EP2585800A1

EP2585800A1 - Self-cleaning film thickness measuring apparatus, and method of cleaning film thickness measuring apparatus

Info

Publication number: EP2585800A1
Application number: EP11798990.5A
Authority: EP
Inventors: Scott F. Grimshaw
Original assignee: Tangidyne Corp
Current assignee: Tangidyne Corp
Priority date: 2010-06-24
Filing date: 2011-06-24
Publication date: 2013-05-01
Also published as: WO2011163584A1

Abstract

There is provided a method of measuring film thickness and/or deposition rate, comprising vibrating a piezoelectric element, exposing the piezoelectric element to emitting deposit material, and applying heat to remove deposit material from the piezoelectric element. Also, a device comprising two piezoelectric elements and a heater which heats a piezoelectric element in a cleaning position. Also, a device comprising two piezoelectric elements movable between cleaning and deposition positions, and a heater which heats a piezoelectric element in a cleaning position. Also, a device comprising two piezoelectric elements, a movable shield element and a heater.

Description

SELF-CLEANING FILM THICKNESS MEASURING APPARATUS, AND METHOD

OF CLEANING FILM THICKNESS MEASURING APPARATUS

Cross-reference to Related Applications

This application claims the benefit of U.S. Provisional Patent Application No;

61/358,160, filed June 24, 2010, the entirety of which is incorporated herein by reference as if set forth in its entirety.

Fieid of the Inventive Subject Matter

The present inventive subject matter relates to an apparatus for measuring the thickness of a film, and/or for monitoring the rate of increase of the thickness of a film, and to a method for carrying out such measuring and/or monitoring. In one aspect, the present inventive subject matter relates to a self-cleaning apparatus for measuring the thickness of a film, and/or for monitoring the rate of increase of the thickness of a film. In another aspect, the present inventive subject matter relates to a method of cleaning apparatus for measuring the thickness of a film and/or for monitoring the rate of increase of the thickness of a film.

Background of the Inventive Subject Matter

Since the early 1960's, quartz crystals have been used to monitor thin film coating processes used in the fabrication of optical devices such as lenses, filters, reflectors and beam splitters. For example, in some cases in which layered devices are being fabricated by laying down one or more layers (and in which the thickness(es) of such layers need to be extremely precise), one or more of such quartz crystal test devices have been included in the same chamber in which the layered devices are being fabricated, so that the thickness of each layer laid down on the quartz crystal test device is substantially the same (and increases at substantially the same rate) as the thickness(es) of such layer being deposited on the layered devices.

Quartz crystals have been used because by applying alternating voltage, they vibrate or oscillate in phase with the voltage (i.e., quartz is a piezoelectric material). At a specific frequency of oscillation, quartz will vibrate with minimal resistance, much like a tuning fork rings when struck. As additional layers are coated on the crystal surface, and/or as a layer becomes thicker, the resonance frequency decreases linearly.

The thickness of a layer (or layers) deposited on a quartz test crystal (and/or the rate at which the thickness of such layer is increasing) can be estimated with excellent accuracy by monitoring changes in the resonant frequency of vibration of the quartz test crystal.

In a quartz crystal thickness monitor, the quartz crystal is coupled to an electrical circuit that causes the crystal to vibrate at its natural (or resonant) frequency, which for most commercial instruments is between 5 and 6 MHz. A microprocessor-based control unit monitors and displays this frequency, or derived quantities, continuously. As material coats the crystal during deposition, the resonant frequency decreases in a predictable fashion, proportional to the rate material arrives at the crystal, and the material density. The frequency change is calculated several times per second, converted in the microprocessor to Angstroms per second and displayed as deposition rate. The accumulated coating is displayed as total thickness, and thus the apparatus can provide coating rate and thickness data in real time. With the use of the expression "resonant frequency", it should be understood that measured values are within normal tolerances.

The sensitivities of these sensors are remarkable. A uniform coating of as little as 10 Angstroms of aluminum will typically cause a frequency change of 20 Hz, easily measured by today's electronics. As the density of the film increases, the frequency shift per Angstrom increases. Brief Summary of the Inventive Subject Matter

As layers are deposited on test crystals, eventually the test crystals cease to provide accurate results. High stress coatings can deform the test crystal to the point that it ceases to oscillate, without warning. For example, if a low stress metal such as aluminum is deposited, layers as thick as 1,000,000 Angstroms have been measured, while at the other extreme, highly stressful dielectric films can cause crystal malfunction at thicknesses as low as 2,000 Angstroms or less, hi addition, splatters of material from the coating source can lead to similar failure.

Research in fields such as nanotechnology, biosensors, thin film displays, and highspeed optical communications have increased the complexity of thin film structures. While an antireflection coating consisting of a single layer of magnesium fluoride may have been sufficient 20 years ago, current designs may call for, e.g., a 24-layer stack of alternating refractive index films. With high-speed optical communications, this stack can be increased ten-fold, leading to filters comprised of up to 256 layers. Similarly, very thick films are typically used in laser power or infrared optics.

In many instances, especially in the case of stacks with a large number of layers, venting the chamber to replace the test crystal (or crystals) can result in undesirable effects, e.g., due to the delay and/or the effect of atmospheric gases on film chemistry.

In other instances, the throughput of layered devices being fabricated is so rapid that replacing the test crystals results in undesirable delay, e.g., in comparison to the fabrication time of the devices.

In accordance with the present inventive subject matter, it has been recognized that in many situations, it would be desirable to be able to remove deposited layers from a test crystal, especially if such removal can be effected quickly and/or without disrupting the deposition process. In a first aspect of the present inventive subject matter, there is provided a method of measuring the thickness of a film made of a deposit material and/or the rate of increase of the thickness of a film made of a deposit material, comprising:

applying a voltage across at least a first piezoelectric element, thereby causing the first piezoelectric element to undergo vibration;

depositing deposit material on the first piezoelectric element (e.g., by exposing the first piezoelectric element to a source of a deposit material that is emitting deposit material, so that some deposit material is applied to the first piezoelectric element);

measuring a rate of vibration of the first piezoelectric element; and

applying heat to the first piezoelectric element to remove from the first piezoelectric element at least a portion of the deposit material applied to the first piezoelectric element.

In some embodiments according to the first aspect of the present inventive subject matter, the method further comprises:

again applying a voltage across at least the first piezoelectric element, thereby causing the first piezoelectric element to again undergo vibration;

again exposing the first piezoelectric element to a source of a deposit material that is emitting deposit material, so that some deposit material is applied to the first piezoelectric element; and

measuring a rate of vibration of the first piezoelectric element.

In some of such embodiments, (1) the source of deposit material to which the piezoelectric element is exposed and the source of deposit material to which the piezoelectric element is again exposed are the same source of deposit material, and/or (2) the method further comprises again applying heat to the first piezoelectric element to remove from the first piezoelectric element at least a portion of the deposit material applied to the first piezoelectric element.

hi some embodiments according to the first aspect of the present inventive subject matter, the method further comprises:

moving the first piezoelectric element to a cleaning position after exposing the first piezoelectric element to the source of deposit material, said applying heat to the first piezoelectric element to remove from the first piezoelectric element at least a portion of the deposit material applied to the first piezoelectric element being carried out while the first piezoelectric element is in the cleaning position,

moving a second piezoelectric element to a deposition position after exposing the first piezoelectric element to the source of deposit material, the second piezoelectric element being exposed to the source of deposit material that is emitting deposit material while the second piezoelectric element is in the deposition position, so that some deposit material is applied to the first piezoelectric element, and

measuring a rate of vibration of the second piezoelectric element.

In some of such embodiments, the method further comprises:

moving the first piezoelectric element to a deposition position after exposing the second piezoelectric element to the source of deposit material, the first piezoelectric element being exposed to the source of deposit material that is emitting deposit material while the second piezoelectric element is in the deposition position, so that some deposit material is applied to the first piezoelectric element,

moving the second piezoelectric element to a cleaning position after exposing the second piezoelectric element to the source of deposit material;

applying heat to the second piezoelectric element while the first piezoelectric element is in the cleaning position, to remove from the second piezoelectric element at least a portion of the deposit material applied to the second piezoelectric element;

again applying a voltage across at least the first piezoelectric element, thereby causing the first piezoelectric element to again undergo vibration; and

measuring a rate of vibration of the first piezoelectric element.

In some embodiments according to the first aspect of the present inventive subject matter, the rate of vibration of the piezoelectric element that is measured is the resonant frequency of vibration.

In some embodiments according to the first aspect of the present inventive subject matter, the piezoelectric element comprises quartz, and in some of such embodiments, the heat applied to the piezoelectric element causes the piezoelectric element to reach a temperature between about 100 degrees C and about 500 degrees C.

In some embodiments according to the first aspect of the present inventive subject matter, the piezoelectric element comprises gallium phosphate, and in some of such embodiments, the heat applied to the piezoelectric element causes the piezoelectric element to reach a temperature between about 100 degrees C and about 900 degrees C.

In some embodiments according to the first aspect of the present inventive subject matter, the piezoelectric element comprises langasite, and in some of such embodiments, the heat applied to the piezoelectric element causes the piezoelectric element to reach a temperature between about 100 degrees C and about 1,400 degrees C.

In some embodiments according to the first aspect of the present inventive subject matter, said applying heat to the first piezoelectric element is carried out by heating a body, the piezoelectric element being heated thereby through direct or indirect contact with the body.

In some embodiments according to the first aspect of the present inventive subject matter, the method further comprises exposing at least one substrate to the source of deposit material that is emitting deposit material, so that some deposit material is applied directly or indirectly onto the substrate.

In a second aspect of the present inventive subject matter, there is provided a device for measuring the thickness of a film and/or the rate of increase of the thickness of a film, comprising:

at least a first piezoelectric element and a second piezoelectric element, the second piezoelectric element being located in a cleaning position;

a first electrode, the first electrode being in contact with at least a first region of the first piezoelectric element;

a second electrode, the second electrode being in contact with at least a second region of the first piezoelectric element, the second region of the first piezoelectric element being spaced from the first region of the first piezoelectric element;

a third electrode, the third electrode being in contact with at least a first region of the second piezoelectric element;

a fourth electrode, the fourth electrode being in contact with at least a second region of the second piezoelectric element, the second region of the second piezoelectric element being spaced from the first region of the second piezoelectric element; and

a heater which heats a piezoelectric element in the cleaning position.

In some embodiments according to the second aspect of the present inventive subject matter:

the device further comprises a source of deposit material, and

the first piezoelectric element is located in a deposition position, where the first piezoelectric element is exposed to the source of deposit material. h a third aspect of the present inventive subject matter, there is provided a device for measuring the thickness of a film and/or the rate of increase of the thickness of a film, comprising:

at least a first piezoelectric element and a second piezoelectric element,

the first piezoelectric element being movable between at least a cleaning position and a deposition position;

the second piezoelectric element being movable between at least a cleaning position and a deposition position;

a first electrode, the first electrode being in contact with at least a first region of the first piezoelectric element; a second electrode, the second electrode being in contact with at least a second region of the first piezoelectric element, the second region of the first piezoelectric element being spaced from the first region of the first piezoelectric element;

a heater which heats a piezoelectric element in a cleaning position.

In some embodiments according to the third aspect of the present inventive subject matter:

the device further comprises a source of deposit material, and

the deposition position is exposed to the source of deposit material.

In a fourth aspect of the present inventive subject matter, there is provided a device for measuring the thickness of a film and/or the rate of increase of the thickness of a film, comprising:

at least a first piezoelectric element and a second piezoelectric element,

a fourth electrode, the fourth electrode being in contact with at least a second region of the second piezoelectric element, the second region of the second piezoelectric element being spaced from the first region of the second piezoelectric element;

a shield element; and

at least one heater, the shield element being movable between at least a first position and a second position, the shield element substantially preventing deposit material from being deposited on the first piezoelectric element if the shield element is in the first position, the shield element substantially preventing deposit material from being deposited on the second piezoelectric element if the shield element is in the second position,

the heater being capable of heating the first piezoelectric element if the shield element is in the first position.

In some embodiments according to the fourth aspect of the present inventive subject matter:

the device further comprises a source of deposit material,

the first piezoelectric element is exposed to the source of deposit material if the shield element is in the second position, and

the second piezoelectric element is exposed to the source of deposit material if the shield element is in the first position.

In some embodiments according to the fourth aspect of the present inventive subject matter, the heater is in direct or indirect contact with the first piezoelectric element if the shield element is in the first position.

In some embodiments according to the second or the third aspect of the present inventive subject matter:

the device further comprises a source of deposit material, and

the cleaning position is shielded from the source of deposit material.

In some embodiments according to the second or the third aspect of the present inventive subject matter, the heater is in direct or indirect contact with a piezoelectric element in the cleaning position.

In some embodiments according to the present inventive subject matter, the piezoelectric element comprises at least one material selected from among the group consisting of quartz, gallium phosphate and langasite.

In some embodiments according to the present inventive subject matter, the device further comprises a power supply which applies a voltage between the first electrode and the second electrode across the first piezoelectric element.

The inventive subject matter may be more fully understood with reference to the accompanying drawings and the following detailed description of the inventive subject matter.

Brief Description of the Drawing Figures:

Fig. 1 schematically depicts an embodiment of a deposition system 10.

Fig. 2 is a sectional view that schematically depicts the device 15 depicted in Fig. 1, with a shield element 18 in a first position.

Fig. 3 is a sectional view that schematically depicts the device 15, with the shield element 18 in a second position.

Fig. 4 is a top view of the device 15 in the first position

Figs. 5-7 are views of a representative example of a conventional piezoelectric element 80 for use in a thin film monitor.

Fig. 8 schematically depicts a second embodiment of a deposition system 50

Fig. 9 is an enlarged top view of the device 55 shown in Fig. 8.

Fig. 10 is a sectional view of a device 115 that is similar to the device 15 depicted in Fig. 2, except that the device 115 includes a temperature detector 65, circuitry 66 and a cooling device (or a heater) 67.

Detailed Description of the Inventive Subject Matter

As noted above, aspects of the present inventive subject matter provide a device that comprises at least first and second piezoelectric elements, each having electrodes, and a heater.

The expression "in contact", as used in the present specification, means that the first structure which is "in contact" with a second structure can be in direct contact with the second structure, or can be separated from the second structure by one or more mteirening structures (i.e., in indirect contact), where the first and second structures, and the one or more intervening structures each have at least one surface which is in direct contact with another surface selected from among surfaces of the first and second structures and surfaces of the one or more intervening structures.

The expression "in direct contact", as used in the present specification, means that the first structure which is "in direct contact" with a second structure is touching the second structure and there are no intervening structures between the first and second structures at least at some location.

The expression "applied onto", as used in the present specification (e.g., in the expression "deposit material is applied directly or indirectly onto the substrate"), means that the material which is "applied onto" a structure can be applied in direct contact with the structure, or can be separated from the structure by one or more intervening structures (i.e., applied indirectly onto), where the material being applied onto the structure, the structure, and the one or more intervening structures each have at least one surface which is in direct contact with another surface selected from among surfaces of the material being applied onto the structure, the structure, and surfaces of the one or more intervening structures.

The expression "applied directly onto", as used in the present specification, means that the material that is being "applied directly onto" a structure is in direct contact with the structure and there are no intervening structures between the material that is being applied directly onto the structure and the structure at least at some location.

Persons of skill in the art are familiar with a wide variety of piezoelectric elements, and any of such piezoelectric elements can be employed in making devices according to the present inventive subject matter. The two or more piezoelectric elements in a device according to the present inventive subject matter can be the same, can all be different, or can include any combination (e.g., a device that includes three or more piezoelectric elements can include some piezoelectric elements that comprise the same piezoelectric material as one or more other piezoelectric elements, and one or more piezoelectric elements that comprise a different piezoelectric material from the other piezoelectric elements).

Persons of skill in the art are familiar with electrodes that can be provided on piezoelectric elements, and are familiar with methods for providing such electrodes, and any such electrodes can be employed in the devices according to the present inventive subject matter. The electrodes can generally be any structure capable of conducting electricity. As noted above, for each piezoelectric element, the first electrode is in contact with at least a first region of the piezoelectric element, and the second electrode is in contact with at least a second region of said piezoelectric element, the second region being spaced from the first region, whereby current from a source of power can pass through the first electrode, through the piezoelectric element from the first region to the second region, and through the second electrode. In general, any suitable source (or sources) of power can be employed, e.g., power can be supplied from the grid, from batteries, from a photovoltaic device (or devices), from a windmill (or windmills), etc.

In some embodiments, the first and second regions of the piezoelectric element can be coated with electrode material, e.g., the first and second regions of the piezoelectric element can be coated with aluminum or aluminum alloy electrode material. Alternatively, any other suitable material, e.g., gold, silicon dioxide, etc. can be used to form electrode coatings on the first and second regions.

For each piezoelectric material, there is a temperature at which the piezoelectric material undergoes a phase change or other change that renders it unsuitable for measuring coating thickness or coating thickness rate of change (such that the material can no longer function for accurately measuring the thickness of a film of deposit material and/or the rate of increase of the thickness of such film). Accordingly, for each piezoelectric element, there is a temperature that should not be reached (or exceeded) during the cleaning step (e.g., the cleaning step should be conducted such that the temperature of each piezoelectric element never reaches its phase change temperature). In embodiments where all of the piezoelectric elements in the device comprise the same piezoelectric material, the temperature for which the cleaning step should always be below is the same for each piezoelectric element in the device.

Representative examples of piezoelectric materials that can be employed in the devices according to the present inventive subject matter include quartz, gallium phosphate and langasite. Quartz undergoes a phase change at about 550 degrees C; gallium phosphate undergoes a phase change at about 920 - 930 degrees C; langasite undergoes a phase change at about 1 ,420 degrees C.

Each piezoelectric element in a device can independently be of any suitable shape. For example, one or more piezoelectric elements can be substantially plano-convex or can have opposite surfaces which are substantially flat and parallel (e.g., generally cylindrical with the axial dimension being much smaller than the radial dimension). In some

embodiments, the edges of the piezoelectric element can be beveled, as is well known in the art.

Representative examples of piezoelectric elements that can be employed in the devices according to the present inventive subject matter are described in:

U.S. Patent No. 7,176,474, the entirety of which is hereby incorporated by reference as if set forth in its entirety; U.S. Patent No. 7,275,436, the entirety of which is hereby incorporated by reference as if set forth in its entirety;

U.S. Patent No. 6,820,485, the entirety of which is hereby incorporated by reference as if set forth in its entirety; and

PCT Publication No. 2006/138,678, the entirety of which is hereby incorporated by reference as if set forth in its entirety.

The frequency of vibration of the piezoelectric elements can be sensed using any suitable device. For example, skilled artisans are familiar with microprocessors which can be readily set up to read frequency of vibration of the piezoelectric element.

Similarly, any suitable device can be used to convert frequency of vibration data to deposition rate (e.g., Angstroms per second) and/or to accumulated coating values (i.e., total thickness, e.g., in Angstroms). For example, skilled artisans are familiar with setting up microprocessors to perform such conversions. A variety of algorithms for performing such calculations are well known to those of skill in the art (see, e.g., Chih-shun Lu, "Mass determination with piezoelectric quartz crystal resonators," J. Vac. Sci. Techno!., Vol. 12, No. 1 , (Jan./Feb. 1975), the entirety of which is hereby incorporated by reference).

Corrections can be made to the thickness calculation algorithm to account for acoustic impedance, as is well known in the art.

In some embodiments, one or more piezoelectric element that is/are undergoing vibration that is being detected in order to measure the thickness of one or more films deposited thereon and/or the rate of deposition thereon can be located near one or more piezoelectric elements to which heat is being applied to remove at least a portion of one or more deposit materials from such piezoelectric element(s).

In some embodiments (e.g., in some embodiments in which one or more piezoelectric element that is/are undergoing vibration that is being detected in order to measure the thickness of one or more films deposited thereon and/or the rate of deposition thereon is sufficiently near one or more piezoelectric elements to which heat is being applied to remove at least a portion of one or more deposit materials from such piezoelectric element(s) that some of the heat being applied to remove at least a portion of one or more deposit materials causes the temperature of the one or more piezoelectric element that is/are undergoing vibration that is being detected in order to measure the thickness of one or more films deposited thereon and/or the rate of deposition thereon to increase and/or vary), temperature variation of one or more piezoelectric elements that is/are undergoing vibration (that is being detected in order to measure the thickness of one or more films deposited thereon and/or the rate of deposition thereon) can be detected and factored into the calculation of deposited film thickness (and/or the calculation of rate of deposited film thickness change) in order to reduce or minimize (or eliminate) any effects of such temperature change on the vibratory characteristics of the piezoelectric element(s). A number of temperature-frequency algorithms are available to persons of skill in the art, for accounting for effects on frequency change caused by temperature changes. Examples of such work include: (1) E.C. van Ballegooijen, "Simultaneous Measurement of Mass and Temperature using Quartz Crystal Microbalances" Chapter 5, Methods and Phenomena 7, C. Lu and A.W. Czanderna, Editors, Applications of Piezoelectric Quartz Crystal Microbalances, Elsevier Publishing, New York, 1984, and (2) E.P. Eernisse, "Vacuum Applications of Quartz Resonators", J. Vac.

Sci.Technol. , Vol. 12, No. 1, Jan./Feb. 1975, pp 564-568.

In some embodiments (e.g., in some embodiments in which one or more piezoelectric element that is/are undergoing vibration that is being detected in order to measure the thickness of one or more films deposited thereon and/or the rate of deposition thereon is sufficiently near one or more piezoelectric elements to which heat is being applied to remove at least a portion of one or more deposit materials from such piezoelectric element(s) that some of the heat being applied to remove at least a portion of one or more deposit materials would otherwise cause the temperature of the one or more piezoelectric element that is/are undergoing vibration that is being detected in order to measure the thickness of one or more films deposited thereon and/or the rate of deposition thereon to increase and/or vary), temperature variation of one or more piezoelectric elements that is/are undergoing vibration (that is being detected in order to measure the thickness of one or more films deposited thereon and/or the rate of deposition thereon) can be reduced, rm^'nimized or elimrnated by applying appropriate cooling (and optionally supplemental heating, e.g., if such cooling overcompensates for a temperature increase resulting from a film material removal operation), e.g., by blowing or pushing (or assisting in blowing) an ambient fluid (such as a liquid and/or air) across or near one or more piezoelectric elements, thermoelectric cooling, phase change cooling, magnetoresistance, etc., using any suitable device (e.g., fluid filled tubing, one or more fans, one or more cartridge coolers, one or more cartridge heaters, etc.

Bi addition, well known electronics and shielding can be employed in order to eliminate radio frequency interference and voltage variations.

The devices according to the present inventive subject matter can be used in a deposition system that includes a source of deposit material positioned within a deposition chamber. In such systems, the source of deposit material can be any suitable source of deposit material, e.g., an electron beam coating source, a thermal evaporation coating source, a sputtering coating source, etc. Typically, deposition is carried out in a vacuum (or substantial vacuum). Persons of skill in the art are familiar with a variety of deposition chambers, and any suitable deposition chamber can be employed in such systems.

In a representative example of a system that employs a device according to the present inventive subject matter, a piezoelectric element test crystal is contained in a housing, mounted in a line-of-sight position relative to a coating source (electron beam, thermal evaporation, sputtering, etc.). Substrates to be coated are positioned close to the test crystal, ensuring that the amount of material (e.g., evaporant) depositing on the substrates and crystal are substantially identical. If this is not the case, a geometrical correction or "tooling factor," can be applied. In such systems, the piezoelectric element can be mounted in a body. When such a body is employed, it can be generally of any suitable shape, and in some instances, a body supports the piezoelectric element along its perimeter, leaving a large inner portion of the piezoelectric element free to vibrate.

Persons of skill in the art are familiar with a variety of heaters, and any suitable heater can be employed in the devices according to the present inventive subject matter. For example, any conduction heater, radiant heater or convection heater can be employed.

In some embodiments, heat is directly applied to a piezoelectric element (or elements) in order to heat the piezoelectric element(s), and in other embodiments, heat is indirectly applied to the piezoelectric element(s), e.g., by being provided to a body that is in contact (direct or indirect) with the piezoelectric element(s).

Representative examples of suitable heaters include Kapton contact heaters (which are well known to those of skill in the art, i.e., which comprise a block with resistive wires positioned inside the block), quartz lamp infrared-heating sources, etc. Such heater or heaters can be positioned inside a body or clamped to a body (with the heat being conducted by the body into a piezoelectric element or elements), or can be separate from but directed toward a piezoelectric element (or elements), or in any other suitable arrangement.

In some arrangements in which heat is supplied to a body, the temperature of the body may be monitored, e.g., using a thermocouple or a thermistor, and a feedback device can optionally be employed in order to maintain the body (and the piezoelectric element or elements) at a substantially constant temperature.

In some embodiments, one or more piezoelectric element test crystals can be exposed to the source of deposit material while deposit material is being applied to one or more layered devices, while one or more piezoelectric element test crystals are not exposed to the source of deposit material, and then at some point (prior to reaching a point at which the thickness of the layering on the piezoelectric element test crystal(s) reaches a point at which the thickness readings generated by that (or those) test crystal(s) becomes inaccurate), (1) one or more piezoelectric element test crystals that were not previously exposed to the source of deposit material become exposed to the source of deposit material (and new thickness readings are generated by that (or those) test crystal(s), and (2) one or more piezoelectric element test crystals that were exposed to the source of deposit material are cleaned by being heating to at least a temperature at which deposit material that has been coated thereon vaporizes or is otherwise removed (events (1) and (2) in this sentence can be in any desired order, can be simultaneous, and/or can overlap in time to any degree).

Event (1) described in the previous paragraph can be carried out in any suitable way, e.g., by removing a shield that had been blocking deposit material from reaching the piezoelectric element test crystal (or crystals), and/or by moving the piezoelectric element test crystal (or crystals) from a "shielded position" (where the piezoelectric element test crystal is not exposed to the deposit material) to a "deposition position" (where the piezoelectric element test crystal is exposed to the deposit material).

Event (2) described in the previous paragraph can be carried out in any suitable way, e.g., by energizing a heater that had already been in contact (direct or indirect) with the piezoelectric element test crystal, by moving a heater into contact (direct or indirect) with the piezoelectric element test crystal, and/or by moving the piezoelectric element test crystal into contact (direct or indirect) with the piezoelectric element test crystal (i.e., moving the piezoelectric element test crystal to a "cleaning position"). In some embodiments, event (2) can be accompanied with shielding the piezoelectric element test crystal that is being cleaned from deposit material, e.g., by moving a shield into a position at which the shield blocks deposit material from reaching the piezoelectric element test crystal, and/or by moving the piezoelectric element test crystal to a position where the piezoelectric element test crystal is shielded from the deposit material (i.e., moving the piezoelectric element test crystal into a "shielded position").

B such a way, the process can be repeated ^definitely, with the piezoelectric element test crystals alternating between being exposed to deposit material and being cleaned, and with at least one crystal always being cleaned when at least one other crystal is exposed to deposit material. In some embodiments, a first piezoelectric element test crystal (or a first group of piezoelectric element test crystals) alternates with a second piezoelectric element test crystal (or a second group of test crystals), but in other embodiments, any number of piezoelectric element test crystals (and/or respective groups of test crystals) can alternate, e.g., one piezoelectric element test crystal (or group of piezoelectric element test crystals) can be exposed to deposit material while two or more other piezoelectric element test crystals (and/or groups of piezoelectric element test crystals) are being cleaned and/or maintained ready to be exposed to deposit material.

A shield element (or elements) can be made of any suitable material (or materials) and can be in any suitable shape, so long as it blocks deposit material (or at least some deposit material).

Fig. 1 schematically depicts an embodiment of a deposition system 10 that comprises a source of deposit material 11, e.g., an electron beam coating source, positioned within a deposition chamber 12. The system also includes a plurality of substrates 13 positioned on respective supports 14, and a device 15 for measuring the thickness of deposit material and/or the rate of increase of the thickness of deposit material on the substrates 13.

Fig. 2 is a sectional view that schematically depicts the device 15 depicted in Fig. 1.

Referring to Fig. 2, the device 15 comprises a first housing element 16, a second housing element 17, shield element 18, a first piezoelectric element 19, a second piezoelectric element 20, a first heater 21, a second heater 22, and a female coaxial connector 31. The first housing element 16 has a first substantially circular opening 23 and a second substantially circular opening 24. Springs 25 hold the first piezoelectric element 19 against a region of the housing element 17 that surrounds the first opening 23, and springs 26 hold the second piezoelectric element 20 against a region of the housing element 17 that surrounds the second opening 24. Screws 27 hold the second housing element 17 in contact with the first housing element 16. Fig. 2 also depicts a power supply 28 which supplies power to the device 15 through a coaxial cable 29, a male connector 30 (connected to the cable 29) and the female connector 31. Electricity is provided from the power supply 28 through the coaxial cable 29, with the positive connection being the stinger (the inner part of the coaxial cable), which is electrically connected to the spring-loaded electrodes, and then into the first piezoelectric element 19 or the second piezoelectric element 20 (depending on which piezoelectric element is being vibrated), and out of the first piezoelectric element 19 or the second piezoelectric element 20, and out through the outer part of the coaxial cable. Electrical connections (not shown) are provided between the springs 25 and 26 and the stinger of the coaxial cable; the springs 25 and 26 and the respective electrical connections are electrically isolated from the remainder of the housing elements 15 and 16.

The shield element 18 has a substantially circular opening 32. The shield element 18 is movable between (1) a first position in which the shield element 18 covers the first opening 23 and the second opening 24 is exposed through the opening 32 (as shown in Fig. 2), and (2) a second position in which the shield element 18_. covers the second opening 24 and the first opening 23 is exposed through the opening 32 (as shown in Fig. 3). The shield element 18 can be slid between the first position and the second position. Fig. 4 is a top view of the device 15 with the shield element 18 in the first position (i.e., as in Fig. 2).

When the shield element 18 is in the first position, the second piezoelectric element 20 is exposed, and deposit material 11 can be deposited on the second piezoelectric element 20, whereby the second piezoelectric element 20 can be used to determine the thickness of deposit material that has been deposited on the substrates 13 while the shield element 18 has been in the first position, and, if desired, the first heater 21 can be energized to heat the first piezoelectric element 19 to remove built-up deposit material from the first piezoelectric element 19 (i.e., the first piezoelectric element 19 is in a cleaning position).

The shield element 18 can then be moved to the second position, in which the first piezoelectric element 19 is exposed, and deposit material 11 can be deposited on the first piezoelectric element 19, whereby the first piezoelectric element 19 can be used to determine the thickness of deposit material that has been deposited on the substrates 13 while the shield element 18 has been in the second position, and, if desired, the second heater 22 can be energized to heat the second piezoelectric element 20 to remove built-up deposit material from the second piezoelectric element 20 (i.e., the second piezoelectric element 20 is in a cleaning position).

A representative example of a conventional piezoelectric element 80 for use in a thin film monitor is depicted in Figs. 5-7. Fig. 5 is a top view showing a first gold electrode 81 and a piezoelectric element 83. Fig. 6 is a bottom view showing a second gold electrode 82. Fig. 7 is a sectional view taken along line 7 - 7 in Fig. 6. The region in which the most pronounced vibration will occur (upon passing a current between the first and second electrodes 81 and 82) is in the center of the chip.

Fig. 8 schematically depicts a second embodiment of a deposition system 50 that comprises a source of deposit material 51, e.g., an electron beam coating source, positioned within a deposition chamber 52. The system also includes a plurality of substrates 53 positioned on respective supports 54, and a device 55 for measuring the thickness of deposit material and/or the rate of increase of the thickness of deposit material on the substrates 53. The device 55 comprises a first piezoelectric element 56, a second piezoelectric element 57, a rotatable support 58, a shield element 59, a first pair of shield members 60 and a second pair of shield members 61, a first heater 62 and a second heater 63. The shield element 59 is supported by an arm 64. The first heater 62 is mounted on one of the first pair of shield members 60, facing the first piezoelectric element 56, and the second heater 63 is mounted on one of the second pair of shield members 61, facing the second piezoelectric element 57.

Fig. 9 is an enlarged top view of the device 55. The device 55 is depicted with the second piezoelectric element 57 in a cleaning position and the first piezoelectric element in a deposition position. When it is desired to move the first piezoelectric element to the cleaning position and the second piezoelectric element to the deposition position, the support 58 is rotated 180 degrees (with the shield element 59 remaining in place), so that the first piezoelectric element 56, the first heater 62 and the first pair of shield members 60 switch positions with the second piezoelectric element 57, the second heater 63 and the second pair of shield members 61. When the first piezoelectric element 56 is in the cleaning position, the first pair of shield members 60 cooperate with the shield element 59 to surround the first piezoelectric element 56 and isolate it from the deposit material. Similarly, when the second piezoelectric element 57 is in the cleaning position, the second pair of shield members 61 cooperate with the shield element 59 to surround the second piezoelectric element 57 and isolate it from the deposit material. Whichever piezoelectric element is in the cleaning position can be cleaned by energizing the respective heater (i.e., the first heater 62 for the first piezoelectric element 56, or the second heater 63 for the second piezoelectric element 57).

While the device 55 depicted in Figs. 8 and 9 includes two piezoelectric elements (and two sets of respective pairs of shield members and heaters), embodiments according to the present invention can have any suitable number of piezoelectric elements (and sets of pairs of shield members and heaters), and any suitable number of shield elements (whereby any suitable number of piezoelectric elements can be exposed to deposit material, and any suitable number of piezoelectric elements can be shielded and/or being cleaned at any given time (and the respective numbers can be altered at any suitable time, as desired).

A third embodiment can comprise a shield element (e.g., that comprises components similar to or analogous to the shield element 59 and the shield members 60, and that can also comprise a heater mounted on any of such structures) that is movable between a position where it covers one piezoelectric element and a position where it covers another piezoelectric element.

Fig. 10 is a sectional view of a device 115 that is similar to the device 15 depicted in Fig. 2, except that the device 115 includes a temperature detector 65, circuitry 66 that adjusts a signal representing a detected rate of vibration of the first piezoelectric element based on a temperature detected by the temperature detector 65 and a cooling device (or a heater) 67.

Any two or more structural parts of the devices described above can be integrated. Any structural part of the devices described above can be provided in two or more parts (which are held together, if necessary).

Claims

1. A method of measuring the thickness of a film made of a deposit material and/or the rate of increase of the thickness of a film made of a deposit material, comprising:

depositing deposit material on the first piezoelectric element;

measuring a rate of vibration of the first piezoelectric element; and

2. A method as recited in claim 1, wherein the method further comprises:

measuring a rate of vibration of the first piezoelectric element.

3. A method as recited in claim 2, wherein the source of deposit material to which the piezoelectric element is exposed and the source of deposit material to which the piezoelectric element is again exposed are the same source of deposit material.

4. A method as recited in claim 2, wherein the method further comprises again applying heat to the first piezoelectric element to remove from the first piezoelectric element at least a portion of the deposit material applied to the first piezoelectric element.

5. A method as recited in claim 1, wherein the method further comprises:

measuring a rate of vibration of the second piezoelectric element.

6. A method as recited in claim 5, wherein the method further comprises:

applying heat to the second piezoelectric element while the first piezoelectric element is in the cleamng position, to remove from the second piezoelectric element at least a portion of the deposit material applied to the second piezoelectric element;

measuring a rate of vibration of the first piezoelectric element.

7. A method as recited in claim 1, wherein the rate of vibration of the piezoelectric element that is measured is the resonant frequency of vibration.

8. A method as recited in claim 1, wherein the piezoelectric element comprises quartz.

9. A method as recited in claim 8, wherein the heat applied to the piezoelectric element causes the piezoelectric element to reach a temperature between about 100 degrees C and about 500 degrees C.

10. A method as recited in claim 1, wherein the piezoelectric element comprises gallium phosphate.

11. A method as recited in claim 10, wherein the heat applied to the piezoelectric element causes the piezoelectric element to reach a temperature between about 100 degrees C and about 900 degrees C.

12. A method as recited in claim 1, wherein the piezoelectric element comprises langasite.

13. A method as recited in claim 12, wherein the heat applied to the piezoelectric element causes the piezoelectric element to reach a temperature between about 100 degrees C and about 1,400 degrees C.

14. A method as recited in claim 1, wherein said applying heat to the first

piezoelectric element is carried out by heating a body, the piezoelectric element being heated thereby through direct or indirect contact with the body.

15. A method as recited in claim 1, wherein the method further comprises exposing at least one substrate to the source of deposit material that is emitting deposit material, so that some deposit material is applied directly or indirectly onto the substrate.

16. A method as recited in claim 1, wherein the depositing deposit material on the first piezoelectric element comprises exposing the first piezoelectric element to a source of a deposit material that is emitting deposit material, so that some deposit material is applied to the first piezoelectric element.

17. A method as recited in claim 1, wherein the method further comprises detecting a temperature of the first piezoelectric element and adjusting a signal representing a detected rate of vibration of the first piezoelectric element based on the detected temperature of the first piezoelectric element.

18. A device for measuring the thickness of a film and/or the rate of increase of the thickness of a film, comprising:

a heater which heats a piezoelectric element in the cleaning position.

19. A device as recited in claim 18, wherein:

the device further comprises a source of deposit material, and

the first piezoelectric element is located in a deposition position, where the first piezoelectric element is exposed to the source of deposit material.

20. A device as recited in claim 18, wherein:

the device further comprises a source of deposit material, and

the cleaning position is shielded from the source of deposit material.

21. A device as recited in claim 18, wherein the piezoelectric element comprises at least one material selected from among the group consisting of quartz, gallium phosphate and langasite.

22. A device as recited in claim 18, wherein the device further comprises a power supply which applies a voltage between the first electrode and the second electrode across the first piezoelectric element.

23. A device as recited in claim 18, wherein the heater is in direct or indirect contact with a piezoelectric element in the cleaning position.

24. A device as recited in claim 18, wherein the device further comprises a temperature detector.

25. A device as recited in claim 24, wherein the device further comprises circuitry that adjusts a signal representing a detected rate of vibration of the first piezoelectric element based on a temperature detected by the temperature detector.

26. A device for measuring the thickness of a film and/or the rate of increase of the thickness of a film, comprising:

at least a first piezoelectric element and a second piezoelectric element,

a fourth electrode, the fourth electrode being in contact with at least a second region of the second piezoelectric element, the second region of the second piezoelectric element being spaced from the first region of the second piezoelectric element; and a heater which heats a piezoelectric element in a cleaning position.

27. A device as recited in claim 26, wherein:

the device further comprises a source of deposit material, and

the deposition position is exposed to the source of deposit material.

28. A device as recited in claim 26, wherein:

the device further comprises a source of deposit material, and

the cleaning position is shielded from the source of deposit material.

29. A device as recited in claim 26, wherein the piezoelectric element comprises at least one material selected from among the group consisting of quartz, gallium phosphate and langasite.

30. A device as recited in claim 26, wherein the device further comprises a power supply which applies a voltage between the first electrode and the second electrode across the first piezoelectric element.

31. A device as recited in claim 26, wherein the heater is in direct or indirect contact with a piezoelectric element in the cleaning position.

32. A device as recited in claim 26, wherein the device further comprises a temperature detector.

33. A device as recited in claim 32, wherein the device further comprises circuitry that adjusts a signal representing a detected rate of vibration of the first piezoelectric element based on a temperature detected by the temperature detector.

34. A device for measuring the thickness of a film and/or the rate of increase of the thickness of a film, comprising:

at least a first piezoelectric element and a second piezoelectric element, a first electrode, the first electrode being in contact with at least a first region of the first piezoelectric element;

a shield element; and

at least one heater,

the shield element being movable between at least a first position and a second position, the shield element substantially preventing deposit material from being deposited on the first piezoelectric element if the shield element is in the first position, the shield element substantially preventing deposit material from being deposited on the second piezoelectric element if the shield element is in the second position,

35. A device as recited in claim 34, wherein:

the device further comprises a source of deposit material,

36. A device as recited in claim 34, wherein the piezoelectric element comprises at least one material selected from among the group consisting of quartz, gallium phosphate and langasite.

37. A device as recited in claim 34, wherein the device further comprises a power supply which applies a voltage between the first electrode and the second electrode across the first piezoelectric element.

38. A device as recited in claim 34, wherein the heater is in direct or indirect contact with the first piezoelectric element if the shield element is in the first position.

39. A device as recited in claim 34, wherein the device further comprises a temperature detector.

40. A device as recited in claim 39, wherein the device further comprises circuitry that adjusts a signal representing a detected rate of vibration of the first piezoelectric element based on a temperature detected by the temperature detector.