A measuring apparatus and method for measuring the parameters of a piezoelectric crystal on which a thin film of a material is deposited, and a thin film deposition system equipped with such apparatus and a method for controlling such a system.

Abstract

The present invention relates to a measurement device (u) for measuring parameters of a piezoelectric crystal (1) on which a thin film of material is deposited (under vacuum), comprising: the crystal (1) having two spaced electrodes (2, 2'), a frequency generator (3) adapted to generate an oscillatory signal at a specified output frequency, a measurement amplifier (4) adapted to apply the oscillatory signal as a drive signal to one of the electrodes (2, 2') of the crystal (1) and to provide a crystal output signal in response to the drive signal, a quadrature demodulator (5) adapted to down-convert the crystal output signal and provide an in-phase output signal and a quadrature output signal, and a calculation unit (7) adapted to determine one or more parameters of the crystal (1) based on the in-phase and quadrature output signals. Furthermore, the present invention relates to a corresponding measurement method, as well as a thin film deposition system (comprising a vacuum chamber) comprising such a device (u) and a method for controlling such a system.

Description

[Technical Field]

[0001] The present invention relates to a measuring apparatus and method for measuring parameters of a piezoelectric crystal on which a thin film of a material is deposited (under vacuum), and also to a thin film deposition system (equipped with a vacuum chamber) equipped with such an apparatus and a method for controlling such a system. [Background technology]

[0002] The so-called quartz microscale method (QCM) is commonly used to monitor the thickness of thin films of material deposited on a substrate under vacuum. This method determines the thickness based on the change in the mass of the quartz on which the thin film of material is also deposited, using the change in the quartz's resonant frequency as a guide. The accuracy with which the film thickness can be determined depends on the precision of specific parameters of the piezoelectric crystal, such as its acoustic properties, which can be expressed as its kinetic resistance (quantifying dissipation loss), capacitance (inversely proportional to stiffness), and inductance (proportional to mass) in the Butterworth-van Dyke equivalent circuit, and can be derived based on the measured resonant frequency. Known measuring devices employ an analog phase-locked loop tuned to the resonant frequency. Often, amplitude in decibels (dB) and the phase angle at the resonant frequency (i.e., polar coordinates) are used to determine the Cartesian coordinates (i.e., real and imaginary parts) of the admittance of an oscillator circuit, for example, determining the parameters of the piezoelectric crystal and calculating the film thickness based on them. Unfortunately, this often results in considerably inaccurate film thickness values. Another problem is that as the film deposited on the quartz thickens, the kinetic resistance increases, resulting in greater damping of vibrations at the resonant frequency, i.e., a decrease in the amplitude of the resonant peak. At the same time, the phase response curve near the resonant frequency becomes flatter, making it more difficult to track the resonant frequency, for example, under noisy conditions. This is particularly noticeable when parallel capacitance is large, due to electrode capacitance, cable capacitance, and input capacitance of the measurement circuit. Consequently, the lifespan of the quartz is limited by parallel capacitance, requiring more frequent quartz replacement. Replacing the quartz usually requires evacuating the vacuum coating system, so the vacuum coating system can only be run during substrate processing. Even if evacuating is not required, replacing the quartz during the operating process presents problems because the process cannot be monitored during the quartz replacement, and subsequently, the measured film thickness of the new quartz does not match (due to the offset) the current thickness of the film deposited on the substrate.

[0003] Therefore, it is necessary to be able to determine the parameters of piezoelectric crystals with higher precision than is currently possible with known measuring devices. Furthermore, it is also necessary to increase the usage time of the crystal to monitor the thickness of the thin film of material deposited on the substrate under vacuum. [Overview of the project] [Problems that the invention aims to solve]

[0004] The object of the present invention is to provide an improved measuring device that can measure the parameters of a piezoelectric crystal on which a thin film of material is deposited, and in particular can obtain more accurate parameter values. This object is achieved by the measuring device described in claim 1.

[0005] Accordingly, an object of the present invention is to provide an improved method for measuring the parameters of a piezoelectric crystal on which a thin film of material is deposited, particularly for obtaining more accurate parameter values. This object is achieved by the measurement method described in claim 14.

[0006] A further object of the present invention is to increase the usage time of a crystal for monitoring the thickness of a thin film of material deposited on a substrate under vacuum (and, similarly, to increase the maximum allowable film thickness of the material deposited on the crystal). This objective is achieved by the measuring apparatus and method described in claims 3 and 16, respectively.

[0007] A further object of the present invention is to provide an improved thin-film deposition system that can deposit thin films of material on a substrate with greater precision, more specifically, a thin-film deposition system that increases the lifespan of the quartz, i.e., reduces the frequency of quartz replacement (equivalently, increases the maximum allowable film thickness of the material deposited on the quartz). Such vacuum coating systems and such (plasma-enhanced) atomic layer deposition (ALD / PEALD) systems are described in claims 11 and 13, respectively.

[0008] Accordingly, another object of the present invention is to provide an improved control method for controlling a thin film deposition system that enables more precise deposition of thin films of material onto a substrate, more specifically, an improved control method that can increase the lifespan of the quartz crystal, i.e., reduce the frequency of quartz crystal replacement. Such methods are specified in claims 25 and 27 for vacuum coating systems and ALD / PEALD systems, respectively. [Means for solving the problem]

[0009] Specific embodiments of the apparatus, system, and method according to the present invention are described in the dependent claims.

[0010] The present invention is a measuring device for measuring the parameters of a piezoelectric crystal on which a thin film of a material is deposited, - A piezoelectric crystal comprising two spaced electrodes, wherein the film of the material is deposited on the crystal (and / or electrodes), and the crystal has a fundamental resonant frequency in the range of, for example, 1 MHz to 100 MHz, more specifically in the range of 2 MHz to 7 MHz, most specifically in the range of 5 MHz to 6 MHz (when the film is not deposited thereon), and the crystal is particularly AT-cut quartz, the piezoelectric crystal and - A frequency generator adapted to produce an oscillating signal at a specified output frequency, - A measuring amplifier adapted to apply the oscillation signal as a drive signal to one of the electrodes of the crystal and to provide a crystal output signal in response to the drive signal, - A quadrature demodulator adapted to downconvert the crystal output signal (to baseband) and provide a common-mode output signal and a quadrature output signal, wherein the common-mode and quadrature output signals are in particular digital signals, - In particular, when the film of the material is deposited on the crystal (and / or the electrode) based on the common-mode output signal and the quadrature output signal, particularly at a plurality of different frequencies, the measuring device includes a calculation unit adapted to determine one or more parameters of the crystal, for example, at the fundamental resonant frequency of the crystal, one or more harmonic resonant frequencies of the crystal, one or more anharmonic resonant frequencies of the crystal, or one or more frequencies higher or lower than the fundamental resonant frequency of the crystal.

[0011] In one embodiment of the apparatus, the parameters of the crystal are as follows: - Crystal series resistor, - Crystal series capacitance, - Crystal series inductance, - Parallel admittance (of crystals), - This is the quality factor of the crystal, and / or the calculation unit is further adapted to determine the rate of increase of the thickness or mass of the film of the material deposited on the crystal (and / or electrode) based on the thickness or mass of the film of the material deposited on the crystal (and / or electrode) and / or the in-phase output signal and the orthogonal output signal.

[0012] In a further embodiment, the apparatus further, - In particular, the system includes a compensation unit adapted to numerically compensate for / eliminate the effects of the (crystal) parallel admittance, especially parallel capacitance, by subtracting the conductance value of the parallel admittance from the signals based on the common-mode output signal and the quadrature output signal to provide a compensated common-mode output signal, and by subtracting the susceptance value of the parallel admittance from further signals based on the common-mode output signal and the quadrature output signal to provide a compensated quadrature output signal.

[0013] In a further embodiment, the apparatus further, - A frequency control unit adapted to generate a frequency control signal as an input to the frequency generator, The frequency control signal is adapted so that the crystal operates at its resonant frequency, and the resonant frequency depends on the thickness or mass of the film of the material deposited on the crystal. Here, the frequency control signal is determined based on (at least) one of the following control variables. - The phase obtained by dividing the inverse negative tangent of the compensated orthogonal output signal by the compensated common-mode output signal, wherein the phase is driven to zero in particular to operate the crystal at the resonant frequency, and the phase is calculated in particular by a CORDIC (Coordinate Rotation Digital Computer) processor, - In particular, the tangent obtained by dividing the compensated quadrature output signal by the compensated common-mode output signal, where the magnitude of the compensated common-mode output signal is such that the tangent is driven to zero in particular to operate the crystal at the resonant frequency, - The imaginary part of the impedance obtained by dividing the compensated quadrature output signal by the sum of the squared compensated common-mode output signal and the squared compensated quadrature output signal, wherein the imaginary part of the impedance is driven to zero in particular in order to operate the crystal at the resonant frequency.

[0014] In a further embodiment, the apparatus - Further comprising an amplitude control unit adapted to generate an amplitude control signal to be applied to the frequency generator in order to amplify the amplitude of the oscillation signal based on the in-mode output signal and / or the quadrature output signal.

[0015] For example, when a quartz crystal is new, that is, when no material has been deposited on it, the amplitude of the oscillation signal decreases in response to, for example, a measured high-level common-mode output signal. Conversely, when a quartz crystal has been used for a long period of time, that is, when a thick film of material has been deposited on it, the amplitude of the oscillation signal increases in response to, for example, a measured low-level common-mode output signal. In this way, the signal-to-noise ratio (SNR) can be kept essentially constant regardless of the thickness of the film of material deposited on the quartz crystal.

[0016] In a further embodiment of the device, - The frequency generator is a quadrature oscillator with a frequency control input to which the frequency control signal is applied, and is adapted to provide a cosine signal as the oscillation signal and a 90° phase-shifted quadrature signal having the same output frequency (e.g., within the range of 4 to 7 MHz with a resolution of millihertz) in response to the frequency control signal, - The measurement amplifier applies the cosine signal as the drive signal to one of the electrodes of the crystal, The quadrature demodulator - A cosine signal mixer adapted to multiply the cosine signal and the crystal output signal to provide an intermediate cosine output signal, - A quadrature signal mixer adapted to multiply the quadrature signal and the crystal output signal to provide an intermediate quadrature output signal, - A cosine signal filter (representing the real part of the crystal output signal) adapted to low-pass filter the intermediate cosine output signal (e.g., at a "cut-off" / 3 dB frequency in the range of 1 kHz to 10 kHz) to provide the cosine output signal, - A quadrature signal filter (representing the imaginary part of the crystal output signal) adapted to low-pass filter the intermediate quadrature output signal (e.g., at a "cut-off" / 3 dB frequency in the range of 1 kHz to 10 kHz) to provide the quadrature output signal, and includes.

[0017] <00000,95>In a further embodiment, the device - The scaled / converted cosine and quadrature signals are adapted to scale / convert the cosine and the quadrature output signals according to the signal amplitude of the cosine and / or the quadrature output signal, and optionally according to the output impedance of the measurement amplifier, so as to represent the admittance of the circuit including the crystal having the measurement amplifier and the electrodes.

[0018] In a further embodiment, the device - Further comprising an equalizer (distortion correction / compensation unit) adapted to equalize / compensate for the influence of the frequency response of the measurement amplifier on the common-mode output signal and the quadrature output signal.

[0019] In a further embodiment of the device, the equalization is based on calibration / compensation data determined based on measurements of the common-mode output signal and the quadrature output signal when the drive signal is applied to an open circuit, a short circuit, and a reference impedance, respectively, the reference impedance being essentially a 50-ohm resistor.

[0020] In a further embodiment of the apparatus, the parallel admittance is determined based on the common-mode output signal and the quadrature output signal measured at a frequency lower than the resonant frequency of the crystal (e.g., at least 1 MHz, e.g., 4.5 MHz), and further based on the common-mode output signal and the quadrature output signal measured at a frequency higher than the resonant frequency of the crystal (e.g., at least 500 kHz, e.g., 6.5 MHz).

[0021] In further embodiments, the apparatus features one or more of the following: - The output frequency is in the range of 4MHz to 6MHz. - The output frequency can be adjusted with precision within the millihertz (mHz) range. - The output frequency is generated by a direct digital synthesizer (DDS) or a numerically controlled oscillator (NCO).

[0022] Furthermore, the present invention relates to a thin film deposition system in the form of a vacuum coating system for depositing a thin film of material on a substrate, the system comprising the aforementioned measuring device, a process chamber, a substrate holder adapted to receive the substrate, an evaporation source, and a (high) vacuum pump, wherein the crystal of the measuring device is positioned very close to the substrate holder, for example, around the substrate holder, on the periphery of the substrate holder, or adjacent to the substrate holder, and a control signal applied to the evaporation source is based on the determined thickness of the film of material deposited on the crystal (and / or electrode) and / or the determined rate of increase of the thickness of the film of material deposited on the crystal. The control signal controls, in particular, the power level applied to the evaporation source.

[0023] In one embodiment, the system further comprises at least one of the following elements: - Circuit board heater, - Shutter, - (High) vacuum valve, - Process gas inlet, - Auxiliary plasma source or ion source, e.g., in the form of a glow discharge electrode, Here, the control signal, or a further control signal based on the determined thickness of the film of the material deposited on the crystal (and / or electrode) and / or the determined rate of increase of the thickness of the film of the material deposited on the crystal, is applied to control at least one of the elements.

[0024] Furthermore, the present invention relates to a thin film deposition system in the form of an atomic layer deposition system or a plasma-enhanced atomic layer deposition system for depositing a thin film of material on a substrate, the system comprising the aforementioned measuring device, a process chamber, a substrate holder adapted to receive the substrate, a precursor gas inlet with associated precursor gas valves and associated precursor gas pumps adapted to control the flow of precursor gas introduced into the process chamber, and / or a reactive gas inlet with associated reactive gas valves and associated reactive gas pumps adapted to control the flow of reactive gas (or a second type of precursor) introduced into the process chamber, and in the case of a plasma-enhanced atomic layer deposition system, a plasma source for generating plasma in the process chamber, wherein the crystal of the measuring device is positioned very close to the substrate holder, for example around the substrate holder, on the periphery of the substrate holder, or adjacent to the substrate holder, and at least one of the following is based on the determined thickness of the film of material deposited on the crystal (and / or electrode), and / or the determined rate of increase of the thickness of the film of material deposited on the crystal. - The flow of the precursor gas, - The flow of the reactive (or second type of precursor) gas, - A plurality of ALD cycles, in which, during each ALD cycle, the precursor gas is introduced into the process chamber, followed by the reactive (or second type of precursor) gas being introduced into the process chamber, - Process time, for example, the duration of the ALD cycle, - Temperature of the precursor gas and / or the reactive gas, - Temperature of the substrate, - Flow of plasma gas into the process chamber (in the case of a plasma-enhanced atomic layer deposition system), - Power applied to the plasma source, in particular the voltage applied by a high-voltage DC power supply to maintain the plasma (in the case of a plasma-enhanced atomic layer deposition system).

[0025] Furthermore, the present invention relates to a measurement method for measuring the parameters of a piezoelectric crystal on which a thin film of material is deposited. - A step of depositing the thin film of a material onto a piezoelectric crystal having two spaced electrodes, wherein the crystal has a fundamental resonant frequency in the range of, for example, 1 MHz to 100 MHz, more specifically in the range of 2 MHz to 7 MHz, and particularly in the range of 5 MHz to 6 MHz (when no film is deposited thereon), and the crystal is particularly AT-cut quartz, - A step of generating an oscillation signal at a specified output frequency (for example, in the range of 4MHz to 7MHz with millihertz resolution), - The steps of applying the oscillation signal as a drive signal to one of the electrodes of the crystal via a measuring amplifier, and providing a crystal output signal in response to the drive signal, - Steps include quadrature demodulating the crystal output signal to provide a digital common-mode output signal and a digital quadrature output signal that have been down-converted (to baseband), - The step of determining one or more parameters of the crystal based on the common-mode output signal and the quadrature output signal, particularly at multiple different frequencies, for example, the fundamental resonant frequency of the crystal, one or more harmonic resonant frequencies of the crystal, one or more anharmonic resonant frequencies of the crystal, or one or more frequencies higher or lower than the fundamental resonant frequency of the crystal.

[0026] In one embodiment of this method, the parameters of the crystal are as follows: - Crystal series resistor, - Crystal series capacitance, - Crystal series inductance, - Parallel admittance (of crystals), - Crystal quality factor, and / or further, the step includes determining the thickness or mass of the film of the material deposited on the crystal (and / or electrode) and / or the rate of increase of the thickness or mass of the film of the material deposited on the crystal (and / or electrode) based on the in-phase output signal and the orthogonal output signal.

[0027] In further embodiments, the method - The process includes numerically compensating for / removing the effects of each of the parallel admittances (of the crystal) by subtracting the conductance value of the parallel admittance from the signal based on the common-mode output signal and the quadrature output signal to provide a compensated common-mode output signal, and by subtracting the susceptance value of the parallel admittance from a further signal based on the common-mode output signal and the quadrature output signal to provide a compensated quadrature output signal.

[0028] In further embodiments, this method is - Further comprising the step of generating a frequency control signal for generating the frequency, wherein the frequency control signal is adapted so that the crystal operates at a resonant frequency, and the resonant frequency depends on the thickness of the film of the material deposited on the crystal. Here, the frequency control signal is controlled by the following control variables, namely - The phase obtained by dividing the inverse negative tangent of the compensated orthogonal output signal by the compensated common-mode output signal, which is driven to zero in particular to operate the crystal at the resonant frequency, and is calculated in particular by the CORDIC processor, - The tangent obtained by dividing the compensated orthogonal output signal by the compensated common-mode output signal, in particular by the magnitude of the compensated common-mode output signal, which is driven to zero in particular to operate the crystal at the resonant frequency, - The imaginary part of the impedance obtained by dividing the compensated quadrature output signal by the sum of the squared compensated common-mode output signal and the squared compensated quadrature output signal, wherein the imaginary part of the impedance is driven to zero in particular in order to operate the crystal at the resonant frequency. It is determined based on (at least) one of the following.

[0029] In further embodiments, the method - Includes the step of generating an amplitude control signal for amplifying the amplitude of the oscillation signal based on the common-mode output signal and / or the quadrature output signal.

[0030] In a further embodiment of this method, the oscillation signal is an in-phase signal, and this method further... - The step includes generating an orthogonal signal that is phase-shifted by 90° with respect to the in-mode signal at the specified output frequency (for example, in the range of 4 MHz to 7 MHz with millihertz resolution), - The in-phase signal is applied as the drive signal to one of the electrodes of the crystal via the measuring amplifier. The orthogonal demodulation described above is - A step of multiplying the in-phase signal and the crystal output signal to provide an intermediate in-phase output signal, - A step of multiplying the orthogonal signal and the crystal output signal to provide an intermediate orthogonal output signal, - The intermediate common-mode output signal is subjected to low-pass filtering (for example, with a "cutoff" frequency in the range of 1 kHz to 10 kHz / 3 dB) to provide the common-mode signal (representing the real part of the crystal output signal), - The process includes the step of low-pass filtering the intermediate quadrature output signal (for example, with a "cutoff" frequency of 3dB in the range of 1kHz to 10kHz) to provide the quadrature output signal (representing the imaginary part of the crystal output signal).

[0031] In further embodiments, the method - The scaling / converted common-mode and quadrature signals include the step of scaling / converting the common-mode and quadrature output signals, depending on the signal amplitude of the common-mode and / or quadrature output signals and optionally depending on the output impedance of the measuring amplifier, so that the scaled / converted common-mode and quadrature signals represent the admittance of the circuit including the measuring amplifier (4) and the crystal having the electrodes.

[0032] In further embodiments, the method - Includes the step of equalizing / compensating for the influence of the frequency response of the measuring amplifier on the common-mode output signal and the quadrature output.

[0033] In a further embodiment of this method, the equalization / compensation is based on calibration / compensation data determined based on measurements of the common-mode output signal and the quadrature output signal when the drive signal is applied to an open circuit, a short circuit, and a reference impedance, respectively, the reference impedance being, in particular, essentially a 50-ohm resistor.

[0034] In further embodiments, the method - The step of determining the parallel admittance based on the common-mode output signal and the quadrature output signal measured at a frequency lower than the resonant frequency of the crystal (e.g., at least 1 MHz, e.g., 4.5 MHz), and further based on the common-mode output signal and the quadrature output signal measured at a frequency higher than the resonant frequency of the crystal (e.g., at least 500 kHz, e.g., 6.5 MHz).

[0035] In a further embodiment, the method further includes a search step during which, based particularly on an analysis of the quadrature output signal and / or the common-mode output signal, a plurality of resonant frequencies of the crystal, in particular the fundamental resonant frequency and a first anharmonic resonant frequency, are determined within a specified frequency range.

[0036] Furthermore, the present invention relates to a control method for controlling the aforementioned vacuum coating system using the aforementioned measurement method, - The step of placing the crystal near the substrate holder, for example, around the substrate holder, on the periphery of the substrate holder, or adjacent to the substrate holder, - The step of applying a control signal to an evaporation source based on a determined thickness of a film of material deposited on the crystal and / or a determined rate of increase of the thickness of the film of material deposited on the crystal, wherein the control signal controls, in particular, a power level applied to the evaporation source.

[0037] In one embodiment, the method further includes the step of applying a further control signal based on a control signal or the determined thickness of the film of the material deposited on the crystal and / or the determined rate of increase of the thickness of the film of the material deposited on the crystal, thereby controlling at least one of the following elements: - Circuit board heater, - Shutter, - (High) vacuum valve, - Process gas inlet, - Auxiliary plasma source or ion source, for example in the form of a glow discharge electrode.

[0038] Furthermore, the present invention relates to a control method for controlling the aforementioned atomic layer deposition system or plasma-enhanced atomic layer deposition system using the aforementioned measurement method, - The process includes the step of placing the crystal close to the substrate holder, for example, around the substrate holder, on the periphery of the substrate holder, or adjacent to the substrate holder. Furthermore, include at least one of the following steps: - A step of controlling the flow of precursor gas introduced into the process chamber by applying a control signal to a precursor gas valve and / or a precursor gas pump based on a determined thickness of the film of material deposited on the crystal and / or the determined rate of increase of the thickness of the film of material deposited on the crystal, - A step of controlling the flow of reactive gas (or a second type of precursor) introduced into a process chamber by applying a control signal to a reactive gas valve and / or a reactive gas pump based on a determined thickness of the film of material deposited on the crystal and / or a determined rate of increase of the thickness of the film of material deposited on the crystal, - A step of controlling the number of ALD cycles, wherein during each ALD cycle, the precursor gas is introduced into the process chamber based on a determined thickness of the film of material deposited on the crystal and / or the determined rate of increase of the thickness of the film of material deposited on the crystal, followed by the introduction of the reactive (or second type of precursor) gas into the process chamber. - A step of controlling the flow of plasma gas to the process chamber based on a determined thickness of the film of material deposited on the crystal and / or the determined rate of increase of the thickness of the film of material deposited on the crystal (in the case of a plasma-enhanced atomic layer deposition system), - The step of controlling the power applied to the plasma source, in particular the voltage applied by a high-voltage DC power supply to maintain the plasma, based on a determined thickness of the film of material deposited on the crystal and / or the determined rate of increase of the thickness of the film of material deposited on the crystal (in the case of a plasma-enhanced atomic layer deposition system).

[0039] Accordingly, the present invention relates to the use of the aforementioned measuring apparatus for controlling a thin film deposition system in the form of a vacuum coating system, an atomic layer deposition system, or a plasma-enhanced atomic layer deposition system, as previously specified, using the aforementioned measuring method, and includes a step of either of the two aforementioned control methods.

[0040] It is particularly noteworthy that more specific embodiments can be obtained by combining the embodiments described above.

[0041] The present invention is further described below by non-limiting specific embodiments with reference to the accompanying drawings illustrating the following.

[0042] In drawings, similar reference numerals refer to the same part. [Brief explanation of the drawing]

[0043] [Figure 1]This is a block diagram of the measuring device according to the present invention (including several optionally selected blocks). [Figure 2] This is a schematic diagram of the vacuum coating system according to the present invention. [Figure 3] a) is a schematic diagram of the atomic layer deposition system according to the present invention, and b) is a schematic diagram of the plasma-enhanced atomic layer deposition system according to the present invention. [Modes for carrying out the invention]

[0044] The thickness of a thin film of material deposited on a substrate can be determined from the weight of the material deposited on a known area. Therefore, the measurement of film thickness can be performed based on the weighing of the amount of material deposited on the substrate. As previously mentioned, piezoelectric crystals such as quartz can be used as a microbalance for this purpose. This allows the weight of the material deposited on the quartz to be used as the series motion resistance R of the Butterworth-van Dyke equivalent circuit of the quartz. m , capacity C m , inductance L m This can be determined based on the parameters of the crystal, such as the quality coefficient Q (this is R m , C m , L m (Related to) When the weight of the material deposited on the quartz changes, the parameters of the quartz change, which in particular leads to a change in the resonant frequency of the quartz. The accuracy with which these parameters of the quartz can be measured determines the accuracy of the film thickness obtained based on these parameters. The object of the present invention is to provide a measuring device for measuring the parameters of a piezoelectric crystal on which a thin film of material is deposited with improved accuracy. A block diagram of the measuring device according to the present invention is shown in Figure 1.

[0045] The central part of the measuring device u in Figure 1 is a crystal oscillator consisting of a piezoelectric crystal 1 and a measuring amplifier 4. Two electrodes 2 and 2' are attached to the opposing surfaces of the crystal 1, with one electrode 2 connected to the measuring amplifier 4 and the other electrode 2' connected to ground (i.e., the reference potential). The output signal of the frequency generator 3 (e.g., a 0° phase / in-phase signal of a quadrature oscillator) is applied as a drive signal to the electrodes 2 attached to the crystal 1 via the measuring amplifier 4. The frequency of the drive signal is usually set to the resonant frequency of the crystal 1, typically in the range of 2 MHz to 7 MHz, for example, a frequency of 6 MHz. In response to this drive signal, the crystal oscillator provides a (crystal) output signal. The desired parameters of the crystal can be determined from this output signal by subsequent signal processing.

[0046] The resonant frequency (or multiple frequencies) can first be determined by sweeping the output frequency of the frequency generator 3 over a specific frequency scanning range (e.g., 2 MHz to 7 MHz) and identifying that frequency (or multiple frequencies), which will result in a resonant peak in the (crystal) output signal.

[0047] To determine the desired parameters of the crystal, the (crystal) output signal from the measurement amplifier 4 is down-converted to baseband (i.e., 0Hz) by a quadrature demodulator. The quadrature demodulator has a common-mode branch where the output signal from the measurement amplifier 4 is multiplied with a 0° phase / common-mode signal from the frequency generator (quadrature oscillator) 3, i.e., the same signal used to drive the crystal oscillator using a common-mode mixer 5 and then filtered by a common-mode low-pass filter 6, typically having a "cutoff" / 3dB frequency in the range of 1kHz to 10kHz. The quadrature demodulator also has a further quadrature branch where the output signal from the measurement amplifier 4 is multiplied with a 90° phase-shift / quadrature signal from the frequency generator (quadrature oscillator) 3 by a quadrature mixer 5' and then filtered by a quadrature low-pass filter 6', also typically having a "cutoff" / 3dB frequency in the range of 1kHz to 10kHz. The baseband signal is a digital signal that can be processed numerically. Various alternatives for realizing a digital baseband signal are shown below.

[0048] The baseband I / common-mode (real part) and Q / quadrature (imaginary part) output signals then pass through a scaling (or transform) unit adapted to scale (or transform) the common-mode and quadrature output signals, optionally depending on the signal amplitude of the common-mode and / or quadrature output signals and optionally depending on the output impedance of the measurement amplifier 4. As a result, the scaled (or transformed) common-mode and quadrature signals together represent the (complex-valued) admittance (Y=G+jB, where conductance G and susceptance B are given by the common-mode (real part) and quadrature (imaginary part) signals at the output of the scaling unit) of the crystal oscillator circuit (comprising the measurement amplifier 4 and the crystal 1 with electrodes 2, 2').

[0049] The baseband I / common-mode (real part) and Q / quadrature (imaginary part) output signals, or the scaled common-mode (real part, G) and scaled quadrature (imaginary part, B) output signals of the scaling unit, then optionally pass through an equalizer (or distortion correction or compensation) unit adapted to equalize / compensate for the effect of the measurement amplifier's frequency response on the common-mode and quadrature output signals. Equalization is based on calibration data determined based on measurements of the common-mode and quadrature output signals when the oscillator circuit is operating in open-circuit mode, short-circuit mode, and with a reference impedance, where the reference impedance is, for example, a 50-ohm resistor.

[0050] As mentioned above, a high value of parallel capacitance C0 (or more generally, parallel admittance Y0) due to electrode capacitance, wiring capacitance, and input capacitance of the measurement circuit limits the usage time of the crystal. Since parallel capacitance C0 does not depend on the material deposited on the crystal, C0 can be determined before using the crystal to measure the film thickness, and the determined value of C0 can be compensated when using the crystal to measure the film thickness. This is achieved by a compensation unit 8 adapted to numerically compensate for / eliminate the effect of parallel admittance Y0 (more specifically, parallel capacitance C0) by subtracting the conductance value G0 of parallel admittance Y0 from a signal based on the common-mode output signal and quadrature output signal to provide a compensated common-mode output signal, and by subtracting the susceptance value B0 of parallel admittance Y0 from a further signal based on the common-mode output signal and quadrature output signal to provide a compensated quadrature output signal. This compensation also depends on the frequency of the oscillation signal generated by the frequency generator (quadrature oscillator) 3. The parallel admittance Y0 (=G0+jB0) is determined based on the common-mode and quadrature output signals measured at frequencies lower than the resonant frequency of crystal 1, and further based on the common-mode and quadrature output signals measured at frequencies higher than the resonant frequency of crystal 1. The parallel admittance Y0 is usually determined before using the measuring device u to measure the parameters of the piezoelectric crystal on which the thin film of the material is deposited.

[0051] Next, the desired parameters of the crystal 1 are determined by the calculation unit 7 (especially when a film of material is deposited on the crystal 1) based on the common-mode output signal and the quadrature output signal, in particular after (optional) compensation of the parallel admittance Y0, and especially after (optional) scaling and / or (optional) equalization by the scaling unit 11 and the equalizer 12, respectively. The calculation unit 7 can also be adapted to determine the rate of increase of the thickness of the film of material deposited on the crystal 1 based on the thickness of the film of material deposited on the crystal 1 and / or based on the common-mode output signal and the quadrature output signal, or based on the parameters of the crystal 1.

[0052] A phase-locked loop (PLL) is used to control the frequency of a frequency generator whose output signal drives the crystal oscillator at the resonant frequency (thickness of the film of material deposited on the crystal 1) in order to determine the parameters of the crystal 1. Many alternative means exist for generating the control signal used to adjust the frequency output signal generated by the frequency control unit 9, which is supplied to the frequency generator (quadrature oscillator) 3 and the parallel admittance / capacitance compensation unit 8. The control signal calculated by the control signal calculation / calculation unit 13 may be a phase signal obtained by dividing the inverse tangent of the compensated quadrature output signal by the compensated common-mode output signal, thereby driving the phase to zero by the frequency control unit 9 to operate the crystal 1 at the desired resonant frequency. The phase can be calculated, for example, using a CORDIC processor. Alternatively, the control signal calculated by the control signal calculation / calculation unit 13 may be the tangent obtained by dividing the compensated quadrature output signal by the compensated common-mode output signal, in particular by the magnitude of the compensated common-mode output signal. This will drive the tangent to zero by the frequency control unit 9 to operate the crystal 1 at the desired resonant frequency. As a more favorable alternative, the control signal calculated by the control signal calculation / calculation unit 13 may be the imaginary part of the impedance obtained by dividing the compensated quadrature output signal by the sum of the squared compensated common-mode output signal and the squared compensated quadrature output signal, thereby driving the imaginary part of the impedance to zero by the frequency control unit 9 in order to operate the crystal 1 at the desired resonant frequency.

[0053] Optionally, the amplitude control unit 10 generates an amplitude control signal that is applied to the frequency generator 3 to amplify the amplitude of the oscillation signal based on the common-mode output signal and / or quadrature output signal. For example, when the crystal 1 is new, i.e., when no material has been deposited on it, the amplitude of the oscillation signal decreases in response to a measured common-mode output signal having a high level, for example (because the resonance peak is large when no material is present on the crystal 1). Conversely, when the crystal 1 has been used for a long period of time, i.e., when a thick film of material has been deposited on the crystal 1, the amplitude of the oscillation signal increases in response to a measured low-level common-mode output signal, for example (because the resonance peak is reduced by the layer of material present on the crystal 1).

[0054] Many different technical implementations of the proposed measuring device are possible. For example, the use of a direct digital synthesizer (DDS) or numerically controlled oscillator (NCO) is proposed to allow adjustment of the frequency output signal of the frequency generator 3 within the range of 2 MHz to 7 MHz, with a resolution of, for example, millihertz (mHz). This is also beneficial for achieving a precise 90° phase difference between the common-mode output signal and the quadrature output signal of the quadrature oscillator 3. The measuring amplifier 4 is implemented as an analog circuit. The mixers 5, 5' and low-pass filters 6, 6' can be implemented as analog or digital circuits. If the mixers 5, 5' and low-pass filters 6, 6' are implemented as analog circuits, the down-converted baseband common-mode and quadrature signals are sampled at a low speed, for example, less than 30 kHz (e.g., 10 kHz), and digitized (converted from analog to digital) with, for example, 16-bit resolution. The other blocks 7-12 are preferably implemented digitally, particularly using programmable logic or a programmable processor (such as a microcontroller). Mixers 5, 5' and the low-pass filter can be implemented as digital circuits, for example, using digital multipliers and digital (FIR) filters, but they can also be implemented in software using a programmable processor (such as a microcontroller). All digital components, e.g., blocks 3 and 5-13, especially high-speed components such as quadrature oscillator 3, multipliers 5, 5' and filters 6, 6' (e.g., when processed at sampling rates above 1 MHz), can all be implemented within a single field-programmable gate array (FPGA). Advanced FPGAs may also include a microcontroller (along with programmable logic) that can perform low-speed functions (e.g., when processed at sampling rates below 100 kHz), such as blocks 7-13 in software / firmware. However, the microcontroller performing these functions can also be separated from the FPGA.When quadrature demodulation of the crystal output signal is performed digitally, the desired parameters of crystal 1 can be determined with great accuracy, thereby allowing the crystal output signal to be sampled at a high speed, for example, over 1 MHz, and converted from analog to digital with, for example, 16-bit precision. At the output of low-pass filters 6, 6', the sampling rate is reduced / decimated to, for example, 10 kHz. This significantly increases the signal-to-noise ratio (SNR) of the digital common-mode and quadrature baseband signals (e.g., 20-30 dB). Complete digital processing, i.e., digitizing the crystal output signal instead of the baseband common-mode and quadrature signals, is preferable in terms of achieving a higher achievable SNR and the resulting improved accuracy in determining the desired parameters of crystal 1.

[0055] A further aspect of the present invention provides an improved thin-film deposition system that can more accurately deposit a thin film of material onto a substrate, particularly when the usage time of the quartz increases. In other words, the frequency of quartz replacement is reduced.

[0056] A schematic diagram of such a thin film deposition system in the form of a vacuum coating system t for depositing a thin film of material on a substrate d is shown in Figure 2. The system t comprises a process chamber a, within which a substrate holder b adapted to receive the substrate d is located opposite the evaporation source f. By applying a certain level of power (and / or heat) to the evaporation source f, the evaporation source f generates a vapor plume e containing the material to be deposited on the substrate d. The process chamber a is evacuated by a (high) vacuum pump J via a (high) vacuum valve i to create a (high) vacuum inside the process chamber a before depositing a thin film of material on the substrate d. The quartz g of the measuring device u described above is located very close to the substrate holder b, for example, around the substrate holder b, or adjacent to the substrate holder b, so that the same or similar amount of material as the amount on the substrate d is deposited on the unit area of ​​the quartz g. If the quartz crystal g is exposed less (or more) to a vapor plume e containing the material to be deposited on the substrate d, and therefore less (or more) material is deposited on a unit area of ​​the crystal g as well as on a unit area of ​​the substrate d, this is calculated by the measuring unit u by applying an appropriate compensation factor to the determined thickness of the material film deposited on the quartz crystal g when calculating the thickness of the material film deposited on the substrate d. The control signal applied to the evaporation source f is based on the determined thickness of the material film deposited on the quartz crystal g and / or the determined rate of increase of the thickness of the material film deposited on the quartz crystal g (or based on the determined parameters of the quartz crystal g). The control signal specifically controls the power level applied to the evaporation source g. The system t may further include a process gas inlet k and a shutter h. The flow of process gas through the inlet k can be controlled based on the determined thickness of the material film deposited on the quartz crystal g and / or the determined rate of increase of the thickness of the material film deposited on the quartz crystal g (or based on the determined parameters of the quartz crystal g). Similarly, the opening and closing time of the shutter h can also be controlled based on a determined thickness of the material film deposited on the quartz g and / or a determined rate of increase of the thickness of the material film deposited on the quartz g (or based on determined parameters of the quartz g).

[0057] A schematic diagram of such a thin film deposition system in the form of an atomic layer deposition (ALD) system t' for depositing a thin film of material on a substrate d is shown in Figure 3a). System t' comprises an internal process chamber a with a substrate holder b adapted to receive the substrate d, and is arranged so that a flow of precursor gas and / or reactive gas flows over the substrate d, introduced into and subsequently pumped out of the process chamber a. The precursor gas and / or reactive gas is introduced into the process chamber a via one or more gas inlets n equipped with associated gas valves and associated gas pumps adapted to control the flow of precursor gas and / or reactive gas introduced into and subsequently pumped out of the process chamber a. The precursor gas and / or reactive gas introduced into the process chamber a chemically reacts with the substrate d so that a thin film of material is deposited on the substrate d. The quartz crystal g of the measuring device u described above is positioned very close to the substrate holder b, for example, around the substrate holder b, or adjacent to the substrate holder b, so that the same or similar amount of material is deposited per unit area of ​​the quartz crystal g as per the unit area of ​​the substrate d. If the quartz crystal g is exposed less (or more) to the precursor gas and / or reactive gas, and therefore less (or more) the material deposited per unit area of ​​the quartz crystal g is deposited per unit area than that of the substrate d, this is calculated by the measuring unit u by applying an appropriate compensation factor to the determined thickness of the material film deposited on the quartz crystal g when calculating the thickness of the material film deposited on the substrate d. i) the flow of the precursor gas, ii) the flow of the reactive gas, iii) the temperature of the precursor gas and / or substrate d, and iv) at least one of the number of ALD cycles (wherein during each ALD cycle, the precursor gas is introduced into process chamber a, then pumped out again from process chamber a, followed by the reactive gas being introduced into process chamber a, and then pumped out again from process chamber a) are controlled based on a determined thickness of the film of material deposited on the quartz g and / or a determined rate of increase of the thickness of the film of material deposited on the quartz g (or based on determined parameters of the quartz g).In the ALD system t' described above, the substrate d remains in the same process chamber a while being exposed to different precursor gases and / or reactive gases. Alternatively, the ALD system may comprise multiple (e.g., two) process chambers, between which the substrate is transported, and in which it is exposed to a specific one of the precursor gases and / or reactive gases.

[0058] A schematic diagram of such a thin film deposition system in the form of a plasma-enhanced atomic layer deposition (PEALD) system t'' for depositing a thin film of material on a substrate d is shown in Figure 3b). System t'' comprises a process chamber a inside, and a substrate holder b adapted to receive the substrate d is introduced into the process chamber a, and then a flow of precursor gas and / or reactive gas, pumped out of the process chamber a, is arranged to flow over the substrate d. The precursor gas and / or reactive gas is introduced into the process chamber a via one or more gas inlets n equipped with associated gas valves and associated gas pumps adapted to control the flow of precursor gas and / or reactive gas introduced into and then pumped out of the process chamber a. Furthermore, system t'' comprises a plasma source into which plasma gas p is introduced into the process chamber a and distributed toward the substrate d via electrodes equipped with, for example, showerheads s. By applying power to ignite the plasma gas p, plasma a is formed near the substrate d, for example, by a high-voltage DC or RF power supply r. The quartz crystal g of the measuring device u described above is positioned very close to the substrate holder b, for example, around the substrate holder b, or adjacent to the substrate holder b, so that the same or similar amount of material is deposited per unit area of ​​the quartz crystal g as per the unit area of ​​the substrate d. If the quartz crystal g is exposed less (or more) to the precursor gas and / or reactive gas, and therefore less (or more) the material deposited per unit area of ​​the quartz crystal g is deposited per unit area than that of the substrate d, this is calculated by the measuring unit by applying an appropriate compensation factor to the determined thickness of the material film deposited on the quartz crystal g when calculating the thickness of the material film deposited on the substrate d.i) The flow of the precursor gas, ii) the flow of the reactive gas, iii) the number of ALD cycles (wherein, during each ALD cycle, the precursor gas is introduced into the process chamber a, then pumped out of the process chamber a again, subsequently the reactive gas is introduced into the process chamber a, and then pumped out of the process chamber a again), iv) the flow of the plasma gas into the process chamber a, and v) the power applied to the plasma, for example, at least one of the voltages applied by the high-voltage DC power supply r to maintain the plasma is controlled based on the determined thickness of the film of the material deposited on the quartz g and / or the determined rate of increase in the thickness of the film of the material deposited on the quartz g (or based on the determined parameters of the quartz g).

Explanation of Signs

[0059] 1 Piezoelectric / Quartz 2, 2’ Electrodes (made of quartz) 3 Frequency generator, quadrature oscillator 4 Measurement amplifier 5 In-phase signal mixer 5’ Quadrature signal mixer 6 In-phase low-pass filter 6’ Quadrature low-pass filter 7 Calculation unit (for thickness and crystal parameters) 8 Parallel admittance / capacitance compensation unit 9 Frequency control unit 10 Amplitude control unit 11 Scaling / conversion unit (→ admittance) 12 Distortion correction unit (equalizer) 13 Control signal calculation unit a Process / vacuum chamber b Substrate holder c Substrate heater d Substrate e Vapor plume f Evaporation source g Piezoelectric / Quartz h Shutter i (High) vacuum valve J (High) vacuum pump k Process gas inlet L Power supply m Auxiliary plasma source or ion source, glow discharge electrode n Precursor gas inlet o Pump p Plasma gas inlet q Plasma r High voltage DC power supply s Electrode with shower head t Vacuum coating system, thin film deposition system t’ Atomic layer deposition system t’’ Plasma enhanced atomic layer deposition system u Measuring device GND Grounding, reference potential B Susceptance B0 Parallel susceptance C0 Parallel capacitance C m Crystalline series capacitance [[ID=3--8]]G Conductance G0 Parallel conductance L m Crystalline series inductance Q Quality factor of crystal R m Crystalline series resistance Y Admittance Y0 Parallel admittance

Claims

1. A measuring device (u) for measuring one or more parameters of a piezoelectric crystal (1) on which a thin film of material is deposited, - The piezoelectric crystal (1) having two spaced electrodes (2, 2'), wherein the thin film of the material is deposited on the piezoelectric crystal (1), - A frequency generator (3) adapted to generate an oscillation signal at a specified output frequency, - A measuring amplifier (4) adapted to apply the oscillation signal as a drive signal to one of the electrodes (2, 2') of the piezoelectric crystal (1) and generate a crystal output signal, - A quadrature demodulator adapted to downconvert the crystal output signal and provide a common-mode output signal and a quadrature output signal, - A calculation unit (7) for determining one or more parameters of the piezoelectric crystal (1) based on the in-phase output signal and the orthogonal output signal, Parallel admittance (Y ０ A compensation unit (8) adapted to numerically compensate for the effects of ) is included, The parameters of the piezoelectric crystal (1) are: - Crystal series resistance (Rm), - Crystal series capacitance (Cm), - Crystal series inductance (Lm), - Parallel admittance (Y ０ ), - This is the crystal quality factor (Q), Measuring device (u).

2. The apparatus (u) according to claim 1, wherein the calculation unit (7) is further adapted to determine, based on the in-phase output signal and the quadrature output signal, the thickness or mass of the thin film of the material deposited on the piezoelectric crystal (1), and / or the rate of increase of the thickness or mass of the thin film of the material deposited on the piezoelectric crystal (1).

3. The compensation unit (8) calculates the parallel admittance (Y) from the signal based on the common-mode output signal and the orthogonal output signal. ０ The conductance value (G) ０ By subtracting the parallel admittance (Y) from ０ ) susceptance value (B ０ By subtracting ) and providing a compensated quadrature output signal, the parallel admittance (Y ０ The apparatus (u) according to claim 1 or 2, which is adapted to numerically compensate for the aforementioned effects of ).

4. - Further includes a frequency control unit (9) adapted to generate a frequency control signal as an input to the frequency generator (3), The frequency control signal is adapted so that the piezoelectric crystal (1) operates at a resonant frequency, and the resonant frequency depends on the thickness or mass of the thin film of the material deposited on the piezoelectric crystal (1). The frequency control signal is controlled by the following control variables, namely - The phase obtained by dividing the inverse negative tangent of the compensated quadrature output signal by the compensated common-mode output signal, - The tangent obtained by dividing the compensated quadrature output signal by the compensated common-mode output signal, - The imaginary part of the impedance obtained by dividing the compensated quadrature output signal by the sum of the squared compensated common-mode output signal and the squared compensated quadrature output signal. The apparatus (u) according to claim 2, determined based on one of the following.

5. - The apparatus (u) according to any one of claims 1 to 4, further comprising an amplitude control unit (10) adapted to generate an amplitude control signal applied to the frequency generator (3) to amplify the amplitude of the oscillation signal based on the common-mode output signal and / or the quadrature output signal.

6. - The frequency generator (3) is a quadrature oscillator (3) equipped with a frequency control input, and is adapted to receive the frequency control signal and to provide an in-phase signal and a 90° phase-shifted quadrature signal having the same output frequency according to the frequency control signal as the oscillation signal. - The measuring amplifier (4) applies the in-phase signal as the drive signal to one of the electrodes (2, 2') of the piezoelectric crystal (1), The aforementioned quadrature demodulator is - A common-mode signal mixer (5) is configured to multiply the common-mode signal and the crystal output signal to provide an intermediate common-mode output signal, - A quadrature signal mixer (5') adapted to multiply the orthogonal signal with the crystal output signal to provide an intermediate orthogonal output signal, - A common-mode signal filter (6) is configured to low-pass filter the intermediate common-mode output signal and provide the common-mode output signal, - The apparatus (u) according to claim 4, comprising: an orthogonal signal filter (6') adapted to low-pass filter the intermediate orthogonal output signal and provide the orthogonal output signal.

7. - Apparatus (u) according to any one of claims 1 to 6, further comprising a scaling unit (11) adapted to scale the in-phase and quadrature output signals depending on the signal amplitude of the in-phase and / or quadrature output signals, wherein the scaled in-phase and quadrature signals represent the admittance of a circuit comprising the measuring amplifier (4) and the piezoelectric crystal (1) having electrodes (2, 2').

8. - The apparatus (u) according to any one of claims 1 to 7, further comprising an equalizer (12) adapted to equalize the effect of the frequency response of the measuring amplifier (4) on the common-mode output signal and the quadrature output signal.

9. The apparatus (u) according to claim 8, wherein the equalization is based on calibration data determined based on measurements of the common-mode output signal and the quadrature output signal when the drive signal is applied to an open circuit, a short circuit, and a reference impedance, respectively.

10. The aforementioned parallel admittance (Y ０ The apparatus (u) according to claim 4, wherein the frequency is determined based on the common-mode output signal and the quadrature output signal measured at a frequency lower than the resonant frequency of the piezoelectric crystal (1), and further based on the common-mode output signal and the quadrature output signal measured at a frequency higher than the resonant frequency of the piezoelectric crystal (1).

11. A thin film deposition system in the form of a vacuum coating system (t) for depositing a thin film of material on a substrate (d), wherein the vacuum coating system (t) comprises a measuring device (u) according to any one of claims 2, 4, 6, and 10, and further comprises a process chamber (a), a substrate holder (b) adapted to receive the substrate (d), an evaporation source (f), and a vacuum pump (J), wherein the piezoelectric crystal (g) of the measuring device (u) is positioned in close proximity to the substrate holder (b), and a control signal applied to the evaporation source (f) is based on the determined thickness of the thin film of material deposited on the piezoelectric crystal (g) and / or the determined rate of increase of the thickness of the thin film of material deposited on the piezoelectric crystal (g).

12. The following elements, - Circuit board heater (c), - Shutter (h), - Vacuum valve (i), - Process gas inlet (k), - Auxiliary plasma source or ion source (m) It further includes at least one of the following: A further control signal is applied to control at least one of the elements, based on the control signal or the determined thickness of the thin film of the material deposited on the piezoelectric crystal (g) and / or the determined rate of increase of the thickness of the thin film of the material deposited on the piezoelectric crystal (g), according to claim 11.

13. A thin film deposition system in the form of an atomic layer deposition (ALD) system (t') or a plasma-enhanced atomic layer deposition (PEALD) system (t'') for depositing a thin film of material on a substrate (d), wherein the atomic layer deposition system (t') or the plasma-enhanced atomic layer deposition system (t'') includes a measuring device (u) according to any one of claims 2, 4, 6, and 10, further comprising: a process chamber (a); a substrate holder (b) adapted to receive the substrate (d); a precursor gas inlet (n) equipped with an associated precursor gas valve and associated precursor gas pump adapted to control the flow of a precursor gas introduced into the process chamber (a); and / or a reactive gas inlet equipped with an associated reactive gas valve and associated reactive gas pump adapted to control the flow of a reactive gas introduced into the process chamber (a); and in the case of a plasma-enhanced atomic layer deposition system, a plasma source, wherein the piezoelectric crystal (g) of the measuring device (u) is positioned in close proximity to the substrate holder (b). - The flow of the precursor gas, - The flow of the reactive gas, - The number of ALD cycles, during each ALD cycle, the precursor gas is introduced into the process chamber (a), and subsequently the reactive gas is introduced into the process chamber (a), - Process time, - Temperature of the precursor gas and / or the reactive gas, - Temperature of the substrate A thin film deposition system, wherein at least one of the following is based on the determined thickness of the thin film of the material deposited on the piezoelectric crystal (g), and / or the determined rate of increase of the thickness of the thin film of the material deposited on the piezoelectric crystal (g).

14. A measurement method for measuring one or more parameters of a piezoelectric crystal (1) on which a thin film of material is deposited, - A step of depositing the thin film of the material on the piezoelectric crystal (1) having two spaced electrodes (2, 2'), - A step of generating an oscillation signal at a specified output frequency, - The oscillation signal is applied as a drive signal to one of the electrodes of the piezoelectric crystal (1) via the measuring amplifier (4) to generate a crystal output signal. - The steps of quadrature demodulating the crystal output signal to provide down-converted common-mode output signal and quadrature output signal, - A step of determining one or more parameters of the piezoelectric crystal (1) based on the in-mode output signal and the orthogonal output signal, - Numerically compensating for the influence of the parallel admittance (Y ０ ), and The parameters of the piezoelectric crystal (1) are: - Crystal series resistance (Rm), - Crystal series capacitance (Cm), - Crystal series inductance (Lm), - The parallel admittance (Y ０ ), - The measurement method for the crystal quality factor (Q).

15. The measurement method according to claim 14, further comprising the step of determining the thickness or mass of the thin film of the material deposited on the piezoelectric crystal (1) and / or the rate of increase of the thickness or mass of the thin film of the material deposited on the piezoelectric crystal (1) based on the in-phase output signal and the orthogonal output signal.

16. The aforementioned parallel admittance (Y ０ The step of numerically compensating for the aforementioned influence of ) is performed by taking the parallel admittance (Y) from the signal based on the common-mode output signal and the quadrature output signal. ０ The conductance value (G) ０ By subtracting the parallel admittance (Y) from ０ ) susceptance value (B ０ The measurement method according to claim 14 or 15, which is performed by subtracting ) to provide a compensated quadrature output signal.

17. - Further includes the step of generating a frequency control signal for generating the specified output frequency, The frequency control signal is adapted so that the piezoelectric crystal (1) operates at a resonant frequency, the resonant frequency depending on the thickness of the thin film of the material deposited on the piezoelectric crystal (1), and the frequency control signal is controlled by the following control variables: - The phase obtained by dividing the inverse negative tangent of the compensated quadrature output signal by the compensated common-mode output signal, - The tangent obtained by dividing the compensated quadrature output signal by the compensated common-mode output signal, - The imaginary part of the impedance obtained by dividing the compensated quadrature output signal by the sum of the squared compensated common-mode output signal and the squared compensated quadrature output signal. The measurement method according to claim 15, determined based on one of the following.

18. - The measurement method according to any one of claims 14 to 17, further comprising the step of generating an amplitude control signal for amplifying the amplitude of the oscillation signal based on the common-mode output signal and / or the quadrature output signal.

19. The oscillation signal is an in-phase signal, and the method is - Further includes the step of generating an orthogonal signal that is phase-shifted by 90° with respect to the in-mode signal at the specified output frequency, - The in-phase signal is applied as the drive signal to one of the electrodes (2, 2') of the piezoelectric crystal (1) via the measuring amplifier (4). The orthogonal demodulation described above is - A step of multiplying the in-phase signal and the crystal output signal to provide an intermediate in-phase output signal, - A step of multiplying the orthogonal signal and the crystal output signal to provide an intermediate orthogonal output signal, - The intermediate common-mode output signal is subjected to low-pass filtering to provide the common-mode signal, - A measurement method according to any one of claims 14 to 18, comprising the step of low-pass filtering the intermediate quadrature output signal to provide the quadrature output signal.

20. - A measurement method according to any one of claims 14 to 19, further comprising the step of scaling the in-phase and / or quadrature output signals depending on the signal amplitude of the in-phase and / or quadrature output signals, wherein the scaled in-phase and quadrature signals represent the admittance of a circuit comprising the measuring amplifier (4) and the piezoelectric crystal (1) having electrodes (2, 2').

21. - The measurement method according to any one of claims 14 to 20, further comprising the step of equalizing the influence of the frequency response of the measuring amplifier (4) on the common-mode output signal and the quadrature output signal.

22. The measurement method according to claim 21, wherein the equalization is based on calibration data determined based on measurements of the common-mode output signal and the quadrature output signal when the drive signal is applied to an open circuit, a short circuit, and a reference impedance, respectively.

23. - Based on the common-mode output signal and the quadrature output signal measured at a frequency lower than the resonant frequency of the piezoelectric crystal (1), and further based on the common-mode output signal and the quadrature output signal measured at a frequency higher than the resonant frequency of the piezoelectric crystal (1), the parallel admittance (Y ０ The measurement method according to claim 17, further comprising the step of determining ).

24. The measurement method according to any one of claims 14 to 23, further comprising a search procedure during which a plurality of resonant frequencies of the piezoelectric crystal are determined within a specified frequency range.

25. A control method for controlling the vacuum coating system (t) according to claim 11 or 12 using the measurement method according to claim 15 or 17, - The step of arranging the piezoelectric crystal (g) in close proximity to the substrate holder (b), A control method comprising the steps of: applying a control signal to an evaporation source (f) based on the determined thickness of the thin film of the material deposited on the piezoelectric crystal (g), and / or based on the determined rate of increase of the thickness of the thin film of the material deposited on the piezoelectric crystal (g).

26. The step further includes applying a further control signal based on the control signal, or based on the determined thickness of the thin film of the material deposited on the piezoelectric crystal (g), and / or based on the determined rate of increase of the thickness of the thin film of the material deposited on the piezoelectric crystal (g), the following elements, namely - Circuit board heater (c), - Shutter (h), - Vacuum valve (i), - Process gas inlet (k), - Auxiliary plasma source or ion source (m) The control method according to claim 25, which controls at least one of the following.

27. A control method for controlling an atomic layer deposition system (t') or a plasma-enhanced atomic layer deposition system (t'') according to claim 13, using the measurement method according to claim 15 or 17, - The step includes arranging the piezoelectric crystal (g) in close proximity to the substrate holder (b), moreover, - A step of controlling the flow of precursor gas introduced into the process chamber by applying a control signal to the precursor gas valve and / or the precursor gas pump based on the determined thickness of the thin film of the material deposited on the piezoelectric crystal (g) and / or based on the determined rate of increase of the thickness of the thin film of the material deposited on the piezoelectric crystal (g). - A step of controlling the flow of reactive gas introduced into the process chamber by applying a control signal to the reactive gas valve and / or the reactive gas pump based on the determined thickness of the thin film of the material deposited on the piezoelectric crystal (g) and / or based on the determined rate of increase of the thickness of the thin film of the material deposited on the piezoelectric crystal (g). A control method comprising at least one of the steps of controlling the number of ALD cycles, wherein during each ALD cycle, the precursor gas is introduced into the process chamber, and subsequently, the reactive gas is introduced into the process chamber based on the determined thickness of the thin film of the material deposited on the piezoelectric crystal (g) and / or the determined rate of increase of the thickness of the thin film of the material deposited on the piezoelectric crystal (g).

28. The apparatus (1) according to claim 1, wherein the piezoelectric crystal (1) has a fundamental resonant frequency between 1 MHz and 100 MHz when no thin film is deposited thereon.

29. The apparatus (1) according to claim 1, wherein the piezoelectric crystal (1) is an AT-cut quartz crystal.

30. The apparatus (1) according to claim 1, wherein the in-mode output signal and quadrature output signal are digital signals.

31. The apparatus (1) according to claim 1, wherein the calculation unit is adapted to determine one or more parameters of the piezoelectric crystal (1) at a plurality of different frequencies.

32. The measurement method according to any one of claims 14 to 16 and 18 to 23, wherein the common-mode output signal and the quadrature output signal are digital signals.

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