Patent Application
20200348237
The present invention relates to a gas analyzer and more particularly relates to a gas analyzer that uses discharge optical emission having a low lower limit of detection.
It is effective for conducting process management in various vacuum equipment including a vacuum equipment for manufacturing electronic devices to perform gas analyzing in vacuum process. In the explanation below, extents of vacuum will be referred to as a medium vacuum for 10−1 Pa to 102 Pa, a high vacuum for 10−5 Pa to 10−1 Pa and an ultrahigh vacuum for 10−9 Pa to 10−5 Pa, according to Japanese Industrial Standards (JIS).
Gas analyzers that can be applied to various vacuum equipment require following matters:
(1) to have a wide operable range from an ultrahigh vacuum of 10−7 Pa to a medium vacuum of 102 Pa, and
(2) to have a low lower limit of detection of partial pressure with an ultralow concentration of 10−7 Pa. With a quadrupole mass spectrometer that can detect a tiny amount of gas concentration, among conventional gas analyzers, a hot-filament wears in a vacuum over a medium vacuum of 1 Pa and carry distance of ionized gas for analyzing mass is long as of several centimeters or more, so that ionized gas collides with other gas, making it difficult to classify gasses for each mass number. Hence, operation in a medium vacuum is difficult in principle.
In general, discharge generated by applying a high voltage between a cathode and an anode confronted with each other in a vacuum occurs in a medium vacuum and has a lower limit of pressure of about 1 Pa. For maintaining discharge in a high vacuum range below it, modules that maintain discharge by applying a high voltage electric field and a magnetic field are utilized for a cold cathode ionization gauge, an ion pump or the like. Such gas analyzers detecting optical emission of excited gas with discharge generated by applying a high voltage electric field and a magnetic field (referred to as magnetic discharge below) are seen to be useful as gas analyzers that can be operated in a wide vacuum range from a high vacuum to a medium vacuum and a number of prior techniques have been proposed.
Patent Document 1 discloses a gas analyzer used for a vacuum equipment that employs a Penning discharge method as one of magnetic field discharge methods for a method of exciting gas and is equipped with a total pressure measurement mechanism by measuring ion current and a partial pressure measurement mechanism by measuring intensity of optical emission of various gases. In a case of Penning discharge method, however, a high voltage electric field is not perpendicular to a magnetic field, so that it is difficult to maintain steady discharge in a vacuum below 10−4 Pa and discharge generates weak optical emission. Due to this, a lower limit of partial pressure detection by measuring optical emission is about 10−3 Pa, which exhibits a problem in attaining a lower limit of partial pressure detection as of an ultralow concentration of 10−7 Pa.
Patent Document 2 and Patent Document 3 disclose gas analyzers that employ an inverted magnetron discharge method as one of magnetic field discharge methods for exciting gas and are equipped with a total pressure measurement mechanism by measuring ion current and a partial pressure measurement mechanism by measuring intensity of optical emission of various gases. A structure of a gas analyzer detecting optical emission by magnetic field discharge using an inverted magnetron discharge method will be explained referring to
Electric field E is created between the electrode 2 as an anode and the vacuum casing 1 as a cathode when direct current voltage of several kV is applied to the electrode 2. On the other hand, magnetic field M is created with magnetic field applying module 6. Electrons emitted from the vacuum casing 1 of a cathode are accelerated with the electric field E as well as subjected to a Lorentz force with an electric field E and a magnetic field M, thus making a spiral movement so as to coil around the magnetic field M. Hence, carry distance of electrons in a vacuum space becomes long and electrons are localized in the magnetic field M. Due to collision of the electrons with gas, gas is excited to be ionized or radicalized, thus creating discharge. As seen in
The light of discharge optical emission L by the excited gas passes a plate 7 having a hole and is focused on a light receiving element as light detecting module 9 using a focusing lens 8 so that light is detected. Here, cation gas excited by discharge collides with the vacuum casing 1 as a cathode, generating a sputter deposition phenomenon knocking out particles (atoms or molecules) from the material of the vacuum casing 1 and causing scattered particles to be attached to the insides of the vacuum casing. The plate 7 having a hole is placed for preventing a focusing lens 8 from getting dirt due to the scattered particles by the sputter deposition phenomenon. While the light of discharge optical emission L consists of optical emission of atoms or molecules for each gas species, wave length of the light is various according to gas species. It is possible to measure intrinsic optical mission of multitudes of gas species in a time shorter than several seconds by measuring light of discharge optical emission L using a multichannel spectrometer that can measure light of multiple wave lengths simultaneously as light detecting module 9. Intensity of intrinsic optical emission and pressure (partial pressure) of gas are measured preliminarily for each gas species and the intensity of optical emission is converted to a pressure of gas.
With magnetic field discharge by a prior art inverted magnetron method shown in
With a gas analyzer using discharge optical emission with magnetic field discharge of Patent Document 2 shown in a schematic view of
While a central hole of a cathode disc has a diameter of several mm in Patent Document 2 ([0041]), the metal plate serves as an earth shield in this case, so that discharge is not generated inside of the hole. Actually, it is also described in [0047] that sputter deposition is not generated inside of the hole and optical emission is somewhat lowered. Even if intensive optical emission can be obtained inside of the central hole of the metal plate having holes, there is a problem in focusing optical emission in the central hole of the metal plate 10 having holes on the light detecting module 9 with a high efficiency and raising detection accuracy, because the focusing lens 8 is disposed far from the optical emission (described as about 10 cm) and a plate having a hole 7 for preventing the lens from getting dirt is placed in front of the lens.
A gas analyzer using discharge optical emission with magnetic field of Patent Document 3 shown schematically in
As explained above, although discharge can be maintained in an ultrahigh vacuum of 10−7 Pa with gas analyzers using magnetic field discharge by an inverted magnetron method of Patent Document 2 and Patent Document 3 as prior arts, a lower limit of detection of partial pressure with an ultralow concentration of 10−7 Pa has not been attained. It is considered to set a high voltage for discharge in order to solve this. However, this is not a practical way, because high sputter deposition is generated in this case and detection accuracy is lowered due to dirt of a focusing lens. On the other hand, it is also considered to employ a photon counting method enabling detection of extremely weak light for light detecting module. However, also this case is not a practical way because measurement of such extremely weak light requires a long time more than several minutes and equipment therefor is of a high cost.
JP Published Patent Application No. S52-131780
JP Patent No. 5,415,420
JP Published Patent Application No. 2016-170072
With vacuum equipment including a vacuum equipment for manufacturing electronic devices, it is effective to perform gas analyzing in a vacuum process for process managing. For a gas analyzer that can be applied to various vacuum equipment, following matters are required. That is,
(1) to have a wide operable range from an ultrahigh vacuum of 10−7 Pa to a medium vacuum of 102 Pa, and
(2) to have a low lower limit of detection of partial pressure with an ultralow concentration of 10−7 Pa.
However, while a quadrupole mass spectrometer among conventional gas analyzers attains a low limit of detection of the above (2), it cannot attain in principle a wide operable range of the above (1). Under such background, gas analyzers detecting discharge optical emission in process gas or residual gas in a vacuum have been proposed. However, although a wide operable range of the above (1) is attained to some extent, current situation of a low lower limit of detection of the above (2) is of 10−7 Pa, thus requiring a significant improvement. It is an object of the present invention to provide a gas analyzer that enables a high defection accuracy with a lower limit of detection in an ultrahigh vacuum of 10−7.
The present invention is created to solve the aforementioned problems and a gas analyzer according to a first aspect of the present invention is a gas analyzer using discharge optical emission that comprises a tightly closable vacuum casing, an anodic electrode and a cathode electrode provided in the vacuum casing, magnetic field applying module generating magnetic field in a direction crossing electric field generated when a high voltage is applied between the anodic electrode and the cathode electrode, and light detecting module for detecting discharge optical emission generated in magnetic field when a high voltage is applied between the anodic electrode and the cathode electrode;
wherein at least one of the anodic electrode and cathode electrode, and the magnetic field applying module is/are composed so as to concentrate and/or enhance magnetic field generated in an area of discharge optical emission when a high voltage is applied between the anodic electrode and the cathode electrode and thus to localize as well as enhance discharge optical emission, enabling a lower limit of detection to be attained.
A gas analyzer according to a second aspect of the invention is a gas analyzer according to the first aspect, wherein the vacuum casing is formed to have a generally pipe shape as well as to be made of a conductive material so as to serve as the cathode electrode, the anodic electrode is made up of an elongated conductive member fixed to the vacuum casing on one end face side thereof so as to extend in a longitudinal direction of the vacuum casing within the vacuum casing as a cantilever and at least a tip side portion thereof is formed of a conductive ferromagnetic material, and a magnet as magnetic field applying module is placed in an area of discharge optical emission between the anodic electrode and an inner peripheral portion of the vacuum casing serving as the cathode electrode so as to concentrate magnetic field, so that discharge optical emission is localized in a vicinity of a tip of the anodic electrode.
A gas analyzer according to a third aspect of the invention is a gas analyzer according to the first aspect, wherein the vacuum casing is formed to have a generally pipe shape as well as to be made of a conductive material so as to serve as the cathode electrode, the anodic electrode is made up of an elongated conductive and non-magnetic member fixed to the vacuum casing on one end face side thereof so as to extend in a longitudinal direction within the vacuum casing as a cantilever, an elongated ferromagnetic member extending near to and along the anodic electrode as a cantilever is also fixed to the vacuum casing on the one end face side thereof so as to cause a tip thereof to be at an equivalent position to the tip of the anodic electrode, and a magnet as magnetic field applying module is placed in an area of discharge optical emission between the anodic electrode and an inner peripheral portion of the vacuum casing serving as the cathode electrode so as to concentrate magnetic field, so that discharge optical emission is localized in a vicinity of a tip of the anodic electrode.
A gas analyzer according to a fourth aspect of the invention is a gas analyzer according to any one of the second aspect and the third aspect, wherein the magnet as the magnetic field applying module is provided on a peripheral face of the vacuum casing surrounding a position of the tip of the anodic electrode, so that discharge optical emission is localized in a vicinity of the tip of the anodic electrode.
A gas analyzer according to a fifth aspect of the invention is a gas analyzer according to any one of the second aspect and the third aspect, wherein the anodic electrode is fixed to the vacuum casing on one end face side thereof and, along therewith, a bar magnet as a bar magnetic field applying module is fixed to the vacuum casing on the other end face side so as to extend as a cantilever in a direction of extension of the anodic electrode, and a tip of the anodic electrode of the ferromagnetic material and one pole of the bar magnet are in an opposed positional relation with each other to concentrate magnetic field in a vicinity of the tip of the anodic electrode, so that discharge optical emission is localized in a vicinity of the tip of the anodic electrode.
A gas analyzer according to a sixth aspect of the invention is a gas analyzer according to the first aspect, wherein the vacuum casing has a generally pipe shape and is formed of a conductive, ferromagnetic and soft magnetic material so as to serve as a cathode electrode, the anodic electrode consists of an elongated conductive member fixed to the vacuum casing on one end side thereof so as to extend as a cantilever in a longitudinal direction within the vacuum casing as well as a tip portion of the anodic electrode is formed of a conductive and ferromagnetic material, and a magnet as magnetic field applying module is placed so as to concentrate magnetic field in an area of discharge optical emission between the anodic electrode and an inner peripheral portion of the vacuum casing serving as a cathode electrode, so that most of magnetic flux from the magnet as the magnetic field applying module passes within the vacuum casing of a ferromagnetic and soft magnetic material for magnetic flux to be permeable well to concentrate magnetic field in a vicinity of the tip of the anodic electrode and localize discharge optical emission.
A gas analyzer according to a seventh aspect of the invention is a gas analyzer according to the first aspect, wherein the vacuum casing has a generally pipe shape and is formed of a conductive, ferromagnetic and soft magnetic material so as to serve as a cathode electrode, the anodic electrode consists of an elongated conductive and non-magnetic member fixed to the vacuum casing on one end side thereof so as to extend as a cantilever in a longitudinal direction within the vacuum casing, an elongated ferromagnetic member extending near to and along the anodic electrode as a cantilever is also fixed to the vacuum casing on the one end face side thereof so as to cause a tip thereof to be at an equivalent position to the tip of the anodic electrode, and a magnet as magnetic field applying module is placed so as to concentrate magnetic field in an area of discharge optical emission between the anodic electrode and an inner peripheral portion of the vacuum casing serving as a cathode electrode, so that most of magnetic flux from the magnet as the magnetic field applying module passes within the vacuum casing of a ferromagnetic and soft magnetic material for magnetic flux to be permeable well to concentrate magnetic field in a vicinity of the tip of the anodic electrode and localize discharge optical emission.
A gas analyzer according to an eighth aspect of the invention is a gas analyzer according to any one of the sixth aspect and the seventh aspect, wherein the magnet as the magnetic field applying module is provided on a peripheral face of the vacuum casing surrounding a position of the tip of the anodic electrode, so that discharge optical emission is localized in a vicinity of the tip of the anodic electrode.
A gas analyzer according to a ninth aspect of the invention is a gas analyzer according to any one of the sixth aspect and the seventh aspect, wherein the anodic electrode is fixed to the vacuum casing on one end face side thereof and, along therewith, a bar magnet as a bar magnetic field applying module is fixed to the vacuum casing on the other end face side so as to extend as a cantilever in a direction of extension of the anodic electrode, and a tip of the anodic electrode of the ferromagnetic material and one pole of the bar magnet are in an opposed positional relation with each other to concentrate magnetic field in a vicinity of the tip of the anodic electrode, so that discharge optical emission is localized in a vicinity of the tip of the anodic electrode.
A gas analyzer according to a tenth aspect of the invention is a gas analyzer according to the first aspect, wherein the vacuum casing has a generally pipe shape and is formed of a ferromagnetic and soft magnetic material, an elongated ferromagnetic member is fixed to the vacuum casing on one end side thereof so as to extend as a cantilever in a longitudinal direction within the vacuum casing, a bar magnet as a bar magnetic field applying module is fixed to the casing on the other end face side so as to extend as a cantilever in a direction of extension of the anodic electrode, a tip of the ferromagnetic member and one pole of the bar magnet are in an opposed positional relation with each other, and an anodic electrode and a cathode electrode are provided respectively in a manner to be opposed to each other with the tip of the elongated ferromagnetic member disposed between the electrodes, so that most of magnetic flux from the magnet as the magnetic field applying module passes within the vacuum casing of a ferromagnetic and soft magnetic material for magnetic flux to be permeable well to concentrate magnetic field in a vicinity of the tip of the anodic electrode and localize discharge optical emission.
A gas analyzer according to an eleventh aspect of the invention is a gas analyzer using discharge optical emission that comprises a tightly closable vacuum casing, an anodic electrode and a cathode electrode provided in the vacuum casing, magnetic field applying module generating magnetic field in a direction crossing electric field generated when a high voltage is applied between the anodic electrode and the cathode electrode, and light detecting module for detecting discharge optical emission generated in magnetic field when a high voltage is applied between the anodic electrode and the cathode electrode;
wherein discharge optical emission is enhanced and a low lower limit of detection can be attained by introducing a tiny amount of gas, other than one to be detected, that has a metastable excitation energy higher than an excitation energy for discharge optical emission of gas to be detected into the tightly closable vacuum casing in gas analyzing.
A gas analyzer according to a twelfth aspect of the invention is a gas analyzer according to the eleventh aspect, wherein the tiny amount of gas, other than one to be detected, that has a metastable excitation energy higher than an excitation energy for discharge optical emission of gas to be detected is helium gas, nitrogen gas, air gas or argon gas.
In a gas analyzer using discharge optical emission according to the present invention, in which a magnetic field is caused to be generated in a direction crossing an electric field generated when a high voltage is applied between electrodes and discharge optical emission generated in the magnetic field is detected,
(1) an anodic electrode is formed of a ferromagnetic material or a ferromagnetic material/materials is/are placed in a vicinity of the anodic electrode, and
(2) a vacuum casing is formed of a ferromagnetic and soft magnetic material so that a magnetic circuit for magnetic flux to be permeable is composed, thus intensifying a magnetic field generated between the magnet as magnetic field applying module and the ferromagnetic anodic electrode.
Due to this, discharge optical emission in the magnetic field is localized, thus increasing intensity of optical emission and, along with this, detection accuracy can be raised so that a lower limit of detection in an ultrahigh vacuum of 10−7 Pa can be secured.
Further, in a gas analyzer using discharge optical emission according to the present invention, in which a magnetic field is caused to be generated in a direction crossing an electric field generated when a high voltage is applied between electrodes and discharge optical emission is detected, a tiny amount of gas other than one to be detected is introduced, so that intensity of optical emission of the gas to be detected is increased as well as detection accuracy can be raised.
While a gas analyzer using discharge optical emission according to the present invention is similar to one by a conventional case shown in
An anodic electrode is formed of a ferromagnetic material or a ferromagnetic material/materials is/are placed in a vicinity of the anodic electrode, so that discharge optical emission in a magnetic field is localized in a vicinity of a tip of an anodic electrode to increase intensity of optical emission and raise detection accuracy.
A vacuum casing is formed of a ferromagnetic and soft magnetic material so that a magnetic circuit for magnetic flux to be permeable is composed, thus intensifying a magnetic field generated between the magnet as magnetic field applying module and the ferromagnetic anodic electrode. Due to this, discharge optical emission in the magnetic field is further localized, intensity of optical emission is increased and, along with this, detection accuracy is raised.
While discharge optical emission is localized so that detection accuracy is raised, this is due to a situation such that an area of intensive optical emission on an optical emission detecting portion in a direction of optical axis of a focusing lens is narrowed, so that the area of optical emission is concentrated effectively in a vicinity of focusing point of a focusing lens, allowing more optical emission to be detected.
A tiny amount of gas other than one to be detected is introduced. Due to this, when ionized gas or radical gas having a long life collides with gas to be detected, the gas to be detected is excited to create optical emission, thus increasing discharge optical emission of gas to be detected.
Embodiments of the present invention will be explained below. Manners of using gas analyzers according to the Embodiments will be explained relating to performance of the gas analyzers.
A gas analyzer according to Embodiment 1 of the present invention is shown in
The anodic electrode 22 extends up to some distance before the other end side of the pipe-shaped vacuum casing 21 as a cantilever beam within the vacuum casing and a magnet as magnetic field applying module 26 is provided on an outer periphery of the vacuum casing 21 at a position surrounding the tip portion of the anodic electrode 22. The magnet may be disposed so as to surround the pipe-shaped vacuum casing 21 or may be disposed in such a manner that two magnets are disposed in opposing positions with the tip portion of the anodic electrode 22 therebetween. A window portion is formed on the other end side of the vacuum casing 21 at a position in a direction of an extension of the anodic electrode 22 and a light detecting portion 28 is attached to the other end side of the vacuum casing to abut thereon. A focusing lens 29 is attached to the other end side of the vacuum casing 21 so as to cover the window portion thereof and a plate 27 having a hole is attached to an inside of the vacuum casing 21 in a position near to the anodic electrode 22 from the other end side of the vacuum casing. The plate 27 having a hole is placed for preventing scattered particles due to sputter deposition from attaching to the focusing lens. A controlling unit, denoted by 30 and connected to a power source including a direct current power source 24 and an ammeter 25 and to a light detecting portion 28, conducts control of optical emission by discharge and calculation for analyzing gas based on a light intensity of discharge optical emission detected with the light detecting portion 28.
A hole is formed in the plate 27 having a hole at a position in a direction of extension of the anodic electrode 22, so that light emitted in a vicinity of the tip of the anodic electrode 22 passes through this hole as well as the focusing lens 29 to be directed towards the light detecting portion 28. While the vacuum casing 21, including the focusing lens 29 and its mounting portion, is tightly closable, the inside of the light detecting portion 28 may be under atmospheric pressure without necessity to be tightly closable. The light detecting portion 28 has an arrangement of multichannel spectrometer in which respective optical elements are disposed such that emitted light, after having passed through the focusing lens 29, passes through a hole of an aperture a, is reflected by a concave mirror b to be directed towards a diffraction grating c, and then diffracted light is reflected by a mirror d to arrive at a light receiving element e.
When the elongated ferromagnetic anodic electrode 22 is disposed at the center of a cylindrical magnet as magnetic field applying module 26, with the vacuum casing being of a cylindrical shape, a magnetic field M generated by the N-pole side of the magnetic field applying module 26 is concentrated in a vicinity of the tip of the elongated ferromagnetic anodic electrode 22. As the magnetic field M in a vicinity of tip of the ferromagnetic anodic electrode 22 is substantially perpendicular to an electric field E, electrons are localized in this area, so that intensive localized discharge optical emission is generated. As this discharge optical emission is intensive and localized, it can be focused on the light detecting module 28 in a high efficiency with the focusing lens 29, so that optical emission in a low partial pressure of gas of 10−7 Pa can be measured.
On the other hand, as the elongated ferromagnetic anodic electrode 22 has a character attracting a magnetic field, a magnetic field in an area on the S-pole side of the magnetic field applying module 26 becomes sparse and is not perpendicular to an electric field E. Due to this, discharge in an area of the S-pole side of the magnetic field applying module 26 is weak one to restrain sputter deposition in a vicinity of this area, thus having an effect of preventing the focusing lens from getting dirt by scattered particles.
Requirements of composition for a gas analyzer according to Embodiment 1 with the vacuum casing 21 being of a cylindrical shape is as follows.
The inner diameter of the vacuum casing 21 is of 10 mm to 100 mm.
While discharge is generated with the vacuum casing 21 as a cathode electrode and the ferromagnetic anodic electrode 22 as an anode, discharge is not generated due to a shield effect in a case where a distance between the two electrodes is short. Here, as a result of preparing vacuum casings having various inner diameters and studying about stability of discharge, discharge is not generated with a vacuum casing having an inner diameter of 8 mm. On the other hand, while, with a vacuum casing having an inner diameter of 10 mm, discharge is stable in a high pressure of a medium vacuum, discharge is not stable in a low pressure of a high vacuum. From such a result, it can be said that an inner diameter of the vacuum casing 21 is preferable to be larger than 10 mm.
On the other hand, when the vacuum casing has a large inner diameter, concentration extent of magnetic field concentrated on the ferromagnetic anodic electrode 22 changes. The concentration extent of magnetic field depends on a magnetic force and a length of the magnet as magnetic field applying module 26 as well as permeability of the ferromagnetic material. As a result of simulation conducted on preset magnetic field, it can be said that an inner diameter of the vacuum casing 21 of 100 mm or less may be good and specifically an inner diameter of 50 mm or less is preferable.
(1b-1)
The ferromagnetic anodic electrode 22 serves as an electrode for applying a high voltage and has a role of concentrating a magnetic field M generated by a magnet as magnetic field applying module 26, and a ferromagnetic and soft magnetic material or a ferromagnetic and hard magnetic material is used for the electrode.
(i) Soft Magnetic Material:
Soft magnetic metal materials having electric conductivity and a relative permeability of 2 or higher, such as iron, carbon steel or magnetic stainless steel are used. In a case where these material are used, discharge optical emission with a gas analyzer exhibited substantially same intensity. Further, as a result of having conducted magnetic field simulation in a gas analyzer with varied permeability of the ferromagnetic anodic electrode 22, magnetic field generated by the magnet as magnetic field applying module 26 was concentrated on the ferromagnetic anodic electrode 22 when the relative permeability is 2 or higher. From these results, it is preferable to use a conductive metal of soft magnetic material and having relative permeability of 2 or higher for the ferromagnetic anodic electrode 22 in a case of a soft magnetic material.
(ii) Hard Magnetic Material: A Permanent Magnet Having Electric Conductivity
On the other hand, a permanent magnet having electric conductivity may be used in a case where a permanent magnet of a hard magnetic material is used as the ferromagnetic anodic electrode 22, and it is preferable to use a neodymium magnet or a samarium-cobalt magnet as such a magnet. Here, in a case where a magnet of a hard magnet material is used for the ferromagnetic anodic electrode 22, a magnetic pole at a tip of the electrode is placed so as to concentrate a magnetic field generated by the magnet as magnetic field applying module 26.
(1b-2) Position of a Tip of the Electrode
While the ferromagnetic anodic electrode 22 concentrates a magnetic field M generated by a magnet as magnetic field applying module 26, it is preferable here that the concentrated magnetic field is parallel to an axis of the electrode as well as the magnetic field has a high extent of concentration. Here, magnetic field simulation was conducted varying a position of a tip of the ferromagnetic anodic electrode 22 relative to the magnet as magnetic field applying module 26. As a result of this, a position of a tip of the ferromagnetic anodic electrode 22 may be anywhere from a position where the tip of the electrode protrudes by a half of a length of the magnet as magnetic field applying module 26 in an axial direction of the magnetic field to a position at an end of the magnet, and, further, it is desirable to position the tip of the electrode in a vicinity of the center of the magnet as magnetic field applying module 26.
As discharge occurs at a direct current voltage of several kV, a power source that can apply up to maximum voltage of 10 kV may be good.
As the magnet as magnetic field applying module 26 is necessary for maintaining discharge in a pressure range over a high vacuum and more intensive magnetic force is preferable for it, its material is desirable to be a neodymium magnet or a samarium-cobalt magnet. On the other hand, while it has been taken as preferable in a case of conventional inverted magnetron magnetic field discharge method that an intensive magnet has a length in a direction of magnetic field axis of 5 mm or more, for example of 10 mm or more, in order to apply magnetic field parallel to an electrode axis in a vicinity of the anodic electrode, the length of a magnet as the magnetic field applying module 26 for discharge by the present invention may be shorter than the above so as to concentrate magnetic field on the ferromagnetic anodic electrode 22. Having measured intensity of discharge optical emission regarding some of magnets of various lengths, it was found that a length of a magnet of 5 mm or more may be good.
While material of the vacuum casing 21 is scattered due to sputter deposition by discharge, a plate 27 having a hole is placed in order to prevent the focusing lens 29 from getting dirt by this particles of sputter deposition. It is preferable for the position of the plate 27 having a hole to be apart from a tip of the anodic electrode 22 by the inner diameter or more of the vacuum casing. A material thereof may be either a metal or an insulator (dielectric) material. A material of a metal is subjected to sputter deposition by discharge, as the plate 27 having a hole serves as a cathode. In order to prevent this, the distance of the plate 27 having a hole from the tip of the ferromagnetic anodic electrode 22 is desirable to be longer than the inner radius of the vacuum casing 21. Further, in order to prevent abnormal discharge, a peripheral face of an opening of the hole in the plate 27 having a hole is desirable to have a smooth convex roundness.
In a case where the plate 27 having a hole is of an insulator material, the insulator material undergoes dielectric polarization when electric field is applied and a surface of the plate having a hole on the side where discharge occurs bears positive electricity, so that sputter deposition of the plate having a hole by discharge can be avoided. Consequently, a material of the plate 27 having a hole is preferable to be of an insulator material. In a case where a conductive material is used for a plate 27 having a hole, it is preferable to attach the plate 27 having a hole to the inside of the vacuum casing 21 via an insulator member.
The focusing lens 19 is desirable to be a quartz glass lens and its focusing length is determined taking a position of discharge optical emission and a position of the plate 27 having a hole into account. While the focusing lens 29 is placed so as to focus emitted light on the light receiving element e in the light detecting portion 28, it is required for the focusing lens 29 to transmit atomic optical emission and molecular optical emission of various gases as well as light of a measurable wave length range of the light detecting portion 28. In general, most of multichannel spectrometers used for the light detecting portion 28 are ones that detect light of 200 nm to 1000 nm. In this case, the focusing lens 29 is desirable to be a quartz glass lens transmitting ultraviolet light. Here, a lens made of silicate glass of a low cost may be used, as this transmits light of 400 nm or longer.
With a gas analyzer according to the present invention, a plate 27 having a hole is placed between light of discharge optical emission L and the focusing lens 29, so that light having passed through the hole in the plate having a hole is focused. While the focusing length is determined taking a position of optical emission by discharge and a position of the plate having a hole into account in this case, it may be preferable in general to adopt a lens having a focusing length by a half of the distance between the plate having a hole and the lens with a point light source at the position of the plate 27 having a hole.
It is preferable to use a multichannel spectrometer. A multichannel spectrometer that can measure a plurality of wavelengths simultaneously in a high sensitivity is used for the light detecting portion 28. A multichannel spectrometer disperses incident light with a diffraction grating and detects the dispersed light with a CMOS sensor in which a multitude of CMOS (complementary metal oxide film semiconductors) are arrayed or a CCD sensor in which a multitude of CCD (charge coupled devices) are arrayed, thus conducting high sensitive detection of light for a plurality of wavelengths simultaneously.
The controlling unit 30, controlling the gas analyzer, has a function of controlling discharge in magnetic field and a function of converting signal of discharge optical emission into partial pressure. The gas analyzer according to the present invention controls discharge so that intensity of discharge optical emission of various gas molecules generally responds linearly to a total pressure and converts intensity of optical emission into a pressure of gas with intensity of intrinsic optical emission peculiar to gas species and pressure of gas (partial pressure) measured preliminarily.
A gas analyzer according to Embodiment 2 shown in
In the gas analyzer shown in
While magnetic field M is particularly concentrated between a tip of the ferromagnetic anodic electrode 32 and the magnetic pole opposed thereto of the bar magnet, so that localized discharge optical emission is generated in a vicinity of a tip of the anodic electrode when a high voltage is applied to the ferromagnetic anodic electrode 32, a light detecting portion 38 for detecting light of optical emission is provided on a peripheral side of the cylindrical vacuum casing 31. That is, the light detecting portion 38 is provided outside of the cylindrical casing so as to detect light advancing in one direction (upward direction in
A focusing lens 39 is attached to the outside of the plate 37 having a hole via a plate for attaching a focusing lens and the light detecting portion 38 is attached thereto at a further outside position. Portions up to the plate for attaching a focusing lens and the focusing lens 39 along with the pipe-shaped vacuum casing 21 form a tightly closed composition and inside of the light detecting portion 38 may be in atmospheric pressure. It is preferable to use a multichannel spectrometer for the light detecting portion 38 similarly as Embodiment 1.
As magnetic field M generated by the bar magnet as magnetic field applying module 36 is concentrated on a tip of the ferromagnetic anodic electrode 32 and perpendicular to an electric field E with the gas analyzer shown according to Embodiment 2 shown in
Requirements of composition for Embodiment 2 is as follows.
A magnet that has a high Curie temperature without losing magnetic force even at a high temperature is suitable for the magnet as the magnetic field applying module, as the magnet is exposed to discharge at a high temperature. A samarium-cobalt magnet or a ferrite magnet is desired for such a magnet.
The other requirements for Embodiment 2 are similar to ones for Embodiment 1, and a controlling unit (not shown) that has a function of controlling discharge in magnetic field and a function of converting signal of discharge optical emission into partial pressure is provided similarly as Embodiment 1.
With Embodiments 1 to 2, a ferromagnetic electrode is placed in an area of discharge where Electric field E and magnetic field M are applied, and, by concentrating the magnetic field M generated by the magnet as magnetic field applying module on a tip of the elongated ferromagnetic anodic electrode, electrons are restrained to this area and light of discharge optical emission L is localized, thus increasing intensity of optical emission. In contrast to these two Embodiments, discharge optical emission can be further localized by composing a magnetic circuit for magnetic flux to be permeable well. Embodiments arranged as such will be explained below.
With a gas analyzer according to Embodiment 3 of the present invention shown in
Requirements of composition for Embodiment 3 is as follows.
While the ferromagnetic portion 21-2 of the vacuum casing is of a ferromagnetic material considering of composing a magnetic circuit for magnetic flux to be permeable well, it is desirable to be of a ferromagnetic and soft magnetic material. Here, the non-magnetic portion 21-1 of the vacuum casing and the ferromagnetic portion 21-2 of the vacuum casing may be integrated causing both opposing ends to abut against each other thus joining both as through welding, or concave portions may be formed outside of the non-magnetic vacuum casing 21-1 with ferromagnetic sleeves placed on both sides of the magnet as magnetic field applying module 26 respectively.
The plate 37 having a hole is of a ferromagnetic material in order to compose a magnetic circuit for magnetic flux to be permeable from the magnet as the magnetic field applying module 26 to the plate having a hole. Here, in order to prevent abnormal discharge and to generate magnetic field M effectively concentrated on the ferromagnetic anodic electrode 22, an inner peripheral face of an opening of the hole in the plate 27 having a hole is desirable to have a smooth convex roundness.
The other requirements for Embodiment 3 are similar to ones for Embodiment 1, and a controlling unit (not shown) that has a function of controlling discharge in magnetic field and a function of converting signal of optical emission by discharge into partial pressure is provided similarly as Embodiment 1.
With a gas analyzers according to Embodiments 4 to 5, a magnetic circuit is formed for magnetic flux to be permeable well in an arrangement that provides a bar magnet as magnetic field applying module 26 as in Embodiment 2. The gas analyzer according to Embodiment 4 shown in
In a case where the ferromagnetic anodic electrode 32 and the thick bar magnet as the magnetic field applying module 36 are attached respectively via an insulator members 33-1, 33-2 in
Requirements of composition for Embodiments 4 to 5 are as follows.
While the ferromagnetic vacuum casing 31 is of a ferromagnetic material considering of composing a magnetic circuit for magnetic flux to be permeable well similarly as the ferromagnetic portion 21-2 of the vacuum casing in Embodiment 3, it is desirable to be of a ferromagnetic and soft magnetic material.
A magnet that has a high Curie temperature without losing magnetic force even at a high temperature is suitable for a magnet in Embodiments 4 to 5, as the magnet is exposed to discharge at a high temperature similarly to a magnet in Embodiment 2, and a samarium-cobalt magnet or a ferrite magnet is desired for such magnet.
While a light detecting portion 38 is shown with a dotted-line in Embodiment 5 shown in
While magnetic field M generated by a magnet as magnetic field applying module is concentrated on a tip of a ferromagnetic anodic electrode by using a ferromagnetic material for the electrode in Embodiments 1 to 4, the ferromagnetic anodic electrode can take another form as shown in
With the present invention, it was found that discharge optical emission is enhanced when a tiny amount of gas other than one to be detected is introduced in detecting gas. While this utilizes a phenomenon such that, when ionized gas or excited gas having a long life collides with gas to be detected, the gas to be detected is excited, the phenomenon is different from a Penning ionization used in conventional lowering of voltage for discharging or enhancement of gas ionization.
Penning ionization is a phenomenon such that, when gas B having an ionization energy higher than an ionization energy of gas A desired to be ionized or having a metastable excitation energy near to the ionization energy is introduced into the gas A, the gas A is ionized with the gas B having been excited to a high energy state by discharge colliding with the gas A. In a discharging lamp, for example, mercury vapor is effectively ionized by introducing a tiny amount of argon gas, due to which breakdown voltage for discharge of the discharging lamp can be lowered. In film formation by sputter deposition, for another example, argon gas is effectively ionized by introducing a tiny amount of helium gas, due to which there is such an effect that sputter deposition by argon ions for forming film can be increased and speed of film formation can be raised.
With the present invention, a phenomenon was found such that, also when not only gas B having an ionization energy higher than an ionization energy of gas A desired to be ionized or having a high metastable excitation energy but also gas C having an ionization energy lower than the ionization energy of the gas A are introduced into the gas A, the gas A to be detected is excited and discharge optical emission is enhanced. This is because the gas A can be excited even using the gas C having a low ionization energy, as an excitation energy of the gas A for discharge optical emission is lower than an ionization energy or a high metastable excitation energy. That is, the introduced gas C is one having a metastable excitation energy higher than an excitation energy of the gas A for discharge optical emission.
In a case, for example, where the gas A to be detected was nitrogen gas and when helium gas (gas B) having an ionization energy higher than one of nitrogen gas was introduced, discharge optical emission of nitrogen gas was naturally enhanced. On the other hand, even when oxygen gas (gas C) having an ionization energy lower than one of nitrogen energy was introduced, discharge optical emission of nitrogen gas was enhanced. Besides, in a case where gas A to be detected was neon gas or argon gas and when helium gas (gas B) was introduced, discharge optical emission of these inert gases was naturally enhanced. On the other hand, even when nitrogen gas (gas C) having a low ionization energy was introduced, discharge optical emission of these inert gases was enhanced. The gases to be introduced in a tiny amount are desired to be helium gas, nitrogen gas, air gas and argon gas, taking safety, inertness and cost into consideration.
Here, with an amount of the introduced gas B or gas C being 1/100 to 1/10, discharge optical emission of gas to be detected was enhanced by two times to three times. Due to this, a lower limit of detection with the gas analyzer according to the present invention can be lowered.
In actual experiments, argon was used for gas to be detected. Helium gas, carbon dioxide gas, nitrogen gas and air were used for excitation assisting gases. An introduced amount of any of the excitation assisting gases was about 1/10 of the gas to be detected. As a result, optical emission of argon gas was enhanced by about 2 times to 2.5 times with any of the excitation assisting gases. First ionization energy of gaseous atom is shown in Table 1.
Performance of a gas analyzer according to the present invention was certified using a gas analyzer performance measuring apparatus shown in
In test of a gas analyzer, causing a flow rate Q [Pam3s−1] of gas to flow through, a pressure p [Pa] was obtained from a relation of Q=Se×p. On the other hand, an intrinsic optical mission of gas introduced then into the gas analyzer was measured. Helium, nitrogen, oxygen, argon and carbon dioxide, as typical gases, were used for gas species and flow rate Q were set to be varied sequentially in a range of 10−9 to 10−4 Pam3s−1. Here, a standard conductance element according to a national secondary standard was used as the gas flow rate drawing-in equipment 52.
In order to demonstrate performance of a gas analyzer using discharge optical emission according to the present invention, performance of the following four gas analyzers were compared respectively, in which various gases were introduced using a gas analyzing-evaluating equipment shown in
(1) a gas analyzer corresponding to
(2) a gas analyzer corresponding to
(3) a gas analyzer according to Embodiment 1 of the present invention that has an electrode of a magnetic material, and
(4) a gas analyzer according to Embodiment 3 of the present invention with a magnetic circuit composed.
Here, with the gas analyzer according to Embodiment 3, sleeves of a ferromagnetic material according to Embodiment 1 were provided on both sides of the magnet as magnetic field applying module as well as a plate of a ferromagnetic material having a hole was placed in the gas analyzer. The results are shown in Table 2.
By introducing a tiny amount of gas other than a gas to be detected, in detecting gas, discharge optical emission was enhanced by several times and a lower limit of detection of partial pressure was lowered further with the present invention, so these results are also shown in the Table 2. Gas analyzers according to Embodiments 1 and 3 of the present invention can upgrade a lower limit of detection of partial pressure by 2 digits or more, is excellent in linearity of sensitivity and improves durability.
Here, it was also certified that the gas analyzer according to Embodiment 2 of the present invention exhibits similar performance as one according to Embodiment 1 and the gas analyzer according to Embodiments 4 to 5 exhibits similar performance as Embodiment 3.
As the gas analyzer according to the present invention was applied to a film forming apparatus by sputter deposition and a leakage inspection apparatus and then operated, argon gas as process gas, in the first, and remaining gases such as water vapor were detected. Further, with a practical leakage inspection apparatus, it was possible to detect a leakage flow rate of 10−8 Pam3s−1 within a practical short machine time of 60 sec.
The present invention is applicable to gas analyzing using various vacuum equipment such as (1) a vacuum equipment for manufacturing devices, (2) a leakage inspection apparatus and (3) a vacuum melting furnace, a vacuum freezing-drying apparatus.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-205223 | Oct 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/039358 | 10/23/2018 | WO | 00 |
