KR101108901B1 - Improved megasonic cleaning efficiency using auto-tuning of an rf generator at constant maximum efficiency - Google Patents

Abstract

The substrate 202 cleaning system and method includes a megasonic chamber 206 that includes a transducer 210 and a substrate 202. The transducer 210 is directed towards the substrate 202. The variable distance d separates the transducer 210 and the substrate 202. System 200 also includes a dynamically adjustable RF generator 212 having an output coupled to the transducer. The dynamically adjustable RF generator 212 may be controlled by a phase comparison of the output 306 voltage of the oscillator and the phase of the RF generator output voltage. Dynamically adjustable RF generator 212 may also be controlled by monitoring the peak voltage of the output signal and controlling the RF generator to maintain the peak voltage within a predetermined voltage range. The dynamically adjustable RF generator 212 can also be controlled by dynamically controlling the variable DC power supply voltage.

RF generator, instantaneous resonant frequency, VCO, cleaning chamber, feedback circuit

Description

Improved megasonic cleaning action using auto-tuning of the RF generator with a constant maximum efficiency {IMPROVED MEGASONIC CLEANING EFFICIENCY USING AUTO-TUNING OF AN RF GENERATOR AT CONSTANT MAXIMUM EFFICIENCY}

background

1. Field of the Invention

The present invention generally relates to systems and methods for calibrating an RF generator, and more particularly, to a method and system for automatically adjusting an RF generator with respect to a substrate cleaning system.

2. Description of related technology

The use of acoustic energy is highly related to the removal of small-particles from substrates such as semiconductor wafers, flat panel displays, micro-electro-mechanical systems (MEMS), micro-opto-mechanical systems (MOEMS), etc., in various manufacturing conditions. It is an advanced non-contact cleaning technology. The cleaning process generally involves the propagation of acoustic energy through the liquid medium to remove particles from the substrate surface and to clean the substrate surface. In general, megasonic energy propagates at frequencies in the range of about 700 GHz (0.7 MHz) and above and about 1.0 MHz. The liquid medium may be a deionized aqueous solution or any one or more of several substrate cleaning chemicals, and combinations thereof. The propagation of acoustic energy through the liquid medium is mainly due to the activation of activation energy to promote the formation and destruction of bubbles from the dissolved gas, microstreaming, and improved mass transport or chemical reactions in the liquid medium called cavitation. Providing achieves non-contact substrate cleaning through enhanced chemical reactions when chemicals are used as the liquid medium.

1A is a diagram of a general batch substrate cleaning system 10. 1B is a plan view of the batch substrate cleaning system 10. Tank 11 is filled with a cleaning solution 16, such as a deionized aqueous solution or other substrate cleaning chemical. The substrate carrier 12, which is generally a cassette of substrates, has an arrangement of substrates 14 to be cleaned. One or more transducers 18A, 18B, 18C produce emitted acoustic energy 15 that propagates through the cleaning solution. In general, the relative position and distance between the substrate 14 and the transducers 18A, 18B, and 18C are approximately at each placement of the substrate 14 through the position fixing devices 19A and 19B for contacting and positioning the carrier 12. It is constant.

The released energy 15 achieves substrate cleaning through enhanced mass transport when cavitation, acoustic streaming, and cleaning chemicals are used, with or without appropriate chemical reactions that control particle re-adhesion. . In general, a batch substrate cleaning process requires a very long processing time and can also consume an excessive amount of cleaning chemical 16. In addition, consistency and substrate-to-substrate control are difficult to achieve. States such as "shadowing" and "hot spot" are common in batch and other substrate megasonic processes. Shading occurs due to reflected and / or constructive and destructive interference of the emitted energy 15 and is mixed with additional substrate surface areas of the plurality of substrates 14, walls of the process tank, and the like. The occurrence of hot spots, primarily the result of constructive interference due to the use of multiple transducers and reflections, can also be increased with additional multi-substrate surface areas. In general, these controversial issues are raised by relying on the average effect on multiple reflections of acoustic energy on the substrate, which leads to low average power on the substrate surface. In order to compensate for the lower average power and to provide effective cleaning and particle removal, the power to the converter is increased, thereby increasing the emission energy 15, cavitation and acoustic streaming, thereby increasing the cleaning efficiency. Let's do it. In addition, pulsed multiple transducer arrays 18A, 18B, 18C (ie, providing a duty cycle such as turning on the transducer for 20 ms and then turning off for 10 ms) is used. The transducers 18A, 18B, 18C may also operate in other phases (eg, sequentially activated) to reduce complex reflections and interference.

1C is a prior art and diagram 30 of an RF source for supplying one or more transducers 18A, 18B, 18C. Adjustable voltage controlled oscillator 32 (VCO) outputs signal 33 to RF generator 34 at the selected frequency. RF generator 34 amplifies signal 33 to produce signal 35 with increased power. The signal 35 is output to the converter 18B. The power sensor 36 monitors the signal 35. The converter 18B outputs the released energy 15.

The exact impedance of the transducer 18B may vary depending on many variables such as the number, size and spacing of the substrate 14 in the carrier 12, and the distance between the substrate 14 and the transducer 18B. . The exact impedance of the transducer 18B may also change as the transducer 18B ages through repeated use. By way of example, if signals 33 and 35 have a frequency of about 1 MHz, the wavelength is about 1.5 mm (0.060 inch) in a deionized aqueous medium such as cleaning solution 16. As a result, referring again to FIG. 1A, if the position of the substrate 14 and the carrier 12 are about 0.5 mm (0.020 inch) or even less apart, the impedance of the transducer 18B may actually vary. Also, if the substrates 24 and 24a are rotated, the impedance can change cyclically.

Adjusting the frequency of the VCO can adjust the impedance of the converter 18B by varying the frequency and thus changing the wavelength of the signals 33, 35 and the emitted energy 15. In general, the carrier 12 loaded with the substrate 14 is located in the tank 11, and the VCO 32 is indicated by the minimum value of the reflected signal 38 detected by the power meter 36. As is, the frequency of the signals 33 and 35 and the emitted energy 15 are adjusted until the impedance of the transducer 18B is matched. Once the VCO 32 is adjusted to obtain the minimum reflected signal 38, the VCO 32 is generally not regulated again unless significant maintenance or maintenance is performed on the substrate cleaning system 10.

When the impedance of the transducer 18B does not match, a portion (ie, wave) of the emitted energy 17 emitted from the transducer 18B is reflected back toward the transducer 18B. On the surface of the transducer 18B, the reflected energy 17 is interfered with the emission 15 energy causing constructive or destructive interference. Since part of the emitted energy 15 is effectively canceled by the reflected energy 17, the extinction interference reduces the effective cleaning power of the emitted energy 15. As a result, the efficiency of the RF generator 34 is reduced.

Constructive interference can cause excessive energy that can cause hot spots on the surface of the substrate 14 to be cleaned. Hot spots may exceed the energy threshold of the substrate 14 and may damage the substrate 14. 1D is a typical transducer 18B. 1E is a graph 100 relating to the energy distribution across the transducer 18B. Curve 102 is a curve of energy emitted across transducer 18B in the x-axis. Curve 104 is a curve of energy emitted across transducer 18B in the y-axis. Curve 120 is a curve of synthetic energy emitted across transducer 18B in both the x- and y-axes. The synthetic energy emitted through the transducer 18B in both the x-axis and the y-axis is generally dependent on known variables (eg, the position of the substrate, aging of the transducer, and shaking of the rotating substrate relative to the transducer, etc.). It can vary between curve 120 and curve 122. The threshold energy level T is the damage threshold for the substrate (s) 14. In general, the maximum power of the RF signal 35 and the resulting emission energy 15 output by the converter 18B are such that the energy of the substrate 14 is such that maximum constructive interference prevents damage to the substrate 14. Is reduced to a level that results in a peak magnitude less than the threshold T (ie, the peak of curve 120). However, the reduced power of the RF signal 35 and the released energy 15 increase the cleaning process time required to achieve the desired cleaning result. In some examples, the reduced power and emitted energy 15 of the signal 35 are not sufficient to remove some targeted particles from the substrate 14. As shown, the actual released energy can vary up to a much lower level (represented by the valleys in curve 122), which has a significant impact on the efficiency of the cleaning process because the effective energy is very low (about 3). And thus results in an energy window that extends from about 3 to about 17 as shown on the energy scale.

In general, the transducer 18B is a piezoelectric device such as a crystal. The constructive and destructive interference caused by the reflected energy 17 can also exert sufficient force on the surface of the transducer 18B to cause the transducer 18B to produce a corresponding reflected signal 38. The power sensor 36 can detect the reflected signal 38 reflected from the converter 18B toward the RF generator 34. The reflected signal 38 can constructively or destructively interfere with the signal 35 output from the RF generator 34 to further reduce the efficiency of the RF generator 34.

As described above, there is a need for an improved megasonic cleaning system that provides increased efficiency RF generators and reduced energy windows of emitted acoustic energy and reduces the probability of substrate damage.

summary

In general, the present invention meets this need by providing a dynamically tuned RF generator that is constantly adjusted to maintain the resonance of the transducer and the energy emitted from the transducer. The present invention can be implemented in various ways, including as a process, apparatus, system, computer readable medium, or device. Several inventive embodiments of the invention are described below.

One embodiment includes a method of dynamically adjusting an RF generator to an instantaneous resonant frequency of a transducer. The method includes inputting an RF input signal from an oscillator to an RF generator. The first phase with respect to the input voltage of the RF input signal is measured. A second phase with respect to the voltage of the RF signal output from the RF generator is measured. The RF signal output from the RF generator is coupled to the transducer input. The frequency control signal is generated when the first phase is not equal to the second phase. The frequency control signal is applied to the frequency control input of the oscillator.

Measuring the first phase can include scaling the measured voltage of the first phase. Measuring the second phase can include scaling the measured voltage of the second phase. Applying the frequency control signal to the frequency control input of the oscillator may comprise scaling the frequency control signal.

Applying the frequency control signal to the frequency control input of the oscillator may also include combining the frequency control signal with a set point control signal.

Generating a frequency control signal when the first phase is not equal to the second phase: if the first phase lags behind the second phase, the frequency control signal reduces the frequency of the oscillator; If the first phase is ahead of the second phase, the frequency control signal increases the frequency of the oscillator; If the first phase is equal to the second phase, the frequency control signal may include not changing the frequency of the oscillator. The resonance of the transducer changes as the distance between the transducer and the target changes.

The first and second phases are measured and a frequency control signal is generated for each cycle of the RF input signal. The method may also include applying at least one of the proportional control signal and the integral control signal to the frequency control signal.

Another embodiment includes a system for providing RF to a converter. The system includes an oscillator, an RF generator, and a voltage phase detector. The oscillator has a frequency control input and an RF signal output. The RF generator has an input coupled to the RF signal output of the oscillator and an output of the RF generator coupled to the transducer. The voltage phase detector includes a first phase input coupled to the RF signal output of the oscillator, a second phase input coupled to the output of the RF generator, and a frequency control signal output coupled to the frequency control voltage input of the oscillator do.

The first phase input may be coupled to the RF signal output of the oscillator via a scaling device. The second phase input can be coupled to the output of the RF generator via the scaling device.

The frequency control signal output can be coupled to the frequency control input of the oscillator via a control amplifier. The control amplifier may include a first input coupled to the frequency control signal output, a second input coupled to the set point control signal, and an output coupled to the frequency control input of the oscillator. The RF generator may be a Class-E RF generator.

The transducer may face a target which is a variable distance from the transducer. The transducer may be included in a megasonic cleaning chamber. The target may be a semiconductor substrate. The RF generator may operate in the range of about 400 Hz to about 2 MHz.

Yet another embodiment includes a converter RF source that includes a voltage controlled oscillator (VCO), a Class-E RF generator, and a voltage phase detector. The VCO has a frequency control input and an output. The Class-E RF generator has an input coupled to the output of the VCO and an output of the RF generator coupled to the converter having a variable impedance. The voltage phase detector has a first phase input coupled to the output of the VCO, a second phase input coupled to the output of the RF generator, and a voltage control signal output coupled to the frequency control voltage input of the VCO via a control amplifier. Contains wealth. The control amplifier includes a first input coupled to the voltage control signal output, a second input coupled to the set point control signal, and an output coupled to the frequency control voltage input of the VCO.

One embodiment includes a substrate cleaning method comprising applying an RF signal to a converter at an f frequency. The transducer is directed towards the substrate to emit acoustic energy towards the substrate at frequency f. The substrate moves relative to the transducer. The RF signal is dynamically adjusted to maintain resonance of acoustic energy.

Dynamically adjusting the frequency f may include automatically adjusting the frequency f for each cycle of the RF signal. Moving the substrate relative to the transducer may include rotating the substrate.

The substrate may also be submerged in the cleaning solution. The cleaning solution may be a deionized aqueous solution. The cleaning solution may include one or more plurality of cleaning chemicals. Dynamically adjusting the RF signal to maintain resonance of the acoustic energy may include maintaining a constant voltage of the RF signal applied to the transducer.

The RF generator can apply an RF signal to the converter, and maintaining a constant voltage of the RF signal applied to the converter is to measure the first voltage of the RF signal, and to compare the first voltage with a desired set point voltage. And inputting a control signal to the variable DC power supply to regulate the output voltage of the variable DC power supply supplying the DC power to the RF generator. Dynamically adjusting the RF signal to maintain resonance of the acoustic energy may include dynamically adjusting the frequency f of the RF signal applied to the transducer.

The RF generator can apply an RF signal to the converter, and dynamically adjusting the frequency f of the RF signal applied to the converter measures the supply voltage applied to the RF generator, the peak through the output amplifier included in the RF generator. Measuring the voltage, generating a frequency control signal if the peak voltage is not equal to the selected ratio of the supply voltage, and applying the frequency control signal to the frequency control input of the oscillator generating the RF signal. have.

The RF generator may apply an RF signal to the converter, and dynamically adjusting the frequency f of the RF signal applied to the converter may include inputting an RF input signal from the oscillator into the RF generator and amplifying the RF signal of the RF generator. It may include. The first phase with respect to the input voltage of the RF input signal is measured and the second phase with respect to the voltage of the RF signal output from the RF generator. The frequency control signal is generated when the first phase is not equal to the second phase. The frequency control signal is applied to the frequency control input of the oscillator.

Another embodiment includes a system for substrate cleaning that includes a cleaning chamber that includes a transducer and a substrate. The transducer is towards the substrate. Separate the transducer from the substrate by a variable distance d. The system also includes a dynamically adjustable RF generator having an output coupled to the transducer and a feedback circuit coupled to the control input of the adjustable RF generator. The substrate can be rotated. As the substrate rotates, the distance d can vary by about one-half wavelength of the RF signal output from the RF generator.

The dynamically adjustable RF generator may include a variable DC power supply having a control input and a DC output coupled to the RF generator. The feedback circuit includes a first comparator coupled to a set point control signal, a second input coupled to an RF output of the RF generator, and a first comparator coupled to a control signal output coupled to the control input of the adjustable RF generator. It may include. The control input includes a voltage control input for a variable DC power supply.

The dynamically adjustable RF generator may include an oscillator, an output amplifier coupled to the output of the oscillator, and a load network. The oscillator has a control signal input and an RF signal output. The load network is coupled between the output of the output amplifier and the output of the RF generator. The feedback circuit can include a peak voltage detector and a second comparator. The peak voltage detector can be coupled across the output amplifier. The second comparator includes a third input coupled to the output of the variable DC power source, a fourth input coupled to the output of the peak voltage detector, and a second comparator output coupled to the control input of the adjustable RF generator. do. The control input unit may include a control signal input unit of the oscillator.

The dynamically adjustable RF generator may include an oscillator and an RF generator input coupled to the RF signal output of the oscillator. The oscillator has a frequency control input and an RF signal output. The feedback circuit can include a voltage phase detector. The voltage phase detector includes a first phase input coupled to the RF signal output of the oscillator, a second phase input coupled to the output of the RF generator, and a frequency control signal coupled to the control input of the adjustable RF generator. can do. The control input may include a frequency control voltage input of the oscillator.

The dynamically adjustable RF generator includes an oscillator with a supply voltage source, a control signal input and an RF signal output, an output amplifier coupled to the output of the oscillator, a load network coupled between the output of the output amplifier and the output of the RF generator. It may include. The feedback circuit can include a peak voltage detector coupled across the output amplifier, and a comparator circuit. The comparator circuit may include a first input coupled to the supply voltage source, a second input coupled to the output of the peak voltage detector, and a comparator output coupled to the control input of the adjustable RF generator. The control input unit may include a control signal input unit of the oscillator.

The dynamically adjustable RF generator may include an oscillator and an RF generator input coupled to the RF signal output of the oscillator, and the feedback circuit may include a voltage phase detector. The oscillator has a frequency control input and an RF signal output. The voltage phase detector includes a first phase input coupled to the RF signal output of the oscillator, a second phase input coupled to the output of the RF generator, and a frequency control signal output coupled to the control input of the adjustable RF generator. Include. The control input may include a frequency control voltage input of the oscillator.

The transducer may comprise two or more transducers. The dynamically adjustable RF may include two or more dynamically adjustable RF generators, each having individual outputs coupled to one of the two or more transducers. The transducer may comprise a first transducer facing the active surface of the substrate and a second transducer facing the non-active surface of the substrate.

One embodiment includes a method of dynamically adjusting an RF generator to an instantaneous resonant frequency of a transducer. The method includes providing an RF input signal from the oscillator to the RF generator and measuring the supply voltage applied to the RF generator. Peak voltage is measured at the RF generator. The frequency control signal is generated when the peak voltage is not equal to the selected ratio of the supply voltage. The frequency control signal is applied to the frequency control input of the oscillator.

Measuring the peak voltage can include measuring the peak voltage of each cycle of the RF input signal. Measuring the peak voltage may include measuring across the output amplifier included in the RF generator. The output amplifier can be a CMOS device, the peak voltage being equal to the voltage from the drain to the source of the output amplifier. Measuring the supply voltage applied to the RF generator may include scaling the measured supply voltage. Measuring the peak voltage may also include scaling the measured peak voltage.

The selected ratio of peak voltage to supply voltage may be equal to a range between about 3 to 1 and about 6 to 1. More specifically, the selected ratio of peak voltage to supply voltage may be equal to about 4 to 1 or about 3.6 to 1. The method may also include applying at least one proportional control signal and an integral control signal to the frequency control signal. The method may also include applying an amplified RF signal output from the RF generator to the converter, the converter facing the target, and the distance between the converter and the target is a variable distance.

Yet another embodiment includes a system for generating RF that includes a supply voltage source, an oscillator, an output amplifier, a load network, a peak voltage detector, and a comparator circuit. The oscillator has a control signal input and an RF signal output. The output amplifier is coupled to the output of the oscillator. The load network is coupled between the output of the output amplifier and the output of the RF generator. The peak voltage detector is coupled across the output amplifier. The comparator circuit includes a first input coupled to the supply voltage source, a second input coupled to the output of the peak voltage detector, and a comparator output coupled to the control signal input of the oscillator. The output of the RF generator can also be coupled to the transducer.

The control signal can be output from the comparator output when the supply voltage is not equal to the selected ratio of peak voltage output by the peak voltage detector. The peak voltage detector may include a first capacitor coupled in series with the second capacitor and a diode coupled in parallel with the second capacitor. The first input of the comparator is coupled to the supply voltage source via the first scaling device. The peak voltage detector can include a second scaling device. The comparator may comprise an op-amp. The oscillator may operate in the region of about 400 Hz to about 2 MHz.

Yet another embodiment includes an RF generator system including a voltage controlled oscillator (VCO) having a supply voltage source, a control voltage input and an output, and an output amplifier coupled to the output of the VCO. Also included is a Class-E load network coupled between the output of the output amplifier and the output of the RF generator. The peak voltage detector is coupled across the output amplifier. A comparator circuit comprising a first input coupled to a supply voltage source, a second input coupled to an output of a peak voltage detector, a comparator output coupled to a VCO control voltage input, and a control voltage, wherein the supply voltage is peak voltage. It is output from the comparator output when it is not equal to the ratio of about 3.6 to 1 to the peak voltage output by the detector. The converter is coupled to the output of the RF generator.

One embodiment includes a method of maintaining a constant input voltage to a converter. The method includes applying an RF signal from an RF generator to a converter, measuring a first voltage of the RF signal, comparing the first voltage with a desired setpoint voltage, and supplying DC power to the RF generator. Inputting a control signal to the variable DC power supply to regulate the output voltage of the DC power supply. Measuring the first voltage can include scaling the measured first voltage.

The first voltage is a function of the impedance of the transducer. The impedance of the transducer can change as the distance between the transducer and the target changes.

Comparing the first voltage with the desired set point voltage can include determining a control signal. The control signal is approximately equal to the difference between the first voltage and the desired set point voltage.

Adjusting the output voltage of the variable DC power supply may include applying at least one of proportional control and integral control to the control signal. The method may also include directing the transducer towards the target, wherein the distance between the transducer and the target is a variable distance.

Another embodiment includes an RF generation system that includes an RF generator, a variable DC power supply, and a comparator. The RF generator has an RF output coupled to the input of the converter. The variable DC power supply has a control input and a DC output coupled to the RF generator. The comparator includes a first input coupled to the set point control signal, a second input coupled to the RF output of the RF generator, and a control signal output coupled to the voltage control input on a variable DC power supply.

The second input is coupled to the RF output of the RF generator by a voltage scaling device. The comparator may also include at least one of a proportional control input and an integral control input. The RF generator may be a Class-E RF generator. The voltage of the RF signal is a function of the impedance of the transducer. The impedance of the transducer changes as the distance between the transducer and the transducer target changes.

The transducer may be included in a megasonic cleaning chamber. The converter target may be a semiconductor substrate. The comparator may be an operational amplifier.

Another embodiment includes a converter RF source that includes a Class-E RF generator, a variable DC power supply, and a comparator. The Class-E RF generator has an RF output coupled to the input of the megasonic transducer in the megasonic cleaning chamber. The variable DC power supply has a control input and a DC output coupled to the RF generator. The comparator includes a first input coupled to the set point voltage source, a second input coupled to the RF output of the RF generator, and a control signal output coupled to the voltage control input on a variable DC power source.

The present invention provides the advantage of a significantly reduced cleaning processing time since higher power acoustic energy can be used without damaging the substrate to be cleaned (eg no acoustic energy "hot spot" is produced). The present invention thereby reduces the number of substrates that are damaged due to excessive acoustic energy supplied to the substrates.

The auto-tuning RF generator can also automatically adjust for process changes such as different cleaning chemistries, different positions of the substrate, etc., thereby providing a more flexible and robust cleaning process.

Other aspects and advantages of the invention will become apparent with reference to the following detailed description and accompanying drawings, which illustrate, by way of example, the principles of the invention.

Brief description of the drawings

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be readily understood in the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements.

1A is a diagram of a general batch substrate cleaning system.

1B is a plan view of a batch substrate cleaning system.

1C is a prior art, schematic diagram of an RF supply for supplying one or more transducers.

1D is a typical transducer 18B.

1E is a graph of the energy distribution through the transducer.

2A and 2B illustrate a dynamic, single substrate cleaning system, in accordance with one embodiment of the present invention.

FIG. 2C is a flow diagram of a method of operation of an auto-tuning RF generator system used in a megasonic cleaning system, as described in FIGS. 2A and 2B above, in accordance with an embodiment of the present invention.

3 is a block diagram of an auto-tuning RF generator system in accordance with an embodiment of the present invention.

4 is a flow diagram of a method of operating an auto-tuning RF generator system while an RF generator is supplying an RF signal to a converter, in accordance with an embodiment of the present invention.

5A is a block diagram of a peak V _ds detector according to an embodiment of the present invention.

5B is a waveform graph of peak voltage (V _ds ) detected by a peak voltage detector, in accordance with an embodiment of the invention.

6 is a block diagram of an auto-tuning RF generator system in accordance with an embodiment of the present invention.

7 is a flowchart of a method of operation of an auto-tuning RF generator system in accordance with an embodiment of the present invention.

8A-8C show three exemplary graphs relating to the relationship between phase P1 and phase P2 in accordance with one embodiment of the present invention.

9 is a block diagram of an auto-tuning RF generator system in accordance with an embodiment of the present invention.

10 is a flowchart of a method of operation of an auto-tuning RF generator system in accordance with an embodiment of the present invention.

11 is a diagram of a megasonic module according to an embodiment of the present invention.

12 is a graph of energy distribution through a transducer in accordance with an embodiment of the present invention.

Detailed Description of Exemplary Embodiments

Several exemplary embodiments for automatically and dynamically adjusting the RF signal applied to the transducer will now be described. It will be apparent to those skilled in the art that the present invention may be practiced without some or all of the specific details disclosed herein.

As mentioned above, while reducing the possibility of damage to the substrate, it is very important to enhance the cleaning effect, the efficiency and throughput of the substrate cleaning system. These requirements are exacerbated by the ever decreasing device size and the fact that many cleaning systems are being developed into single substrate cleaning systems.

2A and 2B illustrate a dynamic, single substrate cleaning system 200, in accordance with an embodiment of the present invention. 2A shows a side view of a dynamic, single substrate cleaning system 200. 2B shows a top view of a dynamic, single substrate cleaning system 200. The substrate 202 is immersed in the cleaning solution 204 included in the cleaning chamber 206. The cleaning solution 204 can be a deionized aqueous solution (DI aqueous solution) or other cleaning chemicals well known in the art, and combinations thereof.

The substrate 202 is substantially circular and has three or more edge rollers 208A, 208B so that the substrate 202 can rotate (eg, in the direction 209A) as the cleaning process is applied to the substrate 202. , 208C) (or similar edge support device). One or more of the three edge rollers 208A, 208B, 208C may be driven to rotate the substrate 202 in the direction 209A (eg, in the direction 209B). The substrate 202 can be rotated at rates up to about 500 RPM.

The transducer 210 is also included as part of the cleaning chamber 206. The transducer 210 can be a piezoelectric device such as a crystal that can convert the RF signal 220 into acoustic energy 214 emitted into the cleaning solution 204. The transducer 210 may be composed of piezoelectric materials such as piezoelectric ceramic, lead zirconium titanate, piezoelectric quartz, gallium phosphate, where the piezoelectric material is a resonator such as ceramic, silicon carbide, stainless metal or aluminum, or quartz. Is coupled to.

As shown in FIG. 2B, the transducer 210 is significantly smaller than the substrate 202. Smaller transducers can be made cheaper and can also provide improved control over the narrower area of the substrate 202 where the emission energy 214 emitted from the smaller transducer 210 is affected. The active surface 218 of the substrate 202 (ie, the surface with the active device thereon) generally faces the transducer 210. However, in some embodiments, the active surface 218 can be on the side of the substrate 202 opposite the transducer 210.

The three edge rollers 208A, 208B, 208C maintain the substrate 202 from the transducer 210 approximately by a fixed distance d1 as the substrate 202 rotates past the transducer 210. The distance d1 may be in the range of just a few millimeters to about 100 mm or more. The distance d1 is selected as the distance that matches the impedance of the transducer 210. In one embodiment, the distance d1 is selected as the resonance distance with respect to the frequency of the emission energy 214. Alternatively, the frequency of the emission energy 214 can be selected such that the distance d1 is the resonance distance. In both embodiments, at resonance, the minimum reflected energy 216 is reflected from the substrate 202 back side toward the transducer 210. As described above, the reflected energy 216 may interfere with the emission energy 214, which may reduce the power efficiency of the RF signal 220, and reduce the cleaning efficiency (eg, Interference patterns).

However, the substrate 202 can be somewhat “rocked” such that the distance between the substrate 202 and the transducer 210 is between the first distance d1 and the second distance d2 as the substrate 202 rotates past the transducer 210. Can change from The difference between the first distance d1 and the second distance d2 may be about 0.5 mm (0.020 inch) or even larger. The improved edge rollers 208A, 208B, 208C and other similar techniques can keep the substrate 202 at a more constant distance d1 from the transducer 210, while the improved edge rollers cannot guarantee a certain constant distance d1. Therefore, the change in distance d1 still occurs. In addition, the distance between the substrate 202 and the transducer 210 may also change due to other reasons (eg, placement of the substrate 202 within the edge rollers 208A, 208B, 208C, etc.). As will be described in more detail below, the change in distance between the substrate 202 and the transducer 210 can severely affect the performance and efficiency of the cleaning system 200.

The transducer 210 is coupled to the RF generator 212. 2C is a flow diagram of a method 250 of operating an auto-tuning RF generator system used in a megasonic cleaning system 200, as shown in FIGS. 2A and 2B above, in accordance with an embodiment of the present invention. to be. In operation 255, the RF generator supplies an RF signal 220 to the converter 210. RF signal 220 may have a frequency between about 400 Hz and about 2 MHz, but is generally between about 700 Hz and about 1 MHz. The wavelength of the high frequency acoustic energy 214 emitted from the converter 210 is about 1.5 mm (0.060 inches) in length in the cleaning solution 204.

In operation 260, the distance to the target (eg, the substrate 202) changes as the target moves relative to the transducer 210. Since the emission energy 214 is not always in resonance when the distance d1 changes (ie, when the impedance of the converter 210 does not match), the amount of the reflected energy 216 also changes as the distance d1 changes. In operation 270, the RF generator 212 is automatically and dynamically adjusted so that the RF signal 220 continues to adjust to correct any impedance dismatching as the distance d1 changes.

Since the wavelength of the emission energy 214 is about 1.5 mm (0.060 inch), even with a movement of only 0.50 mm (0.020 inch), for example, a voltage change by 50% and a power between about 25% and 100% It can result in a significant impedance change that causes a change. Without the auto-tuning RF generator to compensate for the dl change, the peak energy level of the emission energy 214 is determined by the energy absorption capacity of the substrate 202 so as to prevent the peak emission energy 214 from damaging the substrate 202. Should be reduced to a sufficiently low value not exceeding the energy threshold).

The auto-tuning RF generator 212 can be automatically adjusted to compensate for the change in distance d1 through various methods. In one embodiment, the peak voltage is detected to maintain the RF generator 212 at the impedance optimized frequency of the RF signal 220. In another embodiment, the phase of the voltage is maintained to produce an impedance optimized frequency of the RF signal 220. In yet another embodiment, the power supply may be adjusted to impedance optimize the RF signal 220. Various embodiments may also be used in combination within a single auto-tuning RF generator system.

3 is a block diagram of an auto-tuning RF generator system 300 in accordance with an embodiment of the present invention. The auto-tuning RF generator 302 supplies a feedback control signal to the VCO 306 to adjust the frequency of the VCO RF signal 310 output from the voltage controlled oscillator 306 (VCO). VCO 306 may also be included as part of RF generator 302. A DC power supply 312 is included and provides DC power for amplification of the VCO RF signal 310 in the RF generator 302. The auto-tuning RF generator 302 includes an inductor 314 at the input portion of the RF generator 302. Also included in the RF generator 302 is one or more amplifiers 320 that amplify the VCO RF signal 310.

In one embodiment, amplifier 320 is a CMOS and VCO RF signal 310 is applied to gate G. Drain D is coupled to DC bias rail 322 and source S is coupled to ground potential rail 324. The peak voltage drain for the source (peak V _ds ) detector 326 is coupled across drain D and the source S terminal of amplifier 320 to capture the peak voltage drain as the source of amplifier 320.

The output of the amplifier 320 is coupled to the input of a Class-E load network 330. Class-E load network 330 is a common device well known in the art that performs large scale impedance matching function between RF source (ie, RF generator 302) and RF load (ie, converter 332). to be. Class-E load network 330 generally includes an LC network. The output of the Class-E load network 330 is coupled to the input of the converter 332.

4 relates to a method 400 of operation of the auto-tuning RF generator system 300 while the RF generator 302 supplies the RF signal 220 to the converter 332, in accordance with an embodiment of the present invention. It is a flow chart. In operation 405, the DC supply voltage is measured or detected by the comparator device 340. A voltage divider network 342 may also be included to scale or reduce the magnitude of each voltage coupled from the DC power supply 312 to the comparator device 340 to a level usable by the comparator device 340. . In order to allow the rate and amount of change in the control signal to be selected, proportional, differential and integral control may be included in the comparator device 340.

In operation 410, the peak V _ds is detected by the peak V _ds detector 326 and applied to the second input of the comparator device 340. The peak V _ds detector 326 also includes a circuit diagram to scale or reduce the magnitude of the voltage coupled from the peak V _ds detector 326 to the comparator device 340 to a level usable by the comparator device 340. can do.

By way of example, DC power supply 312 may output 200 VDC, and comparator device 340 may compare a 5 VDC signal such that voltage divider network 342 may convert a DC power supply voltage of 200 VDC into a comparator device ( 340 may be scaled to a voltage of 5 VDC representing 200 VDC. Similarly, peak V _ds detector 326 may also include a scaling device, such as a voltage divider network, to cause the actual peak V _ds voltage applied to comparator device 340 to be about 5 VDC.

In operation 415, computer device 340 compares the peak V _ds with the DC supply voltage from the DC power supply 312. If the DC supply voltage is the peak V _ds of the desired ratio, no correction signal is output from the comparator device, and the method of operation continues at operation 405 described above.

Alternatively, if the DC supply voltage is not the desired rate of peak V _ds , then the method of operation continues at operation 420. In operation 420, the corresponding correction signal is output from the comparator device 340 to the VCO 306 to adjust the frequency of the VCO output signal 310, and the method of operation continues in operation 405 described above. The correction signal can adjust the frequency of the VCO RF signal 310 to a higher or lower frequency as needed.

The desired ratio of the DC supply voltage to the peak V _ds depends on the specific values of the various components in the RF generator 302 and the converter 332, and the RF generator 302 such as the substrate cleaning system of FIG. 2 described above and It depends on the system, which may include a transducer 332. In one embodiment, the desired ratio is in the range of about 3: 1 to about 6: 1, where the peak V _ds is a voltage that is greater than the DC supply voltage. In one embodiment, the desired ratio is about 4: 1, more specifically about 3.6: 1, where the peak V _ds is approximately equal to about 3.6 times the DC supply voltage.

5A is a block diagram of a peak V _ds detector 326 according to one embodiment of the present invention. Capacitors 502, 504 coupled in series are coupled across drain D and source S of amplifier 320. Diode 506 is coupled in parallel with capacitor 504. In operation, capacitor 502 couples the peak V _ds for each cycle of the amplified RF signal to capacitor 504. Capacitor 504 stores the peak V _ds for each cycle of the amplified RF signal output from amplifier 320. Diode 506 coupled to the peak V _ds to the comparator device 340 through the capturing and peak V _ds terminal peak V _ds.

5B is a graph 550 relating to the waveform of the peak voltage V _ds detected by the peak voltage detector 326, in accordance with an embodiment of the present invention. When the amplifier device 320 is operating, the peak voltage detector 326 does not detect much voltage because there is little voltage drop through the amplifier 320. When the amplifier stops operating, the current stored in the inductors and capacitors of the RF generator 302 and the load network 330 is discharged, and the voltage waveforms 552, 554, 556 as detected by the peak voltage detector 326. ) Results in Amplifier 320 is designed such that as voltage V _ds through amplifier 320 drops to zero, amplifier 320 begins to operate to produce a regulated amplification circuit. The adjusted amplification circuit is affected by any change in resonance of the transducer 332 (eg, any movement of the substrate 202 associated with the transducer 332), which is via the load network 330. The reflected waveforms 552, 554, 556 are changed. In the case of resonance, amplifier 320 operates as a well tuned Class-E amplifier and waveform 554 occurs. When out of resonance, the converter 332 may have either capacitive or inductive reactance that results in added capacitive or inductive reactance, which detunes the Class-E load network 330. ). The back-tuned Class-E load network 330 results in either of the waveforms 552 or 556, with either too high peak voltage V1 or too low peak voltage V3.

Through experiments and calculations, it has been found that the peak voltage V _ds is a function of the resonance of the transducer 332, and the peak V _ds compared to the applied DC bias voltage is a function of the components of the RF generator circuit 302. Has a resonance ratio. For example, in a typical RF generator, the ratio of the peak voltage compared to the DC bias voltage from the DC power supply is about 4: 1, that is, the peak V _{ds, which} is about four times the bias voltage from the DC power supply 312, is It indicates that transducer 332 is in resonance.

6 is a block diagram of an auto-tuning RF generator system 600 in accordance with an embodiment of the present invention. The phase P1 with respect to the voltage of the RF signal 310 output from the VCO 306 is compared with the phase P2 of the voltage input to the converter 332. If the voltage phases P1 and P2 do not match, a correction signal is applied to the frequency control input of the VCO 306. RF generator system 600 includes an RF generator 602. The RF generator 602 can be any type of RF generator known in the art. Phase detector 604 includes two inputs 606, 608. The first and second inputs 606, 608 are respective scaling circuits 610, 612 capable of scaling the detected signals (eg, phases P1 and P2) to levels usable by the phase detector 604. (Eg, voltage divider network) may also be included. Phase detector 604 can be any type of phase detector known in the art that can compare and detect the phase of each input voltage signal. The conventional phase detector compared the phase of the voltage and current of the output RF signal 220. Testing has shown that comparing the voltage phases P1 and P2 can be completed more simply and easily, thus providing the necessary signal for adjusting the VCO 306.

7 is a flowchart of a method of operation of an auto-tuning RF generator system 600 in accordance with an embodiment of the present invention. In operation 705, an input RF signal 310 from the VCO 306 is applied to the RF generator 602, where the RF generator 602 amplifies the input RF signal 310 and amplifies the RF signal 220. Is coupled to the transducer 332.

In operation 710, the first input 606 couples a first phase P1 with respect to the voltage of the RF signal 310 output from the VCO 306 to the phase detector 604. In operation 715, the second input 608 couples a second phase P2 relating to the voltage of the signal input to the converter 332 to the phase detector 604.

In operation 720, the phase detector compares phase P1 and phase P2 to determine whether phase P1 matches phase P2. 8A-8C show graphs of three examples relating to the relationship between phases P1 and P2, according to one embodiment of the invention. In FIG. 8A, graph 800 shows that phase P1 precedes phase P2 (eg, phase P1 is peak at time T1 and phase P2 is peak at subsequent time T2). This indicates that the impedance of the transducer 332 does not match, and the transducer 332 applies the reflected signal 222 to the RF generator 602.

In FIG. 8B, graph 820 shows that phase P1 lags behind phase P2 (eg, phase P2 is peak at time T1 and phase P1 is peak at subsequent time T2). This indicates that the impedance of the transducer 332 does not match, and the transducer 332 applies the reflected signal 222 back to the RF generator 602. The reflected signal output by the transducer 332 may interfere constructively or destructively with the signal output from the RF generator 602.

In FIG. 8C, graph 850 shows that phase P1 is equal to phase P2 (eg, both phase P1 and phase P2 are peaks at time T1). This indicates that the impedance of the transducer 332 matches and that the transducer 332 does not apply any reflected signal 222 to the RF generator 602.

At operation 720, if phase P1 and phase P2 are the same, the method operation continues (repeats) at operation 705. However, if at operation 720, phase P1 and phase P2 are not the same, the method operation continues at operation 730. In operation 730, an appropriate control signal is applied to the frequency control input of the VCO 306 to adjust the frequency of the RF signal 310 accordingly, and the method operation continues (repeats) in operation 705. The control signal applied to the frequency control input of the VCO 306 can adjust the frequency to a higher frequency in response to a state in which the phase P1 precedes the phase P2. Alternatively, the control signal applied to the frequency control input of the VCO 306 may adjust the frequency to a lower frequency in response to the state in which the phase P1 lags behind the phase P2.

The auto-tuning RF generator system 600 can also include a control amplifier 620 that can scale the control signal output by the phase detector 604 to a correction signal level to control the VCO 306. The control amplifier 620 may also include a set point input, such that the control amplifier 620 may combine the set point input with a control signal input from a phase detector. In this way the VCO RF signal 310 can be selected by the set point and the control signal output by the phase detector 604 can then automatically adjust the selected set point.

The systems and methods described in FIGS. 3-8C above can automatically adjust RF generators 302, 602 with very high correction rates (eg, RF signal 310 in each cycle of input RF signal 310). And may cause subsequent corrections in the frequency of and the output of the RF signal 220). As a result, the frequency of the input RF signal 310 can be corrected, for example, several times during each rotation of the substrate 202, thereby with respect to the acoustic energy 214 applied to the substrate 202. Provide much more precise control.

By way of example, if the substrate 202 rotates at 60 RPM (ie, one revolution per second) and the RF signal 310 is about 1 MHz, then the frequency of the RF signal 310 may be about twice per second during each rotation of the substrate 202. It can be adjusted one million times (ie once per microsecond). Increased control of the acoustic energy 214 applied to the substrate 202 means that the average energy can be very close to the energy minima and the maximum energy peak of the emission energy 214. Thus, higher average energy can be applied to the substrate 202, thereby resulting in significantly reduced cleaning processing time and improved cleaning effect.

9 is a block diagram of an auto-tuning RF generator system 900 in accordance with an embodiment of the present invention. The system includes a VCO 306 coupled to the input of the RF generator 602. The variable DC power supply 902 is coupled to the RF generator 602 and provides DC power to the RF generator to amplify the RF signal 310 from the VCO 306. The output of the RF generator is coupled to the converter 332.

A typical conventional acoustic energy cleaning system concentrates on maintaining a constant net power input to the converter 332 (ie, the forwarding power of the RF signal 220, which is the less reflected power of the reflected signal 222). Through experiments, it has been found that the magnitude of the emission energy 214 output from the converter 332 is generally constant if the voltage of the RF signal 220 is maintained at a constant voltage. In addition, maintaining the voltage of the RF signal 220 at a constant level below the energy threshold limit of the substrate 202 protects the substrate from damage while allowing maximum acoustic energy 214 to be applied to the substrate 202. .

10 is a flowchart of a method of operating an auto-tuning RF generator in accordance with an embodiment of the present invention. In operation 1005, the RF generator 602 outputs an RF signal to the converter 332. In operation 1010, the voltage of the RF signal output to the converter 332 is measured and coupled to the comparator 904.

In operation 1015, the comparator 904 compares the voltage of the RF signal output from the RF generator 602 with a desired set point voltage. If the output voltage is equal to the desired set point voltage, the method operation continues at operation 1010. Alternatively, if the output voltage is not equal to the set point voltage, the method operation continues at operation 1030.

In operation 1030, the comparator 904 outputs a control signal to the control input on the variable DC power supply 902. By way of example, if the output voltage is too high (ie, greater than the desired setpoint voltage), the control signal will reduce the DC voltage output from the variable DC power supply 902 and thereby generate within the RF generator 602. Reduce the gain with respect to the amplification of the RF signal, thereby reducing the magnitude of the RF signal output by the RF generator 602. Proportional, differential and integral control may also be included in the comparator 904 so that the rate of change and amount of change in the control signal can be selected.

Scaling circuit 906 may also be included to scale the voltage output from RF generator 602 to a level that is more easily compared to the setpoint signal. By way of example, scaling circuit 906 may scale a 200V RF signal to 5V for comparison with a 5V setpoint signal. Scaling circuit 906 can include a voltage divider. Scaling circuit 906 may also include a rectifier for rectifying the voltage of RF signal 220 output from RF generator 602 to a DC voltage for comparison with a DC set point signal.

As discussed above, the method described above in FIGS. 3-8C can automatically adjust the RF generators 302, 602 at very high correction rates (eg, once for each few cycles of the RF signal 310). have. In other words, the systems and methods described in FIGS. 9 and 10 are also slightly slower than those described in FIGS. 3-8C, but are more than likely a change in impedance of the transducer 332 due to movement of the substrate 202. The RF generator 602 can be adjusted automatically at a high rate. The systems and methods described in FIGS. 9 and 10 are slightly slower due in part to hysteresis included in the variable DC power supply 902.

The systems and methods described in FIGS. 9 and 10 may be used in combination with one or more of the systems and methods described in FIGS. 3-8C above. As such, the systems and methods described in FIGS. 9 and 10 can be used to provide a very wide area for adjusting the RF generator to the dynamic resonance of the transducer 332, whereas the system described in FIGS. 3 to 8c above. And the method can be used to provide very fine control and adjustment to calibrating the RF generator.

11 is a diagram of a megasonic module 1100 according to one embodiment of the present invention. Megasonic module 1100 is jointly owned, entitled "Megasonic Substrate Processing Module," filed on September 26, 2002, which is hereby incorporated by reference in its entirety for all purposes. Megasonic modules, such as the components described in US patent application Ser. No. 10 / 259,023.

Megasonic module 1100 includes a substrate processing tank 1102 (hereinafter referred to as tank 1102), and a tank lid 1104 (hereinafter referred to as lid 1104). The lead megasonic transducer 1108 and the tank megasonic transducer 1106 are located on the lid 1104 and the tank 1102, respectively, and provide megasonic energy for simultaneously processing the active surface and the back side of the substrate 1110. . The substrate 1110 is located at the drive wheel 1112 and is fixed to a proper position with the substrate fixing arm / wheel 1114. In one embodiment, the substrate fixing arm / wheel 1114 opens and closes the fixing arm / wheel 1114 to receive, fix, and release the substrate 1110 to be processed in the megasonic module 1100. 1120 and placement rod 1122. The lid 1104 can be positioned in an open or closed position with an actuator system (not shown) that raises and lowers the lid 1104 while the tank 1102 remains stationary. Alternatively, the tank 1102 can move and engage with the lid 1104.

In one embodiment, the substrate fixing arm / wheel 1114 is configured to fix and support the substrate 1110 in the horizontal direction for processing and to allow rotation of the substrate 1110. In another embodiment, substrate processing is performed with the substrate 1110 in the vertical direction. The drive wheel 1112 contacts the peripheral edge of the substrate 1110 and rotates the substrate 1110 during processing. The substrate fixing arm / wheel 1114 may include a wheel that freely rotates in consideration of the substrate 1110 rotation when supporting the substrate 1110 in the horizontal direction.

Once substrate 1110 is located in tank 1102, tank 1102 is filled with a deionized (DI) aqueous solution, or processing fluid containing the desired processing chemical. Once the closed megasonic module 1100 is filled with the desired processing fluid and the substrate 111 is immersed therein, the megasonic processing of the substrate 1110 is directed to the substrate 1110 facing the tank megasonic transducer 1106. A lead megasonic transducer 1108 directing the megasonic energy with respect to the surface of the substrate 1110 towards the lead megasonic transducer 1108 and a tank megasonic transducer 1106 directing the megasonic energy with respect to Is achieved by Once the substrate 1110 is immersed in processing chemicals, the drive wheel 1112 rotates the substrate 1110 to ensure complete and uniform processing through the entire surface of both the active surface and the backside of the substrate 1110. In one embodiment, drive motor 1116 is provided to drive drive wheel 1112 via mechanical coupling 1118 (eg, drive belts, gears, sprockets, chains, etc.).

The auto-tuning RF generator system as described in FIGS. 3-10 above can be coupled with one or all of the reed converter 1108 and the tank converter 1106, so that each transducer 1108, 1106 is connected to a substrate ( As the 1110 rotates, it is constantly and automatically adjusted for the dynamic impedance of each transducer 1108, 1106.

12 is a graph 1200 of energy distribution through a transducer in accordance with an embodiment of the present invention. Compared with the conventional energy windows shown by curves 120 and 122, the auto-tuning RF generator can cause a much narrower energy window 1202 between curve 1210 and curve 1212. Since the energy window 1202 is much narrower, the energy window can move upwards closer to the energy threshold T of the substrate, thereby providing a more efficient acoustic energy cleaning process.

As used herein in connection with the description of the present invention, the term "about" means +/- 10%. For example, a phrase such as "about 250" represents an area between 225 and 275. It will be apparent that the instructions represented by the operations in FIGS. 4, 7, and 10 need not be performed in the order shown, and not all processing represented by the operations may be necessary to practice the invention.

Although the foregoing invention has been described in detail for clarity of understanding, it will be apparent that certain variations and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of equivalents of the appended claims.

Claims (33)

A method of adjusting the RF generator to the instantaneous resonant frequency of a transducer, Inputting an RF input signal from an oscillator to the RF generator; Measuring a first phase of an input voltage of the RF input signal; Measuring a second phase of the voltage of the RF signal output from the RF generator and coupled to a converter input; Generating a frequency control signal when the first phase is not equal to the second phase; And Applying said frequency control signal to a frequency control input of said oscillator, said combining step comprising combining said frequency control signal with a set point control signal. delete The method of claim 1, Generating the frequency control signal when the first phase is not the same as the second phase, If the first phase lags behind the second phase, the frequency control signal reduces the frequency of the oscillator; If the first phase precedes the second phase, the frequency control signal increases the frequency of the oscillator; If the first phase is the same as the second phase, the frequency control signal comprises not changing the frequency of the oscillator. The method of claim 1, For each cycle of the RF input signal, the first phase and the second phase are measured and the frequency control signal is generated. An oscillator having a frequency control input and an RF signal output; An RF generator having an input coupled to the RF signal output of the oscillator and an output of the RF generator coupled to the converter; And With a voltage phase detector, The voltage phase detector, A first phase input coupled to the RF signal output of the oscillator; A second phase input coupled to an output of the RF generator; And A frequency control signal output coupled to the frequency control voltage input of the oscillator, The frequency control signal output is coupled to a frequency control voltage input of the oscillator via a control amplifier, The control amplifier, A first input coupled to the frequency control signal output; A second input coupled to the set point control signal; And And an output coupled to the frequency control voltage input of the oscillator. delete delete The method of claim 5, And the transducer is included in a megasonic cleaning chamber. A voltage controlled oscillator (VCO) having a frequency controlled voltage input and an output; A Class-E RF generator having an input coupled to an output of the VCO and an output of an RF generator coupled to a converter having a variable impedance; And With a voltage phase detector, The voltage phase detector, A first phase input coupled to the output of the VCO; A second phase input coupled to an output of the RF generator; And A voltage control signal output coupled to a frequency control voltage input of the VCO via a control amplifier, The control amplifier, A first input coupled to the voltage control signal output; A second input coupled to the set point control signal; And And an output coupled to the frequency control voltage input of the VCO. Applying an RF signal to a transducer at frequency f, wherein the transducer is oriented towards the substrate to emit acoustic energy towards the substrate at frequency f; Moving the substrate relative to the transducer; And Adjusting the RF signal to maintain resonance of the acoustic energy between the substrate and the transducer, comprising maintaining a constant voltage of the RF signal applied to the transducer. The substrate cleaning method. delete 11. The method of claim 10, An RF generator applies the RF signal to the transducer, Maintaining a constant voltage of the RF signal applied to the converter, Measuring a first voltage of the RF signal; Comparing the first voltage with a desired set point voltage; And Inputting a control signal to the variable DC power source to adjust the output voltage of the variable DC power source, And the variable DC power supply supplies DC power to the RF generator. 11. The method of claim 10, Adjusting the RF signal to maintain resonance of the acoustic energy comprises adjusting a frequency f of the RF signal applied to the transducer. The method of claim 13, The RF signal is applied by an RF generator, Adjusting the frequency f of the RF signal applied to the converter, Measuring a supply voltage applied to the RF generator; Measuring a peak voltage across an output amplifier included in the RF generator; Generating a frequency control signal when the peak voltage is not equal to a selected ratio of the supply voltage; And Applying the frequency control signal to a frequency control input of an oscillator that generates the RF signal. 13. The method of claim 12, The RF signal is applied by an RF generator, Adjusting the frequency f of the RF signal applied to the converter, Inputting an RF input signal from an oscillator to the RF generator and amplifying the RF input signal at the RF generator; Measuring a first phase of an input voltage of the RF input signal; Measuring a second phase of the voltage of the RF signal output from the RF generator; Generating a frequency control signal if the first phase is not equal to the second phase; And Applying the frequency control signal to a frequency control input of the oscillator. A cleaning chamber comprising a transducer and a substrate, the transducer being oriented toward the substrate, the transducer and the substrate separated by a variable distance d; An adjustable RF generator having a control input and an output, said output being coupled to said transducer; And The control of the adjustable RF generator to adjust the output of the adjustable RF generator to maintain resonance of acoustic energy between the substrate and the transducer, including maintaining a constant voltage of the RF signal applied to the transducer. And a feedback circuit coupled to the control input. The method of claim 16, The substrate can be rotated, The distance d varies by ½ wavelength of the RF signal output from the RF generator as the substrate rotates. The method of claim 16, The adjustable RF generator, A variable DC power supply having a control input and a DC output coupled to the adjustable RF generator, The feedback circuit, A first comparator, The first comparator, A first input coupled to the set point control signal; A second input coupled to an RF output of the adjustable RF generator; And A control signal output coupled to the control input of the adjustable RF generator, And the control input includes a voltage control input for the variable DC power supply. The method of claim 18, The adjustable RF generator, An oscillator having a control signal input and an RF signal output; An output amplifier coupled to the output of the oscillator; And A load network coupled between the output of the output amplifier and the output of the adjustable RF generator, The feedback circuit, A peak voltage detector coupled across the output amplifier; And A second comparator, The second comparator, A third input coupled to an output of the variable DC power supply; A fourth input coupled to an output of the peak voltage detector; And A second comparator output coupled to the control input of the adjustable RF generator, And the control input includes a control signal input of the oscillator. The method of claim 18, The adjustable RF generator, An oscillator having a frequency control input and an RF signal output; And An RF generator input coupled to the RF signal output of the oscillator, The feedback circuit comprises a voltage phase detector, The voltage phase detector, A first phase input coupled to the RF signal output of the oscillator; A second phase input coupled to an output of the adjustable RF generator; And A frequency control signal output coupled to said control input of said adjustable RF generator, And the control input comprises a frequency control voltage input of the oscillator. The method of claim 16, The adjustable RF generator, Supply voltage source; An oscillator having a control signal input and an RF signal output; An output amplifier coupled to the output of the oscillator; And A load network coupled between the output of the output amplifier and the output of the adjustable RF generator, The feedback circuit, A peak voltage detector coupled across the output amplifier; And Includes a comparator circuit, The comparator circuit, A first input coupled to the supply voltage source; A second input coupled to an output of the peak voltage detector; And A comparator output coupled to the control input of the adjustable RF generator, And the control input includes a control signal input of the oscillator. The method of claim 16, The adjustable RF generator, An oscillator having a frequency control input and an RF signal output; And An RF generator input coupled to the RF signal output of the oscillator, The feedback circuit comprises a voltage phase detector, The voltage phase detector, A first phase input coupled to the RF signal output of the oscillator; A second phase input coupled to an output of the adjustable RF generator; And A frequency control signal output coupled to said control input of said adjustable RF generator, And the control input comprises a frequency control voltage input of the oscillator. A method of adjusting the RF generator to the instantaneous resonant frequency of a transducer, Providing an RF input signal from an oscillator to the RF generator; Measuring a supply voltage applied to the RF generator; Measuring a peak voltage at the RF generator; Generating a frequency control signal if the peak voltage is not equal to a selected ratio of the supply voltage; And Applying the frequency control signal to a frequency control input of the oscillator. The method of claim 23, wherein Measuring the peak voltage, Measuring the peak voltage across the output amplifier included in the RF generator. The method of claim 23, wherein And said selected ratio of said peak voltage to said supply voltage is equal to a range between 3 to 1 and 6 to 1. Supply voltage source; An oscillator having a control signal input and an RF signal output; An output amplifier having an input coupled to an output of the oscillator; A load network coupled between the output of the output amplifier and the output of an RF generator; A peak voltage detector coupled between the output of the output amplifier and a reference voltage rail; And With a comparator circuit, The comparator circuit, A first input coupled to the supply voltage source; A second input coupled to an output of the peak voltage detector; And And a comparator output coupled to the control signal input of the oscillator. The method of claim 26, If a supply voltage is not equal to a selected ratio of peak voltages output by the peak voltage detector, a control signal is output from the comparator output. Supply voltage source; A voltage controlled oscillator (VCO) having a control voltage input and an output; An output amplifier coupled to the output of the VCO; A Class-E load network coupled between the output of the output amplifier and the output of an RF generator; A peak voltage detector coupled across the output amplifier; Comparator circuits; And A transducer coupled to the output of the RF generator, The comparator circuit, A first input coupled to the supply voltage source; A second input coupled to an output of the peak voltage detector; And A comparator output coupled to a control voltage input of the VCO, For a peak voltage output by the peak voltage detector, a control voltage is output from the comparator output when a supply voltage is not equal to a ratio of 3.6 to 1. Applying an RF signal from the RF generator to the converter; Measuring a first voltage of the RF signal; Comparing the first voltage with a desired set point voltage; And Inputting a control signal to the variable DC power source to adjust the output voltage of the variable DC power source, And the variable DC power supply supplies DC power to the RF generator. 30. The method of claim 29, The first voltage is a function of the impedance of the transducer, And the impedance of the transducer changes as the distance between the transducer and the target changes. 30. The method of claim 29, Comparing the first voltage with a desired set point voltage comprises determining a control signal, And the control signal is approximately equal to the difference between the first voltage and the desired set point voltage. An RF generator having an RF output coupled to an input of the converter; A variable DC power supply having a control input and a DC output coupled to the RF generator; And Equipped with a comparator, The comparator, A first input coupled to the set point control signal; A second input coupled to an RF output of the RF generator; And And a control signal output coupled to a voltage control input for the variable DC power supply. A Class-E RF generator having an RF output coupled to an input of a megasonic transducer of the megasonic cleaning chamber; A variable DC power supply having a control input and a DC output coupled to the Class-E RF generator; And Equipped with a comparator, The comparator, A first input coupled to the set point voltage source; A second input coupled to an RF output of the class-E RF generator; And And a control signal output coupled to a voltage control input for the variable DC power supply.

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