Patent Description:
Ion emitters of charge neutralizers generate and supply both positive ions and negative ions into the surrounding air or gas media. To generate gas ions, the amplitude of the applied voltage must be high enough to produce a corona discharge between at least two electrodes arranged as an ionization cell. In the ionization cell, at least one electrode is an ion emitter and another one may be a reference electrode. <CIT> describes an ionizer, a static charge eliminating system, an ion balance adjusting method, and a workpiece static charge eliminating method. <CIT> describes a control system of a balanced micro-pulsed ionizing blower. <CIT> describes a voltage source adapted to excite a gas-ionization electrode so as to generate copious amounts of ionized gas without producing measurable amounts of undesirable reactive or toxic chemical by-products.

An apparatus for adaptive charge neutralization is disclosed, substantially as illustrated by and described in connection with at least one of the figures, as set forth more completely in the claims.

Ionizers, or charge neutralizers, emit positive and/or negative ions to discharge static electricity that may be present on a surface or substrate, such as in a manufacturing facility. Disclosed example methods and apparatus for charge neutralization can be used in class <NUM> cleanroom production environments, and are particularly useful for semiconductor chip manufacturing.

Conventional charge neutralizers emit a predetermined balance of positive ions to negative ions, which can be adjusted by the operator via software and/or an input device. However, conventional charge neutralizers lack feedback mechanisms to accurately determine whether the predetermined balance is appropriate to the charge present at the target during operation.

Disclosed example apparatus for charge neutralization adapt an output ion balance based on balance voltage feedback. Example methods and apparatus for charge neutralization disclosed herein modulate a high voltage, high frequency AC signal using a DC offset signal to control generation of positive and negative ions. To adapt the output ion balance and thereby increase accuracy of the resulting balance voltage at the target, disclosed example methods and apparatus for charge neutralization increase or decrease the duty cycles of the DC offset signal to adapt the modulation of the high voltage, high frequency AC signal. Disclosed example methods and apparatus for charge neutralization are capable of more accurate balance voltages and substantially reduced swing voltages relative to conventional charge neutralizers. Some disclosed methods and apparatus for charge neutralization achieve a swing voltage of +/-5V, which has substantial benefits for voltage-sensitive and charge-sensitive applications, such as semiconductor manufacturing.

As used herein, "exceeding" a threshold voltage can occur in either the positive (e.g., more positive than the threshold) or negative (e.g., more negative than the threshold) directions.

As used herein, a "balance voltage" refers to a net voltage from ionization by the emitter.

The terms "ionization" and "charge neutralization" are used interchangeably in this document.

Disclosed example apparatus for charge neutralization include: a first emitter nozzle; a power supply configured to supply a high frequency alternating current (AC) signal to the first emitter nozzle; and control circuitry configured to: provide a polarity signal to the power supply to generate a DC offset signal, wherein a combination of the high frequency AC signal and the DC offset signal causes the power supply to output a positive ion generation pulse or a negative ion generation pulse; control the polarity signal to cause the power supply to provide a period of positive ion generation and a period of negative ion generation; determine a balance voltage at an output of the first emitter nozzle; and control the polarity signal to adjust a relative durations of the period of positive ion generation and the period of negative ion generation based on the balance voltage.

In some example apparatus, the combination of the high frequency AC signal and the DC offset signal has a peak voltage higher than a corona generating threshold voltage for the first emitter nozzle. In some example apparatus, the combination of the high frequency AC signal and the DC offset signal causes a voltage at the first emitter nozzle to exceed only one of a positive corona generating threshold voltage or a negative corona generating threshold voltage per high frequency AC cycle.

In some example apparatus, the control circuitry is configured to determine the balance voltage based on a feedback signal from an antenna. In some example apparatus, the antenna is positioned adjacent an ionization target. In some example apparatus, the control circuitry is configured to determine the balance voltage based on a feedback signal from a closed loop controller.

In some example apparatus, the power supply applies a resultant signal to the first emitter nozzle based on the combination of the high frequency AC signal and the DC offset signal, wherein the resultant signal causes a voltage at the first emitter nozzle to exceed a positive corona generating threshold voltage or a negative corona generating threshold voltage. In some example apparatus, the high frequency AC signal does not exceed either of the positive corona generating threshold voltage or a negative corona generating threshold voltage when the control circuitry controls the polarity signals to not generate the DC offset at the power supply.

In some example apparatus, the emitter point is silicon-based or titanium-based. Some example apparatus include a plurality of emitter nozzles including the first emitter nozzle. In some example apparatus, the control circuitry is configured to modulate the polarity signal based on the balance voltage to control a duty cycle of the positive ion generation pulses or the negative ion generation pulses. In some example apparatus, the control circuitry is configured to determine the balance voltage based on a feedback signal from an antenna. In some example apparatus, the first emitter nozzle includes an emitter point held within a stainless steel sleeve, wherein the power supply is configured to apply the combination of the high frequency AC signal and the DC offset signal to the emitter point with respect to the sleeve.

<FIG> illustrates an example AC charge neutralization system <NUM> configured to control an ionization output based on balance voltage feedback. The example AC charge neutralization system <NUM> outputs positive and negative ions <NUM> to neutralize electric charges on a target device or substrate <NUM>.

To generate the ions <NUM>, the example system <NUM> includes one or more ion emitter nozzles <NUM>, which are coupled to one or more power supplies that provide a high voltage, high frequency AC signal for generation of the ions <NUM>. The system <NUM> may include any number of emitter nozzles <NUM> to disperse ions <NUM> to a desired area or size of the target device or substrate <NUM>. By alternating positive and negative ions, the example system <NUM> effectively neutralizes static charge present on the target device or substrate <NUM>, while reducing or avoiding charging the target device or substrate <NUM> with the ions <NUM>.

The system <NUM> of <FIG> alternates positive and negative ions by controlling the output voltage at the nozzles <NUM> to output periods of positive ions and periods of negative ions. The relative durations of the positive period to the negative period may be controlled based on a desired balance. In contrast with conventional charge neutralization systems, the example system <NUM> achieves a balance voltage within +/- 5V by measuring the balance voltage via an antenna <NUM> and adjusting the ion balance based on the measurements. For example, the system <NUM> may adjust the relative durations of positive ion periods and negative ion periods to adjust the output balance. The antenna <NUM> may be positioned near the target <NUM> such that the antenna <NUM> measures a balance voltage representative of the output of system <NUM>. Using the feedback from the antenna <NUM>, the system <NUM> repeatedly (e.g., constantly) adjusts the relative balance of positive and negative ion generation periods.

<FIG> is a block diagram of an example implementation of the AC charge neutralization system <NUM> of <FIG>. The example of <FIG> includes an in-line ionizer <NUM> having a high voltage, high frequency (HVHF) power supply <NUM> which outputs an HVHF signal to an emitter assembly <NUM> having a number of emitters <NUM>. In some examples, the emitters <NUM> are silicon-based or titanium-based. Based on the HVHF signal from the power supply <NUM>, the emitters <NUM> create and output positive and negative ions.

The HVHF power supply <NUM> includes a DC-DC converter <NUM>, an AC HV inverter <NUM>, a DC offset generator <NUM>, and an AC HV amplifier <NUM>. The DC-DC converter <NUM> outputs a DC signal to the inverter <NUM>, which generates an AC signal. The DC offset generator <NUM> selectively generates a DC offset signal based on polarity control signals <NUM>, <NUM>. If a positive polarity control signal <NUM> is active, the DC offset generator <NUM> generates a positive DC offset. Conversely, if a positive negative control signal <NUM> is active, the DC offset generator <NUM> generates a negative DC offset. If neither of the polarity control signals <NUM>, <NUM> are active, the DC offset generator <NUM> does not generate a DC offset. The DC offset voltage, whether positive or negative, is combined with the AC signal output by the AC HV inverter <NUM> to generate a combined signal.

The AC HV amplifier <NUM> amplifies the voltage of the combined signal output by the DC offset generator <NUM>.

The example ionizer <NUM> includes control circuitry <NUM> to control the HVHF power supply <NUM>. The example control circuitry <NUM> may include a general purpose microprocessor, a microcontroller, a system-on-a-chip (SoC), an application specific integrated circuit (ASIC), and/or any other type of digital and/or analog circuitry.

The control circuitry <NUM> includes at least one controller or processor that controls the operations of the ionizer <NUM>. The control circuitry <NUM> receives and processes multiple inputs associated with the performance and demands of the system. The control circuitry <NUM> may include one or more microprocessors, such as one or more "general-purpose" microprocessors, one or more special-purpose microprocessors and/or ASICS, and/or any other type of processing device. For example, the control circuitry <NUM> may include one or more digital signal processors (DSPs).

The example control circuitry <NUM> may include one or more storage device(s) and one or more memory device(s). Storage device(s) (e.g., nonvolatile storage) may include ROM, flash memory, a hard drive, and/or any other suitable optical, magnetic, and/or solid-state storage medium, and/or a combination thereof. The storage device stores data (e.g., ionization configuration data), instructions, and/or any other appropriate data. Memory device(s) may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory device(s) and/or the storage device(s) may store a variety of information and may be used for various purposes. For example, the memory device(s) and/or the storage device(s) may store processor executable instructions (e.g., firmware or software) for the control circuitry <NUM> to execute.

The example control circuitry <NUM> outputs a target voltage level signal to the DC-DC converter <NUM> to control a DC output voltage to the AC HV inverter <NUM>, and controls the polarity signals <NUM>, <NUM> to the DC offset generator <NUM> to control the output. By controlling the polarity signals <NUM>, <NUM>, the example control circuitry <NUM> may control a balance of positive and negative ion output by the emitters <NUM>.

The example control circuitry <NUM> further receives an balance voltage input <NUM> from a remote ion balance sensor, such as the antenna <NUM> of <FIG>. The example control circuitry <NUM> may further include, or receive an input from, a balance detector which is connected to an antenna located near the ionization target. The balance detector may be implemented using a Simco-Ion™ Novx-based control system, such as the Novx <NUM> Closed-loop Ionizer Controller or the Novx <NUM> Closed-loop Ionizer Controller. In other examples, the control circuitry <NUM> or the ionizer <NUM> may include the balance detector, which receives the feedback signal directly from the antenna <NUM>.

The example control circuitry <NUM> may execute a PID controller, and/or other type of filter, to filter the balance voltage measurement received via the antenna <NUM>. In some examples, the balance voltage input <NUM> is determined using an analog-to-digital converter (ADC) circuit configured to receive the input signal from the antenna <NUM>, and the control circuitry <NUM> applies one or more filters and/or control loops to the balance voltage input <NUM> to adjust a balance value for controlling the polarity signals <NUM>, <NUM>. The control circuitry <NUM> receives the balance voltage input <NUM> at a regular interval, as often as the ADC or other circuit can sample and deliver the balance voltage input <NUM>, in response to one or more event types, and/or at any other times.

A pressurized source of air, nitrogen, or argon may be connected to the in-line ionizer <NUM> via an inlet to create an air flow or gas flow. In other examples, the emitter assembly <NUM> may permit flow of ambient air to carry the ions toward the output of the emitter assembly <NUM>. When present, the air flow or gas flow entrains positive and negative ions and carries the ions through an ionizer outlet toward a target (e.g., target <NUM> of <FIG>).

<FIG> illustrates example input signals to the power supply <NUM> of <FIG> to control output of positive and negative ions via a DC offset signal. The example control circuitry <NUM> compares a count signal <NUM> to a balance value <NUM>, which is set by the control circuitry <NUM> based on a balance setpoint and based on the balance voltage input <NUM>. The example control circuitry <NUM> may control the count signal to increment and decrement based on a clock signal of the control circuitry <NUM> to maintain a consistent timing. While the count signal <NUM> is less than the balance value <NUM>, the control circuitry <NUM> controls the negative polarity signal <NUM> to be active and the positive polarity signal <NUM> to be inactive. Conversely, while the count signal is greater than the balance value <NUM>, the control circuitry <NUM> controls the negative polarity signal <NUM> to be inactive and the positive polarity signal <NUM> to be active. Accordingly, the positive polarity signal <NUM> will be active longer as the balance value decreases (e.g., a less positive or more negative balance voltage is measured), and the negative polarity signal <NUM> will be longer as the balance value increases (e.g., a more positive or less negative balance voltage is measured). In some examples, the control circuitry <NUM> may further implement a pulse signal <NUM> to control the power supply <NUM>. For example, the pulse signal <NUM> may be used to control an output of the AC HV inverter <NUM> to turn on and turn off the AC high frequency signal. While the polarity signals <NUM>, <NUM> may be active at a given time, a low value (e.g., off) of the pulse signal <NUM> turns off the output of the power supply <NUM> until the pulse signal <NUM> is changed to a high value (e.g., on). The pulse signal <NUM> may be used to reduce the ionization swing voltage without significantly affecting the decay time, in some types of applications in which achieving both decay time and swing voltage requirements is difficult to achieve. Additionally or alternatively, the pulse signal <NUM> may be used to discourage ion recombination.

In the example of <FIG>, the pulse signal <NUM> has a specific period and duty cycle, which may be controlled based on a clock signal of the control circuitry <NUM>. However, in other examples, the period and/or duty cycle of the pulse signal <NUM> may be adjusted as desired, such as to achieve specific ionization rates.

In some examples, the control circuitry <NUM> may output a warning or alert if the balance value <NUM> reaches and/or remains at an upper or lower limit value. In such a case, there may be an error in the balance voltage measurements and/or the ionizer <NUM> is unable to provide sufficient ionization for the application.

<FIG> illustrates an example output signal <NUM> from the power supply <NUM> to the emitters <NUM> of <FIG> to output positive and negative ions and to control a balance voltage, in which a pulse output (e.g., the pulse signal <NUM> of <FIG>) is turned off. <FIG> illustrates a more detailed view of a portion of the output signal <NUM>, showing the high frequency waves. In the example of <FIG>, the output signal <NUM> has a defined emitter period <NUM>, which includes a negative portion <NUM>, a positive portion <NUM>, and one or more off portions <NUM>. The off portion <NUM> may include one or more predetermined time periods that occur between sequential negative and positive portions, at the beginning of an emitter period <NUM>, and/or at the end of an emitter period <NUM>, to provide sufficient time for the power supply <NUM> to perform switching.

During the negative portion <NUM>, the negative polarity signal <NUM> is active, and the emitters <NUM> generate and eject negative ions toward the target <NUM>. During the positive portion <NUM>, the positive polarity signal <NUM> is active, and the emitters <NUM> generate and eject positive ions toward the target <NUM>. During the off portion <NUM>, neither of the polarity signals <NUM>, <NUM> are active, and the emitters <NUM> do not generate ions because the generated output signal <NUM> from the power supply <NUM> is not sufficient to exceed either a positive threshold voltage <NUM> or negative threshold voltage <NUM>. The positive portion <NUM> and/or the negative portion <NUM> may have respective duty cycles with respect to the emitter period <NUM>.

In response to the balance voltage input <NUM>, the example control circuitry <NUM> may adjust the duty cycles of the negative portion <NUM> and/or the positive portion <NUM> by adjusting the balance signal <NUM> of <FIG>, which in turn adjusts the polarity signals <NUM>, <NUM>.

The control circuitry <NUM> may respond to changes in the balance value <NUM> by determining corresponding durations of the negative portion <NUM> and/or the positive portion <NUM>.

<FIG> illustrates an example output signal <NUM> from the power supply <NUM> to the emitters <NUM> of <FIG> to output positive and negative ions and to control a balance voltage, in which a pulse output (e.g., the pulse signal <NUM> of <FIG>) is turned on. <FIG> illustrates a more detailed view of a portion of the output signal <NUM>, showing the high frequency waves. The example output signal <NUM> is similar to the output signal <NUM> of <FIG>, with the exception that the HV output signal to the emitters <NUM> is turned off based on the pulse signal <NUM>.

<FIG> is a flowchart representative of an example method <NUM> to control an ionization output of the AC charge neutralization system of <FIG> and <FIG> based on balance voltage feedback.

At block <NUM>, the example HVHF power supply <NUM> generates a high voltage, high frequency AC signal. For example, the DC-DC converter <NUM> and the AC high voltage inverter <NUM> generate a high voltage, high frequency AC signal. At block <NUM>, the control circuitry <NUM> sets a balance value based on a desired ion output balance. For example, the control circuitry <NUM> may set an initial balance value <NUM> based on a balance input, which controls the negative portion <NUM> and/or the positive portion <NUM>.

At block <NUM>, the control circuitry <NUM> determines a positive ion duty cycle (e.g., the positive portion <NUM> of the emitter period <NUM>) and a negative ion duty cycle (e.g., the negative portion <NUM> of the emitter period <NUM>) based on the balance value <NUM>. For example, the control circuitry <NUM> may calculate the positive duty cycle and negative duty cycle based on the balance value <NUM> (e.g., within a predetermined range) and based on a predetermined off time <NUM>. In some other examples, the control circuitry <NUM> does not calculate the positive ion duty cycle and negative ion duty cycle, and instead controls the polarity signals based on a comparison of the balance value <NUM> with a count signal <NUM> (e.g., in real-time).

At block <NUM>, the control circuitry <NUM> controls ion output by the power supply <NUM> based on the positive ion duty cycle and the negative ion duty cycle. An example method to implement block <NUM> are disclosed below with reference to <FIG>.

At block <NUM>, the control circuitry <NUM> measures a balance voltage. For example, the control circuitry <NUM> may receive a balance voltage input <NUM> representative of the balance voltage. At block <NUM>, the control circuitry <NUM> updates the balance value <NUM> based on the measured balance voltage and a balance setpoint. For example, the control circuitry <NUM> may apply the measured balance voltage and the balance setpoint to a PID controller to adjust the balance value <NUM>. The PID controller, or other control loop, adjusts a commanded balance value <NUM> based on the difference between the measured balance voltage and the balance setpoint.

After updating the balance values (block <NUM>), control returns to block <NUM> to continue updating the positive and negative duty cycles and continue outputting the HVHF signals to the emitters <NUM>.

<FIG> is a flowchart representative of an example method <NUM> to control ion output by a ionizer power supply, such as the power supply <NUM> of <FIG>. The example method <NUM> may be performed by the control circuitry <NUM> of <FIG> to implement block <NUM> of <FIG>. Prior to performance of the method <NUM>, the example control circuitry <NUM> has determined a positive ion duty cycle and a negative ion duty cycle based on a balance signal <NUM>.

At block <NUM>, the control circuitry <NUM> generates a positive polarity control signal <NUM> based on a positive ion duty cycle to control a DC offset (e.g., at the DC offset generator <NUM>). For example, the control circuitry <NUM> may hold the positive polarity control signal <NUM> active (e.g., on) and the negative polarity control signal <NUM> inactive (e.g., off) for the duration of the positive ion duty cycle.

At block <NUM>, the DC offset generator <NUM> combines the high voltage, high frequency AC signal (e.g., from the AC HV inverter <NUM>) with the DC offset to control the ion output balance. For example, the DC offset generator <NUM> combines the high voltage, high frequency AC signal with the DC offset generated based on the positive polarity control signal <NUM>. For example, the AC HV amplifier <NUM> amplifies the combined DC offset and AC HVHF signal for output to the emitters <NUM>.

At block <NUM>, the power supply <NUM> outputs the combined signal to generate positive ions for the duration of the positive ion duty cycle. For example, the emitters <NUM> generate positive ions while the DC offset generator <NUM> generates a positive DC offset based on the positive polarity signal <NUM>.

Following the positive ion duty cycle (e.g., block <NUM>-<NUM>), at block <NUM> the control circuitry <NUM> generates a negative polarity control signal <NUM> based on a negative ion duty cycle to control a DC offset (e.g., at the DC offset generator <NUM>). For example, the control circuitry <NUM> may hold the negative polarity control signal <NUM> active (e.g., on) and the positive polarity control signal <NUM> inactive (e.g., off) for the duration of the negative ion duty cycle.

At block <NUM>, the DC offset generator <NUM> combines the high voltage, high frequency AC signal (e.g., from the AC HV inverter <NUM>) with the DC offset to control the ion output balance. For example, the DC offset generator <NUM> combines the high voltage, high frequency AC signal with the DC offset generated based on the negative polarity control signal <NUM>. For example, the AC HV amplifier <NUM> amplifies the combined DC offset and AC HVHF signal for output to the emitters <NUM>.

At block <NUM>, the power supply <NUM> outputs the combined signal to generate negative ions for the duration of the negative ion duty cycle. For example, the emitters <NUM> generate negative ions while the DC offset generator <NUM> generates a negative DC offset based on the negative polarity signal <NUM>.

The positive and negative duty cycles may be separated by an off period (e.g., the off period <NUM>) and/or may be interrupted by periodic pulses based on the pulse signal <NUM> of <FIG>.

perform processes as described herein.

Claim 1:
An apparatus (<NUM>) for charge neutralization, the apparatus comprising:
a first emitter nozzle;
a power supply (<NUM>) configured to supply a high frequency alternating current (AC) signal to the first emitter nozzle; and
control circuitry (<NUM>) configured to:
provide a polarity signal (<NUM>, <NUM>) to the power supply (<NUM>) to generate a DC offset signal, wherein a combination of the high frequency AC signal and the DC offset signal causes the power supply (<NUM>) to output a positive ion generation pulse or a negative ion generation pulse;
control the polarity signal (<NUM>, <NUM>) to cause the power supply (<NUM>) to provide a period of positive ion generation and a period of negative ion generation;
determine a balance voltage (<NUM>) at an output of the first emitter nozzle; and
control the polarity signal (<NUM>, <NUM>) to adjust a relative durations of the period of positive ion generation and the period of negative ion generation based on the balance voltage (<NUM>).