Patent ID: 12227846

The attached drawings are for purposes of illustration and are not necessarily to scale.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, some aspects will be described in terms that would ordinarily be implemented as software programs. Those skilled in the art will readily recognize that the equivalent of such software can also be constructed in hardware, firmware, or micro-code. Because data-manipulation algorithms and systems are well known, the present description will be directed in particular to algorithms and systems forming part of, or cooperating more directly with, systems and methods described herein. Other aspects of such algorithms and systems, and hardware or software for producing and otherwise processing the signals involved therewith, not specifically shown or described herein, are selected from such systems, algorithms, components, and elements known in the art. Given the systems and methods as described herein, software not specifically shown, suggested, or described herein that is useful for implementation of any aspect is conventional and within the ordinary skill in such arts.

Using a λ/2 cable in quartz crystal deposition controllers is not practical because the crystal frequency (thus λ) changes with use. This crystal frequency change reduces the window of operation. Only certain frequency shift is permissible for a given cable length because phase deteriorates as λ changes. Such phase deterioration decreases the frequency stability and resolution of the measurement system.

Impedance and frequency change with deposition, so fixed impedance matching is also not effective. Wide band and wide load impedance matching at the crystal is difficult to achieve with components that can tolerate vacuum. Also, any additional element in vacuum can cause additional line downtime due to failure. It is therefore desirable to measure the crystal resonance frequency in a way that is insensitive to the phase of the crystal excitation (high frequency, e.g., 6 MHz).

Various aspects are directed to overcome reflection limited length of coaxial cables connecting a passive deposition monitor circuit to a remote quartz crystal sensor housed inside a vacuum chamber. Various aspects provide a deposition monitoring circuit substantially immune to problems caused by standing waves in long cables connecting a passive crystal interrogation circuit to a quartz crystal mounted in large deposition systems, which will then include any systems. Various aspects reduce frequency pulling of the impedance spectrum mainly caused by cable capacitance load, especially in the case of long cables. Various aspects are effective with active modes, whether it is fundamental, spurious or overtone, independent of cable length, cable type or sensor head type. Various aspects do not require a varactor-limited bridge circuit for cable compensation. Various aspects have increased frequency bandwidth to cover crystals with fundamental frequency above 6 MHz, limited only by the capability of the device synthesizing the drive waveform. Various aspects can measure the filter quality (Q) of the crystal. This is useful because measurement speed is related to Q. Various crystals permit a measurement speed of 100 ms. Various aspects can measure a crystal without using an interface circuit such as an XIU. Various aspects include a high stability quartz crystal passive resonance circuit for thin film deposition monitoring in a large system. The circuit can be used with existing rate monitors and controllers, e.g., by INFICON.

FIG.1is a high-level diagram showing the components of a system. The system100is an exemplary data-processing system for analyzing data and performing other analyses described herein, and related components. The system includes a processor4286, a peripheral system4220, a user interface system4230, and a data storage system4240. The peripheral system4220, the user interface system4230and the data storage system4240are communicatively connected to the processor4286. The processor4286can be communicatively connected to a network4250, such as the Internet or an X.425 network, as discussed below. The processor4286can include one or more of systems4220,4230,4240, and can connect to one or more network(s)4250. The processor4286, and other processing devices described herein, can each include one or more microprocessors, microcontrollers, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), programmable logic devices (PLDs), programmable logic arrays (PLAs), programmable array logic devices (PALs), or digital signal processors (DSPs).

The processor4286can implement processes of various aspects described herein. The processor4286can be or include one or more device(s) for automatically operating on data, e.g., a central processing unit (CPU), microcontroller (MCU), desktop computer, laptop computer, mainframe computer, personal digital assistant, digital camera, cellular phone, smartphone, or any other device for processing data, managing data, or handling data, whether implemented with electrical, magnetic, optical, biological components, or otherwise. In an example, the processor4286can include Harvard-architecture components, modified-Harvard-architecture components, or Von-Neumann-architecture components.

The phrase “communicatively connected” includes any type of connection, wired or wireless, for communicating data between devices or processors. These devices or processors can be located in physical proximity or not. For example, subsystems such as the peripheral system4220, user interface system4230, and data storage system4240are shown separately from the data processing system4286but can be stored completely or partially within the data processing system4286.

The peripheral system4220can include one or more devices configured to provide digital content records to the processor4286. For example, the peripheral system4220can include digital still cameras, digital video cameras, cellular phones, or other data processors. The processor4286, upon receipt of digital content records from a device in the peripheral system4220, can store such digital content records in the data storage system4240.

The user interface system4230can include a mouse, a keyboard, another computer (connected, e.g., via a network or a null-modem cable), or any device or combination of devices from which data is input to the processor4286. The user interface system4230also can include a display device, a processor-accessible memory, or any device or combination of devices to which data is output by the processor4286. The user interface system4230and the data storage system4240can share a processor-accessible memory.

In various aspects, the processor4286includes or is connected to the communication interface4215that is coupled via a network link4216(shown in phantom) to the network4250. For example, the communication interface4215can include an integrated services digital network (ISDN) terminal adapter or a modem to communicate data via a telephone line; a network interface to communicate data via a local-area network (LAN), e.g., an Ethernet LAN, or wide-area network (WAN); or a radio to communicate data via a wireless link, e.g., WiFi or GSM. The communication interface4215sends and receives electrical, electromagnetic or optical signals that carry digital or analog data streams representing various types of information across the network link4216to the network4250. The network link4216can be connected to the network4250via a switch, gateway, hub, router, or other networking device.

Processor4286can send messages and receive data, including program code, through network4250, network link4216and communication interface4215. For example, a server can store requested code for an application program (e.g., a JAVA applet) on a tangible non-volatile computer-readable storage medium to which it is connected. The server can retrieve the code from the medium and transmit it through network4250to communication interface4215. The received code can be executed by processor4286as it is received, or stored in data storage system4240for later execution.

Data storage system4240can include or be communicatively connected with one or more processor-accessible memories configured to store information. The memories can be, e.g., within a chassis or as parts of a distributed system. The phrase “processor-accessible memory” is intended to include any data storage device to or from which processor4286can transfer data (using appropriate components of peripheral system4220), whether volatile or nonvolatile; removable or fixed; electronic, magnetic, optical, chemical, mechanical, or otherwise. Exemplary processor-accessible memories include but are not limited to: registers, floppy disks, hard disks, tapes, bar codes, Compact Discs, DVDs, read-only memories (ROM), erasable programmable read-only memories (EPROM, EEPROM, or Flash), and random-access memories (RAMs). One of the processor-accessible memories in the data storage system4240can be a tangible non-transitory computer-readable storage medium, i.e., a non-transitory device or article of manufacture that participates in storing instructions that can be provided to processor4286for execution.

In an example, data storage system4240includes code memory4241, e.g., a RAM, and disk4243, e.g., a tangible computer-readable rotational storage device such as a hard drive. Computer program instructions are read into code memory4241from disk4243. Processor4286then executes one or more sequences of the computer program instructions loaded into code memory4241, as a result performing process steps described herein. In this way, processor4286carries out a computer implemented process. For example, steps of methods described herein, blocks of the flowchart illustrations or block diagrams herein, and combinations of those, can be implemented by computer program instructions. E.g., processor4286can command the DDS to sweep HF, can record data from the lock-in amp, and can determine a control signal to send to a flat-panel deposition system to adjust the rate according to the measured resonant frequency. Code memory4241can also store data, or can store only code.

The system100also includes a measurement card300. The measurement card includes a circuit for monitoring thin film deposition. The circuit can be a passive resonance circuit. The circuit generate a modulated signal which is grounded through a quartz. The signal is modulated such that a length of a cable connecting the measurement card300to a deposition chamber does not affect monitoring of the thin film thickness. A signal is received from the quartz and demodulated. The signal is analyzed to determine the thickness of the deposited film.

FIG.2shows a problem with long cables. When the cable length exceeds one-quarter wavelength of the RF impulse, the crystal's impedance spectrum reverses its phase and the operable frequency span decreases with length.

FIG.3is a high-level diagram of a measurement card. A long cable304connecting the measurement card300and the deposition chamber302is shown by the heavy black line. Detection of the fundamental resonance of a crystal has been tested successfully using a rudimentary circuit and general electronic lab equipment such as a function generator, a phase detector316, and a voltmeter (or an oscilloscope). The processor4286can close a control loop to measure crystal resonance and, e.g., control deposition rate. Processor4286can also control the frequencies generated by the synthesizer306, such as a DDS. Acronyms include:

PMPhase modulationFMFrequency modulationAMAmplitude modulationDDSDirect Digital synthesizerPM orPhase modulated or Frequency modulatedFM DDSDirect Digital synthesized signal

A synthesizer306(e.g., a direct digital synthesizer) generates a frequency- or phase-modulated signal. That signal is grounded through a quartz crystal308in the deposition chamber302. The crystal308has a conductance that varies with frequency. At the resonance frequency of the crystal, conductance reaches its peak. Since high conductance (low impedance) is used, it doesn't matter how long the cable304is as long as the cable304has low enough impedance at the measurement frequencies that cable impedance doesn't swamp the impedance change of the crystal. In other words, the minimum reflection at resonance converts the FM to AM.

FM or PM modulation can be implemented directly with a synthesizer306(see, e.g., Analog Device application note AN-543—High Quality, All-Digital RF Frequency Modulation Generation with the ADSP-2181 DSP and the AD9850 Direct Digital Synthesizer), such as a DDS or other frequency synthesizer or waveform generator. A low frequency is approximately in the range 1-1000 Hz sinusoidal. A high frequency is approximately in the range 4-7 MHz sinusoidal.

A phase detector316is to receive a signal from the quartz308. The phase detector316can be any suitable phase detector, such as a lock-in amplifier. The phase detector316is to determine a phase of a signal from the crystal308in order to determine a thickness of a thin film.

The T-Network310can include a resistor312on each arm, as shown, or a resistor in series with a capacitor on each arm to block DC. The T-network310can also include an LCR series circuit shunted by a static parallel capacitor representing the quartz crystal as in Butterworth van dyke model. In an example, ground is as same as the BNC shield314and tied to the measurement card ground and the body of the metal deposition chamber.

This and other circuits described herein can be used as thin film thickness rate monitoring circuits. As thin-film material is deposited on the surface of the crystal, its resonant frequency changes. The change in frequency can be measured and used to determine the amount of mass on the crystal. Repeated measurements over time permit determining deposition rate.

FIG.4shows magnitude (correlated to impedance) and phase measurements from the lock-in amplifier as the high frequency is swept. A wide range sweep did not show any peaks due to cable resonances. A frequency pulling of only 13 Hz was noted going from 0.1 to 30 m of cable length, which is much reduced compared to prior devices. The absence of the bulky controller cable and the simplistic nature of the circuit can result in reduced cost.

FIGS.5a-5bshow an exemplary transformed phase modulated signal. The exemplary phase modulated signal is transformed to an amplitude modulated signal by the monitor crystal. The diode and the filter form the demodulation of AM (as is conventionally done) to produce a signal similar to the frequency of the carrier. The phase of the signal is in sync with that of the carrier when the modulation frequency of the DDS signal matches the crystal's resonance frequency and the frequency of the carrier signal is within the FM/PM modulation bandwidth. In this example, the low frequency is 10 Hz and the high frequency is ˜5.97 MHz. (5.972960 MHz on the top, i.e., 10 Hz off resonance, and 5.972950 MHz on the top, i.e., at resonance).

The crystal is a shunt for every frequency except those absorbed due to resonance Using sinusoidal signals, a PM sinusoid is a sum of Bessel functions. One component corresponds to the crystal frequency. When the crystal absorbs that component, there is a Bessel function missing from the sum. The resulting signal is thus amplitude modulated (the crystal has absorbed a component at the resonance frequency). Crystal absorption is not phase-dependent; however long the cable is, the crystal will absorb that component. A cable with a velocity factor of 0.66 can be used, giving λ approx. 32 m for 6 MHz example.

The T network acts as a directional coupler. The crystal draws current at the resonance frequency, so the signal into the demodulator is amplitude modulated. Demodulation gives the envelope of the signal. The phase of the envelope is in phase with the low frequency (LF, e.g., from the Textronix described below) signal when the crystal is at resonance Thus, the high frequency is swept (HF, e.g., from the SRS described below) and the envelope phase is monitored. The zero-crossing of the envelope phase indicates the resonance frequency, as discussed below. (Longer cables used with prior devices may not see a zero crossing of phase.) Even if reflections obscure HF phase information, the demodulated envelope still has a clean zero crossing.

Unlike prior schemes, in various aspects, the modulation index is selected so that at resonance, the high frequency matches the crystal frequency. In a counterexample, when the modulation voltage is high, the resonance condition can happen away from the natural frequency of the crystal. For example, in overmodulation, when crystal is in resonance, AM signal is not 100% modulated—is slightly overmodulated. However, for properly adjusted modulation conditions, detected resonance freq. is close to the crystal's natural frequency (with deposition—independent variations). In other conditions, detection is e.g. 400 Hz away. As frequency moves away from resonance, the signal is reduced and there is less ability to detect deposition. Accordingly, modulation conditions are selected (e.g., experimentally) to provide desired results.

FIG.6shows the admittance curve of a canned crystal (fundamental resonance at 5.996913 MHz) obtained with the proposed circuit showing the resonance of the crystal. The length of the cable used was 36.75 m. The second graph obtained using phase modulation and SR850 DSP Lock-in amplifier shows the cable pulling of the resonance frequency when the length was changed from 0.1 m to 30 m.

An experiment was performed.FIGS.7A-7Dshow the results of this experiment. Phase vs. frequency and amplitude vs. frequency curves were obtained by using a prototype (circuit components laid out on a breadboard) and connecting a Textronix function generator as the low-frequency source (e.g., 10-100 Hz), an SRS function generator as the high-frequency source (e.g., 5-7 MHz) and a Dynatrac or SRS Lock-in amplifier to monitor the output.

Phase modulation of the high-frequency signal was obtained by connecting the Textronix generator to the external modulation input of the SRS. RF amplitude, Modulation amplitude, RF shape, Mod shape and Mod Frequency were kept constant. Using a LabVIEW program and a National Instrument GPIB-USB cable, the frequency of the SRS output was changed (high-frequency sweep) and the Lock-In outputs (amplitude and phase) were queried and written to a file. The frequency was changed from below resonance to above resonance.

The low frequency is selected according to the crystal quality Q. Q depends on the type of piezoelectric material used, quality of the cultured crystal, processing of the blanks and many other things. Q is inversely proportional to full width at half maximum of amplitude (FWHM) of the admittance peak of crystal resonance. The modulation bandwidth (which relates to the speed of measurement and to the low frequency) needs to be less than FWHM of crystal. In other words, high Q crystal decreases the measurement speed.

The low frequency can be selected based on bandwidth (BW). BW of PM should be less than the full-width at half maximum (FWHM) of admittance peak of crystal resonance Characterize per crystal type. Q was measured using network analyzer at different states of coating to determine FWHM. BW=2*(low frequency)*(1+Modulation Index). For example, for a mod index of 1, low freq of 10 Hz, BW=40 Hz. Higher-Q crystals require lower low frequencies (Textronix). Therefore measurements are slower because it takes longer to determine the phase of the lower-frequency signal.

The measured magnitudes during the HF sweep can be used to derive the Q of the crystal. The detected signal strength can be used to derive the reflection coefficient and the quality of the crystal.

FIG.8is a flowchart illustrating an example of a method of monitoring thin film deposition. Various steps of the method can be performed in any order except when otherwise specified, or when data from an earlier step is used in a later step. The method can be carried out by a system, such as the system described above with relation toFIG.1.

At block802, a modulated signal can be selected via a processor. The modulated signal can be a phase modulated signal or a frequency modulated signal. At block804, the modulated signal is grounded through a quartz crystal to excite the crystal. At block806, a signal is received from the crystal. At block808, the signal is demodulated. At block810, the phase of the demodulated signal is measured to determine a thin film deposition thickness.

Example 1

A system for monitoring thin film deposition is described herein. The system includes a quartz crystal and a synthesizer to generate a modulated signal, the modulated signal to be grounded through the quartz crystal. The system further includes a phase detector to determine a phase of the modulated signal from the quartz crystal in order to determine a thin film thickness.

The modulated signal can be a frequency modulated signal. The modulated signal can be a phase-modulated signal. A modulation index can be selected such that, at resonance, a frequency of the signal matches a crystal frequency. A frequency of the signal can be selected such that crystal conductance reaches a peak. The system can further include a cable to couple the system to a deposition chamber, wherein a length of the cable does not decrease thin film deposition detection. A change in frequency of the crystal is to change as a thin film is deposited on a surface of the quartz crystal and the change in frequency is to be monitored to detect thin film deposition.

Example 2

A method for monitoring thin film deposition is described herein. The method includes selecting, via a processor, a modulated signal. The method also includes grounding the modulated signal through a quartz crystal to excite the crystal. The method further includes receiving a modulated signal from the crystal and demodulating the signal from the crystal. The method additionally includes measuring a phase of the demodulated signal to determine a thin film deposition thickness.

The modulated signal can be a frequency modulated signal. The modulated signal can be a phase-modulated signal. The modulated signal can be selected such that, at resonance, frequency of the modulated signal matches frequency of the quartz crystal. A cable can connect a thin film monitoring system to a deposition chamber and the modulated signal can be selected such that length of the cable does not affect thin film thickness detection. The modulated signal can be selected such that crystal conductance reaches a peak. The method can further include determining a change in frequency of the demodulated signal to monitor thin film deposition.

Exemplary method(s) described herein are not limited to being carried out by components specifically identified herein.

In view of the foregoing, various aspects provide measurement of crystal resonance frequencies. A technical effect is to excite the crystal with a drive signal and measure the effect of the crystal on that signal.

Various aspects described herein may be embodied as systems or methods. Accordingly, various aspects herein may take the form of an entirely hardware aspect, an entirely software aspect (including firmware, resident software, micro-code, etc.), or an aspect combining software and hardware aspects These aspects can all generally be referred to herein as a “service,” “circuit,” “circuitry,” “module,” or “system.”

Furthermore, various aspects herein may be embodied as computer program products including computer readable program code stored on a tangible non-transitory computer readable medium. Such a medium can be manufactured as is conventional for such articles, e.g., by pressing a CD-ROM. The program code includes computer program instructions that can be loaded into processor4286(and possibly also other processors), to cause functions, acts, or operational steps of various aspects herein to be performed by the processor4286(or other processor). Computer program code for carrying out operations for various aspects described herein may be written in any combination of one or more programming language(s), and can be loaded from disk4243into code memory4241for execution. The program code may execute, e.g., entirely on processor4286, partly on processor4286and partly on a remote computer connected to network4250, or entirely on the remote computer.

The invention is inclusive of combinations of the aspects described herein. References to “a particular aspect” and the like refer to features that are present in at least one aspect of the invention. Separate references to “an aspect” (or “embodiment”) or “particular aspects” or the like do not necessarily refer to the same aspect or aspects; however, such aspects are not mutually exclusive, unless so indicated or as are readily apparent to one of skill in the art. The use of singular or plural in referring to “method” or “methods” and the like is not limiting. The word “or” is used in this disclosure in a non-exclusive sense, unless otherwise explicitly noted.

The invention has been described in detail with particular reference to certain preferred aspects thereof, but it will be understood that variations, combinations, and modifications can be effected by a person of ordinary skill in the art within the spirit and scope of the invention.