESD detection.

Based upon actual tests, the repeatability estimate for this method ranges between approximately <NUM>%-<NUM>% probabilities. In controlled manufacturing environments, ambient pulse noise occurrence is typically held to a minimum, with pulse noise shots/spikes largely originating from nearby tools and processes.

A method, in an embodiment of the invention, requires the use of the control native inputs to the "MiniPulse" detector <NUM> (ESD detector <NUM>) by the host tool or process. Modern processing tools have control interfaces which track product movement and process functions. The "MiniPulse" detector acquisition control method allows the tool to signal specific processing windows (e.g., process windows <NUM> and <NUM> in <FIG>) where an ESD signature detection is desired. With process windowing, randomly occurring background pulse EM signals do not register to the tool as possible ESD events.

The electronic part of an ESD Detector device (detector <NUM>) is controlled by the tool to activate only during the process window when an actual device is being handled or tested. As an example, when the tool processes an individual device, the tool signals the ESD detector <NUM> to switch to active mode. When the processing window is closed (e.g., no device is being handled/tested), then the tool signals the detector <NUM> to return to standby mode. During the active processing window, the detector <NUM> will signal the tool if any ESD events of interest occur.

When the processing window is closed and the detector <NUM> is returned to standby status, no ESD or other signals will be reported by the detector <NUM> to the tool.

In <FIG>, the system <NUM> includes the tool which is processing an individual device <NUM> in a tool processing area <NUM>. The MiniPulse ESD detector <NUM> (detector <NUM>) intercepts the electromagnetic waves <NUM>, and the Robot Placement Effector <NUM> (or another suitable type of robotic arm <NUM>) places a charged device <NUM> into a test socket <NUM>. The test socket <NUM> is typically placed on a suitable test bed <NUM>, base <NUM>, or another suitable platform <NUM>. As the charged device <NUM> approaches the test socket <NUM>, a discharge (ESD) occurs and the antenna <NUM> (coupled to the MiniPulse Detector <NUM>) intercepts the waves <NUM> of the discharge event. In this example, the ESD event is a discharge <NUM> that takes place in the form of a spark between two parts (device <NUM> and test socket <NUM>) that are both characterized by different voltage potentials.

The tool controller <NUM> (of tool <NUM>) will signal (via control signal <NUM>) the robot controller <NUM> to process the device <NUM> thereby activating tool process window <NUM> (<NUM>) (see <FIG>).

The device <NUM> is moved to the tool test socket <NUM> for example testing. The tool controller <NUM> also activates (via control signal <NUM>) the detector <NUM> to report ESD events of interest related to device processing. The detector <NUM> reports any ESD events which occur when the device <NUM> contacts the socket <NUM>. When this process is finished, the tool controller <NUM> closes process window <NUM> (<NUM>) and signals the detector <NUM> to return to a standby mode. Depending upon the tool process throughput, the tool <NUM> will continue to process windows as devices are handled.

As an example, when the robot controller <NUM> has finished processing a device <NUM>, the robot controller will send control signal <NUM> to the tool controller <NUM> that the process window <NUM> is to be closed and the tool controller <NUM> will then close the process window <NUM>. The tool controller <NUM> then sends a control signal <NUM> to the detector <NUM> so that the detector <NUM> has information that the process window <NUM> is now closed. This control signal <NUM> will deactivate the detector <NUM> so that the detector <NUM> returns to the standby mode, while the control signal <NUM> will activate the detector <NUM> so that the detector <NUM> can measure, compare, and record the waves <NUM> which may be ESD events.

In an embodiment of the invention, the control signal <NUM> may be represented by rising edges of process windows such as, for example rising edges <NUM> and <NUM> of process window <NUM> (<NUM>) and process window <NUM> (<NUM>), respectively, in the tool device handling window <NUM>, as shown in <FIG> which illustrates a diagram of a tool device handling workflow <NUM>. The handling window <NUM> may have at least one process window and the number of process windows in the handling window <NUM> may vary.

Alternatively, the control signal <NUM> (<FIG>) may be pulses <NUM> and the control signal <NUM> may be non-pulse intervals <NUM> between the pulses <NUM> in the handling window <NUM>. <FIG> is a diagram of a system (or apparatus) <NUM>, in accordance with another embodiment of the invention. The system <NUM> is shown in a top plan view for purposes of clarity of discussion. As similarly discussed previously with regard to the system <NUM> in <FIG>, the system <NUM> is configured for electrostatic discharges (ESD) events monitoring and may incorporates a charged device model event simulator (CDMES) unit <NUM>.

In an embodiment of the invention, the system <NUM> includes at least one antenna 382a that is positioned in a process area 389a, and an ESD detector <NUM> coupled to the antenna 382a. Since the antenna 382a is configured to receive the event signal <NUM> radiating from a CDMES unit <NUM>, the antenna 382a is inductively coupled to the CDMES unit <NUM>. The ESD detector <NUM> is calibrated for different discharge energies generated by the CDMES unit <NUM>.

An ESD monitored process area would typically comprises an area bounded by a distance of up to approximately <NUM> circumference from the antenna location.

In another embodiment of the invention, a process area (generally shown as area <NUM>) includes a first process area 389a and a second process area 389b. The first antenna 382a is positioned in the first process area 382a and a second antenna 382b positioned in the second process area 389b.

In an embodiment of the invention, the first antenna 382a is coupled to the ESD detector <NUM> and the second antenna 382b is also coupled to ESD detector <NUM>. In another embodiment of the invention, the second antenna 382b is coupled to another ESD detector <NUM> and is not coupled to the ESD detector <NUM>.

Typically, the first process area 389a is separated from the second process area 389b by a distance <NUM>, and the first antenna 382a and second antenna 382b form multi-channels. The distance <NUM> is adjustable.

In one embodiment, the first antenna 382a and second antenna 382b may be similar in an antenna response sensitivity. In another embodiment, the first antenna 382a and second antenna 382b are different in antenna response sensitivities.

The process areas <NUM> may vary in number from one or more process areas. For example, the process areas <NUM> can be presented as a cluster of tools. Therefore, more than two process areas may be included in the system <NUM>.

At least one of the process areas <NUM> may include a socket <NUM> (<FIG>) that is configured to receive a semiconductor chip <NUM> or other device <NUM> (<FIG>), or may include a plurality of sockets <NUM> that are configured to receive a plurality of semiconductor chips or other devices.

At least one of the process areas <NUM> may include a tweezer <NUM> that is configured to receive a wafer <NUM> in another embodiment as best identified by reference <NUM>. Of course, the tweezer <NUM> may be another type of wafer processing tool <NUM>.

At least one of the process areas <NUM> (or wafer <NUM>) may include conductive traces <NUM> that are accessible by a test probe <NUM> in an embodiment as best identified by reference <NUM>. Any of the process areas <NUM> may be of another suitable type of area.

Reference is now made to <FIG>, <FIG>, and <FIG> in order to discuss additional details of various embodiments of an ESD antenna <NUM>. The features described in <FIG>, <FIG>, and/or 4c may be incorporated in the antenna <NUM> (<FIG>), antenna 382a (<FIG>), and/or antenna 382b (<FIG>). Therefore, the antenna discussed in <FIG>, <FIG>, and <FIG> can be embodied as an antenna <NUM>, antenna 382a, and/or antenna 382b.

<FIG> is a diagram illustrating a Micro strip ESD antenna assembly, in accordance with an embodiment of the invention. <FIG> is a diagram illustrating a shielded antenna with an aperture, in accordance with an embodiment of the invention. <FIG> is a diagram illustrating space gain characteristics of the micro strip antenna, in accordance with an embodiment of the invention.

Reference is first made to <FIG> which illustrates a micro strip antenna assembly <NUM>. The elements of the micro strip antenna are a focal element 401d, backplane shield 402d, additional shield enclosure 404c (shown in <FIG>), connector(s) (feed point) 403d, and coaxial cable 404d. The antenna design characteristics are: a) focal element area of approximately <NUM>/square to <NUM>/square, b) antenna focal element shape (for example: rectangular or triangular), and c) antenna attenuating backplane (blocking shield) to limit signal acquisition to the front side (directional) antenna focal element. These characteristic elements define the antenna area (physical gain which is a ratio of antenna field energy to antenna voltage output) to accomplish the directional detection sensitivity level and physical range of coverage required for any specific application. Referring to <FIG>, an example antenna gain pattern <NUM> is shown in relationship to an ESD event target 401e (for example, a sensitive device placed in a socket for testing). In <FIG>, the antenna focal element is (C) <NUM>, the front face of the antenna focal element has the highest directional gain (line (A) or front gain <NUM>, for example, approximately <NUM> dBi), and is oriented toward the ESD event source 401e. The backplane side of the antenna has a lower gain (line (B) or back gain <NUM>, for example, approximately <NUM> dBi or decibels relative to an isotropic antenna), which faces away from the ESD event source 401e. The antenna focal element has a side gain represented by the lines <NUM> and <NUM> between the lines represented by the front gain <NUM> and back gain <NUM>. Another key factor in ESD event detection to a specific process point is the form and placement of the antenna <NUM> (<FIG>). The physical gain characteristics of the antenna <NUM> play a significant part in controlling ESD signal acquisition. The directional gain (see <FIG>) feature of the specifically designed antenna (connected to the "MiniPulse" detector <NUM>) can be used to calibrate the detector <NUM> for given ESD events of interest to the user.

Antenna performance and noise insensitivity: The antenna <NUM> ("MicroESD" antenna <NUM> or micro antenna <NUM> or "MiniPulse" antenna <NUM>) is specifically designed for electrostatic discharge (ESD) event detection. The engineered characteristics of the antenna <NUM> allow ESD radiated energy to be directionally detected for the discharge (event source) location while ignoring/suppressing other nearby events not of interest.

Variant of this antenna is designed specifically for ESD event detection. The antenna comprises a proprietary micro-strip designed antenna surrounded by a metal casing 404c with an aperture 402c (see <FIG>). The antenna is designed to reject unwanted signals from surrounding areas in electromagnetically noisy tool processing areas. The aperture allows the internal antenna to acquire signals up to approximately <NUM> degree angle focused on a specific location or small area. Energy from any ESD event occurring in this focal area enters the aperture and couples to the micro strip antenna element.

Specific improvements of embodiments of the invention are provided over conventional technology and other available ESD event monitoring products.

The other type of antenna comprises a custom designed small printed circuit board (PCB) 401c, engineered to enhance directionality and the distance to be monitored. This antenna assembly (<FIG>) (comprising the PCB 401c) uses a ground plane on one side of the circuit board 401c and an active element on the other side of the circuit board 401c, thereby providing a back and side lobe rejection ratio of approximately <NUM> dB to <NUM> dB. The electrical link <NUM> (e.g., cable) is coupled to the circuit board 401c and removably coupled to an ESD detector <NUM> (<FIG>). The antenna also includes an integral RF connector 403c (<FIG>) which can be a general RF connector of any type.

Antennas used to detect ESD radiated pulse transients have traditionally been standard antennas with a very high gain. Whereas this makes detecting ESD events quite easy, it has made it virtually impossible to determine event origins. This weakness has made traditional antennas of little use in monitoring critical processes.

The "MicroESD" antenna <NUM> (e.g., the antenna <NUM> coupled to the MiniPulse detector <NUM> in <FIG>) was developed for the sole purpose of detecting ESD events in close proximity to their source. The MicroESD antenna <NUM> is embodied with various versions of designed microstrip antennas, as shown in the example antenna assembly <NUM> in <FIG>, which has an excellent ESD near-field radiant pulse reception, while rejecting other near and far-field pulse signatures due to engineered directional gain characteristics. This allows the MicroESD antennas to perform well where other antennas do not do so in identifying localized ESD events of interest.

In addition, the designed characteristics of this antenna allow a very wide signal discrimination range (approximately 10V - 3000V) which is not the case with general antennas commonly used in ESD detection due to saturation effects. When used in conjunction with attenuators, very large ESD events can be captured effectively.

ESD events should preferably be monitored as close to their expected source as practical. Typical monitoring distances for the antenna installation range from, for example, approximately <NUM>" (<NUM>) and approximately <NUM>" (<NUM>), although other distances can be accommodated. The Micro ESD antenna <NUM> will purposefully become less efficient with greater distance from the source due to signal amplitude reduction and detection threshold settings.

Multiple antennas can be deployed as arrays of dipole structures in almost any configuration. For example, five antennas can be deployed to form an array. However, the array of dipole structures may have more than five antennas or less than five antennas.

A block diagram of the details of the ESD Event Detector is now discussed in an embodiment of the invention. For example, the ESD event detector <NUM> of <FIG> comprises the system <NUM> (or circuit <NUM>) of <FIG>.

The antenna <NUM> generates a signal (RF or radio frequency signal) <NUM> delivered via an attached coaxial cable <NUM>. The signal <NUM> is first processed by a digital attenuator <NUM>. This processing limits the ESD signal and noise levels to keep the subsequent ladder network filter and demodulating log-amplifier from saturation. The attenuator <NUM> is programmable via the microprocessor <NUM>, thus allowing the detector <NUM> to accommodate a wide variety of noise environments by attenuating the signal and noise up to, for example, approximately <NUM> dB.

The <NUM> order high-pass ladder network filter <NUM> blocks any DC signals and passes the ESD Event signals above <NUM> (megahertz) typical of an ESD event to the log-amplifier <NUM>.

A very fast (in micro seconds) six stage demodulating log amplifier <NUM> (e.g., Analog Devices AD8310) extracts multi-frequency amplification levels (dBm or decibel-milliwatts) from the detected ESD signal. This allows the MiniPulse detector <NUM> to discriminate signal levels for threshold control more accurately.

The output signal <NUM> of the log amplifier <NUM> is inverted so when a signal is input the log amplifier's output will be between approximately +<NUM>. 5V (no signal) and approximately +<NUM>. 0V or less (maximum signal). Therefore, embodiments of the invention provide a demodulating log amplifier <NUM> that operates in a measurement mode and generates an output signal <NUM> that is matched with a selected threshold for discriminating signal levels. This technology and method has not been used by other known ESD detectors.

The data <NUM> from the microprocessor <NUM> is used to set a threshold voltage level of a digital potentiometer <NUM>, wherein that threshold voltage level is in the range of approximately +<NUM>. An ultra-high speed comparator <NUM> (e.g., Analog Devices AD8561) compares the demodulating log amplifier <NUM> output signal with this threshold voltage. If the comparator <NUM> "sees" a true condition, a momentary pulse is passed to a pair of multi-vibrator one-shots <NUM>. The one-shots <NUM> are configured to reject any pulse that is too short (<~10nSec) or too long (>~500nSec) meaning that the pulse is not an ESD event of interest. As shown in <FIG>, the log amplifier <NUM> generates the output signal <NUM> after receiving an input signal from the filter/integrator <NUM> which will discussed further below with reference to <FIG>.

True event pulses <NUM> are then counted (e.g., by a counter <NUM>) and that count (from counter <NUM>) is available to the Novx microprocessor (e.g., Atmel microcontroller) <NUM> for processing. Each time the count is read by the microprocessor <NUM>, the count is then subsequently and automatically reset to zero by the microprocessor.

Reference is now made to the block diagram <NUM> of <FIG> and the circuit diagram <NUM> of <FIG>, in an embodiment of the invention. As noted above, <FIG> is a block diagram of an ESD detector <NUM> (MiniPulse <NUM>), in accordance with an embodiment of the invention. <FIG> is a schematic diagram of the ESD monitor circuit <NUM>, and this schematic diagram shows additional details of the block diagram <NUM> of the ESD event detector <NUM> of <FIG>, in accordance with an embodiment of the invention. The MiniPulse <NUM> is also shown as (and described as) the ESD detector <NUM> in <FIG>.

The MiniPulse <NUM> uses a six-dimension algorithm by analyzing EMI events in the time domain and threshold discrimination to detect pulse electrostatic discharge of certain electromagnetic energy. Through the use of specific antenna configurations and antenna placement relative to the object being monitored, the MiniPulse <NUM> can provide ESD event detection for specific small areas of interest or for wider area coverage.

The ESD detector presented uses a demodulating log amplifier <NUM> to measure signal power. The first stage of the threshold detector uses a slope determination algorithm as a comparator to determine ESD pulse qualification based upon a 350ns envelope characteristic of the majority of ESD signal types.

The second stage of the detector rectifies the ESD signal, thereby ignoring positive or negative elements since ESD event peak amplitude is the only measurement of concern for discrimination purposes.

The third stage of the detector then compresses the ESD signal.

The fourth stage of the detector demodulates the signal across a <NUM> spectrum.

The fifth stage of the detector is the peak amplitude measurement output given as the log of the rectified signal envelope.

The sixth and final stage is a threshold comparator <NUM> which evaluates the output signal amplitude to the variable threshold representing the demarcation of a valid ESD event signal.

The ESD event signal <NUM> is detected by an antenna <NUM> (shown as antenna <NUM> in <FIG>) connected to shielded cable <NUM> and attached to an input connector (e.g., an input SMA connector). The signal (signal plus noise) is first passed through an attenuator <NUM>. The attenuator <NUM> using data from the microprocessor controller <NUM> is programmed in <NUM> dB steps from zero to <NUM> dB. This allows the circuit to be adjusted to reduce the signal so that the noise falls below the detection threshold while leaving signals of interest detectable (discussed later).

The signal <NUM> from the attenuator <NUM> is then passed to a filter/integrator <NUM> (e.g., a <NUM> order RC (resistor-capacitor) high-pass filter) which is tuned to pass the distorted frequencies (><NUM>) typical of a true ESD event and reject signals outside that frequency range. The filtered signal <NUM> (from the filter/integrator <NUM>) is then passed to a log-amplifier <NUM>, which is a very fast six stage demodulating log-amp (e.g., Analog Devices AD8310), and the log-amplifier <NUM> filters the incoming signal, and discriminates by power, duration, and amplitude. The log-amplifier <NUM> inverts its output signal so the stronger the input ESD event signal strength, the lower the log-amplifier's output voltage <NUM>. Typically, this signal <NUM> will range between approximately <NUM>. 5V and approximately <NUM>.

A reference threshold voltage is generated using the +<NUM>. 3V supply and a digital potentiometer <NUM> voltage divider. The digital potentiometer <NUM> is controlled by data from the microprocessor <NUM>.

The output voltage <NUM> from the log-amplifier <NUM> is then compared to a preset DC voltage <NUM> from the digital potentiometer <NUM>, using an ultra fast comparator <NUM> (e.g., Analog Devices AD8561).

If the comparator (AD8561) <NUM>, detects a signal (on the "-" or negative input) which goes below reference voltage <NUM> (on the "+" or positive input) a negative true condition <NUM> is momentarily developed on the output of the comparator <NUM>. This pulse <NUM> is then passed to the timing discriminator <NUM>, comprising a pair of one-shot multi-vibrators 657a and 657b. One-shot vibrator 657a will be clocked on and Q = true (assuming the J input is true). When the one-shot pulse <NUM> resets (due to the RC timeout, of approximately 250nSec (nanoSeconds)) the second one-shot vibrator 657b will set Q to true only provided the output <NUM> of comparator <NUM> has returned high because the output <NUM> of comparator <NUM> is a single, sufficiently fast pulse. If a pulse (in output <NUM>) is too long in duration, e.g., > ~500nSec, thereby indicating that the pulse (in output <NUM>) is not an ESD event of interest, then that pulse is ignored.

Therefore, the one-shot vibrator 657b causes Q to be set to true only because a pulse has been determined to be an ESD event of interest. The output of one-shot vibrator 657b then causes the counter <NUM> to "add <NUM>" to any existing count already present in that counter <NUM>.

<FIG> shows a general view of a MiniPulse ESD detector <NUM> as seen externally in one embodiment of the invention. The detector enclosure <NUM> has small dimensions of approximately <NUM>" x <NUM>" x. As previously discussed, the detector <NUM> can include a set of different antennas depending upon the object of in-situ ESD detection, tool, or/and monitoring task. However, the ESD detector <NUM> may have another type of configuration that differs from <FIG>.

In one embodiment, the MiniPulse panel of detector <NUM> includes a <NUM>-pin power connector <NUM> where approximately 7VDC-24VDC is typically provided to power the instrument (detector <NUM>). The external antenna's coaxial cable (e.g., cable 404d in <FIG>) will be attached to the SMA (SubMiniature version A) connector <NUM> of the detector <NUM>. A test point for ground <NUM> is provided by the detector <NUM>. There is a test point <NUM> in the detector <NUM> where a voltmeter probe may be inserted to be used while adjusting and or checking the threshold level potentiometer <NUM> setting.

The ESD Event Alarm circuitry drives an Audible transducer which lies directly below the sound port <NUM>, a pair of LED indicators <NUM> and <NUM> and the externally accessible output connector <NUM> in the detector <NUM>. The green LED <NUM> indicates power is on and there is no alarm. As an example, when an ESD event is detected, the audible alarm <NUM> sounds, the green LED <NUM> is extinguished, the red LED <NUM> illuminates and the open collector Alarm Output <NUM> is pulled to ground.

An optional self-contained external LCD counter may be attached to the open collector Alarm Output <NUM> to register the total detected events until the count is cleared manually. Alternatively, the open collector Alarm Output <NUM> may be connected to some other circuit, e.g., a computer input, which may be used for machine control, communication, reporting, etc..

<FIG> is a flowchart of a calibration method 800a and implementation for an ESD detector, in accordance with an embodiment of the invention. It is noted that the order of the steps in the method 800a may vary, and some particular steps may also be performed concurrently. At 801a and 802a in the calibration method 800a, formal laboratory device CDM tests are performed on randomly sampled candidate devices. At 803a, a determination is performed on the device of interest voltage/current failure level. At 804a, a determination is made if the ESD voltage failure threshold monitoring level is lower than a device failure threshold. How much lower the ESD voltage failure threshold (than the device failure threshold) will be dependent on the device type and critical manufacturing process points for monitoring for presence of ESD events (examples: e.g., testers and/or handlers). At 805a, the method 800a comprises establishing a miniPulse ESD detector threshold using a CDMSES calibration protocol.

<FIG> also illustrates a flowchart of a MiniPulse ESD calibration process 800b, in accordance with one embodiment of the invention.

For process 800b, an in-situ ESD event calibration process is conducted with a CDM Event Simulator (CDMES). Examples of the in-situ ESD event calibration process have been described above with reference to the apparatus <NUM> in <FIG>.

At 801b, the basic MiniPulse calibration procedure starts.

At 802b, a MiniPulse ESD Event Detector with an appropriate antenna is installed in a tool or process point.

At 803b, a CDMES tool is used to calibrate a MiniPulse antenna ESD signal reception.

At 804b, the MiniPulse ESD Detector is calibrated for ESD signal voltage level (typically, approximately <NUM>%-<NUM>% below a device failure threshold).

At 804b, a continuous ESD monitoring protocol may be instituted with a MiniPulse ESD detector to assure quality compliance.

When the MiniPulse ESD detector <NUM> is calibrated for a specific device withstand voltage threshold, this voltage/energy threshold will typically be set at a voltage level that is less than the actual voltage failure level of the device (at 804b). For example, if a device has an actual voltage failure level of approximately <NUM> volts, then the voltage threshold will be set below <NUM> volts such as, e.g., approximately <NUM>% of the voltage failure level or approximately <NUM> volts. This approach prevents actual damages to occur in devices. Therefore, at 805b, an allowable applied voltage threshold is determined for each device type to be tested. At 805b, a signal-to-noise ratio (SNR) filter in the detector <NUM> is adjusted to suppress EMI in the tool and/or process.

At 806b, the CDMES calibration output waveforms may be confirmed using an oscilloscope connection (this procedure at 806b is optional).

At 807b, the MiniPulse ESD detection reliability may verified using a minimal statistical sample. The verification in 807b may be performed after the confirmation in 806b is performed.

At 808b, a continuous ESD event monitoring is instituted according to a quality assurance protocol.

At 808b, a minimum statistical sample/shot is applied for PASS/FAIL ESD event detection validation for each location. For example, about <NUM> or <NUM> shots are applied to obtain accurate calibration.

At 806b, an ESD detector <NUM> (e.g., a MiniPulse detector) is calibrated for a specific device withstand voltage threshold. It is noted that after the procedures in blocks 803b, 805b, and/or 808b are performed, the procedures in block 806b may then be performed.

The following discussion provides additional details on the sequence of the in-situ calibration process in one embodiment of the invention:.

There is ambient tool/background noise, and there are ESD events outside of the application focal area which can interfere with detection of signals of interest. Therefore there are multiple noise sources to be considered.

This makes the Signal-to-Noise (SNR) ratio difficult to maintain for some applications.

Under some circumstances (SNR Collapse), the detector will not be able to function (i.e., separate target ESD signals from all sources of background interference).

<FIG> is a graph <NUM> showing how ESD signal amplitude is reduced by distance from the detector antenna <NUM> (signal to noise ratio by distance), which makes the signal amplitude close to the noise amplitude. As the SNR collapses, it becomes difficult to separate the ESD signal from the noise signal.

Under some circumstances (SNR collapse), the detector will not be able to function (i.e., separate target ESD signals from all sources of background interference). For example, the example function <NUM> (SNR versus distance in centimeters) indicates (at point <NUM>) an SNR minimum level of approximately <NUM> at a distance of approximately <NUM> centimeters from the source of the ESD.

<FIG> is a graph <NUM> showing a basic <NUM> V/m CDMES calibration at approximately <NUM>" distance with zero attenuation. Graph <NUM> shows the following functions based on a millivolts (of the MiniPulse antenna <NUM>) versus signal measurements that are occurring during the calibration procedure: Target ESD events <NUM>, background noise level <NUM>, rejected ESD events <NUM>, and MiniPulse threshold setting <NUM>.

Additionally, the following parameters <NUM> are applicable in the graph <NUM>:.

<FIG> is a graph <NUM> showing an induced signal with approximately 10dB attenuation. Graph <NUM> shows the following functions based on a millivolts (of the MiniPulse antenna <NUM>) versus signal measurements that are occurring during the calibration procedure: Target ESD events <NUM>, background noise level <NUM>, rejected ESD events <NUM>, and MiniPulse threshold setting <NUM>.

This example (in <FIG>) shows that the SNR ratio is getting smaller. But both background noise and false ESD events are now rejected. Also the significant signal space left and maximum SNR (mV) is <NUM>.

The signal-to-noise ratio (SNR), as mentioned above, can be very unfavorable for discriminating signals of interest (in this case ESD events caused by charged products) as the distance between the signal source and the interception point (of the signal from the signal source) grows. In general, electromagnetic tool noise created by electrical components is lower than the radiated amplitude of the ESD signals of interest.

However, without filtering, many of the ESD signal amplitudes as source distance increases are too close to the peak noise level to allow effective discrimination. The MiniPulse ESD detector <NUM> in its various forms has had signal time domain (duration) filtering and ESD signal threshold filtering since its inception. Whereas this has allowed a better resolution than other detectors, there have still been certain applications where noise levels have made this filtering approach problematic as well. With the addition of the noise filtering method described above, this has made SNR discrimination much more effective.

The MiniPulse ESD detector <NUM> has a proprietary electromagnetic noise filter to condition the input signal in high-noise environments. This variable impedance filter is an amplitude attenuation function for background broadband noise from all sources, but most commonly in automated tools. Automated tools commonly have variable levels of noise (EMI) from tool electrical components which can cause ESD signal interception problems. Usual methods for filtering electromagnetic signals involve band-pass filters, which attenuate signals by frequency.

The proprietary method cited herein uses digitally controlled variable impedance to attenuate general signal amplitude as a first threshold to remove radiated circuit noise below a given level. The MiniPulse ESD detector <NUM> also includes a second settable threshold (previously referenced) to act as an amplitude filter for ESD signals of interest.

<FIG> is a graph <NUM> showing an example of unfiltered ambient pulse noise representing ESD pulse signal interference. This type of interference, common for other ESD detection systems, has made tool adaptation very difficult and often impossible. Actual embedded ESD events of interest are shown by the signals <NUM>, <NUM>, <NUM>, and <NUM>. Graph <NUM> shows the number of false ESD event counts (background noise) on the Y-axis versus the counts of electrostatic discharge occurrences (ESD count) on the X-axis.

<FIG> is a graph <NUM> showing the use of variable signal attenuation/impedance that allows the detector to effectively ignore ambient/tool noise. In particular, graph <NUM> shows the ESD count <NUM> based on decibel measurements versus the counts of electrostatic discharge occurrences.

<FIG> is a graph <NUM> showing that after variable impedance filtering has been applied, true ESD signals of interest can be easily separated from background noise levels. Shown in graph <NUM> is a series of four (<NUM>) real ESD events <NUM>, <NUM>, <NUM>, and <NUM> which would have been lost in the general noise of an unfiltered input to the ESD detector. The Y-axis of graph <NUM> indicates an ESD event count and the X-axis of graph <NUM> indicates the counts of electrostatic discharge occurrences.

The samples of in-situ calibration with selectively moving up or down of the attenuation factor (in practice, the threshold of monitoring energy levels) make possible to analyze real in-tool level signals and optimize the signal noise ratio (SNR) for each application.

In summary, the product, apparatus embodiments, and methods described herein provide real information on ESD events in tools and processes. This allows the customer to determine ESD event risk relating to product charge related vulnerabilities. Also, the product, apparatus embodiments, and methods described herein allow the customer to evaluate the need for remediation to eliminate the risk including possible tool ionization and other methods of neutralization or protection.

It is also understood that other systems according to an embodiment of the invention can have various forms and can have different components that are arranged in other ways or orientations.

Other variations and modifications of the above-described embodiments and methods are possible in light of the teaching discussed herein.

While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

Claim 1:
An apparatus for detecting electrostatic discharge ESD events, the apparatus comprising:
- an ESD detector (<NUM>) the ESD detector being configured to detect an ESD event;
- at least one antenna (<NUM>) coupled to said ESD detector (<NUM>); and
- a controller (<NUM>) configured to activate a process window (<NUM>, <NUM>) to enable the ESD detector (<NUM>) to report the ESD event occurring during the process window (<NUM>, <NUM>); and
- deactivate the process window (<NUM>, <NUM>) to cause the ESD detector (<NUM>) to ignore electromagnetic signals;
characterised in that
- said ESD detector (<NUM>) comprises an attenuator; and
- said ESD detector (<NUM>) is calibrated for at least one discharge energy threshold or range of discharge energies by adjusting the attenuator to suppress electromagnetic interference outside the at least one discharge energy threshold or the range of discharge energies detected during the process window.